JP6029167B2 - Noise removing method and noise removing device, recording / reproducing method and recording / reproducing device, and image measuring method and image measuring device - Google Patents

Description

  The present invention relates to a noise removing method and a noise removing device, a recording / reproducing method and a recording / reproducing device, and an image measuring method and an image measuring device.

  Unlike photographic technology that records only light intensity information, holography can record light intensity information and phase information, so it can be applied to 3D display, optical storage, and optical information processing. Is expected. The reason why holography can record both intensity information and phase information is because the hologram records interference fringes formed by light interference. The interference fringes are formed by causing interference between object light including recorded information and reference light coherent with the object light.

  A hologram is a hologram in which the interference fringes thus formed are recorded as a light transmittance distribution or a refractive index distribution. In holography, reproduction is performed based on the principle that the recorded object light appears as diffracted light by irradiating the hologram with reference light used during recording. Many holograms such as Fresnel holograms, Fraunhofer holograms, Fourier transform holograms, and image holograms have been proposed so far, and there are many methods for realizing optical holograms. However, the difference between these hologram methods is the difference in the propagation method of the object light, and there is no difference in that two types of light waves of the object light and the reference light are required.

  As an application in which reduction of the hologram recording optical system is strongly demanded, there is a holographic memory that is a terabyte optical storage technology having a recording capacity exceeding that of Blu-ray (registered trademark) (Non-patent Document 2).

  In this holographic memory, a high recording density is achieved by multiplex recording a data page in which bit information is arranged two-dimensionally as a hologram in the same location of a recording medium. In order to multiplex-record a plurality of pages and selectively read out a desired page, it is necessary to change the wavefront (phase) or incident angle of the reference light for each data page, or to displace the recording medium itself. The minimum amount of displacement necessary to avoid diffraction from a non-reproduced hologram is called “angle selectivity” or “shift selectivity”.

  For example, in the case of a collinear shift multiplex recording system having high compatibility with an optical memory, if a laser light source with a wavelength of 407 nm and an objective lens with a numerical aperture of 0.65 are used, the recording medium in the in-plane direction of about 0.4 μm is used. Proud of shift selectivity (Non-Patent Document 1).

International Publication No. 2012/053198 (April 26, 2012 International Publication)

L. Hesselink, S. S. Orlov, and M.C.Bashaw, “Holographic Data Storage Systems”, Proc. IEEE, Vol. 92, no. 8, pp.1231-1280 (2004). Kenji Tanaka, Masaaki Hara, Kazutatsu Tokuyama, Koji Ishioka, Atsushi Fukumoto, and Kenjiro Watanabe, “Improved performance in coaxial holographic data recording,” Opt. Express, Vol. 15, 16196-16209 (2007). Osamu Matoba, Yusuke Yonetani, and Kouichi Nitta, “Improvement of Storage Capacity Using Confocal Scheme in Reflection-Type Holographic Memory System with Speckle Shift Multiplexing,” Jpn. J. Appl. Phys., Vol. 50, 09ME08 (1-5) (2011). Nobuhiro Kinoshita, Tetsuhiko Muroi, Norihiko Ishii, Koji Kamijo, Hiroshi Kikuchi, Naoki Shimidzu, and Osamu Matoba, “Half-data-page insertion method for increasing recording density in angular multiplexing holographic memory,” Appl. Opt., Vol. 50, 2361-2369 (2011). Masaaki Hara, Kenji Tanaka, Kazutatsu Tokuyama, Mitsuru Toishi, Kazuyuki Hirooka, Atsushi Fukumoto, and Kenjiro Watanabe, “Linear Reproduction of a Holographic Storage Channel using Coherent Addition of Optical DC Components,” Jpn. J. Appl. Phys., Vol. 47, 5885-5890 (2011). Masanori Takabayashi, Atsushi Okamoto, Akihisa Tomita, and Masatoshi Bunsen, “Symbol Error Characteristics of Hybrid-Modulated Holographic Data Storage by Intensity and Multi Phase Modulation,” Jpn. J. Appl. Phys., Vol. 50, 09ME05 (1-5 (2011). Erdem Ulusoy, Levent Onural, and Haldum M. Ozaktas, “Full-complex amplitude modulation with binary spatial light modulators,” J. Opt. Soc. Am. A, Vol. 28, 2310-2321 (2011). Lakshmi D. Ramamoorthy and B. V. K. Vijaya Kumar, “Two-Dimensional Equalization and Error Correction Using Low Density Parity Check Codes for Holographic Data Storage,” Jpn. J. Appl. Phys., Vol. 45, 1305-1310 (2006). Junya Tanaka, Atsushi Okamoto, and Motoki Kitano, “Development of Image -Based Simulation for Holographic Data Storage System by Fast Fourier Transform Beam-Propagation Method,” Jpn. J. Appl. Phys., Vol. 48, 03A028 (1-5 (2009). Lyle G. Shirley and Nicholas George, “Wide-angle diffuser transmission functions and far-zone speckle,” J. Opt. Soc. Am. A, Vol. 4, 734-745 (1987). S. Yun, G. Tearney, Johannes de Boer, N. Iftimia, and B. Bouma High-speed optical frequency-domain imagingOptics Express, Vol. 11, Issue 22, pp. 2953-2963 (2003) http: // dx .doi.org / 10.1364 / OE.11.002953 Masamitsu Haruna "Optical Coherence Tomography", Medical Photonics, No.1, pp.1-5 (printed version pp.29-33), 2010

  However, in the holographic memory system described in Non-Patent Document 1, the medium shift pitch in the in-plane direction is set to about 10 μm, which corresponds to about 25 times the shift selectivity, and the original multiplexing system has. There is a problem that the multiple performance is not exhibited.

  For example, the storage capacity is 1 / (25 × 25) = 1/625 as compared with the case of recording at a recording density of about shift selectivity. In this way, the medium shift pitch is made larger than the shift selectivity when the hologram is spread at a pitch close to the shift selectivity, and crosstalk from a non-reproduced hologram (hereinafter referred to as “inter-page crosstalk”). ) Significantly deteriorates the quality of the reproduction signal and greatly limits the number of multiplexed pages.

  In fact, the theoretical three-dimensional recording density limit is about 1 PB / disc (1 PB = 1000 TB), whereas the recording density reported so far is only about 500 GB / disc, which is clearly holographic memory. The potential of is not utilized. From the above, it can be seen that in order to bring the actual recording density closer to the potential recording density, it is necessary to introduce a new technology that can significantly reduce crosstalk between pages.

  Here, as a technique for reducing crosstalk between pages, pinholes (spatial filters) are installed in the reproduction optical system to eliminate crosstalk between pages with high spatial frequency components and improve the recording density of holographic memory. Research aimed at has recently been reported (Non-Patent Document 3).

  However, a technique for separating high-frequency noise by installing a pinhole in the spatial frequency region is already widely used in the field of optics. Also in the field of holographic memory, pinholes are installed in the reproduction optical systems disclosed in Non-Patent Document 4 and Non-Patent Document 5, and a recording density of about 500 GB / disc is finally reported using this. I'm just doing it. From this, it can be seen that the reduction of inter-page crosstalk by a spatial filter such as a pinhole is clearly insufficient.

  In order to improve the recording density of the holographic memory, various multiplex systems and multilevel recording techniques have been proposed or studied. As for the multiplexing method, research and development have been promoted with a view to practical application, centering on the collinear shift multiplexing method and the angle multiplexing method. In any of the multiplexing systems, the potential recording density determined from shift selectivity and angle selectivity, which is an index of multiplexing performance, boasts several hundred TB / disc.

However, in any of these multiplexing systems, the actual recording density actually reported is only about 500 GB / disc. This is because the interval between adjacent holograms is set to 20 to 30 times the shift selectivity in consideration of inter-page crosstalk that rapidly increases its influence as the number of multiplexing increases. That is, it can be seen that the current holographic memory suppresses the potential multiplexing capability. On the other hand, the holographic memory is regarded as a promising means for extending the recording density in the simplest and most effective manner with respect to the multi-value recording technique (Non-patent Document 6). Ideally, when an m-value multilevel modulation signal is used, the amount of information per data page is log ₂ (m) times as compared with conventional binary modulation.

  However, for example, in the case of m-value phase modulation, each signal point is only distributed between 0 and 2π according to 2π / m × N (N = 0, 1, 2,..., M−1). Absent.

  That is, the multi-level modulation signal is realized simply by increasing the interval between the signal points, and is more vulnerable to noise. Therefore, while the amount of information that can be expressed in one page increases, the number of pages that can be recorded in the recording medium decreases. After all, it is important to optimize the trade-off relationship between inter-page crosstalk and signal multilevel number.

  Based on the above, the development of technology that can suppress crosstalk between pages is the most effective way to dramatically increase recording density, and it will blossom the original performance of multiplexing and multilevel recording technology. It can be said that it leads to.

  The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to remove noise that can bring the actual information density at the time of recording, reproduction or measurement closer to the potential information density than before. It is to provide a method and the like. In this specification, the amount of information per unit volume in which unit information can be recorded on the object, the amount of information per unit area where unit information can be reproduced from the object, and the image included in the transmitted light of the object irradiated with light The amount of information per unit volume capable of measuring unit information by measurement is referred to as information amount density.

  In order to solve the above problems, the noise removal method of the present invention includes a light irradiation step of irradiating an object with phase-modulated light generated by performing spatial phase modulation processing on at least predetermined signal light, and the phase Output light including the complex amplitude of the emitted light emitted from the object irradiated with the modulated light or the phase conjugate light of the phase modulated light emitted from the object irradiated with the predetermined reference light On the other hand, the method includes a noise removal step of performing a process of removing a noise component from the emitted light by performing the same phase modulation process as the spatial phase modulation process.

  Further, in order to solve the above problems, the noise removing device of the present invention includes a light irradiating unit that irradiates an object with phase modulated light generated by performing spatial phase modulation processing on at least predetermined signal light, For the complex amplitude of the emitted light emitted from the object irradiated with the phase-modulated light, or the phase conjugate light of the phase-modulated light emitted from the object irradiated with the predetermined reference light And noise removal means for performing a process of removing a noise component from the emitted light by performing the same phase modulation process as the spatial phase modulation process on the emitted light.

  Here, the complex amplitude of the emitted light emitted from the object irradiated with the phase-modulated light, or the emitted light (including the phase conjugate light of the phase-modulated light) emitted from the object irradiated with the predetermined reference light The reproduction (or reproduction) component due to) is referred to as “reproduction component”. On the other hand, a component that is not necessary for reproduction of information included in complex amplitude or outgoing light (of course, a crosstalk component between unit information included in the reproduction component is also included in this component) is referred to as a “noise component”.

  According to the above method or configuration, the signal light is output with respect to the complex amplitude of the emitted light emitted from the object irradiated with the phase-modulated light or the emitted light emitted from the object irradiated with the predetermined reference light. The same phase modulation processing as the spatial phase modulation processing performed for the above is performed.

  Here, the reproduction component is despread (converged) by canceling the spatial phase modulation component performed on the signal light by this phase modulation processing, but the noise component has no phase correlation with the spatial phase modulation component, so it has a wide range. To be separated from the regenerated components.

  Therefore, the crosstalk component between the unit information of the reproduction component is also diffused and separated from the reproduction component over a wide range, so that the information amount density at which the unit information can be recorded on the object and the information amount density at which the unit information can be reproduced from the object The information density that can measure unit information by measuring the image included in the transmitted light of the object can be greatly improved.

  Therefore, the actual information density at the time of recording, reproduction or measurement can be made closer to the potential information density than before.

  In addition to the above-described configuration, the noise removal method of the present invention can be implemented by using outgoing light emitted from an object irradiated with the phase-modulated light, or using light from which the noise component has been removed. An information generation step for performing processing for generating dimensional information may be included.

  In addition to the above-described configuration, the noise removal apparatus of the present invention further uses emitted light emitted from an object irradiated with the phase-modulated light, or uses light from which the noise component has been removed. Information generating means for performing processing for generating two-dimensional information may be provided.

  According to the method or configuration described above, two-dimensional information can be generated with an information amount density closer to the potential information amount density than in the past.

  In the noise removal method of the present invention, in addition to the above-described configuration, the two-dimensional information may be output light emitted from an object irradiated with the phase-modulated light, or light from which the noise component has been removed. Alternatively, it may be generated by forming an image using a lens system.

  This makes it possible to perform each of the above processes using only an optical system such as a lens system.

  In addition to the above configuration, the noise removal method of the present invention may generate the phase-modulated light by transmitting the signal light through a random phase plate in the light irradiation step.

  This makes it possible to perform each of the above processes (mainly recording process) using only an optical system such as a random phase plate.

  In addition to the above-described configuration, the noise removal method of the present invention transmits the emitted light including the phase conjugate light of the phase-modulated light through the random phase plate in the noise removing step, thereby allowing noise from the emitted light. Components may be removed.

  This makes it possible to perform each of the above-described processes (mainly read / reproduce processes) using only an optical system such as a random phase plate.

  In addition to the above configuration, the noise removal method of the present invention makes the arrangement position of the random phase plate different when the phase modulation light includes a plurality of signals to which different phase modulation patterns are added. Accordingly, the different phase modulation patterns may be generated.

  According to the above method, the cross-correlation between the phase modulation patterns can be reduced by adjusting the arrangement position of the corresponding random phase plate so that the spatial cross-correlation of each phase modulation pattern becomes sufficiently small. The crosstalk component between unit information can be suppressed.

  However, when each of the above processes is performed using only an optical system such as a lens system, secondary problems described below arise.

  That is, in order to perform the above-described processes all optically, for example, it is necessary to newly add a spatial phase modulation means (or element) such as a random diffusion plate described later to the recording optical system. Further, for example, the readout / reproduction optical system requires phase conjugate readout of the holographic memory, which complicates the entire system, and unit information (for example, phase conjugate readout light with insufficient phase conjugate fidelity) "Reproduction page") may be degraded.

  Therefore, in order to solve the above-mentioned secondary problem, in addition to the above-described configuration, the noise removal apparatus of the present invention includes a light irradiation unit that performs the spatial phase modulation process on the signal light in advance. The phase-modulated light may be directly emitted.

  This eliminates the need to newly add a spatial phase modulation means (or element) such as a random diffuser. That is, the recording optical system can be simplified. For this reason, the structure of the whole system can be simplified.

  In order to solve the above secondary problem, in addition to the above configuration, the noise removal method of the present invention is configured so that the two-dimensional information is output from an object irradiated with the phase-modulated light. It is generated by applying a predetermined function transformation to the two-dimensional intensity distribution or phase distribution of incident light or to the two-dimensional intensity distribution or phase distribution of light from which the noise component has been removed. Also good.

  Accordingly, for example, it is not necessary to realize a predetermined function conversion function (for example, a Fourier transform function) or an inverse function conversion function (for example, an inverse Fourier transform function) with an optical system such as a lens system. For this reason, the structure of the whole system can be simplified.

  In order to solve the above secondary problem, in addition to the above configuration, the noise removal method of the present invention further includes a complex amplitude of light emitted from the object irradiated with the phase-modulated light. A complex amplitude detecting step for detecting the noise component, and performing the phase modulation calculation corresponding to the spatial phase modulation processing on the complex amplitude detected in the complex amplitude detecting step in the noise removing step. May be removed.

  In order to solve the above-mentioned secondary problem, in addition to the above-described configuration, the noise removal apparatus of the present invention further includes a complex amplitude of emitted light emitted from an object irradiated with the phase-modulated light. Complex noise detection means for detecting the noise component, and the noise removal means performs the phase modulation calculation corresponding to the spatial phase modulation processing on the complex amplitude detected by the complex amplitude detection means, thereby the noise component. May be removed.

  According to the above method or configuration, when removing the noise component, the object is irradiated with reproduction reference light, or the diffracted light from the object is spatially phase modulated means (or element) such as a random diffuser. There is no need to go through. That is, optical phase conjugate readout / reproduction is not required. For this reason, the structure of the whole system can be simplified.

  By effectively coexisting the optical processing process and the electronic processing process as described above, crosstalk between unit information can be greatly reduced without adding a new optical element to the conventional optical system.

  The recording / reproducing apparatus of the present invention is a recording / reproducing apparatus provided with any one of the above-described noise removing devices in addition to the above-described configuration, wherein the light irradiation means includes the phase modulation along with the recording reference light. The information is recorded by irradiating the hologram recording medium as the object with the light, and the noise removing unit is generated by irradiating the hologram recording medium with the reference light for reproduction as the predetermined reference light. By performing the same phase modulation process as the spatial phase modulation process on the diffracted light as the output light including the phase conjugate light, the noise component is removed from the diffracted light, and further, the diffraction is performed by the noise removing unit. Reproducing means for outputting the light from which the noise component has been removed from the light as the reproducing light of the information recorded on the hologram recording medium may be provided.

  According to the above configuration, it is possible to realize a recording / reproducing apparatus capable of bringing the actual information amount density during recording or reproduction closer to the potential information amount density than before. In addition, crosstalk from multiplexed non-reproducing holograms can be greatly reduced, and the recording density of the holographic recording medium can be dramatically improved.

  The recording / reproducing method of the present invention is a recording / reproducing method using any one of the above-described noise removing devices in addition to the above-described configuration, wherein the phase-modulated light is recorded together with the recording reference light by the light irradiation means. Is generated by irradiating the hologram recording medium as the object by recording information and irradiating the hologram recording medium with the reference light for reproduction as the predetermined reference light by the noise removing means. A noise removing step for removing a noise component from the diffracted light by performing the same phase modulation processing as the spatial phase modulation processing on the diffracted light as the outgoing light including the phase conjugate light, and the noise component A reproducing step of outputting the removed light as reproducing light of information recorded on the hologram recording medium.

  According to the above method, it is possible to realize a recording / reproducing method capable of bringing the actual information amount density at the time of recording or reproducing closer to the potential information amount density than before. In addition, crosstalk from multiplexed non-reproducing holograms can be greatly reduced, and the recording density of the holographic recording medium can be dramatically improved.

  The image measurement device of the present invention is an image measurement device including any one of the above-described noise removing devices in addition to the above-described configuration, wherein the light irradiation unit uses the phase-modulated light as the object. The observation sample is irradiated with the complex amplitude of the emitted light emitted from the observation sample irradiated with the phase-modulated light or with the predetermined reference light. Noise component is removed from the emitted light by performing the same phase modulation processing as the spatial phase modulation processing on the outgoing light including the phase conjugate light of the phase modulated light emitted from Information generating means may be provided that performs processing for generating two-dimensional information using emitted light emitted from the observation sample irradiated with modulated light or using light from which the noise component has been removed.

  According to the above configuration, it is possible to realize an image measurement device that can bring the actual information density at the time of measurement closer to the potential information density than before.

  The image measurement method of the present invention is an image measurement method using any one of the above-described noise removing devices in addition to the above-described configuration, wherein the phase-modulated light is used as the object by the light irradiation means. The light irradiation step of irradiating the observation sample, and the complex amplitude of the emitted light emitted from the observation sample irradiated with the phase-modulated light by the noise removing unit, or the predetermined reference light is irradiated A process for removing noise components from the emitted light is performed by performing the same phase modulation process as the spatial phase modulation process on the emitted light including the phase conjugate light emitted from the observation sample. An information production process for generating two-dimensional information using a noise removal step and outgoing light emitted from the observation sample irradiated with the phase-modulated light, or using light from which the noise component has been removed And the process may contain.

  According to the above configuration, it is possible to realize an image measurement method capable of bringing the actual information amount density at the time of measurement closer to the potential information amount density than before.

  As described above, the noise removal method of the present invention includes a light irradiation step of irradiating an object with phase modulated light generated by performing spatial phase modulation processing on at least predetermined signal light, and irradiation with the phase modulated light. With respect to the complex amplitude of the emitted light emitted from the target object or to the emitted light including the phase conjugate light of the phase-modulated light emitted from the object irradiated with the predetermined reference light, A noise removal step of performing a process of removing a noise component from the emitted light by performing the same phase modulation process as the spatial phase modulation process.

  Further, as described above, the noise removing device of the present invention includes a light irradiating unit that irradiates an object with phase modulated light generated by performing spatial phase modulation processing on at least predetermined signal light, and the phase modulated light described above. With respect to the complex amplitude of the emitted light emitted from the object irradiated with or to the emitted light including the phase conjugate light of the phase-modulated light emitted from the object irradiated with the predetermined reference light And a noise removing unit that performs a process of removing a noise component from the emitted light by performing the same phase modulation process as the spatial phase modulation process.

  Therefore, the actual information density at the time of recording, reproduction or measurement can be made closer to the potential information density than before.

It is a figure which shows the principal part structure of the recording / reproducing apparatus which concerns on one Embodiment of this invention, (a) shows the form which performs a spatial phase modulation with the combination of a spatial light modulator and a random diffuser, (b) ) Shows a form in which spatial phase modulation is performed only by a spatial light modulator as a modification of (a). It is a figure which shows the principal part structure of the recording / reproducing apparatus which concerns on one Embodiment at the time of applying this invention to a two-beam optical system, (a) shows the form at the time of a recording process, (b) Indicates a form when a reading / reproducing process is performed. It is a figure which shows the optical model equivalent to each process performed in a computer using the complex amplitude measured with the recording / reproducing apparatus shown in FIG. 1, (a) shows the optical model corresponding to a digital modulation signal production | generation process. (B) shows the optical model corresponding to the recording process, (c) shows the optical model corresponding to the reading process, and (d) shows the optical model corresponding to the digital phase conjugate reproduction process. It is a figure which shows the principal part structure of the recording / reproducing apparatus which concerns on the other form of this invention, (a) shows the form which shifts a random diffuser plate in a recording process, (b) shows optical phase conjugate reading A mode in which the random diffusion plate is shifted in the reproduction process is shown. It is a figure which shows the form which comprised the optical system with two lenses before and behind a random diffuser, (a) is the form which comprised the optical system of the predetermined magnitude | size with two lenses before and after a random diffuser (B) shows the form which comprised the reduction optical system which reduced the optical system shown to (a). 1A and 1B are diagrams illustrating a configuration of a main part of a recording / reproducing apparatus according to an embodiment when the present invention is applied to a collinear optical system, in which FIG. 1A illustrates a form in a recording process, and FIG. The form in the process is shown. It is a figure which shows the principal part structure of the recording / reproducing apparatus which concerns on the further another form of this invention, (a) is the form devised not to permeate | transmit a random diffuser plate by arrange | positioning reference light outside a lens aperture diameter. (B) shows the form which prepares reference light from another optical path, after signal light permeate | transmits a random diffuser plate. It is a figure which shows the principal part structure of the recording / reproducing apparatus which concerns on the further another form of this invention, (a) shows the optical model corresponding to a digital modulation signal production | generation process, (b) performs a recording process. (C) shows the form when the reading process is performed, and (d) shows the optical model corresponding to the digital phase conjugate reproduction process. It is a figure which shows the analysis model used by the numerical calculation by a computer, (a) shows an example of the analysis model corresponding to a digital modulation | alteration signal light production | generation process, (b) is correspondence of the recording and reading process in a two-beam optical system (C) shows an example of an analysis model corresponding to a recording and reading process in a collinear optical system, and (d) shows an example of an analysis model corresponding to a digital phase conjugate reproduction process. , (E) shows the coordinates and mesh definitions on the SLM surface, (f) shows the coordinates and mesh definitions inside the recording medium, and (g) shows the coordinates and mesh definitions on the binary phase mask surface. Indicates. It is a figure which shows an example of an intensity modulation type data page. The propagation state of the modulated signal light immediately after passing through the random diffusion plate is shown. (A) shows the case of the diffusion angle θ _dif = 0.0 °, and (b) shows the case of the diffusion angle θ _dif = 10.0 °. Show the case. It is a figure which shows the transmission function of a random diffuser. It is a figure which shows an example of the intensity distribution of a SLM surface. It is a figure which shows an example of the intensity distribution of the diffracted light in a phase detection surface. It is a figure which shows the component contained in reproduction | regeneration light, (a) shows an example of a reproduction data page component, (b) shows an example of a crosstalk component between pages. It is a figure which shows an example of the reproduction | regeneration data page. It is a figure which shows the example of the page arrangement | positioning for multiplex recording, (a) shows an example of the page arrangement | positioning in a collinear shift multiplex system, (b) shows an example of the page arrangement | positioning in a speckle shift multiplex system. It is a figure which shows the example of shift selectivity, (a) shows an example of the shift selectivity in a collinear shift multiplexing system, (b) shows an example of the shift selectivity in a speckle shift multiplexing system. It is a figure for demonstrating the effectiveness at the time of applying this invention to a speckle shift multiplexing system, (a) is multiplexing when the optical system of Example 1 of this invention and a normal speckle shift multiplexing system are compared. The transition of the noise component with respect to the number is shown, and (b) shows the transition of SNR with respect to the multiplex number. It is a figure for demonstrating the effectiveness at the time of applying this invention to a collinear shift multiplexing system, (a) is multiplexing when the optical system of Example 2 of this invention and a normal speckle shift multiplexing system are compared. The transition of the noise component with respect to the number is shown, and (b) shows the transition of SNR with respect to the multiplex number. It is a figure for demonstrating the effectiveness of the performance improvement at the time of performing the shift operation of a random diffuser, (a) is a transition of the noise component with respect to the multiplex number when there is no shift operation of the random diffuser (B) shows the transition of the SNR with respect to the multiplex number. It is a figure for demonstrating the difference in a function of a normal mirror and a phase conjugate mirror, (a) shows reflection of the light by a normal mirror, (b) shows reflection of the light by a phase conjugate mirror. . It is a figure for demonstrating the formation method of the hologram by signal light and reference light. It is a figure for demonstrating each diffracted light at the time of making reference light enter into a hologram. It is a figure which shows the structural example at the time of applying 2ch-HDI to the read-out process of FIG.3 (c). FIG. 10 is a diagram showing analysis parameters in the analysis model shown in FIG. 9, (a) shows analysis parameters of the collinear shift multiplexing method, and (b) shows analysis parameters of the speckle shift multiplexing method. It is a conceptual diagram for demonstrating the outline | summary structure of the image measuring device which concerns on other embodiment of this invention, (a) shows the outline | summary of the structure in a phase modulation process, (b) is in a digital phase demodulation process. An overview of the configuration is shown. It is a figure for demonstrating the various noise in the phase measurement by 2ch-HDI. It is a conceptual diagram for demonstrating the schematic structure of the biological image measuring device which concerns on other embodiment of this invention, (a) shows the outline | summary of the structure in the measurement process of a biological sample, (b) is an object. The outline of the structure in the digital extraction process of light is shown.

  One embodiment of the present invention will be described with reference to FIGS. Descriptions of configurations other than those described in the following specific items may be omitted as necessary. However, in the case where they are described in other items, the configurations are the same. For convenience of explanation, members having the same functions as those shown in each item are given the same reference numerals, and the explanation thereof is omitted as appropriate.

[Overview of conventional problems]
As described above, the current holographic memory has a shift selectivity of about 0.4 μm, but there is a problem of inter-page crosstalk noise from a non-reproduced hologram, so the actual shift pitch is set to about 10 μm. Thus, there is a problem that the maximum storage capacity has been reduced to 1 / (10 / 0.4) ^ 2 = 1/625. In the following, an embodiment of the present invention that effectively removes the inter-page crosstalk noise and dramatically increases the storage capacity of the holographic memory will be described.

[Noise removal method]
The basic processing (noise removal method) of the present embodiment will be described below assuming the case of a collinear hologram.

(Hologram recording process) FIG. 1 (a)
The configuration used in the hologram recording process of the present embodiment is a spatial phase modulation optical system 11, a lens 12, and a recording medium (hologram recording medium, object) 13 shown in FIG.

(Spatial phase modulation optical system 11)
As shown in the figure, the spatial phase modulation optical system 11 irradiates the recording medium 13 with the reference light E and the phase modulation light A ′ generated by performing spatial phase modulation processing on the signal light A. In the present embodiment, a spatial light modulator (light irradiation means) 11a and a random diffuser plate 11b are further provided.

(Spatial light modulator 11a)
The spatial light modulator 11a of this embodiment includes a beam expander (BE: Beam Expander) as a laser light source and an expanding optical system that expands the laser beam diameter, and corresponds to the data page portions of the data pages P1 to Pm. The signal light A and the reference light E corresponding to the reference light ring are output (or displayed).

  The signal modulation method by the spatial light modulator 11a may be any of an intensity modulation type, a phase modulation type, a spatial quadrature amplitude modulation type, and a multilevel modulation type thereof.

  For example, in the case of the phase modulation type, the signal light A is an optical phase signal having a phase distribution. More specifically, the signal light A generated by the spatial light modulator 11a has, for example, a phase distribution in which binary phases of 0 and φ are two-dimensionally arranged (arranged in a matrix) for each data pixel. Signals (two-dimensional information) can be listed. It is desirable that the spatial light modulator 11a can modulate only the phase in the range of 0 to 2π.

  In the case of the intensity modulation type, the signal light A is a light intensity signal having an intensity distribution. That is, the signal light A generated by the spatial light modulator 11a is, for example, a signal (two-dimensional) having an intensity distribution in which a high part with high light intensity and a low part with low light intensity are two-dimensionally arranged for each data pixel. Information).

  Here, as the spatial light modulator 11a, either a spatial phase modulator or a spatial intensity modulator can be used. Any one of the spatial light modulators can generate a complex amplitude (both phase and intensity) of light.

(Random diffuser 11b)
The random diffusion plate 11b, which is an example of the spatial phase modulation element, is an optical element having a random uneven distribution formed on the surface, and has an effect of diffusing light waves. Therefore, the signal light A is transmitted through the random diffusion plate 11b. Then, spatial phase modulation processing is performed, and phase-modulated light A ′ is output. The details of the uneven distribution formed on the surface of the random diffusion plate 11b will be described later.

  In addition, although there is no particular restriction on the arrangement location of the random diffusion plate 11b, the random diffusion plate 11b is arranged in the Fresnel region of the signal light A in the embodiment shown in FIG.

(Lens 12, recording medium 13)
The lens 12 is a condenser lens (objective lens), collects the reference light E and the phase-modulated light A ′, and causes interference (image formation) in the recording medium 13 to form an interference fringe. Record as. In addition, the constituent material of the lens 12 should just be a glass material or resin material which has translucency, and is not specifically limited. For example, a photopolymer can be used as the recording medium 13. In recording the hologram, the beam expanded by BE is condensed into the recording medium 13 by the lens 12.

(Details of recording process)
The recording process of the present embodiment includes at least the following processes (a) to (c).

  (A) The signal light A and the reference light E are generated by the spatial light modulator 11a. Since this procedure is the same as the conventional procedure, its description is omitted.

  (B) Spatial phase modulation exp {jΦ} is added to the signal light A via the random diffuser plate 11b to obtain phase modulated light A ′ = Aexp {jΦ}. As the spatial phase modulation element, an element having an effect of diffusing light waves is desirable, and in this embodiment, the random diffusion plate 11b is used, but the present invention is not limited to this. For example, a spatial light modulator that realizes the same spatial phase modulation effect as the random diffuser plate 11b may be used. In the form shown in FIG. 1A, a random diffuser plate 11b for spatial phase modulation processing is installed, but as will be described later, signal light A ′ including this spatial phase modulation effect at the stage of signal generation. By generating, it is possible to exclude an additional optical system such as the illustrated random diffusion plate 11b.

  (C) The signal light A and the phase-modulated light A ′ are condensed on the recording medium 13 using the lens 12 and interfered in the recording medium 13 to form interference fringes, which are recorded as holograms. This procedure is conventional.

  Actually, it is not always necessary to install the random diffuser plate 11b. When the signal light A is generated, the phase distribution or intensity of the phase-modulated light A ′ including the random diffuser plate 11b and the front and rear optical wave propagation effects. The distribution may be obtained by calculation, and this distribution may be directly generated and emitted using the spatial light modulator 11a.

  That is, in the case where the phase modulation light A ′ including the spatial phase modulation element such as the random diffuser plate 11b and the front and rear light wave propagation effects is obtained by calculation and this distribution is directly generated by the spatial light modulator 11a, exp {jΦ } Is a known phase distribution or intensity distribution given in calculation, so that it is not necessary to measure in advance.

  This also eliminates the need to newly add phase modulation means (or elements) such as the random diffuser plate 11a. That is, the recording optical system can be simplified. For this reason, the structure of the whole system can be simplified.

(Hologram reading process) FIG. 1 (b)
The configuration used in the hologram reading process of the present embodiment is a spatial light modulator 11 a, a lens 12, a recording medium 13, a lens 14, and an image sensor (complex amplitude detection means) 15.

(Spatial light modulator 11a)
In the hologram reading process, the spatial light modulator 11a outputs (or displays) only the reference light E corresponding to the reference light ring.

(Lens 12, recording medium 13, lens 14)
The lens 12 and the recording medium 13 are as described above. The lens 14 is a collimator lens, and collimates the transmitted light (diffracted light D) that has passed through the recording medium 13 so as to enter the imaging element 15.

(Image sensor 15)
The image sensor 15 measures (detects) a complex amplitude distribution (two-dimensional information) of transmitted light that passes through the recording medium 13 by a phase detection method.

  For example, a charge coupled device (CCD) and a complementary metal-oxide semiconductor (CMOS) can be used. In this detection, even when the original signal (data pages P1 to Pm) has only information of intensity, it is necessary to measure a complex amplitude including phase and intensity. As the phase detection means, for example, the method disclosed in Patent Document 1 can be used.

  Next, in the present embodiment, a digital phase conjugate reproduction process is performed by a process in a computer (not shown) below using the complex amplitude measured by the image sensor 15.

  More specifically, in digital phase conjugate reproduction, the following calculation is performed using the detected complex amplitude (hereinafter referred to as “complex amplitude A ″”).

The phase conjugate (A ″) ^* of the detected complex amplitude A ″ is calculated, and the complex amplitude when the light wave is propagated to the left side of the figure is calculated assuming that this is displayed at the position of the image sensor 15. To do. When this calculation is performed, in the corresponding optical model, the complex amplitude of the reproduced light wave just before the random diffusion plate 11b is obtained by adding the reproduction signal (A ′) ^* and the noise component.

Here, since (A ′) ^* = A ^* exp {−jΦ}, when this is retransmitted through the random diffusion plate 11b, the phase exp {Φ} is added, and the signal component A ^* exp {− after transmission is added. jΦ} exp {jΦ} = A ^{* and the} signal A ^* is demodulated.

  On the other hand, the noise component is randomly diffused by adding the phase exp {jΦ} in the random diffusion plate 11b, and most of the noise component is separated outside the signal region, so that noise can be reduced.

  As described above, by detecting the complex amplitude of the signal light reproduced by the normal hologram reproducing procedure, the processing by the random diffusion plate 11b shown in FIG. 1A can be performed digitally (processing in the computer). And no additional optical system is required.

  In addition, when recording is performed by actually installing a spatial phase modulation element such as the random diffusion plate 11b, it is necessary to measure the transmission characteristic exp {jΦ} of the random diffusion plate 11b in advance in order to perform the above calculation. There is. However, when an element capable of electrically controlling the characteristic (phase value), such as a spatial light modulator, is used as the spatial phase modulation element, the characteristic of the spatial phase modulation element is known, and thus no prior measurement is necessary. Further, as described above, when the intensity distribution or phase distribution of the phase-modulated light A ′ including the random diffuser plate 11b and the front and rear light wave propagation effects is obtained by calculation, and this distribution is generated by the spatial light modulator 11a, , Exp {jΦ} is a known intensity distribution or phase distribution given in calculation, so that it is not necessary to measure in advance.

  According to the above, between the data pages (between unit information) while maintaining a simple optical system by the digital phase conjugate reproduction technology without adding a new optical element such as the random diffuser plate 11b at the time of recording and / or reproducing. ) Crosstalk (hereinafter referred to as inter-page crosstalk) can be greatly reduced.

  In addition, as described above, the inter-page crosstalk component as the noise component is also diffused over a wide range and separated from the reproduction component. Therefore, the information amount density at which the data page can be recorded on the recording medium 13 and the data page from the recording medium 13 are The reproducible information amount density and the information amount density at which unit information can be measured by image measurement included in the transmitted light of the object can be greatly improved.

  Therefore, the actual information density at the time of recording, reproduction or measurement can be made closer to the potential information density than before. Here, the amount of information per unit volume where unit information can be recorded on the object, the amount of information per unit area where unit information can be reproduced from the object, and unit information based on image measurement included in the transmitted light of the object irradiated with light The amount of information per unit volume that can be measured is referred to as the information amount density.

(Summary of this embodiment)
The point in the above form is that the cross-talk between pages is greatly reduced by utilizing the beam diffusion effect by spatial phase modulation, and the potential capability of multi-recording and multi-level recording is blossomed. The object is to realize the same simple optical system as before without adding a new optical element.

  In the present embodiment, spatial phase modulation is added to the signal light A in advance using a spatial phase modulation element having an effect equivalent to that of the random diffusion plate 11b during recording.

  At the time of reproduction, the same spatial phase modulation is added again to the phase conjugate diffracted light read from the hologram.

  If the diffracted light contains a playback data page component and an inter-page crosstalk component, the playback data page component is demodulated and played back by canceling the phase modulation received during recording. Is randomly diffused over a wide range because there is no phase correlation with the phase distribution of the random diffusion plate 11b. The above is the basic concept of separating the inter-page crosstalk component from the reproduction data page component. However, in order to perform these operations all optically, it is necessary to newly add a spatial phase modulation element to the recording optical system. In addition, since the readout / reproduction optical system requires phase conjugate readout of the hologram, the entire system becomes complicated, and phase conjugate readout light with insufficient phase conjugate fidelity leads to degradation of the quality of the reproduced page. there is a possibility. In the present embodiment, the phase-modulated light A ′ including the phase modulation effect is directly expressed by the spatial light modulator 11a at the stage of signal generation, thereby eliminating the need for additional elements such as the random diffuser plate 11b and recording optical. Simplify the system. Further, the complex amplitude of the diffracted light obtained by the normal hologram reading procedure is detected, and the subsequent processing is performed digitally (processing in the computer), thereby eliminating the need for optical phase conjugate reading / reproduction. As described above, according to the present embodiment, the optical processing process and the electronic processing process coexist effectively so that crosstalk between pages can be performed without adding a new optical element to the conventional optical system. Since it can be greatly reduced, it can be said that this is a highly practical form.

(Regarding the scope of the present invention)
In the above description, the form related to the removal of the noise component at the time of reproducing the hologram recording medium has been described. However, the form embodying the present invention is not limited to such a form.

  For example, the present invention can also be applied to an image measuring device or the like as will be described later.

  This image measurement apparatus includes the spatial phase modulation optical system 11 (or the spatial light modulator 11a), and is configured to irradiate the observation sample (target object) with the phase modulation light A ′.

  In addition, this image measurement apparatus includes the spatial phase modulation optical system 11 (or spatial light modulator 11a) described above, and with respect to the complex amplitude of the emitted light emitted from the observation sample irradiated with the phase modulated light A ′. Or, by performing the same phase modulation processing as that of the random diffusion plate 11b on the outgoing light including the phase conjugate light of the phase modulated light A ′ emitted from the observation sample irradiated with the reference light E, You may comprise so that a noise component may be removed from emitted light.

  Further, in this image measurement apparatus, two-dimensional information (phase distribution or intensity) is used by using the outgoing light emitted from the observation sample irradiated with the phase-modulated light A ′, or using the light from which the noise component is removed. (Distribution) generation processing may be performed.

[Two-beam optical system] ... Fig. 2
Although the scope of application of the present invention is not limited to a specific optical system, an embodiment in which the basic concept of inter-page crosstalk reduction according to the present invention is applied to a two-beam optical system will be described below based on FIG.

  The signal modulation method in the spatial light modulator 11a is as described in the form shown in FIG.

  Next, the arrangement location of the random diffuser plate 11b can be arranged in the Fresnel region (Fresnel diffraction region) of the signal light A as shown in FIG. 1A, but in this embodiment, FIG. As shown to (a), it arrange | positions to the Fourier surface which can diffuse a crosstalk component between pages most efficiently. The “Fourier plane” is a plane including a coincidence point between the focal point of the lens 12a and the focal point of the lens 12b.

  In addition, the spatial phase modulation element is not particularly limited as long as it can perform beam diffusion, but in the following, description will be made assuming that the random diffusion plate 11b is used.

(Hologram recording process) FIG. 2 (a)
Here, the operation of the recording process will be described with reference to FIG. First, the signal light A in which the data pages P1 to Pm are modulated is generated by irradiating the spatial light modulator 11a with a plane wave. The signal light amplitude at this time is defined as a _j (r). The subscript j (j = 1, 2, 3,..., M...) Indicates the page number of each of the data pages P1 to Pm.

  Next, the signal light A Fourier-transformed by the lens 12a passes through the random diffusion plate 11b, so that the signal light A is subjected to spatial phase modulation and diffused in a wider range.

At this time, the amplitude, g _j (r) of the phase-modulated light A ′ is given by the following equation (1).

  Here, the suffix j (j = 1, 2, 3,..., M...) Indicates the page number of each of the data pages P1 to Pm.

A _j (r) represents the signal light amplitude after Fourier transform.

Next, the phase distribution φ _j (r) of the random diffusion plate 11b is given by the following equation (2).

  Here, n is the refractive index of the random diffusion plate 11b, λ is the wavelength of the laser light source, and h (r) is the random uneven distribution of the random diffusion plate 11b.

  Thereafter, the modulated signal light A 'is condensed again on the recording medium 13 through the 4f optical system including the lens 12b and the lens 12c, and is made to interfere with the reference light E prepared from another optical path, thereby recording a hologram. When performing multiple recording, the above recording process may be repeated in the same procedure while sequentially shifting the incident conditions (incident angle, wavefront phase, etc.) of the reference light E for each data page.

(Hologram reading / reproducing process) ... FIG. 2 (b)
Next, the operation of the optical phase conjugate reading / reproducing process will be described with reference to FIG. First, the hologram in the recording medium 13 is irradiated with the phase conjugate light E ^* of the reference light E emitted from the phase conjugate mirror 16. The basic properties of the phase conjugate mirror 16 and the phase conjugate light E ^* will be described in the supplementary explanation items described later.

  When holograms are multiplexed and recorded in the recording medium 13, the diffracted light is mixed with inter-page crosstalk components in addition to the phase conjugate reproduction data page component. The diffracted light read from the recording medium 13 then reaches the surface of the random diffusion plate 11b (hereinafter referred to as “diffusion plate surface”) via the lens 12c and the lens 12b.

  The diffracted light on the diffusion plate surface is given by the following equation (3).

  Here, the subscript k represents the reproduction data page number, the first term represents the phase conjugate reproduction data page component, the second term represents the inter-page crosstalk component, α (r) is a random intensity distribution, and β (r ) Is a random phase distribution.

  Next, the diffracted light is retransmitted through the random diffusion plate 11b, so that phase modulation similar to that at the time of recording is added as shown in the following equation (4).

  At this time, the phase modulation of the reproduced data page component is canceled out, but the random inter-page crosstalk component is further spread over a wide range (see the following equation (5)).

A _k ^* (r) reaches the image sensor surface via the lens 3, and the final reproduction data page a _k ^* (r) is detected.

  On the other hand, since the inter-page crosstalk component of the second term is diffused in a wider range than during recording, most of it deviates from the lens 12a. The above is the basic concept for reducing crosstalk between pages.

(Each process in the computer and optical model) ... Fig. 3
However, as shown in FIGS. 2A and 2B, the random diffusion plate 11b, the lenses 12a to 12c associated therewith, and the phase conjugate mirror 16 are provided in order to realize the above-mentioned basic principle all optically. It is necessary to newly add to the optical system.

Furthermore, there is a concern that the quality of the reproduced data pages P1 ′ to Pm ′ may be deteriorated by the incomplete phase conjugate light E ^* emitted from the phase conjugate mirror 16.

  The present inventor eliminates the need for additional elements such as the random diffuser plate 11b by expressing (emitting) the phase-modulated light A ′ including the phase modulation effect by the spatial light modulator 11a at the stage of signal generation. The present inventors have newly found that the recording optical system can be simplified.

  In addition, the complex amplitude of the diffracted light obtained in the normal hologram reading process is detected, and the above reproduction process is performed digitally (in-computer processing), thereby eliminating the need for optical phase conjugate reading and reproduction. It turns out that you can.

  FIGS. 3A to 3D show optical models and configuration examples corresponding to the processes described above.

FIG. 3A shows an optical model of a digital modulation signal generation process processed in the computer. Here, phase modulation is applied to the signal light A by the virtual random diffuser plate 11b to generate the modulated signal light A ′. The amount of calculation in this process is only the fast Fourier transform (function transform) and inverse fast Fourier transform (inverse function transform), multiplication of the signal light A and the transmission function of the spatial phase modulation element,
Represented by 2N ² log ₂ N + N ² .

Here, N ² is the number of analysis samples in the in-plane direction.

  Next, in the recording process shown in FIG. 3B, the complex amplitude of the modulation signal generated in the computer in FIG. 3A is used instead of the normal recording data page by the spatial light modulator 11a. Express.

  As a form of complex amplitude expression by the spatial light modulator 11a, the method disclosed in Non-Patent Document 7 can be used, but is not limited thereto. For example, a method using the first-order diffracted light of the spatial light modulator 11a can be used. Thereafter, the generated modulated signal light A ′ is irradiated onto the recording medium 13 through the lens 12 to record a hologram.

  After all, this recording optical system can have the same structure as that of a general holographic memory recording optical system except that the phase-modulated light A ′ (modulation signal) is expressed by the spatial light modulator 11a. It can be seen that it is.

  In the readout process shown in FIG. 3C, optical phase conjugate readout is not actually performed, diffracted light is obtained from the hologram in accordance with a normal procedure, and the complex amplitude is measured by the phase detection method. The phase detection method may be appropriately selected according to the optical system to be used. As a specific example, a measurement procedure when the phase detection method disclosed in Patent Document 1 is applied to this reading process, and an overall configuration diagram are shown. It is shown in the item of supplementary explanation mentioned later. However, when phase modulation or quadrature amplitude modulation is used as a signal modulation method, a phase detector is eventually required regardless of whether or not the present invention is applied.

  According to this embodiment, once the complex amplitude of a certain light wave is measured, various operations and propagation calculations can be performed on the light wave in the computer at high speed and with high accuracy.

  In this embodiment, the complex amplitude of the diffracted light is measured by a phase detector (imaging device 15) disposed behind the recording medium 13, and the subsequent processing is left in the computer, so that the reproducing optical system is completely To make it unnecessary.

  Next, FIG. 3D shows an optical model of the digital phase conjugate reproduction process. First, the phase conjugate wave of the diffracted light measured is calculated.

  Next, Fourier transformation is performed, and phase modulation exp {−iφ (r)} by the spatial phase modulation element is added again (phase modulation calculation).

  The above series of processing is equivalent to performing Fourier transform on the measured diffracted light itself without calculating the phase conjugate wave and multiplying the spatial phase modulation exp {iφ (r)} with the sign inverted, Therefore, the same inter-page crosstalk reduction effect can be expected by either method.

  However, calculation using a phase conjugate wave may compensate for phase distortion in the recording / reading optical system. For example, when an objective lens such as the lens 12 has aberration and its design specifications are known, the aberration can be corrected using a phase conjugate wave on a computer.

  In addition, after the spatial phase modulation is added again, inverse Fourier transform (inverse function transform) is performed to obtain a reproduction data page that is phase conjugate.

The amount of calculation in the digital phase conjugate reproduction process is basically represented by 2N ² log ₂ N + N ² as in the digital modulation signal generation process.

According to the above embodiment, when removing the noise component, the object is irradiated with the reproduction reference light E or the phase conjugate light E ^* , or the diffracted light from the object is subjected to the spatial phase of the random diffuser plate 11b or the like. It is not necessary to pass through the modulation means (or element). That is, optical phase conjugate readout / reproduction is not required. For this reason, the structure of the whole system can be simplified.

[Modification of noise removal method]
In the following, as a modification of the above-described noise removal method, the performance improvement by adding the shift operation of the random diffuser plate 11b, a solution to the enlargement of the lens aperture diameter, the problem of the form in which the present invention is applied to the collinear optical system A solution to that will be described.

(Shift operation of the random diffusion plate 11b) FIG.
As will be described below, by adding a shift operation to the random diffusion plate 11b, further performance improvement of the above-described embodiment is possible.

(Hologram recording process) FIG. 4 (a)
First, in the recording process shown in FIG. 4A, the position of the random diffusion plate 11b is sequentially displaced for each of the recording data pages P1 to Pm to give different phase modulation patterns φ _k (r).

  At this time, the arrangement position of the random diffusion plate 11b is varied (displaced) until the spatial cross-correlation of each phase modulation pattern becomes sufficiently small. Thereby, the cross-correlation between the holograms can be reduced, and the crosstalk component between pages can be suppressed.

  However, it should be noted that this form is intended to reduce the inter-page crosstalk component itself emitted from the recording medium 13.

(Hologram readout / reproduction process) FIG. 4 (b)
On the other hand, in the optical phase conjugate reading / reproducing process shown in FIG. 4B, when the kth data page is read out, the random diffuser plate 11b is returned to the kth position, and the phase conjugate diffracted light is again applied. The phase modulation pattern φ _k (r) may be multiplied.

  When this improvement plan is optically realized, a large mechanical drive unit for precisely controlling the random diffusion plate 11b on the order of microns is required.

  However, as described above, the digital modulation signal generation and the digital phase conjugate reproduction are used (the optical processing process and the electronic processing process are effectively coexisted), so that the shifting operation of the random diffusion plate 11b can be performed quickly and easily. Since it is possible to perform electronic processing, the above-described physical problems can be easily overcome. That is, an optical element such as the random diffusion plate 11b is not actually installed, and its function is expressed by processing in the computer assuming an optical model for operating the random diffusion plate 11b virtually installed in the computer. .

  According to the above aspect, the cross-correlation between the phase modulation patterns is reduced by adjusting the arrangement position of the corresponding virtual random diffusion plate 11b so that the spatial cross-correlation of each phase modulation pattern is sufficiently small. The crosstalk component between unit information can be suppressed.

  By effectively coexisting the optical processing process and the electronic processing process as described above, crosstalk between unit information can be greatly reduced without adding a new optical element to the conventional optical system.

(Regarding the lenses before and after the random diffuser) FIG. 5
Next, as shown in FIG. 5A, since the light wave after passing through the spatial phase modulation element such as the random diffuser 11b propagates to a wider angle, a lens having a larger aperture diameter must be prepared. This leads to an increase in the size of the entire optical system.

  To solve this problem, for example, the reduction of the beam diameter of the signal light A can be achieved by assembling a reduction optical system with two lenses 12a and 12b before and after the random diffusion plate 11b as shown in FIG. Can be prevented. In practice, the reduction optical system can be omitted by expressing the phase-modulated light A 'by the spatial light modulator 11a as described above.

(Collinear optical system) ... Fig. 6
Next, a case where the present invention is applied to a collinear optical system will be described with reference to FIG. Unlike the two-beam optical system, when the collinear optical system is used, the signal light A and the (modulation) reference light E are arranged on the same axis as shown in FIG. It passes through the diffusion plate 11b. Thereafter, a hologram is recorded by the phase-modulated light A ′ to which spatial phase modulation is added and the reference light E.

Next, in the optical phase conjugate reading / reproduction process shown in FIG. 6B, the hologram of the recording medium 13 is irradiated with the phase conjugate light C (corresponding to the above-described phase conjugate light E ^* ) of the reference light E, and diffraction is performed. Light D is obtained. Thereafter, the reference light E and the diffracted light D are re-transmitted through the random diffusion plate 11b, and thus spatial phase modulation is added again. At this time, the reproduction data page component and the reference light E are demodulated / reproduced, but the inter-page crosstalk component is further spread over a wide range. As a result, the inter-page crosstalk with the reference light E arranged outside the signal light A is separated out of the lens 12a.

  However, since the reference light E is actually subject to phase disturbance when passing through the recording medium 13 in which a large number of holograms are written, the reference light is received during recording when it passes through the random diffusion plate 11b again. Spatial phase modulation is not canceled out completely, and the reference light component remains in the reproduction data page area, resulting in quality degradation.

(Separation of signal light and reference light) FIG. 7
As a form for solving the above problems, for example, a form for avoiding the transmission of the reference light E through the random diffuser plate 11b is conceivable.

  Hereinafter, two optical systems capable of avoiding the transmission of the reference light E through the random diffusion plate 11b will be described with reference to FIG.

  The optical system shown in FIG. 7A is an optical system devised so that the reference light E is arranged outside the lens aperture diameter so as not to pass through the random diffusion plate 11b.

  On the other hand, the optical system shown in FIG. 7B is an optical system that prepares the reference light E from another optical path after the signal light A has transmitted through the random diffusion plate 11b. The reference light data page R is a data page including only the reference light ring excluding the “data page” portion of the recording data pages P1 to Pm.

  However, the optical system shown in FIG. 7A has another problem that the reference light E cannot pass through a column portion that supports the lens 12a in front of the random diffusion plate 11b.

  On the other hand, the optical system shown in FIG. 7B also requires another optical path for the reference light E, which causes another problem of losing the advantages of the collinear optical system such as simplicity of the entire system and resistance to vibration. In other words, it is difficult to optically avoid the transmission of the reference light E through the random diffusion plate 11b.

(The transmission effect of the reference light random diffuser is realized by digital processing) FIG.
However, as described above, the above-described problem is solved by expressing the modulated signal light A ′ including the effect of the random diffusion plate 11b and the unmodulated reference light surrounding the periphery in advance by the spatial light modulator 11a. it can.

  More specifically, in the signal generation process processed in the computer based on the optical model shown in FIG. 8A, the phase-modulated light A ′ to which spatial phase modulation is added by the random diffusion plate 11b is spatially modulated. Directly generated by the vessel 11a. That is, in the recording process shown in FIG. 8B, the modulated signal light A 'and the surrounding (unmodulated) reference light E surrounding it are expressed by the spatial light modulator 11a.

  On the other hand, in the reading process shown in FIG. The diffracted light D is extracted from the recording medium 13 using the reference light E, and the complex amplitude of the diffracted light D is measured by the image sensor 15 (phase detector). The reference light E may be either optically spatially filtered as shown in the figure, or may be virtually filtered within the computer after detecting the complex amplitude. In the digital phase conjugate reproduction process shown in FIG. 8D, the same procedure as before is taken.

  In the holographic memory, a high recording density is achieved by multiplex recording data pages P1 to Pm on the recording medium 13 as holograms. On the other hand, crosstalk between pages has a great influence because a large number of holograms are overwritten, and the potential of the multiplexing method is greatly limited. In the above background, according to the present embodiment, it is possible to greatly reduce crosstalk between pages while completely maintaining the conventional optical system having a simple structure. For this reason, multiplex recording is possible at a minimum interval equivalent to the selectivity of each multiplexing method, and a dramatic improvement in recording density of 10 times or more can be expected.

  Currently, there are many studies aiming to improve the recording density steadily by improving the performance of the recording medium 13 and signal processing technology (see Non-Patent Document 8), and this embodiment can dramatically improve the recording density. Yes, it can be a breakthrough. For example, according to the above-described embodiment, an optical memory device having an ultrahigh recording density of about 10 to 100 TB / disc can be constructed, so that it can be expected to play an active role in various areas such as super high-definition video, digital archives, and data centers. In addition, the long-term reliability and power saving of optical memory can be utilized to make a significant contribution to green IT. Specifically, in a data center where power consumption has become a major issue in recent years, if an HDD (Hard Disk Drive) can be replaced with an optical memory, power savings of about a quarter can be achieved.

[Confirmation of basic operation and demonstration of effectiveness]...
In the following, the basic operation described above is confirmed and the effectiveness is verified. Furthermore, it will be demonstrated that the performance can be further improved by adding the shift operation of the random diffuser plate 11b.

  Here, all of these evaluations are performed by numerical calculation, and the fast Fourier transform beam propagation method is used for the propagation calculation of the light wave in the inhomogeneous medium (Non-patent Document 9).

  The recording medium 13 is assumed to be a photopolymer, and the interference fringes between the signal light A and the reference light E are converted into a refractive index distribution (hologram) according to the following equation (6).

Here, Δn _max is the maximum amplitude of the refractive index modulation amount, Δn _N−1 (x, y, z) is the refractive index distribution at the (N−1) th recording, and I _N (x, y, z). ) Is the interference fringe intensity (W / cm ² ) in the Nth recording, T is the exposure time (s), and E _sat is the saturation energy flux density (J / cm ² ).

  Further, a random diffusion plate having a Gaussian autocorrelation is assumed as the spatial phase modulation element (Non-patent Document 10). In addition, analysis models and analysis parameters used in the following numerical calculations are shown in FIGS. 9 and 26, respectively. In this analysis, pinholes are installed in the recording / reproducing optical system, respectively, and the aperture size is set to twice the Nyquist aperture.

(Confirmation of basic operation) ... FIG. 8, FIG. 10 to FIG.
Hereinafter, the basic operation of the above-described embodiment will be confirmed while following the collinear optical system shown in FIG.

  First, in the digital modulation signal generation process (actually processed in the computer) shown in FIG. 8A, signal light A obtained by modulating the data page shown in FIG. 10 is generated.

  Next, FIG. 11 shows a state of light wave propagation immediately after the signal light A has passed through the random diffusion plate 11b.

Compared with the diffusion angle θ _dif = 0.0 ° (FIG. 11A), when θ _dif = 10.0 ° (FIG. 11B), the signal light A diffuses over a wide range. Can be observed. The transmission function of the random diffusion plate 11b used here is shown in FIG. Further, originally, it is necessary to construct a reduction optical system so that there is no overlap between the region of the phase modulated light A ′ and the region of the reference light E. However, in this analysis, this is omitted for the sake of simplicity. In addition, the signal light size before transmission through the random diffusion plate 11b is set to be small in advance.

  Next, in the recording process shown in FIG. 8B, the normal ring-type reference light E is added to the phase-modulated light A ′ as shown in FIG. This distribution is expressed by the actual spatial light modulator 11a. Looking at the signal light region, it can be seen that the structure of the original data pages P1 to Pm has changed to a state where it cannot be discriminated at all. Thereafter, the phase-modulated light A ′ and the reference light E are collected by the lens 12, and the interference fringes are recorded in the recording medium 13 as a hologram. At this time, for the purpose of generating crosstalk between pages, in addition to the data page shown in FIG. 10, three different data pages were recorded in a multiplexed manner by the same procedure.

  Next, in the reading process shown in FIG. 8C, first, the normal reading reference light shown in FIG. 13 is generated by the spatial light modulator 11a. Thereafter, the reference light E is irradiated onto the hologram in the recording medium 13 through the lens 12 to obtain the diffracted light D shown in FIG. The diffracted light D includes a reproduction data page component and an interpage crosstalk component which is a non-reproduction page component. The reproduction data page component is handled as a pure component that does not contain any noise component. Finally, the complex amplitude of the diffracted light D is measured by the image sensor 15 (phase detector). However, since this time it is performed by numerical calculation, complex amplitude measurement by the phase detection method is not performed.

  Next, in the digital phase conjugate reproduction process shown in FIG. 8D, first, the phase conjugate wave of the acquired diffracted light D is calculated. Next, the phase conjugate wave is Fourier transformed to calculate the complex amplitude of the diffusion plate surface. Thereafter, the complex amplitude is multiplied by the transmission function of the random diffusion plate 11b. FIG. 15 shows the light wave propagation immediately after the reproduction page component and the inter-page crosstalk component retransmit the random diffusion plate 11b.

  In FIG. 15A, it can be observed that the reproduction page component is despread after the spatial phase modulation received in the signal generation process is compensated. On the other hand, in FIG. 15B, it can be observed that the inter-page crosstalk component is diffused over a wide range because there is no phase correlation with the random diffusion plate 11b. Finally, the intensity distribution of the reproduction data page on the output surface OS is shown in FIG. According to the figure, it can be seen that the data page is reproduced with very high quality.

[Demonstration of effectiveness]...
Next, in the following, it will be demonstrated that the crosstalk between pages can be greatly reduced by the above-described embodiment.

  Note that the present invention can be applied to any multiplexing scheme, but in the following, demonstration examples in the speckle shift multiplexing scheme and the collinear shift multiplexing scheme are shown.

  In addition, FIG. 17A and FIG. 17B show page layouts used for multiplex recording. The shift interval of each page arrangement is set to about 3 times the shift selectivity shown in FIG.

  This is a sufficiently small value compared to the actual shift interval set to about 20 to 30 times the selectivity.

(Speckle shift multiplex method)
Here, the effectiveness when the present invention is applied to the speckle shift multiplexing system (Example 1) will be demonstrated.

  The speckle shift multiplexing method is a form in which data pages are multiplexed and recorded using a speckle-shaped reference beam generated by a random phase mask while slightly shifting the medium position in the in-plane direction.

  FIGS. 19A and 19B show the transition of the noise component of the reproduction data page and the signal-to-noise ratio (SNR) as the multiplexing number M increases. Here, the SNR follows the following definition formula (7).

Here, μ _on is the average intensity of on pixels, μ _off is the average intensity of off pixels, σ _on is the variance of on pixels, and σ _off is the variance of off pixels.

  Also, the strength of the noise component is

Represented by

  According to FIG. 19A, the noise component is clearly reduced in the first embodiment to which the present invention is applied, compared with the case of the normal speckle shift multiplexing system. This result shows that crosstalk between pages that cannot be removed by the pinhole is dramatically suppressed by the present invention.

  On the other hand, according to FIG. 19 (b), the SNR rapidly deteriorates due to the influence of inter-page crosstalk in the case of the conventional method, but the inter-page crosstalk is greatly increased in the case of the first embodiment to which the present invention is applied. Therefore, a high SNR is maintained.

  In addition to the above, the SNR when the multiplex number M = 64 in the first embodiment to which the present invention is applied and the SNR when the multiplex number M = 11 in the conventional method are the same. This indicates that there is a possibility of improving the recording density by about 6 times.

  However, there remains room for further improving the recording density by using the random diffusion plate 11b having a larger diffusion angle than that set in this analysis.

(Collinear shift multiplexing)
Next, the effectiveness of the second embodiment in which the present invention is applied to the collinear shift multiplexing method will be demonstrated.

  The collinear shift multiplexing system refers to a mode in which data pages P1 to Pm are multiplexed and recorded using a collinear optical system while slightly displacing the medium position in the in-plane direction.

  20A and 20B show how the noise components and the SNR of the reproduction data pages P1 'to Pm' change with the number M of multiplexing. 20 (a) and 20 (b) show the same tendency as in Example 1 described above, indicating that the present invention is useful for the collinear shift multiplexing method.

(More crosstalk reduction between pages by the shift operation of the random diffuser plate 11b)
Next, it is demonstrated using the speckle shift multiplexing method that the crosstalk between pages can be further reduced by adding the shift operation of the random diffusion plate 11b.

  However, in this analysis, for simplicity. Instead of actually shifting the random diffusion plate 11b, a random diffusion plate profile was sequentially generated for each page.

  21 (a) and 21 (b), the noise component of the reproduction data page and the SNR transition with the increase of the multiplexing number M are compared with the presence or absence of the diffusion plate shift function.

  According to FIG. 21A, it can be seen that the inter-page crosstalk can be suppressed by adding the shift function of the random diffusion plate 11b. Further, according to FIG. 21B, it can be seen that the SNR of the reproduction data page is naturally improved by suppressing the crosstalk between pages. In addition, the SNR when the multiplexing number M = 64 when the shifting function of the random diffusion plate 11b is added coincides with the SNR when the multiplexing number M = 34 when the shifting function of the random diffusion plate 11b is not provided. Yes. This indicates that the recording density can be further improved by nearly twice by adding the shift operation of the random diffusion plate 11b.

  As described above, the effect of improving the storage capacity according to the above-described embodiment is 12 times (it may be expanded to about 100 times by future system optimization).

  Further, the above-described embodiment can be widely applied to the improvement of the storage capacity in all existing hologram memories including an angle multiplexed hologram memory and a collinear hologram memory.

  Further, the above-described embodiment can be applied to all modulation methods such as intensity modulation type, phase modulation type, spatial quadrature amplitude modulation type, and multi-level modulation type thereof.

  Furthermore, the above-described embodiment is applicable not only to optical memory but also to noise reduction in image processing apparatuses such as digital cameras and 3D imaging.

[Supplemental explanation] ... 22 to 25
(Difference in function between normal mirror and phase conjugate mirror) FIG.
The phase conjugate light is a light wave that has a complex conjugate in terms of space with respect to a certain light wave and has the same wavefront and propagates in the opposite direction.

  The electric field of electromagnetic waves propagating along the z-axis direction

Write.

  Here, ω is an angular frequency, k is a wave number vector, and amplitude A and phase φ are real functions of position (x, y, z).

  For this arbitrary electromagnetic wave, its phase conjugate wave is

It is.

Here, E and E _c is the conjugate relationship.

  These two light waves have exactly the same wavefront at any point in space. However, the motions of these two wavefronts are in opposite directions.

In fact, reversing the sign of t in E yields E _c .

  Therefore, the phase conjugate wave is often called a “time reversal wave”.

  Here, FIG. 22 shows the difference in properties between the light reflected by a normal mirror and the phase conjugate light. This figure shows a case where a plane wave passes through a phase-distorted object such as a diffuser plate and then enters a normal mirror or a phase conjugate mirror.

  FIG. 22A shows a case where incident light is reflected by a normal mirror. In this case, with respect to incident light that has passed through the phase-distorted object and the phase of a part of the wavefront is delayed, the reflected light has a wavefront that is folded back by the mirror surface. Therefore, when the reflected light passes through the phase-distorted object again, the phase delay is doubled.

  On the other hand, FIG. 22B shows a case where phase conjugate light of incident light is generated by a phase conjugate mirror. In this case, since the same wavefront as the light incident on the phase conjugate mirror propagates in the opposite direction, the phase delay of the wavefront is canceled when the light passes through the phase-distorted object again. As described above, the phase conjugate light has a correction effect on the distortion of the incident wavefront.

(Hologram Forming Method Using Signal Light and Reference Light) FIGS. 23 and 24
Next, it is shown that a complex amplitude distribution of arbitrary signal light can be generated by using the primary light of the spatial light modulator 11a.

Hereinafter, the principle will be described. As shown in FIG. 23, the signal light A _s and the reference light A _r, respectively, the recording medium 13, a case where incident at an angle 0 ° and theta. A _s is the complex amplitude of the signal light, A _r represents the complex amplitude of the reference beam.

  These are expressed by the following equations.

Here, a _s (x, y) and a _r (x, y) are amplitude distributions of the signal light and the reference light, respectively, and φ (x, y) is a spatial phase distribution of the signal light.

Here, when the recording medium is in a position of z = 0, A _s and A _r are each rewritten as follows.

  Due to the interference of these two light waves, the following hologram is recorded in the recording medium.

Then, by irradiating the reference beam A _s in the hologram, diffracted light is expressed by the following equation is obtained.

At this time, as shown in FIG. 24, the 0-order light direction _{| A} ^s _| 2 A _r and _{| A} ^r _{| 2} A ^r, the + 1-order light direction ^{_{A s | A r | 2,}} -1 order light In the direction, A _s ^* A _r ² is diffracted. Since the complex amplitude A _s of the signal light is diffracted into the +1 order light direction, a right side first term and the second term unnecessary information of formula (B-6), required only the third and fourth terms It turns out that it is information.

As described above, to display a hologram distribution of the third and fourth terms by the spatial light modulator is irradiated with plane wave is a reference beam A _r at angle theta, + 1 complex amplitude A _s of the primary light direction signal light A can get. Here, as the spatial light modulator, either a spatial phase modulator or a spatial intensity modulator can be used. Any one of the spatial light modulators can generate a complex amplitude (both phase and intensity) of light.

  When the third term and the fourth term of the formula (B-5) are transformed,

It becomes.

Here, when the amplitude a _r (x, y) of the reference light E is considered to be a plane wave,
Formula (B-7) is

Can be written. Therefore, if the spatial light modulator 11a is provided with an image obtained by multiplying the amplitude a _s (x, y) of the signal light shown in Expression (B-8) by the wave of cos {kxsinθ + φ (x, y)}. It will be good. When a spatial intensity modulator is used as the spatial light modulator, a value obtained by adding a certain value to the hologram distribution of Expression (B-8) is displayed so that the displayed value does not become a negative value.

[Configuration Example when 2ch-HDI is Applied to Reading Process] FIG. 25
Next, a procedure for performing complex amplitude measurement of diffracted light by 2-channel holographic diversity interferometry (2ch-HDI) will be described.

  FIG. 25 shows a configuration diagram when 2ch-HDI is applied to the reading process of FIG.

  First, the diffracted light D and the interference light are respectively transmitted through the half-wave plate WB1 and the quarter-wave plate WB2 to become 45-degree linearly polarized light and circularly polarized light.

  Next, two light waves of the diffracted light D and the interference light are combined by BS (BS: Beam Splitter).

  Thereafter, two interference fringes having a spatial phase difference of π / 2 are generated on the image sensor (complex amplitude detector) 15a and the image sensor (complex amplitude detector) 15b by the polarization BS.

When the light intensity distributions measured by the image sensor 15a and the image sensor 15b are V ₀ and V _{π / 2} respectively, and the light intensity distribution of the reference light measured in advance is R ₀ , the following equation (C-1) To obtain the complex amplitude.

Where I ₀ is

It is. From this, each of phase distribution and intensity distribution is calculated | required by following Formula (C-3).

[Application to image (biological sample) measurement]
The present invention can also be applied to the field of image measurement. For example, the image measurement apparatus to which the present invention is applied can greatly reduce various noise components mixed while the object light reaches the image sensor 15 (photodetector). FIG. 27 shows a conceptual diagram thereof.

(Phase modulation process)
In the phase modulation process shown in FIG. 27A, first, a plane wave is irradiated onto the object 18 to be measured. Next, the obtained object light O passes through the random diffusion plate 11b having the effect of beam diffusion, so that spatial phase modulation is added.

  When there is a noise component such as reflected light or background light of each optical element between the random diffuser plate 11b and the image sensor 15 (having a complex amplitude measurement function), the modulated object light O ′ mixed with the noise component is present. Is measured by the image sensor 15.

  In the present embodiment, the noise included in the object light O is obtained by performing an equivalent calculation in the computer using the measured complex amplitude distribution for the optical process of the phase demodulation process shown in FIG. Components can be removed.

  Specifically, first, a phase conjugate wave of the detected light wave distribution (complex amplitude distribution) is calculated. Next, the light wave propagation calculation of the phase conjugate wave is performed, and the distribution of the complex amplitude on the diffusion plate surface of the random diffusion plate 11b is obtained. And this distribution and the phase distribution of the random diffuser plate 11b measured in advance are multiplied. At this time, the phase modulation of the object light O is canceled out, but the noise component is diffused over a wide range because there is no correlation with the phase distribution of the random diffusion plate 11b. As a result, a complex amplitude distribution of the object light O from which noise components are largely separated is obtained. In this embodiment, one or both noise components of the phase and intensity of the image to be measured can be reduced and detected.

[Application to image measurement using 2ch-HDI]
Next, FIG. 28 shows various noise components when the present invention is applied to the image measurement using the 2ch-HDI described above.

  For example, the reflected light of the lens 12b becomes a noise source as shown. The lens 12b has a reflectance of less than 1% even when the antireflection film is coated, and generates reflected light that causes a phase detection error. Similarly, the reflected light of the BS and the polarization BS becomes a noise source. Further, in addition to the reflected light of these optical elements, it is also assumed that background light enters the image sensor 15. In the image measurement using the 2ch-HDI of this embodiment, most of these noise sources can be greatly reduced, and the phase detection accuracy can be increased.

[Application to optical tomography (optical CT, optical tomography, optical tomography)]
Next, it is widely required in the medical field to acquire a tomographic image (three-dimensional image) in a living body.

  Optical coherence tomography has been put into practical use as a tomographic imaging technique having high spatial resolution (about 10 μm). This is a measurement method based on the fact that the position of the reflection point along the optical axis can be identified with the resolution of the coherence length using low coherence light interference.

  In general, the OCT technique used is a method in which scanning in the horizontal and depth directions is alternately performed and an optical interference signal is detected by a point detector, so that the tomographic imaging speed is several frames / second (fps). ). FD-OCT (Fourier domain OCT) that converts the detection light into the frequency domain with a spectroscope and linearly changing the oscillation frequency of the wavelength tunable laser as a method that does not require mechanical optical delay operation for speeding up. SS-OCT (Swept Source OCT) for obtaining reflected light intensity in the depth direction of a living body has been developed. Both techniques require a broadband laser light source or a wavelength tunable laser light source.

  Since the OCT apparatus in practical use uses an interferometer using an optical fiber, as shown in Non-Patent Document 11, mechanical scanning is required in the lateral direction of the measurement sample. (Non-patent document 12).

  In the following, the application of the present invention to biological image measurement, particularly optical tomographic imaging (optical CT), which is a medically important application, will be considered. An important point in tomographic imaging is a technique for extracting only the necessary scattered light (signal component) from the tomographic plane from the scattered light (noise components) generated from a number of tomographic planes of the measurement object. This is highly similar to the operation of selectively extracting only a specific image from a large number of images stored in the optical memory. That is, according to the present embodiment, a coherence control technique required for OCT (optical CT) or the like is not required for extracting an image from a specific tomographic plane. In addition, by applying the present invention to biological image measurement, it is possible to develop an optical tomographic imaging apparatus that is significantly less expensive than the current optical CT technology such as OCT, and more accurately and quickly. A tomographic image of a living body can be measured. Furthermore, in the conventional optical tomographic imaging, only the intensity information of the image is measured. However, in the method of this embodiment, it is possible to acquire not only the intensity information of the image but also the phase information of the image. Can contribute greatly to progress.

  An outline of the case where the present invention is applied to biological image measurement will be described step by step with reference to FIG.

  First, in the measurement process of the biological sample 19 shown in FIG. 29A, the plane wave P emitted from the laser light source is transmitted through the random diffusion plate 11b disposed on the Fourier plane. As a result, spatial phase modulation φ is added to the plane wave P, and phase-modulated light Pexp {−iφ} = P ′ is generated.

  Next, the phase-modulated light P ′ reaches the biological sample 19 via the lens 12 b and the lens 12 c. Assuming that the layer (target layer) that coincides with the Fourier plane in the biological sample 19 has the amplitude reflectance distribution S (x, y), the phase-modulated light Pexp {−iφ} has the amplitude reflectance of the target layer. The following modulated object light to which the distribution S (x, y) is added is generated. This S (x, y) is a signal component to be detected.

  At this time, as shown in the figure, the multiple scattered light (noise component) from the non-target layer is also mixed into the modulated object light. In addition, assuming that reflected light from the optical elements in the lenses 12a to 12c and the image sensor 15 (phase detector) is also mixed, these light waves are expressed by the following equation (D-2).

Here, B _j is random scattering noise, the subscript j is the layer number, k is the number of the target layer (the position in the depth direction having the signal to be detected), M is the number of layers, and C is the reflection of each optical element. Let it be noise. The “layer” is a structure in the depth direction virtually modeled in the biological sample 19, and it is assumed that the biological sample 19 is composed of a number of layers. In an actual biological sample 19, such a layer does not exist, and the resolution in the depth direction of the detection system is an amount corresponding to the thickness of the layer.

  Finally, after passing through the lens 12c, the complex amplitude of the light in which the noise component and the signal light modulated by the imaging element 15 (phase modulated light P ') are mixed is measured. The distribution to be measured is a distribution obtained by spatial Fourier transform of the above equation (D-2) by the action of the lens 12c.

  When it is desired to change the target layer to be measured, the entire measuring apparatus or the biological sample 19 itself is moved in the optical axis direction, or the lens 12c is replaced with a spatial light modulator or a variable focus lens, and the focal position is changed in the optical axis direction. You just need to operate. When performing a focus operation using a spatial light modulator, no movable part is required in both the depth direction and the lateral direction.

  In the conventional OCT, the reflectance distribution of the biological sample 19 is obtained by point scanning, but in the present embodiment, the reflectance distribution can be obtained collectively in units of lateral planes.

  For this reason, as described above, in the living body measurement according to the present embodiment, the measurement time can be significantly shortened as compared with the conventional OCT. In addition, in the conventional OCT, a special laser light source having a coherence length of about several tens of μm is necessary. However, in the living body measurement of the present embodiment, a normal inexpensive laser light source may be prepared. In addition, since an optical element such as a low-quality lens that is not coated with an antireflection film can be used, the cost of the entire apparatus can be significantly reduced according to the biological measurement of this embodiment.

  Next, a process for digitally extracting object light will be described. The optical model is shown in FIG. The following description will be made along an optical model. However, since the following processes can be digitally processed in a computer, an optical system (element) is not actually physically required. First, a phase conjugate wave of the detected light wave is calculated, and then this phase conjugate wave is Fourier transformed to obtain a complex amplitude on the diffusion plate surface of the random diffusion plate 11b.

  Thereafter, by passing through the random diffusion plate 11b, the spatial phase modulation of the random diffusion plate 11b is added again as follows.

  As a result, the phase modulation of the modulated object light is canceled out. On the other hand, scattered noise and reflected light of each element are diffused over a wide range by the effect of the added spatial phase.

  The object light extracted from the scattering noise from the non-target layer is finally observed on the output surface via the lens 12b and the lens 12c. The noise components of the second term and the third term in the above equation (D-5) are easily separated because they diffuse outside the signal light.

At this time, since P ^* is a plane wave (uniform amplitude distribution), the amplitude reflectance S (x, y) ^{* of} the target layer is obtained.

[Another expression of the present invention]
The present invention can also be expressed as follows.

  A noise removal method according to an aspect of the present invention includes a step of irradiating a target with phase-modulated light, a step of removing a noise component from transmitted light, reflected light, or scattered light obtained from the target, and the target The step of constructing the two-dimensional information may be included.

  “Phase-modulated light” is light obtained by passing planar light through a random phase plate. The “object” is a hologram recording medium in the hologram memory, or a sample to be observed in the image measuring device. The “configuration of two-dimensional information” is an imaging system using a lens system in the case of an optical element, and in the case of calculation processing, reconstruction processing is performed from the intensity / phase distribution by Fourier transformation or the like. That is.

  Further, in the conventional OCT, the depth direction of the object to be measured is identified using the coherence of light, whereas the noise removal method according to one aspect of the present invention performs spatial phase modulation and digital phase conjugate reproduction. Only a signal (scattered light) from a specific depth of the detection target may be extracted.

  Because of the difference in operation principle, the image measurement method according to one aspect of the present invention eliminates the need for an optical fiber interferometer and a mechanical scanning system associated therewith required in conventional OCT. This is because the image measurement method according to one aspect of the present invention can greatly contribute to the cost reduction of the optical CT apparatus, and the image measurement method according to one aspect of the present invention has potentially high speed and high spatial resolution characteristics. It can be a basis for what you are doing.

  In addition, the conventional optical fiber interferometer can measure only one point at a time. As described above, improvements in time-domain OCT include FD-OCT that simultaneously measures the depth direction z of a medium using a frequency space, and SS-OCT that measures while changing the frequency.

  On the other hand, in the image measurement method according to one aspect of the present invention, two-dimensional (x, y) simultaneous measurement is possible because image measurement is the basis.

  The depth method z in the image measurement method according to one aspect of the present invention is controlled by controlling the focal position of the diffusive phase-modulated light. Generally, the focal position is controlled by fine movement of the measurement system or lens control. However, it is also possible to control the focal position using a spatial light modulator instead of the lens, and in this case, a measurement system that does not require any movable part can be realized.

  Further, according to the image measurement method according to one aspect of the present invention, three-dimensional (x, y, z) simultaneous measurement that simultaneously measures information in a plurality of depth directions from information on one fixed focal position is also possible. It is.

  When the focal position is set at the position of the layer k in the figure (spatial phase modulation φ in this layer), the spatial phase modulation φ ′ in the layer k ′ different from k is calculated or measured, and the back propagation calculation formula is obtained. By using the spatial phase modulation φ ′ when performing the above equations (D-3) to (D-5), the information on the tomographic plane of k ′ is demodulated from the measured data when the focus position is on the k layer. it can.

  The lateral spatial resolution (x, y) in the image measurement method according to one aspect of the present invention depends on the spatial resolution of the phase detection technology, but the spatial resolution of the phase detection technology is that of an image sensor (CCD / CMOS or the like). Since the resolution is basically the same, high-speed and high-resolution measurement can be expected compared to OCT.

  The depth direction resolution (z) in the image measurement method according to one embodiment of the present invention is determined by the focal depth of the lens used, and even a lens having a numerical aperture NA of about 0.6 has selectivity of about 5 μm. (About 10 μm). If a high NA (numerical Aperture) lens is used, tomography with a layer thickness of 1 μm or less is theoretically possible. Note that this calculated value may be slightly modified because it is based on selectivity in a multi-layered memory.

  Next, in the conventional optical tomographic imaging, only the intensity information of the image is measured, but in the image measuring method according to one aspect of the present invention, not only the intensity information of the image but also the phase information of the image can be acquired. Is possible.

  As for the light source, OCT requires an expensive and special light source such as a broadband light source or a wavelength tunable light source. However, a general inexpensive laser light source is sufficient for the image measurement method according to one aspect of the present invention. This can greatly contribute to the cost reduction of the optical CT technology.

  In addition, according to the image measurement method according to an aspect of the present invention, if a general image measurement optical system (an optical system that irradiates an observation target with a laser and images it) is provided based on the phase measurement technique. Other than that, it is possible to perform tomographic imaging of a living body without requiring a special light source, a precise interferometer, a mechanical scanning system, and a large amount of calculation.

[Additional Notes]
The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The present invention can be applied to technologies such as a large-capacity optical memory, image processing, and 3D imaging. For example, the present invention can be widely applied to the improvement of the storage capacity in all existing hologram memories including an angle multiplexed hologram memory and a collinear hologram memory. In addition, the present invention can be applied to all modulation schemes such as an intensity modulation type, a phase modulation type, a spatial quadrature amplitude modulation type, and a multilevel modulation type thereof.

  The present invention is applicable not only to optical memories but also to noise reduction in image processing apparatuses such as digital cameras and 3D imaging.

11 Spatial phase modulation optical system 11a Spatial light modulator (light irradiation means)
11b Random diffuser plate 12 Lens 12a to 12c Lens 13 Recording medium (hologram recording medium, object)
14 Lens 14a, 14b Lens 15 Imaging device (complex amplitude detecting means)
15a, 15b Image sensor (complex amplitude detection means)
16 phase conjugate mirror 18 object 19 biological sample A signal light A ′ phase modulated light A ″ complex amplitude C phase conjugate light D diffracted light E reference light O object light O ′ phase modulated light P plane wave P ′ phase modulated light IS input surface OS output surface P1 to Pm Data page P1 'to Pm' Reproduction data page R Reference beam data page

Claims (13)

A light irradiation step of irradiating an object with phase modulated light generated by performing spatial phase modulation processing on at least predetermined signal light; and
For the complex amplitude of the emitted light emitted from the object irradiated with the phase-modulated light, or the phase conjugate light of the phase-modulated light emitted from the object irradiated with the predetermined reference light A noise removal step for performing a process of removing a noise component from the emitted light by performing the same phase modulation process as the spatial phase modulation process on the emitted light;
An information generation step for performing processing for generating two-dimensional information using the emitted light emitted from the object irradiated with the phase-modulated light or using the light from which the noise component has been removed;
A complex amplitude detection step of detecting a complex amplitude of the emitted light emitted from the object irradiated with the phase-modulated light, and
In the above noise removal step,
A noise removal method, wherein the noise component is removed by performing a phase modulation calculation corresponding to the spatial phase modulation process on the complex amplitude detected in the complex amplitude detection step . The above two-dimensional information is
Light emitted from the object irradiated with the phase-modulated light, or
2. The noise removing method according to claim 1 , wherein the light from which the noise component is removed is generated by forming an image using a lens system. The above two-dimensional information is
For the two-dimensional intensity distribution or phase distribution of the outgoing light emitted from the object irradiated with the phase-modulated light, or
For the two-dimensional intensity distribution or phase distribution of light from which the noise component has been removed,
The noise removal method according to claim 1 , wherein the noise removal method is generated by applying a predetermined function transformation. In the light irradiation step,
Noise removing method according to any one of claims 1 to 3, characterized in that to generate the phase modulated light by transmitting a random phase plate the signal light. In the above noise removal step,
The noise component is removed from the said emitted light by transmitting the emitted light containing the phase conjugate light of the said phase modulation light to a random phase plate, The any one of Claim 1 to 4 characterized by the above-mentioned. Noise removal method. The different phase modulation patterns are generated by changing the arrangement positions of the random phase plates when the phase modulation light includes a plurality of signals to which different phase modulation patterns are added. 6. The noise removal method according to 4 or 5 . Light irradiating means for irradiating an object with phase modulated light generated by performing spatial phase modulation processing on at least predetermined signal light; and
For the complex amplitude of the emitted light emitted from the object irradiated with the phase-modulated light, or the phase conjugate light of the phase-modulated light emitted from the object irradiated with the predetermined reference light A noise removing unit that performs a process of removing a noise component from the emitted light by performing the same phase modulation process as the spatial phase modulation process on the emitted light;
A complex amplitude detecting means for detecting the complex amplitude of the emitted light emitted from the object irradiated with the phase-modulated light, and
The noise removing means is
A noise removing apparatus that removes the noise component by performing a phase modulation calculation corresponding to the spatial phase modulation processing on the complex amplitude detected by the complex amplitude detecting means . 8. The noise removing apparatus according to claim 7 , wherein the light irradiating unit directly emits the phase-modulated light obtained by performing the spatial phase modulation process on the signal light in advance. Furthermore, an information generation unit is provided that performs processing for generating two-dimensional information using the emitted light emitted from the object irradiated with the phase-modulated light or using the light from which the noise component is removed. The noise removal device according to claim 7 or 8 , characterized in that A recording / reproducing apparatus comprising the noise removing apparatus according to any one of claims 7 to 9 ,
The light irradiation means is
The information is recorded by irradiating the hologram recording medium as the object with the phase-modulated light together with the recording reference light,
The noise removing means is
The same phase modulation as the spatial phase modulation processing is applied to the diffracted light as the outgoing light including the phase conjugate light generated by irradiating the hologram recording medium with the reference light for reproduction as the predetermined reference light. By removing the noise component from the diffracted light,
The recording / reproducing apparatus further comprises reproducing means for outputting the light from which the noise component has been removed from the diffracted light by the noise removing means as the reproducing light of the information recorded on the hologram recording medium. An image measuring device comprising the noise removing device according to any one of claims 7 to 9 ,
The light irradiation means irradiates the observation sample as the object with the phase-modulated light,
The noise removing means is
For the complex amplitude of the emitted light emitted from the observation sample irradiated with the phase-modulated light, or
For the outgoing light including the phase conjugate light of the phase-modulated light emitted from the observation sample irradiated with the predetermined reference light,
By performing the same phase modulation processing as the spatial phase modulation processing, noise components are removed from the emitted light,
Furthermore, using the outgoing light emitted from the observation sample irradiated with the phase-modulated light, or
An image measuring apparatus comprising: information generation means for performing processing for generating two-dimensional information using light from which the noise component has been removed. A recording / reproducing method using the noise removing device according to any one of claims 7 to 9 ,
A recording step of recording information by irradiating the hologram recording medium as the object with the phase-modulated light together with the recording reference light by the light irradiation means;
The spatial phase modulation process on the diffracted light as the output light including the phase conjugate light generated by irradiating the hologram recording medium with the reproduction reference light as the predetermined reference light by the noise removing unit A noise removing step of removing a noise component from the diffracted light by performing the same phase modulation processing as
A reproduction step of outputting the light from which the noise component has been removed as reproduction light of information recorded on the hologram recording medium. An image measurement method using the noise removal device according to any one of claims 7 to 9 ,
A light irradiation step of irradiating the observation sample as the object with the phase-modulated light by the light irradiation means;
The phase-modulated light emitted from the observation sample irradiated with the predetermined reference light with respect to the complex amplitude of the emitted light emitted from the observation sample irradiated with the phase-modulated light by the noise removing unit A noise removal step of performing a process of removing a noise component from the emitted light by performing the same phase modulation process as the spatial phase modulation process on the emitted light including the phase conjugate light;
An information generation step of performing processing for generating two-dimensional information using the emitted light emitted from the observation sample irradiated with the phase-modulated light or using the light from which the noise component has been removed. An image measurement method characterized by the above.