JP3101355B2 - Recording / reproducing method for optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable optical recording medium recording / reproducing method.

[0002]

2. Description of the Related Art In recent years, research on using a photochromic material for a recording layer of an optical recording medium has been actively conducted. When a photochromic material is irradiated with light of a predetermined wavelength, it undergoes a photochemical reaction to change the molecular structure and change optical properties such as absorbance for light of a specific wavelength. In addition, it has the property that upon irradiation with light of a predetermined wavelength, the molecular structure returns to its original state.

[0003] Using such properties, reproduction of information recorded on an optical recording medium containing a photochromic material is described in, for example, "Optical Memory Symposium '88" published by the Optoelectronic Industry and Technology Promotion Association (September 1988). Pages 3 and 4 of the "Symposium on Papers" and the symposium "Current and Future Prospects of Photochromism" (November 20, 1990) sponsored by the Kinki Chemical Society Functional Dye Group and Electronics Group. As disclosed on pages 39 to 40, it is generally performed by irradiating an optical recording medium with a laser beam for reproduction at low power and detecting a change in absorbance associated with a photochemical reaction as, for example, a change in reflectance. I have.

However, the information reproduction signal mainly includes noise (hereinafter, referred to as medium noise) mainly related to the surface properties of the medium and noise (hereinafter, referred to as noise) caused by fluctuations in the intensity of the reproduction laser beam related to the stability of the light source. Laser noise)
Therefore, there is a problem that a high C / N reproduction signal cannot be obtained.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high C / N reproduction signal in view of the above problems.

[0006]

Serial optical recording medium SUMMARY OF THE INVENTION The present invention
The recording / reproducing method is an optical recording medium for recording / reproducing information by irradiating an optical recording medium containing a photochromic material with light.
In the recording / reproducing method , recording of single information is performed by irradiating a single piece of information with light whose polarization state has been changed corresponding to a signal of the information to cause optical anisotropy. Performed, for the optical recording medium on which the recording was performed,
Generated by irradiating polarized light corresponding to optical anisotropy
Separates the light into two polarization components and separates each polarization component
Information by taking the difference between the two outputs
Reproduction is performed.

The method of reproducing an optical recording medium according to the present invention is directed to an optical recording medium containing a photochromic material on which information is recorded by irradiating polarized light to generate optical anisotropy. Reproduction of information by splitting light generated by irradiating light in a polarization state corresponding to optical anisotropy into two polarization components and detecting the difference between the two outputs obtained by detecting each polarization component. Is performed.

[0008]

According to the present invention, for a single piece of information,
The optical recording medium containing the photochromic material that records information by generating optical anisotropy by irradiating light whose polarization state has been changed accordingly has a polarization state corresponding to the optical anisotropy. When the light generated by irradiating light is separated into two polarization components, noises such as medium noise and laser noise included in each detection power of the two polarization components have the same phase and the same amplitude. , The noise can be effectively reduced.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of the present invention will be described with reference to FIG.

An optical recording medium having a recording layer containing a photochromic material is disclosed in SPIE Vol.
Page 51 of g and Information Handling (1979)
Page 56 and Proceedings of the 59th Annual Meeting of the Chemical Society of Japan (198
9) 3IH30 on page 427 and 3IH on page 429
34, dichroism is induced by irradiating, for example, linearly polarized light. As a result, after irradiating the optical recording medium with linearly polarized light and measuring the absorbance with linearly polarized light having a polarization plane that forms a predetermined angle with the polarization plane, for example, the absorbance as shown in FIG. Since it has the property (optical anisotropy), information is recorded / reproduced using this property.

[0011] Information is recorded in a signal contained in a single piece of information.
By irradiating light with a correspondingly changed polarization state
For example , in the case of data 1, a linearly polarized light having a polarization plane of θ = 0 ° is irradiated, and in the case of data 0, a single linearly polarized light having a polarization plane of θ = 90 ° is irradiated . It records information.

For reproducing information, for example, when irradiating circularly or randomly polarized light onto an optical recording medium, emitted light (reflected light or transmitted light) emitted from the optical recording medium in accordance with the recorded information. Is used to change the polarization state of the light.

For example, in the case of an optical recording medium having the characteristics shown in FIG. 2 on which information is recorded as described above, the emitted light has a stronger polarization component of θ = 0 ° with respect to data 1 and θ = 90.
The intensity of the polarization component of ° becomes weak, and θ =
The intensity of the polarization component at 0 ° is weak, and the intensity of the polarization component at θ = 90 ° is high. For example, when irradiating an optical recording medium with circularly polarized light having the intensity distribution shown in FIG. 3, the emission light corresponding to data 1 is elliptically polarized light having the intensity distribution as shown in FIG. Is elliptically polarized light having an intensity distribution as shown in FIG.

Therefore, θ is determined by a polarizing beam splitter or the like.
The reproduced signal can be obtained by separating the polarization component of = 0 ° and the polarization component of θ = 90 °, detecting them as separate outputs, and taking the difference between the outputs.

[0015] Noise such as medium noise and laser noise is almost equally contained in any polarization component of the emitted light.
And the same phase and the same amplitude (performed by appropriately increasing / decreasing the width). Therefore, by taking the difference between the output based on the polarization component of θ = 0 ° and the output based on the polarization component of θ = 90 ° as described above, Media noise and laser noise can be removed.

Hereinafter, embodiments will be described in detail.

As the material used for the recording layer, for example, JP-A-2-260127 (G11B7 / 00), JP-A-2-255380 (B41M 5/26), S
PIE Vol.200 laser Recording and Information Ha
ndling (1979), pp. 51-56, The Chemical Society of Japan 59th Annual Meeting Proceedings (1989), page 427, 3I.
Various photochromic materials, such as the photochromic materials disclosed in H30 and 3IH34 on page 429, etc., can be used. 1 by coating
A description will be given using an optical recording medium in which a recording layer having a thickness of μm is formed, and a reflective layer made of Al having a thickness of 1000 Å is formed on the recording layer by a vacuum evaporation method. This optical recording medium causes a coloring reaction by ultraviolet light, and a visible light (for example,
A decoloring reaction occurs at a wavelength of 500 nm).

FIG. 7 shows an example of a recording optical system for recording information on an optical recording medium. Using this optical system, information was recorded on the optical recording medium.

The optical recording medium 1 is colored by ultraviolet light. Laser light having a wavelength of 514.5 nm (intensity: 10 m
The linearly-polarized laser light output from the recording light source 5a of the Ar laser device that outputs W) is beam-shaped by the beam-shaping optical element 4 composed of a beam expander, and then linearly-polarized in response to the recording information signal. The light is incident on the polarization state conversion optical element 3 for rotating the polarization plane.

The polarization state conversion optical element 3 comprises a Faraday rotator or an electro-optical element. In the case of a Faraday rotator, the polarization plane can be rotated by changing the applied current. Can rotate the plane of polarization by changing the applied voltage.

The laser light incident on the polarization state conversion optical element 3 is driven by the modulation element 6 in response to data 0 and 1 (recording information signal) contained in the single information. Then, the polarization planes of the laser light are converted so as to be orthogonal to each other according to the data 0 and 1 (for example, the polarization plane is θ = 0 ° for data 1 and θ = 90 ° for data 0). ) And condensed on the recording layer of the optical recording medium 1 by the objective lens 2 to record a single piece of information.

When the recording light source is a semiconductor laser device or the like which outputs divergent light, a beam shaping optical element 4 composed of a collimating lens is used. When the recording light source is a gas laser device, An optical element 4 composed of a beam expander is used.

The electro-optical element can convert linearly polarized light into elliptically polarized light, circularly polarized light, and the like, and vice versa, so that information can be recorded in other polarization states.

FIG. 1 shows an example of a reproducing optical system for reproducing information from an optical recording medium on which information has been recorded as described above. Replayed.

Reference numeral 5b denotes a reproducing light source, and the intensity of the output light is set sufficiently low. Here, the wavelength 51
This is an Ar laser device that outputs 4.5 nm laser light (for example, intensity: 0.5 mW).

The linearly-polarized laser light output from the reproducing light source 5b is beam-shaped by a beam shaping optical element 4 composed of a beam expander.
After being converted into random polarized light, the light passes through a non-polarizing beam splitter 7 having the same reflectance (transmittance) for P-polarized light and S-polarized light, and is condensed on the recording layer of the optical recording medium 1 by the objective lens 2.

The laser beam condensed on the recording layer is subjected to intensity modulation of the polarization components of θ = 0 ° and θ = 90 ° in accordance with the recorded information, and then is reflected as light on the optical recording medium 1. Released from The reflected light is, for example,
The intensity of the polarization component of θ = 0 ° is strong, and the intensity of the polarization component of θ = 90 ° is weakly modulated.
Is weak, and the intensity of the polarization component at θ = 90 ° is strongly modulated.

The modulated reflected light passes through the objective lens 2 and is reflected by the non-polarizing beam splitter 7, after which the above-mentioned polarization component of θ = 0 ° and the above-mentioned polarization component of θ = 90 ° are separated. Into the polarizing beam splitter 9 whose orientation is set as described above. For example, the polarization component of θ = 0 ° passes through the polarization beam splitter 9 and is condensed on the photodetector 12a by the lens 11a, and the current-voltage converter 1
3a, is converted into a voltage, and the polarized light component at θ = 90 ° is reflected by the polarizing beam splitter 9 to form a lens 11b.
Is collected by the photodetector 12b, and is converted into a voltage by the current-voltage converter 13b. As shown in FIG.
Since the output voltages corresponding to the recorded information signals output from the current-voltage converters 13a and 13b have opposite phases, the output voltage is subtracted by the operating amplifier 14 to obtain a reproduced signal (output voltage).

Here, the intensity fluctuation of the reflected light due to the medium noise and the laser noise does not depend on the polarization component.
Among the outputs obtained by the current-voltage converters 13a and 13b, noise caused by medium noise and laser noise is shown in FIG.
Since the amplitude and phase are the same as shown in FIG.
By taking the difference between the output voltages according to No. 4, the noise could be effectively removed from the reproduced signal.

It should be noted that even if a quarter-wave plate is provided instead of the depolarizing plate 8 and circularly polarized light is applied to the optical recording medium, noise due to medium noise and laser noise can be obtained in the same manner as described above. Was effectively removed.

When the reproducing light source is a semiconductor laser device or the like that outputs divergent light, a beam shaping optical element 4 composed of a collimating lens is used. When the reproducing light source is a gas laser device, An optical element 4 composed of a beam expander is used.

FIG. 10 shows an optical system of another recording / reproducing system for recording and reproducing information on and from an optical recording medium. 51a, 51
b is a light source that can be driven directly by current, such as a semiconductor laser device. The linearly polarized lights output from the light sources 51a and 51b have the same wavelength, and are set so that the polarization planes are orthogonal to each other when the information is recorded on the optical recording medium 1.

First, information recording will be described. A recording information signal A shown in FIG.
a is transmitted as a recording information signal C to the point C in FIG.
As shown in FIG. 11, the recording information signal B obtained by inverting the recording information signal A is transmitted to the point B of the drive circuit 52b of FIG.

Therefore, when the light source 51a emits laser light (ON state), the light source 51b does not emit laser light (OFF state).
The ON / OFF state of 1b is reversed, and the ON / OFF state is switched according to the information recording signal.

The linearly polarized laser light output from the light source 51a is beam-shaped by a beam shaping optical element 4a such as a collimator lens or a beam expander, passes through a half mirror 53a, and is reflected by a polarization beam splitter 55. Thereafter, the linearly-polarized laser light, which is focused on the recording layer of the optical recording medium 1 by the objective lens 2 and output from the light source 51b, is beam-shaped by a beam shaping optical element 4b such as a collimator lens or a beam expander. After being transmitted through the half mirror 53b and transmitted through the polarization beam splitter 55, the light is condensed on the recording layer of the optical recording medium 1 by the objective lens 2. The polarization beam splitter 55 and the light sources 51a and 51b
The orientations of the laser beams output from a and 51b are set such that the polarization planes are orthogonal to each other in the recording layer of the optical recording medium 1.

Therefore, in accordance with the recording information signal, for example, a laser beam having a linear polarization of θ = 0 ° for data 1 and a linear polarization of θ = 90 ° for data 0 is focused on the recording layer. , Information is recorded.

Next, reproduction of information will be described. When information is reproduced, the switches 15a and 15b are switched by a mode switching control signal for switching between a recording mode and a reproducing mode.
Is switched to the reproduction mode, and control voltages are input to the drive circuits 52a and 52b so that the light sources 51a and 51b output the linearly polarized laser light of constant and weak intensity.

The laser beams output from the light sources 51a and 51b irradiate the recording layer of the optical recording medium 1 in the same orthogonal polarization state as when recording the information.

The laser beams of the polarization states (polarization components) orthogonal to each other applied to the recording layer are emitted from the optical recording medium 1 as reflected light after the respective polarization components are intensity-modulated according to the recording information signal. Is done.

The reflected light is supplied to the polarizing beam splitter 55.
Is again separated into each polarized light component, one of the polarized light components is reflected by a half mirror 53a, is condensed by a photodetector 57a by a lens 56a, is converted into a voltage by a current-voltage converter 58a, and is converted into a voltage by the other. Is reflected by the half mirror 53b, is condensed on the photodetector 57b by the lens 56b, and is converted into a voltage by the current-voltage converter 58b.

As described above, the output voltages corresponding to the recording information signals output from the current-voltage converters 58a and 58b have opposite phases, and the noise output due to the medium noise and the laser noise has the same phase and the same output. Since the amplitude becomes the amplitude, the reproduction signal obtained by subtracting the output voltages from each other by the differential amplifier 60 effectively eliminates noise due to medium noise and laser noise.

In the above description, information is recorded by irradiating linearly polarized light beams orthogonal to each other in correspondence with data 0 and data 1. However, information is recorded in correspondence with either data 0 or data 1. For an optical recording medium that irradiates linearly polarized light and records information by not irradiating the other light,
Even when information is reproduced by the above-described reproducing apparatus, noise caused by medium noise and laser noise can be effectively removed. Further, there is an effect even if the planes of polarization of the linearly polarized light are not orthogonal to each other.

Further, even when data 0 was irradiated with circularly or randomly polarized light and data 1 was irradiated with linearly polarized light to record information, noise was effectively reduced. Information can be reproduced and can be changed as appropriate.

Even if elliptically polarized light is used instead of linearly polarized light, optical anisotropy occurs, so that information can be recorded, and information can be reproduced with noise effectively reduced.

Further, information is reproduced by irradiating light consisting of circularly polarized light, random polarized light, or linearly polarized light orthogonal to each other. Even if information is reproduced by irradiating light containing a linearly polarized component that does not match, noise due to medium noise or laser noise can be reduced. In addition, the light containing a linearly polarized light component that does not coincide with the plane of polarization of linearly polarized light or the major axis or minor axis of elliptically polarized light includes linearly polarized light, circularly polarized light, elliptically polarized light, and the like, and two lights are simultaneously irradiated. Things are also included. For example, if information is recorded in linearly polarized light orthogonal to each other in accordance with a recorded information signal, even if information is reproduced with linearly polarized light having a plane of polarization that is at 45 ° to the plane of polarization of the two linearly polarized lights, Noise and laser noise can be reduced, and the polarization planes of the two linearly polarized lights are
Linear polarized light having a polarization plane at an angle other than ° is also possible.

Further, in the recording / reproducing method or the reproducing method of the present invention, various photochromic materials can be used as appropriate, but it is necessary to appropriately select the wavelength of light to be irradiated and the like depending on the material used. Further, it can be used for a transmission type optical recording medium. Further, in the above embodiment, the linearly polarized light output from the light source is converted into another polarization state by a quarter-wave plate or the like, but the light source that outputs the polarization state light is used. Of course, it is good.

Furthermore, the wavelengths of the light used for recording and reproduction according to the present invention need not be the same, and can be changed as appropriate. Further, the reproducing method of the optical recording medium of the present invention can be performed as long as the optical recording medium has optical anisotropy.

[0048]

According to the present invention, since a noise resulting from medium noise and laser noise is removed from a reproduced signal obtained by reproducing information, a reproduced signal having a high C / N can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an optical system for reproducing an optical recording medium according to an embodiment of the present invention.

FIG. 2 is a diagram showing the polarization plane angle dependence of the absorbance of a photochromic material.

FIG. 3 is a diagram showing an intensity distribution of circularly polarized light applied to an optical recording medium.

FIG. 4 is a diagram showing an intensity distribution of elliptically polarized light emitted from an optical recording medium according to data.

FIG. 5 is a diagram illustrating an intensity distribution of elliptically polarized light emitted from an optical recording medium according to another data.

FIG. 6 is a diagram showing a structural formula of a photochromic material.

FIG. 7 is a diagram showing an example of an optical system for recording information on the optical recording medium according to the embodiment.

FIG. 8 is a diagram showing an output voltage according to the embodiment.

FIG. 9 is a diagram illustrating noise included in an output voltage according to the embodiment.

FIG. 10 is a diagram showing an example of an optical system for performing recording and reproduction on an optical recording medium according to another embodiment of the present invention.

FIG. 11 is a diagram showing a recording information signal according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical recording medium 3 Optical element for polarization state conversion 9 Polarization beam splitter 12a Photodetector 12b Photodetector 13a Current-voltage conversion part 13b Current-voltage conversion part 14 Differential amplifier 52a Light source 52b Light source 53a Half mirror 53b Half mirror 55 Non-polarization Beam splitter 57a Photodetector 57b Photodetector 58a Current-voltage converter 58b Current-voltage converter 60 Differential amplifier

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G11B ⁷ /00-7/013 G11B 7/30 G03C 1/00 531 G03C 5/08 351 G03C 5/56 511

Claims (2)

(57) [Claims] An optical recording medium for recording and reproducing information by irradiating an optical recording medium containing a photochromic material with light.
In the recording / reproducing method , recording of single information is performed by irradiating a single piece of information with light whose polarization state has been changed corresponding to a signal of the information to cause optical anisotropy. Performed, for the optical recording medium on which the recording was performed,
Generated by irradiating polarized light corresponding to optical anisotropy
Separates the light into two polarization components and separates each polarization component
Information by taking the difference between the two outputs
Recording / reproduction method for optical recording medium characterized by performing reproduction
Law . 2. An optical recording medium containing a photochromic material, on which information is recorded by irradiating polarized light to generate optical anisotropy, is polarized in accordance with the optical anisotropy. Optical recording characterized by separating light generated by irradiating light in a state into two polarized components, and reproducing information by taking a difference between two outputs obtained by detecting the respective polarized components. Media playback method.