JP4633005B2 - Optical switching unit, optical switching unit array and image display device - Google Patents

Description

  The present invention relates to an optical switching unit, an optical switching unit array, and an image display device. The present invention can be applied to optical communication, optical recording, printer switching devices, electronic viewfinders, and the like.

  As an element for performing optical switching, one using a liquid crystal or one using a micromirror is conventionally known, and Patent Document 1 proposes “an element that utilizes interference of light”. A “reflective wavelength filter with a narrow band” based on a principle different from these “one using liquid crystal or micromirror, one using light interference” has been reported (Non-Patent Document 1).

  The wavelength filter disclosed in Non-Patent Document 1 uses the “anomaly phenomenon due to the diffraction grating and the wavelength of light” in principle.

JP2002-287047 R. Magnusson and S.M. S. Wang, Transmission band pass-guided-mode resonance filters, Appl. Opt. Vol. 34, no. 35, 8106 (1995)

  The present invention realizes a novel optical switching unit based on the principle of “anomaly phenomenon due to diffraction grating and wavelength of light” reported in Non-Patent Document 1, and uses such an optical switching unit to create a new optical switching unit. An object is to realize an optical switching unit array and an image display device.

First, the resonance filter and the incident angle varying means will be described .

A “resonance filter” is a filter that resonantly reflects incident light having a specific wavelength by resonating a periodic structure with fine irregularities with the incident light. The “periodic structure with fine irregularities” is a periodic structure in which the period of irregularities is “approximately the same as or smaller than the wavelength used”.
The resonance filter transmits light other than “narrow band light (light of a specific wavelength)” causing resonance reflection with high transmittance.
The “incident angle varying means” is means for relatively changing the incident angle of incident light having a specific wavelength with respect to the resonance filter. The “incident angle with respect to the resonance filter” is an incident angle with respect to the periodic structure of the resonance filter.

That is, “light having a specific wavelength” means monochromatic light having a specific wavelength or light in a wavelength range including a specific wavelength and included in a “narrow band” in which the resonance filter causes resonance reflection.
The phrase “relatively changing the incident angle of the incident light with respect to the resonance filter” means that the change in the incident angle of the incident light to the resonance filter is relative, and the direction of the incident light with respect to the resonance filter is changed. Changing the direction of the resonance filter with respect to the incident light, and combining these.

The “switching” of the light by the optical switching unit is performed by changing the resonance wavelength by the resonance filter from a specific wavelength by changing the incident angle by the incident angle variable means, thereby changing the reflection state and the transmission state of the incident light. This is done by switching.

For example, when the incident angle of light having a specific wavelength to the resonance filter is set so that “resonance reflection occurs”, light having the specific wavelength is resonantly reflected and cannot pass through the resonance filter in this setting state. In this state, when the incident angle is changed, the resonance wavelength changes, so that resonance reflection does not occur with respect to the incident “light with a specific wavelength”, and the light with the specific wavelength passes through the resonance filter. Therefore, it is possible to switch between the “transmitting state” and the “reflecting and not transmitting state” through the resonance filter by changing the incident angle .

Optical switching unit according to claim 1 wherein is for performing optical switching to a plurality of light beams of different wavelengths, having a filter element and a incidence angle varying means.

"Filter elements" refers to two or more resonant filter: Fi (i = 1,2, ·· n) the formed by "disposed to overlap in series in a direction in which the passage of light".

  Each of the n resonance filters: Fi constituting the filter element has a different “specific wavelength causing resonance reflection”. That is, a specific wavelength: λi at which a certain resonance filter: Fi is resonantly reflected is different from a specific wavelength: λj at which another resonance filter: Fj is resonantly reflected. Therefore, each resonance filter reflects and reflects only “light of a specific wavelength corresponding to each resonance filter”.

In other words, the filter element is “incident light having a specific wavelength: λi (i = 1, 2,... N, i) (Li = 1, 2,. N (≧ 2) resonance filters that resonate and reflect n): Fi (i = 1, 2,... N) are arranged in series in the direction in which light passes.
Each resonance filter constituting the filter element has a light-transmitting waveguide layer and a cover layer, and the “periodic structure” has a fine uneven structure at the boundary between the waveguide layer and the cover layer. This is a one-dimensional structure in which fine regions having different refractive indexes are alternately arranged periodically in one direction.

  There are n “incident angle variable means” corresponding to n resonance filters and 1: 1. If these n incident angle varying means are C1, C2,... Ci,... Cn, for i = 1 to n, the incident angle varying means: Ci corresponds to the resonance filter: Fi, and the incident angle varying means. : Ci changes the incident angle: θi of “incident light: Li having a specific wavelength: λi” to the resonance filter: Fi. The change of the incident angle: θi by the n incident angle varying means: Ci is performed independently of each other.

In this way, by changing the incident angle: θi (i = 1, 2,... N) independently by the incident angle varying means: Ci (i = 1, 2,... N), the resonance filter: Fi. By changing the resonance wavelength due to (i = 1, 2,... N) from the specific wavelength: λi (i = 1, 2,... N), incident light: Li (i = 1, 2,... N) ) Are switched independently between the reflection state and the transmission state.
Incident angle varying means: Ci is provided for each resonance filter Fi, and the resonance filter Fi is tilted independently of the incident direction of incident light by a voltage applied to one or both of them, and the incident angle θi. (I = 1, 2,... N) is changed.

It is preferable that “n types of specific wavelengths: λi (i = 1, 2,... N)” in the optical switching unit according to claim 1 can express natural colors ( claim 2 ). For example, if n = 3, λ1 is a red (R) wavelength, λ2 is a green (G) wavelength, and λ3 is a blue (B) wavelength, a natural color is expressed by the output light from the optical switching unit. it can. If n ≧ 4 and the number of specific wavelengths is increased, a finer hue can be expressed.

3. The optical switching unit according to claim 1, wherein the incident angle varying means is “incident angle of incident light with respect to the resonance filter ” , and each incident angle varying means: Ci is incident on the resonance filter: Fi: resonance of Li. Filter: Incident angle with respect to Fi: θi is changed relatively.

That is, the incident angle varying means is a means for changing the direction of the resonance filter with respect to the direction of the incident light.

An optical switching unit array according to the present invention comprises the optical switching units according to claim 1 or 2 arranged in a one-dimensional or two-dimensional array ( claim 3 ).

According to a fourth aspect of the present invention, there is provided an image display device comprising an optical switching unit array, light irradiation means, and an imaging lens.
The “optical switching unit array” is the optical switching unit array according to claim 3 .

The “light irradiation means” is means for supplying light having a specific wavelength to each optical switching unit of the optical switching unit array.
The “imaging lens” forms an image of light transmitted through the optical switching unit array. The image formation by the imaging lens may be a real image or a virtual image. In the former case, the image display device can be implemented as a projector device, and in the latter case, the imaging lens is used as an eyepiece and transmitted through the optical switching unit array. It can be implemented as a viewfinder for viewing an image formed by an imaging lens with light.

According to a fourth aspect of the present invention, in the image display device, the optical switching unit constituting the optical switching unit array is the one according to the first or second aspect , and the light irradiation means is “specific wavelength: λi (i = 1, 2, ... Which supplies n types of light having n). In this case, a color image can be displayed by using the optical switching unit according to claim 3 ( claim 5 ).

Here, the principle of the resonance filter and optical switching will be described with reference to FIG.
FIG. 1A shows a general configuration of a resonance filter.
As shown in the figure, the resonance filter FA is configured by laminating a waveguide layer 12 and a cover layer 14 in this order on a light-transmitting substrate 10. The waveguide layer 12 and the cover layer 14 are translucent in material.

  The “upper surface in the drawing” of the waveguide layer 12 has a fine uneven structure, and the material of the cover layer 14 enters the recess. The waveguide layer 12 and the cover layer 14 are made of different materials, and thus have different refractive indexes. For this reason, the fine concavo-convex structure at the boundary between the waveguide layer 12 and the cover layer 14 is a “periodic structure in which fine regions having different refractive indexes are alternately arranged periodically”.

In the example being described, the periodic structure is “a one-dimensional structure having the horizontal direction in the drawing as the periodic direction”, and the uneven shape does not change in a direction orthogonal to the drawing.
As a reference example of the periodic structure, it is also conceivable that the cover layer 14 is omitted and the uneven structure on the top surface of the waveguide layer 12 is in contact with air .
In this case, the waveguide layer 12 and air constitute “a minute periodic structure in which minute regions having different refractive indexes are alternately arranged periodically”.

  When light is incident on the resonance filter FA shown in FIG. 1A so as to be “perpendicular to the fine periodic structure” as shown in the figure, the substrate 10, the waveguide layer 12, and the cover layer 14 are all translucent. Therefore, the incident light is transmitted through the resonance filter FA in “most wavelength region”, but “light in a narrow wavelength band including a specific wavelength λA” is reflected as shown in FIG. Is done.

In FIG. 1A, this state is depicted as a state in which light of wavelength λA incident on the resonance filter FA is reflected and does not pass through the resonance filter.
The phenomenon that “light in a narrow wavelength band including a specific wavelength: λA” is reflected by the resonance filter FA is an anomalous phenomenon caused by the diffraction grating constituted by the “micro periodic structure” and the wavelength of light, and is guided by the wave. This phenomenon is called “resonance reflection”, which is a phenomenon in which strong resonance occurs when the propagation constant of a light wave propagating in the layer 12 coincides with a “lattice vector having a minute periodic structure”, resulting in strong reflected light. The wavelength that produces the above (the upper wavelength: λA) is called the “resonance wavelength”.

FIG. 1B shows a state in which the incident angle of incident light having a specific wavelength λA incident on the resonance filter FA is tilted from “orthogonal incidence” shown in FIG.
That is, if the incident angle in the state of FIG. 1A is 0, the incident angle (referred to as α) shown in FIG. 1B is “α ≠ 0”.

  As shown in FIG. 1D, the resonance wavelength when the light having the wavelength λA is incident on the resonance filter FA at “incidence angle other than 0” is as follows. By changing from λA, the resonance wavelengths become λB and λC. Generally, as the incident angle changes from 0, the resonance wavelength is shifted so as to be separated approximately symmetrically into “incident angle: both sides of the resonance wavelength at 0”. The amount of separation is proportional to the incident angle.

  When light having a wavelength of λA is incident on the resonance filter FA at an incident angle of 0, the resonance wavelength is λA, and the incident light is resonantly reflected and does not pass through the resonance filter FA, but by changing the incident angle, When the resonance wavelength changes like λB and λC different from the wavelength λA, the light having the wavelength λA passes through the resonance filter FA as shown in FIG.

  Accordingly, the resonance wavelength of the resonance filter FA changes by switching the incident angle of the incident light, and the light that switches between the reflection state (incident angle: 0 in the above example) and the transmission state (non-zero incident angle) with respect to the wavelength: λA. Switching can be performed.

  The resonance wavelength λA in the resonance filter FA depends on the refractive index and dimensions of the substrate 10, the waveguide layer 12, and the cover layer 14, the pitch of a fine periodic structure, and the like. Can be adjusted. That is, the resonance filter FA can be designed and manufactured as “having a desired resonance wavelength”.

  The above example is a “resonance filter in which the resonance wavelength is λA when incident at an incident angle of 0”, but the resonance wavelength is λA when incident at a finite incident angle: α (for example, 5 degrees). It is possible to design and manufacture a “resonance filter”.

FIG. 8 is a diagram illustrating an example of a change in resonance wavelength due to a change in incident angle.
The curve denoted by reference numeral 80 is the transmittance at an incident angle of 0 degree, the curve 81 is incident angle: 1 degree, the curve 82 is incident angle: 2 degrees, the curve 83 is incident angle: 3 degrees, and the curve 84 is incident angle: 4 degrees, curve 85 is the transmittance at an incident angle of 5 degrees, and the wavelength giving transmittance of 0 in these curves is the “resonance wavelength at each incident angle”.

FIG. 2 shows another example of the resonance filter. In order to avoid confusion, the same symbols as in FIG.
In the resonance filter FB shown in FIG. 2A, the portion in which the waveguide layer 12 and the cover layer 14 are laminated in this order on the translucent substrate 10 is the same as the resonance filter FA shown in FIG. Structure.

  In the resonance filter FB shown in FIG. 2, PZT elements 16 </ b> A and 16 </ b> B whose height changes with voltage are fixed on the free surface (lower surface in the drawing) of the substrate 10. By applying a voltage to one or both of the PZT elements 16A and 16B, the actual part of the resonance filter FA (the part in which the waveguide layer 12 and the cover layer 14 are laminated in this order on the translucent substrate 10) is tilted. be able to.

  In the example shown in FIG. 2, as shown in FIG. 2B, the resonance filter FB is tilted by 5 degrees with respect to the light of wavelength: λA entering from the upper side to the lower side of the figure. 2 "(incident angle: 5 degrees) is designed and manufactured so that resonance reflection occurs, and when the inclination angle of the resonance filter FB is changed from 5 degrees to 2 degrees, the resonance wavelength changes, so that FIG. As shown in c), the light of wavelength: λA is set in a transmission state.

  That is, in the example shown in FIG. 2, the PZT elements 16A and 16B provided in the resonance filter FB and the voltage applying means (not shown) for applying a voltage to one or both of them are “incident angle variable means”. Will be composed.

  In the example of FIG. 2, the case where the PZT element is used as the means for changing the incident angle to the resonance filter FB has been described. However, an element using electrostatic force or “magnetostriction due to a magnetic field” may be used. Is possible.

  As described above, in the optical switching unit of the present invention, optical switching can be performed by “relatively changing the incident angle of incident light with respect to the resonance filter”. With such an optical switching unit array in which optical switching units are arrayed, an image can be displayed by independent optical switching of each element.

FIG. 3 is a view for explaining one embodiment of the optical switching unit according to claim 2 . FIG. 3A is a diagram illustratively showing a portion that performs optical switching.
In FIG. 3A, the symbol FE indicates a “filter element”. Reference numerals F1, F2, and F3 denote resonance filters. The resonance filters F1 to F3 constitute a filter element FE.
The resonance filters F1, F2, and F3 have different resonance wavelengths for incident light that is vertically incident (incident at an incident angle of 0), the resonance wavelength of the resonance filter F1 is λ1, the resonance wavelength of the resonance filter F2 is λ2, and the resonance filter F3. The resonance wavelength of λ3 is λ3. These resonance filters F1 to F3 are of the same type as the resonance filter FA described with reference to FIG.

  In FIG. 3A, symbol L1 indicates incident light having a wavelength: λ1 and incident on the resonance filter F1, and symbol RL1 indicates light having a wavelength: λ1 that is resonantly reflected by the resonance filter F1. The symbol TL1 is incident on the resonance filter F1 with a wavelength: λ1 at “finite incident angle: θ”, and “light that passes through the resonance filter F1 without being resonantly reflected” due to a change in the resonance wavelength due to the change in the incident angle. Show.

  Similarly, symbol L2 indicates incident light having a wavelength: λ2 and incident on the resonance filter F2, and symbol RL2 indicates light having a wavelength: λ2 that is resonantly reflected by the resonance filter F2. The symbol TL2 indicates “light that is incident on the resonance filter F2 with a wavelength: λ2 at a finite incident angle: θ and is transmitted through the resonance filter F2 without being resonantly reflected by a change in the resonance wavelength due to the change in the incidence angle”. Yes.

  Reference symbol L3 indicates incident light having a wavelength: λ3 and incident on the resonance filter F3, and reference symbol RL3 indicates light having a wavelength: λ3 that is resonantly reflected by the resonance filter F3. The symbol TL3 indicates “light that is incident on the resonance filter F3 with a wavelength: λ3 at a finite incident angle: θ and is transmitted through the resonance filter F3 without being resonantly reflected by a change in the resonance wavelength due to the change in the incident angle”. Yes.

  That is, the resonance filters F1, F2, and F3 are arranged in series in the direction in which light passes (downward in FIG. 3A).

  Since the “wavelength band where resonance reflection occurs” is narrow, the resonance filter F1 transmits light with wavelengths λ2 and λ3 with high transmittance, and the resonance filter F2 transmits light with wavelengths λ1 and λ3 with high transmittance. The resonance filter F3 transmits light having wavelengths λ1 and λ2 with high transmittance.

FIG. 3B illustrates the usage state of the reference example of the optical switching unit.

  Reference numerals LS1, LS2, and LS3 indicate light sources, reference numeral M1 indicates a mirror, and reference numerals M2 and M3 indicate dichroic mirrors. These mirrors M1 and dichroic mirrors M2 and M3 are “rockable” as shown in the figure, and the “mirror position” can be switched by driving means D1, D2 and D3.

  As the light sources LS1 to LS3, for example, semiconductor lasers or LEDs are used. The light source LS1 emits light of wavelength λ1, and the light sources LS2 and LS3 emit light of wavelengths λ2 and λ3, respectively. As described with reference to FIG. 3A, the wavelengths: λ1 to λ3 are resonance wavelengths of the resonance filters F1 to F3 (when the incident angle is 0), respectively.

  The dichroic mirror M2 transmits light having a wavelength: λ1, and reflects light having a wavelength: λ2. The dichroic mirror M3 transmits light having wavelengths λ1 and λ2, and reflects light having wavelength λ3.

  The mirror M1 and the dichroic mirrors M2 and M3 are set so that the reflected light is incident on the resonance filters F1, F2 and F3 at an incident angle of 0 in the “reference position”, and is driven by the driving means D1, D2 and D3. In the “driving state” by driving, the incident angle of the reflected light to the resonance filters F1 to F3 is set to the incident angle: θ in FIG. Therefore, the mirror M and the drive means D1 constitute “incident angle variable means: C1”, and the dichroic mirror M2 and the drive means D2 constitute “incident angle variable means: C2,” and the dichroic mirror M3 and the drive means D3. Constitutes "incident angle variable means: C3".

  Incident angle varying means: C1 to C3 change the incident angle of incident light to the corresponding resonance filter from “0 to θ”. At an incident angle: θ, the resonance wavelength of each resonance filter varies from λ1 to λ3, and light having wavelengths λ1 to λ3 passes through the resonance filters F1 to F3.

  That is, the optical switching unit shown in FIG. 3 has incident light: Li (i = 1) having a specific wavelength: λi (i = 1, 2, 3) because the periodic structure with fine irregularities resonates with the incident light. , 2, 3) to three resonance filters: Fi (i = 1, 2, 3) arranged in series in the light passing direction, and to the resonance filter: Fi. The incident angle variable means: Ci (i = 1, 2, 3) for relatively changing the incident angle of light having a specific wavelength: λi (i = 1, 2, 3). By changing the incident angle independently by the variable means: Ci (i = 1, 2, 3), the resonance wavelength by the resonance filter: Fi (i = 1, 2, 3) is changed to the specific wavelength: λi (i = 1, 1). 2, 3) by changing the reflection state and transmission state of incident light: Li (i = 1, 2, 3) Which is the optical switching unit for switching independently.

If the wavelength: λ1 is the red (R) color wavelength, the wavelength: λ2 is the green (G) wavelength, and the wavelength: λ3 is the blue (B) wavelength, the incident angle variable means: C1 to C3, these wavelengths: λ1 If the “transmission state / reflection state” of the resonance filters F1 to F3 with respect to λ3 is independently switched, the color of the light transmitted through the filter element FE can be switched and displayed in a natural color range .

In the example described with reference to FIG. 3B , the incident angle varying means: C1 to C3 are “means for changing the direction of the incident light L1 to L3”.

In the form of FIG. 3, by increasing the number of resonance filters having different resonance wavelengths and arranging them in series in the direction in which light passes, the number of light sources having different emission wavelengths and the number of swingable dichroic mirrors are increased accordingly. The color of transmitted light can be changed more finely.

  Conversely, if the number of resonance filters is two, for example, the wavelength: λ1, λ2, or “mixed color” can be expressed by combining the optical switching of the wavelengths: λ1 and λ2. If one is used, for example, light having a specific wavelength: λ1 can be optically switched.

In the embodiment shown in FIG. 3, the resonance filters F1 to F3 are of the type of the resonance filter FB described with reference to FIG. 2, and the mirror M1, the dichroic mirrors M2 and M3 are fixedly provided, and the resonance filters Optical switching can be performed by changing the incident angle by tilting the filter by “height change” of the PZT element by applying a voltage .
This case is the embodiment of claim 1.

  FIG. 4 is a diagram for explaining an embodiment of an image display device for displaying color images.

  FIG. 4A illustrates the optical switching unit array in an explanatory manner. The optical switching unit array 41R illustrated as an example is formed by arraying a number of minute resonance filters 410 in a two-dimensional array on a single transparent substrate.

  The individual resonance filters 410 are of the type shown in FIG. 2, and can change the incident angle by individually changing the inclination with respect to the incident light by a PZT element that changes in height when an external voltage is applied. A drive circuit for applying a voltage is also built with a resonance filter on a transparent substrate. Accordingly, the individual arrayed resonance filters 410 can be driven independently.

  A large number of resonance filters 410 formed in an array on the optical switching unit array 41R are of the “same type”, and each resonance filter 410 has an “inclination angle of 5 degrees shown in FIG. Resonance wavelength: λR is set so that the “state” is “off state” in which no voltage is applied to the PZT element 16A, etc., and the red (R) light of the incident light is resonantly reflected and light of other wavelengths is transmitted. Has been.

  In FIG. 4B, the optical switching unit arrays denoted by reference numerals 41G and 41BL are structurally similar to the optical switching unit array 41R described above. In the optical switching unit arrays 41G and 41BL, a large number of resonance filters are “arranged congruently with the arrangement of the resonance filters 410 in the optical switching unit array 41R”.

  The resonance filters arranged in the optical switching unit array 41G are of the same type, and in the off state where they are not driven, the green (G) color light of the incident light is resonantly reflected and light of other wavelengths is transmitted. The resonance wavelength: RG is set so that The resonance filters arranged in the optical switching unit array 41BL are of the same type, and in the off state where they are not driven, the blue (BL) color light of the incident light is resonantly reflected and light of other wavelengths is transmitted. The resonance wavelength: λBL is set so that

  As shown in the figure, the optical switching unit arrays 41BL, 41G, and 41R are arranged so as to overlap each other in the light passing direction (the vertical direction in FIG. 4B), and the individual resonance filters of each optical switching unit array are In other optical switching unit arrays, resonance filters at corresponding positions overlap with each other in the “light passing direction”.

That is, the optical switching unit arrays 41BL, 41G, 41R shown in FIG. 4B are two-dimensionally arrayed optical switching units according to claim 3.
Reference numerals 10BL, 10G, and 10R in FIG. 4B denote light sources that constitute the light source unit of the color light source means. In this embodiment, a high output LD is used. The blue (BL) light, green (G) light, and red (R) light emitted from the light sources 10BL, 10G, and 10R are converted into parallel light fluxes by the coupling lens 42, and the light passing direction is shown in FIG. b) The light enters the optical switching unit arrays 41BL, 41R, and 41G that are arranged in series in the vertical direction.

  When the drive state of each resonance filter of the optical switching unit array is “off state”, the incident angle to each resonance filter of the optical switching unit array is 5 degrees, and the light of the corresponding wavelength is resonantly reflected. In the “state (tilt angle: 2 degrees)”, the incident angle is 2 degrees, and light of the above wavelength is transmitted.

  When each optical switching unit of the optical switching unit arrays 41BL, 41G, and 41R is in an off state (a state in which the resonance filter is not driven), blue light from the light source 10BL is resonantly reflected by the optical switching unit array 41BL. The unit arrays 41G and 41R are transparent. The green light from the light source 10G is resonantly reflected by the optical switching unit array 41G, but the optical switching unit arrays 41BL and 41R are transmitted, and the red light from the light source 10R is resonantly reflected by the optical switching unit array 41R. The optical switching unit arrays 41G and 41BL are transmitted.

  After all, when each optical switching unit of the optical switching unit arrays 41R, 41G, and 41BL is in an OFF state, red light is resonantly reflected by the optical switching unit array 41R, and green light and blue light are resonated by the optical switching unit arrays 41G and 41B, respectively. Since it is reflected, the light of each color from the light sources 10R, 10G, and 10BL does not pass through the series arrangement of the optical switching unit arrays 41R, 41G, and 41BL.

  In the ON state where each optical switching unit of the optical switching unit array 41BL is driven, the blue light from the light source 10BL is transmitted through the optical switching unit arrays 41BL, 41G, and 41R, and each optical switching unit of the optical switching unit array 41G is driven. In the ON state, the green light from the light source 10G passes through the optical switching unit arrays 41BL, 41G, and 41R.

  Further, in the ON state where each optical switching unit of the optical switching unit array 41R is driven, the red light from the light source 10R passes through the optical switching unit arrays 41BL, 40G, and 41R. Accordingly, the optical switching unit arrays 41BL, 41G, and 41R can display a color image by transmitted light by “controlling the voltage application to the PZT element of each resonance filter” by the control means 44 in accordance with the image signal. it can.

The color image display apparatus shown in FIG. 4 can be implemented as, for example, a “viewfinder”.
Further, a “projection lens” (not shown) is added to the portion shown in FIG. 4B, and the color image light transmitted through the light switching unit arrays 41R to 41BL is enlarged and projected onto the screen by the projection lens. Can also be implemented. Such a projector has a thin and compact image display unit as compared with a color projector using three liquid crystal panels.

  Referring now to FIG. 5, FIG. 5 shows a resonance filter of the type shown in FIG. 1. In FIG. 5, the thickness indicated by reference numeral t1 is “the thickness of the waveguide layer 12”. , The thickness indicated by t2 is “the thickness of the periodic structure by the fine irregularities formed on the upper surface of the waveguide layer 12 (the depth of the concave portions in the fine irregularities)”, and the symbol Λ indicates the above period The “pitch” of the structure, indicated by the symbol d, is the “width of the convex portion in the periodic structure”. At this time, “fill factor: f” is defined by “f = d / Λ”.

Hereinafter, a method for manufacturing a resonance filter will be described with reference to FIG.
A quartz substrate 60 having a polished surface is prepared, and after the surface is cleaned, a TiO ₂ thin film 62 is formed by vacuum deposition (FIG. 6A). The “TiO ₂ thin film” has a large refractive index and can be formed relatively easily.

  A photoresist thin film is formed on the upper surface of the formed thin film 62, and fine patterning is performed to form a lattice in the photoresist layer. The patterning method can be formed by a method such as exposure using a stepper, exposure using EB (electron beam), exposure performed by scanning a condensed beam, and exposure using two-beam interference.

In this example, an exposure method using two-beam interference is used in consideration of productivity in increasing the area. A gas laser having a wavelength of 351 nm was used as the light source, and “i-line positive photoresist” was used as the photoresist. In this case, the pitch of the grating to be formed (corresponding to the pitch: Λ in the periodic structure formed on the thin film 62) can be adjusted by the “intersection angle of two exposure light beams”, and the exposure shown in FIG. Light beams L1 and L2 can be formed from Λ = λ / (sin θ) using one-side incident angle: θ. Here, λ is the wavelength of the two exposure light beams LA and LB. In FIG. 6E, the symbol PR indicates a photoresist layer.
The fine structure fill factor f can be adjusted by the exposure intensity.

The “TiO ₂ thin film 62” is etched using the lattice-formed photoresist as a mask to form a “periodic structure with fine irregularities” in the TiO ₂ thin film 62 as shown in FIG. 6B. In this example, since the depth of the irregularities formed by etching is shallow, etching using a photoresist as a mask is possible, but a metal thin film is deposited using the photoresist pattern as a mask and the metal pattern after removing the photoresist is used. It is also possible to perform etching using a mask. In this example, the cross-sectional shape of the fine concavo-convex structure is rectangular, but trapezoidal, corrugated and other shapes can also be realized.

  A cover layer 64 is formed on the thin film 62 having such fine irregularities (FIG. 6C). In this example, “acrylic ultraviolet curable resin” was used as a material for the cover layer 64 and cured by irradiation with ultraviolet rays. At that time, an ultraviolet curable resin having a “viscosity: 10 cP or less” was used in order for the resin to sufficiently enter the concave portion of the periodic structure due to fine irregularities and to flatten the surface satisfactorily.

  In the steps (a) to (c) in FIG. 6, the “resonance filter of the type described with reference to FIG. 1” is obtained. Further, elements 66A and 66B having a piezoelectric effect such as PZT elements are formed on the bottom surface of the quartz substrate 60, and electrodes are attached to the respective elements (FIG. 6D). A type of resonance filter "is obtained.

The waveguide layer 62 is formed of a TiO ₂ thin film on the quartz substrate 60 described above, a periodic structure with fine irregularities is formed on the upper surface thereof, a cover layer 64 is formed, and finally PZT is formed on the bottom surface of the quartz substrate 60. Using a manufacturing process in which elements 66A and 66B having a piezoelectric effect such as elements are formed and electrodes are attached to each element, wavelength: 635 nm (red: R), wavelength: 532 nm (green: G), wavelength: 440 nm (blue: Resonant filters FR, FG, and FBL that produce “resonance reflection at an inclination angle of 5 degrees and transmit these lights at an inclination angle of 2 degrees” for the light of BL) were prepared.

  The only difference between these resonance filters is the fine structure pitch: Λ. Hereinafter, specific values of the above-mentioned thicknesses: t1, t2, pitch: Λ, fill factor: f are listed.

Resonance filter FBL FG FR
Pitch: Λ 230nm 290nm 360nm
Fill factor: f 0.5 0.5 0.5
Thickness: t2 20nm 20nm 20nm
Thickness: t1 80 nm 80 nm 80 nm.

  FIG. 7 shows transmission curves of the resonance filters FR, FG, and FBL at incident angles: 2 degrees and 5 degrees. 7A shows a transmission curve for the resonance filter FR, FIG. 7B shows a transmission curve for the resonance filter FG, and FIG. 7C shows a transmission curve for the resonance filter FBL.

In the case of the resonance filter FBL, when light from a blue LD having a wavelength of 440 nm is incident at an incident angle of 5 degrees, the refractive index of the quartz substrate is 1.45, the refractive index of TiO ₂ is 2.25, and the acrylic ultraviolet curable resin. The refractive index is 1.50, and as shown in FIG. 7C, resonance reflection occurs in a narrow band near the wavelength: 440 nm (curve 74), but light of other wavelengths is substantially transmitted. When the incident angle is 2 degrees, the resonance wavelength is approximately 453 nm (curve 75). Therefore, the “light from the blue LD having a wavelength of 440 nm” incident at the incident angle: 2 degrees passes through the resonance filter FBL.

  In the case of the resonance filter FG, when light from a green LD having a wavelength of 532 nm is incident at an incident angle of 5 degrees, as shown in FIG. 7B, resonance reflection (curve 72) is performed in a narrow band near the wavelength of 532 nm. Occurs but transmits light of other wavelengths. When the incident angle is 2 degrees, the resonance wavelength is approximately 550 nm (curve 73). Therefore, the “light from the green LD having the wavelength: 532 nm” incident at the incident angle: 2 degrees passes through the resonance filter FG.

  In the case of the resonance filter FR, when light from a red LD having a wavelength of 635 nm is incident at an incident angle of 5 degrees, as shown in FIG. 7A, resonance reflection (curve 70) is performed in a narrow band near the wavelength of 635 nm. Occurs but transmits light of other wavelengths. When the incident angle is 2 degrees, the resonance wavelength is approximately 648 nm (curve 71). Therefore, the “light from the red LD with the wavelength: 635 nm” incident at the incident angle: 2 degrees passes through the resonance filter FBL.

It is a figure for demonstrating one example of a resonance filter. It is a figure for demonstrating another example of a resonance filter. It is a figure for demonstrating one Embodiment of an optical switching element unit. It is a figure for demonstrating one Embodiment of an image display apparatus. It is a figure for demonstrating the structure of a resonance filter. It is a figure for demonstrating an example of the manufacturing process of a resonance filter. It is a figure for demonstrating the characteristic in the specific example of a resonance filter. It is an example which shows the change by the incident angle of the resonant wavelength of a resonant filter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Translucent board | substrate 12 Waveguide layer 14 Cover layer 14
FA resonance filter λA Specific wavelength

Claims (5)

Resonant reflection of incident light: Li (i = 1, 2,... N) having a specific wavelength: [lambda] i (i = 1, 2,... N) due to resonance of the periodic structure with fine irregularities with the incident light. A filter element in which n (≧ 2) resonance filters: Fi (i = 1, 2,... N) are stacked in series in the light passing direction;
Resonance filter: Incident angle varying means for independently changing the incident angle: θi (i = 1, 2,... N) of light having a specific wavelength λ i (i = 1, 2,... N) to Fi: Ci (i = 1, 2,... N),
The incident angle varying means Ci (i = 1, 2,... N) is provided for each resonance filter Fi as a pair, and the resonance filter Fi is applied to one or both of the resonance filters Fi by the incident light. Inclining independently with respect to the incident direction to change the incident angle θi (i = 1, 2,... N),
By changing the incident angle: θi (i = 1, 2,... N) independently by the incident angle varying means: Ci (i = 1, 2,... N), the resonance filter: Fi (i = 1, 2,... N) by changing the resonance wavelength from the specific wavelength: λi (i = 1, 2,... N), the incident light: Li (i = 1, 2,... N) Independently switching between reflective and transmissive states
Each resonance filter constituting the filter element has a light-transmitting waveguide layer and a light-transmitting cover layer,
The periodic structure has a one-dimensional structure in which a fine uneven structure at the boundary between the waveguide layer and the cover layer is formed by alternately arranging fine regions having different refractive indexes in one direction. optical switching unit, characterized in that it. The optical switching unit according to claim 1, wherein
An optical switching unit characterized in that n kinds of specific wavelengths: λi can express natural colors.   An optical switching unit array comprising the optical switching units according to claim 1 or 2 arranged in a one-dimensional or two-dimensional array. An optical switching unit array according to claim 3,
Light irradiation means for supplying light having a specific wavelength to each optical switching unit of the optical switching unit array;
An image display device having an imaging lens for forming an image of light transmitted through the optical switching unit array. The image display device according to claim 4.
The optical switching unit constituting the optical switching unit array is the one according to claim 1 or 2, and the light irradiation means has n types of light having a specific wavelength: λi (i = 1, 2,... N). An image display device for supplying

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