JPH0833530B2 - Light modulator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a light modulator, and more particularly to a light that has been subjected to light modulation such as light passage or light shielding using a refractive index variable substance such as a diffraction grating and a liquid crystal. The present invention relates to a flexible optical modulator suitable for devices for display, optical recording, optical coupling, optical communication, and optical calculation.

(Prior Art) Conventionally, a refractive index variable substance, for example, a liquid crystal is filled between substrates having at least one of the optically isotropic diffraction grating structures, and the refractive index of the liquid crystal is increased by applying an electric field to the liquid crystal. Various light modulators have been proposed which are changed and perform light modulation such as passing or blocking of light by utilizing the diffraction effect of a diffraction grating.

For example, USP42511375 is disclosed as a variable color reduction filter.

FIG. 1 is a perspective view of a conventional light modulator. 12, 1 in the figure
Reference numeral 5 is a transparent electrode, 13 is a transparent diffraction grating, 14 is a transparent refractive index variable material, for example, liquid crystal, 16 is a transparent substrate, and these elements constitute the first light modulator 8-1. . Ten
Is a transparent spacer. Reference numeral 8-2 is a second light modulator having the same function as the light modulator 8-1 symmetrically provided with the transparent spacer 10 interposed therebetween.

12 'and 15' are transparent electrodes, 13 'is a transparent diffraction grating, 1
Reference numeral 4'denotes a transparent refractive index variable material such as liquid crystal, and 16 'denotes a transparent substrate.

The transparent spacer 10 is generally made of a transparent material such as a glass plate or a plastic plate. The thickness of the transparent spacer 10 must be configured to be as thin as possible in order to prevent so-called image shift that occurs when light passing through the transparent spacer 10 has a spread and is linear.

A transparent electrode 15 (15 ') is provided on the transparent substrate 16 (16'). The diffraction grating 13 (13 ') is a transparent electrode 15 (15')
It is formed on the upper surface by a method such as photolithography, etching, and lift-off. The grating grooves of the diffraction gratings 13 and 13 'are arranged so as to be orthogonal to each other.

FIG. 2 is an operation explanatory view of the optical modulator shown in FIG. 1, 8-1 is a first optical modulator of the first layer, and 8-2 is a second optical modulator of the second layer. is there. Reference numeral 26 is incident light, and 27 and 27 'are polarization components of the incident light 26 which are orthogonal to each other, 27 is a polarization component parallel to the paper surface, and 27' is a polarization component perpendicular to the paper surface.
23 and 23 'are diffraction gratings and 24 and 24' are liquid crystals.
Has an optical axis in the lattice groove direction, and the liquid crystal 24 'has an optical axis in the lattice groove arrangement direction. The refractive indices of the liquid crystals 24 and 24 'are controlled by applying an electric field by the transparent electrodes 22 (22') and 25 (25 ').

In the static state where no electric field is applied, in the first layer, the polarization component 27 ′ of the incident light 26 feels the extraordinary refractive index n _e of the liquid crystal 24, and the polarization component 27 has the ordinary refractive index n _{o of the} liquid crystal 24. Feel or,
In the second layer, the polarization component 27 'LCD 24''feel _o, polarized component 27 crystal 24' ordinary index of refraction n of the extraordinary refractive index n '
I feel _e . Here, the refractive index of the member forming the diffraction grating of the first layer is n _g , the refractive index of the member forming the diffraction grating of the second layer is n ′ _g , the wavelength of incident light is λ, the first layer and the second layer. Assuming that the thickness of the diffraction grating of the layer is T, T ', and the refractive index difference between the liquid crystal and the member of the diffraction grating is Δn, Δn', the diffraction efficiency of the zero-order transmitted diffracted light in the diffraction grating of each layer. η _o and η _o ′ can be expressed by the following equations (1) and (1) ′.

From the above equation, when Δn = 0 or Δn ′ = 0, η _o = 1 or η ′ _o = 1 and ΔnT = (m + 1/2) λ, or Δn ′
It can be seen that η _o = 0 or η ′ _o = 0 when the condition of T ′ = (m + 1/2) λ (m = 0,1,2,3, ...) Is satisfied.

If n _e = n _g is satisfied in the first layer, the polarization component 27
Pass through, and the other is modulated according to equation (1). Two
Also in the layer, n ′ _o = n ′ _g or n ′ _e = n ′
_{If g} is satisfied, the polarization component 27 'will pass through, and the other will be modulated according to equation (1)'.

Next, when an electric field is applied to the liquid crystals 24 and 24 ', the directions of the optical axes of the liquid crystals 24 and 24' change, and the polarized components
Since the refractive indexes of 27 and 27 'change, the first layer and 2 respectively
Modulation according to the equations (1) and (1) 'is performed in the layer.

For example, if the same liquid crystal is used for the liquid crystals 24 and 24 ',
n _e = n ′ _e , n _o = n ′ _o , and n _g =
If n ′ _g = n _o and T = T ′ are set, the equations representing the diffraction efficiency of the zero-order transmitted diffracted light in the first layer and the second layer are both equation (1).

The refractive index of the spacer 21 is assumed to be substantially equal to _ng . At this time, in the static state, the polarization component 27 of the incident light 26 passes through the first layer, and the polarization component 27 ′ becomes η _o = 0 according to the equation (1), so that the zero-order transmitted light is not emitted and all are higher-order diffracted light. Become. Further, in the second layer, the polarization component 27 becomes η _o = 0 according to the equation (1), and the zero-order transmitted light is not emitted and becomes all higher-order diffracted light. The polarization component 27 '
Passes through the second layer as it is as high-order diffracted light. Therefore, there is no light emitted in the zero-order direction. Next, when a predetermined electric field is applied and the optical axis directions (orientation directions) of the liquid crystals 24 and 24 'are oriented perpendicular to the diffraction grating surface, that is, in the incident direction of the light flux, the polarization components 27 and 27' are the first layer and In the second layer, the ordinary refractive index n _o of the liquid crystal is sensed, and the light passes through it to become zero-order transmitted light. Therefore, by applying an electric field, it is possible to control the transmittance of the zero-order transmitted diffracted light having a desired polarization characteristic. Although the zero-order diffracted light is considered as the modulated light in the above description, it goes without saying that the higher-order diffracted light can be used.

The optical modulators shown in FIGS. 1 and 2 perform optical modulation on incident light having an arbitrary polarization component by overlapping two optical modulators.

However, since the glass plates are used for both the upper and lower transparent substrates, the entire optical modulator tends to be thick. Again 2
Since the transparent spacer that sandwiches the two light modulation parts is also made of a glass plate or a plastic plate, the entire light modulation device becomes thicker, and the so-called image shift as described above is more likely to occur, and when contacting with the transparent electrode. The adhesiveness of was not so good, and there was a tendency that a puff was formed.

(Problems to be Solved by the Invention) The present invention is capable of easily light-modulating light having an arbitrary polarization component with a simple configuration, and particularly, of a high-precision light modulator for thinning the entire device. For the purpose of provision.

(Means for Solving Problems) A pair of transparent substrates arranged so that their substrate surfaces face each other, a transparent electrode formed on the substrate surfaces of the pair of transparent substrates, and a pair of transparent substrates A first diffraction grating formed on the transparent electrode of one transparent substrate, and a grating groove formed on the transparent electrode of the other transparent substrate of the pair of transparent substrates and orthogonal to the grating groove of the first diffraction grating. Second with
A transparent spacer, which is sandwiched between the diffraction grating and the first and second diffraction gratings and has transparent electrodes on both sides, and arranged in the grating grooves of the first and second diffraction gratings, is provided with liquid crystal molecules by applying an electric field. A light modulator having a liquid crystal whose state changes,
That is, each of the pair of transparent substrates is made of a plastic film.

Besides, the features of the present invention are described in the embodiments.

(Embodiment) FIG. 3 is a perspective view of an embodiment of the present invention. The same 32,3
Reference numeral 5 is a transparent electrode, 33 is a diffraction grating, 34 is a liquid crystal as a transparent variable refractive index material, 36 is a transparent substrate, and these elements constitute the first light modulating section 30-1. 31 is a transparent spacer. Reference numeral 30-2 is a second light modulation section having the same function as the first light modulation section 30-1 symmetrically arranged with the transparent spacer 31 interposed therebetween. 32 ', 35' are transparent electrodes, 33 'is a diffraction grating, 34
Is a liquid crystal and 36 'is a transparent substrate.

The light modulators 30-1 and 30-2 are arranged such that the grating grooves of the diffraction gratings 33 (33 ') are orthogonal to each other.

In this embodiment, the transparent substrates 36 and 36 'are each made of a uniaxially stretchable plastic film having a thickness of about 0.1 mm. The two optical axes of the two plastic films are arranged so that the directions of the optical axis H having the highest refractive index are orthogonal to each other.

The optical principal axis H of these plastic films is arranged to be orthogonal or parallel to the grating groove direction of the diffraction grating 33 (33 ').

At this time, in order to satisfactorily control the amount of passing light, it is preferable to set the optical principal axis H of the plastic film within ± 2 ° from the state perpendicular to or parallel to the grating groove direction of the diffraction grating.

In this embodiment, the transparent spacer 31 is replaced by the transparent substrate 36 (36 ').
It is composed of a uniaxially stretchable plastic film having a thickness of about 0.1 mm, which is similar to the above. As a result, the first light modulator 30-1
The distance between the second light modulation unit 30-2 and the second light modulation unit 30-2 is reduced to prevent so-called image shift.

The plastic film for the transparent spacer is constructed so that the optical principal axis H'having the highest refractive index in the optical principal axis direction of the plastic film is orthogonal or parallel to the grating groove direction of the diffraction grating 33 (33 '). ing.

At this time, in order to satisfactorily control the amount of light passing through the transparent spacer, it is preferable to set the optical principal axis H'of the plastic film within ± 2 ° from the state orthogonal or parallel to the grating groove direction of the diffraction grating.

As described above, in this embodiment, by using a uniaxially stretchable thin plastic film for the transparent spacer, it is possible to easily suppress the clearance of the transparent electrode, and the substrate and the mask at the time of photolithography at the time of forming the diffraction grating. We are trying to improve the adhesion.

The light modulation of the light modulation device in this embodiment is substantially the same as that of the light modulation device shown in FIG.

For example, it is assumed that light 26 having the same polarization characteristics 27 and 27 'as shown in FIG.

At this time, in the static state where no electric field is applied, in the first layer, the polarization component 27 ′ of the incident light 26 feels the extraordinary refractive index n _e of the liquid crystal 34, and the polarization component 27 is the ordinary refractive index of the liquid crystal 34. feel n _o. Further, in the second layer, the polarization component 27 'LCD 34''feel _o, polarized component 27 crystal 34' ordinary index of refraction n of feel extraordinary refractive index n _'e of. Here, the refractive index n _{g of the} member forming the first-layer diffraction grating is n ′ _g .

At this time, if n _o = n _g is satisfied in the first layer, the polarization component 27 will pass through, and the other will be modulated according to the above-mentioned equation (1). Also in the second layer, if _n'o = _n'g is satisfied, either one of the polarization components 27 and 27 'will pass through, and the other will be modulated according to the above-mentioned equation (1)'.

Next, when an electric field is applied to the liquid crystals 34 and 34 ', the directions of the optical axes of the liquid crystals 34 and 34' are changed, and the polarization components
Since the refractive indexes of 27 and 27 'change, the first layer and 2 respectively
Modulation according to the equations (1) and (1) 'is performed in the layer.

As described above, the light 26 is modulated in this embodiment.

In the present invention, the transparent substrate and the transparent spacer are 2
Although an axially stretchable plastic film and an isotropic plastic film were used, thinning and reduction of image shift were similarly achieved.

(Effect of the invention) According to the present invention, by using a plastic film for both the upper and lower transparent substrates in the light modulation device, it is possible to reduce the thickness of the entire device, and if a similar plastic film is used for the transparent spacer, the entire device is further improved. It is possible to achieve a high-precision optical modulation device that can be thinned and that has less occurrence of so-called image shift.

[Brief description of drawings]

FIG. 1 is a perspective view of a conventional optical modulator, FIG. 2 is an explanatory view of the operation of FIG. 1, and FIG. 3 is a perspective view of an embodiment of the present invention. In the figure, 30-1, 30-2, 8-1, 8-2 are optical modulators, 36, 3 respectively.
6 ', 16, 16' are transparent substrates, 32, 35, 32 ', 35', 12, 15, 12 ',
15 'is a transparent electrode, 33, 33', 13, 13 'are diffraction gratings, 34, 34', 14, 14 'are liquid crystals, and 31 and 10 are transparent spacers.

Front Page Continuation (72) Inventor Yukitoshi Okubo 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference US Patent 4251137 (US, A)

Claims (10)

[Claims] 1. A pair of transparent substrates arranged so that their substrate surfaces face each other, a transparent electrode formed on the substrate surfaces of the pair of transparent substrates, and one transparent substrate of the pair of transparent substrates. A second diffraction grating having a first diffraction grating formed on the transparent electrode and a grating groove formed on the transparent electrode of the other transparent substrate of the pair of transparent substrates and orthogonal to the grating groove of the first diffraction grating. A transparent spacer sandwiched between the grating and the first and second diffraction gratings and having transparent electrodes on both sides, and arranged in the grating grooves of the first and second diffraction gratings. And a liquid crystal in which the liquid crystal changes, wherein each of the pair of transparent substrates is made of a plastic film. 2. The light modulation device according to claim 1, wherein the plastic film is an isotropic film. 3. The light modulation device according to claim 1, wherein the plastic film is a biaxially stretchable film. 4. The light modulation device according to claim 1, wherein the plastic film is a uniaxially stretchable film. 5. The plastic film according to claim 4, wherein the two plastic films are arranged such that the optical main axis directions having the highest refractive index in the optical main axis directions of the plastic films are orthogonal to each other. The light modulator described. 6. The light modulation device according to claim 1, wherein the transparent spacer is formed of an isotropic film. 7. The light modulation device according to claim 1, wherein the transparent spacer is made of a biaxially stretchable film. 8. The light modulator according to claim 1, wherein the transparent spacer is composed of a uniaxially stretchable film. 9. The angle formed by the optical axis direction having the highest refractive index and the grating groove direction of the diffraction grating among the optical axis directions of the uniaxially stretchable film for transparent spacers is 0 ° ± 2 °.
9. The light modulator according to claim 8, wherein the light modulator is within the range. 10. The angle formed between the optical axis direction having the highest refractive index and the grating groove direction of the diffraction grating among the optical axis directions of the uniaxially stretchable film for the transparent spacer is 90 ° ± 2.
Claim 8 characterized in that it is set within °
An optical modulator according to the item.