JPH0743663A - Optical switching element - Google Patents

Abstract

PURPOSE:To provide an optical switching element capable of efficiently using an incident light and obtaining a transmission light with a high contrast ratio. CONSTITUTION:This element is a laminated body provided with plural liquid crystal layers 163 whose optical path is varied by applying external field and which are laminated through at least one interference layer 165 and whose refractive index anisotropy is suppressed, transparent electrodes 155, 157 applying the external field to the liquid crystal layer 163 and the interference layer 159 or 161 formed at least on one side of the liquid crystal layer 163 and having the refractive index different from the refractive index of the liquid crystal layer 163, and is constituted so that the interference of the light transmitting through the laminated body is controlled by varying the optical path length of the liquid crystal layer 163, and the light with required intensity is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical switching element whose light transmittance can be controlled by utilizing light interference.

[0002]

2. Description of the Related Art Recently, a liquid crystal element is known as a means for performing light modulation. Of these, for example, those using a twisted nematic liquid crystal element are required to include a pair of polarizing plates. However, in a system provided with a polarizing plate, since the loss of the amount of transmitted light in the polarizing plate is large, it is necessary to perform light modulation in consideration of the loss.

Further, as the light modulating means, there is an optical switching element for changing the transmittance of the liquid crystal to obtain a bright / dark binary state of the transmitted light intensity in a predetermined wavelength range. For example, the birefringence of a layer of a nematic liquid crystal is changed. It is conceivable to utilize the birefringence effect obtained by control. The liquid crystal has adjacent layers having different refractive indexes, and utilizes the fact that the refractive index of the layers changes due to application of an electric field.

When such an optical switching element is used as a shutter for exposure, it is necessary to increase the light amount of the light source or extend the exposure time in consideration of the loss of the light amount. In particular, when the exposure time is extended to cope with the problem, it causes a drop in the throughput of the printer or the like.

[0005]

As described above, in an optical system using a polarizing plate, it cannot be said that the loss of the amount of light in the polarizing plate is unavoidable and the light is efficiently modulated. Further, in the case of utilizing the interference effect of nematic liquid crystal, in order to obtain the desired interference effect, it is necessary to consider the refractive indexes of a plurality of layers, and a structure for obtaining the desired interference effect at the wavelength of interest is designed. Is difficult.

On the other hand, a switching means for efficiently utilizing light using a nematic liquid crystal is disclosed in, for example, Japanese Patent Laid-Open No.
It is disclosed in Japanese Patent No. 140714. The means separates the incident light into P-polarized light and S-polarized light with a birefringent prism, and deflects the S-polarized light into P-polarized light with a half-wave plate so that the two P-polarized lights enter the nematic liquid crystal. It is a thing. According to the means, it is possible to enhance the light utilization efficiency by utilizing polarized light in two directions, but it is possible to avoid the loss of light in these polarization conversion systems and the complication of the structure due to the provision of the polarization conversion system. Absent.

Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide an optical switching element capable of efficiently utilizing incident light to obtain transmitted light having a high contrast ratio.

[0008]

In the optical switching element according to the present invention, the optical path length is changed by the application of an external field and the refractive index anisotropy laminated via at least one optical path length invariant layer is suppressed. A plurality of variable optical path length layers,
An external field applying means for applying the external field to the optical path length variable layer, and an optical path length invariant layer formed on at least one side of the optical path length variable layer and having a refractive index different from the refractive index of the optical path length variable layer. Wherein the optical path length of the variable optical path length layer is varied to control interference of light passing through the laminated body,
The optical path length variable layer is a twisted liquid crystal, or the optical path length variable layer is a light modulating means having a scattering effect, or The switching element is arranged in an optical system having a light source, an original image irradiated with the light of the light source, and a photosensitive material to which the image light of the original image is exposed, and controls a voltage applied to the optical switching element. Then, the photosensitive material is exposed to image light having a required light amount.

[0009]

According to the above-mentioned means according to the present invention, the lights incident on the laminated body interfere with each other and mutually strengthen or weaken each other. The interference characteristics of light transmitted through the stacked body depend on the optical path length of each layer. Therefore, it is possible to control the interference light by changing the optical path length of the variable optical path length layer and changing the optical path length of the laminated body.

Since the variable optical path length layer modulates natural light,
The refractive index anisotropy is suppressed, and as a result, the average refractive index anisotropy is set to about zero. The interference characteristics of transmitted light are
Although different for each wavelength range, a good contrast ratio can be obtained in a predetermined wavelength range. Therefore, a good switching characteristic can be obtained by determining the optical path length of each layer so that a good contrast ratio can be obtained in a specific wavelength range. Further, by controlling the interference light, light having an intermediate intensity other than the light and dark binary values can be obtained.

The variable optical path length layer is a layer whose optical path length changes in response to the application of an external field such as an electric field, a magnetic field, or a sound field. The optical path length range of the laminate for obtaining the desired interference effect at the wavelength to be considered (hereinafter referred to as the wavelength of interest) is calculated based on a known method (see HAMacleod: Optical Thin Film, PP47-51 (1989)). To be done. Then, based on the calculation result, the optical path length of each layer is set in order to obtain a better interference effect. The laminated body is sandwiched between glass substrates, for example. However, as a premise of calculation, reflection of incident light on the substrate surface is ignored.

When the optical path length variable layers constituting the optical switching element are plural, the half value width of the peak wavelength can be changed. The full width at half maximum depends on the number of layers of the optical path length variable layer, and the peak characteristic changes flat as the number of layers increases. Therefore,
By laminating the required number of layers, various filter characteristics can be obtained. The plurality of optical path length variable layers are laminated with each other with at least one optical path length invariant layer interposed therebetween. This is to facilitate the design of the optical system and to facilitate the design of the laminated structure.

As the variable optical path length layer, there is twist liquid crystal. The liquid crystal is one in which liquid crystal molecules are continuously twisted and aligned from one side of the layer to the other side. The refractive index anisotropy can be suppressed by twisting the orientation. The range of the twist angle can be set variously, but in order to obtain a high contrast ratio, the twist angle is preferably an integral multiple of 180 °. The twist direction may be either right twist or left twist.

Further, the refractive index anisotropy can be suppressed even if the light modulating means having the scattering effect is applied. Examples of the light modulator include a light-scattering liquid crystal composite or a dynamic scattering liquid crystal. The light-scattering liquid crystal composite is one in which granular liquid crystals are dispersed in the polymer, one in which the granular liquid crystals are linked to the polymer, or one in which a polymer network is formed in the liquid crystals.

The optical switching means having the above means is
Further, it is arranged in an optical system including a light source, an original image irradiated with light from the light source, and a photosensitive material to which the image light of the original image is exposed. By controlling the voltage applied to the optical switching element, it is possible to change the transmittance of the optical switching element, so the applied voltage is controlled according to the exposure conditions and the image light having the required light quantity is exposed to the photosensitive material. To do so.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an optical switching element which is the basis of the present invention. As shown in FIG. 1, the optical switching element is an ITO (Indium Tin Oxcide) arranged in a required pattern on a pair of glass substrates 101 and 103.
Transparent electrodes 105 and 107 and interference layers 109 and 111
And the liquid crystal layer 113 which is aligned in parallel with the glass substrates 101 and 103 is sandwiched between the interference layers 109 and 111.

The alignment state of the liquid crystal layer 113 depends on the interference layer 10.
Alignment treatment of the liquid crystal side surface of 9, 111, for example, rubbing treatment, rubbing treatment after coating the alignment film, silane coupling agent treatment as the surface treatment, or a combination thereof. The liquid crystal layer 113 is formed by injecting liquid crystal into a gap obtained by arranging spacers having a uniform thickness in a predetermined pattern.

The optical path length of each layer forming the optical switching element will be described below. The optical path length of each layer depends on the wavelength of interest λ, and in this embodiment, the wavelength of interest is 427 nm. First, the refractive index n of the glass substrates 101 and 103
s and the layer thickness ds are set to 1.5 and 1 mm, respectively, and the refractive indexes nc and the layer thickness dc of the transparent electrodes 105 and 107 are set to 1.5 and 300 nm, respectively.

The liquid crystal layer 113 has a good contrast ratio when the optical path length when voltage is applied or when no voltage is applied satisfies n / 8 times (n is a positive integer) of the wavelength of interest 427 nm. To be The appropriate layer thickness of the liquid crystal layer 113 depends on the optical conditions of the interference layers 109 and 111, and is n / n of the wavelength of interest.
Selected under 8-fold conditions. In this example, the refractive index nh when no electric field is applied and the refractive index nv when an electric field is applied are 1.7242 and 1.5212, respectively, and the layer thickness dl is 526.
nm and dielectric anisotropy Δε are set to 15.8. As the liquid crystal having the specifications, a nematic liquid crystal of ZLI-3926 (manufactured by Merck & Co., Inc.) can be used.

Here, the refractive index anisotropy Δn (= ne-no) of the unit molecule of the liquid crystal layer 113 is preferably 0.1 or more, more preferably 0.2 or more. Next, the interference layers 109 and 111
Is a first interference layer 10 formed of titanium oxide.
Second formed of 9a, 111a and calcium fluoride
The interference layers 109b and 111b are alternately stacked in five stages. Each of these interference layers is formed by controlling the layer thickness by vacuum film formation such as resistance heating deposition, electron beam deposition, sputtering, ion beam sputtering, or spin coating, bar coating, spraying, or the like.

Glass substrates 101 and 103, interference layer 10
In the laminated body including the liquid crystal layer 113 and the liquid crystal layer 113, the optical path length for obtaining the interference characteristics of the interference layers 109 and 111 can be obtained by a known method. Under the conditions according to this example, the refractive index n1 of the interference layers 109a and 111a is
Is the refractive index nh of the liquid crystal layer 113 when no electric field is applied (= 1.
7242) and n1 = 2.2 to 2.7, and
The refractive index n2 of the interference layers 109b and 111b is determined by the liquid crystal layer 11
N2 = 1.23 to 1.26, which is smaller than the refractive index nv (= 1.5212) when the electric field is applied, can be obtained.

The interference layers 109a and 111a are made of hafnium dioxide (having a refractive index of 2.0-2.
1), tantalum pentoxide (refractive index 2.1 to 2.2), titanium dioxide (refractive index 2.2 to 2.7), zirconium dioxide (refractive index 2.0 to 2.1), and Interference layer 1
09b and 111b are, in addition to calcium fluoride, silicon oxide (refractive index 1.4 to 2.0), aluminum oxide (refractive index 1.5 to 1.7), magnesium fluoride (refractive index 1.3 to 1.4). The refractive index of each material is
It depends on the film forming method, the film forming conditions, and the wavelength of interest.

The refractive indexes of the interference layers 109 and 111 of titanium oxide and calcium fluoride for obtaining the interference effect can be set within the above range, but in this embodiment, n1 =
A case where 2.5 and n2 = 1.25 are set will be described. In addition to the setting of the refractive index, the wavelength of interest 427
In order to obtain the desired interference effect in nm, the interference layer 109a,
The layer thickness d1 of 111a is set to 40 nm, and the interference layer 10
The layer thickness d2 of 9b and 111b was set to 80 nm.

Here, the layer thickness of the interference layers 109 and 111 is
N / 4 (n is a positive integer) times the wavelength of interest 427 nm ± 30%
The following is preferable, and ± 10% or less is more preferable. By designing the optical system of the laminated body based on the known method as described above, ideal transmittance characteristics can be obtained. The transmittance characteristics of the optical switching element shown in FIG. 1 will be described below with reference to FIG. 2 (a) and 2 (b),
The ideal transmittance characteristics are shown respectively when no electric field is applied and when an electric field is applied, and the vertical axis and the horizontal axis respectively show the transmittance and the wavelength.

As shown in FIG. 2, the transmittance of the optical switching element depends on the optical path length of the liquid crystal layer 113 whose molecular orientation changes due to the control of the electric field. Sometimes about 50 each
%, And a transmittance of approximately 0% is obtained. Therefore, the wavelength 42
In the vicinity of 7 nm, a good contrast ratio switching characteristic can be obtained.

The range of the optical path length of each layer will be described below. Under the conditions of the embodiment shown in FIG. 1, the liquid crystal layer 113
When the optical path length of is set to 1/8 of the wavelength of interest λ, a slight contrast ratio is obtained, and when set to 1/4, it is about 1
A contrast ratio of 0: 1 is obtained. Further, when set to 1/2, a contrast ratio of about 50: 1 or more can be obtained. Therefore, considering a slight margin, when the optical path length is set to 1/6 or more, and further 1/3 or more of the wavelength of interest λ, a switching characteristic with a good contrast ratio can be obtained.

On the other hand, when the optical path length is set to 16λ, the full width at half maximum at the wavelength of interest of 400 nm is about 11 nm and 32λ.
When set to, the half-value width is about 5 nm, and when set to 64λ, the half-value width is about 2 nm, and the steepness increases as the optical path length increases. Therefore, when the optical path length 16 is set to λ or less, switching characteristics with an appropriate steepness can be obtained.

From the above contrast ratio and steepness characteristics, the range of the optical path length that the liquid crystal layer 113 can take is preferably λ / 8 or more and 64λ or less, more preferably λ / 6 or more and 32λ, where λ is the wavelength of interest. Below, it is most preferably set to λ / 3 or more and 16λ or less. The contrast ratio of the optical switching element also depends on the interference layer 109a (111
It depends on the refractive index difference between the refractive index n1 of a) and the refractive index n2 of the interference layer 109b (111b).

FIGS. 3A to 3D show the transmittance characteristics when the above-mentioned refractive index differences are set to 0.15, 0.23, 0.43, and 0.63, respectively. The axis and the horizontal axis indicate the transmittance and the wavelength, respectively. Further, the solid line and the dotted line indicate the transmittances when no electric field is applied and when an electric field is applied, respectively. As shown in the figure,
When set to 5, 0.23, 0.43, and 0.63, the contrast ratio at the wavelength of interest is approximately 1.
4: 1, 2: 1, 10: 1, and 50: 1 (arrow range)
Becomes As the difference in refractive index increases, a better contrast ratio can be obtained. Therefore, in order to obtain a substantially satisfactory switching effect, the refractive index difference is 0.2 or more and 100 or less,
It is preferably set to 0.4 or more, and more preferably set to 0.6 or more.

The optical conditions of the device having the characteristics shown in FIGS. 3A to 3D are shown below. That is, FIG. 3 (a)
The interference layer 109a (111) forming the element exhibiting the characteristics of
The refractive index of a) is 1.61, the layer thickness is 86 nm,
The interference layer 109b (111b) has a refractive index of 1.46 and a layer thickness of 95 nm. Further, the interference layer 109a (111a) constituting the element exhibiting the characteristics shown in FIG. 3B has a refractive index of 1.7 and a layer thickness of 83 nm.
The refractive index of (111b) is 1.46, and the layer thickness is 95 nm.
Is.

Further, the refractive index of the interference layer 109a (111a) constituting the element having the characteristics shown in FIG. 3C is 1.9,
The layer thickness is 73 nm, and the interference layer 109b (111b)
Has a refractive index of 1.46 and a layer thickness of 95 nm. In addition, the interference layer 10 constituting the element having the characteristics shown in FIG.
9a (111a) has a refractive index of 2.1 and a layer thickness of 66n.
m, and the refractive index of the interference layer 109b (111b) is
1.46, the layer thickness is 95 nm.

Further, the refractive indexes of the glass substrates 101 and 103 are all set to 1.52, and the above characteristics can be obtained by switching the optical path length variable layers having the refractive indexes of 1.5 and 1.6. To be Under the conditions of the embodiment shown in FIG. 1, when two interference layers, that is, interference layers 109a and 111a are formed on both sides of the liquid crystal layer 113, a slight contrast ratio is obtained, and both sides of the liquid crystal layer 113 are obtained. Interference layers 109a, 109b, 109a, and 111, respectively
When six interference layers of a, 111b, and 111a are formed, a contrast ratio of about 10: 1 is obtained. Further, when the ten interference layers shown in FIG. 1 are formed, a contrast ratio of about 50: 1 or more can be obtained.

Therefore, if the number of interference layers is set to 10 or more, a good contrast ratio switching characteristic can be obtained. Here, the interference layer has only to be formed on at least one side of the liquid crystal layer 113, but the number of layers that the interference layers 109 and 111 can take is preferably two or more layers due to the above contrast characteristics. , And more preferably 6
The number of layers is set to 10 or more, and most preferably 10 or more.

The interference characteristics of the transmitted light of the optical switching element depend on the order of each layer, the number of layers, and the optical path length. The order of each layer is generally a combination of layers having different refractive indexes from the adjacent layers. The optical switching element described above exhibits good switching characteristics at a specific wavelength. Therefore, by using a filter that extracts only the light of the wavelength, it is possible to avoid the influence of light other than the specific wavelength.

The effect of using the filter will be described below with reference to FIG. 4A shows the transmittance characteristic of the filter, FIGS. 4B and 4C show the transmittance characteristics of the optical switching element, and FIG.
4 (e) and 4 (f) show the spectral sensitivity of the photosensitive material, and FIG. 4 (e) and FIG. 4 (f) show the filter shown in FIG. 4 (a) and FIG.
9 shows the transmittance characteristics when combined with the optical switching element shown in FIG.

When the photosensitive material having the spectral characteristic shown in FIG. 4D is irradiated with the transmitted light of the optical switching element having the transmittance characteristic shown in FIGS. 4B and 4C, the photosensitive material is irradiated. Is irradiated with light having a uniform wavelength to expose an image lacking contrast. On the other hand, FIG.
In the transmitted light when the filters having the transmittance characteristics shown in FIG. 4 are combined, only the specific wavelength region is extracted as shown in FIGS. 4 (e) and 4 (f). Therefore, when the light in the wavelength range is applied to the photosensitive material having the characteristics shown in FIG. 4D, an image with excellent contrast is exposed.

An electric field is applied to the liquid crystal layer 113 constituting the optical switching element by the transparent electrodes 105 and 107 which are arranged to face the glass substrates 101 and 103, respectively. However, for example, as shown in FIG.
An electric field may be applied to the liquid crystal layer 113 by the electrode 405 arranged in a required pattern with a required gap in either 01 or 103.

The optical switching element having the above-mentioned structure is composed of the electrode 4
The arrangement of the liquid crystal molecules corresponding to the gap region of No. 05 is changed to control the transmittance characteristic of the light passing through the gap region. Therefore, the transparent electrode may not be required because the area other than the gap area may be shielded from light. Since some transparent electrodes have a problem with durability against ultraviolet rays, the durability of the device can be improved by not requiring the transparent electrode. Further, since the pattern-arranged electrodes have a small surface resistance, the signal waveform is not blunted when a voltage is applied, which enables a high-speed response of the switching element.

In the embodiments described above, the case where a nematic liquid crystal layer is used as the optical path length variable layer and the optical path length is changed by the electro-optical effect generated by the application of an electric field to obtain an ideal switching characteristic has been described. Hereinafter, the case where another modulation means is further applied to the variable optical path length layer will be described. After that, each optical switching element includes an interference layer 109a,
Interference layer 10 with silicon dioxide having a thickness of 85 nm on 111a
Titanium dioxide having a layer thickness of 54 nm is used for 9b and 111b.

FIG. 6 shows an optical switching element using a twisted nematic liquid crystal. As shown in FIG. 6A, the twisted nematic liquid crystal 501 is formed on the glass substrate 10.
1, 103, electrodes 105, 107 and interference layers 109, 1
It is sandwiched by 11 laminated bodies. Twisted nematic liquid crystal 5
01 is the long axis of the liquid crystal molecules, which is a predetermined angle α between the layers.
It is a twisted array.

The conditions for forming the twisted nematic liquid crystal 501 will be described below. Substrate formation: Ultrasonic cleaning (about 10 minutes) of glass substrate (thickness 1.1 mm) in alcohol, pure water cleaning and drying Electrode formation: ITO film is formed by sputtering (thickness about 200)
nm, area resistance about 100 Ω / □) Alignment layer formation: N-methyl-2 virolidinone, 2- (2
-Ethoxy) ethanol and 2-n-butoxyethanol were mixed at a mixing ratio of 1: 2: 2 with respect to the mixed solvent LQ.
A solution in which 1800 (manufactured by Hitachi Chemical Co., Ltd.) was dissolved at a mixing ratio of 1: 0.2 was applied by spin coating (curing temperature 29
5 ° C, 60 minutes) Rubbing treatment: Spin coating with a nylon brushed cloth (50
0 rpm x 30 seconds, 2500 rpm x 25 seconds, 500r
The rubbing direction is set according to the twist angle. Assembly: Shinshin sphere with a diameter of 1.0 μm (Catalyst Kasei Co., Ltd.)
(Made by Haven) via an adhesive SE4500 (made by Haven Co., Ltd.) (curing method: thermosetting under pressure by vacuum packing (60 ° C, 30 minutes, 130 ° C, 30 minutes)) Liquid crystal injection: helical pitch Liquid crystal E8 (manufactured by Merck) to which a necessary amount of chiral agent CB15 (manufactured by Merck) is added (a helical pitch of 1.3 μm is obtained for 10% addition of chiral agent) so as to be suitable for the twist angle. Constituting twisted nematic liquid crystal 50
When the electric field is not applied to the liquid crystal molecule 1, liquid crystal molecules 503
Becomes a state of being twisted at a predetermined angle α. The incident natural light has polarized light in a plurality of directions, and the light incident in this state interferes and the peak wavelength of the transmitted light moves as compared with the peak wavelength when the electric field is applied. Here, the refractive index nh of the twisted nematic liquid crystal layer with respect to natural light when no electric field is applied
Acts as if it is an intermediate value between the two main refractive indices ne and no.

On the other hand, as shown in FIG. 6B, when an electric field is applied to the twisted nematic liquid crystal 501, the liquid crystal molecules 503 are aligned in the electric field application direction. Natural light incident in this state interferes based on the optical path length uniquely determined by the actual thickness of the liquid crystal layer and the refractive index. Here, the refractive index nv of the twisted nematic liquid crystal layer with respect to natural light when an electric field is applied
Behaves as if it were equal to the main refractive index no.

This means that the refractive index anisotropy of the liquid crystal is suppressed, and the average refractive index anisotropy is substantially zero. The refractive index nv of the twisted nematic liquid crystal 501 when an electric field is applied is represented by the main refractive index no. The refractive index nh (nv <nh) when no electric field is applied depends on the twist angle of the liquid crystal molecule 503, and these two refractive indices nh and nv (nv <nh
Switching characteristics can be obtained by changing h) by applying an electric field.

As described above, the refractive index nh of the twisted nematic liquid crystal 501 when no electric field is applied depends on the twist angle of the liquid crystal molecules 503, and therefore the switching characteristics also depend on the twist angle. Hereinafter, the relationship between the twist angle of the liquid crystal molecules and the switching characteristics will be described with reference to FIGS. 7 and 8. Figure 7
(A) to (d) show that the twist angle α of liquid crystal molecules is 0, respectively.
8 (a) to 8 (c) show the transmittance characteristics when the angles are set to °, 45 °, 90 °, and 180 °, the twist angle α of the liquid crystal molecules is set to 270 °, 360 °, and 450 °. The transmittance characteristics when set are shown, and the vertical axis and the horizontal axis respectively show the transmittance and the wavelength.

In FIGS. 7 and 8, the solid and dotted lines are
The transmittance characteristics are shown respectively when no electric field is applied and when an electric field is applied, and the peak wavelength shifts to the lower wavelength side as the electric field is applied. The point to be noted here is that by twisting the liquid crystal molecules, a large contrast ratio can be obtained at a specific wavelength, and when the twist angle α is set to 180 ° and 360 °, the waveform is maintained when no electric field is applied. The transmittance characteristic shifts in the state of From this, the twist angle α is 18
It can be seen that good switching characteristics can be obtained by setting 0 ° × n (n: positive integer). The allowable range of the twist angle α set to 180 ° × n is preferably ± 30% or less, more preferably ± 10% or less.

The above transmittance characteristics are measured under the following conditions. Spectrum meter: IMUC7000 (manufactured by Otsuka Electronics Co., Ltd.) Light source: Xenon lamp Electric field: Waveform generator NF1930 (manufactured by NF Circuit Block Co., Ltd.), amplifier NF4005 (manufactured by NF Circuit Block Co., Ltd.) applied a rectangular wave of 1 V with a frequency of 20 V As the nematic liquid crystal, liquid crystal in which hybrid molecules are arranged may be twisted and aligned.

FIG. 9 shows an optical switching element using a polymer dispersion type liquid crystal. As shown in FIG. 9A, a polymer dispersed liquid crystal 801 having a light scattering effect.
Are sandwiched by a stack of electrodes 105, 107 and interference layers 109, 111. The polymer dispersed liquid crystal 801 is
It is a polymer 803 in which granular nematic liquid crystals 805 are scattered.

The optical switching element is formed under the same conditions as the twisted nematic liquid crystal shown in FIG. 6 except for the liquid crystal layer. The polymer-dispersed liquid crystal layer is obtained by dispersing and injecting liquid crystal E8 (manufactured by Merck & Co., Inc.) and an ultraviolet curable resin into a cell at a mixing ratio of 2: 1 and then curing by ultraviolet irradiation (1 minute). When an electric field is not applied to the polymer dispersed liquid crystal 801 which constitutes the optical switching element, the molecules of the nematic liquid crystal 805 are oriented in different directions. In this state, the difference in refractive index between the nematic liquid crystal 805 and the polymer 803 is large, and the incident natural light is
It is affected by scattering or reflection, which reduces the transmittance of incident light. On the other hand, the light not affected by the scattering is affected by the polymer dispersed liquid crystal layer having the refractive index nh.

Further, as shown in FIG. 9B, when an electric field is applied to the polymer dispersed liquid crystal 801, the molecules of the nematic liquid crystal 805 are aligned in the electric field application direction. In this state, the difference in refractive index between the nematic liquid crystal 805 and the polymer 803 is small, and thus incident natural light is transmitted without being affected by the interface of the nematic liquid crystal 805.

A uniaxial crystal represented by a nematic liquid crystal has two different main refractive indices no and ne, and the refractive index nh of the polymer dispersion type liquid crystal 801 when no electric field is applied is (2
No. + ne) / 3, and the refractive index nv when an electric field is applied
Is represented by no. When these two refractive indices nh and nv (nv <nh) are changed by applying an electric field, the incident light is affected by the interference effect of the element and the scattering effect of the liquid crystal layer. As a result, the transmittance of the incident light changes, so that switching characteristics can be obtained.

The layer of the polymer dispersed liquid crystal 801 can be formed into a thin film by a uniform film forming means such as spin coating if it is a curable polymer. Therefore, the layer can be formed more easily than when the liquid crystal is injected into the gap. There are various curing forms of the polymer, for example, an ultraviolet curing type in which the applied polymer is cured by irradiating ultraviolet rays, a solvent drying type in which the applied polymer is dried by a solvent drying means such as heat or wind, and cured, a high temperature state. Thermal softening type that cools and cures the polymer applied with
Alternatively, a thermosetting type in which heat is applied to the applied polymer to cure the polymer can easily form a thin film having a uniform layer thickness.

FIG. 10 shows the transmittance characteristics of the optical switching element using the polymer dispersion type liquid crystal. In FIG. 10, the vertical axis and the horizontal axis indicate the transmittance and the wavelength, respectively, and the solid line and the dotted line respectively indicate the transmittance characteristics when no electric field is applied and when the electric field is applied. With the optical switching element having the above characteristics, good switching characteristics can be obtained near the wavelength of 570 nm. It goes without saying that this wavelength depends on optical conditions such as the layer thickness.

Further, as a modulation means having a light scattering effect, a ferroelectric liquid crystal and a polymer are compounded to disperse the ferroelectric liquid crystal in the polymer, and liquid crystal molecules in which liquid crystal molecules are randomly aligned or dynamic scattering. Type liquid crystal may be used. In addition to the above liquid crystal, the variable optical path length layer may be a polymer or copolymer of polyvinylidene fluoride, PZT,
Ferroelectric inorganic materials such as PLZT, BTO, STO, BSTO, etc., or electric field induced ferroelectric materials are mentioned, and these materials have an electro-optical effect. The electric field induced ferroelectric material is a substance that changes from a phase other than ferroelectric such as antiferroelectric to a ferroelectric phase when an electric field is applied, and is characterized by a large change in optical path length.

Further, the variable optical path length layer may be a layer whose optical path length is changed by applying a magnetic field or a sound field in addition to the electric field. Further, the variable optical path length layer formed of a liquid crystal phase, a liquid phase, or a gas phase is sandwiched between a pair of substrates, and the variable optical path length layer formed of a solid phase can be supported by one side substrate. The optical switching element having a single-layer variable optical path length layer has been described above. An optical switching element having a plurality of variable optical path length layers according to the present invention will be described below based on the above optical switching element. It should be noted that the plurality of optical path length variable layers are laminated via at least one optical path length invariant layer.

An optical switching element having a plurality of variable optical path length layers will be described below with reference to FIG. Figure 1
FIG. 11A shows the configuration of an optical switching element having a single optical path length variable layer and its transmitted light characteristics.
FIG. 3B shows the configuration of an optical switching element having a plurality of variable optical path length layers and the transmitted light characteristics thereof. In each characteristic diagram, the vertical axis and the horizontal axis respectively show the transmittance Tr.
And the wavelength λ are shown, and the solid line and the dotted line respectively show the transmittance characteristics when the electric field is not applied and when the electric field is applied.

The optical switching element shown in FIG. 11A is composed of glass substrates 151, 153, transparent electrodes 155, 1
57, interference layers 159a and 159b, interference layers 161a and 1
61b, which is a laminated body including interference layers 159a and 161.
The liquid crystal layer 163 is sandwiched between a and the variable optical path length layer. Here, titanium dioxide is used for the interference layers 159a and 161a, silicon dioxide is used for the interference layers 159b and 161b, and polymer dispersed liquid crystal is used for the liquid crystal layer 163.

The optical switching element shown in FIG. 11 (b) has the glass substrates 151 and 153, the transparent electrode 15
5, 157, interference layers 159a, 159b, and interference layer 161.
a 161b and interference layers 165a and 165b, the liquid crystal layer 163 is sandwiched between the interference layers 159a and 165a as variable optical path length layers, and the interference layer 165 is also included.
The liquid crystal layer 163 is sandwiched between a and 161a.
Here, titanium dioxide is used for the interference layer 165a, and silicon dioxide is used for the interference layer 165b.

Refractive index n of liquid crystal layer 163 when no electric field is applied
h and the refractive index nv when an electric field is applied are nh =
1.6 and nv = 1.5 are set, and the layer thickness d1 of the liquid crystal layer 163 is set to d1 = 800 nm. Further, the refractive index n2 of the interference layers 159a and 161a and the layer thickness d2
Are n2 = 2.42 (> nh) and d2 = 58n, respectively.
m, the refractive index n of the interference layers 159b and 161b
3 and the layer thickness d3 are n3 = 1.46 (<n
v), d3 = 95 nm is set.

As shown in FIG. 11B, when a plurality of optical path length variable layers are laminated, the optical path length of each optical path length invariant layer laminated between the optical path length variable layers is the wavelength of interest λ. N
/ 4 (n is a positive integer) times ± 30% or less,
It is preferably set within a range of ± 10% or less. Further, when a plurality of optical path length variable layers are laminated, the required optical characteristics can be obtained even if the interference layers 159 and 161 which are the optical path length invariant layers are composed of a single layer.

The transmitted light characteristic of each optical switching element having the above-mentioned structure when no electric field is applied is shown by a solid line, and the transmitted light characteristic when an electric field is applied is shown by a dotted line. Move to the side. Here, comparing the characteristics of the respective switching elements, the characteristic waveform of the element in which the liquid crystal layer 163 is laminated in multiple layers is larger than the characteristic waveform of the element in which the liquid crystal layer 163 is laminated in a single layer. You can see that is wide. This tendency becomes remarkable as the number of laminated liquid crystal layers increases. Therefore, by designing the number of layers of the optical path length variable layer together with the optical path length of each layer according to the wavelength range, various filter characteristics such as a bandpass filter can be obtained.

The case where the optical switching element is applied to an ND (Neutral Density) filter will be described below with reference to FIG. FIG. 12 shows the layer structure of the element and the transmitted light characteristics. In the characteristic diagram, the vertical axis and the horizontal axis represent the transmittance Tr and the wavelength, respectively. The layer structure shown in FIG. 12 includes a pair of glass substrates 251, 253 supporting transparent electrodes 255, 257, three interference layers 259 made of titanium dioxide, and two liquid crystal layer 2 which is an optical path length variable layer.
65 and 267 (polymer dispersed liquid crystal) are alternately laminated.

The refractive index nh of the liquid crystal layers 265 and 267 when no electric field is applied and the refractive index nv when an electric field is applied are n.
h = 1.6 and nv = 1.5 are set, the layer thickness of the liquid crystal layer 265 is set to 375 nm, and the layer thickness of the liquid crystal layer 267 is set to 210 nm. In addition, the interference layer 25
The respective refractive indices of 9, 261, 263 are set to 2.42, and the respective layer thicknesses of the interference layers 259, 261, 263 are
It is set to 110 nm, 21 nm, and 27 nm, respectively.

The optical path length of the optical path length invariable layer laminated between the optical path length variable layers is set within a range of n / 4 (n is a positive integer) times ± 30% or less of the wavelength of interest λ, preferably. Is ± 1
It is set in the range of 0% or less. The characteristic diagram shown in FIG. 12 shows transmitted light characteristics when an electric field is applied, and flat transmitted light characteristics are obtained in the vicinity of the visible band of 500 nm to 600 nm.

When the application of the electric field to the optical switching element is cut off, the refractive indices of the liquid crystal layers 265 and 267 increase, so that the interference spectrum of the transmitted light changes. Further, since the liquid crystal layers 265 and 267 change to the scattering state, the incident light is scattered. Therefore, since the incident light is affected by the interference effect of the laminate and the scattering effect of the liquid crystal layer,
Its transmittance becomes small. The required transmittance can be obtained in the visible band by changing the applied electric field level.

The case where the optical switching element having the characteristics of the ND filter is applied to the exposure apparatus will be described below with reference to FIG. The light emitted from the light source 351 is
The light is reflected by the reflector 353 and is incident on the ND filter 355. The ND filter 355 is a driving unit 37 described later.
The modulation is controlled by the driving of No. 5, and the required amount of light is emitted. N
The light emitted from the D filter 355 is released by the shutter 357.
Then, the light enters the negative film 361 through the diffusion box 359 in series. The image light obtained by the negative film 361 is condensed by the lens 363, and then is irradiated onto the photographic printing paper 365.

On the other hand, the image light is split by the half mirror 367 and is incident on the image area sensor 369 for photometry. The photometric signal obtained by the image area sensor 369 is input to the exposure amount calculation unit 371 to calculate the exposure amount. The calculation result is input to the control unit 373. Control unit 3
73 obtains a voltage signal for obtaining the required exposure amount based on the calculation result, and inputs the voltage signal to the drive unit 375. The driving unit 375 supplies the required voltage to the ND filter 355 based on the voltage signal.

As described above, the ND filter 355 is feedback-controlled, so that the photographic printing paper 365 is irradiated with an appropriate amount of light. By designing the optical path length of each layer of the ND filter 355 so that each wavelength of B, G, and R can be independently filter-controlled, color correction at the time of exposure also becomes possible. Further, the ND filter can be applied to the aperture of the camera. That is, as shown in FIG. 14, the ND filter 401 is arranged in the front stage or the rear stage of the lens 403, and thereby the optical system of the camera 405 is configured.
The function of the ND filter 401 is to reduce the transmittance when the amount of light is large and to increase the transmittance when the amount of light is small to obtain the required amount of light. Such control of the transmittance is obtained by changing the applied electric field.

For example, a solar cell, which is a photoelectric conversion means, is used as a means for sensing the amount of ambient light, and a voltage corresponding to the amount of light is applied to the ND filter 401. The variable optical path length layer applied in this case has a small transmittance when no electric field is applied and a large transmittance when an electric field is applied. The optical switching element described above can be formed by sequentially laminating each layer, but particularly when each layer is made of an organic material, it can be formed by simultaneous multilayer coating. Further, when the variable optical path length layer is in a solid phase, it does not need to be supported by the substrate and can be easily manufactured. Examples of the solid phase variable optical path length layer include polymer dispersion type liquid crystal, ferroelectric inorganic material, ferroelectric polymer, electric field induced ferroelectric material and the like.

The driving method of the optical switching element will be described below. As a driving method, a known optical address driving method, a thin film transistor driving method, or a simple matrix driving method can be applied. The optical address driving method uses a layered structure of the spatial light modulator. That is,
As shown in FIG. 15, the photoconductive layer 191, the interference layer 10
9, the liquid crystal layer 113, and the interference layer 111, the transparent electrode 10
It is sandwiched by a pair of glass substrates 101 and 103 provided with 5, 107.

When the photoconductive layer 191 is irradiated with the writing light incident from the glass substrate 101 side, the impedance of the photoconductive layer 191 in the irradiated portion is lowered. Then, an electric field is applied to the liquid crystal layer 113 corresponding to the portion where the impedance is lowered, and the liquid crystal molecules are aligned in the electric field application direction. Pattern regions having different reflectances are formed in the liquid crystal layer 113 depending on the arrangement of the liquid crystal molecules. On the other hand, the reading light incident from the glass substrate 103 side is reflected by the pattern region of the liquid crystal layer 113 formed as described above and is led out. A switching effect is obtained by controlling the reflection and derivation of the reading light.

In the thin film transistor driving method, thin film transistors arranged in a matrix are line-sequentially scanned to obtain a switching effect of each element. In the simple matrix method, a plurality of row electrodes are time-divisionally scanned, and the switching effect of each element can be obtained from this. In addition, by driving the liquid crystal whose dielectric anisotropy depends on the frequency by two frequencies,
High-speed switching characteristics can be obtained.

[0072]

According to the invention described above, since the refractive index anisotropy of the optical path length variable layer is suppressed, the light can be modulated without depending on the polarization direction. Further, due to the interference effect of the stacked interference layers, the incident light can be controlled with a high contrast ratio particularly when attention is paid to a specific wavelength. Therefore, it is possible to efficiently use the incident light and obtain good switching characteristics. Also, because it does not depend on the polarization direction,
Does not require a polarizing plate. Therefore, it is possible to avoid deterioration of durability of the element due to the provision of the polarizing plate.

Regarding the optical characteristics of the optical switching element, the half value width of the peak wavelength can be controlled by stacking a plurality of optical path length variable layers constituting the element. Thus, by stacking the required number of optical path length variable layers, various switching characteristics can be obtained with good switching characteristics. Here, the structure for obtaining the desired interference effect at the wavelength of interest is easily designed by considering the optical path length of the optical path length variable layer and the optical path length of the optical path length invariant layer having the enhancement effect.

Furthermore, by arranging an optical switching element having a plurality of variable optical path length layers stacked in an exposure optical system and utilizing it as a wavelength tunable filter whose wavelength band is changed by applying a voltage, a required light amount according to the exposure condition can be obtained. Is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing the concept of the present invention.

FIG. 2 is a characteristic diagram showing the transmittance of the optical switching element shown in FIG.

3 is a characteristic diagram showing the transmittance of the optical switching element shown in FIG.

FIG. 4 is a characteristic diagram for explaining an effect when a filter is combined.

FIG. 5 is a configuration diagram showing another embodiment of the electrode.

FIG. 6 is a diagram showing an optical switching element using a twisted nematic liquid crystal.

7 is a characteristic diagram showing the transmittance of the optical switching element shown in FIG.

8 is a characteristic diagram showing the transmittance of the optical switching element shown in FIG.

FIG. 9 is a diagram showing an optical switching element using polymer dispersed liquid crystal.

10 is a characteristic diagram showing the transmittance of the optical switching element shown in FIG.

FIG. 11 is a diagram showing an optical switching element having different number of optical path length variable layers.

FIG. 12 is a diagram showing an optical switching element having a filter characteristic.

FIG. 13 is a diagram showing an exposure apparatus having an optical switching element.

FIG. 14 is a diagram showing a camera having an optical switching element.

FIG. 15 is a diagram for explaining a driving method of an optical switching element.

[Explanation of symbols]

101, 103, 151, 153, 251, 253 Glass substrate 105, 107, 155, 157, 255, 257 Transparent electrode 109, 111, 159, 161, 165, 259, 2
61, 263 interference layer 113, 163, 265, 267, 501, 801 liquid crystal layer 351 light source 353 reflector 355 ND filter 357 shutter 359 diffusion box 361 negative film 363 lens 365 photographic paper 367 half mirror 369 image area sensor 371 exposure amount calculator 373 Control part 375 Drive part 401 ND filter 405 Electrode 803 Polymer 805 Nematic liquid crystal

Claims (4)

[Claims] 1. A plurality of variable optical-path-length layers whose optical path length is changed by application of an external field and whose refractive index anisotropy is suppressed by laminating at least one optical-path-length invariant layer, and the external field. A laminate having an external field applying means for applying to the variable optical path length layer, and an optical path length constant layer formed on at least one side of the variable optical path length layer and having a refractive index different from the refractive index of the variable optical path length layer. An optical switching element, wherein the optical path length of the variable optical path length layer is varied to control interference of light passing through the laminated body and obtain light of a required intensity. 2. The optical switching element according to claim 1, wherein the variable optical path length layer is a twisted liquid crystal. 3. The optical switching element according to claim 1, wherein the variable optical path length layer is an optical modulator having a scattering effect. 4. The optical switching element is arranged in an optical system having a light source, an original image irradiated with the light of the light source, and a photosensitive material to which the image light of the original image is exposed. 2. The optical switching element according to claim 1, wherein the applied voltage is controlled to expose the photosensitive material with image light having a required light amount.