JP4952415B2 - Transmitted light amount variable element and projection display device - Google Patents

Description

  The present invention relates to a transmitted light amount variable element and a projection display device that switch the amount of incident light and transmit the light.

  As a projection display device that displays a projected image, for example, a liquid crystal projection display device that modulates incident light according to a video signal and projects transmitted light to display an image (see, for example, Japanese Patent Laid-Open No. 2001-264728) And DMD (Digital Micromirror Device (registered trademark)) that modulates the amount of reflected light by changing the reflection angle of a micromirror for each pixel according to a video signal and projects the light obtained by the modulation to display an image Type projection display devices (see, for example, Japanese Patent Application Laid-Open No. 2004-361856).

  As an example, FIG. 7 shows a configuration diagram of a liquid crystal projection display device 50. The light emitted from the light source 1 is reflected by the reflecting mirror 2 to become light substantially parallel to the optical axis, and the light whose light amount is adjusted by the transmitted light amount variable element 8 through the illumination optical system 3 proceeds to the polarizer 4. The light is converted into light having a predetermined linear polarization direction by the polarizer 4. The light emitted from the polarizer 4 is modulated in the polarization state by a liquid crystal panel 5 as a spatial light modulation element for image display, enters the analyzer 6, and passes through the analyzer 6 so that only a predetermined polarization component is projected. The light is emitted to the lens system 7, passes through the projection lens system 7, and is projected and displayed on a screen or the like (not shown).

  Here, the transmitted light amount variable element 8 used in the liquid crystal projection display device is an element that adjusts the light amount according to the brightness of the place to be projected and displayed on a screen or the like, and applies a voltage to the liquid crystal, and the magnitude of the applied voltage. Thus, the adjustment of the amount of light to be transmitted is realized. In addition, the contrast of the projected image is maximized according to the brightness of the place by adjusting the amount of light transmitted through the transmitted light amount variable element for each electrode unit by dividing the electrode for applying the voltage. The function which can be adjusted is realized (Patent Document 1).

The conventional transmitted light amount variable element has a structure in which a multi-layer grating member having a concavo-convex cross section is provided on one of two substrates and liquid crystal is filled. By applying a voltage to this liquid crystal, transmission and diffraction functions are exhibited. The amount of transmitted light was adjusted. In such a design, in order to increase the light utilization efficiency, the refractive index of the multilayer grating member (n _m ) is adjusted in accordance with the ordinary refractive index (n _o ) of the liquid crystal corresponding to the wavelength of light incident in a wide band. It was. The multilayer grating member is composed of a layer of a high refractive index member and a low refractive index member. In Patent Document 1, the average refractive index of the multilayer film is lowered to match the refractive index of the liquid crystal. This is realized by using a material having a low rate of about 1.41. As a translucent material having a refractive index of about 1.41 that becomes a low refractive index member, actually, MgF ₂ or porous SiO _{2 formed} without plasma assist can be considered.

International Publication No. 2006/082901 Pamphlet

However, the film made of MgF ₂ has a problem in the strength of the film itself, and has a difficulty in etching in the process of manufacturing the diffraction grating structure, and porous SiO ₂ has a low mechanical strength, and has a long-term There was a problem in reliability during use. Furthermore, when a multilayer grating member is formed using a SiO ₂ crystal film having excellent mechanical strength and reliability as a low refractive index member, the average refractive index becomes higher than that of a multilayer grating member made of these materials. Since this difference occurs, the average refractive index of the multilayer grating member does not match the ordinary refractive index of the liquid crystal contained in the grating recesses. Then, diffraction occurs due to the difference in refractive index, and there is a problem that the transmittance of light transmitted through the transmitted light amount variable element is lowered even when the ordinary refractive index of the liquid crystal is used by controlling the voltage.

  The present invention has been made to solve such problems. The transmitted light amount that allows easy adjustment of the transmitted light amount that is easy to process, has high reliability, has high light utilization efficiency, and is substantially constant over a wide band with good controllability. A variable element and a projection display device are provided.

The present invention includes at least two transparent substrates arranged in parallel, wherein arranged on one side one of the pair of the transparent substrate opposite the transparent substrate, the cross-sectional shape is periodic uneven diffraction grating A first multilayer film member that forms a convex part, an optical medium provided in a part of the concave part of the diffraction grating, and a liquid crystal sandwiched between the pair of transparent substrates so as to fill the diffraction grating and the optical medium And a transparent electrode for applying a voltage to the liquid crystal, wherein the first multilayer film member has a multilayer structure in which a plurality of types of optical thin films having different refractive indexes are laminated in a direction perpendicular to the substrate. The optical medium has a refractive index that is higher than the ordinary refractive index of the liquid crystal.

  With this configuration, even when a material having a low ordinary refractive index of liquid crystal filling the concave portion of the diffraction grating with respect to the average refractive index of the multilayer film member forming the convex portion of the diffraction grating is used, the concave portion is formed by the optical medium contained in the concave portion This increases the average refractive index, and can reduce the difference from the average refractive index of the protrusions. Thereby, it is possible to suppress the decrease in the transmitted light amount caused by the difference in the refractive index between the concave portion and the convex portion by making the light incident on the transmitted light amount variable element, which is preferable because the degree of freedom in selecting the liquid crystal material is large. Here, the convex part is a part of the multilayer film member having a diffraction grating structure, and the concave part is a part between the convex part and having a height from the bottom to the apex of the multilayer film member. Therefore, the liquid crystal in a portion higher than the top of the convex portion is not included in either the convex portion or the concave portion.

  The first multilayer film member provides the transmitted light amount variable element described above, which is formed of two types of optical materials, a first high refractive index material and a first low refractive index material.

  With this configuration, a multilayer film can be formed with a minimum number of members, which is preferable because production efficiency is improved.

In addition, there is provided the transmitted light amount variable element according to the above, wherein the first high refractive index material is Ta ₂ O ₅ and the first low refractive index material is SiO ₂ .

  This structure is preferable because a stable material can be used, and a highly reliable multilayer film can be obtained.

  The optical medium is formed of a second multilayer member laminated in a direction perpendicular to the substrate, and the average refractive index of the second multilayer member is higher than the ordinary refractive index of the liquid crystal. The transmitted light amount variable element described above is provided.

  With this configuration, the difference between the average refractive index of the multilayer film member forming the convex portion of the diffraction grating and the average refractive index of the concave portion considering the wavelength dispersion of incident light can be adjusted to be smaller. The light use efficiency of the transmitted light amount variable element can be further increased. Furthermore, when the concave portion contains a material having a higher refractive index than the transparent substrate, a multilayer film structure is preferable because a reduction in transmittance due to internal interference can be suppressed.

  Further, the second multilayer film member provides the transmitted light amount variable element described above, which is formed of two types of optical materials, that is, a second high refractive index material and a second low refractive index material.

  With this configuration, a multilayer film can be formed with a minimum number of members, which is preferable because production efficiency is improved.

In addition, the transmitted light amount variable element according to the above, wherein the second high refractive index material is Ta ₂ O ₅ and the second low refractive index material is SiO ₂ .

  This structure is preferable because a stable material can be used, and a highly reliable multilayer film can be obtained.

  The number of the transparent substrates arranged in parallel is three, and the alignment direction of the liquid crystal sandwiched between the pair of transparent substrates and the alignment direction of the liquid crystal sandwiched between the other pair of transparent substrates are approximately. The transmitted light amount variable element described above that is orthogonal to each other is provided.

  With this configuration, the amount of light can be controlled even when the polarization state of incident light is random, and a transmitted light amount variable element having no dependency on incident polarization can be realized.

In addition, there is provided the transmitted light amount variable element according to the above, wherein the transparent electrode is divided into a plurality of regions, and a voltage can be applied to each of the plurality of regions.

  With this configuration, the light incident on the transmitted light amount variable element can be transmitted by changing the light amount for each region, so that the degree of freedom of the light amount control method is improved.

  In addition, the transmission light amount variable element according to the above, wherein the diffraction grating has a grating pitch of 10 μm or less.

  This configuration is preferable because the diffraction angle of light incident on the diffraction grating is increased and can be greatly different from the light path of light traveling straight, so that diffracted light that becomes stray light does not pass through and can be controlled with high accuracy.

Further, the image display spatial light modulation element includes a predetermined light source, an image display light spatial modulation element that modulates and emits light according to a video signal of incident light, and a plurality of lenses. 1 in the optical path until the light emitted from the light source passes through the projection lens system, the illumination optical system that collects and illuminates the light, the projection lens system that projects the light emitted from the light spatial modulation element for image display Provided is a projection display device including at least one of the transmitted light amount variable elements described above.

  With this configuration, it is possible to realize a projection display device that has high light contrast, high reliability, and easy light quantity control.

  In the present invention, a diffraction grating having a concave-convex cross section is formed on one of the opposing surfaces of at least two transparent substrates arranged in parallel, the liquid crystal is filled between a pair of transparent substrates, and the convex portions are sandwiched. Formed with a multilayer film, the concave portion contains an optical medium with a refractive index larger than the ordinary refractive index of the liquid crystal, and by adopting a structure that can apply a voltage to the sandwiched liquid crystal, the light utilization efficiency is high and the reliability is excellent. It is possible to provide a transmitted light amount control element and a projection display device that can easily control the light amount.

(First Embodiment)
FIG. 1 is a cross-sectional view showing a schematic configuration of a transmitted light amount variable element according to the first embodiment of the present invention. In FIG. 1, the transmitted light amount variable element 10 is provided with a pair of transparent substrates 11 a and 11 b arranged in parallel and the opposing surface side of the pair of transparent substrates 11 a, and is periodically uneven by a transparent member having a multilayer structure. Sandwiched between the first multilayer film member 13 arranged so as to form a groove and the single-layer optical member 14 as an optical medium provided in the concave portion so as to make the periodic concave and convex grooves shallow. The liquid crystal 15 includes transparent electrodes 12a and 12b for applying a voltage to the liquid crystal 15, a sealing material 16, and a wiring 17 for applying a voltage having a predetermined waveform between the transparent electrodes 12a and 12b. Is done. The recess is composed of the single-layer optical member 14 and the liquid crystal 15, and the optical path length is changed by changing the refractive index of the liquid crystal contained in the recess.

  In FIG. 1, for example, an acrylic resin, an epoxy resin, a vinyl chloride resin, a polycarbonate, or the like may be used as the transparent substrates 11a and 11b, but a glass substrate is preferable from the viewpoint of durability and the like. Further, an alignment film (not shown) is provided at the interface between the first multilayer film member 13 and the single-layer optical member 14 and the liquid crystal 15 and at the interface between the transparent electrode 12 b and the liquid crystal 15. The alignment film can be realized by a method of forming an alignment film material such as polyimide or PVA and performing a rubbing process, and can improve the alignment controllability of the liquid crystal, which is preferable. In addition, as the alignment film made of an inorganic material, for example, a thin film obtained by obliquely depositing SiON or a film subjected to alignment treatment by ion beam irradiation can be used. These alignment treatments by oblique vapor deposition and ion beam irradiation are preferable because they are excellent in the alignment regulating force of the concave portions of the concavo-convex lattice member, which is difficult to carry out by rubbing.

  Each transparent member constituting the first multilayer film member 13 has a multilayer structure in which a plurality of optical members having different refractive indexes are laminated (hereinafter, a film having such a layer structure is simply referred to as a multilayer film). By using the multilayer grating member 13 having the multilayer structure, the interference state of light in the multilayer film can be changed for each wavelength. This is for effectively controlling the wavelength dispersion of the refractive index of the first multilayer film member 13 and controlling the wavelength dependency of diffraction efficiency and transmittance.

The first multilayer film member 13 periodically deposits a plurality of dielectric thin films having different refractive indexes in the thickness direction using, for example, a vacuum evaporation method or a sputtering method. Thereafter, the convex portion is processed into a multilayer film structure using a photolithography technique and an etching technique. As a material for the optical thin film, oxides such as Si, Ta, Nb, Ti, Al, Mg, and Ca are preferable from the viewpoint of reliability. When combining two types of optical thin film materials, the combination of SiO ₂ and Ta ₂ O ₅ has a large difference in refractive index between each other and is easy to design. In addition, reliability, transmittance in a short wavelength region, light resistance, This is preferable from the viewpoint of controllability of production. In this case, for example, a film whose strength and reliability are improved by forming a film in an atmosphere in which an RF voltage is applied to a vacuum chamber into which oxygen, nitrogen, argon gas, or the like is introduced by an ion plating method, and plasma is generated. Can be formed.

  Table 1 is an example of a table for explaining the material and layer structure of the optical thin film of the first multilayer lattice member 13.

  Table 1 shows an example of the layer structure of the first multilayer film member 13 in which a total of 19 layers of two types of optical thin films (for example, L1 and L2) are alternately stacked. The optical thin film represented by the layer L1 has a refractive index of 1.46 and a film thickness of 0.202 μm, and the optical thin film represented by the layer L2 has a refractive index of 2.20 and a film thickness of 0.038 μm. . The refractive indexes of the transparent substrates 11a and 11b are 1.52.

  In general, the diffraction efficiency of a diffraction grating varies depending on the ratio between the difference in optical path length represented by the product of the refractive index and distance transmitted through the concave and convex portions of the concave-convex grating and the wavelength of incident light. Hereinafter, a method for reducing the wavelength dependency of the diffraction efficiency will be described in detail. In order to reduce the wavelength dependence of the diffraction efficiency, it is necessary to make the optical path length difference / wavelength close to a constant within the wavelength band used. That is, it is necessary to reduce the difference in optical path length on the short wavelength side and increase it on the long wavelength side. In order to bring the wavelength dependency of the optical path length difference close to an appropriate value, it is preferable that the concavo-convex grating is constituted by the first multilayer film member 13.

  Specifically, in the example of the multilayer film shown in Table 1, the wavelength band in which the amount of light is desired to be changed is the use wavelength band, and in this case, the visible light region is in the range of 460 to 660 nm. If the wavelength of light incident from the direction perpendicular to the multilayer film surface is in this utilization wavelength band, the transmittance is high, and the transmittance is low for light having a wavelength different from the utilization wavelength range. Has a reflection band which is a wavelength band for reflecting light, an effective refractive index increases on the short wavelength side, which is a wavelength side shorter than 460 nm, due to light interference in the multilayer film, and conversely, a longer wavelength than 660 nm. On the wavelength side, the effective refractive index is small.

The multilayer film is processed into a concavo-convex lattice shape to form a first multilayer film member 13. In FIG. 1, the concave portion includes the single-layer optical member 14 and the liquid crystal 15, but the liquid crystal contained in the concave portion from the height of the single-layer optical member 14 to the same height as the first multilayer film member 13 as described above. Corresponds to the part to fill. The single layer optical member 14 is made of a material having a refractive index larger than the ordinary light refractive index (n _o ) of the liquid crystal 15, so that the average ordinary light in the recesses can be obtained as compared with the case where an optical medium such as the single layer optical member 14 is not formed. The refractive index can be increased. Further, the narrower the pitch of the concavo-convex diffraction grating, the larger the diffraction angle with respect to the straight traveling direction of light. In the projection display device, the diffracted light becomes unnecessary stray light, so that the diffraction angle is preferably as large as possible. Therefore, in order to obtain a sufficient diffraction angle of the light to be diffracted, the grating pitch is preferably 10 μm or less, more preferably 4 μm or less. In FIG. 1, the longitudinal direction of the diffraction grating is parallel to the Y axis, and the periodic pitch is, for example, a first multilayer film member adjacent to the X axis from the left end of the first multilayer film member forming one convex portion. It corresponds to the length to the left end of.

The optical thin film as shown in Table 1 to form a first multilayer film member 13, the average refractive index n _{m (product} of sum / each layer of the refractive index and thickness of the optical thin film layers of the first multilayer film member 13 The total thickness) is about 1.57. When the material having the ordinary refractive index n _o of the liquid crystal 15 used matches the average refractive index of the first multilayer film member 13, the optical path length difference of the light transmitted through the diffraction grating is brought close to “0”. Therefore, the transmittance can be improved. However, since the ordinary refractive index n _o of the liquid crystal material used is about 1.5, it is impossible to improve the transmittance and constituting a recess only in the liquid crystal material. Therefore, by containing the optical medium as a higher refractive index than n _o in the recess, it is possible to match the average refractive index n _m of the first multilayer grating member 13 by using a liquid crystal material of such properties This is preferable because the degree of freedom in selecting a liquid crystal material is improved.

Specifically, the average refractive index n _m of the first multilayer film member 13, the liquid crystal 15 to match the average refractive index of the recess when the ordinary light, than the ordinary refractive index n _o of the liquid crystal 15 in the recess This can be realized by providing the single-layer optical member 14 having a high refractive index with an appropriate film thickness. The transmittance of incident light can be maximized by matching the refractive indexes of the convex portion and the concave portion, but the first multilayer film member 13 and the single-layer optical device are used to realize the function in a predetermined wavelength band. In consideration of the wavelength dispersion characteristics of the member 14 and the liquid crystal 15, it is necessary to design the maximum transmittance. In addition, it is preferable to use the single-layer optical member 14 having a high refractive index because the thickness of the single-layer optical member can be reduced.

  The light quantity variable element 10 changes the effective refractive index of the liquid crystal depending on the magnitude of the voltage applied to the liquid crystal 15 and adjusts the transmittance of incident light. As a function of the light quantity variable element 10, when light in a desired wavelength band is incident on the diffraction grating, the contrast is large because of a large difference in transmittance between light having low diffraction efficiency and light shielding having high diffraction efficiency. This is preferable in that it can be increased. As the diffraction grating, the optical path length difference between the light passing through the single-layer optical member 14 serving as the recess and the liquid crystal 15 and the light passing through the first multilayer film member 13 serving as the protrusion is the light quantity variable element 10. When the wavelength of the incident light is λ, the function can be realized by designing so that the optical path difference is substantially (2n + 1) · λ / 2 when blocked and nλ when transmitting (n is an integer). . Further, it is particularly preferable that the value of n is “0” because the film thickness can be reduced and the transmittance is improved.

  The application of the present invention is not limited to the example of the multilayer film shown in Table 1. Light passing through the single-layer optical member 14 and the liquid crystal 15 serving as a recess and light passing through the first multilayer film member 13 The optical path length difference may be a material and a film thickness that substantially conform to the above-described design at the time of light shielding and transmission.

The liquid crystal 15 has a refractive index anisotropy and may have a positive or negative dielectric anisotropy as a characteristic. Hereinafter, for convenience of explanation, it is assumed that the liquid crystal 15 has a positive dielectric anisotropy (when the voltage is applied, the major axis direction of the liquid crystal molecules is aligned with the electric field direction). Further, hereinafter, the ordinary refractive index of the liquid crystal 15 and n _o, the extraordinary refractive index and n _e.

Here, the refractive index and the ordinary refractive index n _o and an average refractive index of the average ordinary refractive index n _{O_avr} of a single layer optical member 14 contained in the _recess, the refractive index and an extraordinary refractive monolayer optical member 14 contained in the recess illustrating the average refractive index of the rate _{n e} average extraordinary refractive index _{n e_avr.} In this _case, either the refractive index of _{n O_avr} or _{n E_avr,} substantially match the refractive index _{n m} of the first multilayer film member 13. For _example, when the _{n o_avr} = _{n m,} the optical path difference between the convex portion and the concave portion is an odd multiple of a half wavelength _| design · d = (2n + 1) · λ / 2 and so as to | _n e_avr _-n m (N is an integer). In this way, the light quantity variable element 10 is in any one of the above states when no voltage is applied to the liquid crystal 15 or when a voltage is applied. Therefore, the transmittance can be easily controlled depending on the magnitude of the voltage. In the following description, it is assumed that the refractive index of the convex portion and the concave portion is the same when transmitted through the diffraction grating and the refractive index difference is λ / 2 when the light is shielded.

Transparent electrodes 12a, 12b, the metal oxide thin film such as ITO or SnO _2, may be a metal thin film or the like, ITO, SnO ₂ or the like is preferable because of high transmittance. The transparent electrode only needs to be able to change the orientation direction of the liquid crystal 15 depending on the voltage, and can be provided on the transparent substrate 11a surface or the surface of the concavo-convex portion of the diffraction grating, but the transparent substrate 11a surface is preferable because reliability is improved. . Moreover, the transmittance | permeability can be improved by providing the antireflection film which is not shown in the surface which does not oppose the transparent substrates 12a and 12b.

  FIG. 5 shows a view from the XY plane in order to explain a configuration example when the transparent electrodes 102 a and 102 b are divided into a plurality of divided electrodes 111, 112 and 113. In the following, for convenience of explanation, light is transmitted through the divided electrodes shown in white on the drawing, and part of the light is diffracted according to the applied voltage, and the transmittance is lowered. It shall be.

  FIG. 5A shows a state in which all the divided electrodes 111, 112, and 113 are set to the same potential and light is transmitted through the entire region. Similarly, in FIG. 2B, the potential of the divided electrode 113 is switched, and the transmittance is reduced in the region of the divided electrode 113. In FIG. 2C, the potential of the divided electrode 112 is also switched, and the transmittance of the regions of the divided electrodes 112 and 113 is also reduced. With this configuration, the light transmittance can be changed for each region where the divided electrodes 111, 112, and 113 are provided.

  FIG. 6 is an XY plane view for explaining a configuration example in the case of dividing into a plurality of divided electrode regions in the same manner as the transparent electrodes 12a and 12b shown in FIG. The shape of the divided electrodes 121, 122, and 123 shown in FIG. 6 is suitable for use when a microlens (fly array lens) is included in the illumination optical system that constitutes the projection display device. That is, the shape of the divided electrodes 121, 122, 123 is similar to the shape of the microlens cell at the end, and the light transmittance can be changed for each cell.

  The sealing material 16 is provided to seal the liquid crystal 15 between the pair of transparent substrates 11a and 11b. As the sealing material 16, a resin made of a thermosetting polymer such as an epoxy resin, an ultraviolet curable resin, or the like can be used. Further, as the sealing material 16, a material in which a spacer such as glass fiber is mixed in order to obtain a desired cell interval may be used. The wiring 17 is for applying a voltage having a predetermined waveform between the transparent electrodes 12a and 12b, and a flexible wiring or the like can be used.

Hereinafter, the operation of the transmitted light amount variable element 10 will be described with reference to FIG. By applying a voltage to the liquid crystal 15, the refractive index of light traveling in the Z-axis direction can be effectively changed. When substantially equal to the effective average refractive index of the single layer optical member 14 and the liquid crystal 15 included in the refractive index n _m and the recess of the first multilayer film member 13, light incident on the diffraction grating diffracts Can be transmitted without any problem and high transmittance can be obtained. In contrast, different from the single-layer optical member 14 included in the refractive index n _m and the recess of the first multilayer film member 13 by changing the magnitude of the voltage applied and the effective refractive index of the liquid crystal 15 In this case, the light incident on the diffraction grating causes an optical path length difference, so that diffraction occurs and the transmittance is reduced. When the applied voltage is adjusted and the optical path length difference becomes λ / 2, the diffraction efficiency becomes maximum, and a light-shielding state in which the transmittance is almost “0” can be realized. Hereinafter, the value of the voltage to be applied will be described as V (variable).

Hereinafter, for the sake of simplicity, the light incident on the transmitted light amount variable element 10 is linearly polarized in the Y-axis direction that is the longitudinal direction of the first multilayer film member 13 that coincides with the long-axis direction of the liquid crystal molecules, and The liquid crystal molecules are assumed to be substantially parallel to the substrates 11a and 11b when no voltage is applied. Further, when the applied voltage is sufficiently large value V _o, the long axis direction of liquid crystal molecules, and become (substantially parallel to the Z-axis) substantially perpendicular substrate 11a, to 11b. In this way, the effective refractive index of the liquid crystal 15 with respect to light incident at the Z-axis direction, n _o becomes the applied voltage (V = V _o), when voltage is applied (V = 0) Becomes _ne . Thus, the _{n E_avr} the average refractive index of a single layer optical member 14 and the liquid crystal 15 contained in the recess when the voltage is applied _(V = V _o) to the _{n O_avr} next, when no voltage is applied (V = 0) .

A first multilayer film member 13 effective average ordinary refractive index n _{O_avr} refractive index n _m and the recess of substantially equally high design the transmittance when a voltage is applied (V = V _o). On the other hand, when the applied voltage is gradually lowered, the major axis direction of the liquid crystal molecules approaches the horizontal direction with respect to the transparent substrate accordingly, so that the average refractive index of the concave portion increases and approaches the average extraordinary light refractive index _{ne_avr} . In this case, the optical path difference of the light occurs incident to the diffraction grating by the refractive index difference between n _m and n _{E_avr,} transmittance since diffraction occurs is reduced. When the applied voltage is further decreased to make the voltage non-applied (V = 0), the optical path length difference becomes | _{ne_avr−} n _m | · d = λ / 2 with respect to the wavelength λ of the incident light. A light shielding state is achieved in which the diffraction efficiency is maximum and the transmittance is substantially “0”.

In the above example, the major axis direction of the liquid crystal molecules is parallel to the substrate when no voltage is applied (V = 0), but the major axis direction of the liquid crystal molecules is not applied when the voltage is not applied (V = 0). It is also possible to use a liquid crystal having a negative dielectric anisotropy (Δε) so that the liquid crystal molecules are parallel to the substrate with a sufficiently high applied voltage (V = V _o ) at a substantially perpendicular voltage to the substrate. In this case, since a high transmittance can be obtained when no voltage is applied, a high transmittance can be maintained even in the event of failure where voltage cannot be applied for some reason, and light can be prevented from being blocked during the failure.

(Second Embodiment)
FIG. 2 is a cross-sectional view showing a schematic configuration of the transmitted light amount variable element according to the second embodiment of the present invention, and the same members as those in the configuration according to the first embodiment are denoted by the same reference numerals as in FIG. Is attached. In the first embodiment, the single-layer optical member 14 is provided as an optical medium in the recess, but in the second embodiment, the second multilayer film member 24 is provided in the recess as the optical medium. . Other configurations and functions are the same, and the second multilayer film member 24 has a structure in which at least two kinds of optical members are laminated. Multilayer film member 24 is substantially coincident with respect to the refractive index of the first multilayer film member 13 by designing the optical member and the film thickness so that the high refractive index as compared with the ordinary refractive index n _o of the liquid crystal 15 Can be designed to In addition, the multilayer film structure can suppress internal interference, increase the maximum transmittance, and improve the contrast.

Since the second multilayer film member 24 is composed of a plurality of optical thin films, the refractive index can be adjusted by adjusting the combination and film thickness of the optical thin films. Therefore, the average ordinary light refractive index of the concave portion and the refractive index of the first multilayer film member 13 can be finely adjusted including the wavelength dispersion characteristics, which is preferable because the controllability of the transmittance is improved. The second multilayer film 24 can be composed of two or more types of materials having different refractive indexes. However, it is preferable that the second multilayer film 24 is composed of two types of materials from the viewpoint of productivity. Examples of the optical member include Ta ₂ O ₅ , SiO ₂ , CeO ₂ , HfO ₂ , SnO _2, etc., but it is preferable to use Ta ₂ O ₅ and SiO ₂ from the viewpoint of film stability.

  Table 2 is an example of a table for explaining the material and layer structure of the optical thin film of the second multilayer film member 24.

The operation of the transmitted light amount variable element 20 provided with the second multilayer film member 24 will be described with reference to FIG. The effect is similar to the first embodiment, the average ordinary refractive index n _{O_avr} the ordinary refractive index n _o of the refractive index of the liquid crystal 15 of the second multilayer film member 24 is an optical medium of the recess is, the designing 1 of the multilayer film member 13 refractive index n _m and such that substantially equal to. Furthermore refractive index and the average extraordinary refractive index n _{E_avr} the extraordinary refractive index n _e of the liquid crystal 15 of the second multilayer film member 24, the difference between the refractive index m _n of multilayered grid members 13, the incident light When the wavelength λ and the height of the first multilayer film member 13 are d, | _{ne_avr−} n _m | · d = λ / 2. Under such a design, the transmittance of incident light can be adjusted with good control by the voltage applied to the liquid crystal 15.

(Third embodiment)
FIG. 3 is a cross-sectional view showing a schematic configuration of a transmitted light amount variable element according to the third embodiment of the present invention. In this configuration, the transmitted light amount variable element having the configuration according to the first embodiment is also provided on the back side of the transparent substrate 11a, but has the same optical thin film configuration as the first multilayer film member 13. The difference is that the longitudinal directions of the lattices of the first multilayer film member 23 are arranged orthogonal to each other. Processing is performed so that the alignment directions of liquid crystals 15 and 25 (not shown) are parallel to the longitudinal directions of the first multilayer members 13 and 23, respectively.

  The transmitted light amount variable elements 10 and 20 according to the first and second embodiments function in a polarization state in which the direction of incident linearly polarized light is parallel to the longitudinal direction of the diffraction grating, that is, the Y-axis direction. . The transmitted light amount variable element 30 according to the third embodiment can control the transmitted light amount in both X-axis component light and Y-axis component light even when light having a random polarization direction is incident. It is. FIG. 3 shows an example of a configuration according to the third embodiment. As another configuration for controlling the amount of transmitted light with respect to random polarization as well as the polarization direction, the longitudinal direction of the first multilayer film member 23 is the first. This is a case where the alignment direction of the liquid crystal 25 is the X direction although it is parallel to the Y axis as in the multilayer film member 13. Thus, it is useful to arrange the transmitted light amount variable element 30 according to the third embodiment in a device that modulates and projects randomly polarized light, such as a DMD projection display device.

  Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1
Hereinafter, the transmitted light amount variable element 10 according to the first embodiment of the present invention will be described with reference to FIG. A quartz glass substrate having a thickness of 0.6 mm is used as the transparent substrates 11a and 11b. An ITO film having a sheet resistance of about 300Ω / □ is formed on the surfaces of the transparent substrates 11a and 11b by sputtering, and the transparent electrodes 12a and 12b are formed by a photolithography technique and an etching technique.

After cleaning and drying the substrate on which the transparent electrode is formed, a sputtering method is used to form a SiO ₂ film on the surface of the transparent substrate 11a on which the transparent electrode 12a is formed so as to have the layer structure and film thickness shown in Table 1. A Ta ₂ O ₅ film is alternately formed to form a multilayer film. Each film is formed in an atmosphere in which plasma is generated by an ion plating method. In Table 1, the optical thin film corresponding to the refractive index of 1.46 of the odd layer (for example, L19 layer) is SiO ₂ , and the optical thin film corresponding to the refractive index of 2.20 of the even layer (for example, L18 layer) is Ta ₂ O. ₅ . Etching is performed on the multilayer film so that the multilayer film structure is separated from the photolithography technique, thereby forming a first multilayer film member 13 that becomes a diffraction grating having a periodic pitch of 6 μm.

After etching, the _{the Ta} 2 _{O 5} film was 190nm formed by vacuum evaporation, to remove _{the Ta} 2 _{O 5} film on the convex portions by a lift-off process. Thereby, a Ta ₂ O ₅ film having a film thickness of 190 nm corresponding to the single-layer optical member 14 is formed in the recess. Polyimide is formed to a thickness of 50 nm as an alignment film material (not shown) on the opposing surfaces of the transparent substrates 11a and 11b by flexographic printing. Thereafter, the polyimide film is rubbed in parallel with the Y direction, which is the longitudinal direction of the diffraction grating, to perform an alignment treatment.

Next, the sealing material 16 made of an epoxy resin is printed on the surface facing the transparent substrate 11b, and a liquid crystal cell is manufactured by thermocompression bonding. Here, a glass fiber (not shown) is mixed in the sealing material 16 to make the cell gap uniform. Subsequently, a low-molecular liquid crystal is injected into a liquid crystal cell serving as a gap between two transparent substrates using a vacuum injection method, and an injection port of the liquid crystal cell is sealed using a sealing material (not shown). Here, the ordinary refractive index _{n o} for 589nm light of 1.52, the extraordinary refractive index _{n e} uses a liquid crystal having a refractive index anisotropy of 1.65. Next, the flexible circuit board which is the wiring 17 is provided so as to be electrically connected to the transparent electrodes 12a and 12b. An electrical signal for controlling the amount of light shielding is input to the transparent electrodes 12a and 12b via the flexible circuit board as the wiring 17.

When linearly polarized light parallel to the Y direction is incident on the transmitted light amount variable element 10 manufactured as described above in parallel to the Z axis, the refractive index of the first multilayer film member 13 is applied when no voltage is applied to the liquid crystal 15. And a difference in the average extraordinary refractive index, which is the average refractive index between the refractive index of Ta ₂ O ₅ that is a single-layer optical member and the extraordinary refractive index of the liquid crystal, causes a diffraction effect. On the other hand, when a voltage is applied to the liquid crystal 15 so that the electric field is parallel to the Z-axis direction, the tilt angle in the major axis direction of the liquid crystal molecules changes according to the magnitude of the voltage. Then, the effective refractive index for the light in the polarization direction parallel to the Y direction changes, and the diffraction efficiency of the incident light also changes. As a result, the transmittance of light transmitted in the Z-axis direction, which is the light traveling direction, changes, and the transmitted light amount variable element 10 that can be controlled by the applied voltage can be realized.

  FIG. 8 shows the wavelength dependency of the transmittance when linearly polarized light parallel to the Y axis of the diffraction grating is incident on the transmitted light quantity variable element 10 manufactured as described above. The six curves show the wavelength dependence of the transmittance when the magnitude of the voltage applied between the transparent electrodes 12a and 12b is changed and the effective refractive index of the liquid crystal is changed. The curves shown in FIG. 8 indicate that the effective refractive index n of the liquid crystal is 1.64, 1.62, 1.60, 1.58, 1.56 in order from the lowest transmittance with respect to light having a wavelength of 650 nm. And a voltage of 1.52 is applied.

  Thus, the transmittance changes according to the effective refractive index (applied voltage) of the liquid crystal, and the transmittance variation is within 20% in the wavelength range of 460 to 660 nm that is the visible light region. The transmitted light amount variable element 10 is obtained.

(Example 2)
Hereinafter, the transmitted light amount variable element 20 according to the second embodiment of the present invention will be described with reference to FIG. In Example 1, the second multilayer film member 24 is used in place of the single-layer optical member 14 as the optical medium of the concave portion, and the lattice pitch is 4 μm. These members are also the same as those shown in the first embodiment. The substrate on which the transparent electrode 12a is formed is washed, dried, and then sputtered to form SiO ₂ so as to have the layer structure and film thickness shown in Table 1 on the surface of the transparent substrate 11a on which the transparent electrode 12a is formed. Films and Ta ₂ O ₅ films are alternately formed to form a multilayer film. Etching is performed on the multilayer film so as to separate the multilayer film structure from the photolithography technique, thereby forming a diffraction grating having a periodic pitch of 4 μm. After the etching process, the second multilayer film member 24 is formed by alternately depositing SiO ₂ films and Ta ₂ O ₅ films so as to have the layer structure and film thickness shown in Table 2 by vacuum deposition. Thereafter, the SiO ₂ film and the Ta ₂ O ₅ film on the convex portion are removed by a lift-off process. As a result, a film having a film thickness of 257 nm corresponding to the second multilayer film member 24 is formed in the recess.

  An alignment film made of polyimide (not shown) is formed, and a sealing material 16 made of an epoxy resin is printed on the facing surface of the transparent substrate 11b, and a liquid crystal cell is manufactured by thermocompression bonding. Here, a glass fiber (not shown) is mixed in the sealing material 16 to make the cell gap uniform. Subsequently, a low-molecular liquid crystal is injected into a liquid crystal cell serving as a gap between two transparent substrates using a vacuum injection method, and an injection port of the liquid crystal cell is sealed using a sealing material (not shown). An electric signal for controlling the light shielding amount is input to the transparent electrodes 12a and 12b via a flexible circuit board corresponding to the wiring 17.

  FIG. 9 shows the wavelength dependency of the transmittance when linearly polarized light parallel to the Y-axis of the diffraction grating is incident on the transmission light amount variable element 20 manufactured as described above. The six curves show the wavelength dependence of the transmittance when the magnitude of the voltage applied between the transparent electrodes 12a and 12b is changed and the effective refractive index of the liquid crystal is changed. The curves shown in FIG. 9 indicate that the effective refractive index of the liquid crystal is 1.64, 1.62, 1.60, 1.58, 1.56, and the like in order from the lowest transmittance with respect to light having a wavelength of 650 nm. A voltage is applied so as to be 1.52.

  Thus, the transmittance changes according to the effective refractive index (applied voltage) of the liquid crystal, and the transmittance variation is within 20% in the wavelength range of 460 to 660 nm that is the visible light region. Is obtained.

(Comparative example)
As a comparative example, FIG. 4 shows a transmitted light amount variable element 30 having a configuration in which only the liquid crystal 15 is filled without forming a film in the concave portion of the diffraction grating. The first multilayer film member 13 is set to the material and film thickness of the optical thin film shown in Table 1, and the liquid crystal 15 is also made of a material having the same physical properties as those in the first and second embodiments.

  FIG. 10 shows the wavelength dependence of the transmittance when linearly polarized light parallel to the Y axis of the diffraction grating is incident on the transmission light amount variable element 30 manufactured as described above. The six curves show the wavelength dependence of the transmittance when the magnitude of the voltage applied between the transparent electrodes 12a and 12b is changed and the effective refractive index of the liquid crystal is changed. The curves shown in FIG. 10 indicate that the effective refractive index of the liquid crystal is 1.64, 1.62, 1.60, 1.52, 1.58 in order from the lowest transmittance to light having a wavelength of 650 nm. A voltage is applied so as to be 1.56.

As described above, the transmittance varies depending on the effective refractive index (applied voltage) of the liquid crystal, but the transmitted light having a refractive index of 1.52 is constant depending on the wavelength in the wavelength range of 460 to 660 nm that is the visible light region. not turned in, the control of the transmittance is difficult characteristics when the liquid crystal 15 by applying a voltage became almost ordinary refractive index n _o. In Example 1 and Example 2, it is stable so that the maximum transmittance is obtained at a voltage (V = V _o ) or higher when the ordinary refractive index is n _o , whereas in the comparative example, at V = V _o or more. Since the transmittance is not constant, fine adjustment of the voltage is necessary to obtain the maximum transmittance.

  The transmitted light amount variable element and the projection display device according to the present invention can efficiently control the light transmittance by the voltage applied to the liquid crystal in the visible light wavelength band. Moreover, since a material excellent in processability and reliability can be selected as the optical material constituting the transmitted light amount variable element, productivity can be improved and a highly reliable transmitted light amount variable element and a projection display device can be realized.

The schematic diagram which shows the structure of the transmitted light amount variable element in the 1st embodiment of this invention. The schematic diagram which shows the structure of the transmitted light amount variable element in the 2nd embodiment of this invention. The schematic diagram which shows the structure of the transmitted light amount variable element in the 3rd embodiment of this invention. The schematic diagram which shows the structure of the transmitted light amount variable element in a comparative example. The schematic diagram which shows an example (substantially circular) of the division | segmentation electrode which comprises the transparent electrode which concerns on embodiment of this invention. The schematic diagram which shows another example (for microlenses) of the division | segmentation electrode which comprises the transparent electrode which concerns on embodiment of this invention. The schematic diagram which shows an example of a structure of the liquid crystal projection type display apparatus which concerns on embodiment of this invention. The characteristic figure of the transmittance | permeability with respect to the wavelength of the incident light in Example 1 of this invention. The characteristic figure of the transmittance | permeability with respect to the wavelength of the incident light in Example 2 of this invention. The characteristic figure of the transmittance | permeability with respect to the wavelength of the incident light in a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Reflecting mirror 3 Illumination optical system 4 Polarizer 5 Liquid crystal panel 6 Analyzer 7 Projection lens system 8, 20, 30, 40 Transmitted light quantity variable element 11a, 11b, 21b Transparent substrate 12a, 12b, 22a, 22b Transparent electrode 13 , 23 First multilayer film member 14 Single layer optical member 15, 25 Liquid crystal 16, 26 Sealing material 17, 27 Wiring 24 Second multilayer film member 50 Liquid crystal projection display device 111, 112, 113, 121, 122, 123 Transparent electrode

Claims (10)

At least two transparent substrates arranged in parallel;
Provided on one side one of the pair of the transparent substrate facing the transparent substrate, a first multilayer element cross-sectional shape to form a protrusion periodic uneven diffraction grating,
An optical medium provided in a part of the concave portion of the diffraction grating;
A liquid crystal sandwiched between the pair of transparent substrates so as to fill the diffraction grating and the optical medium;
A transparent electrode for applying a voltage to the liquid crystal,
The first multilayer film member has a multilayer structure in which a plurality of types of optical thin films having different refractive indexes are stacked in a direction perpendicular to the substrate,
The transmitted light amount variable element in which the refractive index of the optical medium is higher than the ordinary refractive index of the liquid crystal.   2. The transmitted light amount variable element according to claim 1, wherein the first multilayer film member is formed of two types of optical materials, a first high refractive index material and a first low refractive index material. 3. The transmitted light amount variable element according to claim ₂ , wherein the first high refractive index material is Ta ₂ O ₅ and the first low refractive index material is SiO ₂ . The optical medium is formed from a second multilayer member laminated in a direction perpendicular to the substrate,
The transmitted light amount variable element according to any one of claims 1 to 3, wherein an average refractive index of the second multilayer film member has a refractive index higher than an ordinary refractive index of the liquid crystal.   5. The transmitted light amount variable element according to claim 4, wherein the second multilayer film member is formed of two types of optical materials, a second high refractive index material and a second low refractive index material. 6. The transmitted light amount variable element according to claim 5, wherein the second high refractive index material is Ta ₂ O ₅ and the second low refractive index material is SiO ₂ .   The number of the transparent substrates arranged in parallel is three, and the alignment direction of the liquid crystal sandwiched between the pair of transparent substrates and the alignment direction of the liquid crystal sandwiched between the other pair of transparent substrates are substantially orthogonal. The transmitted light amount variable element according to any one of claims 1 to 6. The transmitted light amount variable element according to claim 1, wherein the transparent electrode is divided into a plurality of regions, and a voltage can be applied to each of the plurality of regions.   The transmitted light amount variable element according to claim 1, wherein a grating pitch of the diffraction grating is 10 μm or less. A predetermined light source;
A spatial light modulating element for image display that modulates and emits light according to a video signal of incident light;
An illumination optical system comprising a plurality of lenses and condensing and illuminating the light emitted from the light source on the spatial light modulation element for image display;
A projection lens system for projecting light emitted from the image display light spatial modulation element;
Light emitted from the light source is arranged at least one in the optical path to pass through the projection lens system, a projection display provided with a transmitted light quantity variable element according to any one of claims 1-9 apparatus.

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