JP7317675B2 - optical device - Google Patents

Description

The present invention relates to an optical device, and more particularly to an optical device that distributes illumination light within a field of view.

When a vertically aligned nematic liquid crystal cell having negative dielectric anisotropy is sandwiched between crossed Nicols polarizers, it is possible to realize high light shielding properties equivalent to those of pure crossed Nicols polarizers, and a high contrast ratio. However, in the direction inclined from the direction perpendicular to the display surface, the optical characteristics dependent on the polar angle from the direction perpendicular to the surface also contribute, resulting in anisotropy in the optical characteristics. Therefore, it is preferable to combine a viewing angle compensator such as a retardation layer having negative uniaxial optical anisotropy.

Liquid crystals are generally susceptible to alteration by ultraviolet rays, and their optical characteristics may change. At least on the incident side of the liquid crystal cell, an ultraviolet reflective retardation layer having a function of compensating for the optical anisotropy of the liquid crystal cell and reflecting ultraviolet rays incident on the liquid crystal cell is arranged to reduce the influence of ultraviolet rays. A configuration has been proposed (for example, Patent Document 1).

FIG. 6A is a cross-sectional view schematically showing an example of a liquid crystal display device having a retardation layer with an ultraviolet reflective function. The liquid crystal display device 100 includes a liquid crystal cell 104 , an incident-side polarizing layer 102 A, an exit-side polarizing layer 102 B, and a backlight 106 . Furthermore, a retardation layer 108 with an ultraviolet reflective function is arranged on both sides of the liquid crystal cell 104 in the thickness direction. The polarizing layers 102A and 102B selectively transmit only linearly polarized light, and are opposed to each other in a crossed Nicols state in which the transmission axis directions are perpendicular to each other. A liquid crystal cell 104 disposed between the polarizing layers 102A, 102B includes a number of cells corresponding to pixels to achieve light transmittance in response to respective control voltages.

Here, the liquid crystal cell 104 is assumed to be a vertically aligned (VA) cell in which nematic liquid crystal having negative dielectric anisotropy is sealed. The linearly polarized light that is transmitted through the polarizing layer 102A on the incident side and enters the liquid crystal cell 104 is transmitted without being phase-shifted when transmitted through the non-driven cell, and is blocked by the crossed Nicols polarizing layer 102B on the exit side, When the light is transmitted through the driven cell, the light is phase-shifted and the amount of light corresponding to the amount of phase shift is transmitted through the crossed Nicol polarizing layer 102B on the output side and emitted. A desired light distribution pattern can be formed by appropriately controlling the driving voltage of the liquid crystal cell 104 for each cell.

In the liquid crystal display device 100, a retardation layer 108 with an ultraviolet reflective function is arranged between the liquid crystal cell 104 and the polarizing layer 102A on the incident side and between the liquid crystal cell 104 and the polarizing layer 102B on the exit side. . The retardation layer 108 compensates for the viewing angle dependence of light emitted from the liquid crystal cell 104 or incident on the liquid crystal cell 104 in a predetermined polarized state in a direction inclined from the normal line of the liquid crystal cell 104. can be done.

As an example, the retardation layer 108 has a liquid crystal molecular structure with cholesteric regularity and acts as a negative C plate. The retardation layer has at least part of the selective reflection wavelength band in the ultraviolet region of 100 to 400 nm, has an ultraviolet reflecting function, and has a maximum reflectance of 30% or more in the ultraviolet region.

FIG. 6B is a cross-sectional view schematically showing another example. The retardation layer 108 with an ultraviolet ray reflecting function has a liquid crystal molecular structure with cholesteric regularity, a first retardation layer 103 acting as a negative C plate, and a second retardation layer 103 laminated on the first retardation layer 103. and a second retardation layer 105 having a cholesteric regular liquid crystal molecular structure and acting as a negative C plate. The twist direction of the liquid crystal molecules of the first retardation layer 103 and the twist direction of the liquid crystal molecules of the second retardation layer 105 are opposite directions, and the first retardation layer 103 and the second retardation layer 105 At least a part of the selective reflection wavelength band is included in the ultraviolet region of 100 to 400 nm, and has an ultraviolet reflecting function, and the maximum reflectance in the ultraviolet region as a whole is 60% or more.

The first retardation layer 103 and the second retardation layer 105 have a planar aligned cholesteric regular liquid crystal molecular structure and act as a negative C plate. In the first retardation layer 103 and the second retardation layer 105, at least part of the selective reflection wavelength band of the selectively reflected light is included in the ultraviolet region of 100 to 400 nm, and the maximum reflectance in this ultraviolet region is 30% or more.

The twist direction of the liquid crystal molecules of the first retardation layer 103 and the twist direction of the liquid crystal molecules of the second retardation layer 105 are opposite directions. If the selective reflection wavelength band of the first retardation layer 103 and the second retardation layer 105 are substantially the same, the maximum reflectance in the selective reflection wavelength band is doubled as a whole, resulting in the maximum reflectance in the ultraviolet region. The reflectance is also doubled as a whole.

In the retardation layer 108 with an ultraviolet ray reflecting function, one of the right-handed and left-handed circularly polarized components of the light within the selective reflection wavelength band incident along the helical axis of the cholesteric regular liquid crystal molecular structure is the first It is reflected by the retardation layer 103 and the other is reflected by the second retardation layer 105 . Ultraviolet rays incident on the liquid crystal cell can be reduced more effectively than an ultraviolet reflective retardation layer having a single retardation layer that reflects only one circularly polarized light component.

Since the liquid crystal display device 100 shown in FIG. 6A includes the retardation layer 108 with an ultraviolet reflective function that reduces ultraviolet rays incident on the liquid crystal cell 104, the liquid crystal sealed inside the liquid crystal cell 104 is less likely to deteriorate. , a highly durable and highly reliable liquid crystal display device can be obtained.

FIG. 7 is a block diagram showing a schematic configuration of the headlamp system. The headlight system 200 includes left and right vehicle headlights 110, a light distribution control unit 112, a forward monitoring unit 114, and the like. The vehicle headlamp 110 has a light source, a light distribution pattern forming means, a projection lens, and a lamp housing them.

A forward monitoring unit 114 to which various sensors such as an in-vehicle camera 128, a radar 121, and a vehicle speed sensor 122 are connected performs image processing on image data acquired from the sensors, and detects vehicles in front (oncoming vehicles and preceding vehicles) and other lights on the road. Objects and lane markings are detected, and data necessary for light distribution control such as their attributes and positions are calculated. The calculated data is transmitted to the light distribution control unit 112 and various on-vehicle devices via an in-vehicle LAN or the like.

A light distribution control unit 112 to which a vehicle speed sensor 122, a steering angle sensor 124, a GPS navigation system 126, a high beam/low beam switch 118, etc. are connected, controls the attributes of road bright objects sent from the front monitoring unit 114 (oncoming vehicle, preceding vehicle, etc.). A light distribution pattern corresponding to the driving scene is determined based on the vehicle, reflector, road lighting), its position (front, side), vehicle speed, and the like. For example, when an oncoming vehicle is detected while driving with high beams, the adaptive-driving-beam (ADB) system reduces the lighting brightness of the area containing the oncoming vehicle so as not to give the oncoming vehicle dazzling glare. improve sexuality.

The light distribution control unit 112 determines the content of light distribution pattern control (turning on/off, etc.). The driver 120 converts the information from the light distribution control unit 112 into commands corresponding to the operations of the driving device and the light distribution control element, and controls them.

The headlight shown in FIG. 8 includes, for example, a light source 131 that emits white light, a light control unit 132 that is arranged on the optical path of the light emitted from the light source 131, and has a light control function that controls the luminance distribution and the like. It includes a lens (projection optical system) 133 that projects light emitted from the light source 132 , and a control device 134 that controls the light emission of the light source 131 and the light control of the light control unit 132 . The light source 131 includes, for example, a plurality of light emitting regions, and is configured using an LED element that includes a fluorescent layer and emits white light.

The light control unit 132 includes, for example, a liquid crystal element (liquid crystal cell) 132a, and polarizing plates 132b and 132c arranged in crossed Nicols in front of and behind the liquid crystal element 132a. The liquid crystal element 132 a is arranged near the focal point of the lens 133 . The liquid crystal element 132a has a plurality of regions, and the control device 134 can independently change the alignment state of the liquid crystal molecules in each region of the liquid crystal element 132a, and controls the transmittance, for example, the transmittance/light shielding of each region. do. The light emitted from the dimming unit 132 is projected forward of the vehicle by the lens 133 . Furthermore, an optical member (reflector (reflection plate), lens, etc.) for concentrating light on a predetermined portion of the liquid crystal element 132a can be provided.

An LED element is a light-emitting element that emits light over a wide angle. In the headlamp, even if the optical system is constructed using a reflector and a lens and devised so that the light beam is focused on the liquid crystal element 132a at a narrow angle, the liquid crystal element 132a has an angle of ±30° or more. It is common for light to enter at .

A liquid crystal element normally receives linearly polarized light as input light. Unpolarized light obtained from the light source is incident on the polarizing plate, and polarized emitted light is incident on the liquid crystal element. If the light component whose transmission is rejected by the polarizing plate is discarded, normally 50% or more of the light obtained from the light source is discarded. In order to increase the efficiency of light utilization, a polarizing beam splitter (PBS) splits incident light into first and second polarized components, and one polarized component (for example, the second polarized component) passes through a λ/2 plate. By rotating the polarization axis, first and second polarization components having the same polarization axis can be formed (for example, Patent Document 2).

FIG. 9 is a schematic cross-sectional view showing a vehicle lamp. The light source 131 is formed of a light emitting source such as an LED, and the emitted light is collimated by a collimating lens 141 and illuminates a wire grid polarizing plate 143 . The luminous flux reflected by the wire grid polarizing plate 143 is directed toward the liquid crystal element 132 , and the luminous flux transmitted through the wire grid polarizing plate 143 is reflected by the reflector 146 and directed toward the liquid crystal element 132 . Both of these luminous fluxes are modulated within the liquid crystal element 132 , the content of the modulation is actualized by the polarizing plate 148 , and projected from the projection lens 133 as a light distribution pattern.

A (1/2)λ retardation plate 144 is placed on the optical axis of the transmitted light or the reflected light (either one) of the wire grid polarizer 143, and the polarization axis is rotated by 90 degrees so that the polarization axis of the transmitted light Align the direction of the polarization axis of the reflected light.

In the figure, a (1/2)λ retardation plate 144 is affixed to the output surface of a wire grid polarizer 143 to rotate the polarization axis of transmitted light by 90°. The polarization axis of the light reflected by the reflector 146 is rotated by 90 degrees and has the same polarization direction as the polarized light reflected by the wire grid polarizing plate 143 . Therefore, both polarizations are modulated in the same way in the liquid crystal element 132, and synergistic emitted light can be obtained. Modulated light with an increased light amount is obtained from the liquid crystal element 132, and the output light from the projection lens 133 also increases.

Both the polarized light L1 reflected by the wire grid polarizing plate 143 and the polarized light L2 transmitted through the wire grid polarizing plate 143 are reflected in the same direction (rightward) once from the light source 131 to the liquid crystal element 132. is recieving. Therefore, there is an advantage that the optical characteristics can be made uniform. Reflection may be directed to the left. The (1/2)λ retardation plate 144 may be arranged between the output surface of the wire grid polarizing plate 143 and the input surface of the liquid crystal element 132 . For example, it may be placed between the reflector 146 and the input surface of the liquid crystal element 132 as indicated by the dashed line.

JP 2004-126576 A JP 2019-050134 A

Embodiments of the present invention aim to provide an optical device with high contrast ratio and high light utilization efficiency.

According to an embodiment of the invention,
and a pair of substrates including a plurality of electrode pairs, sandwiched between the pair of substrates, oriented substantially perpendicular to the substrate surface in a state in which no driving voltage is applied between the electrode pairs, and having a negative dielectric constant difference. a liquid crystal element including a first liquid crystal layer having tropism;
polarizing means arranged before and after the liquid crystal element;
a drive circuit that forms a drive voltage to be supplied to the plurality of electrode pairs;
First and second negative C-plate liquid crystal cells arranged to overlap with the liquid crystal element, wherein each of the first and second negative C-plate liquid crystal cells is sandwiched between a counter substrate and the counter substrate. and a second or third liquid crystal layer, wherein the alignment direction of liquid crystal molecules in each of the second and third liquid crystal layers is twisted in the in-plane direction of the substrate, and the refractive index in the in-plane direction is substantially constant. a refractive index in the thickness direction lower than the inward refractive index, each of the second and third liquid crystal layers has a selectively reflected light wavelength belonging to an infrared region with a wavelength of 0.78 μm or more; 2. the third liquid crystal layer comprises first and second negative C-plate liquid crystal cells having different in-plane twist directions;
including
the surfaces of the pair of substrates of the liquid crystal element and the opposed substrates of the first and second negative C-plate liquid crystal cells facing toward the liquid crystal layer are subjected to alignment treatment;
The optical device is provided in which the second and third liquid crystal layers are planarly oriented in a plane parallel to the substrate surface and twisted along the direction normal to the substrate surface.

1A and 1B are cross-sectional views schematically showing a projection optical system adopted as a starting model and an improved projection optical system based on experimental results. ,and FIG. 2A is a schematic cross-sectional view showing the configuration of the original sample, relating to the light distribution pattern forming portion of the projection optical system, FIG. 2B is a cross-sectional view schematically showing the configuration of the improved sample, and FIGS. 2D is a plan view schematically showing the configuration of the (λ/2) plate, FIG. 2E is a cross-sectional view schematically showing the pattern of the polarizer pair, and FIG. 2F is the liquid crystal element. 2G is a diagram schematically showing the function of optical compensation; FIG. 2H is a cross-sectional view schematically showing the structure of a viewing angle compensator; FIG. 3A is a graph showing the change in transmittance with respect to polar angle for the original sample shown in FIG. 2A, FIG. 3B is a graph showing change in transmittance against polar angle for the improved sample shown in FIG. 2B, and FIG. 3C is the cell thickness of the improved sample. 4 is a graph showing changes in contrast ratio with respect to . FIG. 4A is a schematic cross-sectional view showing the structure of a sample in which the orientation processing direction of the liquid crystal element and the orientation processing direction of the viewing angle compensating plate are changed, and FIG. 4B is a graph showing the measurement results of the sample. FIG. 5A is a schematic cross-sectional view showing the configuration of a sample in which two viewing angle compensating plates are changed in alignment processing direction, and FIG. 5B is a graph showing the measurement results of the sample. FIG. 6A is a cross-sectional view schematically showing the configuration of a liquid crystal display device including a retardation plate that constitutes a viewing angle compensator, and FIG. 6B shows two retardation layers that act as negative C plates and have different twist directions. FIG. 4 is a cross-sectional view schematically showing a configuration in the case of constituting a composite structure; FIG. 7 is a block diagram showing a schematic configuration of the headlamp system. FIG. 8 is a schematic perspective view showing one example of a headlamp system. FIG. 9 is a cross-sectional view schematically showing the configuration of a vehicle lamp that recycles divided polarized light.

10 light source, 12 concave reflector,
14 polarizing beam splitter (PBS), 16 reflector,
18 (λ/2) plate, 21 incident-side polarizing plate, 22 exit-side polarizing plate,
23 liquid crystal element, 28 optical compensator, 30 projection optical system

When the projection optical system is configured as shown in FIGS. 6A and 6B, the light emitted from the light source 106 is polarized by passing through the polarizing plate 102A, thereby cutting 50% or more of the light amount. In order to increase the efficiency of light utilization, it is desirable to adopt an optical system that can reuse the cut light by changing the polarization direction thereof, as shown in FIG.

FIG. 1A is a cross-sectional view schematically showing the projection optical system of the starting model. The light source 10 is composed of a light emitting diode (LED). A white LED using phosphor is used. A single chip may be used, but in order to increase the amount of light, for example, a configuration in which LED chips are arranged in a plurality of rows and a plurality of columns may be used. In the sample used in the experiment, two rows of four LEDs arranged in the horizontal direction were arranged in the vertical direction.

Since the luminous flux emitted from the LED light source 10 is distributed over a fairly wide angle, the luminous flux is focused by the concave reflector 12 and made incident on the polarizing beam splitter (PBS) 14 . Although a specular concave reflector is shown, a lens can also be used. The polarizing beam splitter 14 can be composed of a wire grid polarizer using a metal wire grid or an optical multilayer film using Brewster's polarization angle. direction.

2C1 and 2C2 are cross-sectional views schematically showing the function of the wire grid polarizer 14. FIG. A plurality of striped metal wire grids WG are formed on a glass substrate G. As shown in FIG. The width of the wire grid WG is narrow enough to confine the electron cloud, and the length of the wire grid WG is long enough to allow movement of the electron cloud. As shown in FIG. 2C1, polarized light with an electric vector E1 perpendicular to the wire grid WG cannot move electrons and is transmitted through the wire grid WG without being absorbed. As shown in FIG. 2C2, polarized light with an electric vector E2 component parallel to the wire grid WG excites movement of the electron cloud and is absorbed or reflected.

In FIG. 1A, the reflected polarized light L1 from the polarizing beam splitter 14 is condensed and propagated toward the liquid crystal element 23 . The polarized light L2 transmitted through the polarizing beam splitter 14 has a different (orthogonal) polarization axis than the reflected polarized light L1 and travels in a different direction. The transmitted polarized light L2 is reflected by the convex reflector 16 which also adjusts the focal length so that the transmitted polarized light L2 is condensed and propagated onto the liquid crystal element 23 . In order to be able to simultaneously control the polarized light L1 and L2 having orthogonal polarization axes, one of the polarization axes is rotated to align the polarization axes. In the illustrated configuration, a (λ/2) plate 18 is placed in the optical path of the polarized light L2 to align the polarization axes of the polarized lights L1 and L2.

As shown in FIG. 2D, the (λ/2) plate 18 has a different refractive index nx in the in-plane x direction and a different refractive index ny in the in-plane y direction. A phase difference of (λ/2) (±kλ, k is an integer) is produced between polarized light.

Polarized lights L1 and L2 with aligned polarization axes are condensed on the liquid crystal element 23 via the incident side polarizing plate 21 . Although the polarized light beams L1 and L2 are already polarized light beams, it is ensured that the liquid crystal element 23 is irradiated with polarized light beams having aligned polarization axes by passing through the incident side polarizing plate 21 in common.

As shown in FIG. 2E, the entrance-side polarizer 21 and the exit-side polarizer 22 form a crossed Nicols polarizer. In FIG. 1A, each pixel of the liquid crystal element 23 sandwiched between the crossed Nicol polarizers 21 and 22 is controlled by a drive voltage supplied from a drive circuit 29 .

As shown in FIG. 2F, the liquid crystal element 23 has a liquid crystal layer LC sandwiched between a segment substrate G2 having a segment electrode S that can be controlled for each pixel and a common substrate G1 having a common electrode C common to a plurality of pixels. have a configuration. A vertical alignment film AV is formed on the surface of the substrate on which the electrodes are formed. A liquid crystal layer is filled between the segment electrode S and the common electrode C facing each other. When no drive voltage is applied between the segment electrode S and the common electrode C facing each other, the liquid crystal molecules are oriented substantially perpendicular to the substrate surface. When a drive voltage is applied between the opposing segment electrode S and common electrode C, the liquid crystal molecules having negative dielectric anisotropy Δε are tilted from the substrate normal direction according to the applied voltage.

The light transmitted through the output-side polarizing plate 22 is projected by the projection optical system 30 . In the case of vehicle headlamps, a desired orientation pattern is formed in the driver's field of vision in front of the vehicle. When the light distribution control unit 112 receiving information from the forward monitoring unit 114 performs ADB control as shown in FIG. 7, the liquid crystal element 23 controlled by the drive circuit 29 in FIG. The oncoming vehicle included in the light distribution pattern is protected from glare by selective light shielding, enabling safe anti-glare driving.

FIG. 2A is a cross-sectional view schematically showing the configuration of an experimental sample, which was created by extracting a part of the optical device shown in FIG. 1A. The drive circuit 29 can supply a voltage to turn on each pixel and control the orientation of the liquid crystal molecules in each pixel region. The states of the pixels controlled by the drive voltage are made visible by the crossed Nicol polarizers 21 and 22 sandwiching the liquid crystal element 23 .

In the liquid crystal element 23, a liquid crystal material to which an appropriate amount of chiral material was added was filled in the liquid crystal space between the opposing substrates by vacuum injection. For reference, a liquid crystal element was also produced without adding a chiral material.

FIG. 3A is a graph showing the viewing angle dependence of the transmittance measured in the prototype optical device having the configuration shown in FIG. 2A. The horizontal axis indicates the polar angle from the normal to the substrate in units (degrees, degrees), and the vertical axis indicates the transmittance in units (%). The angle of deviation from the polarization axis of the polarizing plate is defined as the azimuth angle, and the transmittance when the polar angle is changed in the directions of azimuth angles of 30 degrees, 45 degrees, 60 degrees, 90 degrees, 120 degrees, 135 degrees, and 150 degrees. It was measured. In the vicinity of the polar angle of 0 degree, the transmittance is very low, and it is considered that the light shielding performance is almost similar to that of the crossed Nicols polarizing plate. However, it is clear that as the polar angle increases, the leakage light gradually increases. For example, when the azimuth angle is 45°, the transmittance exceeds 1% at about 27° as the polar angle is increased. A high contrast ratio cannot be obtained. Note that the plot of x on the horizontal axis is the characteristic of only crossed nicols.

It is considered that optical compensation is necessary to improve the characteristics. A negative C-plate is suitable for compensating vertically aligned liquid crystal cells. Some are commercially available, but the properties available are limited and the heat resistance is poor.

FIG. 2G is a diagram that schematically illustrates the principle of optical compensation. The liquid crystal element 23, in which the major axis having the maximum refractive index Nz1 is oriented in the direction perpendicular to the substrate and the uniform refractive indices Nx1 and Ny1 orthogonal to each other are oriented in the in-plane direction of the substrate, has an optical anisotropy of Nz1>(Nx1, Ny1). have. In order to compensate for this optical anisotropy, a viewing angle compensator 24 having an optical anisotropy of Nz2<(Nx2, Ny2) where the refractive index Nz2 in the direction perpendicular to the substrate is smaller than the uniform refractive indices Nx2, Ny2 in the in-plane direction of the substrate. are combined, and as a whole, (Nz1, Nz2)=(Nx1, Nx2)=(Ny1, Ny2) is assumed to hold.

The present inventor decided to create a pseudo-negative C-plate using liquid crystal. A single liquid crystal molecule has a high refractive index in the long axis direction and a low refractive index in the in-plane direction perpendicular to the long axis, and is often isotropic. A chiral agent is mixed with nematic liquid crystal molecules, the substrate surface is oriented in one direction, aligned in one direction at the position in contact with the substrate surface, rotated in the azimuth direction as it goes in the thickness direction, and rotated several times. Make the refractive index in the in-plane direction substantially constant. The thickness direction pitch corresponding to one rotation determines the wavelength of selective reflection. A (pseudo-)negative C-plate is produced by rotating such planar-aligned nematic liquid crystal molecules in the azimuthal direction with a short pitch.

A short-pitch negative C-plate exhibits a selective reflection that corresponds to the pitch. As illumination for vehicle headlamps, selective reflection of light in the visible region (wavelength 380 to 780 nm) hinders the driver's visibility, so selective reflection is set outside the visible region. Outside the visible range would be the ultraviolet and infrared options.

It has been found that if the pitch is in the ultraviolet region and selective reflection in the visible light region is suppressed, the amount of chiral agent added exceeds 30%, and the temperature range in which the liquid crystal phase is exhibited becomes extremely narrow. Manufacturing costs are also higher.

Therefore, the present inventors have considered avoiding the selective reflection of the visible light region by adjusting the pitch to correspond to the infrared region having a wavelength of 780 nm or longer. The amount of chiral agent added can be reduced, the temperature range in which the liquid crystal phase can be maintained can be widened, and use outdoors at low temperatures is also possible.

FIG. 2H is a cross-sectional view schematically showing the configuration of the viewing angle compensator 26 considered in this way. Two glass substrates G are arranged in parallel, a horizontal alignment film AH is formed on the opposing surfaces, and a liquid crystal layer LC is filled between the opposing surfaces.

The alignment treatment (rubbing treatment) applied to the horizontal alignment films AH of the two glass substrates G is such that the pretilt angles of the liquid crystal molecules are parallel (anti-parallel) when the two glass substrates G are overlapped. set to When viewed from the normal direction of the viewing angle compensating plate 26, the rubbing direction of one glass substrate is opposite to that of the other glass substrate. The anti-parallel alignment state is preferable because the tilt angles of the liquid crystal molecules in the viewing angle compensator 26 are substantially equal to each other and a relatively stable alignment state can be obtained.

1A and 2A, an experimental optical device is assumed in which the viewing angle compensator 26 shown in FIG. 2H is combined with the liquid crystal element 23 as indicated by the dashed line. A test configuration shown in FIG. 2A was constructed and its properties were measured. In the viewing angle compensator 26, a liquid crystal material and a chiral material are blended so that the selective reflection wavelength is about 1 μm.

However, in the liquid crystal cell with a pitch longer than that of visible light, a phenomenon was observed in which the polarization axis of transmitted light was slightly rotated. The polarization axis of outgoing polarized light is rotated about 10 degrees with respect to the polarization axis of incident polarized light. Even if the transmittance of the crossed Nicols polarizing plate is set to an extremely small value, light leakage will occur.

Therefore, a combination of a composite viewing angle compensating cell in which a left-twisted liquid crystal cell and a right-twisted liquid crystal cell are laminated is combined with a liquid crystal element, and it is investigated to cancel out the rotation of the polarization axis.

As shown in FIG. 2B, a composite viewing angle compensation cell 26 is formed by stacking a left-twisted liquid crystal cell 27 and a right-twisted liquid crystal cell 28, and stacked on the liquid crystal element 23 to fabricate an improved sample. bottom. Other than the viewing angle compensation cell, the configuration of the sample in FIG. 2B is equivalent to the configuration of the sample in FIG. 2A.

FIG. 1B is a schematic cross-sectional view showing an optical device in which the single-layer viewing angle compensation cell 26 in the configuration of FIG. 1A is replaced with a two-layer stacked viewing angle compensation cell shown in FIG. 2B.

A pair of negative C-plate liquid crystal cells were prepared by setting the cell thickness of each cell of the composite viewing angle compensation cell 26 to 2.5 μm, 3.0 μm, 3.25 μm, 3.5 μm and 3.7 μm.

FIG. 3B is a graph of transmittance versus polar angle measured for a sample using a pair of negative C-plate liquid crystal cells with a cell thickness of 3.25 μm. The retardation Rth is approximately 520 nm. When a composite viewing angle compensation cell 26 in which a left-twisted liquid crystal cell 27 and a right-twisted liquid crystal cell 28 are laminated is used for optical compensation of an optical device, light leakage in oblique directions is clearly suppressed. there is The transmittance of the sample in FIG. 2B is suppressed to 0.2% or less in the polar angle range of ±30 degrees of the measurement data shown in FIG. 3B. The integral of the measured transmittance for each azimuth angle for the data shown in FIG. 3B was 4.2%. For comparison, the integrated value was 4.5% when the same measurement was performed on a simple crossed Nicols polarizer. In this sample, it is considered that the visual angle compensation is achieved almost to the limit.

FIG. 3C is a graph showing the liquid crystal cell thickness dependence of the contrast ratio of the viewing angle compensation cell, which is assumed from the measurement result of the viewing angle dependence of the transmittance measured in the state where the driving voltage of the liquid crystal element is off. The horizontal axis indicates the liquid crystal cell thickness in units (μm), and the vertical axis indicates the estimated contrast ratio. In the range of sample cell thicknesses of 2.5 μm, 3.0 μm, 3.25 μm, 3.5 μm, and 3.7 μm, a contrast ratio of approximately 170 or more was obtained, and the contrast ratio exceeded 200 at a cell thickness of 3.25 μm. A maximum contrast ratio is obtained. It can be judged that a significantly higher contrast ratio is obtained when compared with the comparative technique without optical compensation.

Next, the relationship between the alignment treatment direction of the vertically aligned liquid crystal element 23 and the alignment treatment direction of the viewing angle compensation cell was investigated. Since the viewing angle compensation cell includes two of a right-twisted cell and a left-twisted cell, it was assumed that the two viewing angle compensation cells had the same direction and the opposite direction.

FIG. 4A is a cross-sectional view schematically showing a state in which two viewing angle compensating cells 27 and 28 are aligned in the same direction and the angle between them and the direction of alignment of the liquid crystal element is changed. FIG. 4B is a graph showing the change in off-state transmittance (average value) with change in the relative angle between the alignment direction of the viewing angle compensation cell and the alignment direction of the liquid crystal element, based on the measurement results. The relative angles were varied at 45 degree intervals. The horizontal axis indicates the relative angle in units (degrees), and the vertical axis indicates the transmittance when the drive voltage is turned off in units (%). Among the total eight samples, the samples with relative angles of 0 degrees, 90 degrees, 180 degrees, and 270 degrees at intervals of 90 degrees have relatively low transmittance, and the sample with a relative angle of 90 degrees has particularly low transmittance. The relative angles would preferably be in the range of 90 degrees ±20 degrees. As a comparative example, a sample without the optical compensation cell was also produced and measured. It is clear that the properties of all samples are superior to the comparative example without the optical compensation cell.

Next, a sample in which two viewing angle compensating cells are aligned in the same direction and a sample in which the alignment processing direction is reversed are prepared and measured. The relative angles between the orientation treatment direction of the liquid crystal element and the orientation treatment direction of the viewing angle compensation cell were set to 45 degrees, 135 degrees, 225 degrees and 315 degrees.

As shown in FIG. 5A, the orientation treatment direction of the viewing angle compensation cells 27 and 28 is changed with respect to the orientation treatment direction (horizontal direction) of the liquid crystal element 23, and the orientation treatment of the two viewing angle compensation cells 27 and 28 is performed. The case of the same direction and the opposite case were created.

FIG. 5B is a graph showing measurement results. The horizontal axis indicates the relative angle of the orientation treatment direction of the viewing angle compensation cell with respect to the orientation treatment direction of the liquid crystal element in units (degrees), and the vertical axis indicates the transmittance when the driving voltage is turned off in units (%). The transmittance is low when the orientation treatment directions of the two viewing angle compensation cells are opposite and the relative angles of the orientation treatment direction of the viewing angle compensation cell to the orientation treatment direction of the liquid crystal cell are 45 degrees, 135 degrees, and 225 degrees. It is low when the relative angle is 135 degrees. The two viewing angle compensation cells are aligned in opposite directions, and the relative angle of the alignment treatment direction of the viewing angle compensation cell to the alignment treatment direction of the liquid crystal cell is in the range of 135 degrees ± 20 degrees. high).

Applying the conditions found to be favorable in the measurement sample to the configuration shown in FIG. 1B will result in a favorable optical device.

Although the present invention has been described along with the embodiments, the present invention is not limited to these. The above materials, numerical values, etc. are merely examples and are not restrictive. In addition, it will be obvious to those skilled in the art that various improvements, substitutions, combinations, and the like are possible.

Claims (5)

and a pair of substrates including a plurality of electrode pairs, sandwiched between the pair of substrates, oriented substantially perpendicular to the substrate surface in a state in which no driving voltage is applied between the electrode pairs, and having a negative dielectric constant difference. a liquid crystal element including a first liquid crystal layer having tropism;
polarizing means arranged before and after the liquid crystal element;
a drive circuit that forms a drive voltage to be supplied to the plurality of electrode pairs;
First and second negative C-plate liquid crystal cells arranged to overlap with the liquid crystal element, wherein each of the first and second negative C-plate liquid crystal cells is sandwiched between a counter substrate and the counter substrate. and a second or third liquid crystal layer, wherein the alignment direction of the liquid crystal molecules in each of the second and third liquid crystal layers is twisted in the in-plane direction of the substrate, and the refractive index in the in-plane direction is substantially constant. a refractive index in the thickness direction lower than the inward refractive index, each of the second and third liquid crystal layers has a selectively reflected light wavelength belonging to an infrared region with a wavelength of 0.78 μm or more; 2. first and second negative C-plate liquid crystal cells, wherein the third liquid crystal layer has different in-plane twist directions;
including
the surfaces of the pair of substrates of the liquid crystal element and the opposed substrates of the first and second negative C-plate liquid crystal cells facing toward the liquid crystal layer are subjected to alignment treatment;
The optical device , wherein the second and third liquid crystal layers are planar-aligned in a plane parallel to the substrate surface and twisted along a direction normal to the substrate surface. The orientation treatment of the surfaces of the substrates constituting the first and second negative C-plate liquid crystal cells facing the liquid crystal layer is performed so that the pretilt angles of the liquid crystal molecules of the second and third liquid crystal layers are antiparallel. 2. The optical device according to claim 1 , wherein . 3. The liquid crystal element according to claim 1 , wherein one substrate of said liquid crystal element is a common substrate having a common electrode common to a plurality of pixels , and the other substrate is a segment substrate having segment electrodes that can be controlled for each pixel. optical device. A light source, a projection means, and the optical device according to any one of claims 1 to 3 arranged on an optical path between the light source and the projection means,
The light from the light source is arranged so as to enter from one side of the polarizing means arranged in front of the liquid crystal element,
The vehicle lamp is arranged so that the projecting means projects the light emitted from the other side of the polarizing means arranged behind the liquid crystal element in a predetermined direction. 5. The vehicular lamp according to claim 4 , further comprising: a monitoring unit for monitoring the situation in the predetermined direction; and a control unit for controlling the drive circuit based on a signal from the monitoring unit, and capable of realizing an ADB function. .

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