TWI769735B - Spatial light modulator for suppressing fringe field effect - Google Patents

Abstract

The present invention discloses a spatial light modulator for suppressing fringe field effect, including: a transparent electrode layer; a reflective electrode layer, which includes a pixel electrode in which a pixel area is surrounded by a boundary of the pixel electrode; a liquid crystal layer, which is located between the transparent electrode layer and the reflective electrode layer to establish a pixel formed by the liquid crystal layer in the pixel area covering the pixel electrode; and an alignment film having a first pattern and a second pattern cover the pixel area. Due to the first pattern and the second pattern in the pixel area, the liquid crystal in the liquid crystal layer of the pixel generates a first azimuth angle and a second azimuth angle, respectively. The first azimuth angle is different from the second azimuth angle.

Description

Spatial Light Modulator for Suppressing Fringing Field Effects

The present invention relates to a spatial light modulator (hereinafter referred to as SLM), in particular to a spatial light modulator that uses a pattern of an alignment film to suppress fringe field effect (hereinafter referred to as FFE).

FFE is the leakage of the electric field generated by the boundary of the pixel electrode to an adjacent pixel, which affects the alignment of the liquid crystal (hereinafter referred to as LC) of the adjacent pixel, thereby causing an unexpected phase shift to the light incident on the adjacent pixel. The phase shift is different at different locations of adjacent pixels and is most pronounced around the boundaries of adjacent pixels. Since FFE will greatly impair the SLM performance, for example, the diffraction efficiency and phase distribution accuracy will be significantly reduced.

One of the objectives of the present invention is that the spatial light modulator utilizes the pattern on the alignment film to make the LC layer exhibit uneven distribution on the pixel electrode to suppress FFE.

One of the objectives of the present invention is that the spatial light modulator uses the pattern on the alignment film to make the LC of each pixel in the LC layer have at least two different alignments. angle.

The invention discloses a spatial light modulator for suppressing fringe field effect, comprising: a transparent electrode layer; a reflective electrode layer, which includes a pixel electrode, a pixel area in the pixel electrode is surrounded by the boundary of the pixel electrode; a liquid crystal layer, which is located between the transparent electrode layer and the reflective electrode layer to establish a pixel, the pixel is formed by the liquid crystal layer in the pixel area covering the pixel electrode; and an alignment film having a first pattern and A second pattern covers the pixel area. In the pixel area, a first alignment angle and a second alignment angle are generated by the liquid crystal in the liquid crystal layer of the pixel due to the first pattern and the second pattern, respectively. arrangement, and the first alignment angle is different from the second alignment angle.

In an embodiment of the spatial light modulator for suppressing fringing field effect of the present invention, the first alignment angle is greater than the second alignment angle.

In an embodiment of the spatial light modulator for suppressing fringe field effect of the present invention, the liquid crystal layer is regarded as parallel to the XY plane, then each liquid crystal in the liquid crystal layer in the first region is at the angle between the XY plane and the X axis is the first alignment angle, and the first alignment angle is greater than 0 degrees and less than or equal to 5 degrees.

1~9: Pixel electrode

100: SLM

120: transparent electrode layer

130: Reflective electrode layer

110: LC layer

140: Substrate

142: rigid board

145: glass plate

182: Pixel area

181: Border

111, 112: pixels

101: Incident light

102: Reflected or diffracted light

15: Alignment film

15a, 15b: Area

205, 305: pixel length

210: One-dimensional canonical distribution

211: pixel boundaries

212: Affected Parts

240: Ideal Phase Delay Profile

310, 315, 330, 335, 550: Curves

611~622: Optimized pixels

631: External Area

632: Inner area

635: pixel boundaries

636: Imaginary Line

637: Gap

[FIG. 1] is a schematic diagram showing an embodiment of the present invention.

[Figure 2] is a typical distribution of phase delay affected by FFE, and a There is an ideal phase delay profile affected by FFE.

[FIG. 3] A schematic cross-sectional view of the fringing field effect through alignment angle correction.

[FIG. 4] shows a schematic diagram of a liquid crystal in a three-dimensional coordinate system.

[Fig. 5] is a schematic diagram of a non-uniformly distributed FFE-cancellation feature.

[Fig. 6] shows that the FFE is effectively canceled by the uneven distribution of the alignment angle

Please refer to FIG. 1. FIG. 1 shows a schematic diagram of a spatial light modulator 100 (Spatial light modulator, hereinafter referred to as SLM) of the present invention. The SLM 100 includes a transparent electrode layer 120, a reflective electrode layer 130, and the transparent electrode layer 120 and the reflective electrode layer. The liquid crystal (hereinafter referred to as LC) layer 110 and the alignment film 15 between the 130 .

Please note that the reflective electrode layer 130 includes a plurality of pixel electrodes (including the pixel electrodes 1 to 9), which are arranged in an array to form a plurality of pixels (Pixels), and each pixel includes a pixel electrode and a part of the LC layer 110 thereon. . The pixel regions 182 in the pixel electrodes 1 to 9 are surrounded by the pixel electrode boundary 181 .

The LC layer 110 is located between the transparent electrode layer 120 and the reflective electrode layer 130 to create a pixel formed by the LC layer 110 in the pixel area 182 covering the pixel electrode.

A first pattern and a second pattern are formed on the alignment film 15 and cover the pixel area. The pixel area 182 generates a first pattern due to the first pattern and the second pattern respectively in the liquid crystal of the LC layer 110 of the pixel area 182 The alignment angle (azimuth angle) and the arrangement of a second alignment angle, and the first alignment angle is different from second alignment angle.

In one embodiment, the reflective electrode layer 130 is formed on the substrate 140 , so that the SLM 100 is a liquid crystal on silicon (also called liquid crystal on silicon or single crystal silicon reflective liquid crystal, English: Liquid Crystal On Silicon, LCoS) SLM. A rigid plate 142 such as a ceramic substrate or a metal plate may be used to mechanically support the substrate 140 and components thereon. Glass plate 145 is mounted on transparent electrode layer 120 to provide mechanical protection and allow light to pass through to LC layer 110 (if SLM 100 is used to modulate visible light).

Indium tin oxide (ITO) can be used to form the transparent electrode layer 120. In most practical implementations, the LC layer 110 is uniformly planar (wherein the LC molecules are aligned along a direction parallel to the transparent electrode layer 120), vertical ( The LC molecules are arranged in a direction perpendicular to the transparent electrode layer 120), or twisted (the LC molecules are arranged in a helical structure).

One aspect of the present invention is to provide an SLM for modulating incident light, wherein the SLM displays an uneven distribution of the alignment angle on the pixel electrode by configuring the LC layer of the SLM, that is, the alignment film 15 has two different pattern regions, and The difference in alignment angle between the corresponding regions is generated to suppress FFE, so it is not necessary to change the shape of the pixel electrode. For example, if rectangular pixel electrodes are used in the initial design, the same rectangular pixel electrodes can still be used after applying the present invention to the initial design.

FIG. 1 depicts an exemplary SLM 100 structure of the present invention. SLM 100 includes a transparent electrode layer 120, a reflective electrode layer 130, and a The LC layer 110 is located between the transparent electrode layer 120 and the reflective electrode layer 130 . The reflective electrode layer 130 includes a plurality of pixel electrodes (including pixel electrodes 1 to 9) arranged in an array to form a plurality of pixels, each pixel includes a pixel electrode and a part of the LC layer 110 thereon. In one embodiment, reflective electrode layer 130 is formed on substrate 140 such that SLM 100 is an LCOS SLM. A rigid plate 142 such as a ceramic substrate or metal plate may be used to mechanically support the substrate 140 and components thereon. Preferably, a glass plate 145 is mounted on the transparent electrode layer 120 to provide mechanical protection and allow light to pass through to the LC layer 110 (if the SLM 100 is used to modulate visible light). Those of ordinary skill in the art know that indium tin oxide (ITO) may be used to form the transparent electrode layer 120 . In most practical implementations, the LC layer 110 is uniformly planar (in which the LC molecules are aligned in a direction parallel to the transparent electrode layer 120 ), vertical (in which the LC molecules are aligned in a direction perpendicular to the transparent electrode layer 120 ) , or twisted (LC molecules arranged in a helical structure).

For the sake of brevity, only pixel electrodes 1 to 9 are used as representative pixel electrodes for description below. The pixel electrode 1 has a pixel area 182 , which is an area surrounded by the border 181 of the pixel electrode 1 . The pixel 111 is formed on the pixel electrode 1 and is the LC layer 110 covering the pixel region 182 . Since the pixel 111 is located on the pixel area 182 , the pixel boundary of the pixel 111 is also the boundary 181 . A large pixel 112 including the pixel 111 and an adjacent pixel is also set. When the incident light 101 enters the pixels 111 and 112, the incident light 101 undergoes an optical phase delay, and the amount of delay depends on the pixel electrodes 1, 5 (or 3, 7 and 9) and the voltage difference between the transparent electrode layer 120. When the incident light 101 reaches the pixel electrodes 1, 5 (or 3, 7 and 9), the incident light 101 is reflected or diffracted to form a reflected or diffracted light 102. While passing through the LC layer 110 again, the reflected or diffracted light ray 102 also undergoes another phase delay, the amount of delay being substantially close to that just described. There is therefore a total of twice the phase delay just described.

The pixel 111 has adjacent pixels adjacent to the pixel 111, and these adjacent pixels are formed by a part of the LC layer 110 on the pixel electrodes 2-9. When the voltage applied to any one of the pixel electrodes 2 to 9 is different from the voltage applied to the pixel electrode 1 , FFE will be generated, which negatively affects the pixel 111 . As a result, the phase delay generated by the pixels 111 may become non-uniform on the pixel area 182, so that the phase delay distribution of the pixels 111 is two-dimensionally non-uniform.

Please refer to FIG. 2, which depicts a typical one-dimensional distribution 210 of phase delay along a pixel length 205 under the influence of FFE, and an ideal phase delay distribution 240 that is not affected by FFE. When the typical profile 210 is compared to the ideal phase delay profile 240, it can be seen that the FFE causes large fluctuations in phase delay over some affected portion 212 of the pixel length 205 near the pixel boundary 211.

The inventors have discovered that by fine-tuning the "FFE-opposing feature" on the affected portion 212, the phase delay fluctuations can be significantly reduced to counteract the FFE. The FFE-cancellation feature is a tunable property of the LC layer. As discovered by the inventors, an available set of "FFE-cancellation features" contains an alignment angle. The alignment angle is related to the alignment density and alignment strength of LC, respectively. The arrangement density and arrangement strength of the LC determine the corresponding LC offset of the FFE ability.

In accordance with the present invention, at least one pixel in the LC layer 110 is implemented as an optimized pixel, which is a pixel specifically set to cancel the FFE in accordance with micro-modulation of a selected FFE-cancellation feature. Each pixel in the LC layer 110 is preferably implemented as an optimized pixel. In the following description, the pixel 111 on the pixel electrode 1 is regarded as an exemplary pixel implemented as an optimized pixel. Non-uniformly distributed FFE-cancelling features (ie, non-uniform distribution) on pixel region 182 are selected or determined to counteract FFE caused by adjacent pixels on pixel electrodes 2-9.

Since the FFE mainly affects the pixel boundary 181 of the pixel 111, it can be further simplified. The affected portion 212 of the pixel 111 is an outer area of the pixel 111, wherein the outer area refers to the distance between the pixel boundary 181 and a certain distance inward from the boundary 181. Area. The certain distance can be estimated by calculation or computer analogy.

Please refer to FIG. 3 . FIG. 3 shows an area diagram of a first pattern and a second pattern on the alignment film 15 ; each square solid frame represents a pixel area, and the pixel area of each pixel has a first area 15 a and the second area 15b (inside the square dotted line frame); the first area 15a is the position of the first pattern, the top view of the first area in this embodiment is a square ring, and the first area 15a surrounds the second area 15b, the first area The two regions 15b are square-shaped regions that fill the interior of the square-shaped ring, and the width of the square-shaped ring is greater than or equal to the range of the fringe field effect of the pixel.

Please refer to FIGS. 1 , 3 and 4 at the same time. FIG. 4 shows a schematic diagram of a liquid crystal in a three-dimensional coordinate system, wherein the liquid crystal layer is regarded as parallel to the XY plane, and each liquid crystal in the liquid crystal layer in the first region 15a is in the XY plane and the XY plane. The included angle of the X axis is the first alignment angle α, and the first alignment angle α is greater than 0 degrees and less than or equal to 5 degrees.

In one embodiment, as described above, the second alignment angle β (not shown) in the second region 15b is 0 degrees, and the first alignment angle α, the second alignment angle β and the Z axis are both 90 degrees. , that is, the first area 15a and the second area 15b are located on the XY plane.

Because the pixel area of each pixel has two different patterns to form two different alignment angles α, β, in other words, the liquid crystal in each pixel area forms a square annular uneven distribution to offset the FFE, as shown in Figure 5. The embodiment describes the unevenly distributed FFE-cancellation feature of 12 optimized pixels 611-622. The following description takes the optimized pixel 611 as a representative optimized pixel. Pixel 611 has a pixel boundary 635. The outer area 631 of the pixel 611 is an area between the pixel boundary 635 and the imaginary line 636 . An imaginary line 636 is located on the optimized pixel 611 and a distance 633 from the pixel boundary 635. Distance 633 is determined such that outer region 631 is an affected portion (ie, affected portion 212 described above). The inner area 632 is an area enclosed by an imaginary line 636 . Pixels 611 are configured such that outer regions 631 have a first value of FFE-cancellation characteristics and inner regions 632 have a second value of FFE-cancellation characteristics. Notice Thus, the pixels 611-622 are formed on a continuous LC layer (eg, the LC layer 110). Between two adjacent pixels, there is an inter-pixel gap, such as gap 637 between two pixels 611, 612; in fact, the LC layer over gap 637 can be configured to have a first value of FFE-offset feature. Thus, discontinuities of 635 FFE-offset features along pixel boundaries can be avoided.

Next, please refer to FIG. 6 , which shows that the FFE is effectively canceled by the uneven distribution of the alignment angle. In Figure 6, phase delay curves 310, 315, 320 and equipotential curves 330, 335, 340 over pixel length 305 plot a case using a non-uniform alignment angle distribution and a reference case using a uniform distribution. Using computer analogy to obtain curves 310, 315, 320, 330, 335, 340 under the following conditions: pixel length 6.2 μm; inter-pixel gap 0.2 μm; worst-case voltage difference 5V between two adjacent pixels; The outer region is between the pixel boundary and 1 μm from it. Obviously, over the pixel length 305, the flat area of the phase delay curve 320 of the uneven alignment angle distribution is longer than the corresponding flat areas of the phase delay curves 310, 315 of the uniform distribution scenario. Similar conclusions can be obtained when examining the equipotential curves 330, 335, 340 and the phase delay curves. The effectiveness of using a non-uniform alignment angle distribution is shown.

In one embodiment, a nanostructure alignment layer (not shown) is added on the alignment film 15 to change the alignment angle, so that the liquid crystal has an uneven distribution of the alignment angle. The nanostructure alignment layer is patterned to form nanostructures on its alignment film 15, and the size and shape of the nanostructures are used to realize the first pattern and the second pattern, so that the liquid crystal in which the pixel area is located has Non-uniform alignment angle distribution; i.e., The nanostructure alignment layer is directly patterned by nanoimprinting on the mother board, resulting in a micro-groove structure with high and low undulations on the surface, thereby controlling the arrangement of liquid crystal molecules.

Fig. 3 is a schematic cross-sectional view showing fringe field effect through alignment angle correction, wherein the difference in alignment angle of liquid crystal molecules is shown enlarged; based on the photo-alignment process, it is difficult to precisely control the pretilt angle and the anchoring energy method; Alignment process, the alignment angle method is easier to control and more precise in the production process. In addition, the fringing field effect noise (crosstalk) can be reduced and completely suppressed by the alignment angle method.

In one embodiment, the alignment film includes a liquid crystal material and a polymer material formed by polymerization of monomers for stabilizing the LC material; wherein the polymer material is composed of a monomer having a degree of polymerization unevenly distributed on the pixel area. forming; the alignment film uses a light beam with no gradient intensity to irradiate the monomer to form a first pattern and a second pattern, so that the liquid crystal layers in the first region 15a and the second region 15b have two different alignment angles. That is, photo-alignment is to irradiate the polymer with photosensitive groups in a specific direction with polarized ultraviolet light (UV), so that the molecular chain is destroyed and rearranged, resulting in micro-grooves on the surface of the alignment film or irregularities in the polymer main chain. The isotropic distribution in turn controls the alignment of the liquid crystal molecules.

Please note that if the alignment film 15 of the present invention uses a photo-alignment method, the alignment film 15 uses a light beam with no gradient intensity to irradiate the monomer to form the first pattern and the second pattern in stages, so that the liquid crystal layer has The first alignment angle and the second alignment angle are used to achieve uneven alignment angle distribution.

To sum up, the alignment film of the present invention has different regions and corresponds to different patterns, so that the liquid crystal in the region where the original FFE is located has a specific alignment angle, so as to achieve the purpose of suppressing fringe field effects.

Claims (9)

A spatial light modulator for suppressing fringe field effect, comprising: a transparent electrode layer; a reflective electrode layer, which includes a pixel electrode, a pixel area in the pixel electrode is surrounded by the boundary of the pixel electrode; a liquid crystal layer, which between the transparent electrode layer and the reflective electrode layer to establish a pixel, the pixel is formed by the liquid crystal layer in the pixel area covering the pixel electrode; and an alignment film having a first pattern and a second and cover the pixel area; the pixel area causes a liquid crystal in the liquid crystal layer of the pixel to generate a first alignment angle and a second alignment angle respectively due to the first pattern and the second pattern, And the first alignment angle is different from the second alignment angle; wherein, the plane where the liquid crystal layer is located is the XY plane, and the first alignment angle and the second alignment angle are the angle between the XY plane where the liquid crystal layer is located and the X axis . The spatial light modulator according to claim 1, wherein the pixel area of the pixel has a first area and a second area, the first pattern is disposed in the first area, and the second pattern is disposed in the first area two regions, and the first pattern surrounds the second pattern. The spatial light modulator of claim 2, wherein the first alignment angle is greater than the second alignment angle. The spatial light modulator according to claim 3, wherein the first alignment angle is greater than 0 degrees and less than or equal to 5 degrees. The spatial light modulator according to claim 4, wherein the liquid crystal layer is of a uniform planar type, or a vertical type, or a twisted type. The spatial light modulator according to claim 5, wherein the alignment film is irradiated by a light beam with no gradient intensity to form the first pattern and the second pattern in stages, so that the liquid crystal layer has the first pattern. A non-uniform distribution of the alignment angle and the second alignment angle. The spatial light modulator according to claim 4, wherein the first area is a square ring, the first area surrounds the second area, and the second area is a square area that fills the square ring internal. The spatial light modulator according to claim 7, wherein the width of the square ring is greater than or equal to the range of the fringe field effect of the pixel. The spatial light modulator according to claim 5, further comprising: a nanostructure alignment layer, the nanostructure alignment layer is patterned to form nanostructures on the alignment film, the nanostructures The size and shape of are used to realize the first pattern and the second pattern, so that the liquid crystal in which the pixel area is located has a non-uniform alignment angle distribution.

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