Adjustable liquid crystal holographic device and preparation method thereof, and holographic light field modulation device

Abstract

The embodiments of the present invention disclose an adjustable liquid crystal holographic device, a preparation method thereof, and a holographic light field modulation device. The adjustable liquid crystal holographic device includes a first substrate and a second substrate arranged opposite to each other, and a first chiral cholesteric liquid crystal layer and a second chiral cholesteric liquid crystal layer stacked between the first substrate and the second substrate; the first substrate is provided with a first orientation layer, and the second substrate is provided with a second orientation layer, and the first orientation layer and the second orientation layer both have rewritable orientation directions; the second chiral cholesteric liquid crystal layer is oriented according to a first control pattern, and the first chiral cholesteric liquid crystal layer is oriented according to a second control pattern; a spacer is provided between the first substrate and the second substrate. The adjustable liquid crystal holographic device provided by the embodiment of the present invention can independently perform geometric phase modulation on two types of circularly polarized light, realizing dynamically adjustable dual-channel holographic display, thereby improving the multiplexing dimension and flexibility of the holographic device.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid crystal microstructure manipulation and light field regulation, and in particular to an adjustable liquid crystal holographic device and a preparation method thereof, and a holographic light field modulation device. Background Art

[0002] In recent years, light field manipulation technologies have continued to advance, finding widespread application in fields such as display, communications, astronomical observation, and security. Holography, in particular, has long been a research hotspot within this field, demonstrating enormous potential in applications such as optical display and information encryption. With the increasing integration of modern photonic technologies, multi-channel, high-efficiency, easily integrated, and dynamically adjustable holographic devices are urgently needed.

[0003] Traditional holographic devices, primarily based on systems such as holographic plates, spatial light modulators, and metasurfaces, can achieve diverse holographic displays. However, most suffer from limitations such as lack of tunability, single-channel operation, or limited efficiency, which restricts the development of holographic technology. Summary of the Invention

[0004] Embodiments of the present invention provide an adjustable liquid crystal holographic device, a preparation method thereof, and a holographic light field modulation device. The adjustable liquid crystal holographic device can independently perform geometric phase modulation on two types of chiral circularly polarized light, realizing dynamically adjustable dual-channel holographic display, thereby improving the multiplexing dimension and flexibility of the holographic device.

[0005] According to one aspect of the present invention, there is provided a tunable liquid crystal holographic device, comprising a first substrate and a second substrate disposed opposite to each other, and a first chiral cholesteric liquid crystal layer and a second chiral cholesteric liquid crystal layer stacked between the first substrate and the second substrate;

[0006] A first alignment layer is provided on the side of the first substrate facing the second substrate, and a second alignment layer is provided on the side of the second substrate facing the first substrate. The first alignment layer does not contain a photoinitiator, while the second alignment layer contains a photoinitiator. Both the first alignment layer and the second alignment layer have rewritable alignment directions.

[0007] The first chiral cholesteric liquid crystal layer is adjacent to the first alignment layer, the second chiral cholesteric liquid crystal layer is adjacent to the second alignment layer, and the chiral directions of the first chiral cholesteric liquid crystal layer and the second chiral cholesteric liquid crystal layer are opposite; the second chiral cholesteric liquid crystal layer is aligned according to a first control pattern, and the first chiral cholesteric liquid crystal layer is aligned according to a second control pattern;

[0008] A spacer is provided between the first substrate and the second substrate to control the total thickness of the first chiral cholesteric liquid crystal layer and the second chiral cholesteric liquid crystal layer.

[0009] Optionally, the first handed cholesteric liquid crystal layer is a left-handed spiral structure, and the second handed cholesteric liquid crystal layer is a right-handed spiral structure; or the first handed cholesteric liquid crystal layer is a right-handed spiral structure, and the second handed cholesteric liquid crystal layer is a left-handed spiral structure;

[0010] The first chiral cholesteric liquid crystal layer and the second chiral cholesteric liquid crystal layer have overlapping Bragg reflection bands.

[0011] Optionally, the first chiral cholesteric liquid crystal layer includes only first chiral unpolymerized liquid crystal molecules, or includes both first chiral unpolymerized liquid crystal molecules and a first chiral polymer network; the second chiral cholesteric liquid crystal layer includes both second chiral unpolymerized liquid crystal molecules and a second chiral polymer network support.

[0012] Optionally, the first control graph satisfies The first control pattern is used to control the distribution of the starting directors of the liquid crystal molecules on both sides of the second chirality cholesteric liquid crystal layer, and the second control pattern satisfies The second control pattern is used to control the distribution of starting directors of liquid crystal molecules on a side of the first chiral cholesteric liquid crystal layer close to the first substrate;

[0013] Wherein, m1 and m2 are the relative intensities of the first target image and the second target image of the holographic display, respectively. These are the CGH phase distributions of the first target image and the second target image respectively.

[0014] Optionally, the alignment materials of the first alignment layer and the second alignment layer include at least one of a photo-crosslinking material, a photo-degradable material, and a photo-induced cis-trans isomerization material.

[0015] Optionally, the spacer includes quartz microspheres or quartz columns, which are used to support the first substrate and the second substrate to form a filling space for the first chirally-directed cholesteric liquid crystal layer and the second chirally-directed cholesteric liquid crystal layer;

[0016] Along a direction perpendicular to the plane where the first substrate is located, an extension length of the spacer is greater than or equal to 20 times a helical pitch of liquid crystal molecules in the first chirality cholesteric liquid crystal layer.

[0017] According to another aspect of the present invention, a method for preparing a tunable liquid crystal holographic device is provided, for preparing the above-mentioned tunable liquid crystal holographic device, the preparation method comprising:

[0018] providing a first substrate and a second substrate;

[0019] forming a first alignment layer on one side of the first substrate and forming a second alignment layer on one side of the second substrate;

[0020] placing the first substrate and the second substrate opposite to each other, and providing a spacer between the first substrate and the second substrate;

[0021] preparing a first chiral cholesteric liquid crystal layer and a second chiral cholesteric liquid crystal layer between the first substrate and the second substrate to form the tunable liquid crystal holographic device;

[0022] The first alignment layer is located on a side of the first substrate close to the second substrate, the second alignment layer is located on a side of the second substrate close to the first substrate, the second chiral cholesteric liquid crystal layer is oriented according to a first control pattern, and the first chiral cholesteric liquid crystal layer is oriented according to a second control pattern.

[0023] Optionally, forming a first alignment layer on one side of the first substrate and forming a second alignment layer on one side of the second substrate includes:

[0024] Spin coating a solution containing an alignment material on one side of the first substrate, and after spin coating, annealing the first substrate to form the first alignment layer;

[0025] A uniform mixed solution containing an alignment material and a photoinitiator is spin-coated on one side of the second substrate. After the spin coating is completed, the second substrate is annealed to form the second alignment layer.

[0026] Optionally, a first chiral cholesteric liquid crystal layer and a second chiral cholesteric liquid crystal layer are prepared between the first substrate and the second substrate to form the tunable liquid crystal holographic device, comprising:

[0027] Performing ultraviolet light alignment on an empty cell consisting of the first substrate, the second substrate, and the spacer, so that the alignment directions of the first alignment layer and the second alignment layer are consistent with the first control pattern;

[0028] Filling a mixture of a second handed cholesteric liquid crystal and a polymer monomer into the filling space between the first substrate and the second substrate, irradiating the second substrate with ultraviolet light from one side to perform surface induced photopolymerization to form a second handed polymer network scaffold connected to the surface of the second substrate;

[0029] Soak the polymerized liquid crystal cell in acetone until the molecules that have not undergone polymerization are washed away;

[0030] The washed liquid crystal cell is taken out from the acetone, the second-handed polymer network support shrinks, and the external conditions of the liquid crystal cell are changed to control the resilience of the second-handed polymer network support;

[0031] Performing ultraviolet light rewriting on the liquid crystal cell so that the alignment directions of the first alignment layer and the second alignment layer are both consistent with the second control pattern;

[0032] The liquid crystal cell is refilled with the first chiral cholesteric liquid crystal, or a mixture of the first chiral cholesteric liquid crystal, a polymer monomer and a photoinitiator and polymerized to form the tunable liquid crystal holographic device.

[0033] According to another aspect of the present invention, there is provided a holographic light field modulation device, comprising a laser, a first polarizer, a quarter-wave plate, any one of the above-mentioned adjustable liquid crystal holographic devices, a second polarizer, a light screen, and an external field control unit;

[0034] The light beam output by the laser passes through the first polarizer and the quarter-wave plate in sequence and then enters the first substrate side of the tunable liquid crystal holographic device. The tunable liquid crystal holographic device independently performs geometric phase modulation on the incident left-handed circular polarization component and right-handed circular polarization component and reflects them. The reflected light beam passes through the second polarizer and then is received by the light screen.

[0035] The external field control unit is used to control the external field environment of the adjustable liquid crystal holographic device to change the reflection phase difference between left-handed circularly polarized light and right-handed circularly polarized light.

[0036] An embodiment of the present invention provides a tunable liquid crystal holographic device comprising a first substrate and a second substrate disposed oppositely, and a first and second chiral cholesteric liquid crystal layers stacked between the first and second substrates. The first and second chiral cholesteric liquid crystal layers have opposite chiral orientations but overlap with Bragg reflection bands. Using processes such as secondary photoalignment, surface-induced photopolymerization, and wash-and-refill, the second chiral cholesteric liquid crystal layer can be oriented according to a first control pattern, while the first chiral cholesteric liquid crystal layer can be oriented according to a second control pattern. Within the Bragg reflection band, the cholesteric liquid crystal can reflect a circular polarization component with the same chiral orientation as the liquid crystal layer, imparting a geometric phase related to the initial orientation of the cholesteric liquid crystal, while transmitting a circular polarization component with an opposite chiral orientation. Therefore, the tunable liquid crystal holographic device provided by the embodiment of the present invention can independently modulate the geometric phases of two chiral circular polarization components, thereby achieving dual-channel holographic display with orthogonal linear polarization multiplexing. Furthermore, the cholesteric liquid crystal exhibits multi-factor responsiveness, responding to external stimuli such as thermal, electrical, optical, and magnetic fields, thereby forming a tunable optical device. The adjustable liquid crystal holographic device provided in the embodiment of the present invention can adjust the reflection phase difference between left-handed and right-handed circularly polarized light, that is, the linear polarization direction of the reflected light field, through thermal and electrical stimulation, thereby realizing dynamically adjustable dual-channel holographic display, effectively improving the limitations of traditional holographic devices such as low multiplexing dimension and poor flexibility.

[0037] It should be understood that the content described in this section is not intended to identify the key or important features of the embodiments of the present invention, nor is it intended to limit the scope of the present invention. Other features of the present invention will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0039] Figure 1 A schematic diagram of the yz side structure of an adjustable liquid crystal holographic device provided by an embodiment of the present invention;

[0040] Figure 2 A schematic diagram of a calculation flow for the initial director distribution of a liquid crystal layer of a tunable liquid crystal holographic device provided by an embodiment of the present invention;

[0041] Figure 3 A schematic flow chart of a method for preparing an adjustable liquid crystal holographic device provided in an embodiment of the present invention;

[0042] Figure 4 A schematic diagram of a specific preparation process of an adjustable liquid crystal holographic device provided in an embodiment of the present invention;

[0043] Figure 5 A schematic diagram of spectrum characterization results of a tunable liquid crystal holographic device after refilling provided by an embodiment of the present invention;

[0044] Figure 6 A schematic structural diagram of a holographic light field modulation device provided by an embodiment of the present invention;

[0045] Figure 7 A static diffraction spot pattern of the tunable liquid crystal holographic device provided in an embodiment of the present invention;

[0046] Figure 8 A dynamic diffraction spot pattern of the adjustable liquid crystal holographic device provided in an embodiment of the present invention under thermal stimulation;

[0047] Figure 9 This is a dynamic diffraction spot pattern of the adjustable liquid crystal holographic device under electrical stimulation provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0048] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0049] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0050] Figure 1 This is a schematic diagram of the yz side structure of an adjustable liquid crystal holographic device provided by an embodiment of the present invention. Figure 1 The tunable liquid crystal holographic device provided in this embodiment includes a first substrate 10 and a second substrate 20 arranged opposite to each other, and a first chiral cholesteric liquid crystal layer 31 and a second chiral cholesteric liquid crystal layer 32 stacked between the first substrate 10 and the second substrate 20; wherein, a first orientation layer 41 is provided on the side of the first substrate 10 facing the second substrate 20, and a second orientation layer 42 is provided on the side of the second substrate 20 facing the first substrate 10; the first orientation layer 41 does not contain a photoinitiator, and the second orientation layer 42 contains a photoinitiator; the first orientation layer 41 and the second orientation layer 42 both have rewritable orientation directions; the first chiral cholesteric liquid crystal layer 31 is adjacent to the first orientation layer 41, and the second chiral cholesteric liquid crystal layer 32 is adjacent to the second orientation layer 42; the chiral directions of the first chiral cholesteric liquid crystal layer 31 and the second chiral cholesteric liquid crystal layer 32 are opposite; the second chiral cholesteric liquid crystal layer 32 is adjusted according to the first control pattern ( Figure 1 (not shown) is oriented, and the first chirped cholesteric liquid crystal layer 31 is oriented according to the second control pattern ( Figure 1 spacer 50 is provided between the first substrate 10 and the second substrate 20 to control the total thickness of the first chirped cholesteric liquid crystal layer 31 and the second chirped cholesteric liquid crystal layer 32.

[0051] The first substrate 10 and the second substrate 20 can be flexible substrates, such as polyimide, or rigid substrates, such as quartz substrates or glass substrates. Optionally, the orientation material in the first orientation layer 41 and the second orientation layer 42 can be at least one of a photocrosslinking material, a photodegradable material, and a photoinduced cis-trans isomerization material, such as a photosensitive azo material SD1. These materials are photo-controlled orientation materials that can undergo physical or chemical reactions under the irradiation of linearly polarized ultraviolet light to generate anisotropic surface forces, thereby inducing the directional alignment of liquid crystal molecules. In addition to the orientation material, the second orientation layer 42 also contains a uniformly mixed photoinitiator, such as benzophenone, which can induce a polymerization reaction to proceed from the surface of the second orientation layer 42.

[0052] Continue to refer Figure 1 Under the action of the alignment layer anchoring and the chiral agent, the first handed cholesteric liquid crystal layer 31 and the second handed cholesteric liquid crystal layer 32 both exhibit periodic spiral structures of a specific handedness. The first handedness can be left-handed or right-handed, and the second handedness can be right-handed or left-handed. Optionally, the first handed cholesteric liquid crystal layer 31 has a left-handed spiral structure and the second handed cholesteric liquid crystal layer 32 has a right-handed spiral structure, or the first handed cholesteric liquid crystal layer 31 has a right-handed spiral structure and the second handed cholesteric liquid crystal layer 32 has a left-handed spiral structure. The selection can be made based on actual conditions during implementation. The first handed cholesteric liquid crystal layer 31 and the second handed cholesteric liquid crystal layer 32 have similar pitches and therefore have overlapping Bragg reflection bands. Optionally, the first chiral cholesteric liquid crystal layer 31 may include only first chiral unpolymerized liquid crystal molecules, or may include first chiral unpolymerized liquid crystal molecules and first chiral polymer networks at the same time, which can be selected according to actual conditions during specific implementation; the second chiral cholesteric liquid crystal layer 32 includes second chiral unpolymerized liquid crystal molecules and second chiral polymer network supports at the same time. Optionally, the second chiral cholesteric liquid crystal layer 32 may be oriented according to the first control pattern, while the first chiral cholesteric liquid crystal layer 31 may be oriented according to the second control pattern. Within the Bragg reflection band, the cholesteric liquid crystal can reflect the circular polarization component with a chiral orientation consistent with that of the liquid crystal layer, and impart it with a geometric phase equal to ±2 times the initial orientation of the cholesteric liquid crystal layer, while transmitting the circular polarization component with the opposite chiral orientation. Therefore, the technical solution of this embodiment can independently perform geometric phase modulation on the two chiral circular polarization components, thereby realizing a dual-channel holographic display with orthogonal linear polarization multiplexing.

[0053] Optionally, the spacer 50 may be a quartz microsphere or a quartz column, which may be disposed at the boundary between the first substrate 10 and the second substrate 20 to support the first substrate 10 and the second substrate 20, forming a filling space for the first chiral cholesteric liquid crystal layer 31 and the second chiral cholesteric liquid crystal layer 32. Along the direction perpendicular to the first substrate 10 and the second substrate 20, the extension length of the spacer 50 must be greater than or equal to 20 times the helical pitch of the liquid crystal molecules in the first chiral cholesteric liquid crystal layer 31, so that the thickness of each of the first chiral cholesteric liquid crystal layer 31 and the second chiral cholesteric liquid crystal layer 32 can be greater than or equal to 10 times the helical pitch of the liquid crystal molecules in the layer, thereby enabling the first chiral cholesteric liquid crystal layer 31 and the second chiral cholesteric liquid crystal layer 32 to have high reflectivity when undergoing circularly polarized selective Bragg reflection. It is understandable that Figure 1 The figure only exemplarily shows the positional relationship of the spacer 50 used to support the first substrate 10 and the second substrate 20 rather than the actual size and proportion.

[0054] For example, Figure 2 The schematic diagram of the calculation process of the initial director distribution of the liquid crystal layer of a tunable liquid crystal holographic device provided by the embodiment of the present invention can be used to calculate the first control pattern and the second control pattern required to realize the above-mentioned orthogonal linear polarization multiplexing dual-channel holographic display. Figure 2 First, according to the first target image ( Figure 2 LC) and the second target image ( Figure 2 The GS algorithm is used to calculate the phase distribution of the first target image. and the CGH phase distribution of the second target image Then, according to the relative intensities m1 and m2 of the first target image and the second target image, the first control pattern is obtained. And the second control graphic The first control pattern is used to control the distribution of the starting director vectors on both sides of the cholesteric liquid crystal layer of the second chirality, thereby controlling the geometric phase distribution obtained by the circular polarization component consistent with the second chirality; the second control pattern is used to control the distribution of the starting director vectors on the side of the cholesteric liquid crystal layer of the first chirality close to the first substrate, thereby controlling the geometric phase distribution obtained by the circular polarization component consistent with the first chirality. It can be understood that the technical solution of this embodiment can impart independent geometric phase distributions to the two chiral circular polarization components. When linearly polarized incident, the adjustable liquid crystal holographic device oriented according to the first control pattern and the second control pattern can respectively reproduce the first target image and the second target image in the orthogonal linear polarization channels in the far field.

[0055] It should be noted that Figure 2The calculation process of the liquid crystal layer starting director distribution is only provided as an example, and is not a limitation of the present invention. In other embodiments, other calculation processes can be used according to specific needs to obtain a liquid crystal layer starting director distribution control pattern with similar functions.

[0056] The adjustable liquid crystal holographic device provided in an embodiment of the present invention provides a first and a second cholesteric liquid crystal layer with opposite rotation directions and overlapping Bragg reflection bands, and orients the second cholesteric liquid crystal layer according to a first control pattern and the first cholesteric liquid crystal layer according to a second control pattern, so that the two chiral circular polarization components can be independently geometrically phase modulated, thereby realizing a dual-channel holographic display with orthogonal linear polarization multiplexing. In addition, the cholesteric liquid crystal also has multi-stimulus responsiveness and can respond to external field stimuli such as heat, electricity, light, and magnetism to form an adjustable optical device. The adjustable liquid crystal holographic device provided in this embodiment can regulate the orientation of unpolymerized liquid crystal molecules through thermal, electrical and other stimuli, thereby changing the reflection phase difference between left-handed and right-handed circularly polarized light, that is, the linear polarization direction of the reflected light field, and ultimately realizing a dynamically adjustable dual-channel holographic display. This adjustable liquid crystal holographic device can effectively improve the limitations of traditional holographic devices such as low multiplexing dimension and poor flexibility.

[0057] Figure 3 A schematic diagram of a process for preparing a tunable liquid crystal holographic device according to an embodiment of the present invention is provided, which is used to prepare the above-mentioned tunable liquid crystal holographic device. Figure 3 , the preparation method comprises:

[0058] S110 , providing a first substrate and a second substrate.

[0059] The first and second substrates can be flexible or rigid substrates with high light transmittance (greater than or equal to 85%) and must include conductive electrodes with high light transmittance. For example, the first and second substrates can be made of ITO glass, and the thickness of the substrates can be 1mm-2mm.

[0060] S120 , forming a first alignment layer on one side of the first substrate, and forming a second alignment layer on one side of the second substrate.

[0061] The first alignment layer is located on a side of the first substrate close to the second substrate, the second alignment layer is located on a side of the second substrate close to the first substrate, the first alignment layer has no photoinitiator, and the second alignment layer contains a photoinitiator.

[0062] Optionally, forming a first alignment layer on one side of the first substrate and forming a second alignment layer on one side of the second substrate includes:

[0063] Spin coating a solution containing an alignment material on one side of a first substrate, and after spin coating, annealing the first substrate to form a first alignment layer;

[0064] A uniform mixed solution containing an alignment material and a photoinitiator is spin-coated on one side of the second substrate. After the spin coating is completed, the second substrate is annealed to form a second alignment layer.

[0065] For example, in this embodiment, the orientation material is the photosensitive azo material SD1, and the spin coating solution without a photoinitiator contains 0.35% of SD1 and 99.65% of dimethylformamide; the photoinitiator is benzophenone, and the spin coating solution containing the photoinitiator contains 0.35% of SD1, 0.15% of benzophenone and 99.5% of dimethylformamide.

[0066] For example, the spin coating process may include: first, adjusting the spin speed to 600-900 rpm and controlling the first-stage spin coating time to 5-10 seconds to ensure uniform distribution of the material on the substrate surface; then adjusting the spin speed to 2500-3500 rpm and controlling the second-stage spin coating time to 30-50 seconds to ensure that the material is applied to a specific thickness. Optionally, the thickness of the first alignment layer without a photoinitiator and the second alignment layer containing a photoinitiator can be 30-50 nm.

[0067] Exemplarily, the annealing process may include: an annealing atmosphere of air, an annealing temperature of 80° C.-120° C., and an annealing time of 8 min-12 min.

[0068] It should be noted that the above-mentioned spin coating solution composition, spin coating parameters, and annealing parameters are only exemplary descriptions, and in other embodiments, they can be adjusted according to actual needs.

[0069] S130 , placing the first substrate and the second substrate opposite to each other, and providing a spacer between the first substrate and the second substrate.

[0070] When the first substrate and the second substrate are opposite to each other, the first alignment layer and the second alignment layer are arranged opposite to each other. The spacers can be quartz microspheres or quartz columns and can be arranged at the boundary between the first substrate and the second substrate.

[0071] S140 , preparing a first chiral cholesteric liquid crystal layer and a second chiral cholesteric liquid crystal layer between the first substrate and the second substrate to form a tunable liquid crystal holographic device.

[0072] The second chiral cholesteric liquid crystal layer is oriented according to the first control pattern, and the first chiral cholesteric liquid crystal layer is oriented according to the second control pattern.

[0073] Figure 4 This is a schematic diagram of a specific preparation process of an adjustable liquid crystal holographic device provided by an embodiment of the present invention. Figure 4Optionally, a first chiral cholesteric liquid crystal layer and a second chiral cholesteric liquid crystal layer are prepared between the first substrate and the second substrate to form a tunable liquid crystal holographic device, comprising:

[0074] Performing UV alignment on an empty cell consisting of a first substrate, a second substrate, and a spacer so that the alignment directions of the first alignment layer and the second alignment layer are consistent with the first control pattern;

[0075] A mixture of cholesteric liquid crystals of a second handedness (taking right-handedness as an example, which is not a limitation of the present invention) and polymer monomers is filled into the filling space between the first substrate and the second substrate, and ultraviolet light is irradiated from one side of the second substrate to perform surface-induced photopolymerization to form a polymer network scaffold of the second handedness connected to the surface of the second substrate;

[0076] Soak the polymerized liquid crystal cell in acetone until the molecules that have not undergone polymerization are washed away;

[0077] The washed liquid crystal cell is taken out of acetone, and the second-handed polymer network scaffold shrinks, thereby changing the external conditions of the liquid crystal cell to control the resilience of the second-handed polymer network scaffold;

[0078] Performing ultraviolet light rewriting on the liquid crystal cell so that the alignment directions of the first alignment layer and the second alignment layer are both consistent with the second control pattern;

[0079] The liquid crystal box is refilled with cholesteric liquid crystal of the first hand direction (taking left-handed as an example), or a mixture of cholesteric liquid crystal of the first hand direction, polymer monomer and photoinitiator is refilled and polymerized to form a tunable liquid crystal holographic device.

[0080] After the above-mentioned steps of secondary photo-orientation, surface-induced photopolymerization, washing and refilling, a first chiral cholesteric liquid crystal layer and a second chiral cholesteric liquid crystal layer are prepared between the first substrate and the second substrate, and the second chiral cholesteric liquid crystal layer is controlled to be oriented according to the first control pattern, and the first chiral cholesteric liquid crystal layer is controlled to be oriented according to the second control pattern, thereby forming an adjustable liquid crystal holographic device.

[0081] Optionally, ultraviolet light orientation and ultraviolet light rewriting include: using a digital micromirror projection system to synchronously control the exposure pattern and the polarizer angle according to the exposure order, and performing ultraviolet exposure treatment in the areas where the first alignment layer and the second alignment layer are located, so that the first alignment layer and the second alignment layer form a first control pattern or a second control pattern.

[0082] Exemplarily, the cholesteric liquid crystal can be a mixture of a nematic liquid crystal and a chiral agent. In this embodiment, the nematic liquid crystal is selected from mixed crystal E7, and the chiral agent is selected from either the left-handed chiral agent S5011 or the right-handed chiral agent R5011. In the aforementioned mixture of the second chiral orientation cholesteric liquid crystal and a polymer monomer, the polymer monomer is selected from RM257, and the weight percentage of the polymer monomer is selected from 20%. In the aforementioned mixture of the first chiral orientation cholesteric liquid crystal, a polymer monomer, and a photoinitiator, the polymer monomer is selected from RM257, and the photoinitiator is selected from benzophenone, with the weight percentages of the polymer monomer and the photoinitiator being selected from 15% and 0.8%, respectively.

[0083] It should be noted that the above-mentioned cholesteric liquid crystal components and ratios are merely exemplary descriptions and are not limitations on the embodiments of the present invention. In other implementations, other components and ratios may be used according to specific requirements.

[0084] Changing the external conditions of the liquid crystal cell involves heating the liquid crystal cell for a certain period of time and then cooling it to room temperature. The heating temperature and duration can control the resilience of the second-handed polymer network scaffold. In practice, the heating temperature and duration can be determined based on actual conditions. Exemplary examples of changing the external conditions of the liquid crystal cell include heating at a temperature of 80°C to 140°C and a heating time of 0 to 20 minutes.

[0085] For example, Figure 5 A schematic diagram of the spectrum characterization results of a tunable liquid crystal holographic device after refilling provided by an embodiment of the present invention. Figure 5 , the horizontal axis represents the wavelength of the incident light, in nanometers (nm), and the vertical axis represents the transmittance; the transmission spectrum corresponding to left-handed circularly polarized light is represented by a dotted line a, the transmission spectrum corresponding to linearly polarized light is represented by a solid line b, and the transmission spectrum corresponding to right-handed circularly polarized light is represented by a dotted line c. Figure 5 It can be seen that the tunable liquid crystal holographic device in this embodiment can simultaneously reflect left-handed and right-handed circularly polarized light within the wavelength range of 585nm-677nm with high reflectivity. This is because the first and second chiral cholesteric liquid crystal layers have opposite chiral orientations and overlap in the Bragg reflection bands between 585nm and 677nm. Furthermore, the thicknesses of the first and second chiral cholesteric liquid crystal layers both meet the Bragg reflection conditions.

[0086] It should be noted that Figure 5 The spectrum of a tunable liquid crystal holographic device after refilling is merely shown as an example, and is not intended to limit the present invention. In other embodiments, other Bragg reflection band positions may be selected for the tunable liquid crystal holographic device according to actual needs.

[0087] Figure 6A schematic diagram of the structure of a holographic light field modulation device provided by an embodiment of the present invention. Figure 6 The holographic light field modulation device includes a laser 1, a first polarizer 2, a quarter-wave plate 3, the tunable liquid crystal holographic device 4 provided in the above embodiment, a second polarizer 5, a light screen 6, and an external field control unit 7; the light beam output by the laser 1 passes through the first polarizer 2 and the quarter-wave plate 3 in sequence and is incident from the first substrate side of the tunable liquid crystal holographic device 4. The tunable liquid crystal holographic device 4 independently performs geometric phase modulation on the incident left-handed circularly polarized component and right-handed circularly polarized component and reflects them. The reflected light beam passes through the second polarizer 5 and is received by the light screen 6; the external field control unit 7 is used to control the external field environment in which the tunable liquid crystal holographic device is located to change the reflection phase difference between the left-handed circularly polarized light and the right-handed circularly polarized light.

[0088] The external field environment can be at least one of thermal, electrical, optical, magnetic and other external field stimuli. Figure 7 The external field control unit 7 shown in FIG. 7 may include a voltage source 71 or a heat stage 72. For example, the voltage source 71 can control the external electric field on the tunable liquid crystal holographic device 4 within a control range of 0-16 V / μm. The heat stage 72 can control the temperature of the tunable liquid crystal holographic device 4 within a control range of 20°C-60°C. The specific implementation can be designed based on actual conditions. By controlling the temperature or the external electric field, the linear polarization direction of the light field reflected by the tunable liquid crystal holographic device 4 can be changed, thereby dynamically switching the far-field reproduced image after passing through the second polarizer.

[0089] The first polarizer 2 and quarter-wave plate 3 are used to alter the polarization state of the incident light. When the desired incident light is circularly polarized, the quarter-wave plate 3 is positioned at an angle of ±45° relative to the first polarizer 2. When the desired incident light is linearly polarized, the quarter-wave plate 3 is positioned parallel to or perpendicular to the first polarizer 2, or the quarter-wave plate 3 can be removed. The second polarizer 5 is used to filter the specific linearly polarized component of the light field reflected by the tunable liquid crystal holographic device 4.

[0090] For example, in this embodiment, a He-Ne laser with an output wavelength of 632.8 nm is selected, and the incident angle of the laser incident on the tunable liquid crystal holographic device 4 can be 0°-15°.

[0091] For example, Figure 7 The static diffraction spot pattern of the adjustable liquid crystal holographic device provided in the embodiment of the present invention is: Figure 8 The dynamic diffraction spot pattern of the adjustable liquid crystal holographic device under thermal stimulation provided by the embodiment of the present invention is as follows: Figure 9 The dynamic diffraction spot pattern of the adjustable liquid crystal holographic device under electrical stimulation provided by the embodiment of the present invention. Figure 7When the incident light is 632.8nm left-handed circularly polarized light (the arrow in the lower right corner of the figure shows the polarization direction), the tunable liquid crystal holographic device in this embodiment reproduces the superimposed image of the first target image and the second target image on the far-field light screen; when the incident light is right-handed circularly polarized light, the superimposed image of the first target image and the second target image is also reproduced in the far field; and when the incident light is linearly polarized light, the tunable liquid crystal holographic device can reproduce the first target image and the second target image respectively in the orthogonal polarization channel, and there is basically no aliasing between the first target image and the second target image.

[0092] refer to Figure 8 When the first chiral cholesteric liquid crystal layer in a tunable liquid crystal holographic device consists only of unpolymerized liquid crystal molecules of the first chiral orientation, the far-field reproduced image of the tunable liquid crystal holographic device can be adjusted by temperature. Under vertical polarization, the device reproduces the first target image at 30°C. By raising the temperature to 50°C without changing the polarizer orientation, the liquid crystal structure changes with temperature, and the reproduced image gradually changes to the second target image.

[0093] refer to Figure 9 When the first chiral cholesteric liquid crystal layer in a tunable liquid crystal holographic device comprises both unpolymerized liquid crystal molecules of the first chiral orientation and a polymer network of the first chiral orientation, the far-field reproduced image of the tunable liquid crystal holographic device can be adjusted by an electric field. Under horizontal polarization, the device reproduces the second target image when no electric field is applied. By applying a 15.5V / μm electric field to the device without changing the polarizer orientation, the orientation of the unpolymerized liquid crystal molecules changes with the electric field, and the reproduced image quickly shifts to the first target image.

[0094] It should be noted that the embodiments of the present invention only illustrate the dynamically adjustable dual-channel holographic display effect corresponding to 632.8nm incident light, and do not limit the scope of the tunable liquid crystal holographic device provided by the present invention. In other embodiments, the pitch or composition of the first chiral cholesteric liquid crystal layer and the second chiral cholesteric liquid crystal layer can be adjusted according to actual needs to make the tunable liquid crystal holographic device provided by the present invention applicable to different wavelength ranges or have different dynamic responsiveness.

[0095] The technical solution of the embodiment of the present invention is to independently perform geometric phase modulation on the two chiral circular polarization components by providing a first chiral cholesteric liquid crystal layer and a second chiral cholesteric liquid crystal layer with opposite chiral directions and overlapping Bragg reflection bands, and orienting the second chiral cholesteric liquid crystal layer according to a first control pattern and the first chiral cholesteric liquid crystal layer according to a second control pattern. In addition, the cholesteric liquid crystal also has multi-stimulus responsiveness and can respond to external field stimuli such as heat, electricity, light, and magnetism to form an adjustable optical device. The adjustable liquid crystal holographic device provided in this embodiment can realize a dual-channel holographic display with orthogonal linear polarization multiplexing, and can change the liquid crystal structure through thermal, electrical and other stimuli, thereby changing the reflection phase difference between left-handed and right-handed circularly polarized light, that is, the linear polarization direction of the reflected light field, and ultimately realize a dynamically adjustable dual-channel holographic display, effectively improving the limitations of traditional holographic devices such as low multiplexing dimension and poor flexibility.

[0096] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A tunable liquid crystal holographic device, characterized in that: The invention comprises a first substrate and a second substrate which are arranged opposite to each other, and a first chirally-oriented cholesteric liquid crystal layer and a second chirally-oriented cholesteric liquid crystal layer which are stacked between the first substrate and the second substrate; A first alignment layer is provided on the side of the first substrate facing the second substrate, and a second alignment layer is provided on the side of the second substrate facing the first substrate. The first alignment layer does not contain a photoinitiator, while the second alignment layer contains a photoinitiator. Both the first alignment layer and the second alignment layer have rewritable alignment directions. The first chiral cholesteric liquid crystal layer is adjacent to the first alignment layer, the second chiral cholesteric liquid crystal layer is adjacent to the second alignment layer, and the chiral directions of the first chiral cholesteric liquid crystal layer and the second chiral cholesteric liquid crystal layer are opposite; the second chiral cholesteric liquid crystal layer is aligned according to a first control pattern, and the first chiral cholesteric liquid crystal layer is aligned according to a second control pattern; The first control graph satisfies α1=arg(m1e iφ1 +m2e iφ2 ) / 2, the first control pattern is used to control the distribution of the starting directors of the liquid crystal molecules on both sides of the second chirality cholesteric liquid crystal layer, and the second control pattern satisfies α2=-arg(m1e iφ1 -m2e iφ2 ) / 2, the second control pattern is used to control the distribution of the starting directors of the liquid crystal molecules on the side of the first chiral cholesteric liquid crystal layer close to the first substrate; Wherein, m1 and m2 are the relative intensities of the first target image and the second target image of the holographic display, respectively; φ1 and φ2 are the CGH phase distributions of the first target image and the second target image, respectively; A spacer is provided between the first substrate and the second substrate to control the total thickness of the first chiral cholesteric liquid crystal layer and the second chiral cholesteric liquid crystal layer.

2. The tunable liquid crystal holographic device according to claim 1, characterized in that: The first handed cholesteric liquid crystal layer has a left-handed spiral structure, and the second handed cholesteric liquid crystal layer has a right-handed spiral structure, or the first handed cholesteric liquid crystal layer has a right-handed spiral structure, and the second handed cholesteric liquid crystal layer has a left-handed spiral structure; The first chiral cholesteric liquid crystal layer and the second chiral cholesteric liquid crystal layer have overlapping Bragg reflection bands.

3. The tunable liquid crystal holographic device according to claim 1, characterized in that: The first chiral cholesteric liquid crystal layer includes only first chiral unpolymerized liquid crystal molecules, or includes first chiral unpolymerized liquid crystal molecules and first chiral polymer network at the same time; the second chiral cholesteric liquid crystal layer includes second chiral unpolymerized liquid crystal molecules and second chiral polymer network support at the same time.

4. The tunable liquid crystal holographic device according to claim 1, characterized in that: The alignment materials of the first alignment layer and the second alignment layer include at least one of a photo-crosslinking material, a photo-degradable material, and a photo-induced cis-trans isomerization material.

5. The tunable liquid crystal holographic device according to claim 1, characterized in that: The spacer includes quartz microspheres or quartz columns, and is used to support the first substrate and the second substrate to form a filling space for the first chirally-directed cholesteric liquid crystal layer and the second chirally-directed cholesteric liquid crystal layer; Along a direction perpendicular to the plane where the first substrate is located, an extension length of the spacer is greater than or equal to 20 times a helical pitch of liquid crystal molecules in the first chirality cholesteric liquid crystal layer.

6. A method for preparing an adjustable liquid crystal holographic device, characterized in that: Used for preparing the tunable liquid crystal holographic device according to any one of claims 1 to 5, the preparation method comprising: providing a first substrate and a second substrate; forming a first alignment layer on one side of the first substrate and forming a second alignment layer on one side of the second substrate; placing the first substrate and the second substrate opposite to each other, and providing a spacer between the first substrate and the second substrate; preparing a first chiral cholesteric liquid crystal layer and a second chiral cholesteric liquid crystal layer between the first substrate and the second substrate to form the tunable liquid crystal holographic device; The first alignment layer is located on a side of the first substrate close to the second substrate, the second alignment layer is located on a side of the second substrate close to the first substrate, the second chiral cholesteric liquid crystal layer is oriented according to a first control pattern, and the first chiral cholesteric liquid crystal layer is oriented according to a second control pattern.

7. The preparation method according to claim 6, characterized in that Forming a first alignment layer on one side of the first substrate and forming a second alignment layer on one side of the second substrate, comprising: Spin coating a solution containing an alignment material on one side of the first substrate, and after spin coating, annealing the first substrate to form the first alignment layer; A uniform mixed solution containing an alignment material and a photoinitiator is spin-coated on one side of the second substrate. After the spin coating is completed, the second substrate is annealed to form the second alignment layer.

8. The preparation method according to claim 6, characterized in that A first chiral cholesteric liquid crystal layer and a second chiral cholesteric liquid crystal layer are prepared between the first substrate and the second substrate to form the tunable liquid crystal holographic device, comprising: Performing ultraviolet light alignment on an empty cell consisting of the first substrate, the second substrate, and the spacer, so that the alignment directions of the first alignment layer and the second alignment layer are consistent with the first control pattern; Filling a mixture of a second handed cholesteric liquid crystal and a polymer monomer into the filling space between the first substrate and the second substrate, irradiating the second substrate with ultraviolet light from one side to perform surface induced photopolymerization to form a second handed polymer network scaffold connected to the surface of the second substrate; Soak the polymerized liquid crystal cell in acetone until the molecules that have not undergone polymerization are washed away; The washed liquid crystal cell is taken out from the acetone, the second-handed polymer network support shrinks, and the external conditions of the liquid crystal cell are changed to control the resilience of the second-handed polymer network support; Performing ultraviolet light rewriting on the liquid crystal cell so that the alignment directions of the first alignment layer and the second alignment layer are both consistent with the second control pattern; The liquid crystal cell is refilled with the first chiral cholesteric liquid crystal, or a mixture of the first chiral cholesteric liquid crystal, a polymer monomer and a photoinitiator and polymerized to form the tunable liquid crystal holographic device.

9. A holographic light field modulation device, characterized in that: The device comprises a laser, a first polarizer, a quarter-wave plate, the adjustable liquid crystal holographic device according to any one of claims 1 to 5, a second polarizer, a light screen and an external field control unit; The light beam output by the laser passes through the first polarizer and the quarter-wave plate in sequence and then enters the first substrate side of the tunable liquid crystal holographic device. The tunable liquid crystal holographic device independently performs geometric phase modulation on the incident left-handed circular polarization component and right-handed circular polarization component and reflects them. The reflected light beam passes through the second polarizer and then is received by the light screen. The external field control unit is used to control the external field environment of the adjustable liquid crystal holographic device to change the reflection phase difference between left-handed circularly polarized light and right-handed circularly polarized light.

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