Terahertz liquid crystal spatial light modulator with large modulation depth and ultra wide band

Abstract

The invention discloses a terahertz liquid crystal spatial light modulator with large modulation depth and ultra wide band, which belongs to the field of novel artificial electromagnetic materials and terahertz science and comprises an upper-layer quartz substrate, an upper-layer metal grating, an upper-layer pre-oriented film, a liquid crystal layer, a lower-layer pre-oriented film, a lower-layer metal grating and a lower-layer quartz substrate which are sequentially stacked and arranged, the upper-layer metal grating and the lower-layer metal grating are orthogonally arranged in space to form a Fabry-Perot cavity; the liquid crystal layer is filled between the upper pre-oriented film and the lower pre-oriented film, and the liquid crystal director has in-plane pre-orientation; the upper-layer metal grating and the lower-layer metal grating serve as a first electrode and a second electrode respectively and are used for receiving external voltage and controlling the liquid crystal director to be dynamically switched between an in-plane state and an out-of-plane state; according to the invention, the spatial modulation of the incident terahertz wave intensity can be realized, and the problems of photoelectric function conflict and pixel crosstalk of a metal structure are effectively solved.

Description

Technical Field

[0001] This invention belongs to the fields of novel artificial electromagnetic materials and terahertz science and technology, and particularly relates to a terahertz liquid crystal spatial light modulator with large modulation depth and ultra-wideband. Background Technology

[0002] Liquid crystal spatial light modulators can change the liquid crystal director via electrical addressing to achieve pixel-level amplitude and phase modulation, which has significant application value in display, information transmission, and spectral technology. In the terahertz band, due to the long wavelength, to enhance the interaction between terahertz waves and liquid crystals, the industry generally integrates artificially designed metal metasurface structures with liquid crystal materials. Utilizing the resonance enhancement effect of metasurfaces can significantly improve the amplitude and phase modulation depth, and this technical approach has become the mainstream research direction for terahertz dynamic control devices.

[0003] However, terahertz liquid crystal spatial light modulators still face multiple technical bottlenecks. First, while the resonant characteristics of metallic metasurfaces can enhance modulation depth, they severely limit the operating bandwidth of the device, resulting in a contradictory relationship between modulation depth and bandwidth. Although existing technologies have achieved a certain modulation depth through metasurface structure optimization, the modulation bandwidth typically does not exceed 20 GHz, making it difficult to meet the application requirements of broadband terahertz systems. Second, the lack of transparent electrode materials in the terahertz band similar to ITO thin films in the optical band forces metallic metasurfaces to simultaneously perform the dual functions of optical field modulation and liquid crystal driving. This conflict between optoelectronic roles leads to insufficient liquid crystal driving, affecting modulation performance. Furthermore, significant electromagnetic coupling crosstalk exists between pixel electrodes at the subwavelength scale, and there is a lack of effective crosstalk characterization and suppression methods, severely restricting array size expansion and spatial resolution improvement, thus limiting the further development of terahertz imaging, sensing, and spectral systems. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a terahertz liquid crystal spatial light modulator with large modulation depth and ultra-wideband, comprising:

[0005] The upper quartz substrate, the upper metal grating, the upper pre-aligned film, the liquid crystal layer, the lower pre-aligned film, the lower metal grating, and the lower quartz substrate are stacked in sequence.

[0006] The upper metal grating and the lower metal grating are arranged orthogonally in space to form a Fabry-Perot cavity;

[0007] The liquid crystal layer is filled between the upper pre-aligned film and the lower pre-aligned film, and the liquid crystal pointer has in-plane pre-alignment;

[0008] The upper metal grating and the lower metal grating serve as the first electrode and the second electrode, respectively, to receive external voltage and control the liquid crystal pointing vector to dynamically switch between in-plane and out-of-plane states.

[0009] The modulator controls the state of the liquid crystal pointing vector to change the polarization conversion characteristics of the terahertz wave in the Fabry-Perot cavity, thereby achieving spatial modulation of the intensity of the incident terahertz wave.

[0010] Preferably, the upper metal grating and the lower metal grating have the same deep subwavelength periodic structure;

[0011] The upper and lower metal gratings have a grating period range of 30-50 micrometers, a grating width of 15-25 micrometers, and a thickness of 100-300 nanometers. Furthermore, within the operating frequency band of 0.2-1 THz, the grating period size is smaller than the terahertz wavelength, enabling the metal grating to selectively transmit and reflect orthogonal polarization components.

[0012] Preferably, the materials used to manufacture the upper and lower metal gratings include gold, aluminum, and copper;

[0013] The upper metal grating has high transmittance for terahertz waves in the first polarization direction and high reflectivity for terahertz waves in the second polarization direction.

[0014] The lower metal grating has high transmittance for terahertz waves in the second polarization direction and high reflectivity for terahertz waves in the first polarization direction.

[0015] Preferably, the liquid crystal layer is made of a nematic liquid crystal material with a high birefringence coefficient, an ordinary light refractive index of 1.59±0.05, an extraordinary light refractive index of 1.88±0.05, and a thickness of 200-400 micrometers.

[0016] Preferably, the upper pre-aligned film and the lower pre-aligned film define the pre-alignment direction of the liquid crystal pointer as an in-plane direction, and the pre-alignment direction forms a 45° angle with both the upper metal grating and the lower metal grating.

[0017] Preferably, the upper metal grating and the lower metal grating both serve as a pixelation control electrode array;

[0018] The upper metal grating includes multiple parallel first electrode lines, and the lower metal grating includes multiple parallel second electrode lines. The first electrode lines and the second electrode lines intersect orthogonally in space to form multiple modulation units.

[0019] Preferably, the vertical spacing between the upper metal grating and the lower metal grating constitutes the resonant cavity length of the Fabry-Perot cavity;

[0020] The length of the resonant cavity is determined by the thickness of the liquid crystal layer, and the resonant cavity supports broadband resonant modes in the 0.2-1 THz frequency band.

[0021] Preferably, when no voltage is applied between the upper metal grating and the lower metal grating, the liquid crystal director maintains an in-plane pre-alignment state, and the liquid crystal layer exhibits in-plane anisotropy. After the first polarization component of the incident terahertz wave is selected by the upper metal grating, it undergoes phase delay in the liquid crystal layer and is converted into a second polarization component, which is finally output through the lower metal grating.

[0022] When a 1kHz square wave AC voltage is applied and the voltage amplitude gradually increases from 0V to 20V, the liquid crystal pointing vector gradually shifts from the in-plane state to the out-of-plane state, the in-plane anisotropy of the liquid crystal layer gradually weakens to isotropy, and the intensity of the transmitted second polarization component gradually decreases as the voltage increases.

[0023] Preferably, the modulator includes N first electrode lines and M second electrode lines, wherein both N and M are not less than 40, forming an N×M pixel array;

[0024] Each first electrode line and each second electrode line are independently connected to an external control circuit via wire bonding, enabling the modulation unit in each cross region to apply voltage control independently.

[0025] Preferably, the external control circuit includes a printed circuit board and a multi-channel programmable voltage source;

[0026] The printed circuit board is connected to the multi-channel programmable voltage source via a ribbon cable;

[0027] Under the control of the host computer, the multi-channel programmable voltage source outputs an independent 0-20V programmable voltage to each first electrode line and second electrode line. Through the voltage encoding combination of the upper and lower electrodes, different spatial modulation patterns are generated on the N×M pixel array.

[0028] Compared with the prior art, the present invention has the following advantages and technical effects:

[0029] This invention combines an orthogonal deep subwavelength metal grating structure with the tunable anisotropy of liquid crystal. Through the resonant switching of the Fabry-Perot cavity, it achieves compatibility with large modulation depth and wide bandwidth of transmitted terahertz wave intensity. At the same time, it achieves compatibility with optical field resonance enhancement and large-scale array control. This ultra-wideband large-scale spatial light modulator with large modulation depth provides a core functional device for applications such as target acquisition, tracking and aiming, near-field projection display, and single-pixel imaging in terahertz mobile communication systems.

[0030] This invention achieves compatibility between modulation depth and ultra-wide bandwidth, with a modulation depth greater than 75% in the 0.2-1 THz frequency band. It also supports independent control of large-scale pixel arrays of 40×40 and above, effectively solving the problems of optoelectronic functional conflict and pixel crosstalk in metal structures. It provides a core device foundation for applications such as terahertz dynamic beamforming and single-pixel imaging. Attached Figure Description

[0031] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0032] Figure 1 This is a schematic diagram of the system structure according to an embodiment of the present invention;

[0033] Figure 2 This is a diagram showing the correspondence between the liquid crystal pointing vector and the applied voltage in an embodiment of the present invention;

[0034] Figure 3 This is a schematic diagram of the structural unit structure of an embodiment of the present invention in a switching state;

[0035] Figure 4 This is a schematic diagram of the terahertz wave transmission spectrum of the unit structure in the switching state according to an embodiment of the present invention;

[0036] Figure 5 This is a broadband response diagram of the modulation depth according to an embodiment of the present invention;

[0037] Figure 6 This is a schematic diagram of the control circuit of the modulator according to an embodiment of the present invention;

[0038] Figure 7 This is a schematic diagram of various spatial coding patterns generated by the modulator in an embodiment of the present invention.

[0039] Among them, 1. upper quartz substrate; 2. upper metal grating; 3. upper pre-aligned film; 4. liquid crystal layer; 5. lower pre-aligned film; 6. lower metal grating; 7. lower quartz substrate. Detailed Implementation

[0040] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0041] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0042] like Figure 1 As shown, this embodiment provides a terahertz liquid crystal spatial light modulator with large modulation depth and ultra-wideband, featuring large modulation depth, ultra-wideband, and large-scale array characteristics. Through pixelated electrical addressing, various spatial modulation patterns can be generated in the intensity distribution of the transmitted terahertz wave. Specifically, it includes:

[0043] The upper quartz substrate 1, the upper metal grating 2, the upper pre-aligned film 3, the liquid crystal layer 4, the lower pre-aligned film 5, the lower metal grating 6, and the lower quartz substrate 7 are stacked in sequence.

[0044] Among them, the upper metal grating 2 and the lower metal grating 6 are arranged orthogonally in space to form a Fabry-Perot cavity, and the transmitted wave can achieve a large modulation depth of ultra-wideband.

[0045] The liquid crystal layer 4 is filled between the upper pre-aligned film 3 and the lower pre-aligned film 5, and the liquid crystal pointer has in-plane pre-alignment.

[0046] The upper metal grating 2 and the lower metal grating 6 serve as the first electrode and the second electrode, respectively, to receive external voltage and control the dynamic switching of the liquid crystal pointing vector between the in-plane state and the out-of-plane state.

[0047] The modulator controls the state of the liquid crystal pointing vector to change the polarization conversion characteristics of the terahertz wave in the Fabry-Perot cavity, thereby achieving spatial modulation of the intensity of the incident terahertz wave.

[0048] More specifically, in this embodiment, the upper metal grating 2 and the lower metal grating 6 are grown on the upper quartz layer and the lower quartz layer, respectively, and their directions are orthogonal;

[0049] The upper pre-aligned film 3 and the lower pre-aligned film 5 are located on the upper metal structure and the lower metal structure, respectively, and the liquid crystal is placed between the upper pre-aligned film 3 and the lower pre-aligned film 5 to achieve the pre-alignment of the liquid crystal pointing vector.

[0050] Furthermore, the broadband modulation principle of this embodiment is as follows: when no voltage is applied between the upper metal grating 2 and the lower metal grating 6, the liquid crystal pointer is in-plane, and the in-plane anisotropy combined with the polarization selectivity of the metal grating achieves broadband orthogonal polarization conversion output of the transmitted light; when a voltage is applied between the upper metal grating 2 and the lower metal grating 6, the liquid crystal pointer is out-of-plane, exhibiting in-plane isotropy, and the orthogonality of the upper metal grating 2 and the lower metal grating 6 leads to broadband extinction of the transmitted light.

[0051] Furthermore, the upper metal grating 2 and the lower metal grating 6 have the same deep subwavelength periodic structure;

[0052] The grating period of the upper metal grating 2 and the lower metal grating 6 ranges from 30 to 50 micrometers, the grating width is 15 to 25 micrometers, and the thickness is 100 to 300 nanometers. Furthermore, within the operating frequency band of 0.2 to 1 THz, the grating period size is smaller than the terahertz wavelength, enabling the metal grating to selectively transmit and reflect orthogonal polarization components.

[0053] Furthermore, the materials used to manufacture the upper metal grating 2 and the lower metal grating 6 include gold, aluminum, and copper;

[0054] Among them, the upper metal grating 2 has high transmittance for terahertz waves in the first polarization direction and high reflectivity for terahertz waves in the second polarization direction.

[0055] The lower metal grating 6 has high transmittance for terahertz waves in the second polarization direction and high reflectivity for terahertz waves in the first polarization direction.

[0056] Furthermore, in this embodiment, the upper metal grating 2 and the lower metal grating 6 are made of good conductors such as gold, aluminum, and copper.

[0057] Furthermore, in this embodiment, the upper metal grating 2 and the lower metal grating 6 are grown on the upper quartz layer and the lower quartz layer respectively by gold film evaporation, photolithography, and etching processes, and their directions are orthogonal.

[0058] Furthermore, the upper quartz substrate 1 and the lower quartz substrate 7 have a thickness of 500 micrometers, and the upper metal grating 2 and the lower metal grating 6 have a grating period of 40 micrometers, a grating width of 20 micrometers, and a thickness of 200 nm. In the operating frequency range of 0.2-1 THz, the grating period is much smaller than the wavelength.

[0059] Furthermore, the upper metal grating 2 and the lower metal grating 6 exhibit excellent polarization selectivity characteristics. The upper metal grating 2 has high transmittance for y-polarized light and high reflectivity for x-polarized light, while the lower metal grating 6 has high transmittance for x-polarized light and high reflectivity for y-polarized light.

[0060] Furthermore, the liquid crystal layer 4 is made of a nematic liquid crystal material with a high birefringence coefficient, an ordinary light refractive index of 1.59±0.05, an extraordinary light refractive index of 1.88±0.05, and a thickness of 200-400 micrometers.

[0061] Furthermore, the liquid crystal layer 4 involved in this embodiment uses a high birefringence nematic liquid crystal with an ordinary light refractive index of n. o =1.59+0.02i; the unusual refractive index is n e =1.88+0.01i, liquid crystal thickness 300 micrometers.

[0062] Furthermore, the upper pre-alignment film 3 and the lower pre-alignment film 5 define the pre-alignment direction of the liquid crystal pointer as an in-plane direction, and the pre-alignment direction forms a 45° angle with both the upper metal grating 2 and the lower metal grating 6.

[0063] Furthermore, in this embodiment, the upper pre-aligned film 3 and the lower pre-aligned film 5 are located on the upper metal grating 2 and the lower metal grating 6, respectively, and the liquid crystal layer 4 is placed between the upper pre-aligned film 3 and the lower pre-aligned film 5 to achieve in-plane 45-degree pre-alignment of the liquid crystal pointing vector.

[0064] Furthermore, the upper metal grating 2 and the lower metal grating 6 both serve as a pixelation control electrode array;

[0065] The upper metal grating 2 includes multiple parallel first electrode lines, and the lower metal grating 6 includes multiple parallel second electrode lines. The first electrode lines and the second electrode lines intersect orthogonally in space to form multiple modulation units.

[0066] Furthermore, the upper metal grating 2 and the lower metal grating 6 involved in this embodiment have a high extinction ratio and also serve as pixelation control electrodes to control the dynamic switching of the liquid crystal pointing vector.

[0067] Furthermore, the upper metal grating 2 and the lower metal grating 6 simultaneously serve as pixelation control electrodes, controlling the dynamic switching of the liquid crystal pointing vector in the intersection region. The liquid crystal pointing vectors of the upper metal grating 2 and the lower metal grating 6 under different applied voltages are as follows: Figure 2 As shown.

[0068] Furthermore, the vertical spacing between the upper metal grating 2 and the lower metal grating 6 constitutes the resonant cavity length of the Fabry-Perot cavity;

[0069] The length of the resonant cavity is determined by the thickness of the liquid crystal layer 4, and the resonant cavity supports broadband resonant modes in the 0.2-1 THz frequency band.

[0070] Furthermore, when no voltage is applied between the upper metal grating 2 and the lower metal grating 6, the liquid crystal director maintains an in-plane pre-alignment state, and the liquid crystal layer 4 exhibits in-plane anisotropy. After the first polarization component of the incident terahertz wave is selected by the upper metal grating 2, it undergoes phase delay in the liquid crystal layer 4 and is converted into the second polarization component, which is finally output through the lower metal grating 6.

[0071] When a 1kHz square wave AC voltage is applied and the voltage amplitude gradually increases from 0V to 20V, the liquid crystal pointing vector gradually shifts from the in-plane state to the out-of-plane state, the in-plane anisotropy of the liquid crystal layer 4 gradually weakens to isotropy, and the intensity of the transmitted second polarization component gradually decreases as the voltage increases.

[0072] Furthermore, the principle of broadband modulation is as follows: Figure 3 As shown: When no voltage is applied between the upper metal grating 2 and the lower metal grating 6, the liquid crystal pointer is in-plane, and the in-plane anisotropy combined with the polarization selectivity of the metal grating achieves broadband orthogonal polarization conversion output of the transmitted light; when a voltage is applied between the upper metal grating 2 and the lower metal grating 6, the liquid crystal pointer is out-of-plane, exhibiting in-plane isotropy, and the orthogonality of the upper metal grating 2 and the lower metal grating 6 leads to broadband extinction of the transmitted light.

[0073] The intensity spectrum of the transmitted wave under unfed and uniformly fed conditions is as follows: Figure 4 As shown, when a 20V, 1kHz square wave AC voltage is applied, broadband extinction is achieved, and the transmission intensity is almost 0, indicating that the pixel is off. As the applied voltage gradually decreases, the transmission spectrum gradually increases. When no voltage is applied, the maximum light intensity reaches 0.7, indicating that the pixel is on.

[0074] According to the intensity I in the switching state on and I off The modulation depth is defined as:

[0075] ;

[0076] Figure 5 The modulation depth spectral curves show that, in the broadband range of 0.2 THz to 1 THz, the modulation depth is greater than 75% except for the two frequency points of 0.4 THz and 0.7 THz.

[0077] Furthermore, the modulator includes N first electrode lines and M second electrode lines, where both N and M are not less than 40, forming a pixel array of size N×M;

[0078] Each first electrode line and each second electrode line are independently connected to an external control circuit via wire bonding, enabling the modulation unit in each cross region to apply voltage control independently.

[0079] Furthermore, the external control circuitry includes a printed circuit board and a multi-channel programmable voltage source;

[0080] The printed circuit board is connected to a multi-channel programmable voltage source via ribbon cables;

[0081] Under the control of the host computer, the multi-channel programmable voltage source outputs an independent 0-20V programmable voltage to each first electrode line and second electrode line. Through the voltage encoding combination of the upper and lower electrodes, different spatial modulation patterns are generated on the N×M pixel array.

[0082] Furthermore, in this embodiment, the overlapping area of ​​the upper metal grating 2 and the lower metal grating 6 is a liquid crystal injection area. The exposed portions on both sides are connected to an external control circuit by wire bonding. The external control circuit is connected to a multi-channel programmable voltage source. The voltage on each grating of the upper metal grating 2 and the lower metal grating 6 can be independently controlled by the host computer to generate different spatial modulation patterns.

[0083] More specifically, the overlapping area of ​​the upper metal grating 2 and the lower metal grating 6 is the liquid crystal injection area. The exposed portions on both sides are connected to the electrodes of the printed circuit board via wire bonding. The printed circuit board is further connected to a multi-channel programmable voltage source via ribbon cables. The voltage on each grating of the upper metal grating 2 and the lower metal grating 6 can be independently controlled by the host computer. The control process is as follows: Figure 6 As shown.

[0084] This embodiment includes 40 independently controllable upper-layer metal gratings 2 and 40 independently controllable lower-layer metal gratings 6. Through upper and lower layer voltage encoding, different 40*40 pixel spatial modulation patterns can be generated. Some results are shown below. Figure 7 As shown.

[0085] As an additional implementation method, the performance testing steps for the modulator in this embodiment include:

[0086] The terahertz liquid crystal spatial light modulator is connected to a multi-channel programmable voltage source and placed on a two-dimensional translation stage. Its position is adjusted so that it is located at the terahertz focusing spot of the terahertz time-domain spectroscopy system.

[0087] Adjust the terahertz transmitting and receiving antennas so that the polarization direction of the incident terahertz wave is perpendicular to the first grating of the modulator, and the polarization direction of the probe antenna is perpendicular to the second grating of the modulator. Test the terahertz spectrum of the orthogonal polarization components. By making the polarization direction of the probe antenna the same as that of the transmitting antenna, the transmission spectrum of the same polarization components can be tested without applying voltage, and then the polarization conversion rate spectrum can be calculated.

[0088] Apply the same square wave voltage of 1 kHz to all upper electrodes of the modulator and gradually increase it from 0V to 20V. With all lower electrodes grounded, test the terahertz spectral changes of the orthogonal polarization components. It can be seen that the broadband amplitude spectrum gradually weakens to complete extinction, thus obtaining the modulation depth of the amplitude in the broadband range.

[0089] By applying different coded voltages to the upper and lower electrodes, and simultaneously scanning the modulator step-by-step through the two-dimensional translation stage, and probing the spectrum at each position, the spatial modulation pattern of the modulator at different frequencies can be obtained.

[0090] This embodiment simultaneously overcomes the technical bottlenecks in three aspects: large modulation depth, wide bandwidth, and large-scale array, greatly improving the overall performance of terahertz spatial light modulators and demonstrating extremely flexible spatial light field modulation capabilities. It has excellent application prospects in realizing terahertz dynamic beam scanning and terahertz single-pixel imaging.

[0091] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A terahertz liquid crystal spatial light modulator with large modulation depth and ultra-wideband, characterized in that, Comprise: Upper layer quartz substrate, upper layer metal grating, upper layer pre-alignment film, liquid crystal layer, lower layer pre-alignment film, lower layer metal grating and lower layer quartz substrate are arranged in sequence; Wherein, the upper layer metal grating and the lower layer metal grating are arranged orthogonally in space, forming a Fabry-Perot cavity; The liquid crystal layer is filled between the upper layer pre-alignment film and the lower layer pre-alignment film, and the liquid crystal director has in-plane pre-alignment; The upper layer metal grating and the lower layer metal grating are used as first electrode and second electrode respectively, for receiving external voltage, controlling the dynamic switching of liquid crystal director between in-plane state and out-of-plane state; The modulator changes the polarization conversion characteristics of terahertz wave in the Fabry-Perot cavity by controlling the state of liquid crystal director, realizing the spatial modulation of incident terahertz wave intensity.

2. The terahertz liquid crystal spatial light modulator according to claim 1, wherein: The upper layer metal grating and the lower layer metal grating have the same deep subwavelength periodic structure; The grating period of the upper layer metal grating and the lower layer metal grating ranges from 30 to 50 microns, the grating width ranges from 15 to 25 microns, the thickness ranges from 100 to 300 nanometers, and in the working frequency band of 0.2-1 THz, the grating period size is smaller than the terahertz wavelength, so that the metal grating has selective transmission and reflection characteristics for orthogonal polarization components.

3. The terahertz liquid crystal spatial light modulator according to claim 1, wherein: The material of the upper layer metal grating and the lower layer metal grating includes gold, aluminum and copper; The upper layer metal grating has high transmissivity for terahertz wave of the first polarization direction and high reflectivity for terahertz wave of the second polarization direction; The lower layer metal grating has high transmissivity for terahertz wave of the second polarization direction and high reflectivity for terahertz wave of the first polarization direction.

4. The terahertz liquid crystal spatial light modulator according to claim 1, wherein: The liquid crystal layer adopts high-birefringence nematic liquid crystal material, the ordinary light refractive index is 1.59±0.05, the extraordinary light refractive index is 1.88±0.05, and the liquid crystal layer thickness is 200-400 microns.

5. The terahertz liquid crystal spatial light modulator according to claim 1, wherein: The upper layer pre-alignment film and the lower layer pre-alignment film limit the pre-alignment direction of the liquid crystal director to in-plane direction, and the pre-alignment direction forms a 45° angle with the upper layer metal grating and the lower layer metal grating.

6. The terahertz liquid crystal spatial light modulator according to claim 1, wherein: The upper layer metal grating and the lower layer metal grating simultaneously serve as a pixelated control electrode array; The upper layer metal grating includes a plurality of first electrode lines arranged in parallel, the lower layer metal grating includes a plurality of second electrode lines arranged in parallel, and the first electrode lines and the second electrode lines orthogonally intersect in space to form a plurality of modulation units.

7. The terahertz liquid crystal spatial light modulator according to claim 1, wherein: The vertical spacing between the upper layer metal grating and the lower layer metal grating constitutes the resonant cavity length of the Fabry-Perot cavity. The length of the resonant cavity is determined by the thickness of the liquid crystal layer, and the resonant cavity supports broadband resonant modes in the 0.2-1 THz frequency band.

8. The terahertz liquid crystal spatial light modulator according to claim 1, characterized in that, When no voltage is applied between the upper metal grating and the lower metal grating, the liquid crystal director maintains an in-plane pre-alignment state, and the liquid crystal layer exhibits in-plane anisotropy. After the first polarization component of the incident terahertz wave is selected by the upper metal grating, it undergoes phase delay in the liquid crystal layer and is converted into the second polarization component, which is finally output through the lower metal grating. When a 1kHz square wave AC voltage is applied and the voltage amplitude gradually increases from 0V to 20V, the liquid crystal pointing vector gradually shifts from the in-plane state to the out-of-plane state, the in-plane anisotropy of the liquid crystal layer gradually weakens to isotropy, and the intensity of the transmitted second polarization component gradually decreases as the voltage increases.

9. The terahertz liquid crystal spatial light modulator according to claim 1, characterized in that, The modulator includes N first electrode lines and M second electrode lines, where both N and M are not less than 40, forming an N×M pixel array; Each first electrode line and each second electrode line are independently connected to an external control circuit via wire bonding, enabling the modulation unit in each cross region to apply voltage control independently.

10. The terahertz liquid crystal spatial light modulator according to claim 9, characterized in that, The external control circuit includes a printed circuit board and a multi-channel programmable voltage source; The printed circuit board is connected to the multi-channel programmable voltage source via a ribbon cable; Under the control of the host computer, the multi-channel programmable voltage source outputs an independent 0-20V programmable voltage to each first electrode line and second electrode line. Through the voltage encoding combination of the upper and lower electrodes, different spatial modulation patterns are generated on the N×M pixel array.

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