A range-extending reflective phase shifter for in-plane isotropic liquid crystals and its fabrication method

Abstract

This invention relates to a range-extending reflective phase shifter for in-plane isotropic liquid crystals and its fabrication method, belonging to the field of terahertz modulation device technology. It addresses the issue of expanding the applicability of reflective phase-shifting liquid crystals. The invention comprises a first quartz substrate, a wire grid layer, a first polyimide alignment layer, a liquid crystal layer, a second polyimide alignment layer, a rod-shaped metasurface layer, a polyimide layer, a reflective layer, and a second quartz substrate connected sequentially. The wire grid layer is a subwavelength strip array structure composed of periodically arranged metal strips extending along the y-direction. The wire grid layer serves as a polarization selector, enabling terahertz waves in the x-direction to pass through with high transmittance and terahertz waves in the y-direction to be reflected with high reflectivity. The rod-shaped metasurface layer is composed of periodically arranged metal rods. The rod-shaped metasurface layer, along with the polyimide layer and the reflective layer, works together to achieve polarization conversion. This invention achieves wide-range, reconfigurable phase modulation in the terahertz frequency band.

Description

Technical Field

[0001] This invention belongs to the field of terahertz modulation device technology, specifically relating to a range extender reflective phase shifter for in-plane isotropic liquid crystals and its fabrication method. Background Technology

[0002] Terahertz waves, with frequencies between microwaves and infrared (0.1-10 THz), have broad application potential in fields such as security detection, communication, materials analysis, and medical imaging, thus becoming an important area in scientific research and technological development. Traditional terahertz functional devices often suffer from problems such as large size, fixed function, and low efficiency. However, liquid crystal metasurfaces, with their subwavelength-scale unit structure, can flexibly and efficiently control the amplitude, phase, and polarization state of terahertz waves, providing a unique solution for achieving the thinning and integration of terahertz systems.

[0003] Terahertz reflective liquid crystal phase shifters are key components in terahertz wavefront dynamic modulation and beamforming systems, and have attracted much attention in recent years due to their outstanding advantages in precise phase control and system integration. Based on the electric field-tunable birefringence properties of liquid crystal materials, combined with a reflective unit structure, a wide range of reconfigurable phase modulation can be achieved in the terahertz band, and the device configuration is compact, providing a reliable path for the development of high-performance, programmable terahertz functional components.

[0004] With the increasing application of terahertz technology in fields such as 6G communication, high-resolution imaging, and precision sensing, reflective liquid crystal phase shifters, with their large modulation depth, have become an ideal choice for realizing terahertz phased array systems. This device can serve as an array unit, enabling functions such as dynamic beam scanning, multi-beam generation, and directional signal transmission, which can greatly promote the development of terahertz beam control systems towards low power consumption, high integration, and reconfigurability.

[0005] Current optical path phase accumulation terahertz reflective phase shifters often employ a sandwich structure containing a gold reflective layer and transparent electrodes, and primarily use nematic liquid crystals. Other types of liquid crystals, especially in-plane isotropic liquid crystals (ICLs), are not suitable, including cholesteric, twisted nematic, polymer network liquid crystals, and blue phase liquid crystals. Because the phase shift modulation range of these liquid crystals is evenly distributed along orthogonal polarization directions, polarized light can theoretically only utilize the maximum half of the maximum birefringence. These other types of liquid crystals have advantages over nematic liquid crystals in terms of response time, driving voltage, and crosstalk spacing. Therefore, there is an urgent need to develop a device design method that can incorporate in-plane isotropic liquid crystals, expanding the applicability of reflective phase shifting devices. Summary of the Invention

[0006] The problem to be solved by this invention is to expand the application range of liquid crystal reflective phase shifting devices, and to propose a range-extending reflective phase shifter for in-plane isotropic liquid crystals and its preparation method.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A range-extending reflective phase shifter for in-plane isotropic liquid crystals includes a first quartz substrate, a wire grid layer, a first polyimide alignment layer, a liquid crystal layer, a second polyimide alignment layer, a rod-shaped metasurface layer, a polyimide layer, a reflective layer, and a second quartz substrate.

[0009] The first quartz substrate, the wire grid layer, the first polyimide orientation layer, the liquid crystal layer, the second polyimide orientation layer, the rod-shaped metasurface layer, the polyimide layer, the reflective layer, and the second quartz substrate are connected in sequence.

[0010] The wire grid layer is a subwavelength strip array structure, composed of periodically arranged metal strip structures. The metal strips extend along the y-direction. The function of the wire grid layer is polarization selection, enabling terahertz waves in the x-direction to pass through with high transmittance and terahertz waves in the y-direction to be reflected with high reflectance.

[0011] The rod-shaped metasurface layer is composed of a periodically arranged metal rod structure. The metal rods are tilted at 45° relative to the x-direction. The rod-shaped metasurface layer, the polyimide layer, and the reflective layer work together to excite dipole resonance. The transmission component of the dipole resonance is reflected by the polyimide layer and the reflective layer and then superimposed with the reflection component to achieve polarization conversion.

[0012] Furthermore, the period of the wire grid layer is 0.1-0.4 times the wavelength, the width of each period of the wire grid layer is 0.3-0.7 times the period, the metal material of the wire grid layer is gold, silver or aluminum, and the thickness is 10-300nm.

[0013] Furthermore, applying different voltages to the grid layer adjusts the overall deflection effect of the liquid crystal layer.

[0014] Furthermore, the period of the rod-shaped metasurface layer is 0.2-0.4 times the center wavelength of the design band, and the metal material of the rod-shaped metasurface layer is gold, silver or aluminum, with a thickness of 10-300 nm.

[0015] Furthermore, the thickness of the polyimide layer is 0.15-0.2 times the wavelength.

[0016] Furthermore, the metallic material of the reflective layer is gold, silver, or aluminum, and the thickness is 10-300 nm.

[0017] Furthermore, the liquid crystal layer is made of a liquid crystal material with the same equivalent refractive index in the horizontal and vertical directions, including one of cholesteric phase, twisted nematic phase, polymer network liquid crystal, and blue phase liquid crystal.

[0018] Furthermore, the total phase shift of the range extender / reflector phase shifter for in-plane isotropic liquid crystal is:

[0019]

[0020] in, λ represents the birefringence of the liquid crystal, d is the thickness of the liquid crystal layer, and λ is the incident wavelength.

[0021] A method for fabricating a range-extending reflective phase shifter for in-plane isotropic liquid crystals includes the following steps:

[0022] Step 1. Spin-coat photoresist onto a clean No. 1 quartz substrate, and perform pre-baking, exposure, post-baking, and development to prepare a grid layer pattern structure;

[0023] Step 2. Deposit metal material on the wire grid layer pattern structure obtained in Step 1, and remove residual photoresist to obtain the first sample;

[0024] Step 3. Deposit a metallic material as a reflective layer on a clean No. 2 quartz substrate to obtain the second sample;

[0025] Step 4. Prepare a polyimide layer on the second sample and bake it at high temperature. First, keep it at 100-150℃ for 1-1.2h, then keep it at 240-300℃ for 0.5-2h. The heating rate during the heating process shall not exceed 1℃ / min to obtain the third sample.

[0026] Step 5. Spin-coat photoresist onto the third sample, perform pre-baking, exposure, post-baking, and development to prepare a rod-shaped metasurface pattern structure;

[0027] Step 6. Deposit metal material on the rod-shaped metasurface pattern structure and remove residual photoresist to obtain the fourth sample;

[0028] Step 7. Spin-coat the first polyimide orientation layer onto the first sample and the second polyimide orientation layer onto the fourth sample, and bake at high temperature of 200-300℃ for 0.5-2h; then perform rubbing orientation on the two types of samples, with the orientation directions of the two types of samples being antiparallel to each other and perpendicular to the grid direction.

[0029] Step 8. Adhere the first and fourth samples after the treatment in Step 7. Use gaskets to support the two sides of the samples, leave space in the central area, cover the space with the structure, and place the alignment layer inward to obtain the liquid crystal cell.

[0030] Step 9. Fill the prepared liquid crystal cell with liquid crystal and encapsulate it to obtain the range extender reflector phase shifter for in-plane isotropic liquid crystal.

[0031] Furthermore, the methods for preparing patterned structures include ultraviolet exposure, laser direct writing, electron beam exposure, or nanoimprinting; the methods for depositing metallic materials include magnetron sputtering, spin coating, electron beam evaporation, or chemical vapor deposition.

[0032] The beneficial effects of this invention are:

[0033] This invention discloses a range-extending reflective phase shifter for in-plane isotropic liquid crystals, addressing the need to increase the phase shift range of in-plane isotropic liquid crystals for terahertz reflective phase shifters. By introducing a cross-polarized metasurface into the sandwich liquid crystal phase shifter structure, incident polarized light can pass through the liquid crystal dielectric layer in an orthogonal polarization manner, effectively doubling the optical path. This allows full utilization of the maximum birefringence of the in-plane isotropic liquid crystal, increasing the phase shift depth while reducing the driving voltage and crosstalk spacing. The device can be fabricated using only a sandwich liquid crystal cell structure and ultraviolet lithography, resulting in low cost, high integration, simple fabrication process, and compatibility with semiconductor processes. This device achieves wide-range, reconfigurable phase modulation in the terahertz band and features a compact configuration, providing a reliable path for the development of high-performance, programmable terahertz functional components. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of a range extender reflector phase shifter for in-plane isotropic liquid crystal according to the present invention;

[0035] Figure 2 This is a schematic diagram of the periodically arranged metal rod structure units in the rod-shaped metasurface layer of the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described specific embodiments are merely a part of the embodiments of the invention, and not all of them. The components of the specific embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations, and the invention may also have other embodiments.

[0037] Therefore, the following detailed description of specific embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected specific embodiments of the invention. All other specific embodiments obtained by those skilled in the art based on these specific embodiments without inventive effort are within the scope of protection of this invention.

[0038] To further understand the invention's content, features, and effects, the following specific embodiments are provided, along with accompanying drawings. Figure 1 and attached Figure 2 Detailed explanation is as follows:

[0039] Example 1:

[0040] A range-extending reflective phase shifter for in-plane isotropic liquid crystal includes a first quartz substrate 1, a wire grid layer 2, a first polyimide alignment layer 3, a liquid crystal layer 4, a second polyimide alignment layer 5, a rod-shaped metasurface layer 6, a polyimide layer 7, a reflective layer 8, and a second quartz substrate 9.

[0041] The first quartz substrate 1, the wire grid layer 2, the first polyimide alignment layer 3, the liquid crystal layer 4, the second polyimide alignment layer 5, the rod-shaped metasurface layer 6, the polyimide layer 7, the reflective layer 8, and the second quartz substrate 9 are connected in sequence.

[0042] The wire grid layer 2 is a subwavelength strip array structure, composed of periodically arranged metal strip structures. The metal strips extend along the y-direction. The function of the wire grid layer 2 is polarization selection, enabling terahertz waves in the x-direction to pass through with high transmittance and terahertz waves in the y-direction to be reflected with high reflectance.

[0043] The rod-shaped metasurface layer 6 is composed of a periodically arranged metal rod structure. The metal rods are inclined at 45° relative to the x-direction. The rod-shaped metasurface layer 6, the polyimide layer 7, and the reflective layer 8 work together to excite dipole resonance. The transmission component of the dipole resonance is reflected by the polyimide layer 7 and the reflective layer 8 and then superimposed with the reflection component to achieve polarization conversion.

[0044] Furthermore, the period of the wire gate layer 2 is 0.1-0.4 times the wavelength, the width of each period of the wire gate layer 2 is 0.3-0.7 times the period, the metal material of the wire gate layer is gold, silver or aluminum, and the thickness is 10-300nm.

[0045] Furthermore, applying different voltages to the grid layer 2 adjusts the overall deflection effect of the liquid crystal layer 4.

[0046] Furthermore, the period of the rod-shaped metasurface layer 6 is 0.2-0.4 times the center wavelength of the design band, and the metal material of the rod-shaped metasurface layer 6 is gold, silver or aluminum, with a thickness of 10-300nm.

[0047] Furthermore, the thickness of the polyimide layer 7 is 0.15-0.2 times the wavelength.

[0048] Furthermore, the metallic material of the reflective layer 8 is gold, silver, or aluminum, and the thickness is 10-300 nm.

[0049] Furthermore, the liquid crystal layer 4 is made of a liquid crystal material with the same equivalent refractive index in the horizontal and vertical directions, including one of cholesteric phase, twisted nematic phase, polymer network liquid crystal, and blue phase liquid crystal.

[0050] Furthermore, the total phase shift of the range extender / reflector phase shifter for in-plane isotropic liquid crystal is:

[0051]

[0052] in, λ represents the birefringence of the liquid crystal, d is the thickness of the liquid crystal layer, and λ is the incident wavelength.

[0053] The device operates as follows: When a terahertz wave with x-polarization is incident on the device, it first passes through the wire grating metasurface layer 2. Since the wire grating metasurface extends in the y-direction, the terahertz wave will achieve high transmittance as it passes through the wire grating. After the terahertz wave passes through the in-plane isotropic liquid crystal layer, phase accumulation is achieved. The terahertz wave reaches the cross-polarized metasurface layer 4, where it is reflected and converted into a wave in the y-direction. This terahertz wave then passes through the liquid crystal layer again, resulting in phase accumulation. The reflected terahertz wave reaches the grating metasurface layer 2. Since the polarization direction is the y-direction and coincides with the direction of grating extension, the terahertz wave is prevented from escaping, resulting in high reflectivity. The reflected terahertz wave remains along the y-direction and, after passing through the liquid crystal layer again, achieves phase accumulation. The wave then reaches the cross-polarized metasurface layer 4 again, where it is reflected and converted into a wave in the x-direction. This terahertz wave then passes through the liquid crystal layer again, resulting in phase accumulation. The terahertz wave then reaches the wire grid metasurface layer 2 again. Since the polarization direction is perpendicular to the x-direction and the direction of wire grid extension, the terahertz wave will achieve higher transmittance as it passes through the wire grid and eventually exits the device.

[0054] Since in-plane isotropic liquid crystals achieve the same optical path accumulation when polarized light in both the x and y directions passes through the liquid crystal layer, their birefringence in the x and y directions is equal. Furthermore, the birefringence of the cholesteric liquid crystal is provided by the nematic liquid crystal matrix, and its texture is formed by the twisting and rotation of nematic liquid crystal matrix molecules in different planes. The helical axis is along the thickness direction, and the pitch is much smaller than the wavelength. Additionally, the projection of the director of the nematic liquid crystal matrix molecules onto the helical axis is negligible. Let the birefringence of the nematic liquid crystal matrix be... Then there is Since the terahertz wave oscillates four times within the device, the total phase shift is... .

[0055] If a traditional reflective phase shifter architecture is used, for an in-plane isotropic liquid crystal, the terahertz wave will pass through twice and exit, resulting in a total phase shift of... It is half the phase shift of the range extender phase shifter used for in-plane isotropic liquid crystals.

[0056] Therefore, the liquid crystal layer thickness required to achieve the same phase shift is also halved, which reduces parameters such as threshold voltage and crosstalk length, thus making it more advantageous in reflective arrays.

[0057] The in-plane isotropic liquid crystal layer described in this embodiment can be replaced with other liquid crystal layers such as twisted nematic liquid crystals, polymer network liquid crystals, and blue phase liquid crystals. Furthermore, this device expands the application of in-plane isotropic liquid crystals in phase shifters, helping to further improve the overall device performance. Specifically, even at the same thickness, cholesteric liquid crystals can reduce parameters such as the threshold voltage of the device compared to matrix nematic liquid crystals; this improvement is achieved through the electroelastic effect of liquid crystals. According to the electroelastic theory of liquid crystals, the threshold voltage of the liquid crystal is... The equivalent elastic constant of a nematic liquid crystal during operation is: The equivalent elastic constant of cholesteric liquid crystal is After screening, the threshold voltage reduction can be obtained by calculating the elastic constant of the nematic liquid crystal substrate used.

[0058] Example 2:

[0059] A method for fabricating a range-extending reflective phase shifter for in-plane isotropic liquid crystals includes the following steps:

[0060] Step 1. Spin-coat photoresist onto a clean No. 1 quartz substrate, and perform pre-baking, exposure, post-baking, and development to prepare a grid layer pattern structure;

[0061] Step 2. Deposit metal material on the wire grid layer pattern structure obtained in Step 1, and remove residual photoresist to obtain the first sample;

[0062] Step 3. Deposit a metallic material as a reflective layer on a clean No. 2 quartz substrate to obtain the second sample;

[0063] Step 4. Prepare a polyimide layer on the second sample and bake it at high temperature. First, keep it at 100-150℃ for 1-1.2h, then keep it at 240-300℃ for 0.5-2h. The heating rate during the heating process shall not exceed 1℃ / min to obtain the third sample.

[0064] Step 5. Spin-coat photoresist onto the third sample, perform pre-baking, exposure, post-baking, and development to prepare a rod-shaped metasurface pattern structure;

[0065] Step 6. Deposit metal material on the rod-shaped metasurface pattern structure and remove residual photoresist to obtain the fourth sample;

[0066] Step 7. Spin-coat the first polyimide orientation layer onto the first sample and the second polyimide orientation layer onto the fourth sample, and bake at high temperature of 200-300℃ for 0.5-2h; then perform rubbing orientation on the two types of samples, with the orientation directions of the two types of samples being antiparallel to each other and perpendicular to the grid direction.

[0067] Step 8. Adhere the first and fourth samples after the treatment in Step 7. Use gaskets to support the two sides of the samples, leave space in the central area, cover the space with the structure, and place the alignment layer inward to obtain the liquid crystal cell.

[0068] Step 9. Fill the prepared liquid crystal cell with liquid crystal and encapsulate it to obtain the range extender reflector phase shifter for in-plane isotropic liquid crystal.

[0069] Furthermore, the methods for preparing patterned structures include ultraviolet exposure, laser direct writing, electron beam exposure, or nanoimprinting; the methods for depositing metallic materials include magnetron sputtering, spin coating, electron beam evaporation, or chemical vapor deposition.

[0070] Furthermore, the method for removing residual photoresist in steps 2 and 6 can be one or more of the following: acetone / NMP organic solvent dissolution / reactive ion etching, preferably NMP organic solvent dissolution. The polyimide preparation method in step 4 can be one or more of the following: spin coating, blade coating, multiple spin coating / blade coating, casting, molding, etc., preferably spin coating.

[0071] Example 3:

[0072] A range-extending reflective phase shifter for in-plane isotropic liquid crystal includes a quartz substrate, a wire grid layer, a liquid crystal layer, and a metasurface layer stacked sequentially; specifically, it includes: a quartz substrate 1, a wire grid metasurface layer 2, an in-plane isotropic liquid crystal layer 3, a cross-polarized metasurface 4, and a quartz substrate 5.

[0073] The period of the wire grating metasurface 2 is below the wavelength; in a specific example, one-fifth of the wavelength is used as the wire grating period. The wire grating is fabricated using standard photolithography, extending in the y-direction, and the gold layer used for the wire grating is 100 nm thick. This wire grating metasurface is used for polarization selection in the device, allowing only light perpendicular to the wire grating extension direction to enter and exit the wire grating with high transmittance, while orthogonally polarized directions are reflected. This wire grating also serves as an electrode for the liquid crystal layer, and the metal material of the wire grating is conductive.

[0074] Furthermore, this wire grid is used in the device as a terahertz transparent electrode with polarization selectivity.

[0075] The in-plane isotropic liquid crystal layer 3 is characterized in that when polarized light in both the x and y directions passes through the liquid crystal layer, the same optical path accumulation is obtained. Here, the liquid crystal layer is used to provide the overall phase retardation of the device. Typical isotropic liquid crystal layers include cholesteric phase, twisted nematic phase, polymer network liquid crystal, and blue phase liquid crystal, etc., and cholesteric liquid crystal is used as an example here.

[0076] The cross-polarized metasurface 4 employs a two-layer metasurface structure, comprising a rod-shaped metasurface 6, a polyimide dielectric layer 7, and a gold reflective layer 8. The unit period of the rod-shaped metasurface is one-third of the wavelength. The thickness of the polyimide dielectric layer is 30 μm.

[0077] In the preparation of the cross-polarized metasurface, a gold layer with a thickness of 100 nm is first magnetron sputtered on a quartz substrate, followed by a polyimide layer spin-coated at a speed of 1000 r / min, and finally the rod-shaped metasurface structure is fabricated using standard ultraviolet lithography.

[0078] Cross-polarized metasurfaces are used to convert incident linearly polarized light in the x / y polarization direction into linearly polarized light in the y / x polarization direction with higher reflectivity.

[0079] The cholesteric liquid crystal used was prepared by adding chiral agent S811 to a nematic liquid crystal, with a birefringence of 0.3 in the nematic liquid crystal matrix. The liquid crystal layer was filled with liquid crystal by capillary filling, and the thickness of the liquid crystal layer was 500 μm. The alignment method was double-sided antiparallel tribological alignment. The alignment layer was a polyimide alignment layer, which was prepared by spin coating on the side of the wire grid metasurface 2 and the cross-polarized metasurface 4 near the liquid crystal.

[0080] Overall, the device operates as follows: When a terahertz wave with x-polarization is incident on the device, it first passes through the wire grating metasurface layer 2. Since the wire grating metasurface extends in the y-direction, the terahertz wave will achieve high transmittance as it passes through the wire grating. After the terahertz wave passes through the in-plane isotropic liquid crystal layer, phase accumulation is achieved. The terahertz wave reaches the cross-polarized metasurface layer 4, where it is reflected and converted into a wave in the y-direction. This terahertz wave then passes through the liquid crystal layer again, resulting in phase accumulation. The reflected terahertz wave reaches the grating metasurface layer 2. Since the polarization direction is the y-direction and coincides with the direction of grating extension, the terahertz wave is prevented from escaping, resulting in high reflectivity. The reflected terahertz wave remains along the y-direction and, after passing through the liquid crystal layer again, achieves phase accumulation. The wave then reaches the cross-polarized metasurface layer 4 again, where it is reflected and converted into a wave in the x-direction. This terahertz wave then passes through the liquid crystal layer again, resulting in phase accumulation. The terahertz wave then reaches the wire grid metasurface layer 2 again. Since the polarization direction is perpendicular to the x-direction and the direction of wire grid extension, the terahertz wave will achieve higher transmittance as it passes through the wire grid and eventually exits the device.

[0081] Since in-plane isotropic liquid crystals achieve the same optical path accumulation when polarized light in both the x and y directions passes through the liquid crystal layer, their birefringence in the x and y directions is equal. Furthermore, the birefringence of the cholesteric liquid crystal is provided by the nematic liquid crystal matrix, and its texture is formed by the twisting and rotation of nematic liquid crystal matrix molecules in different planes. The helical axis is along the thickness direction, and the pitch is much smaller than the wavelength. Additionally, the projection of the director of the nematic liquid crystal matrix molecules onto the helical axis is negligible. Let the birefringence of the nematic liquid crystal matrix be... Then there is Since the terahertz wave oscillates four times within the device, the total phase shift is... .

[0082] If a traditional reflective phase shifter architecture is used, for an in-plane isotropic liquid crystal, the terahertz wave will pass through twice and exit, resulting in a total phase shift of... It is half the phase shift of the range extender phase shifter used for in-plane isotropic liquid crystals.

[0083] Therefore, the liquid crystal layer thickness required to achieve the same phase shift is also halved, which reduces parameters such as threshold voltage and crosstalk length, thus making it more advantageous in reflective arrays.

[0084] The in-plane isotropic liquid crystal layer described in this embodiment can be replaced with other liquid crystal layers such as twisted nematic liquid crystals, polymer network liquid crystals, and blue phase liquid crystals. Furthermore, this device expands the application of in-plane isotropic liquid crystals in phase shifters, helping to further improve the overall device performance. Specifically, even at the same thickness, cholesteric liquid crystals can reduce parameters such as the threshold voltage of the device compared to matrix nematic liquid crystals; this improvement is achieved through the electroelastic effect of liquid crystals. According to the electroelastic theory of liquid crystals, the threshold voltage of the liquid crystal is... The equivalent elastic constant of a nematic liquid crystal during operation is: The equivalent elastic constant of cholesteric liquid crystal is After screening, the threshold voltage reduction can be obtained by calculating the elastic constant of the nematic liquid crystal substrate used.

[0085] In summary, this implementation scheme aims to meet the urgent need for general-purpose integrated devices in the terahertz field. Addressing the requirements of basic units in terahertz liquid crystal devices, it proposes a design method for a range-extending reflective phase shifter for in-plane isotropic liquid crystals using a metasurface platform. By utilizing the cross-polarization function of the metasurface, combined with the polarization filtering function of the wire grid, the incident polarized light passes through the liquid crystal four times, effectively doubling the optical path. This allows for full utilization of the maximum birefringence of the in-plane isotropic liquid crystal, increasing the phase shift depth and reducing the driving voltage and crosstalk spacing. The advantages of this scheme include simple device structure, low cost, high integration, and good compatibility with semiconductor processes.

[0086] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0087] Although this application has been described above with reference to specific embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of this application. In particular, as long as there is no structural conflict, the features in the specific embodiments disclosed in this application can be combined with each other in any way. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, this application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A range-extending reflective phase shifter for in-plane isotropic liquid crystals, characterized in that, It includes a first quartz substrate (1), a wire grid layer (2), a first polyimide orientation layer (3), a liquid crystal layer (4), a second polyimide orientation layer (5), a rod-shaped metasurface layer (6), a polyimide layer (7), a reflective layer (8), and a second quartz substrate (9). The first quartz substrate (1), the wire grid layer (2), the first polyimide orientation layer (3), the liquid crystal layer (4), the second polyimide orientation layer (5), the rod-shaped metasurface layer (6), the polyimide layer (7), the reflective layer (8), and the second quartz substrate (9) are connected in sequence. The wire grid layer (2) is a subwavelength strip array structure, composed of periodically arranged metal strip structures. The metal strips extend along the y direction. The function of the wire grid layer (2) is polarization selection, so that terahertz waves in the x direction can pass through with high transmittance and terahertz waves in the y direction can be reflected with high reflectance. The rod-shaped metasurface layer (6) is composed of periodically arranged metal rods. The metal rods are tilted at 45° relative to the x-direction. The rod-shaped metasurface layer (6), the polyimide layer (7), and the reflective layer (8) work together to excite dipole resonance. The transmission component of the dipole resonance is reflected by the polyimide layer (7) and the reflective layer (8) and then superimposed with the reflection component to achieve polarization conversion.

2. The range extender / reflector phase shifter for in-plane isotropic liquid crystal according to claim 1, characterized in that, The period of the wire grid layer (2) is 0.1-0.4 times the wavelength, the width of the wire grid layer (2) in each period is 0.3-0.7 times the period, the metal material of the wire grid layer is gold, silver or aluminum, and the thickness is 10-300nm.

3. A range-extending reflective phase shifter for in-plane isotropic liquid crystals according to claim 2, characterized in that, Applying different voltages to the grid layer (2) adjusts the overall deflection effect of the liquid crystal layer (4).

4. A range-extending reflective phase shifter for in-plane isotropic liquid crystals according to claim 3, characterized in that, The period of the rod-shaped metasurface layer (6) is 0.2-0.4 times the center wavelength of the design band, and the metal material of the rod-shaped metasurface layer (6) is gold, silver or aluminum, with a thickness of 10-300nm.

5. A range-extending reflective phase shifter for in-plane isotropic liquid crystals according to claim 4, characterized in that, The thickness of the polyimide layer (7) is 0.15-0.2 times the wavelength.

6. A range-extending reflective phase shifter for in-plane isotropic liquid crystals according to claim 5, characterized in that, The reflective layer (8) is made of gold, silver or aluminum and has a thickness of 10-300 nm.

7. A range-extending reflective phase shifter for in-plane isotropic liquid crystals according to claim 6, characterized in that, The liquid crystal layer (4) is made of liquid crystal material with the same equivalent refractive index in the horizontal and vertical directions, including one of cholesteric phase, twisted nematic phase, polymer network liquid crystal and blue phase liquid crystal.

8. A range extender / reflector phase shifter for in-plane isotropic liquid crystals according to claim 7, characterized in that, The total phase shift of the range extender / reflector phase shifter for in-plane isotropic liquid crystals is: in, λ represents the birefringence of the liquid crystal, d is the thickness of the liquid crystal layer, and λ is the incident wavelength.

9. A method for fabricating a range-extending reflective phase shifter for in-plane isotropic liquid crystals as described in any one of claims 1-8, characterized in that, Includes the following steps: Step 1. Spin-coat photoresist onto a clean No. 1 quartz substrate, and perform pre-baking, exposure, post-baking, and development to prepare a grid layer pattern structure; Step 2. Deposit metal material on the wire grid layer pattern structure obtained in Step 1, and remove residual photoresist to obtain the first sample; Step 3. Deposit a metallic material as a reflective layer on a clean No. 2 quartz substrate to obtain the second sample; Step 4. Prepare a polyimide layer on the second sample and bake it at high temperature. First, keep it at 100-150℃ for 1-1.2h, then keep it at 240-300℃ for 0.5-2h. The heating rate during the heating process shall not exceed 1℃ / min to obtain the third sample. Step 5. Spin-coat photoresist onto the third sample, perform pre-baking, exposure, post-baking, and development to prepare a rod-shaped metasurface pattern structure; Step 6. Deposit metal material on the rod-shaped metasurface pattern structure and remove residual photoresist to obtain the fourth sample; Step 7. Spin-coat the first polyimide orientation layer onto the first sample and the second polyimide orientation layer onto the fourth sample, and bake at high temperature of 200-300℃ for 0.5-2h; then perform rubbing orientation on the obtained first and fourth samples, with the orientation directions of the first and fourth samples being antiparallel to each other and perpendicular to the grid direction. Step 8. Adhere the first and fourth samples after the processing in Step 7. Use gaskets to support the first and fourth samples on both sides, leave space in the central area, cover the space area with the structure, and place the alignment layer inward to obtain the liquid crystal cell. Step 9. Fill the prepared liquid crystal cell with liquid crystal and encapsulate it to obtain the range extender reflector phase shifter for in-plane isotropic liquid crystal.

10. A method for fabricating a range-extending reflective phase shifter for in-plane isotropic liquid crystals according to claim 9, characterized in that, Methods for preparing patterned structures include ultraviolet exposure, laser direct writing, electron beam exposure, or nanoimprinting; methods for depositing metallic materials include magnetron sputtering, spin coating, electron beam evaporation, or chemical vapor deposition.

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