Ultra-wideband light field phase control device, preparation method thereof and liquid crystal element preparation method

Abstract

The application discloses an ultra-wide-band light field phase control device and a preparation method thereof, and a liquid crystal element preparation method. The light field phase control device comprises a second liquid crystal element and a first liquid crystal element which are stacked in an up-down mode. The first liquid crystal element comprises an upper glass substrate and a lower glass substrate, and a first liquid crystal body is filled between the upper glass substrate and the lower glass substrate. Liquid crystal molecules of the first liquid crystal body are uniformly arranged, and the arrangement directions of the liquid crystal molecules are consistent. The second liquid crystal element comprises an upper glass substrate and a lower glass substrate, and a second liquid crystal body is filled between the upper glass substrate and the lower glass substrate. Liquid crystal molecules of the second liquid crystal body are arranged in a non-uniform patterned twisted mode. The light field phase control device can efficiently and freely control the phase parameters of an incident light field in the visible near-infrared and even mid-infrared band, and the preparation process is simple, so that the light field phase control device can be widely used in the fields of vortex light generators, polarization gratings and holographic devices.

Description

Technical Field

[0001] This invention relates to the field of optical field phase modulation technology, specifically to an ultra-wideband optical field phase modulation device and its fabrication method, as well as a liquid crystal element fabrication method. Background Technology

[0002] With the rapid development of optical information science, optical field manipulation devices are playing an increasingly crucial role in modern optics and optical communication. Optical field manipulation is essentially the customized control of a series of physical parameters of light, such as amplitude, phase, wave vector, polarization, and frequency. Among these, the manipulation techniques targeting the phase parameter of the optical field can produce novel physical phenomena and rich optical effects, thus possessing significant research and application prospects. For example, vortex optical fields, polarization gratings, and phase holography are representative research areas in the field of optical field phase manipulation.

[0003] An optical vortex is a special type of optical field with a helical phase structure. For example... Figure 1 As shown in (a), the vortex light field possesses a unique helical phase surface and a phase singularity at the beam center, forming a special phase spatial distribution structure. This results in a ring-shaped light spot resembling an onion ring and intrinsic physical properties such as orbital angular momentum (OAM). Thanks to these novel properties, the vortex light field can be widely applied in fields such as optical communication, super-resolution imaging, particle manipulation, and quantum information processing.

[0004] A polarization grating is a type of diffractive optical device that provides polarization selection and beam deflection. For example... Figure 1 As shown in (b), its typical feature is that left-handed and right-handed circularly polarized incident light is diffracted into different propagation directions, and the left-handed / right-handed polarized diffracted light propagates only along a single diffraction order, thereby achieving polarization selectivity and near-100% diffraction efficiency. Polarization gratings have important application value in fields such as lidar, optical communication, laser processing, and polarization imaging.

[0005] Phase holography is a type of applied device that generates a target image using a specific phase distribution of an optical field. Taking Fourier transform phase holography as an example... Figure 1 As shown in (c), the phase distribution in the phase hologram records the spectral information of the target image. The propagation of the holographic light field satisfies the optical Fourier transform in the far field, thereby generating the target image at a distance or on the focal plane of a lens. Phase holographic devices have been applied in various fields such as 3D display, optical storage, optical computing, and anti-counterfeiting encryption.

[0006] In principle, optical field phase modulation devices generally use their own patterned structural units to modulate an incident light field with a uniform phase distribution into a light field with a specific spatial phase distribution. Traditional dielectric phase plates, liquid crystal waveplates, and spatial light modulators can achieve phase modulation of the optical field, but the phase modulation effect of these devices is severely wavelength dependent, which means that they are only suitable for incident light of specific wavelengths. It is difficult to maintain good performance over a wide wavelength range, which greatly limits the wide-band compatibility of vortex light and its promotion in multiple application scenarios.

[0007] To achieve broadband optical field phase modulation, there are currently two main technical approaches: metasurfaces and multilayer liquid crystal polymers. Taking vortex optical fields as an example... Figure 2 and Figure 3 The principles and practical effects of generating vortex light fields using metasurfaces and multilayer liquid crystal polymers are illustrated respectively. Among them, Figure 2 (a) shows the structure and phase distribution of the metasurface. Figure 2 (b) is a schematic diagram of the vortex light field effect in the range of 450~650nm; Figure 3 Image (a) is a schematic diagram of a multilayer liquid crystal polymer structure. Figure 3 (b) is a schematic diagram of the vortex light field effect in a wide band.

[0008] Metasurfaces are array structures containing a series of subwavelength-scale micro / nano units. By designing the structural parameters of these micro / nano units, flexible control of the optical field phase parameters can be achieved. Thanks to the rich design freedom of the metasurface unit structure (such as unit shape, size, and arrangement), optimizing the parameter combinations of each structural unit in the metasurface can effectively broaden the wavelength range compatible with optical field phase control.

[0009] Multilayer liquid crystal polymer structures can be viewed as vertically stacked monolayer liquid crystal devices. Considering that the phase modulation effect of monolayer liquid crystal devices is highly sensitive to wavelength, by using different liquid crystal materials in different layers or adjusting the alignment direction of liquid crystal molecules, corresponding dispersion compensation can be provided for light of different wavelengths, enabling the device as a whole to produce a consistent phase modulation effect over a wide wavelength range.

[0010] However, the wavelength range compatible with the optical field phase modulation performance of existing technologies for both metasurface and liquid crystal polymer devices remains insufficient, with the widest range not exceeding 500 nm, limited to the visible light band and a small portion of the near-infrared band. Furthermore, both metasurface and liquid crystal polymer devices suffer from inherent drawbacks in their fabrication methods. Metasurface devices require extremely expensive photolithography processes, resulting in complex processes, high costs, low efficiency, low tolerance for processing defects, and low yield. Multilayer liquid crystal polymer devices require multiple spin-coating and exposure operations, with stringent requirements for the thickness accuracy of each spin-coated liquid crystal polymer layer, thus also exhibiting complex processes, low tolerance for defects, and low yield. Summary of the Invention

[0011] This invention provides an ultra-wideband optical field phase modulation device and its fabrication method, as well as a liquid crystal element fabrication method, to significantly broaden the operating wavelength range of the device, reduce the process difficulty of device fabrication, and improve fabrication efficiency and yield.

[0012] Therefore, the embodiments of the present invention provide the following technical solutions:

[0013] On one hand, embodiments of the present invention provide an ultra-wideband optical field phase modulation device, comprising: a second liquid crystal element and a first liquid crystal element stacked on top of each other;

[0014] The first liquid crystal element includes an upper glass substrate and a lower glass substrate, and a first liquid crystal is filled between the upper glass substrate and the lower glass substrate; the liquid crystal molecules of the first liquid crystal are uniformly arranged, and the arrangement direction of each liquid crystal molecule is consistent, wherein the arrangement direction refers to the direction of the long axis of the liquid crystal molecule.

[0015] The second liquid crystal element includes an upper glass substrate and a lower glass substrate, with a second liquid crystal filling the space between the upper glass substrate and the lower glass substrate. The liquid crystal molecules of the second liquid crystal are arranged in a non-uniform manner, and the second liquid crystal as a whole presents a patterned spatial distribution of twist angles and is divided into different regions. The liquid crystal molecules in each region form a layer-by-layer twisted arrangement with a specific total twist angle.

[0016] Optionally, the arrangement direction of the bottom layer of liquid crystal molecules in the second liquid crystal is perpendicular to the overall arrangement direction of the liquid crystal molecules in the first liquid crystal.

[0017] Optionally, a spacer material is further filled between the upper glass substrate and the lower glass substrate to maintain a uniform thickness between the upper glass substrate and the lower glass substrate.

[0018] Optionally, the thickness of the second liquid crystal is the same as the thickness of the first liquid crystal.

[0019] Optionally, the second liquid crystal and the first liquid crystal are liquid crystal materials with fluidity or solid liquid crystal polymer materials.

[0020] Optionally, the lower surface of the lower glass substrate of the second liquid crystal element is bonded to the upper surface of the upper glass substrate of the first liquid crystal element by optical adhesive.

[0021] Optionally, the lower glass substrate of the second liquid crystal element and the upper glass substrate of the first liquid crystal element are integrally formed.

[0022] On the other hand, embodiments of the present invention also provide a method for fabricating a liquid crystal element, the method comprising:

[0023] A basic liquid crystal element is prepared, the basic liquid crystal element comprising an upper glass substrate and a lower glass substrate, wherein a liquid crystal is filled between the upper glass substrate and the lower glass substrate; the liquid crystal molecules of the liquid crystal are uniformly arranged, and the arrangement direction of each liquid crystal molecule is consistent.

[0024] The basic liquid crystal element is subjected to patterned in-situ dynamic light alignment processing, so that liquid crystal molecules form specific non-uniform arrangements in different regions between the upper and lower glass substrates, and liquid crystal molecules in each region form a layer-by-layer twisted arrangement. The liquid crystal element as a whole presents a patterned twisted angle spatial distribution, and each region has a specific total twist angle.

[0025] Optionally, the fabrication of the basic liquid crystal element includes:

[0026] Prepare two glass substrates, one of which will be used as the upper glass substrate and the other as the lower glass substrate.

[0027] A fixed alignment layer with consistent orientation and non-erasable is prepared on one side surface of the lower glass substrate; and a photosensitive alignment material is coated on one side surface of the upper glass substrate to form a photosensitive alignment layer that can be repeatedly erased and rewritten.

[0028] The alignment layers of the upper and lower glass substrates are placed facing each other with their inward sides, and spacer material is filled in so that the thickness of each region inside the two glass substrates remains the same.

[0029] Liquid crystal material or liquid crystal polymer material is poured into the upper and lower glass substrates, and then the edges of the two glass substrates are sealed with curing adhesive.

[0030] Optionally, the fabrication of the basic liquid crystal element includes:

[0031] Prepare two glass substrates, and coat one side of each substrate with a rewritable photosensitive alignment material. Use linearly polarized light to uniformly align the photosensitive alignment layer of one glass substrate, ensuring that the photosensitive alignment material within the substrate is aligned perpendicular to the polarization direction of the linearly polarized light. Place the aligned glass substrate and the other glass substrate with their alignment layers facing inwards, and fill with spacer material to maintain the same thickness in all areas of both substrates. Mix a light-absorbing dye with a liquid crystal material or liquid crystal polymer material, pour the mixture into the two glass substrates, and then seal the perimeter of the two glass substrates with a curing adhesive. Or...

[0032] Prepare two glass substrates, and coat one side of each glass substrate with an erasable photosensitive alignment material. First, place the alignment layers of the two glass substrates facing each other with their inward sides, and fill them with spacer material to ensure that each area of ​​the two glass substrates has the same thickness. Then, use linearly polarized light to uniformly align the photosensitive alignment layers of the two glass substrates so that the photosensitive alignment materials in the two glass substrates are aligned perpendicular to the polarization direction of the linearly polarized light. Mix a light-absorbing dye material with a liquid crystal material or a liquid crystal polymer material, pour the mixture into the two glass substrates, and then use a curing adhesive to firmly seal the edges of the two glass substrates.

[0033] Optionally, the patterned in-situ dynamic light alignment processing of the basic liquid crystal element includes:

[0034] The basic liquid crystal element is divided into various regions, and each region undergoes an independent exposure process, the exposure process including:

[0035] The exposure beam is shone onto the basic liquid crystal element from top to bottom;

[0036] Based on the twist angle distribution pattern that the basic liquid crystal element is to form, the continuous twist angle distribution is discretized and converted into a discrete twist angle distribution.

[0037] The exposure process is divided into multiple sub-processes, and the total exposure in each sub-process is greater than a set threshold.

[0038] Based on the discretized torsion angle distribution and the divided exposure sub-processes, the exposure process experienced by each region in the basic liquid crystal element is determined.

[0039] Based on the exposure process experienced by each region in the basic liquid crystal element, all images that need to be loaded are designed, and each image is loaded and exposed sequentially.

[0040] Optionally, the exposure beam is linearly polarized light, and the polarization direction of the linearly polarized light can be arbitrarily controlled.

[0041] On the other hand, embodiments of the present invention also provide a method for fabricating a liquid crystal element, the method comprising:

[0042] Prepare two glass substrates, and coat one side of one of the glass substrates with an alignment material and perform an alignment treatment to form an alignment layer with the same orientation direction;

[0043] A glass substrate with an alignment layer is aligned with another glass substrate with the alignment layer facing inward, and a spacer material is filled between the two glass substrates to keep the thickness of each region inside the two glass substrates the same.

[0044] A photosensitive chiral material capable of guiding a twisted arrangement structure is mixed with a liquid crystal material or a liquid crystal polymer material. The mixture is poured into two glass substrates, and then the edges of the two glass substrates are sealed with a curing adhesive to obtain the element to be exposed.

[0045] The mixture within the element to be exposed is subjected to exposure processes of a certain intensity and duration, so that liquid crystal molecules form specific twisted arrangements in different regions between the upper and lower glass substrates, and the liquid crystal element as a whole presents a patterned twisted angle distribution.

[0046] Optionally, the element to be exposed is divided into several regions, each undergoing an independent exposure process, the exposure process including:

[0047] Based on the twist angle distribution pattern that the exposed element is to form, the continuous twist angle distribution is discretized and converted into a discrete twist angle distribution.

[0048] The exposure process is divided into multiple sub-processes, and the total exposure in each sub-process is greater than a set threshold.

[0049] Based on the discretized torsion angle distribution and the divided exposure sub-processes, the exposure process experienced by each region in the element to be exposed is determined.

[0050] Based on the exposure process experienced by each region in the element to be exposed, all images that need to be loaded are designed, and each image is loaded and exposed sequentially.

[0051] Optionally, the wavelength of the exposure beam is within the range of wavelengths in which the photosensitive chiral material can respond and thus undergo photoinduced changes.

[0052] Optionally, the photosensitive chiral material can be any of the following: photosensitive microparticles, photosensitive left- or right-handed materials, or photosensitive open- or closed-loop materials.

[0053] On the other hand, embodiments of the present invention also provide a method for fabricating an ultra-wideband optical field phase modulation device, the method comprising:

[0054] Two basic liquid crystal elements are prepared, one of which is used as the first liquid crystal element and the other is used as the element to be processed; the basic liquid crystal element includes an upper glass substrate and a lower glass substrate, and a first liquid crystal is filled between the upper glass substrate and the lower glass substrate; the liquid crystal molecules of the first liquid crystal are uniformly arranged.

[0055] Based on the element to be processed, a second liquid crystal element is prepared using the liquid crystal element preparation method described above. The second liquid crystal element includes an upper glass substrate and a lower glass substrate, and a second liquid crystal is filled between the upper glass substrate and the lower glass substrate. The liquid crystal molecules of the second liquid crystal are non-uniformly arranged, and the second liquid crystal is divided into different regions. The liquid crystal molecules in each region form a layer-by-layer twisted arrangement. The second liquid crystal as a whole presents a patterned twist angle spatial distribution, and each region has a specific total twist angle.

[0056] An ultra-wideband optical field phase modulation device is obtained by bonding the lower surface of the lower glass substrate of the second liquid crystal element to the upper surface of the upper glass substrate of the first liquid crystal element using optical adhesive.

[0057] Optionally, when bonding the lower surface of the lower glass substrate of the second liquid crystal element to the upper surface of the upper glass substrate of the first liquid crystal element with optical adhesive, an alignment operation is performed to make the alignment direction of the upper glass substrate in the first liquid crystal element perpendicular to the alignment direction of the lower glass substrate in the second liquid crystal element.

[0058] Alternatively, the two basic liquid crystal elements may be prepared using the same or different methods.

[0059] On the other hand, embodiments of the present invention also provide a method for fabricating an ultra-wideband optical field phase modulation device, the method comprising:

[0060] A first liquid crystal element is prepared, the first liquid crystal element comprising an upper glass substrate and a lower glass substrate, wherein a first liquid crystal body is filled between the upper glass substrate and the lower glass substrate; the liquid crystal molecules of the first liquid crystal body are uniformly arranged.

[0061] A second liquid crystal element is prepared using the liquid crystal element preparation method described above. The second liquid crystal element includes an upper glass substrate and a lower glass substrate, and a second liquid crystal is filled between the upper glass substrate and the lower glass substrate. The liquid crystal molecules of the second liquid crystal are non-uniformly arranged, and the second liquid crystal is divided into different regions. The liquid crystal molecules in each region form a layer-by-layer twisted arrangement. The second liquid crystal as a whole presents a patterned spatial distribution of twist angles, and each region has a specific total twist angle.

[0062] An ultra-wideband optical field phase modulation device is obtained by bonding the lower surface of the lower glass substrate of the second liquid crystal element to the upper surface of the upper glass substrate of the first liquid crystal element using optical adhesive.

[0063] Optionally, when bonding the lower surface of the lower glass substrate of the second liquid crystal element to the upper surface of the upper glass substrate of the first liquid crystal element with optical adhesive, an alignment operation is performed to make the alignment direction of the upper glass substrate in the first liquid crystal element perpendicular to the alignment direction of the lower glass substrate in the second liquid crystal element.

[0064] On the other hand, embodiments of the present invention also provide a method for fabricating an ultra-wideband optical field phase modulation device, the method comprising:

[0065] A first liquid crystal element is prepared, the first liquid crystal element comprising an upper glass substrate and a lower glass substrate, wherein a first liquid crystal body is filled between the upper glass substrate and the lower glass substrate; the liquid crystal molecules of the first liquid crystal body are uniformly arranged.

[0066] The upper glass substrate of the first liquid crystal element is used as the lower glass substrate of the second liquid crystal element. The second liquid crystal element is prepared by the liquid crystal element preparation method described above. The second liquid crystal element includes an upper glass substrate and a lower glass substrate, and a first liquid crystal is filled between the upper glass substrate and the lower glass substrate. The liquid crystal molecules of the second liquid crystal are non-uniformly arranged. The second liquid crystal is divided into different regions, and the liquid crystal molecules in each region form a layer-by-layer twisted arrangement. The second liquid crystal as a whole presents a patterned spatial distribution of twist angles, and each region has a specific total twist angle.

[0067] The first liquid crystal element and the second liquid crystal element constitute an ultra-wideband optical field phase modulation device sharing a common intermediate layer substrate.

[0068] The ultra-wideband optical field phase modulation device provided in this invention can be compatible with an ultra-wide spectral band, significantly expanding the operating band range of the device to include the visible to near-infrared and even mid-infrared bands. Taking a vortex light field as an example, compared with the existing technology's compatible band of around 500nm, the vortex light generating device provided in this invention can efficiently modulate incident light into an outgoing vortex light field within the visible to near-infrared and even mid-infrared bands, and the vortex light field has high purity within the compatible band range. Furthermore, according to the Morgan condition that the applicable band of the device should satisfy (i.e., when the product of the thickness d of the liquid crystal layer and its refractive index anisotropy Δn is much greater than the incident light wavelength λ (i.e., Δn×d >>λ), the rotation angle of the polarization plane of light of different wavelengths is the same after passing through the liquid crystal layer), it can be seen that by using a liquid crystal material with a larger refractive index anisotropy (Δn) and increasing the thickness d of the liquid crystal device, the band range of this optical field phase modulation device can be further expanded.

[0069] This invention provides a method for fabricating a liquid crystal element. Based on a liquid crystal element with uniformly arranged liquid crystal molecules, it can fabricate a liquid crystal element with liquid crystal molecules arranged in a layer-by-layer twisted pattern, exhibiting a patterned spatial distribution of twist angles. Furthermore, different fabrication methods can be employed depending on the fabrication method for liquid crystal elements with uniformly arranged liquid crystal molecules. An in-situ dynamic photoorientation fabrication process can be used; this process is simple, requiring only conventional liquid crystal device processes and directly guiding the twisted liquid crystal arrangement structure. The fabrication process exhibits high consistency and high efficiency.

[0070] Another liquid crystal element fabrication method provided in this embodiment of the invention can also be based on liquid crystal doping with photosensitive chiral materials to prepare liquid crystal elements in which liquid crystal molecules are arranged in a layer-by-layer twisted pattern and exhibit a patterned spatial distribution of twist angles.

[0071] The method for fabricating an ultra-wideband optical field phase modulation device provided in this invention can separately fabricate a first liquid crystal element in which the liquid crystal molecules of the liquid crystal body are uniformly arranged, and a second liquid crystal element in which the liquid crystal molecules of the liquid crystal body are non-uniformly arranged and exhibit a patterned twisted angular spatial distribution. The two liquid crystal elements are then longitudinally bonded to obtain the ultra-wideband optical field phase modulation device. Alternatively, after fabricating the first liquid crystal element, the upper glass substrate of the first liquid crystal element can be used as the lower glass substrate of the second liquid crystal element, and the second liquid crystal element can be obtained in various ways, i.e., the second liquid crystal element and the first liquid crystal element share the intermediate glass substrate, thus obtaining the ultra-wideband optical field phase modulation device. Regardless of the method, the obtained ultra-wideband optical field phase modulation device can efficiently and freely structurally control the phase parameters of the incident light field within the visible, near-infrared, and even mid-infrared bands. Moreover, as long as the thickness d of the twisted liquid crystal arrangement in the second liquid crystal element is sufficiently large, or the refractive index anisotropy Δn of the liquid crystal material is sufficiently large, an ultra-wideband optical field phase modulation effect can be generated. Therefore, the absolute thickness of the liquid crystal layer does not need to be strictly controlled during the fabrication process, which can effectively improve the yield of the device. Attached Figure Description

[0072] Figure 1 This is a schematic diagram illustrating the principles of vortex optical fields, polarization gratings, and phase holography.

[0073] Figure 2 This is a schematic diagram illustrating the principle and effect of generating a vortex light field using metasurfaces;

[0074] Figure 3 This is a schematic diagram illustrating the principle and effect of generating a vortex light field using multilayer liquid crystal polymers.

[0075] Figure 4 This is a schematic diagram of the optical field phase modulation element provided in an embodiment of the present invention;

[0076] Figure 5 This is a schematic diagram of the principle of the optical field phase modulation element provided in the embodiment of the present invention;

[0077] Figure 6 This is a schematic diagram of the measured and simulated results of the ultra-wideband vortex optical field provided in the embodiments of the present invention;

[0078] Figure 7 This is a schematic diagram of the patterned arrangement structure of the optical field phase modulation element provided in the embodiment of the present invention and the resulting phase space distribution effect;

[0079] Figure 8 This is a flowchart of a liquid crystal element fabrication method provided in an embodiment of the present invention;

[0080] Figure 9 This is a flowchart illustrating one method for preparing a basic liquid crystal element in an embodiment of the present invention;

[0081] Figure 10 It corresponds Figure 7 Schematic diagram of the sample structure at each step;

[0082] Figure 11 This is a schematic diagram of the orientation process of a photosensitive alignment material;

[0083] Figure 12 This is another flowchart for preparing a basic liquid crystal element in an embodiment of the present invention;

[0084] Figure 13 These are schematic diagrams of liquid crystal arrangement structures under different orientations in embodiments of the present invention;

[0085] Figure 14 This is a schematic diagram illustrating the principle of in-situ dynamic light alignment of a basic liquid crystal element in an embodiment of the present invention;

[0086] Figure 15 This is a schematic diagram of the absorption spectrum of a typical light-absorbing dye molecule;

[0087] Figure 16 This is a schematic diagram of a liquid crystal arrangement structure with arbitrary twist angle achieved using in-situ dynamic exposure and alignment technology in an embodiment of the present invention;

[0088] Figure 17 This is another flowchart of the liquid crystal element fabrication method provided in the embodiments of the present invention;

[0089] Figure 18 This is a schematic diagram illustrating the principle of a liquid crystal twisted arrangement structure with arbitrary twist angle generated by photosensitive chiral materials in an embodiment of the present invention;

[0090] Figure 19 This is a flowchart of a method for fabricating an ultrawideband optical field phase modulation device provided in an embodiment of the present invention;

[0091] Figure 20 This is another flowchart of the fabrication method of the ultra-wideband optical field phase modulation device provided in the embodiments of the present invention;

[0092] Figure 21 This is another flowchart of the fabrication method of the ultra-wideband optical field phase modulation device provided in the embodiments of the present invention. Detailed Implementation

[0093] The principles and spirit of the invention will now be described with reference to exemplary embodiments shown in the accompanying drawings. It should be understood that these embodiments are described merely to enable those skilled in the art to better understand and implement the invention, and are not intended to limit the scope of the invention in any way.

[0094] To address the common problems of narrow spectral compatibility bands, complex fabrication processes, and low efficiency in existing optical field phase modulation elements, this invention provides an ultra-wideband optical field phase modulation device and its fabrication method, as well as a liquid crystal element fabrication method. This device can achieve efficient optical field phase modulation effects in the visible to near-infrared and even mid-infrared bands, and the fabrication process is simple.

[0095] like Figure 4 The diagram shown is a structural schematic of an ultra-wideband optical field phase modulation device provided in an embodiment of the present invention. The ultra-wideband optical field phase modulation device 400 includes a second liquid crystal element 42 and a first liquid crystal element 41 stacked vertically. The second liquid crystal element 42 and the first liquid crystal element 41 each include an upper glass substrate and a lower glass substrate, respectively, with liquid crystal filling the space between the upper and lower glass substrates. The difference lies in the arrangement of the liquid crystal molecules in the two liquid crystal elements. Wherein:

[0096] The first liquid crystal element 41 is filled with a first liquid crystal body 401. The liquid crystal molecules of the first liquid crystal body 401 are uniformly arranged, and the arrangement direction of each liquid crystal molecule is consistent. The arrangement direction refers to the direction of the long axis of the liquid crystal molecule.

[0097] The second liquid crystal element 42 is filled with a second liquid crystal body 402, and the liquid crystal molecules in the second liquid crystal body 402 are non-uniformly arranged. The second liquid crystal body 402 can be divided into different regions, and the liquid crystal molecules in each region are arranged in a layer-by-layer twisted pattern, with the twist angle of the liquid crystal molecules between adjacent layers being the same. Taking any given region as an example, the twist angle of the liquid crystal molecules is the same layer-by-layer, that is, assuming the twist angle of the second layer relative to the first layer is... Then the twist angle of the third layer relative to the second layer is also... The twist angle of the fourth layer relative to the third layer is also... And so on. Accordingly, each region in the second liquid crystal has a specific total twist angle, so the second liquid crystal as a whole presents a patterned spatial distribution of twist angles.

[0098] In some embodiments, a spacer material is further filled between the upper and lower glass substrates of each liquid crystal element to maintain a uniform thickness between the upper and lower glass substrates. The spacer material can be disposed at the four corners of the upper and lower glass substrates. The spacer material is a spacer material between the two glass substrates, used to maintain the distance between the two glass substrates, so that the liquid crystal in each region of the liquid crystal element maintains a uniform thickness, thereby meeting the prerequisites for ultra-wideband optical field phase modulation devices. The spacer material can be, for example, a microsphere material, which can be inorganic or organic microspheres, such as silicon dioxide (SiO2) microspheres, polystyrene (PS) microspheres, etc.; the spacer material can also be a sheet-like material, etc., which is not limited in this embodiment of the invention.

[0099] Preferably, the first liquid crystal 401 and the second liquid crystal 402 have the same thickness.

[0100] The arrangement direction of the bottom layer of liquid crystal molecules in the second liquid crystal 402 is perpendicular to the overall arrangement direction of the liquid crystal molecules in the first liquid crystal 401.

[0101] In specific implementations, the second liquid crystal 402 and the first liquid crystal 401 can be liquid crystal materials with fluidity or solid liquid crystal polymer materials.

[0102] To ensure the stability of the liquid crystal between the upper and lower glass substrates, the upper and lower glass substrates of each of the above liquid crystal elements can be encapsulated with a curing adhesive.

[0103] In some embodiments, the first liquid crystal element 41 and the second liquid crystal element 42 can be fabricated separately, and then the lower surface of the lower glass substrate of the second liquid crystal element 42 is bonded to the upper surface of the upper glass substrate of the first liquid crystal element 41 by optical adhesive to obtain an ultra-wideband optical field phase modulation device 400.

[0104] In some embodiments, after the first liquid crystal element 41 is fabricated, the upper glass substrate of the first liquid crystal element 41 can be used simultaneously as the lower glass substrate of the second liquid crystal element 42 to fabricate the second liquid crystal element 42. That is, the lower glass substrate of the second liquid crystal element 42 and the upper glass substrate of the first liquid crystal element 41 are integrally formed.

[0105] The following is combined Figure 5 This explains the principle behind achieving ultra-wideband optical field phase modulation based on the stacked arrangement structure.

[0106] like Figure 5 The diagram shown is a schematic diagram of the optical field phase modulation element provided in an embodiment of the present invention.

[0107] Figure 5 The light beam propagates from left to right along the positive direction of the Z-axis in the coordinate system, and the relative vertical positions of the liquid crystal element and the liquid crystal molecule layer are defined with the positive direction of the Z-axis as the reference.

[0108] In this embodiment of the invention, the liquid crystal molecules of the first liquid crystal 401 are uniformly arranged in a consistent direction, referred to as nematic liquid crystal (NLC); the liquid crystal molecules in each region of the second liquid crystal 402 are non-uniformly arranged in a layer-by-layer twisted manner, referred to as twisted nematic liquid crystal (TNLC). NLC refers to a liquid crystal phase in which the liquid crystal molecules of a rod-shaped liquid crystal material tend to align in a uniform direction; TNLC refers to a layered arrangement of rod-shaped liquid crystal molecules, with molecules within the same liquid crystal layer arranged uniformly; and between two adjacent liquid crystal layers, the molecular arrangement direction forms a certain twist angle, and the twist angles of any two adjacent layers are the same. Here, the sign of the twist angle is defined: if the bottommost layer of liquid crystal molecules twists counterclockwise upwards, the twist angle is positive; conversely, a clockwise twist angle is negative.

[0109] In this embodiment of the invention, the refractive index anisotropy of the liquid crystal molecules in each layer, that is, the difference in refractive index of the liquid crystal molecules along the long axis and the short axis, is expressed as Δn.

[0110] Preferably, the thickness of the first liquid crystal 401 is the same as the thickness of the second liquid crystal 402, such as... Figure 5 The thickness shown is d.

[0111] Preferably, the arrangement direction of the bottom layer of liquid crystal molecules in the first liquid crystal 401 is perpendicular to the overall arrangement direction of the liquid crystal molecules in the second liquid crystal 402.

[0112] First, taking a certain region in the second liquid crystal 402 as an example, assume that the total twist angle of the liquid crystal molecules in this region is... Directly below this region (in the opposite direction of the Z-axis), there is a region corresponding to the first liquid crystal, and the two together form a stacked structure of NLC (Nematic Liquid Crystal) and TNLC (Twisted Nematic Liquid Crystal).

[0113] A beam of polarized light can be represented by a two-dimensional Jones vector, where the first component represents the electric field vector along the X-axis and the second component represents the electric field vector along the Y-axis. The Jones matrix of an optical element is a 2×2 matrix that describes the change in the electric field vector of a beam of polarized light after it passes through the optical element.

[0114] The Jones matrix is ​​used to describe the light field modulation form corresponding to the liquid crystal molecule arrangement structure in the light field phase modulation device of the present invention. The NLCs in the first liquid crystal are arranged along the Y-axis, and their Jones matrix T... NLC It can be represented as:

[0115] (1)

[0116] The meanings of each parameter are as follows:

[0117] k represents the wave vector in vacuum. , It is the wavelength of light;

[0118] The average refractive index represents the liquid crystal material. , and These are the refractive indices along the long and short axes of the liquid crystal molecules, respectively.

[0119] , representing the birefringence phase delay matrix experienced by the beam as it passes through the NLC structure, where The birefringence phase retardation representing the liquid crystal molecules along the long and short axes. , The refractive index anisotropy of liquid crystal molecules, i.e. .

[0120] For the TNLC arrangement structure in the second liquid crystal described above, the bottom layer of liquid crystal molecules are arranged along the X-axis. When the refractive index anisotropy Δn and thickness d of the liquid crystal molecules satisfy the Morgan condition (Δn × d ≫ λ), its Jones matrix T... TNLC It can be represented as:

[0121] (2)

[0122] in, The birefringence phase delay matrix represents the phase delay experienced by the beam as it passes through the TNLC structure;

[0123] This represents the rotation matrix caused by the TNLC twisted arrangement structure.

[0124] In summary, the birefringence phase delay experienced by the beam when passing through NLC and TNLC array structures can be determined. and On the contrary.

[0125] Mathematically, left-handed circularly polarized light can be represented by the Jones vector as follows: When left-handed circularly polarized incident light passes through the stacked arrangement of NLC and TNLC in the optical field phase modulation element of this embodiment, the transmitted light... The light field expression is the incident light , and The matrix product of the three in sequence is:

[0126] (3)

[0127] From the above transmitted light As can be seen from the expression, when the liquid crystal material and thickness of the NLC-TNLC stacked structure remain unchanged, The phase term is considered a negligible constant, while the additional phase term... Indicates the emitted light The phase and the twist angle of the TNLC arrangement Linear correlation exists, and the outgoing light maintains the same circular polarization state as the incident light. When the twist angle... When the value of can reach the range of -π to π, the phase modulation of the light field can cover the entire space of 0 to 2π, that is, the arbitrary modulation of the phase of the light field is realized.

[0128] On the other hand, since the Morgan condition for the twisted TNLC structure holds over a very wide wavelength range, this phase modulation principle has the significant advantage of being compatible with ultra-wide wavelengths. For example, when the refractive index anisotropy of the liquid crystal material is Δn = 0.39 and the thickness is d = 40 μm (both fabricable parameters), the Morgan condition holds over the visible to near-infrared and even mid-infrared wavelength range, thus achieving ultra-wide wavelength phase modulation. Taking a vortex optical field as an example, such as... Figure 6 The measured results of the vortex light spot pattern, interference fringe pattern, and simulation results of the purity of the vortex light field show that the vortex light generating device provided in this embodiment of the invention can efficiently modulate the incident light into an outgoing vortex light field in the visible to mid-infrared band, and the generated vortex light field has high purity.

[0129] In this embodiment of the invention, the second liquid crystal 402 has a patterned twisted arrangement structure, and each region has a specific total twist angle, such as... Figure 7 As shown. For the optical field phase modulation device composed of the first liquid crystal 401 and the second liquid crystal 402, when circularly polarized incident light passes through the device, the optical field form of the outgoing light will exhibit a specific phase spatial distribution, thereby achieving the desired optical field phase modulation effect.

[0130] The ultra-wideband optical field phase modulation device provided in this invention is compatible with an ultra-wide spectral band, significantly expanding the device's operating wavelength range to include the visible to near-infrared and even mid-infrared bands. Compared to the approximately 500nm compatible wavelength range of existing technologies, the ultra-wideband optical field phase modulation device provided in this invention can achieve efficient optical field phase modulation across a vast wavelength range from the visible to the near-infrared and even mid-infrared bands. Furthermore, based on the Morgan condition that the device's applicable wavelength range should meet, the wavelength range of this optical field phase modulation device can be further expanded by using a liquid crystal material with greater refractive index anisotropy and increasing the thickness of the liquid crystal device.

[0131] For different application areas, for example, this ultra-wideband optical field phase modulation device can be used to fabricate vortex light generating devices, polarization grating devices, and phase holographic devices.

[0132] (1) Vortex light generating device

[0133] Phase spatial distribution of vortex light field Spatial azimuth The function, expressed as .in It is called the topological charge, which can take any integer value. The absolute value of the integer represents the degree of spirality of the phase of the vortex light field in space, and the positive or negative value represents the left or right spirality of the spiral phase of the vortex light field. It is a constant phase term (generally, it can be set as follows). Based on the liquid crystal ultrawideband phase modulation principle in this patent, the phase distribution of the vortex light field is... Mapped to the spatial distribution function of the twist angle in the second liquid crystal. The specific mapping relationship is as follows: For example, for The phase distribution of the second liquid crystal and the twist angle distribution of the second liquid crystal are as follows: Since the twist angle in the second liquid crystal ranges from -π to π, the twist angle in the region exceeding -π to π can be kept within -π to π by adding or subtracting several integer multiples of 2π.

[0134] (2) Polarization grating device

[0135] Phase spatial distribution of polarization grating Let x be a function of spatial coordinates x and y. Taking a periodic polarization grating along the x-direction as an example, its phase distribution function is: .in The period of the grating is the polarization grating period. Different polarization grating periods correspond to different beam diffraction angles. The expression is Based on the liquid crystal ultra-wideband phase modulation principle in this patent, the phase distribution of the polarization grating is also adjusted. Mapped to the spatial distribution function of the twist angle in the second liquid crystal. The specific mapping relationship is as follows: The twist angle distribution of the second liquid crystal can be obtained as follows: Similarly, since the twist angle in the second liquid crystal is in the range of -π to π, the twist angle in the region exceeding -π to π can be kept within -π to π by adding or subtracting several integer multiples of 2π.

[0136] (3) Phase holographic device

[0137] Phase distribution of holographic devices This is a function of spatial coordinates x and y, and its specific expression can be obtained based on the intensity characteristics of the target image using algorithms such as iterative optimization or artificial neural networks. Based on the principle of ultra-wideband phase modulation of liquid crystals, this phase distribution... Mapped to the spatial distribution function of the twist angle in the second liquid crystal. The specific mapping relationship is as follows: Similarly, since the twist angle in the second liquid crystal is in the range of -π to π, the twist angle in the region exceeding -π to π can be kept within -π to π by adding or subtracting several integer multiples of 2π.

[0138] Accordingly, this invention also provides a method for preparing a liquid crystal element. This method only requires conventional liquid crystal device processes to prepare a basic liquid crystal element in which liquid crystal molecules are uniformly arranged. Based on this, in-situ dynamic optical alignment and other preparation processes are used to guide a distorted liquid crystal arrangement structure. The preparation process is simple and has high consistency and high efficiency.

[0139] like Figure 8 The diagram shown is a flowchart of a liquid crystal element fabrication method provided in an embodiment of the present invention, including the following steps:

[0140] Step 801: Prepare a basic liquid crystal element, which includes an upper glass substrate and a lower glass substrate, and a liquid crystal is filled between the upper glass substrate and the lower glass substrate; the liquid crystal molecules of the liquid crystal are uniformly arranged, and the arrangement direction of each liquid crystal molecule is consistent.

[0141] Step 802: The basic liquid crystal element is subjected to patterned in-situ dynamic light alignment processing, so that liquid crystal molecules form specific non-uniform arrangements in different regions between the upper and lower glass substrates, and liquid crystal molecules in each region form a layer-by-layer twisted arrangement, and the twisting angle of liquid crystal molecules between adjacent layers is the same. The liquid crystal element as a whole presents a patterned twisted angle spatial distribution, and each region has a specific total twist angle.

[0142] The basic liquid crystal element can be fabricated in various ways, such as using a lower glass substrate with a fixed orientation and an upper glass substrate with an erasable light orientation; or using both upper and lower glass substrates with an erasable light orientation. These will be described in detail below.

[0143] like Figure 9 The diagram shown is a flowchart of one method for preparing a basic liquid crystal element according to an embodiment of the present invention. Figure 10 It corresponds Figure 9 Schematic diagram of the sample structure for each step in the process.

[0144] In the illustrated embodiment, the lower glass substrate is fixed in orientation, and the upper glass substrate is erasable in orientation. Fixed orientation can be achieved using methods such as rubbing alignment, photocrosslinking or photodegradable material alignment, and photoresist microstructure alignment; erasable in orientation can be achieved using photosensitive alignment materials (such as photoisomerized photosensitive alignment materials). Taking rubbing alignment as an example of fixed orientation, the fabrication process of the basic liquid crystal element includes the following steps:

[0145] In step 901, two glass substrates are prepared, one of which is used as the upper glass substrate and the other as the lower glass substrate.

[0146] Specifically, two transparent glass substrates are selected, and the glass substrates are cleaned and dried to remove surface contaminants and particles, ensuring a smooth and clean surface.

[0147] In step 902, a fixed orientation layer with regular molecular arrangement and orientation direction is formed on one side surface of the lower glass substrate by a frictional orientation method.

[0148] Frictional alignment is a technique that controls the alignment direction of liquid crystal molecules by micro-processing the substrate surface. Its core principle is to create regular microgrooves or surface energy gradients on the substrate surface through friction treatment. These physical or chemical changes guide the alignment of liquid crystal molecules, causing them to interact between the substrate surface and the groove structure, forming a specific alignment direction.

[0149] The process of frictional orientation is as follows:

[0150] A layer of alignment material is coated onto the cleaned glass substrate surface. This alignment material can be, for example, polyimide (PI) or other polymeric materials. Coating methods include spin coating, blade coating, or dip coating. After coating, the alignment material needs to be dried or baked to cure, ensuring the formation of a uniform film. Then, a friction treatment is performed using a friction machine. The key component of the friction machine is a roller covered with a soft cloth or other soft material. The roller contacts the substrate surface at a fixed direction and speed and moves along a straight line. During friction, the cloth creates microgrooves or stretches the chain segments of the alignment layer molecules on the substrate surface, thereby forming a regular molecular arrangement and orientation.

[0151] It should be noted that during the preparation of friction orientation, key control parameters such as friction pressure, friction speed, type of fabric, and number of friction cycles are required to obtain the best orientation effect.

[0152] In step 903, a photosensitive alignment material is coated on one side surface of the upper glass substrate to form a uniform photosensitive alignment layer.

[0153] The photosensitive alignment material refers specifically to a photosensitive material that can undergo photo-induced isomerization under linearly polarized light irradiation within a specific wavelength range, thereby generating surface interactions along a specific direction, anchoring adjacent liquid crystal molecules and guiding the liquid crystal to form a specific arrangement structure.

[0154] In particular, this photosensitive alignment material has the property of being rewritable. Specifically, under the illumination of linearly polarized light in a specific wavelength band, the alignment molecules will eventually align perpendicular to the polarization direction of the linearly polarized light. When the polarization direction of the linearly polarized light is changed, the alignment molecules will adjust their alignment accordingly, making them perpendicular to the polarization direction of the linearly polarized light again.

[0155] Reference Figure 10 As shown in (a), the process of erasable photo-alignment is as follows: First, a photosensitive alignment material is coated on a glass substrate. Specifically, the photosensitive alignment material is first coated on the glass substrate. The coating method can be spin coating, scraping coating, or dip coating, etc., so that the photosensitive alignment material is coated evenly.

[0156] In step 904, the alignment layers of the two glass substrates are placed facing each other with their inward sides, and spacer material is filled in so that each region of the two glass substrates maintains the same thickness.

[0157] Reference Figure 10As shown in (b), the dried lower glass substrate covered with friction alignment material and the upper glass substrate covered with photosensitive alignment material are placed facing each other, with the alignment layers facing inward. A spacer material of a certain thickness is applied between the two glass substrates by spraying or spin coating to raise the interior of the two glass substrates to the same thickness, that is, the thickness of each region inside the two glass substrates is the same.

[0158] In step 905, the upper glass substrate is photo-oriented using linearly polarized light of uniform intensity, so that the photosensitive orientation molecules in the upper glass substrate are aligned along the polarization direction perpendicular to the linearly polarized light.

[0159] Reference Figure 10 As shown in (c), the upper glass substrate is photo-oriented using linearly polarized light of uniform intensity, so that the photosensitive orientation molecules in the upper glass substrate are aligned perpendicular to the polarization direction of the linearly polarized light.

[0160] For photosensitive orientation materials, photoisomerization reactions occur under irradiation with linearly polarized light within a specific wavelength range. For example... Figure 11 As shown, for randomly arranged photosensitive orientation molecules, under the illumination of linearly polarized light in a specific wavelength band, the orientation molecules eventually exhibit a uniform arrangement perpendicular to the polarization direction of the linearly polarized light.

[0161] In step 906, linearly polarized light is used to orient the photosensitive material on the upper glass substrate. After photoorientation, the arrangement direction of the photosensitive material is made consistent with the direction of rubbing orientation in the lower glass substrate.

[0162] In step 907, liquid crystal material or liquid crystal polymer material is poured into the upper and lower glass substrates, and then the two glass substrates are sealed with curing adhesive around their edges.

[0163] Reference Figure 12 , Figure 12 The embodiment shown uses an erasable optical alignment method for both upper and lower glass substrates to fabricate the basic liquid crystal element, including the following steps:

[0164] In step 1201, two glass substrates coated with a photosensitive alignment material are prepared.

[0165] In step 1202, the photosensitive alignment layers of the two glass substrates are placed facing each other with their inward sides, and spacer material is filled in so that each region of the two glass substrates maintains the same thickness.

[0166] Specific process and Figure 9 Step 904 is similar and will not be repeated here.

[0167] In step 1203, the two glass substrates are optically aligned using linearly polarized light of uniform intensity, so that the photosensitive orientation molecules in the two glass substrates are aligned along the polarization direction perpendicular to the linearly polarized light.

[0168] Specific process and Figure 9 Step 905 is similar and will not be repeated here.

[0169] In step 1204, a light-absorbing material is mixed with a liquid crystal material or a liquid crystal polymer material, the mixture is poured into the two glass substrates, and then the edges of the two glass substrates are sealed with a curing adhesive.

[0170] The light-absorbing material can be a dye-based material. This material blocks light from shining from above from exposing the photo-alignment layer in the lower glass substrate, thereby ensuring the stability of the lower substrate's alignment direction during subsequent in-situ dynamic photo-alignment processing of the basic liquid crystal element.

[0171] It should be noted that in the preparation method of dye-doped liquid crystal, the doping concentration of the dye in the liquid crystal can be reasonably controlled. For example, in some embodiments, the mass fraction of the light-absorbing dye can be controlled at about 0.5 wt%.

[0172] Reference Figure 10 As shown in (d) and (e), a mixture of liquid crystal or liquid crystal polymer material doped with light-absorbing material is poured into two glass substrates. Then, the edges of the glass substrates are sealed with a curing adhesive. The liquid crystal molecules inside will form a uniform arrangement structure under the guidance of photosensitive orientation molecules.

[0173] Based on the above Figure 9 and Figure 12 The basic liquid crystal element prepared by the method shown can be patterned through in-situ dynamic optical alignment treatment, resulting in a non-uniform arrangement of liquid crystal molecules in the upper and lower glass substrates. In different regions, the liquid crystal molecules form a layer-by-layer twisted arrangement, with adjacent layers exhibiting the same twist angle. The liquid crystal element as a whole displays a patterned spatial distribution of twist angles, with each region possessing a specific total twist angle.

[0174] Specifically, the in-situ dynamic light alignment process is divided into multiple independent sub-processes; each sub-process is executed sequentially. The exposure intensity and time in each sub-process can be the same or different, as long as the total exposure (i.e., exposure intensity × time) reaches a certain level, sufficient to make the photosensitive alignment molecules complete the rotation and drive the liquid crystal molecules to twist. The linear polarization directions of two adjacent sub-processes differ by a certain angle.

[0175] The arrangement of liquid crystal molecules can be controlled by applying boundary conditions. When a specific alignment direction is pre-applied to the top and bottom of the liquid crystal, the liquid crystal molecules inside will spontaneously form an oriented alignment structure according to the alignment directions of the upper and lower boundaries. This process of guiding the oriented alignment of liquid crystal molecules is called orientation. As mentioned earlier, photosensitive orientation refers to using special photosensitive materials as boundary alignment molecules. Under exposure conditions of linearly polarized light, the photosensitive alignment molecules will eventually tend to align perpendicular to the linear polarization direction of the light. Therefore, by adjusting the linear polarization direction of ultraviolet exposure, the alignment direction of the photosensitive alignment molecules at the upper and lower boundaries can be arbitrarily changed. Thus, through the guiding effect of the photosensitive alignment molecules at the upper and lower boundaries, the liquid crystal molecules inside the liquid crystal can ultimately be controlled to form a specific overall alignment structure. Figure 13 A schematic diagram of liquid crystal arrangement structures with different orientations is shown.

[0176] Based on the above principle, after obtaining a uniform liquid crystal molecule arrangement structure, in-situ dynamic exposure and alignment processes can be performed on it to make the liquid crystal molecules inside the liquid crystal form a layer-by-layer twisted arrangement structure.

[0177] like Figure 14 The diagram shown is a schematic representation of the principle of in-situ dynamic light alignment of a basic liquid crystal element in an embodiment of the present invention.

[0178] The basic liquid crystal element with a uniform arrangement of liquid crystal molecules is exposed to linearly polarized light again. The exposure beam shines on the basic liquid crystal element from top to bottom, that is, the beam enters the upper glass substrate and the lower glass substrate successively. When the linear polarization direction of the exposure beam is rotated, the orientation of the photosensitive alignment molecules in the upper glass substrate will rotate accordingly, thus tending to align again perpendicular to the linear polarization direction.

[0179] Consider the orientation of the lower glass substrate. During the exposure process described above, the orientation of the lower glass substrate remains unaffected. The principle behind this is briefly explained below.

[0180] (1) Targeting Figure 9 The basic liquid crystal element prepared by the method shown has an alignment layer formed by a fixed alignment method (such as rubbing alignment) on the lower glass substrate. Therefore, during the in-situ dynamic photoalignment of the basic liquid crystal element, the rubbing alignment layer is not affected by the exposure beam, and the alignment direction of the lower glass substrate remains unchanged.

[0181] (2) Regarding Figure 12 The basic liquid crystal element prepared by the method shown incorporates light-absorbing materials, such as dye-based light-absorbing materials. Figure 15 A schematic diagram of the absorption spectrum of a typical light-absorbing dye molecule is shown.

[0182] Depend on Figure 15It can be seen that light-absorbing dye molecules have a significant absorption effect on light within the exposure wavelength range (usually from ultraviolet to blue-violet). Therefore, when the material after mixing light-absorbing dye with liquid crystal is poured between two glass substrates, the light-absorbing dye will absorb the light entering the mixed material during the exposure process, causing the light intensity to gradually decrease from top to bottom. At the bottom photosensitive alignment layer, there is almost no light intensity, which does not change the state of the photosensitive alignment layer in the lower glass substrate, allowing it to maintain its original alignment direction.

[0183] It is evident that the orientation direction in the lower glass substrate remains unchanged in any of the above situations.

[0184] Therefore, under the above-mentioned in-situ dynamic light alignment operation, the rotation of the photosensitive alignment molecules in the upper glass substrate will exert a torsional force on the internal liquid crystal molecules. This torsional force will drive the liquid crystal molecules inside the liquid crystal to rotate synchronously in situ. Thus, during the in-situ dynamic exposure and alignment process, the liquid crystal molecules inside the liquid crystal between the upper and lower glass substrates form a layer-by-layer tortuous arrangement structure.

[0185] Figure 16 This means that by controlling the rotation angle of the polarization direction of the exposure beam, a twisted arrangement structure with arbitrary twist angle can be formed, thereby satisfying the twist angle required for ultra-wideband phase modulation. It can take any value from -π to π.

[0186] Based on the above-mentioned fabrication principle of liquid crystal twisted alignment structure, combined with a patterned exposure system of a specific liquid crystal on silicon (LCOS) device or digital micromirror (DMD) device, a patterned in-situ dynamic light alignment process can be implemented, ultimately producing a liquid crystal element with a patterned twisted angle spatial distribution.

[0187] Specifically, in the process of patterned in-situ dynamic light alignment, the exposure beam shines on the base liquid crystal element from top to bottom, that is, the beam enters the upper glass substrate and the lower glass substrate in sequence. The exposure beam is linearly polarized light, and the polarization direction of the linearly polarized light can be arbitrarily controlled.

[0188] Based on the desired twist angle distribution pattern of the liquid crystal element, the continuous twist angle distribution is discretized and converted into a discrete twist angle distribution. Let the total number of discrete values ​​be 2N. To ensure that the absolute value of the twist angle does not exceed π, that is, all 2N discrete twist angle values ​​are within the range of -π to π, the values ​​are taken as -π+C0, -(N-1)π / N+C0, -(N-2)π / N+C0, ..., -π / N+C0, C0, π / N+C0, 2π / N+C0, 3π / N+C0, ..., (N-1)π / N+C0, where C0 is a constant and 0 ≤ C0 ≤ π / N. The desired twist angle of each region in the element to be exposed is rounded to the nearest discrete value (or the desired twist angle can be converted into a corresponding discrete value by methods such as upward or downward approximation).

[0189] Based on the principle of in-situ dynamic light alignment guiding liquid crystal twisting and alignment, after discretizing the twisting angle distribution pattern of the liquid crystal element, the entire exposure process is sequentially divided into 2N independent sub-processes. Between two adjacent sub-processes, the linear polarization direction of the exposure beam differs by an angle of π / N, thus achieving the effect of gradually rotating the polarization direction during ultraviolet exposure. After executing q sub-exposure processes sequentially, the polarization direction rotates by a total of (q-1)×π / N angles, and the photosensitive alignment molecules of the upper glass substrate also rotate synchronously by the same angle, resulting in the same twisting angle for the final liquid crystal twisting and alignment structure. Considering that the twisting angle of each region in the liquid crystal element ranges from -π to π, the exposure sub-processes are further divided according to the following rules.

[0190] The exposure process is divided into 2N independent sub-processes, and the total exposure amount (the product of exposure intensity and exposure time) of each sub-process must be greater than a set threshold. In this embodiment, it is assumed that the total exposure amount of each sub-process is equal (of course, they can also be unequal, and this is not limited). For the first N exposure sub-processes, the linear polarization direction of the exposure beam in the first sub-process is set to π / 2 + C0. Between adjacent sub-processes, the linear polarization direction of the exposure beam in the later sub-process increases by an angle of π / N compared to the linear polarization direction in the previous sub-process. For the last N exposure sub-processes, the linear polarization direction of the exposure beam in the first sub-process is set to (N-2)π / 2N + C0. Between adjacent sub-processes, the linear polarization direction of the exposure beam in the later sub-process decreases by an angle of π / N compared to the linear polarization direction in the previous sub-process.

[0191] Based on the discretized torsion angle distribution and a series of predefined exposure sub-processes, the exposure process experienced by each region in the basic liquid crystal element is determined. For each region in the liquid crystal element with discretized torsion angles of C0, π / N+C0, 2π / N+C0, 3π / N+C0, ..., (N-1)π / N+C0 (a total of N different torsion angles), the region selectively undergoes the first N exposure sub-processes according to the desired final torsion angle value. If the discretized torsion angle of the region is jπ / N+C0, then the region is exposed in the first j+1 exposure sub-processes and is not exposed in subsequent exposure sub-processes; for liquid crystal elements... Each region in the crystal element with a discretized twist angle of -π+C0, -(N-1)π / N+C0, -(N-2)π / N+C0, ..., -π / N+C0 (a total of N different twist angles) must selectively undergo the next N exposure sub-processes according to the discretized twist angle value of the region. If the discretized twist angle of the region is -jπ / N+C0, then the region will be exposed in the N+1 to N+j exposure sub-processes, and will not be exposed in subsequent exposure sub-processes.

[0192] Based on the exposure sub-processes experienced by each region in the basic liquid crystal element, a total of 2N images to be loaded into the patterning exposure system are designed. Each pixel in the image corresponds to a region in the basic liquid crystal element. The p-th image represents the overall state of whether each region of the liquid crystal element has been exposed during the p-th exposure sub-process. These images are sequentially loaded into the LCOS element or DMD element in the exposure system, and 2N exposure sub-processes are performed in sequence to fabricate the basic liquid crystal element into a liquid crystal element with a specific twist angle distribution pattern.

[0193] It should be noted that in this in-situ dynamic photo-alignment exposure process, the total exposure amount and the number of exposure sub-processes are both key parameters that need to be controlled. If the total exposure amount (the product of exposure intensity and exposure time) is insufficient, or if the number of exposure sub-processes (2N) is too small, the change in the alignment direction of the photosensitive alignment molecules will not keep up with the change in the polarization direction of the exposure beam. This will cause the liquid crystal twisted alignment structure guided by the photosensitive alignment molecules to gradually mismatch with the polarization direction of the exposure, ultimately resulting in the actual twist angle of the liquid crystal twisted alignment not matching the desired twist angle. In addition, discretizing the phase space distribution is an approximation method to simplify the ideal twist angle space distribution to an actually fabricable twist angle space distribution. However, as the number of discretized values ​​and the number of exposure sub-processes (both 2N) decrease, the twist angle space distribution of the fabricated liquid crystal device will deviate further from the ideal twist angle distribution, ultimately reducing the light field phase modulation effect of the device.

[0194] like Figure 17 This is another flowchart of the liquid crystal element fabrication method provided in the embodiments of the present invention.

[0195] In this embodiment, a layer-by-layer twisted arrangement structure of liquid crystal molecules is achieved by incorporating a photosensitive chiral material (different from the aforementioned photosensitive alignment material) into the liquid crystal. The photosensitive chiral material can be, for example, but not limited to, the following types: photosensitive microparticles, photosensitive left- or right-handed materials, or photosensitive open- or closed-loop materials, etc.

[0196] The method for fabricating this liquid crystal element includes the following steps:

[0197] In step 1701, two glass substrates are prepared, and one side surface of one of the glass substrates is oriented (e.g., the aforementioned fixed orientation method can be used) to form an orientation layer with regular molecular arrangement and orientation direction.

[0198] In step 1702, a glass substrate with an alignment layer is aligned with another glass substrate with the alignment layer facing inward, and a spacer material is filled between the two glass substrates to keep the thickness of each region inside the two glass substrates the same.

[0199] In step 1703, a mixture of photosensitive chiral material and liquid crystal material or liquid crystal polymer material is poured into the two glass substrates, and then the two glass substrates are sealed with a curing adhesive to obtain the element to be exposed.

[0200] In step 1704, the upper glass substrate of the element to be exposed is facing upwards, and the mixture in the element to be exposed is subjected to an exposure process of a certain intensity and duration in sequence, so that the liquid crystal molecules form a specific non-uniform arrangement structure in different regions between the upper and lower glass substrates.

[0201] Specifically, liquid crystal molecules in each region are arranged in a layer-by-layer twisted pattern, with adjacent layers twisting at the same angle. The liquid crystal element as a whole exhibits a patterned spatial distribution of twist angles, with each region having a specific total twist angle.

[0202] In a mixture of liquid crystal and photosensitive chiral materials, the photosensitive chiral molecules exert a certain torsional force on the liquid crystal molecules, inducing them to form a layer-by-layer tortuous arrangement. Chirality indicates whether the tortuous arrangement is left-handed or right-handed, i.e., the sign of the tortuous angle. Under certain exposure conditions (the wavelength and intensity of the exposure depend on the type and concentration of the photosensitive chiral material), the photosensitive chiral material undergoes reactions such as photoisomerization or photoredox, causing changes in the configuration of the photosensitive chiral molecules. For example, the molecular configuration may change from left-handed to right-handed; some chemical functional groups may change from open-ring to closed-ring configurations. Correspondingly, the change in the configuration of the photosensitive chiral molecules alters the magnitude of their tortional force on the liquid crystal molecules, ultimately changing the tortuous angle of the liquid crystal's tortuous arrangement.

[0203] Based on the above principles, by reasonably controlling the exposure conditions (such as adjusting the total exposure amount corresponding to the exposure intensity and exposure time), it is possible to achieve a liquid crystal twisted alignment structure with arbitrary twist angles. Taking a photosensitive chiral material that reduces the liquid crystal alignment twist angle when photoinduced changes as an example, the specific preparation process is as follows: Figure 18 As shown:

[0204] First, the liquid crystal material and the photosensitive chiral material are mixed and poured between two glass substrates. The inner surface of one of the glass substrates is oriented. At this point, the liquid crystal molecules, under the torsional force of the photosensitive chiral molecules, form an initial twisted arrangement structure with a twist angle of φ1. Figure 18 As shown in (a);

[0205] Then, the mixture of liquid crystal material and photosensitive chiral material within the glass substrate is exposed. The exposure time is set to T, and the exposure intensity is adjusted to I2, I3, and I4 respectively (or the exposure intensity can be fixed while adjusting the exposure time). The internal photosensitive chiral molecules undergo different degrees of configurational changes, leading to varying degrees of alteration in the torsional force on the liquid crystal molecules. For example... Figure 18 As shown in (b), (c), and (d), as the exposure intensity increases, the number of photosensitive molecules undergoing internal configuration changes also increases. Therefore, after the exposure stops, the corresponding twist angles are φ1 > φ2 > 0 and φ4 < φ3 < 0, respectively, which means that liquid crystal twisted arrangement structures with different twist angles can be formed.

[0206] Based on the above-mentioned fabrication principle of liquid crystal twisted arrangement structure, a patterned exposure process can be carried out using a specific silicon-based liquid crystal (LCOS) device or a digital micromirror device (DMD) device, and finally a liquid crystal element with a patterned twist angle spatial distribution can be fabricated.

[0207] In the process of patterned exposure, an exposure beam is irradiated onto the liquid crystal element to be exposed, and the wavelength of the exposure beam is within the range in which the photosensitive chiral material can respond and thus undergo photoinduced changes; the liquid crystal element to be exposed is divided into various regions and each region undergoes an independent exposure process, as detailed below:

[0208] (1) Based on the twist angle distribution pattern to be formed by the liquid crystal element, the continuous twist angle distribution is discretized and converted into a discrete twist angle distribution.

[0209] For example, let the total number of discrete values ​​be 2N. To ensure that the absolute value of the twist angle does not exceed π, that is, all 2N discrete twist angle values ​​are within the range of -π to π, the values ​​are taken as -π+C0, -(N-1)π / N+C0, -(N-2)π / N+C0, ..., -π / N+C0, C0, π / N+C0, 2π / N+C0, 3π / N+C0, ..., (N-1)π / N+C0, where C0 is a constant and 0 ≤ C0 ≤ π / N; the theoretical twist angle of each region in the second liquid crystal element is rounded to the nearest discrete value (or the desired twist angle can be converted into the corresponding discrete value by methods such as upward or downward approximation).

[0210] (2) The exposure process is divided into 2N independent sub-processes, and the total exposure amount (the product of exposure intensity and exposure time) of each sub-process must be greater than a set threshold. In this embodiment, the first exposure sub-process is set with a separate total exposure amount, while the total exposure amounts of the second to the 2Nth exposure sub-processes are all equal (of course, they can also be unequal, and this is not limited). Each exposure sub-process can change the overall twist angle of the liquid crystal arrangement in the exposed area by π / N (the twist angle can be increased or decreased by π / N, depending on the type and chirality of the specific photosensitive chiral material incorporated).

[0211] (3) Based on the discretized torsion angle distribution and the series of exposure sub-processes, determine the exposure process experienced by each region in the liquid crystal element to be exposed. Specifically, it can be divided into the following two cases:

[0212] a) Select a specific type and chirality of photosensitive material. In the first exposure sub-process, the total twist angle of the liquid crystal arrangement reaches a uniform initial value. In the second to 2Nth exposure sub-processes, the total twist angle of the liquid crystal arrangement decreases by π / N. For each region in the element to be exposed, several exposure sub-processes are selectively performed based on the desired discrete twist angle value for that region. If the discrete twist angle of the region is (Nj)π / N+C0, then that region is exposed in the first j exposure sub-processes and not exposed in subsequent exposure sub-processes.

[0213] b) Select a specific type and chirality of photosensitive material. In the first exposure sub-process, ensure the total twist angle of the liquid crystal arrangement reaches a uniform initial value. In the second to 2Nth exposure sub-processes, increase the total twist angle of the liquid crystal arrangement by π / N. For each region in the element to be exposed, selectively subject it to several exposure sub-processes based on the desired discrete twist angle value for that region. If the discrete twist angle of the region is (jN-1)π / N+C0, then that region is exposed in the first j exposure sub-processes and not in subsequent exposure sub-processes.

[0214] (4) Based on the exposure sub-process experienced by each region in the liquid crystal element, design all the images that need to be loaded in the patterned exposure system, and load each image in sequence for exposure.

[0215] For example, if 2N images need to be loaded, each pixel in the image corresponds to a region in the liquid crystal element. The p-th image represents the overall state of whether each region of the liquid crystal element is exposed during the p-th exposure sub-process. These images are loaded sequentially into the LCOS element or DMD element in the exposure system, and 2N exposure sub-processes are performed in sequence to fabricate the liquid crystal element with a specific twist angle distribution pattern.

[0216] Accordingly, embodiments of the present invention also provide a method for fabricating an ultra-wideband optical field phase modulation device, such as... Figure 19 The diagram shown is a flowchart of this method, which includes the following steps:

[0217] In step 1901, two basic liquid crystal elements are prepared, one of which is used as the first liquid crystal element and the other is used as the element to be processed. The basic liquid crystal element includes an upper glass substrate and a lower glass substrate, and a first liquid crystal is filled between the upper glass substrate and the lower glass substrate. The liquid crystal molecules of the first liquid crystal are uniformly arranged, and the arrangement direction of each liquid crystal molecule is consistent.

[0218] In step 1902, based on the element to be processed, a second liquid crystal element is prepared. The second liquid crystal element includes an upper glass substrate and a lower glass substrate, and a second liquid crystal is filled between the upper glass substrate and the lower glass substrate. The liquid crystal molecules of the second liquid crystal are non-uniformly arranged, and the second liquid crystal is divided into different regions. The liquid crystal molecules in each region form a layer-by-layer twisted arrangement, and the twist angle of the liquid crystal molecules between adjacent layers is the same. The second liquid crystal as a whole presents a patterned spatial distribution of twist angles, and each region has a specific total twist angle.

[0219] In step 1903, the lower surface of the lower glass substrate of the second liquid crystal element is bonded to the upper surface of the upper glass substrate of the first liquid crystal element using optical adhesive to obtain an ultra-wideband optical field phase modulation device.

[0220] When bonding two liquid crystal elements with optical adhesive, an alignment operation is performed to ensure that the orientation direction of the upper glass substrate in the first liquid crystal element is perpendicular to the orientation direction of the lower glass substrate in the second liquid crystal element.

[0221] In this embodiment, the fabrication methods of the two basic liquid crystal elements can be the same or different, for example:

[0222] In some embodiments, both basic liquid crystal elements are fabricated by filling liquid crystal material between the two glass substrates using a method where the lower glass substrate is aligned in a fixed manner and the upper glass substrate is aligned in an erasable light manner. Then, based on one of the basic liquid crystal elements, a second liquid crystal element is fabricated using an in-situ dynamic light alignment method with rotational exposure of the linear polarization direction.

[0223] In some embodiments, a basic liquid crystal element is prepared by using a method in which a lower glass substrate is in a fixed orientation and an upper glass substrate is in an erasable light orientation, and then liquid crystal material is injected between the two glass substrates; another basic liquid crystal element is prepared by using a method in which both the upper and lower glass substrates are in an erasable light orientation, and then a mixture of liquid crystal material and light-absorbing dye is injected between the two glass substrates; then, based on one of the basic liquid crystal elements, a second liquid crystal element is prepared by using an in-situ dynamic light orientation method with rotational exposure of the linear polarization direction.

[0224] It should be noted that in the actual manufacturing process, a batch of basic liquid crystal elements can be prepared. Then, the thickness of each basic liquid crystal element is measured and marked. Liquid crystal elements with equal thicknesses are then combined for use (one as the first liquid crystal element and the other for preparing the second liquid crystal element). This can further improve the yield rate of the manufacturing process and avoid waste.

[0225] like Figure 20 The diagram shown is another flowchart of a method for fabricating an ultra-wideband optical field phase modulation device provided in an embodiment of the present invention, including the following steps:

[0226] In step 2001, a first liquid crystal element is prepared. The first liquid crystal element includes an upper glass substrate and a lower glass substrate, and a first liquid crystal is filled between the upper glass substrate and the lower glass substrate. The liquid crystal molecules of the first liquid crystal are uniformly arranged, and the arrangement direction of each liquid crystal molecule is consistent.

[0227] In step 2002, a second liquid crystal element is prepared. The second liquid crystal element includes an upper glass substrate and a lower glass substrate, and a second liquid crystal is filled between the upper glass substrate and the lower glass substrate. The liquid crystal molecules of the second liquid crystal are non-uniformly arranged. The second liquid crystal is divided into different regions. The liquid crystal molecules in each region form a layer-by-layer twisted arrangement, and the twist angle of the liquid crystal molecules between adjacent layers is the same. The second liquid crystal as a whole presents a patterned spatial distribution of twist angles, and each region has a specific total twist angle.

[0228] In step 2003, the lower surface of the lower glass substrate of the second liquid crystal element is bonded to the upper surface of the upper glass substrate of the first liquid crystal element using optical adhesive to obtain an ultra-wideband optical field phase modulation device.

[0229] Similarly, when bonding two liquid crystal elements with optical adhesive, an alignment operation is performed to make the orientation direction of the upper glass substrate in the first liquid crystal element perpendicular to the orientation direction of the lower glass substrate in the second liquid crystal element.

[0230] In this embodiment, the first liquid crystal element and the second liquid crystal element can be fabricated in various ways, such as:

[0231] In some embodiments, a first liquid crystal element can be fabricated using two glass substrates with a fixed orientation and an erasable light orientation, and a second liquid crystal element can be fabricated using a method based on doping a liquid crystal material with a photosensitive chiral material.

[0232] In some embodiments, the first liquid crystal element can be prepared by means of fixed orientation of two glass substrates or by means of erasable light orientation, and the second liquid crystal element can be prepared by means of doping the liquid crystal material with photosensitive chiral material.

[0233] Similarly, in the actual manufacturing process, batches of first and second liquid crystal elements can be prepared, and the thickness of each liquid crystal element can be measured and marked. First and second liquid crystal elements with equal thickness can be combined for use, which can further improve the yield of the manufacturing process and avoid waste.

[0234] like Figure 21 The diagram shown is another flowchart of a method for fabricating an ultra-wideband optical field phase modulation device provided in an embodiment of the present invention, including the following steps:

[0235] In step 2101, a first liquid crystal element is prepared. The basic liquid crystal element includes an upper glass substrate and a lower glass substrate, and a first liquid crystal is filled between the upper glass substrate and the lower glass substrate. The liquid crystal molecules of the first liquid crystal are uniformly arranged, and the arrangement direction of each liquid crystal molecule is consistent.

[0236] In step 2102, the upper glass substrate of the first liquid crystal element is used as the lower glass substrate of the second liquid crystal element to prepare the second liquid crystal element. The second liquid crystal element includes an upper glass substrate and a lower glass substrate, and a second liquid crystal is filled between the upper glass substrate and the lower glass substrate. The liquid crystal molecules of the second liquid crystal are non-uniformly arranged, and the second liquid crystal is divided into different regions. The liquid crystal molecules in each region form a layer-by-layer twisted arrangement, and the twist angle of the liquid crystal molecules between adjacent layers is the same. The second liquid crystal as a whole presents a patterned twist angle spatial distribution, and each region has a specific total twist angle.

[0237] In step 2103, the first liquid crystal element and the second liquid crystal element constitute an ultra-wideband optical field phase modulation device sharing a common intermediate substrate.

[0238] When the first liquid crystal element and the second liquid crystal element are fabricated using a shared intermediate substrate, both sides of the intermediate substrate are oriented, and the orientation directions of the two sides are aligned so that the orientation direction of the upper glass substrate in the first liquid crystal element is perpendicular to the orientation direction of the lower glass substrate in the second liquid crystal element.

[0239] In this embodiment, the first liquid crystal element can be fabricated in various ways, such as:

[0240] In some embodiments, a first liquid crystal element may be prepared by using two glass substrates with fixed orientation; then a second liquid crystal element may be prepared by in-situ dynamic light orientation based on the polarization direction of rotational exposure, or by using a method based on liquid crystal doping with photosensitive chiral materials.

[0241] In some embodiments, a first liquid crystal element can be prepared by using two glass substrates with a fixed orientation and an erasable light orientation; then, a second liquid crystal element can be prepared by filling a mixture of liquid crystal material and light-absorbing dye between the two glass substrates and by rotating the exposure linear polarization direction in an in-situ dynamic light orientation method, or by using a method based on liquid crystal doping with photosensitive chiral materials to prepare the second liquid crystal element.

[0242] The above embodiments are merely illustrative examples of some methods for fabricating the ultra-wideband optical field phase modulation device provided in the embodiments of the present invention, and are not intended to limit the scope of the present invention. Various fabrication processes for the above-described liquid crystal elements can be referred to the preceding sections. Figure 8 , Figure 9 and Figure 12 The instructions are as follows, and some steps can be adjusted according to actual needs.

[0243] The method for fabricating ultra-wideband optical field phase modulation devices provided in this invention can be used to fabricate such devices in various ways, especially the in-situ dynamic optical alignment fabrication process. This process is simple, requiring only conventional liquid crystal device processes and the direct guidance of a twisted liquid crystal alignment structure. The fabrication process exhibits high consistency and efficiency. Moreover, as long as the thickness of the twisted liquid crystal alignment structure is sufficiently large, an ultra-wideband optical field phase modulation effect can be achieved. Therefore, the absolute thickness of the liquid crystal layer does not need to be strictly controlled during the fabrication process, effectively improving the device yield.

[0244] The liquid crystal element fabrication method provided in this invention can easily and conveniently fabricate devices with corresponding stacked liquid crystal arrangement structures (uniform arrangement + patterned twist angle spatial distribution). This allows for efficient and free structural control of the phase parameters of the incident light field in an ultra-wide band, from visible and near-infrared to mid-infrared, generating arbitrary light field phase distribution structures. This method can be widely used in applications such as vortex light fields, polarization gratings, and holographic imaging.

[0245] Furthermore, the second liquid crystal element with a twisted arrangement structure in this invention is, in principle, made to exceed the thermal equilibrium steady state by injecting external energy (the twist angle of the twisted arrangement structure will not exceed π / 2 under the thermal equilibrium steady state), and to reach a metastable structure with a twist angle exceeding π / 2. However, under conditions such as drastic temperature changes, pressing, impact, or strong light irradiation, this metastable twisted arrangement structure will change, and the arrangement of the region with a twist angle exceeding π / 2 will change. When it returns to the thermal equilibrium steady state, the twist angle will be less than π / 2 (for example, the twist angle is 3π / 4 in the metastable state, and the twist angle will become π / 4 when it returns to the steady state, that is, it will become the supplementary angle of the twist angle under the metastable state). Therefore, the overall twist angle distribution pattern of the liquid crystal will change, which will destroy the overall phase modulation effect on the incident light field.

[0246] To address the instability issues of liquid crystal devices, certain processing methods can be employed to improve the stability of the twisted arrangement structure. Firstly, liquid crystal polymer materials can be used to fabricate the liquid crystal elements. Compared to ordinary liquid crystal materials with good flowability, liquid crystal polymer materials can undergo polymerization reactions under appropriate conditions (such as light exposure), where liquid crystal molecules polymerize to form a stable arrangement structure identical to that before polymerization. Therefore, after forming the arrangement structure of the first and second liquid crystal devices using liquid crystal polymer materials according to the preparation method of this invention, additional polymerization operations can be performed to maintain the arrangement structure within the liquid crystal devices, preventing it from being affected by the external environment. Secondly, polymer stabilization methods can be used to stabilize the arrangement structure within the liquid crystal devices. In principle, polymer stabilization involves mixing some polymer monomer materials into ordinary liquid crystal materials with good flowability. Under appropriate conditions (such as light exposure), the monomer materials undergo polymerization reactions to form a dense polymer network, which firmly locks the arrangement structure of the liquid crystal molecules within the polymer network, thereby stabilizing the twisted arrangement structure within the liquid crystal device. Therefore, after forming the arrangement structure of the first and second liquid crystal devices according to the preparation method of this invention, additional polymer stabilization operations can be performed to maintain the arrangement structure within the liquid crystal devices, preventing it from being affected by the external environment.

[0247] The difference between the two methods for improving the stability of liquid crystal devices lies in the fact that in the first method, the liquid crystal material itself is polymerizable, and the stability of the arrangement structure is achieved through its own polymerization; in the second method, the liquid crystal material itself is not polymerizable, and a polymer network structure is formed by the polymerization reaction of additional monomer materials to encapsulate and stabilize the overall arrangement structure of the internal liquid crystal molecules.

[0248] Furthermore, polymerization reactions are generally initiated under illumination. Therefore, when combining the erasable photoorientation, in-situ dynamic photoorientation, and liquid crystal doping photosensitive chiral material preparation methods of this invention, multiple exposure steps are involved. It is crucial to carefully distinguish the exposure sequence and its rationality to prevent interference between exposure steps. Specifically, different wavelengths of light sources can be used for photoorientation and photopolymerization operations respectively. For example, a 350-400 nm light source can be used for photoorientation or the reaction of photosensitive chiral materials to prepare a second liquid crystal device, while a 500-550 nm light source can be used for photopolymerization to form a liquid crystal polymer or a polymer network structure, thereby stabilizing the liquid crystal alignment structure.

[0249] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. An ultra-wideband optical field phase modulation device, characterized in that, include: A second liquid crystal element and a first liquid crystal element are stacked one on top of the other; The first liquid crystal element includes an upper glass substrate and a lower glass substrate, and a first liquid crystal is filled between the upper glass substrate and the lower glass substrate; the liquid crystal molecules of the first liquid crystal are uniformly arranged, and the arrangement direction of each liquid crystal molecule is consistent, wherein the arrangement direction refers to the direction of the long axis of the liquid crystal molecule. The second liquid crystal element includes an upper glass substrate and a lower glass substrate, with a second liquid crystal filling the space between the upper glass substrate and the lower glass substrate. The liquid crystal molecules of the second liquid crystal are arranged in a non-uniform manner, and the second liquid crystal as a whole presents a patterned spatial distribution of twist angles and is divided into different regions. The liquid crystal molecules in each region form a layer-by-layer twisted arrangement with a specific total twist angle.

2. The ultra-wideband optical field phase modulation device according to claim 1, characterized in that, The arrangement direction of the bottom layer of liquid crystal molecules in the second liquid crystal is perpendicular to the overall arrangement direction of the liquid crystal molecules in the first liquid crystal.

3. The ultra-wideband optical field phase modulation device according to claim 1, characterized in that, A spacer material is also filled between the upper glass substrate and the lower glass substrate to maintain a uniform thickness between the upper glass substrate and the lower glass substrate.

4. The ultra-wideband optical field phase modulation device according to claim 1, characterized in that, The thickness of the second liquid crystal is the same as the thickness of the first liquid crystal.

5. The ultra-wideband optical field phase modulation device according to claim 1, characterized in that, The second liquid crystal and the first liquid crystal are liquid crystal materials with fluidity or solid liquid crystal polymer materials.

6. The ultra-wideband optical field phase modulation device according to any one of claims 1 to 5, characterized in that, The lower surface of the lower glass substrate of the second liquid crystal element is bonded to the upper surface of the upper glass substrate of the first liquid crystal element by optical adhesive.

7. The ultra-wideband optical field phase modulation device according to any one of claims 1 to 5, characterized in that, The lower glass substrate of the second liquid crystal element and the upper glass substrate of the first liquid crystal element are integrally formed.

8. A method for fabricating a liquid crystal element, characterized in that, The method includes: A basic liquid crystal element is prepared, the basic liquid crystal element comprising an upper glass substrate and a lower glass substrate, wherein a liquid crystal is filled between the upper glass substrate and the lower glass substrate; the liquid crystal molecules of the liquid crystal are uniformly arranged, and the arrangement direction of each liquid crystal molecule is consistent. The basic liquid crystal element is subjected to patterned in-situ dynamic light alignment processing, so that liquid crystal molecules form specific non-uniform arrangements in different regions between the upper and lower glass substrates, and liquid crystal molecules in each region form a layer-by-layer twisted arrangement. The liquid crystal element as a whole presents a patterned twisted angle spatial distribution, and each region has a specific total twist angle.

9. The method for preparing a liquid crystal element according to claim 8, characterized in that, The preparation of the basic liquid crystal element includes: Prepare two glass substrates, one of which will be used as the upper glass substrate and the other as the lower glass substrate. A fixed alignment layer with consistent orientation and non-erasable is prepared on one side surface of the lower glass substrate; and a photosensitive alignment material is coated on one side surface of the upper glass substrate to form a photosensitive alignment layer that can be repeatedly erased and rewritten. The alignment layers of the upper and lower glass substrates are placed facing each other with their inward sides, and spacer material is filled in so that the thickness of each region inside the two glass substrates remains the same. Liquid crystal material or liquid crystal polymer material is poured into the upper and lower glass substrates, and then the edges of the two glass substrates are sealed with curing adhesive.

10. The method for fabricating a liquid crystal element according to claim 8, characterized in that, The preparation of the basic liquid crystal element includes: Prepare two glass substrates, and coat one side of each substrate with a rewritable photosensitive alignment material. Use linearly polarized light to uniformly align the photosensitive alignment layer of one glass substrate, ensuring that the photosensitive alignment material within the substrate is aligned perpendicular to the polarization direction of the linearly polarized light. Place the aligned glass substrate and the other glass substrate with their alignment layers facing inwards, and fill with spacer material to maintain the same thickness in all areas of both substrates. Mix a light-absorbing dye with a liquid crystal material or liquid crystal polymer material, pour the mixture into the two glass substrates, and then seal the perimeter of the two glass substrates with a curing adhesive. Or... Prepare two glass substrates, and coat one side of each glass substrate with an erasable photosensitive alignment material. First, place the alignment layers of the two glass substrates facing each other with their inward sides, and fill them with spacer material to ensure that each area of ​​the two glass substrates has the same thickness. Then, use linearly polarized light to uniformly align the photosensitive alignment layers of the two glass substrates so that the photosensitive alignment materials in the two glass substrates are aligned perpendicular to the polarization direction of the linearly polarized light. Mix a light-absorbing dye material with a liquid crystal material or a liquid crystal polymer material, pour the mixture into the two glass substrates, and then use a curing adhesive to firmly seal the edges of the two glass substrates.

11. The method for fabricating a liquid crystal element according to any one of claims 8 to 10, characterized in that, The patterned in-situ dynamic light alignment processing of the basic liquid crystal element includes: The basic liquid crystal element is divided into various regions, and each region undergoes an independent exposure process, the exposure process including: The exposure beam is shone onto the basic liquid crystal element from top to bottom; Based on the twist angle distribution pattern that the basic liquid crystal element is to form, the continuous twist angle distribution is discretized and converted into a discrete twist angle distribution. The exposure process is divided into multiple sub-processes, and the total exposure in each sub-process is greater than a set threshold. Based on the discretized torsion angle distribution and the divided exposure sub-processes, the exposure process experienced by each region in the basic liquid crystal element is determined. Based on the exposure process experienced by each region in the basic liquid crystal element, all images that need to be loaded are designed, and each image is loaded and exposed sequentially.

12. The method for fabricating a liquid crystal element according to claim 11, characterized in that, The exposure beam is linearly polarized light, and the polarization direction of the linearly polarized light can be arbitrarily controlled.

13. A method for fabricating a liquid crystal element, characterized in that, The method includes: Prepare two glass substrates, and coat one side of one of the glass substrates with an alignment material and perform an alignment treatment to form an alignment layer with the same orientation direction; A glass substrate with an alignment layer is aligned with another glass substrate with the alignment layer facing inward, and a spacer material is filled between the two glass substrates to keep the thickness of each region inside the two glass substrates the same. A photosensitive chiral material capable of guiding a twisted arrangement structure is mixed with a liquid crystal material or a liquid crystal polymer material. The mixture is poured into two glass substrates, and then the edges of the two glass substrates are sealed with a curing adhesive to obtain the element to be exposed. The mixture within the element to be exposed is subjected to exposure processes of a certain intensity and duration, so that liquid crystal molecules form specific twisted arrangements in different regions between the upper and lower glass substrates, and the liquid crystal element as a whole presents a patterned twisted angle distribution.

14. The method for fabricating a liquid crystal element according to claim 13, characterized in that, The element to be exposed is divided into several regions, and each region undergoes an independent exposure process, the exposure process including: Based on the twist angle distribution pattern that the exposed element is to form, the continuous twist angle distribution is discretized and converted into a discrete twist angle distribution. The exposure process is divided into multiple sub-processes, and the total exposure in each sub-process is greater than a set threshold. Based on the discretized torsion angle distribution and the divided exposure sub-processes, the exposure process experienced by each region in the element to be exposed is determined. Based on the exposure process experienced by each region in the element to be exposed, all images that need to be loaded are designed, and each image is loaded and exposed sequentially.

15. The method for fabricating a liquid crystal element according to claim 14, characterized in that, The wavelength of the exposure beam is within the range of wavelengths in which the photosensitive chiral material can respond and thus undergo photoinduced changes.

16. The method for fabricating a liquid crystal element according to claim 14, characterized in that, The photosensitive chiral material can be any of the following types: photosensitive microparticles, photosensitive left- or right-handed materials, or photosensitive open- or closed-loop materials.

17. A method for fabricating an ultra-wideband optical field phase modulation device, characterized in that, The method includes: Two basic liquid crystal elements are prepared, one of which is used as the first liquid crystal element and the other is used as the element to be processed; the basic liquid crystal element includes an upper glass substrate and a lower glass substrate, and a first liquid crystal is filled between the upper glass substrate and the lower glass substrate; the liquid crystal molecules of the first liquid crystal are uniformly arranged. Based on the element to be processed, a second liquid crystal element is prepared using the liquid crystal element preparation method according to any one of claims 8 to 12. The second liquid crystal element includes an upper glass substrate and a lower glass substrate, and a second liquid crystal is filled between the upper glass substrate and the lower glass substrate. The liquid crystal molecules of the second liquid crystal are non-uniformly arranged, and the second liquid crystal is divided into different regions. The liquid crystal molecules in each region form a layer-by-layer twisted arrangement. The second liquid crystal as a whole presents a patterned twist angle spatial distribution, and each region has a specific total twist angle. An ultra-wideband optical field phase modulation device is obtained by bonding the lower surface of the lower glass substrate of the second liquid crystal element to the upper surface of the upper glass substrate of the first liquid crystal element using optical adhesive.

18. The method for fabricating an ultra-wideband optical field phase modulation device according to claim 17, characterized in that, When bonding the lower surface of the lower glass substrate of the second liquid crystal element to the upper surface of the upper glass substrate of the first liquid crystal element with optical adhesive, an alignment operation is performed to make the alignment direction of the upper glass substrate in the first liquid crystal element perpendicular to the alignment direction of the lower glass substrate in the second liquid crystal element.

19. The method for fabricating an ultra-wideband optical field phase modulation device according to claim 17, characterized in that, The two basic liquid crystal elements are prepared using the same or different methods.

20. A method for fabricating an ultra-wideband optical field phase modulation device, characterized in that, The method includes: A first liquid crystal element is prepared, the first liquid crystal element comprising an upper glass substrate and a lower glass substrate, wherein a first liquid crystal body is filled between the upper glass substrate and the lower glass substrate; the liquid crystal molecules of the first liquid crystal body are uniformly arranged. A second liquid crystal element is prepared using the liquid crystal element preparation method according to any one of claims 13 to 16. The second liquid crystal element includes an upper glass substrate and a lower glass substrate, and a second liquid crystal is filled between the upper glass substrate and the lower glass substrate. The liquid crystal molecules of the second liquid crystal are non-uniformly arranged, and the second liquid crystal is divided into different regions. The liquid crystal molecules in each region are arranged in a layer-by-layer twisted pattern. The second liquid crystal as a whole exhibits a patterned spatial distribution of twist angles, and each region has a specific total twist angle. An ultra-wideband optical field phase modulation device is obtained by bonding the lower surface of the lower glass substrate of the second liquid crystal element to the upper surface of the upper glass substrate of the first liquid crystal element using optical adhesive.

21. The method for fabricating an ultra-wideband optical field phase modulation device according to claim 20, characterized in that, When bonding the lower surface of the lower glass substrate of the second liquid crystal element to the upper surface of the upper glass substrate of the first liquid crystal element with optical adhesive, an alignment operation is performed to make the alignment direction of the upper glass substrate in the first liquid crystal element perpendicular to the alignment direction of the lower glass substrate in the second liquid crystal element.

22. A method for fabricating an ultra-wideband optical field phase modulation device, characterized in that, The method includes: A first liquid crystal element is prepared, the first liquid crystal element comprising an upper glass substrate and a lower glass substrate, wherein a first liquid crystal body is filled between the upper glass substrate and the lower glass substrate; the liquid crystal molecules of the first liquid crystal body are uniformly arranged. The upper glass substrate of the first liquid crystal element is used as the lower glass substrate of the second liquid crystal element. The second liquid crystal element is prepared by the liquid crystal element preparation method according to any one of claims 8 to 16. The second liquid crystal element includes an upper glass substrate and a lower glass substrate, and a first liquid crystal is filled between the upper glass substrate and the lower glass substrate. The liquid crystal molecules of the second liquid crystal are non-uniformly arranged. The second liquid crystal is divided into different regions, and the liquid crystal molecules in each region form a layer-by-layer twisted arrangement. The second liquid crystal as a whole presents a patterned spatial distribution of twist angles, and each region has a specific total twist angle. The first liquid crystal element and the second liquid crystal element constitute an ultra-wideband optical field phase modulation device sharing a common intermediate layer substrate.

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