A method for generating structured light based on wedge-shaped liquid crystal structure

Abstract

The present invention relates to a method for generating structured light based on a wedge-shaped liquid crystal structure, comprising: selecting liquid crystal molecules with a birefringence effect, orienting the liquid crystal molecules using an orientation layer; making the upper and lower surfaces of the liquid crystal have a certain angle after orientation to form a wedge-shaped liquid crystal layer, and ensuring that the manufactured wedge-shaped liquid crystal layer contains an anisotropic liquid crystal structure; incident light is incident on the anisotropic liquid crystal structure, making the center of the incident light spot coincide with the liquid crystal center of the anisotropic liquid crystal structure, and the outgoing light passing through the liquid crystal center of the anisotropic liquid crystal structure is structured light. The present invention proposes the principle of birefringence based on the wedge-shaped liquid crystal structure, realizes the use of anisotropically oriented liquid crystal molecules as a generator of structured light, and realizes the separation of orthogonal polarization components (such as radial polarization and tangential polarization) of a complex light field and the orbital angular momentum they carry.

Description

Technical Field

[0001] The present invention relates to a method for generating structured light based on a wedge-shaped liquid crystal structure, and relates to the technical field of generating structured light fields. Background Art

[0002] Structured light fields have broad application prospects in the fields of optical micromanipulation, micromachining, super-resolution imaging, quantum technology, etc. Common structured light fields include vector light and vortex light. The vibration direction of the electric field vector of vector light shows cylindrical anisotropy. Common vector light includes radially polarized light and tangentially polarized light, and their corresponding electric field vectors are along the radial direction and the tangential direction, respectively. In addition, vector light also includes more complex forms, such as "45-degree" polarized light after the superposition of radial light and tangential light. Since vector light exhibits cylindrical anisotropy, high-order vector light can be expressed in the following form: ,in, is the orientation angle of the electric field vibration at the coordinate (x, y), θ(x, y) is the spatial azimuth corresponding to the position (x, y), and k represents the speed relationship between the electric field vibration direction and the spatial azimuth. Indicates the vibration direction of the electric field at the starting position. Vortex light refers to the spiral distribution of the electric field phase on the cross section perpendicular to the propagation direction of the light wave. Vector light field can be combined with vortex light to produce vector vortex light.

[0003] At present, the methods for generating structured light mainly include half-wave plates with spatial spiral changes, gratings, combined polarizers, coherent synthesis, metasurfaces, spatial light modulators, etc. However, the above methods either involve artificially designed structures or are bulky, resulting in low processing efficiency and high costs. Summary of the invention

[0004] In view of the above problems, an object of the present invention is to provide a method for generating structured light based on a wedge-shaped liquid crystal structure, which is capable of separating the orthogonal polarization components of a complex light field and the orbital angular momentum they carry.

[0005] In order to achieve the purpose of the invention, the technical solution adopted by the present invention is: a method for generating structured light based on a wedge-shaped liquid crystal structure, comprising:

[0006] Selecting liquid crystal molecules with a birefringence effect, and orienting the liquid crystal molecules using an orientation layer;

[0007] The upper and lower surfaces of the oriented liquid crystal have a certain angle to form a wedge-shaped liquid crystal layer, and the prepared wedge-shaped liquid crystal layer contains an anisotropic liquid crystal structure;

[0008] The incident light is incident on the anisotropic liquid crystal structure, so that the center of the incident light spot coincides with the liquid crystal center of the anisotropic liquid crystal structure, and the outgoing light passing through the liquid crystal center of the anisotropic liquid crystal structure is structured light.

[0009] Furthermore, the wedge-shaped liquid crystal structure is implemented based on a "sandwich" liquid crystal cell, wherein the manufacturing process of the "sandwich" liquid crystal cell includes:

[0010] A "sandwich" liquid crystal cell is prepared, wherein the "sandwich" liquid crystal cell comprises a transparent lower substrate layer with uniform thickness and an upper transparent cover layer, and the "sandwich" liquid crystal cell has an opening reserved for liquid crystal injection;

[0011] Introducing an alignment layer on the bottom of the upper transparent cover layer and / or the top surface of the lower substrate layer structure of the "sandwich" liquid crystal cell;

[0012] Pour liquid crystal molecules into the "sandwich" liquid crystal cell after the orientation treatment through the reserved opening;

[0013] The oriented liquid crystal layer is wedge-shaped, that is, the upper and lower surfaces of the liquid crystal present a certain angle, forming a "sandwich" wedge-shaped liquid crystal structure.

[0014] Furthermore, two methods are used to make the liquid crystal layer into a wedge shape, including:

[0015] First: using a wedge-shaped upper transparent cover layer to cover the lower substrate layer so that the injected liquid crystal layer is in a wedge shape;

[0016] Second: using a lower substrate layer and an upper transparent cover layer with uniform thickness, adjusting the formed liquid crystal layer by introducing spacers, and controlling the thickness of the spacers in the liquid crystal box to make the liquid crystal layer wedge-shaped.

[0017] Furthermore, the orientation adopts mechanical rubbing orientation or photo orientation.

[0018] Furthermore, the anisotropy of the liquid crystal layer is regulated by using the anisotropic pattern characteristics of the orientation layer, thereby changing the polarization characteristics of the outgoing light. The polarization characteristics of the outgoing light are determined by the spatial arrangement characteristics of the anisotropic liquid crystal molecules. When the liquid crystal layer is oriented to be columnar anisotropy, the polarization directions of the two outgoing vector lights passing through the liquid crystal are columnar, and the two outgoing lights are radially polarized and tangentially polarized, respectively.

[0019] Furthermore, the method also includes adjusting the polarization state of the incident light so that the incident light is circularly polarized light.

[0020] Furthermore, according to the dispersion relationship of the refractive index of the liquid crystal in the two main axis directions, monochromatic light or polychromatic light of a set wavelength is selected for incident, and the wavelength range allowed by the incident circularly polarized light should satisfy that there is a certain difference in the refractive index of the liquid crystal in the two main axis directions at the wavelength, that is, the liquid crystal layer undergoes birefringence in two directions at the inclined interface, wherein the greater the difference in the inclination angles of the upper and lower surfaces of the wedge-shaped liquid crystal, the greater the deviation angle of the two outgoing lights.

[0021] Furthermore, the phase topological charges carried by the two outgoing vector lights are related to the handedness of the incident circularly polarized light and the phase topological charges carried by the incident light.

[0022] Furthermore, the spatial orientation angle of the molecule The relationship with the spatial azimuth angle θ can be expressed as , where k is the speed at which the orientation angle of the liquid crystal molecules changes with the orientation angle of the spatial position. When k(θ) is not an integer of positive or negative 1, the orientation of the molecules is more complicated, that is, it is regarded as a complex columnar anisotropy. The complex columnar anisotropic orientation is achieved by direct light writing combined with controlling the polarization state of light. When the incident light passes through the complex columnar anisotropic orientation, the two outgoing lights are high-order structured lights.

[0023] Furthermore, when the anisotropic liquid crystal molecules are arranged in an array, and the incident light spot can illuminate the liquid crystal orientation area array, the emergent light is an array formed by multiple structured light beams; or, multiple incident light beams are irradiated through one or more liquid crystal orientation areas together, and the emergent light is multiple structured light beams.

[0024] The present invention adopts the above technical solution, and has the following characteristics:

[0025] Since the columnar anisotropic structure can be flexibly modulated by optical orientation technology, it can generate various vector light fields: radial polarized light, tangential polarized light, 45-degree polarized light, high-order vector light, vector vortex light, etc. Compared with the prior art, the present invention proposes the principle of birefringence based on the wedge-shaped liquid crystal structure, realizes the use of columnar anisotropically oriented liquid crystal molecules as a generator of structured light, and realizes the separation of orthogonal polarization components (such as radial polarization, tangential polarization) of complex light fields and the orbital angular momentum they carry. Its advantages are reflected in the following aspects:

[0026] The first is that the sources of liquid crystal materials that produce birefringence are abundant;

[0027] Secondly, the liquid crystal material is easy to present columnar anisotropic orientation characteristics under the action of the orientation layer, so this technology is widely applicable;

[0028] Third, the deflection angle of the emitted light is mainly affected by the refractive index, so for organic molecular materials with insignificant refractive index dispersion effect, it is beneficial to obtain broadband performance;

[0029] Fourth, the preparation process is convenient and efficient, without the need for complex and expensive equipment;

[0030] Fifth, there is no requirement for the absorption of the liquid crystal material used, so this method can be used to generate high-power vector light;

[0031] Sixth, this method of generating structured light based on liquid crystal birefringence can simultaneously obtain two beams of orthogonal polarized structured light.

[0032] In summary, compared with the currently commonly used structured light generation methods, the present invention does not involve complex micro-nano processing methods, and its advantages are significant. It has the advantages of wide applicability, low cost, simple process, high reliability, etc., and can be widely used in structured light generation. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Throughout the accompanying drawings, the same reference numerals are used to represent the same components. In the accompanying drawings:

[0034] Figure 1 This is a schematic diagram of a wedge-shaped column anisotropic liquid crystal structure according to an embodiment of the present invention;

[0035] Figure 2 This is a polarizing microscope photograph of the columnar anisotropic liquid crystal of an embodiment of the present invention;

[0036] FIG3( a ) is a diagram showing the polarization characterization effect of the output light 1 according to an embodiment of the present invention;

[0037] FIG3( b ) is a diagram showing the polarization characterization effect of the output light 2 according to an embodiment of the present invention;

[0038] FIG4( a ) is a diagram showing the interference fringe effect of the output light 1 according to an embodiment of the present invention;

[0039] FIG. 4( b ) is a diagram showing the interference fringe effect of the outgoing light 2 according to an embodiment of the present invention. DETAILED DESCRIPTION

[0040] It should be understood that the terms used herein are only for the purpose of describing specific example embodiments and are not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "one", "an" and "said" as used herein may also be meant to include plural forms. The terms "include", "comprise", "contain", and "have" are inclusive, and therefore specify the existence of stated features, steps, operations, elements and / or parts, but do not exclude the existence or addition of one or more other features, steps, operations, elements, parts, and / or combinations thereof. The method steps, processes, and operations described herein are not interpreted as necessarily requiring them to be performed in the specific order described or illustrated, unless the execution order is clearly indicated. It should also be understood that additional or alternative steps may be used.

[0041] Although the terms first, second, third, etc. can be used in the text to describe multiple elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms can only be used to distinguish an element, component, region, layer or section from another region, layer or section. Unless the context clearly indicates, terms such as "first", "second" and other numerical terms do not imply order or sequence when used in the text. Therefore, the first element, component, region, layer or section discussed below can be referred to as the second element, component, region, layer or section without departing from the teaching of the example embodiments.

[0042] For ease of description, spatially relative terms may be used herein to describe the relationship of one element or feature relative to another element or feature as shown in the figures, such as "inside", "outside", "inner side", "outer side", "below", "above", etc. Such spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation depicted in the figures.

[0043] Since it is difficult to generate structured light conveniently and efficiently with the prior art, the present invention provides a method for generating structured light based on a wedge-shaped liquid crystal structure, comprising: using liquid crystal molecules with a birefringence effect as raw materials, and orienting the liquid crystal molecules using a liquid crystal molecule orientation layer; a wedge-shaped mold can be used as a liquid crystal container so that the upper and lower surfaces of the liquid crystal have a certain angle after orientation; and regulating the polarization state of the incident light, wherein the incident light is incident on a certain surface of the liquid crystal and is obliquely emitted from the other surface, and two emitted lights will appear due to the birefringence effect, and the two emitted lights are orthogonally polarized structured lights.

[0044] The exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0045] The method for generating structured light based on a wedge-shaped liquid crystal structure provided in this embodiment includes the steps of:

[0046] S1. Using liquid crystal molecules with birefringence effect as raw materials (the two main axis directions of the liquid crystal molecules show different refractive indices), the liquid crystal molecules are oriented using an orientation layer, and the upper and lower surfaces of the liquid crystal after orientation have a certain angle to form a wedge-shaped liquid crystal layer, ensuring that the produced wedge-shaped liquid crystal layer contains a columnar anisotropic liquid crystal structure.

[0047] Specifically, the raw material can be a pure liquid crystal molecule material or a mixed material composed of multiple liquid crystal molecule monomers, which is not limited here. The wedge-shaped liquid crystal layer of this embodiment can be obtained by using a "sandwich" wedge-shaped liquid crystal box, introducing an orientation layer on the upper and lower surfaces of the "sandwich" wedge-shaped liquid crystal box, and using an orientation treatment to achieve a columnar anisotropic orientation of the orientation layer molecules; introducing liquid crystal molecules with birefringence characteristics into the liquid crystal box, under the action of the orientation layer, the liquid crystal molecules present the same anisotropic orientation characteristics, and the specific process includes:

[0048] S11. Prepare a "sandwich" liquid crystal box, including a transparent and uniformly thick lower substrate layer, an intermediate liquid crystal layer, and an upper transparent cover layer. The "sandwich" structure is reserved with an opening for liquid crystal to be poured into the intermediate liquid crystal layer. Among them, the lower substrate layer and the upper transparent cover layer of the "sandwich" need to be cleaned, for example, pure water, acetone, and ethanol can be used for ultrasonic cleaning respectively, and then plasma or ultraviolet ozone cleaning treatment is performed; in addition, the glass sheets used for the lower substrate layer and the upper transparent cover layer of the "sandwich" liquid crystal box must have high transparency, but are not limited to a certain material or thickness, and then the lower substrate layer and the upper transparent cover layer are bonded to form a "sandwich" liquid crystal box through gluing.

[0049] S12. Introduce an alignment layer on the bottom of the upper transparent cover layer and / or the top structural surface of the lower substrate layer of the cleaned "sandwich" liquid crystal box.

[0050] Specifically, the purpose of the "orientation layer" is to induce the orientation of the liquid crystal. Usually, the "orientation layer" is very thin, ranging from tens of nanometers to several microns. The "orientation layer" usually selects organic materials. Common commercial "orientation layers" include: PI, PVA, PTFE, azo molecules, etc., taking this as an example, but not limited to this. The specific selection of the orientation layer molecules can refer to the liquid crystal system used to achieve a better orientation effect, which is not limited here.

[0051] The orientation process can be mechanical friction orientation or photo orientation. Mechanical friction orientation is relatively mature in business and will not be described in detail here. Photo orientation means that the arrangement direction of the molecules in the orientation layer after irradiation with polarized light presents a specific angle with the polarization direction of the incident light, that is, the molecules in the orientation layer become parallel, and these parallel molecules will induce the orientation of the liquid crystal molecules under the action of intermolecular forces. Depending on the type and characteristics of the molecular chains of the orientation layer and the molecular chains of the liquid crystal body, there may be different angles between the orientations of the two. If photo orientation is used, the principle of the photo orientation process of the photo orientation layer material is: photoinduced cis-trans isomerism, photo cross-linking, photodegradation, etc. The wavelength conditions, power conditions, and time conditions used in the photo orientation treatment are determined by the photo orientation agent used. The photo orientation pattern can be achieved and controlled by laser direct writing orientation, dynamic mask technology, patterned half-wave plates, etc.

[0052] S13, pouring liquid crystal molecules into the "sandwich" liquid crystal box after the above-mentioned orientation treatment

[0053] The liquid crystal box has a reserved opening for liquid crystal to be poured in. The liquid crystal is placed in the reserved opening and automatically immersed in and fills the liquid crystal box. The liquid crystal molecules have a certain fluidity, and the molecules in the orientation layer are stable solid films. There is an intermolecular interaction between the two, but they will not dissolve each other. If the fluidity of the liquid crystal molecules is not ideal at room temperature, the liquid crystal material can be heated before pouring into the "sandwich" liquid crystal box.

[0054] The liquid crystal molecules will produce anisotropic orientation under the action of the orientation layer. Under the action of the intermolecular interaction force, the orientation layer molecules will induce the orientation of the liquid crystal molecules, and finally the liquid crystal molecules will also show anisotropic orientation characteristics. The characteristics of the orientation pattern of the liquid crystal molecules are consistent with the characteristics of the orientation pattern of the orientation layer molecules, which is columnar anisotropy. Specifically, the orientation layer molecules are first oriented into a columnar anisotropic pattern (for example, the direction of the molecular chain is radial or tangential, forming a radial pattern structure), and then the orientation of the liquid crystal molecules is columnar anisotropy. For the mechanical friction method, when the friction is carried out in an axisymmetric rotation manner, a columnar anisotropic orientation layer can be obtained. For the optical orientation method, when the polarization direction of the incident light presents a columnar symmetric state, or by controlling the polarization state of the light through direct optical writing, a columnar anisotropic orientation layer can be obtained. Under the action of the orientation layer, the liquid crystal molecules will present a columnar anisotropic orientation arrangement according to the anisotropic characteristics of the orientation layer molecules.

[0055] In this embodiment, the liquid crystal material should show refractive index anisotropy, that is, the refractive index of the liquid crystal molecules in the two main axis directions has a certain difference. The greater the difference between the two refractive indices, the more significant the birefringence phenomenon. The liquid crystal molecules can present a liquid crystal phase under the temperature conditions used. There are many types of liquid crystal molecules. The liquid crystal molecules can be rod-shaped molecules or disc-shaped molecules. The conditions to be met are as follows: the liquid crystal molecules can be oriented by the orientation layer under the temperature conditions used, that is, they show the characteristics of columnar anisotropic orientation. There is no requirement for the molecular weight of the liquid crystal molecules.

[0056] Furthermore, the selection of liquid crystal molecules in the raw materials is not limited to the size of the molecular weight, is not limited to the mixture of multiple liquid crystal molecules, and is not limited to whether a polymerization reaction is introduced into the finally obtained organic molecular film.

[0057] S14, making the oriented liquid crystal layer into a wedge shape, that is, the upper and lower surfaces of the liquid crystal present a certain angle, so as to obtain a "sandwich" wedge-shaped liquid crystal box.

[0058] To make the aligned liquid crystal layer into a wedge shape, a wedge-shaped transparent sheet can be used as the upper structure, or a transparent sheet with uniform thickness placed obliquely can be used as the upper structure.

[0059] Furthermore, two methods can be used to make the upper and lower surfaces of the liquid crystal layer present a certain tilt angle, that is, a wedge shape, including:

[0060] First: a wedge-shaped transparent glass sheet can be used as the upper transparent covering layer;

[0061] Second, the upper transparent cover layer with uniform thickness can be tilted and covered on the sample, and the tilt angle can be adjusted by using spacers of different thicknesses. The thickness of the liquid crystal layer formed after cooling can be adjusted by introducing spacers, and the film thickness of the liquid crystal layer can be changed by controlling the thickness of the spacers in the liquid crystal cell to obtain a "sandwich" wedge-shaped liquid crystal cell, so that the obtained liquid crystal layer should contain a columnar anisotropic liquid crystal structure.

[0062] S2. Observe the above materials using a polarizing microscope to confirm the anisotropic orientation characteristics inside the liquid crystal after cooling; for example: observe the anisotropic orientation of the liquid crystal layer under a polarizing microscope. If the liquid crystal molecules are oriented in a columnar symmetry, a typical "black cross extinction" phenomenon will appear under the polarizing microscope.

[0063] S3. Adjust the polarization state of the incident light so that the incident light is circularly polarized light.

[0064] Specifically, according to the dispersion relationship of the refractive index of the liquid crystal in the two main axis directions, a monochromatic light or polychromatic light of a certain wavelength is selected for incident. If the incident light is linearly polarized light, it can be converted into circularly polarized light after passing through a linear polarizer and a quarter wave plate; the incident light can be a monochromatic continuous laser, polychromatic light, pulsed light, etc.; the incident light includes but is not limited to circularly polarized light or linearly polarized light.

[0065] S4. The incident light with circular polarization characteristics is incident on the columnar anisotropic liquid crystal structure, so that the center of the incident light spot coincides with the center of the columnar anisotropic liquid crystal. The two outgoing lights passing through the center of the liquid crystal are structured lights. The two outgoing structured lights are vector lights, and the polarization directions are orthogonal. When the incident light is a complex light field, the technology can separate the orthogonal polarization components (such as radial polarization and tangential polarization) of the complex light field and the orbital angular momentum they carry. Because the generation process of structured light does not involve light absorption effect, the available intensity threshold is high. If the liquid crystal orientation area is smaller than the size of the incident light, an objective lens or a lens can be used to focus the incident light.

[0066] The wavelength range allowed by the circular polarization should satisfy the requirement that the refractive index of the liquid crystal in the two principal axis directions at the wavelength has a certain difference, that is, the liquid crystal layer has birefringence in two directions at the tilted interface. Since the liquid crystal layer is oriented as a columnar anisotropy, the polarization directions of the two outgoing vector lights passing through the liquid crystal are columnar; for example, if the liquid crystal layer is a columnar symmetric anisotropy, the two outgoing lights are radially polarized and tangentially polarized, respectively.

[0067] The refractive index of the liquid crystal molecules in the direction of the principal axis should have a certain difference. For uniaxial anisotropic liquid crystal molecules, its n o and n e Should be different. Due to the difference in refractive index of the liquid crystal in the two main axis directions and the presence of a certain inclination angle between the upper and lower surfaces of the liquid crystal, when circularly polarized light is incident from one surface of the liquid crystal, two beams of light will be inclined to emerge from the other surface of the liquid crystal. The two beams of emitted light present cylindrical vector polarization characteristics, and the polarizations of the two emitted lights are orthogonal, and there is a certain angle between the two emitted lights. The angle between the two emitted lights is related to the difference in refractive index of the liquid crystal in the two main axis directions and the inclination angle of the upper and lower surfaces of the liquid crystal. The greater the refractive index difference, the greater the inclination angle of the upper and lower surfaces of the liquid crystal, and the greater the angle between the two emitted lights. According to the relationship between the refractive index difference of the liquid crystal in the two main axis directions under the selected wavelength conditions, the required inclination angle difference between the upper and lower surfaces of the wedge-shaped liquid crystal is determined; the greater the refractive index difference of the liquid crystal in the radial and tangential directions, the greater the deviation angle of the two emitted lights; the greater the inclination angle difference between the upper and lower surfaces of the wedge-shaped liquid crystal, the greater the deviation angle of the two emitted lights.

[0068] Furthermore, the polarization characteristics of the outgoing light are determined by the spatial arrangement characteristics of the columnar anisotropic liquid crystal molecules; the two obtained outgoing light fields both exhibit columnar polarization characteristics, and the two polarization states are orthogonal, such as: one of the outgoing light is radially polarized, and the other outgoing light is tangentially polarized, etc.; by adopting the columnar anisotropic pattern characteristics of the orientation layer to regulate the columnar anisotropy of the liquid crystal layer, the polarization characteristics of the outgoing light can be changed.

[0069] Furthermore, when multiple circularly polarized light beams are used to irradiate the liquid crystal alignment region, the relative intensity, phase, handedness, and wavelength of the multiple circularly polarized light beams can be set arbitrarily.

[0070] Furthermore, the columnar anisotropic liquid crystal molecules can be arranged in an array. When the incident light spot can illuminate the liquid crystal orientation area array, the emergent light is an array formed by multiple structured light beams; or multiple beams of incident light can be irradiated together through one or more liquid crystal orientation areas, and the emergent light is multiple beams of structured light.

[0071] Furthermore, the incident circularly polarized light is not limited to whether it carries a spiral phase. The phase topological charge carried by the two outgoing vector lights is related to the handedness of the incident circularly polarized light and the phase topological charge carried by the incident light; specifically, the phase topological charge of the outgoing light is m, the phase topological charge of the incident light is n, k is the speed at which the orientation angle of the liquid crystal molecules changes with the orientation angle of the spatial position, then m = n ± k (left-handed circular polarization takes +, right-handed circular polarization takes -); by changing the phase topological charge of the incident circularly polarized light, the phase topological charge of the outgoing structured light can be adjusted; the polarization topological charge of the outgoing light is k, k is the speed at which the orientation angle of the liquid crystal molecules changes with the orientation angle of the spatial position.

[0072] Furthermore, the spatial orientation angle of the molecule The relationship with the spatial azimuth angle θ can be expressed as Where k is the speed at which the orientation angle of the liquid crystal molecules changes with the orientation angle of the spatial position; k can be a function of θ or a constant. By performing complex columnar anisotropic orientation treatment on the liquid crystal molecule layer, the emission of high-order structured light can be obtained. Refer to the formula When k(θ) is not an integer of positive or negative 1 (such as a complex form or other integer that changes with θ), the orientation of the molecules becomes complicated, which is regarded as complex columnar anisotropy. This complex columnar anisotropic orientation can be achieved by direct light writing combined with controlling the polarization state of light. The high-order structured light of this embodiment is relative to the low-order structured light, and the low-order structured light includes radially polarized light and tangentially polarized light. When the incident light passes through this complex columnar anisotropic oriented element, the two outgoing lights are high-order structured light.

[0073] The specific implementation process of the method for generating structured light based on a wedge-shaped liquid crystal structure provided by the present invention is described in detail below through specific embodiments.

[0074] This embodiment uses commercial liquid crystal molecules 5CB, which have different refractive indices in two main axis directions. Commercial orientation molecules SD1 are used, which can be oriented under the irradiation of ultraviolet polarized light, and after orientation, the long axis of the SD1 molecule is perpendicular to the polarization direction of the ultraviolet polarized light.

[0075] First, prepare a "sandwich" liquid crystal box. The lower layer of the liquid crystal box is a glass slide, and the upper layer is a wedge-shaped plate of glass (there is a certain angle between the upper and lower surfaces). The upper and lower glass layers are cleaned: ultrasonic treatment in pure water, acetone, and alcohol for 10 minutes each, and then plasma cleaning. Spin coat the commercial SD1 orientation layer molecules on the surface of the above two glass pieces: the spin coating speed is 3000rpm, and the time is 30s. Among them, the SD1 molecules are dissolved in DMF organic solvent, and the mass fraction is: 5mg / mL. After spin coating, place the sample on a hot plate at 100 degrees Celsius for 10 minutes, and then glue the upper and lower layers together to form a "sandwich" liquid crystal box. Due to the use of a wedge-shaped upper structure, the middle layer of the formed liquid crystal box is also a wedge-shaped structure, that is, the upper and lower surfaces of the middle layer present an angle of 5 degrees (such as Figure 1 ).

[0076] Then, the whole liquid crystal box is oriented, and the orientation light source used is 405nm ultraviolet light. The linearly polarized 405nm ultraviolet light passes through a vortex wave plate (Thorlabs, WPV10L-405). By adjusting the direction of the linear polarization to be consistent with the starting fast axis of the vortex wave plate, the 405nm outgoing light is made radial vector light. The above-mentioned 405nm radial vector light is incident normally into the liquid crystal box to orient the SD1 molecular layer. The incident light of 405nm is 10mW, and the irradiation time is 15min. The oriented SD1 molecular layer presents a columnar symmetric anisotropic orientation.

[0077] Furthermore, 5CB liquid crystal molecules are poured into the above-mentioned oriented liquid crystal box. When in liquid state, 5CB liquid crystal molecules can spontaneously enter the liquid crystal box through the action of surface tension and fill the wedge-shaped middle layer of the "sandwich" liquid crystal box. Under the action of the SD1 orientation layer molecules, the 5CB liquid crystal molecules are oriented and present a columnar symmetric anisotropic orientation. Observed under a polarizing microscope, as shown in Figure 2 As shown, the liquid crystal presents a typical black cross, indicating that the 5CB liquid crystal layer has been successfully treated with columnar symmetric anisotropic orientation.

[0078] Finally, the ability of the above 5CB liquid crystal to produce structured light was analyzed.

[0079] The 532nm circularly polarized light is incident normally into the columnar symmetric anisotropic liquid crystal region to ensure that the center of the circularly polarized light coincides with the columnar symmetry center of the 5CB liquid crystal. Since the 5CB liquid crystal layer is a wedge-shaped structure, the outgoing light is inclined at the exit interface. In addition, due to the birefringence effect of the 5CB liquid crystal molecules, there will be two beams of outgoing light, the two beams of outgoing light present a certain angle, and the two are orthogonally polarized. Since the prepared 5CB liquid crystal layer is a columnar symmetric orientation, one of the two outgoing lights is radially polarized light, as shown in Figure 3(a), and the other is tangentially polarized light, as shown in Figure 3(b).

[0080] This embodiment uses interference method to characterize the spiral phase characteristics of the two outgoing lights. The interference fringe photo of the radial outgoing light is shown in Figure 4(a), and the interference fringe photo of the tangential outgoing light is shown in Figure 4(b). The interference fringes prove that both outgoing lights carry a spiral phase, and the experimental results prove that the two outgoing lights are vector vortex lights. In this embodiment, the spiral phase topological charge of the incident circularly polarized light is 0 circular polarization, and the 5CB liquid crystal layer is cylindrically symmetrical, so it presents Figure 4(a) and 4(b) The interference fringe characteristics in .

[0081] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In the description of this specification, the description of the reference terms "one embodiment", "some implementations", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of this specification. In this specification, the schematic representation of the above terms does not necessarily target the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples without contradiction.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for generating structured light based on a wedge-shaped liquid crystal structure, characterized in that: include: Selecting liquid crystal molecules with a birefringence effect, and orienting the liquid crystal molecules using an orientation layer; The upper and lower surfaces of the oriented liquid crystal have a certain angle to form a wedge-shaped liquid crystal layer, and the produced wedge-shaped liquid crystal layer contains a columnar anisotropic liquid crystal structure; Adjusting the polarization state of the incident light so that the incident light is circularly polarized light; The incident light is incident on the columnar anisotropic liquid crystal structure, so that the center of the incident light spot coincides with the liquid crystal center of the columnar anisotropic liquid crystal structure, and the outgoing light passing through the liquid crystal center of the anisotropic liquid crystal structure is structured light.

2. The method for generating structured light based on a wedge-shaped liquid crystal structure according to claim 1, characterized in that: The wedge-shaped liquid crystal structure is implemented based on a "sandwich" liquid crystal cell, wherein the manufacturing process of the "sandwich" liquid crystal cell includes: Prepare a "sandwich" liquid crystal cell, wherein the "sandwich" liquid crystal cell comprises a lower transparent substrate layer with uniform thickness and an upper transparent cover layer, and the "sandwich" liquid crystal cell has an opening reserved for liquid crystal injection; Introducing an alignment layer on the bottom of the upper transparent cover layer and / or the top surface of the lower substrate layer structure of the "sandwich" liquid crystal cell; Pour the liquid crystal molecules into the "sandwich" liquid crystal cell after the orientation treatment through the reserved opening; The oriented liquid crystal layer is wedge-shaped, that is, the upper and lower surfaces of the liquid crystal present a certain angle, forming a "sandwich" wedge-shaped liquid crystal structure.

3. The method for generating structured light based on a wedge-shaped liquid crystal structure according to claim 2, characterized in that: There are two methods to make the liquid crystal layer into a wedge shape, including: First: using a wedge-shaped upper transparent cover layer to cover the lower substrate layer so that the injected liquid crystal layer is in a wedge shape; Second: using a lower substrate layer and an upper transparent cover layer with uniform thickness, adjusting the formed liquid crystal layer by introducing spacers, and controlling the thickness of the spacers in the liquid crystal box to make the liquid crystal layer wedge-shaped.

4. The method for generating structured light based on a wedge-shaped liquid crystal structure according to claim 1, characterized in that: The orientation is carried out by mechanical rubbing orientation or photo-orientation.

5. The method for generating structured light based on a wedge-shaped liquid crystal structure according to claim 1, characterized in that: The anisotropy of the liquid crystal layer is regulated by using the anisotropic pattern characteristics of the orientation layer, thereby changing the polarization characteristics of the outgoing light. The polarization characteristics of the outgoing light are determined by the spatial arrangement characteristics of the anisotropic liquid crystal molecules. When the liquid crystal layer is oriented to be columnar anisotropy, the polarization directions of the two outgoing vector lights passing through the liquid crystal are columnar, and the two outgoing lights are radially polarized and tangentially polarized, respectively.

6. The method for generating structured light based on a wedge-shaped liquid crystal structure according to claim 1, characterized in that: According to the dispersion relationship of the refractive index of the liquid crystal in the two main axis directions, monochromatic light or polychromatic light of a set wavelength is selected for incident. The wavelength range allowed by the incident circularly polarized light should satisfy that there is a certain difference in the refractive index of the liquid crystal in the two main axis directions at this wavelength, that is, the liquid crystal layer undergoes birefringence in two directions at the inclined interface, wherein the greater the difference in the inclination angles of the upper and lower surfaces of the wedge-shaped liquid crystal, the greater the deviation angle of the two outgoing lights.

7. The method for generating structured light based on a wedge-shaped liquid crystal structure according to claim 1, characterized in that: The phase topological charge carried by the two outgoing vector lights is related to the handedness of the incident circularly polarized light and the phase topological charge carried by the incident light.

8. The method for generating structured light based on a wedge-shaped liquid crystal structure according to claim 1, characterized in that: The spatial orientation angle of the molecule The relationship with the spatial azimuth angle θ can be expressed as Among them, k is the speed at which the orientation angle of the liquid crystal molecules changes with the orientation angle of the spatial position. When k(θ) is not an integer of positive or negative 1, the orientation of the molecules is more complicated, that is, it is regarded as a complex columnar anisotropy. The complex columnar anisotropic orientation is achieved by direct light writing combined with controlling the polarization state of light. When the incident light passes through the complex columnar anisotropic orientation, the two output lights are high-order structured lights.

9. The method for generating structured light based on a wedge-shaped liquid crystal structure according to claim 1, characterized in that: The anisotropic liquid crystal molecules are arranged in an array. When the incident light spot can illuminate the liquid crystal orientation area array, the emergent light is an array formed by multiple structured light beams; or, multiple beams of incident light are irradiated through one or more liquid crystal orientation areas together, and the emergent light is multiple beams of structured light.

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