A polarization volume grating and a preparation method of the polarization volume grating

Abstract

The application discloses a polarization volume grating, comprising a substrate and a grating group arranged on the substrate; the grating group comprises at least two grating units arranged in stacks; wherein each grating unit comprises a directional layer and a chiral liquid crystal layer arranged in mutual adhesion, and the grating units jointly form a structure in which the directional layer and the chiral liquid crystal layer are alternately arranged in stacks; each directional layer is formed by exposing a layer of light directional material by two circularly polarized lights with opposite rotation directions. In the application, the directional layer and the chiral liquid crystal layer are alternately arranged, so that on the basis of realizing the expansion of various different diffraction functions of the polarization volume grating, the good working performance of the polarization volume grating is ensured.

Description

Technical Field

[0001] This invention relates to the field of optical device technology, and in particular to a polarizing grating and a method for fabricating the polarizing grating. Background Technology

[0002] Polarizing gratings are a type of liquid crystal grating that have attracted much attention due to their advantages such as high refractive index modulation, polarization selectivity, and relatively low mass production cost. Furthermore, the combination of high refractive index modulation and low mass production cost makes polarizing gratings a promising candidate for applications in fields such as augmented reality.

[0003] The existing method for fabricating polarimetric gratings involves forming an alignment layer with a specific molecular polarization orientation on a substrate, followed by a liquid crystal layer doped with a chiral agent. The alignment layer's binding effect on the liquid crystal molecules creates a polarization-selective grating. However, to meet the diverse optical needs of polarimetric gratings in practical applications, multiple layers of different liquid crystals are sometimes stacked on the alignment layer to expand the grating's functionality; or, to improve the grating's diffraction rate, a relatively thick liquid crystal layer (e.g., more than 10 times the working light wavelength) is required. But as the thickness of the liquid crystal layer increases or the number of stacked liquid crystal layers on the alignment layer increases, the binding ability of the alignment layer on the liquid crystal gradually decreases, leading to a deviation between the diffraction performance of the polarimetric grating and the design target. Summary of the Invention

[0004] The purpose of this invention is to provide a polarizing grating and a method for fabricating a polarizing grating, which can improve the diffraction performance of the polarizing grating to a certain extent.

[0005] To address the aforementioned technical problems, the present invention provides a polarizer grating, comprising a substrate and a grating assembly disposed on the substrate; the grating assembly comprises at least two grating units stacked together. Each grating unit includes an alignment layer and a chiral liquid crystal layer that are bonded together, and the grating units together form a structure in which the alignment layer and the chiral liquid crystal layer are stacked alternately in sequence; Each of the aforementioned orientation layers is formed by exposing a photo-oriented material layer to two beams of circularly polarized light with opposite directions of rotation.

[0006] In one optional embodiment of this application, at least some of the grating units have different orientation layers and / or different chiral liquid crystal layers; Among them, the incident angle of the exposure beam and / or the light orientation material layer are different for different orientation layers; The different chiral liquid crystal layers correspond to different types and / or concentrations of liquid crystal and / or chiral agents and / or concentrations of chiral agents.

[0007] In one optional embodiment of this application, a light-transmitting isolation layer is provided between two adjacent grating units.

[0008] In one optional embodiment of this application, the light-transmitting isolation layer includes an antireflective film layer; And / or, the light-transmitting isolation layer includes a first film layer and a second film layer with different refractive indices that are bonded together; the interface between the first film layer and the second film layer is a curved surface.

[0009] In one alternative embodiment of this application, the chiral liquid crystal layer and the alignment layer of each grating unit are identical.

[0010] In one optional embodiment of this application, the grating group includes two adjacent and identical grating units, and a phase delay sheet is disposed between the two grating units.

[0011] In an optional embodiment of this application, the grating unit includes at least a first grating unit and a second grating unit; a filter film layer is disposed between the first grating unit and the second grating unit; and the first grating unit is a reflective grating, and the second grating unit is a transmissive grating; The first grating unit includes a first orientation layer and a first chiral liquid crystal layer; the first chiral liquid crystal layer is used for reflective diffraction of light in a first wavelength range. The second grating unit includes a second orientation layer and a second chiral liquid crystal layer; the second chiral liquid crystal layer is used for transmission diffraction of light in a second wavelength range; The filter layer is a film layer that transmits light in the first wavelength range and reflects light in the second wavelength range; or the filter layer is a film layer that reflects light in the first wavelength range and transmits light in the second wavelength range. The first wavelength range and the second wavelength range do not overlap.

[0012] In one alternative embodiment of this application, the orientation layer of at least one of the grating units is formed by exposure with a non-parallel beam.

[0013] In one optional embodiment of this application, the thickness of the orientation layer in the grating unit is 5nm~100nm; and the thickness of the chiral liquid crystal layer is 50nm~100um.

[0014] A method for fabricating a polarizing grating includes the following steps: S1. Apply a light-oriented material to the substrate to form a light-oriented material layer; S2. Expose the photo-oriented material layer with two coherent circularly polarized beams to form an orientation layer with a periodic structure; S3. A chiral liquid crystal material is coated on the alignment layer to form a chiral liquid crystal layer. The chiral liquid crystal layer and the alignment layer together constitute a grating unit. S4. Coat the chiral liquid crystal layer with a new light-oriented material, and repeat steps S2 to S4 until the required number of grating units are formed to obtain a polarizing grating.

[0015] The present invention provides a polarizing grating, comprising a substrate and a grating assembly disposed on the substrate; the grating assembly comprises at least two grating units stacked together; wherein each grating unit comprises an orientation layer and a chiral liquid crystal layer bonded together, and the grating units together form a structure in which the orientation layer and the chiral liquid crystal layer are stacked alternately; each orientation layer is formed by exposing a photo-orienting material layer to two beams of circularly polarized light with opposite directions.

[0016] In the polarizer grating of this application, each chiral liquid crystal layer on the substrate is correspondingly provided with an alignment layer. This allows each chiral liquid crystal layer and its corresponding alignment layer to form a grating unit, and each grating unit can achieve different diffraction functions based on actual needs. Each alignment layer only needs to bind its corresponding chiral liquid crystal layer, thus avoiding the problem of insufficient binding force on the molecular orientation of liquid crystal layers farther from the alignment layer due to a large number or thickness of liquid crystal layers stacked on the same alignment layer. This would make it difficult to arrange the structure according to the required period, leading to insufficient diffraction performance or deviation from the grating design target in the final polarizer grating. In other words, this application alternates between multiple alignment layers and chiral liquid crystal layers, achieving the expansion of various diffraction functions of the polarizer grating while ensuring good working performance. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram showing the ideal distribution of liquid crystal molecules on a single-layer alignment layer; Figure 2 This is a schematic diagram showing the actual distribution of liquid crystal molecules on a single-layer alignment layer. Figure 3 This is a schematic diagram of a first structure of a polarizer grating provided in an embodiment of this application; Figure 4 This is a schematic diagram of a second structure of a polarizer grating provided in an embodiment of this application; Figure 5 for Figure 4 A schematic diagram of a diffraction optical path in a polarizing grating; Figure 6 This is a schematic diagram of the first fabrication process of the polarizer grating provided in the embodiments of this application; Figure 7 A schematic diagram of molecular polarization direction for directional layer exposure provided in an embodiment of this application; Figure 8 A schematic diagram of another molecular polarization direction for the orientation layer exposure provided in this application embodiment; Figure 9 This is a schematic diagram of a third structure of a polarizer grating provided in an embodiment of this application; Figure 10 This is a schematic diagram of a second fabrication process for a polarizer grating provided in an embodiment of this application; Figure 11 This is a schematic diagram of the fourth structure of the polarizer grating provided in the embodiments of this application; Figure 12 A schematic diagram of a diffraction optical path including a quarter-wave plate in a polarizing grating provided in this application embodiment; Figure 13 A schematic diagram of a diffraction optical path including a half-wave plate in a polarizing grating provided in an embodiment of this application; Figure 14 This is a schematic diagram of the optical path of a polarizing grating as a beam splitter provided in an embodiment of this application; Figure 15 This is a schematic diagram of the optical path of a polarizer grating as a light combining device provided in an embodiment of this application; Figure 16 A schematic flowchart illustrating the fabrication method of the polarizer grating provided in this application embodiment; In the attached figure: 100 is a grating unit, 101 is an alignment layer, 102 is a chiral liquid crystal layer, 110 is a first grating unit, 111 is a first alignment layer, 112 is a second chiral liquid crystal layer, 120 is a second grating unit, 121 is a second alignment layer, 122 is a second chiral liquid crystal layer, 2 is a substrate, 3 is a light-transmitting isolation layer, 31 is a first film layer, 32 is a second film layer, 33 is a quarter-wave plate, 34 is a half-wave plate, and 35 is a filter film layer. Detailed Implementation

[0019] like Figure 1 and Figure 2 As shown, Figure 1 and Figure 2These all refer to the schematic diagram of the molecular distribution law of the chiral liquid crystal layer 102 in the direction perpendicular to the alignment layer 101 when multiple chiral liquid crystal layers 102 are sequentially stacked on the same alignment layer 101; as Figure 1 shown, theoretically speaking, in the Z-axis direction (i.e., the direction perpendicular to the alignment layer), the molecular structure of the chiral liquid crystal layer 102 changes according to the fixed period p; but in fact, due to the weaker the binding force of the alignment layer 101 on the liquid crystal layer farther away, so as Figure 2 shown, the distribution period of the molecular structure of the chiral liquid crystal layer 102 in the Z-axis direction increases gradually as p1 < p2 < p3, and to ensure the diffraction performance of the polarization grating, it is required that the molecular structure distribution law of the chiral liquid crystal layer 102 in the Z-axis direction can be arranged according to the Figure 1 shown law.

[0020] Based on this, this application provides a polarization grating and its manufacturing method, which can ensure the diffraction performance of the polarization grating on the basis of ensuring that the polarization grating contains multiple liquid crystal layers realizing different diffraction functions or setting a liquid crystal layer with a larger thickness.

[0021] In order to make the personnel in the technical field better understand the solution of this invention, the following further detailed description of the invention will be given in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, rather than all the embodiments. Based on the embodiments in this invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of this invention.

[0022] As Figure 3 shown, Figure 3 is the first structural schematic diagram of the polarization grating provided by the embodiment of this application; In a specific embodiment of this application, the polarization grating may include: a substrate 2 and a grating group arranged on the substrate 2; the grating group includes at least two grating units 100 stacked; wherein each grating unit 100 includes an alignment layer 101 and a chiral liquid crystal layer 102 arranged in a fitting manner, and each grating unit 100 jointly forms a structure in which the alignment layer 101 and the chiral liquid crystal layer 102 are alternately stacked in sequence; Each alignment layer 101 is formed by exposing a photo-alignment material layer with two circularly polarized lights with opposite rotation directions.

[0023] As Figure 3As shown, the substrate 2 in this embodiment is a support structure, which can be any structure such as a glass slide or an optical waveguide; no further restrictions are imposed in this embodiment. On the substrate 2, the alignment layer 101 and the chiral liquid crystal layer 102 are alternately arranged in the Z-axis direction. Each alignment layer 101 and the chiral liquid crystal layer 102 above it constitute a grating unit 100. Obviously, because each chiral liquid crystal layer 102 is directly disposed on its corresponding alignment layer 101, each alignment layer 101 has a good molecular binding force on its corresponding chiral liquid crystal layer 102, thereby ensuring that the molecular structure arrangement of each chiral liquid crystal layer 102 has a stable periodic arrangement in the Z-axis direction, which in turn ensures the stable and reliable diffraction function of each grating unit 100.

[0024] In addition, in this embodiment, the thickness of each orientation layer 101 can be set to 5nm~100nm; and the thickness of each chiral liquid crystal layer 102 can be set to 50nm~100um.

[0025] Optionally, the orientation layer 101 in each grating unit 100 can be a structural layer formed by exposing a photo-oriented material layer to two beams of circularly polarized light with opposite rotation directions. The orientation layer 101 can include a cis-trans isomeric material layer, a photocrosslinked material layer, and a photodegradable material layer. The cis-trans isomeric photo-oriented material layer can be an azo dye layer, in which molecules undergo a reversible conversion between cis and trans structures upon light irradiation or thermal excitation, and the liquid crystal molecules in the chiral liquid crystal layer 102 are aligned parallel to the cis structure molecular direction. The photocrosslinked photo-oriented material can be a cinnamoyl layer, which polymerizes under light irradiation to form crosslinked side chains aligned along the polarization direction, an irreversible process, and the liquid crystal molecules in the chiral liquid crystal layer 102 are aligned parallel to the crosslinked side chain direction. The photodegradable photo-oriented material can be polyimide, in which polymer chains aligned with the polarization direction absorb energy and break under light irradiation, an irreversible process, and the liquid crystal molecules in the chiral liquid crystal layer 102 are aligned parallel to the unbroken portions. In practical applications, when at least two grating units 100 are sequentially disposed on the substrate 2, the orientation layer 101 in each grating unit 100 can be formed by the same light orientation material layer or by different light orientation materials. This embodiment does not impose specific restrictions on this.

[0026] Furthermore, the chiral liquid crystal layer 102 in this embodiment can specifically include a left-handed chiral liquid crystal layer 102 doped with a left-handed chiral agent and a right-handed chiral liquid crystal layer 102 doped with a right-handed chiral agent. When the chiral liquid crystal layer 102 in the grating unit 100 is a left-handed chiral liquid crystal layer 102, the grating unit 100 is used to diffract left-handed circularly polarized light, and when the chiral liquid crystal layer 102 in the grating unit 100 is a right-handed chiral liquid crystal layer 102, the grating unit 100 is used to diffract right-handed circularly polarized light. Moreover, the pitch, diffraction efficiency, grating vector, and other parameters of the liquid crystal grating formed by the chiral liquid crystal layer 102 vary depending on the type of chiral agent. In practical applications, a suitable chiral agent can be selected based on actual diffraction requirements.

[0027] Therefore, in an optional embodiment of this application, at least some of the grating units 100 in the grating group may have different orientation layers 101 and / or different chiral liquid crystal layers 102; wherein the incident angle of the exposure beam and / or the light orientation material layer are different between the different orientation layers 101; and the liquid crystal type and / or liquid crystal concentration and / or chiral agent type and / or chiral agent concentration are different between the different chiral liquid crystal layers 102.

[0028] by Figure 4 and 5 The illustrated embodiment is an example. Figure 4 Taking a substrate 2 as an example, a first grating unit 110 and a second grating unit 120 are sequentially disposed on the substrate 2. The first grating unit 110 includes a first alignment layer 111 and a first chiral liquid crystal layer 112. The first alignment layer 111 is a photo-aligning material layer formed by exposing two beams of circularly polarized light with opposite rotation directions. The first chiral liquid crystal layer 112 is a liquid crystal layer doped with a left-handed chiral agent. The second grating unit 120 includes a second alignment layer 121 and a second chiral liquid crystal layer 122. The second alignment layer 121 is a photo-aligning material layer formed by exposing two beams of circularly polarized light with opposite rotation directions. The second chiral liquid crystal layer 122 is a liquid crystal layer doped with a right-handed chiral agent.

[0029] Therefore, as Figure 5As shown, the first grating unit 110 is a grating unit 100 capable of realizing left-hand circularly polarized light diffraction, while the second grating unit 120 is a grating unit 100 capable of realizing right-hand circularly polarized light diffraction. Thus, when a beam of unpolarized light is incident on the first grating unit 110, the unpolarized light can be decomposed into left-hand circularly polarized light and right-hand circularly polarized light. Thus, the first grating unit 110 can diffract the left-hand circularly polarized light in the unpolarized light, while the right-hand circularly polarized light in the unpolarized light passes through the first grating unit 110 and is incident on the second grating unit 120, where it can be diffracted. Thus, through the cooperative action of the first grating unit 110 and the second grating unit 120, high-efficiency diffraction output of unpolarized light can be achieved.

[0030] Based on the above discussion, the grating group of the polarizer grating in this embodiment includes multiple grating units 100, and each grating unit 100 contains at least two grating units 100 that are different from each other. Specifically, according to actual functional requirements, at least one of the following may be different: the incident angle of the exposure beam of the orientation layer 101, the light orientation material layer, the type and concentration of the liquid crystal layer of the chiral liquid crystal layer 102, the type and concentration of the chiral agent, etc., that is, forming grating units 100 with different diffraction functions, thereby diversifying the different functions of the polarizer grating in practical applications.

[0031] Optionally, in the polarizer grating of this application, each grating unit 100 has the same chiral liquid crystal layer 102 and orientation layer 101. For example, the grating unit 100 in the polarizer grating may also include a first grating unit 110 and a second grating unit 120, both with the same chiral liquid crystal layer 102 and orientation layer 101, which can achieve high-efficiency diffraction of the same incident light beam. For example, when a beam of light is incident on the first grating unit 110, the first grating unit 110 partially diffracts and partially transmits the beam of light to the second grating unit 120, which can also diffract the incident light beam, thereby enabling the first grating unit 110 and the second grating unit 120 to jointly perform high-efficiency diffraction of the same beam of light.

[0032] Furthermore, such as Figure 6 As shown, when multiple grating units 100 need to be formed on the substrate 2, a first orientation layer 101 can be formed on a clean substrate 2 by any method such as spin coating, spray coating, or roller coating. Then, the first orientation layer 101 is exposed by interference of a left-handed circularly polarized light and a right-handed circularly polarized light. The interference of the left-handed and right-handed circularly polarized light can generate spatially varying polarization states, thereby exposing the orientation layer 101 with a spatially varying cis molecular orientation distribution, such as... Figure 7 As shown, Figure 7The molecular polarization direction distribution of the orientation layer 101 is formed by exposing it to a beam of left-handed circularly polarized parallel light and a beam of right-handed circularly polarized parallel light; such as Figure 8 As shown, Figure 8 The molecular polarization direction distribution of the orientation layer 101 is formed by exposing at least one beam of non-parallel left-handed circularly polarized light and one beam of non-parallel circularly polarized light. In practical applications, if it is necessary to form a grating unit 100 with optical power, the orientation layer 101 can be exposed using at least one beam of non-parallel circularly polarized light; conversely, if it is necessary to form a grating unit 100 without optical power, the orientation layer 101 can be exposed using two beams of parallel circularly polarized light.

[0033] After the first alignment layer 101 is formed, the first chiral liquid crystal layer 102 can be set on the first alignment layer 101 by any of the following methods: spin coating, spray coating, or roller coating. The liquid crystal molecules in the liquid crystal solution that are in contact with the alignment layer 101 will automatically align with the direction of the liquid crystal molecule axis being the same as that of the cis molecules of the alignment layer 101. The liquid crystal molecules self-organize into a helical structure. Then, the liquid chiral liquid crystal layer 102 is cured by ultraviolet light to obtain the first chiral liquid crystal layer 102 with a stable grating structure. After the first chiral liquid crystal layer 102 is formed, the second alignment layer 101 can be further formed on the first chiral liquid crystal layer 102 in the same manner as described above. The second alignment layer 101 is also exposed, and the second chiral liquid crystal layer 102 is formed on the exposed second alignment layer 101. This process is repeated until the Nth alignment layer 101 and the Nth chiral liquid crystal layer 102 are formed. Obviously, the first alignment layer 101 and the first chiral liquid crystal layer 102 are also the first grating unit 100, and the second alignment layer 101 and the second chiral liquid crystal layer 102 form the second grating unit 100. And so on, the polarizer grating contains N grating units 100.

[0034] Based on the above discussion, in each grating unit 100, the orientation layer 101 can be formed of the same material or of different types of photo-orienting materials. The circularly polarized light and exposure parameters (including exposure wavelength, beam divergence angle, beam incident angle, exposure power, exposure time, etc.) used to expose each orientation layer 101 can be the same or different, depending on the actual diffraction requirements. Similarly, for each chiral liquid crystal layer 102, in addition to the chiral agent being different, the liquid crystal material can also have the same or different formulations (type and concentration of liquid crystal material). Furthermore, for each grating unit 100, each chiral liquid crystal layer 102 can be individually UV-cured, or each grating unit 100 can be stacked sequentially and then uniformly UV-cured; this application does not impose specific restrictions on this.

[0035] Furthermore, in order to ensure that the alignment layer 101 has a sufficiently large binding force on the molecular structure in the chiral liquid crystal layer 102, the alignment layer 101 and the chiral liquid crystal layer 102 are alternately arranged layer by layer in this application. This ensures that each chiral liquid crystal layer 102 has a corresponding alignment layer 101 directly attached to it to stably and effectively bind its molecular structure, thereby ensuring that the molecular structure of the chiral liquid crystal layer 102 has a stable periodic size in the Z-axis direction, that is, ensuring good diffraction effect of each chiral liquid crystal layer 102.

[0036] Based on this, such as Figure 9 As shown, in order to further avoid mutual interference between the orientation layer 101 and the chiral liquid crystal layer 102 that are adjacent to each other and belong to different grating units 100 (mainly the interference of the orientation layer 101 to the chiral liquid crystal layer 102), a light-transmitting isolation layer 3 can be further provided between two adjacent grating units 100. That is, a light-transmitting isolation layer 3 is provided between the chiral liquid crystal layer 102 of the lower grating unit 100 and the orientation layer 101 of the upper grating unit 100. The light-transmitting isolation layer 3 can be a resin film layer or a glass film layer.

[0037] like Figure 10 As shown, in the actual fabrication process of polarizer gratings, after the first alignment layer 101 and the first chiral liquid crystal layer 102 are sequentially formed on the substrate 2, the first light-transmitting isolation layer 3 can be set on the first chiral liquid crystal layer 102. Then, the second alignment layer 101, the second chiral liquid crystal layer 102, and the second light-transmitting isolation layer 3 are sequentially set on the first light-transmitting isolation layer 3. The sequential forming of each grating unit 100 can be repeated in a similar manner.

[0038] Based on the above discussion, in order to further extend the diffraction function of the polarizer grating, the light-transmitting isolation layer 3 in this application can also be an isolation structure layer with different optical functions. For example, the light-transmitting isolation layer 3 may include an antireflection film layer to increase the light transmittance between two adjacent grating units 100.

[0039] Optionally, such as Figure 11 As shown, the light-transmitting isolation layer 3 is disposed between adjacent first grating unit 110 and second grating unit 120. The light-transmitting isolation layer 3 may include a first film layer and a second film layer with different refractive indices that are bonded together; the interface between the first film layer and the second film layer is curved. Because the refractive indices of the first film layer and the second film layer are different, and they are connected by a curved contact, the first film layer and the second film layer are equivalent to forming a set of convex lens elements or concave lens elements together. This is equivalent to the polarizing grating in this application being formed by alternating arrangements of several grating units 100 and lens elements, thereby forming a polarizing grating that has both diffraction function and optical power.

[0040] Further optionally, when the light-transmitting isolation layer 3 is disposed between two adjacent and identical grating units 100, the light-transmitting isolation layer 3 can also be a phase retardation plate. In this embodiment, the phase retardation plate can be a thin film layer of birefringent material including liquid crystal, and based on the different delay amounts of light by the phase retardation plate, it can specifically be a quarter-wave plate 33 and a half-wave plate, which can change the polarization state of the beam transmitted by the first chiral liquid crystal layer 112.

[0041] like Figure 12 As shown, Figure 12 Taking the grating unit 100 as an example, which includes a first grating unit 110 and a second grating unit 120, and the first grating unit 110 and the second grating unit 120 are the same grating unit 100 (i.e., have the same diffraction function), the first grating unit 110 includes a first alignment layer 111 and a first chiral liquid crystal layer 112; the second grating unit 120 includes a second alignment layer 121 and a second chiral liquid crystal layer 122; the first alignment layer 111 and the second alignment layer 121 can be completely identical, and the first chiral liquid crystal layer 112 and the second chiral liquid crystal layer 122 can also be completely identical; a quarter-wave plate 33 is disposed between the first chiral liquid crystal layer 112 and the second alignment layer 121.

[0042] like Figure 12 As shown, when a beam of unpolarized light is incident on the first chiral liquid crystal layer 112, the unpolarized light can be decomposed into a first circularly polarized light and a second circularly polarized light that are orthogonal to each other. The first chiral liquid crystal layer 112 diffracts the first circularly polarized light and outputs the second circularly polarized light. The second circularly polarized light in the unpolarized light is transmitted through the quarter-wave plate 33 and forms elliptically polarized light, which is then incident on the second chiral liquid crystal layer 122. The elliptically polarized light can be decomposed into linearly polarized light and the first circularly polarized light. The second chiral liquid crystal layer 122 can diffract the first circularly polarized light and output the second circularly polarized light. When the second circularly polarized light passes through the quarter-wave plate 33 again, it forms a mixed beam of the first circularly polarized light and the linearly polarized light. Thus, it can be seen that the unpolarized light incident on the polarizer grating is ultimately diffracted and output as a combined beam of the second circularly polarized light, the first circularly polarized light, and the linearly polarized light.

[0043] like Figure 13 As shown, in another optional embodiment of this application, the grating unit 100 in the polarizer grating may include: Both the chiral liquid crystal layer 102 and the alignment layer 101 have the same first grating unit 110 and second grating unit 120; a half-wave plate is disposed between the first grating unit 110 and the second grating unit 120.

[0044] like Figure 13As shown, taking a liquid crystal layer where both the first chiral liquid crystal layer 112 and the second chiral liquid crystal layer 122 are doped with a left-handed chiral agent as an example, left-handed circularly polarized light incident on the unpolarized light in the first chiral liquid crystal layer 112 can be diffracted and output as right-handed circularly polarized light; after being delayed by a half-wave plate, the right-handed circularly polarized light becomes left-handed circularly polarized light and is incident on the second chiral liquid crystal layer 122. The second chiral liquid crystal layer 122 diffracts the incident left-handed circularly polarized light and outputs as right-handed circularly polarized light. The right-handed circularly polarized light is then converted back to left-handed circularly polarized light by a half-wave plate and output.

[0045] Understandably, for Figure 13 The first chiral liquid crystal layer 112 and the second chiral liquid crystal layer 122 can both be right-handed circularly polarized light, and the light transmission process is similar to that described above, so it will not be repeated in this embodiment.

[0046] Obviously, in Figure 13 In the illustrated embodiment, the first chiral liquid crystal layer 112 and the second chiral liquid crystal layer 122 can be fabricated using the exact same chiral liquid crystal material, thus achieving high-efficiency diffraction of incident light without the need for two different liquid crystal material formulations, which can reduce the cost of liquid crystal material preparation to a certain extent. Furthermore, the half-wave plate can be a single layer of uniform liquid crystal material or a single layer of birefringent film, resulting in a simple process and low cost.

[0047] Further optional, such as Figure 14 and Figure 15 As shown, in another optional embodiment of this application, the grating unit 100 of the polarizer grating may include: A first grating unit 110 and a second grating unit 120 are provided; a filter film layer 35 is disposed between the first grating unit 110 and the second grating unit 120; and the first grating unit 110 is a reflective grating and the second grating unit 120 is a transmissive grating. The first grating unit 110 includes a first alignment layer 111 and a first chiral liquid crystal layer 112; the first alignment layer 111 is an alignment layer 101 formed by exposure using circularly polarized light in a first wavelength range; The second grating unit 120 includes a second orientation layer 120 and a second chiral liquid crystal layer 122; the second orientation layer 120 is an orientation layer 101 formed by exposure using circularly polarized light in a second wavelength range; The filter layer 35 is a layer that reflects light in a first wavelength range and transmits light in a second wavelength range; or the filter layer 35 is a layer that transmits light in a first wavelength range and reflects light in a second wavelength range. The first wavelength range and the second wavelength range do not overlap.

[0048] like Figure 14 and Figure 15As shown, the first grating unit 110 and the second grating unit 120 included in the polarizer grating in this embodiment can be a reflective grating and a transmissive grating, respectively. Combined with the filter film layer 35 (that is, a type of light-transmitting isolation layer 3), the polarizer grating can realize the optical functions of a light combining device and a light splitting device.

[0049] like Figure 14 As shown, when the polarizer grating is used as a beam splitter, the filter layer 35 is a layer that transmits light in the first wavelength range and reflects light in the second wavelength range. When the light incident on the first chiral liquid crystal layer 112 is a mixture of the first and second wavelengths, the first chiral liquid crystal layer 112 can perform reflective diffraction output on the first wavelength light in the mixture, while the second wavelength light is transmitted through the filter layer 35 to the second chiral liquid crystal layer 122 and then performs transmission diffraction output through the second chiral liquid crystal layer 122. Thus, the beams of the first and second wavelengths in the mixture can be mutually split and output.

[0050] like Figure 15 As shown, when the polarizer grating is used as a light combining device, the filter layer 35 is a layer that reflects light in the first wavelength range and transmits light in the second wavelength range.

[0051] The first wavelength light incident on the first chiral liquid crystal layer 112 undergoes reflection diffraction and outputs, while the second wavelength light incident on the second chiral liquid crystal layer 122 undergoes transmission diffraction and is transmitted through the second chiral liquid crystal layer 122 in sequence.

[0052] In summary, in the polarizer grating of this application, each chiral liquid crystal layer on the substrate is correspondingly provided with an alignment layer. This allows each chiral liquid crystal layer and its corresponding alignment layer to form a grating unit, and each grating unit can achieve different diffraction functions based on actual needs. Each alignment layer only needs to bind its corresponding chiral liquid crystal layer, thus avoiding the problem of insufficient binding force on the molecular orientation of liquid crystal layers farther from the alignment layer due to a large number of stacked liquid crystal layers on the same alignment layer. This would prevent the structure from gradually changing according to the required periodic size, ultimately leading to insufficient diffraction performance of the final polarizer grating. In other words, this application alternates between multiple alignment layers and chiral liquid crystal layers, achieving the expansion of various diffraction functions of the polarizer grating while ensuring good working performance.

[0053] Based on the above discussion, such as Figure 16 As shown, this application also provides an embodiment of a method for fabricating a polarizing grating, which may include the following steps: S1: A light-oriented material is coated onto the substrate to form a light-oriented material layer; S2: Two coherent circularly polarized beams are used to expose the photo-oriented material layer to form an orientation layer with a periodic structure; S3: A chiral liquid crystal material is coated on the alignment layer to form a chiral liquid crystal layer, wherein the chiral liquid crystal layer and the alignment layer together constitute a grating unit; S4: Coat a new light-aligning material on the chiral liquid crystal layer, and repeat steps S2 to S4 until the required number of grating units are formed to obtain a polarizing grating.

[0054] It should be noted that after the chiral liquid crystal material is coated on each alignment layer 101, the chiral liquid crystal material can be further cured with ultraviolet light. Of course, all chiral liquid crystal layers 102 can also be cured with ultraviolet light at one time after all alignment layers 101 and chiral liquid crystal layers 102 have been coated. This application does not specifically limit this.

[0055] Reference Figure 6 The actual fabrication process of a polarizer grating may include: The first step is to lay a first orientation layer 101 on the substrate 2; The second step is to expose the first orientation layer 101 with the first set of dual beams. The first set of dual beams includes a left-handed circularly polarized light and a right-handed circularly polarized light. The interference between the two beams can produce spatially transformed polarized light. The divergence of the two beams can be the same or different. The two beams or one of them can be parallel light. The third step is to set a first chiral liquid crystal layer 102 on the first orientation layer 101. The first chiral liquid crystal layer 102 will self-assemble to form a polarization grating with a spiral structure. The fourth step is to deposit a second alignment layer 101 on the first chiral liquid crystal layer 102. The material formulation of the second alignment layer 101 (including the type and concentration of azo molecules) can be the same as or different from that of the first alignment layer 101. Fifth step, the second set of dual beams exposes the second orientation layer 101. The beam parameters used for exposure (including wavelength, polarization, divergence angle, incident angle, power, exposure time, etc.) can be the same as or different from the first set of dual beams. The sixth step involves depositing a second chiral liquid crystal layer 102 on the second alignment layer 101. The formulation of the second chiral liquid crystal layer 102 can be the same as or different from that of the first chiral liquid crystal layer 102 (including the type and concentration of the chiral agent, the type of liquid crystal, etc.). A third, fourth...Nth grading layer 101 and chiral liquid crystal layer 102 can also be deposited on the second chiral liquid crystal layer 102 following the steps described above. The specific number of layers is determined according to design requirements.

[0056] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that the elements inherent in a process, method, article, or apparatus that includes a list of elements are included. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Additionally, portions of the technical solutions provided in the embodiments of this application that are consistent with the implementation principles of corresponding technical solutions in the prior art have not been described in detail to avoid excessive elaboration.

[0057] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A polarizing grating, characterized in that, It includes a substrate and a grating group disposed on the substrate; the grating group includes at least two grating units disposed in a stacked manner; Each grating unit includes an alignment layer and a chiral liquid crystal layer that are bonded together, and the grating units together form a structure in which the alignment layer and the chiral liquid crystal layer are stacked alternately in sequence; Each of the aforementioned orientation layers is formed by exposing a photo-oriented material layer to two beams of circularly polarized light with opposite directions of rotation.

2. The polarizer grating as described in claim 1, characterized in that, At least some of the grating units have different orientation layers and / or different chiral liquid crystal layers; Among them, the incident angle of the exposure beam and / or the light orientation material layer are different for different orientation layers; The different chiral liquid crystal layers correspond to different types and / or concentrations of liquid crystal and / or chiral agents and / or concentrations of chiral agents.

3. The polarizer grating as described in claim 1, characterized in that, A light-transmitting isolation layer is provided between two adjacent grating units.

4. The polarizer grating as described in claim 3, characterized in that, The light-transmitting isolation layer includes an anti-reflective film layer; And / or, the light-transmitting isolation layer includes a first film layer and a second film layer with different refractive indices that are bonded together; the interface between the first film layer and the second film layer is a curved surface.

5. The polarizer grating as described in claim 1, characterized in that, The chiral liquid crystal layer and the alignment layer of each grating unit are identical.

6. The polarizer grating as described in claim 1, characterized in that, The grating group includes two adjacent and identical grating units, and a phase delay plate is disposed between the two grating units.

7. The polarizer grating as described in claim 1, characterized in that, The grating unit includes at least a first grating unit and a second grating unit; a filter film layer is disposed between the first grating unit and the second grating unit; and the first grating unit is a reflective grating, and the second grating unit is a transmissive grating; The first grating unit includes a first orientation layer and a first chiral liquid crystal layer; the first chiral liquid crystal layer is used for reflective diffraction of light in a first wavelength range. The second grating unit includes a second orientation layer and a second chiral liquid crystal layer; the second chiral liquid crystal layer is used for transmission diffraction of light in a second wavelength range; The filter layer is a film layer that transmits light in the first wavelength range and reflects light in the second wavelength range; or the filter layer is a film layer that reflects light in the first wavelength range and transmits light in the second wavelength range. The first wavelength range and the second wavelength range do not overlap.

8. The polarizer grating as described in claim 1, characterized in that, At least one of the orientation layers of the grating unit is formed by exposure with a non-parallel beam.

9. The polarizer grating as described in claim 1, characterized in that, In the grating unit, the thickness of the orientation layer is 5nm~100nm; the thickness of the chiral liquid crystal layer is 50nm~100um.

10. A method for fabricating a polarizing grating, characterized in that, Includes the following steps: S1. Apply a light-oriented material to the substrate to form a light-oriented material layer; S2. Expose the photo-oriented material layer with two coherent circularly polarized beams to form an orientation layer with a periodic structure; S3. A chiral liquid crystal material is coated on the alignment layer to form a chiral liquid crystal layer. The chiral liquid crystal layer and the alignment layer together constitute a grating unit. S4. Coat the chiral liquid crystal layer with a new light-oriented material, and repeat steps S2 to S4 until the required number of grating units are formed to obtain a polarizing grating.

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