WO2023097850A1

WO2023097850A1 - Diffractive optical element and preparation method therefor, and method for designing master diffraction pattern

Info

Publication number: WO2023097850A1
Application number: PCT/CN2021/142666
Authority: WO
Inventors: 王灵一; 伍未名; 刘风雷
Original assignee: 浙江水晶光电科技股份有限公司
Priority date: 2021-12-03
Filing date: 2021-12-29
Publication date: 2023-06-08
Also published as: CN114137645A; WO2023098897A1; CN114137645B

Abstract

A diffractive optical element (100) and a preparation method therefor, and a method for designing a master diffraction pattern, which relate to the technical field of diffractive optics. The preparation method comprises: providing a transparent substrate (101); forming, by means of a first master, a first grating structure layer (110) on a side surface of the transparent substrate (101); and forming, by means of a second master, a second grating structure layer (120) on the transparent substrate (101) on which the first grating structure layer (110) is formed, wherein a first preset diffraction pattern on the first master is different from a second preset diffraction pattern on the second master, and at least one of the first grating structure layer (110) and the second grating structure layer (120) is a one-dimensional grating structure layer. A dot matrix generated by the first grating structure layer (110) and a dot matrix generated by the second grating structure layer (120) are combined to form a preset array dot matrix. By using two grating structure layers, dot matrices obtained after decomposition are characterized in that the number of same is less, the shape of the dot matrices is regular, etc., thereby greatly reducing the design and processing difficulty of the diffractive optical element (100), high-performance split light beams are obtained, and a better beam splitting uniformity of a two-dimensional dot matrix is maintained.

Description

Diffractive optical element and its preparation method, design method of master diffraction pattern

Cross References to Related Applications

This application claims the priority of the Chinese patent application with the application number 202111465867.0 and titled "diffractive optical element and its preparation method, and design method of master diffraction pattern" submitted to the State Intellectual Property Office of China on December 03, 2021. The entire contents are incorporated by reference in this application.

technical field

The present application relates to the technical field of diffractive optics, in particular to a diffractive optical element and its preparation method, and a design method of a master diffraction pattern.

Background technique

Diffractive Optical Element (DOE) is an optical beam splitting device. The optical index parameters involved in DOE products include the overall beam efficiency, the light intensity of the zero-order diffraction order, and the uniformity of the optical intensity of each diffraction order. Among them, uniformity is an important design index, that is, the uniformity of optical intensity of each diffraction order, which is defined as the ratio of the difference between the highest and lowest light intensity in each diffraction order and the sum value. The lower the index value, the better the performance. good.

The diffractive optical element splits the light source and irradiates it on the receiving screen. When the field angle of the beam splitting is too large and the effective diffraction orders on the receiving screen are too many, it is produced and processed according to the conventional design (that is, single-layer structure DOE). The metric is hardly of a usable standard.

Contents of the invention

The embodiment of the present application provides a diffractive optical element and its preparation method, and a design method of a master diffraction pattern. By forming a first grating structure layer and a second grating structure layer on a transparent substrate to split the beam, it can improve Uniformity of diffraction order optical intensity.

Some embodiments of the present application provide a method for manufacturing a diffractive optical element, which may include providing a transparent substrate; forming a first grating structure layer on one side of the transparent substrate through a first master; forming A second grating structure layer is formed on the transparent substrate with the first grating structure layer through a second master, wherein the first preset diffraction pattern on the first master and the first preset diffraction pattern on the second master are The two preset diffraction patterns are different, and at least one of the first grating structure layer and the second grating structure layer is a one-dimensional grating structure layer.

Optionally, the one-dimensional grating structure layer may be configured as a striped periodic grating pattern.

Optionally, a filling layer may be formed between the first grating structure layer and the second grating structure layer.

Optionally, first the first grating structure layer may be embossed on the transparent substrate through the first master, and then the filling layer may be covered and leveled by spin coating on the first grating structure layer.

Optionally, there is a refractive index difference greater than or equal to 0.2 between the first grating structure layer and the filling layer, and a refractive index difference greater than or equal to 0.2 between the second grating structure layer and the filling layer. difference in refractive index.

Optionally, an optical film is coated between the transparent substrate and the first grating structure layer, and/or an optical film is coated on a side of the transparent substrate away from the first grating structure layer.

Other embodiments of the present application provide a method for designing a master diffraction pattern, which may include: substituting the input light intensity I ₀ and the input phase φ ₀ into the formula

Perform Fourier transform to obtain the output light intensity I _t and output phase φ _t ; where, the input light intensity is 1, the input phase is randomly selected between 0 and π, and i is the coefficient

Calculate the difference I _c between the output light intensity I _t and the target light intensity I _m ; the formula

Fourier transform and binarize to get the target input light intensity I _0m and the target input phase φ _0m ; when the difference I _c between the output light intensity I _t and the target light intensity I _m is less than the light intensity preset value, according to the formula

Calculate the binarized phase φ _t0 of each coordinate point to obtain the preset diffraction pattern.

Optionally, the formula

After Fourier transform and binarization, after obtaining the target input light intensity I _0m and the target input phase φ _0m , the method may also include: when the difference I _c between the output light intensity I _t and the target light intensity I _m is greater than or equal to light intensity preset value, the formula

Fourier transform to obtain the corrected input light intensity I _r and the corrected input phase φ _r ; binarize the corrected input phase φ _r to obtain the circular input light intensity I _n and the circular input phase φ _n ; the circular input light intensity I _n and the cycle input phase φ _n are substituted into the formula

Fourier transform to obtain output light intensity I _t and output binarized phase φ _t ; wherein, i is a coefficient

Calculate the difference I _c between the output light intensity I _t and the target light intensity I _m ; when the difference I c between the output light intensity I _t and the target light intensity _I _m is less than the light intensity preset value, the formula

Fourier transform, obtain target input light intensity I _0m and target input phase φ _0m ; According to the formula

Optionally, according to the formula

After calculating the binarized phase φ _t0 of each coordinate point and obtaining the preset diffraction pattern, the method may further include: comparing the light intensity distribution of each coordinate point of the preset diffraction pattern with each corresponding to the target diffraction pattern The light intensity distribution of the coordinate point; when the uniformity of the light intensity distribution of the coordinate point of the preset diffraction pattern exceeds the uniformity threshold of the light intensity distribution of the coordinate point corresponding to the target diffraction pattern, correct the target The light intensity I _m is used to obtain the light intensity distribution scheme of each coordinate point.

Optionally, when the uniformity of the light intensity distribution of the coordinate point of the preset diffraction pattern exceeds the uniformity threshold of the light intensity distribution of the corresponding coordinate point of the target diffraction pattern, correcting the target light intensity Im, obtaining the light intensity distribution scheme of each coordinate point may include: adjusting the target light intensity _Im =I ₀ ×1/cos(θ), where θ is the angle between the direction of each point in the target lattice and the beam propagation direction .

Still other embodiments of the present application provide a diffractive optical element, which may include: a transparent substrate on which a first grating structure layer and a second grating structure layer are sequentially formed, and the first grating At least one of the structure layer and the second grating structure layer is a one-dimensional grating structure layer, and the light beam incident on the transparent substrate passes through the first grating structure layer and the second grating structure layer, and exits a preset array diffraction spot.

Optionally, the surface pattern of the one-dimensional grating structure layer may be a striped periodic grating pattern.

Optionally, an optical film may be coated between the transparent substrate and the first grating structure layer, and/or, an optical film may be coated on the side of the transparent substrate away from the first grating structure layer .

Optionally, there may be a refractive index difference between the first grating structure layer and the filling layer, and between the second grating structure layer and the filling layer, and the refractive index difference may be ≥0.2.

In the diffractive optical element and its preparation method and the design method of the master diffraction pattern provided in the embodiments of the present application, the first grating structure layer and the second grating structure layer are sequentially formed on the transparent substrate, and the first grating structure layer and the second grating structure At least one of the layers is a one-dimensional grating structure layer, and the other layer is a one-dimensional grating structure layer or a two-dimensional grating structure layer, a striped grating pattern is formed on the one-dimensional grating structure layer, and a complex pattern is formed on the two-dimensional grating structure layer, The above patterns can be obtained by algorithms; the first grating structure layer produces a corresponding dot matrix pattern, and the second grating structure layer produces a corresponding dot matrix pattern. When the first grating structure layer and the second grating structure layer are combined on the transparent substrate The dot matrix produced by the first grating structure layer and the second grating structure layer are combined to form a preset array dot matrix, and the preset array diffraction spot can be received on the receiving screen. It is equivalent to dismantling the formed preset array lattice into two simple lattices, and these two simple lattices can be obtained through the first grating structure layer and the second grating structure layer respectively. After the double-layer grating structure layer is adopted, since the lattice corresponding to each layer of grating after decomposition has the characteristics of less lattice and regular shape, the difficulty of designing and processing diffractive optical elements is greatly reduced, and high-performance beams can be obtained through diffractive optical elements Beam splitting, so as to maintain the two-dimensional lattice also has better beam splitting uniformity.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the accompanying drawings that need to be used in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, so It should not be regarded as a limitation on the scope, and those skilled in the art can also obtain other related drawings according to these drawings without creative work.

FIG. 1 is a schematic structural diagram of a diffractive optical element provided in this embodiment;

Fig. 2 is one of the light path diagrams of the diffractive optical element provided in this embodiment;

Figure 3 is a diagram of the dismantling process of the preset dot matrix;

Fig. 4 is a schematic diagram of a diffraction micro-nano structure pattern corresponding to Fig. 3;

FIG. 5 is a flow chart of a method for preparing a diffractive optical element provided in this embodiment;

Fig. 6 is a flow chart of the design method of the master diffraction pattern provided in this embodiment;

Fig. 7 is the second light path diagram of the diffractive optical element provided in this embodiment;

Fig. 8 is a diffraction pattern of an example 3*5DOE and its corresponding lattice diagram;

Figure 9 is a three-dimensional view of the diffraction pattern in Figure 8;

Fig. 10 is one of the schematic diagrams of the first grating structure layer and the second grating structure layer of the diffractive optical element structure provided by this embodiment;

Figure 11 is a dot matrix diagram corresponding to Figure 10;

Fig. 12 is the second schematic diagram of the first grating structure layer and the second grating structure layer of the diffractive optical element structure provided by this embodiment;

Figure 13 is a dot matrix diagram corresponding to Figure 12;

Fig. 14 is the third schematic diagram of the first grating structure layer and the second grating structure layer of the diffractive optical element structure provided by this embodiment;

FIG. 15 is a dot matrix diagram corresponding to FIG. 14 .

Icons: 100 - diffractive optical element; 101 - transparent substrate; 110 - first grating structure layer; 120 - second grating structure layer; 130 - filling layer; 200 - receiving screen.

Detailed ways

The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

In the description of this application, it should be noted that the orientation or positional relationship indicated by the terms "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, or the usual placement of the application product when it is used. Orientation or positional relationship is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present application. In addition, the terms "first", "second", etc. are only used for distinguishing descriptions, and should not be construed as indicating or implying relative importance.

It should also be noted that, unless otherwise clearly specified and limited, the terms "setting" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct It can also be connected indirectly through an intermediary, or it can be the internal communication of two elements. Those of ordinary skill in the art can understand the specific meanings of the above terms in this application in specific situations.

The optical index parameters involved in DOE products include the overall beam efficiency, the light intensity of the zero-order diffraction order, and the uniformity of the optical intensity of each diffraction order. Among them, uniformity is defined as the ratio of the highest and lowest light intensity difference to the sum value in each diffraction order. The lower the index value, the better the performance.

The source of uniformity requirements is still on the product side. When it is applied in 3D detection, in order to improve the point cloud processing efficiency of depth information, it is required that the light intensity of each spot projected on the receiving screen should be as consistent as possible. If the uniformity is too low, it will affect the efficiency and accuracy of the point cloud analysis process at the receiving end. If the light intensity is too low, it will not even be able to effectively identify the target spot.

To achieve too many beam-splitting diffracted lights (the number of diffraction orders is greater than 60) at large angles (the average horizontal and vertical field angles are greater than 60°), it is difficult to achieve the existing DOE with a single-layer structure, and the DOE with a single-layer structure The design and manufacture of the device have too high requirements on the precision of the micro-nano structure, which makes it difficult to achieve better uniformity (less than 20%). According to the experience of the industry, the uniformity of the DOE obtained under the lithography machining scheme in the form of mass production is generally not ideal.

In order to solve the above problems, the embodiment of the present application provides a diffractive optical element 100, which emits a preset array of diffraction spots, which can improve the uniformity of the diffraction spots received on the receiving screen 200, reduce the difficulty of preparation, and is also suitable for correcting Design, so that the light spots that actually hit the light screen can achieve a better uniformity.

Specifically, referring to FIG. 1 , the embodiment of the present application provides a diffractive optical element 100, including: a transparent substrate 101, on which a first grating structure layer 110 and a second grating structure layer 120 are sequentially formed, the first grating At least one of the structure layer 110 and the second grating structure layer 120 is a one-dimensional grating structure layer, and the light beam incident on the transparent substrate 101 passes through the first grating structure layer 110 and the second grating structure layer 120, and exits the preset array diffraction spot.

The material of the transparent substrate 101 can be glass, sapphire glass, resin or plastic, and the first grating structure layer 110 and the second grating structure layer 120 are sequentially formed on the transparent substrate 101. In other words, two layers of grating structure layers are formed on the transparent substrate 101, so that After the light beam incident on the transparent substrate 101 passes through the first grating structure layer 110 and the second grating structure layer 120 , it can emit a preset array of diffraction spots, so that the uniformity of the light spots received on the receiving screen 200 is close to the target.

Moreover, at least one of the first grating structure layer 110 and the second grating structure layer 120 is a one-dimensional grating structure layer, and the other layer may be a one-dimensional grating structure layer or a two-dimensional grating structure layer. Wherein, the surface pattern of the one-dimensional grating structure layer is a stripe periodic grating pattern, and the two-dimensional grating structure layer is a complex pattern, which can be calculated by the design method of the diffraction pattern of the master plate, and the specific calculation process is described below.

The thickness of the first grating structure layer 110 and the second grating structure layer 120 is on the order of 10 microns, and the effective part is the three-dimensional micro-nano structure on the top, which is exactly the difference in refractive index between the upper and lower layers. interface structure, the thickness is on the order of microns. A filling layer 130 is formed between the first grating structure layer 110 and the second grating structure layer 120. In FIG. Structure interface. The three-dimensional Wiener structure of the grating structure layer can adopt a multi-layer step structure of two to eight steps, or a gray scale structure. The specific pattern is optimized under a series of specifications such as the wavelength of the incident light source, the target lattice, and the field of view. designed to get.

The materials of the grating structure layer and the filling layer 130 have a certain refractive index difference, there is a refractive index difference between the first grating structure layer 110 and the filling layer 130, there is a refractive index difference between the second grating structure layer 120 and the filling layer 130, and the refractive index If the index difference is greater than or equal to 0.2, it may be that the material forming the grating structure layer has a relatively high refractive index, and the material forming the filling layer 130 has a relatively low refractive index; it may also be that the material forming the grating structure layer has a relatively low refractive index, and the composition The material of the filling layer 130 has a relatively high refractive index.

In addition, an optical film is coated between the transparent substrate 101 and the first grating structure layer 110 , and/or an optical film is provided on the side of the transparent substrate 101 away from the first grating structure layer 110 .

The surface of the transparent substrate 101 away from the grating structure layer can be provided with optical elements or coated with an optical film to expand the optical performance of the diffractive optical element 100, such as coated with an anti-reflective film, a wear-resistant layer, and an ITO layer for protection; in addition, the transparent substrate 101 grating structure One side of the layer can also be coated to expand the optical performance of the diffractive optical element 100, or both sides of the transparent substrate 101 can be coated with an optical film at the same time, and the effect is multiplied.

The module light source is collimated and incident on the diffractive optical element 100 provided by the embodiment of the present application, wherein the two grating structure layers of the diffractive optical element 100 split the incident light, and finally form a preset array of diffracted light on the receiving screen 200 Form a preset array of diffraction spots. For example, as shown in Figure 2, it appears as a uniformly distributed light spot, where the module light source can be a VCSEL light source, an EEL light source, a fiber laser light source, and the like. In order to describe the beam-splitting characteristics intuitively, the light source is described by using the example of a point light source.

The diffractive optical element 100 provided in the embodiment of the present application can optimize a high-difficulty regular lattice. The diffractive optical element 100 generates an optical lattice through a periodic pattern formed by a double-layer grating structure layer, and appropriately meets the requirements of a high-difficulty DOE multi-lattice, Dismantling it into a dot-matrix scheme of a double-layer grating structure can reduce the difficulty of the process and improve the yield of the final product. In the dismantling process, one of the grating structure layers is a one-dimensional grating structure layer. Specifically, the surface pattern of the one-dimensional grating structure layer is a stripe-shaped periodic grating pattern, and the generated diffraction orders are arranged in a one-dimensional straight line. Another grating structure layer is combined to form a final preset array diffraction spot, that is, an arrayed lattice spot. As shown in Figure 3, the arrayed dot matrix spot on the left side of the equal sign can be disassembled into two dot matrix schemes on the right side of the equal sign, and the two dot matrix schemes dismantled in Figure 3 correspond to the two The preset pattern formed by the layer grating structure layer, the two grating structure layers, that is, the first grating structure layer 110 and the second grating structure layer 120 respectively generate two lattice schemes, and the light beam passes through the transparent substrate 101 and then passes through the first grating structure layer 110 After combining with the second grating structure layer 120 , the leftmost arrayed dot matrix light spot in FIG. 3 can be formed.

This application shows the dismantling of three lattice schemes. In the first achievable manner, the lattices generated by the two grating structure layers of the diffractive optical element 100 can be connected in a straight line, and the straight lines are mutually arranged. vertical. The number of lattices generated by one of the grating structure layers is Nx1*Ny1, and the number of lattices generated by the other grating structure layer is Nx2*Ny2. One of the grating structure layers must be a strip-shaped periodic grating (which can be calculated by the design method of the master diffraction pattern), and a one-dimensional symmetrical lattice with Nx1 or Ny1 as 1 is formed after the light is incident, and the zero order is at the center of symmetry. Another grating structure layer can be a complex two-dimensional grating structure layer (the complex shape can be calculated by the design method of the master diffraction pattern), which produces an asymmetric one-dimensional lattice, the straight line direction is perpendicular to the former, and the lattice The zero order is not at the center of symmetry.

In the second achievable manner, the one-dimensional lattices generated by the two grating structure layers can be connected in a straight line, and the straight lines of the lattices generated by the two grating structure layers are at any angle and are not perpendicular to each other. Let one of the lattice numbers be Nx1*Ny1, and the other lattice number be Nx2*Ny2. One of the grating structure layers is a strip grating structure layer, and the lattices generated after the light beam is irradiated are all one-dimensional symmetrical lattices, and Nx1 or Ny1 is 1, requiring the zero order to be at the center of symmetry. The other grating structure layer can be a strip grating, which produces a one-dimensional symmetrical lattice, or it can be a complex shape obtained by the design method of the master diffraction pattern, forming an asymmetric one-dimensional lattice. The zero order is not in the center of symmetry, Nx1 Or if Ny1 is 1, the straight line formed by the one-dimensional grating lattice forms a certain angle with the former.

In the third possible way, one of the grating structure layers is a strip grating to generate a one-dimensional symmetric lattice, and the other grating structure layer is calculated by the master diffraction pattern design method to generate a two-dimensional symmetric lattice. One of the grating structure layers (one-dimensional strip grating) produces a lattice number of Nx1*Ny1, wherein it is required that one of Nx1 and Ny1 is 1, and both are odd numbers; the other grating structure layer (by the diffraction pattern of the master plate) The number of lattices generated by the complex image calculated by the design method is Nx2*Ny2 two-dimensional lattice structure. If a direction can be odd, then the lattice is symmetrical in this direction and the zeroth order is at the center of symmetry. If it is an even number, then the lattice The asymmetric zero order is not at the center of symmetry.

In the dot matrixes corresponding to the two grating structure layers, one of the number of rows and columns must be 1. For example, in the above three achievable ways, the number of dot matrix generated by one of the grating structure layers is Nx1* Ny1, Nx1 or Ny1 is 1. Taking Figure 11 again as an example, one dot matrix dismantled in Figure 11 has one horizontal row and two vertical columns, and the other dot matrix has five horizontal rows and one vertical column. The two dot matrixes in Figure 11 all conform to the above One of the number of horizontal rows and vertical columns must be 1; one dot matrix dismantled in Figure 13 has one horizontal row and three vertical columns, and the other dot matrix has five horizontal rows and one vertical column. In Figure 13, two dots The number of arrays all conforming to the above-mentioned horizontal rows and vertical columns must be 1; one dot matrix in Figure 15 is one horizontal row and three vertical columns, and one dot matrix is five horizontal rows and three vertical columns. One of the number of rows and columns of a dot matrix conforming to the above must be 1. Therefore, as long as one of the dot matrix arrangement conforms to the number of rows and columns of the two dot matrixes, one of the numbers of rows and columns must be 1.

Among the above three achievable ways, different DOE periodic topography features can realize different optical lattice arrangements. Some DOEs have a periodic grating shape that produces a symmetrical one-dimensional optical lattice, while some DOEs have a strange periodic shape but can produce an asymmetrical optical lattice arrangement. Here, symmetry refers to the position of the optical zero-order diffraction order of the DOE periodic topography, and whether it is just symmetrically divided into one-dimensional lattice. Symmetrical division means symmetry, and asymmetrical division means asymmetry.

Among them, the period of the graph profile of DOE is about several times of the wavelength, and its characteristic size even reaches the level of hundreds of nanometers. In the process of designing the DOE, this embodiment adopts the GS (Gerchberg-Saxton algorithm) phase recovery algorithm to complete the optimal design process. In addition, various heuristic optimization algorithms such as particle swarm optimization (PSO), genetic algorithm (GA) and other algorithms combined with electromagnetic wave calculation theory (angular spectrum theorem, etc.) can also be used to design DOE.

As can be seen from the above, for the high-difficulty DOE multi-lattice pattern as the target pattern, it is first disassembled into two lattice schemes, and the two lattice schemes each have a corresponding grating structure layer pattern. Through the embodiment of the present application The preparation method of the diffractive optical element provided and the design method of the master diffraction pattern can obtain a diffractive optical element with a double-layer grating structure layer according to two lattice schemes, and the two grating structure layers of the double-layer grating structure layer correspond to For the two lattice schemes, the light beam passes through the diffractive optical element, then passes through two layers of grating structure layers in sequence, and finally obtains the high-difficulty DOE multi-lattice pattern after the combination of the two lattice schemes, that is, the target pattern.

It should be emphasized that the dismantling of the dot matrix scheme in this application is not limited to the above three achievable methods. In addition to the above dismantling methods, of course, a high-difficulty DOE multi-dot matrix can also be disassembled into the other two according to specific needs. Appropriate lattice scheme, the two lattice schemes after dismantling have corresponding surface patterns of the grating structure layer, and the final beam passes through the double-layer grating structure layer to form a preset array of diffracted light to obtain a high-difficulty DOE multi-lattice pattern . Therefore, no matter how it is disassembled, as long as the difficulty of the process can be reduced and the yield rate of the final product can be improved, the preset high-difficulty DOE multi-dot matrix pattern can be obtained after disassembling the double-layer grating structure layers corresponding to the two dot matrix schemes Both are available, and this application does not specifically limit the specific dismantling scheme. Moreover, because the preset high-difficulty DOE multi-dot matrix pattern is the only target, even if it is disassembled into different dot-matrix schemes, the preset high-difficulty DOE multi-dot pattern is finally obtained through the double-layer grating structure layer corresponding to different dot matrixes. Array patterns are unique.

On the other hand, please refer to FIG. 5 , the embodiment of the present application provides a method for manufacturing a diffractive optical element 100, including:

S100: Provide a transparent substrate 101.

S110: Form a first grating structure layer 110 on one side surface of the transparent substrate 101 by using a first master.

First, the first grating structure layer 110 is embossed on the transparent substrate 101 through a first master, and then the first grating structure layer 110 is covered with the filling layer 130 to be leveled by spin coating.

S120: Form a second grating structure layer 120 on the transparent substrate 101 formed with the first grating structure layer 110 by using a second master.

Wherein, the first preset diffraction pattern on the first master is different from the second preset diffraction pattern on the second master, and at least one layer of the first grating structure layer 110 and the second grating structure layer 120 is one-dimensional Grating structure layer.

The glue is cured by an ultraviolet lamp, and the second grating structure layer 120 is embossed on the filling layer 130 .

It should be noted that when the first grating structure layer 110 is formed through the first master and the second grating structure layer 120 is formed through the second master, the first preset diffraction pattern on the first master and the first grating structure layer The patterns of 110 are corresponding, but not necessarily consistent, depending on whether positive photoresist or negative photoresist is used, and the same is true for the second master.

The master plate can be prepared by photolithography and then etching with DUV equipment, or directly by laser direct writing. After the preparation of the master plate is completed, the master plate is pressed on the material of the transparent substrate 101 by nanoimprinting method, and the diffractive optical element 100 is prepared by nanoimprinting on the transparent substrate 101 twice, that is, the diffractive optical element 100 is first passed on the transparent substrate 101. The first master plate imprints the first grating structure layer 110, and then coats the filling layer 130, and then embosses the second grating structure layer 120 through the second master plate. In the embossing process, the alignment accuracy can be improved by adding marks. The alignment error of this structure depends on the alignment angle accuracy between wafers, and its position error requirements are much smaller than those between components in traditional methods. Therefore, the overall optical performance of the diffractive optical element 100 can be improved.

It can be seen that how to form the first grating structure layer 110 and the second grating structure layer 120 on the transparent substrate 101 mainly depends on how the master is designed, and the preset diffraction pattern on the master determines the pattern of the grating structure layer to produce Preset dot matrix spot.

Therefore, referring to FIG. 6, the embodiment of the present application also provides a method for designing a master diffraction pattern, including:

S200: Substitute the input light intensity I ₀ and the input phase φ ₀ into the formula

In the embodiment of the present application, the diffractive optical element 100 is designed as a second-order structure, the height of the steps is determined by the wavelength of the light source and the refractive index of the material, and the second-order top view structure is realized by the GS algorithm. The algorithm is applicable to both one-dimensional grating structure layer and two-dimensional grating structure layer. Because there are steps and different refractive indices everywhere, the phase of the light source changes after passing through the DOE. The phase change here satisfies the thin element approximation, which is equivalent to the phase of Π generated by the change of the structure, where λ is the wavelength of the light source, n1, n2 are the refractive indices of the medium above and below the DOE, so the height h satisfies the following equation:

First, according to the FOV and wavelength of the dot matrix on the screen, the following equation is satisfied to determine the period Px and Py length and width of DOE:

In the formula, FOV_H, V represent the horizontal and vertical viewing angles of the dot matrix, and n _{H, V} represent the horizontal and vertical points. After determining the length and width of the DOE period Px and Py, the GS algorithm is used to optimize the DOE structure. The logic diagrams and optical path diagrams optimized by the algorithm are shown in Figures 7 to 9.

Among them, at the beginning, the light source is set to be a uniform light source I ₀ =1, the input phase φ _t is a random phase distribution between 0 and Π, the lattice light intensity distribution I _m of the target is all 1, and the rest are 0.

S210: Calculate the difference I _c between the output light intensity I _t and the target light intensity I _m .

The first master plate and the second master plate correspond to two dot matrix patterns after dismantling respectively, when designing the first master plate, then the target light intensity _Im is the light intensity of the dot matrix pattern corresponding to the first master plate, When designing the second master, the target light intensity _Im is the light intensity of the dot matrix pattern corresponding to the second master.

S220: put the formula

Fourier transform and binarize to obtain the target input light intensity I _0m and the target input phase φ _0m .

The propagation of the beam can be simplified as a Fourier transform in the mathematical model, so fft and ifft are used in the optimization to simulate the propagation process.

S230: When the difference I _c between the output light intensity I _t and the target light intensity I _m is less than the light intensity preset value, according to the formula

S240: When the difference I _c between the output light intensity I _t and the target light intensity I _m is greater than or equal to the light intensity preset value, the formula

Fourier transform to obtain the corrected input light intensity I _r and the corrected input phase φ _r .

S241: Binarize the corrected input phase φ _r to obtain the cyclic input light intensity I _n and the cyclic input phase φ _n .

Returning to S200, the cyclic input light intensity I _n and the cyclic input phase φ _n are substituted into the formula

Calculate the difference I _c between the output light intensity I _t and the target light intensity I _m , until the difference I c between the output light intensity I _t and the target light intensity _{I m} _is less than the light intensity preset value, the formula

Fourier transform to get the target input light intensity I _0m and the target input phase φ0 _m .

According to the formula

Iteration is performed by continuously modifying the light intensity and phase distribution, so that the preset light intensity target is finally met. Therefore, the second-order distribution structure φ _DOE of DOE is obtained, and the corresponding light intensity value I _0m of each point of the lattice is obtained. The preset diffraction pattern corresponding to the lattice can be obtained from the phase of each coordinate point, and the DUV equipment is used for lithography, and then The preset diffraction pattern is prepared on the master by etching or laser direct writing, and a corresponding grating structure layer is formed on the transparent substrate 101 through the master to obtain the diffractive optical element 100 . The first master forms the first grating structure layer 110 , and the second master forms the second grating structure layer 120 .

In addition, when the light source is projected on the receiving screen 200 through the DOE, due to the excessively large propagation inclination angle of some diffraction orders, pincushion distortion occurs in the position of the overall dot matrix arrangement. In addition, the light intensity will also change, and the edges are relatively The center becomes weaker. Therefore, when designing the dot matrix scheme, it is also necessary to pre-compensate and correct this type of pincushion distortion (by adjusting the width of the grid through an optimization algorithm, or adjusting the edge of the complex image), so that each on the receiving screen 200 The uniform distribution of the light intensity of the diffraction order is shown in the table below, which shows the 3*5 lattice design and the light intensity distribution of the lattice after the lattice is distorted on the receiving screen 200. It can be seen from the table below that for the lattice For example, when the designed light intensity is 1, the light intensity received by the receiving screen 200 may decrease due to distortion, so correction is required.

The specific correction process is: compare the light intensity distribution of each coordinate point of the preset diffraction pattern with the light intensity distribution of each coordinate point corresponding to the target diffraction pattern, when the light intensity distribution of the coordinate point of the preset diffraction pattern exceeds the target diffraction pattern When the pattern corresponds to the light intensity distribution threshold range of the coordinate point, it is judged that the pattern is affected by distortion, and the light spot intensity is too strong or too weak to correct the light intensity. Correct the target light intensity I _m to obtain the light intensity distribution scheme of each coordinate point, adjust the target light intensity I _m =I ₀ ×1/cos(θ), θ is the relationship between the direction of each spot in the target lattice and the beam propagation direction angle. The adjusted target light intensity I _m is resubstituted into the aforementioned corresponding formulas and steps, and recalculated to obtain the final preset diffraction pattern of the master.

For correction, this application also provides some embodiments. In some embodiments, as shown in FIG. 10 and FIG. A part of the first grating structure layer 110 is formed. The first grating structure layer 110 corresponds to other structures of an asymmetric lattice, and may also be a vertical one-dimensional grating of a symmetrical lattice. In FIG. 10 , black represents the portion of the dielectric that has been etched away, and white represents the portion of the dielectric that has not been etched.

Then these embodiments also need to pre-correct the dot matrix first, as shown in the figure below, these embodiments can be applied to the correction design to make the spot intensity uniform. The following table is the light intensity corresponding table. For example, after correction, the light intensity of a preset coordinate point is 1.07, and the light intensity of the corresponding spot formed on the receiving screen 200 is 1. The same is true for other coordinate points.

In some other embodiments, as shown in FIG. 12 and FIG. 13 , the one-dimensional dislocation lattice may be a periodic dislocation lattice or an aperiodic dislocation lattice. The periodicity of dislocation here refers to the horizontal or vertical composition of repeated dislocation units. In the dot matrix of the second embodiment, the first grating structure layer 110 uses an oblique grating, and the second grating structure layer 120 is a one-dimensional grating, so that the final dot matrix arrangement forms a dislocation arrangement, and the white in the pattern represents The structure is convex, and the black represents the structure depression. Among them, attention should be paid to the alignment angle of two pieces of DOE, which requires high precision (less than 0.1°) and forms a fixed angle.

In still some embodiments, as shown in Fig. 14 and Fig. 15, the first grating structure layer 110 is an oblique binary grating, the second grating structure layer 120 is a two-dimensional binary image, and two-dimensional Misplaced dot matrix function. The white in the pattern represents the structure protruding, and the black represents the structure depression. Similarly, the number of pattern steps here can be two to eight, which is determined by the efficiency of design specifications and the ease of processing. Among them, attention should be paid to the alignment angle of the two structures, which requires high precision (less than 0.1°) and forms a fixed angle. Among them, the design of oblique grating is consistent with that of dot matrix in class B, and the design of two-dimensional grating is the same as that of asymmetrical dot matrix.

In the structural design of Fig. 14, since the second grating structure layer 120 has a lattice arrangement in both horizontal and vertical orientations, it is necessary to consider the matching of the FOV of the two types of model lattices in the design of the oblique grating, resulting in a single The dot matrix under the light source is equally spaced and regularly distributed.

To sum up, in the diffractive optical element 100 and its manufacturing method provided by the embodiment of the present application, the first grating structure layer 110 and the second grating structure layer 120 are sequentially formed on the transparent substrate 101, and the first grating structure layer 110 and the second grating structure layer At least one layer in the layer 120 is a one-dimensional grating structure layer, and the other layer is a one-dimensional grating structure layer or a two-dimensional grating structure layer. A striped grating pattern is formed on the one-dimensional grating structure layer, and a complex pattern is formed on the two-dimensional grating structure layer. , the above patterns can be obtained by algorithms; the first grating structure layer 110 generates a corresponding lattice pattern, the second grating structure layer 120 generates a corresponding lattice pattern, and the first grating structure layer 110 and the second grating structure layer 120 are combined When on the transparent substrate 101 , the respective lattices generated by the first grating structure layer 110 and the second grating structure layer 120 are combined to form a preset array lattice, and the preset array diffraction spot can be received on the receiving screen 200 . It is equivalent to decomposing the formed preset array lattice into two simple lattices, and these two simple lattices can be obtained through the first grating structure layer 110 and the second grating structure layer 120 respectively. After adopting the double-layer grating structure layer, since the decomposed lattice has the characteristics of less lattice and regular shape, the difficulty of designing and processing the diffractive optical element 100 is greatly reduced, and high-performance beam splitting can be obtained through the diffractive optical element 100 , so that the two-dimensional lattice also has better beam splitting uniformity. In the follow-up, correction design can be carried out, corresponding to the parameter requirements of different lenses and photosensitive devices, and corresponding correction factors can be set to maximize the uniformity.

The above descriptions are only examples of the present application, and are not intended to limit the scope of protection of the present application. For those skilled in the art, various modifications and changes may be made to the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this application shall be included within the protection scope of this application.

Industrial Applicability

The present application provides a diffractive optical element and its preparation method, and a design method of a master diffraction pattern, including providing a transparent substrate; forming a first grating structure layer on one side surface of the transparent substrate through a first master; forming a A second grating structure layer is formed on the transparent substrate of the first grating structure layer through a second master, wherein the first preset diffraction pattern on the first master is different from the second preset diffraction pattern on the second master, At least one of the first grating structure layer and the second grating structure layer is a one-dimensional grating structure layer. The respective lattices produced by the first grating structure layer and the second grating structure layer are combined to form a preset array lattice. After adopting the double-layer grating structure layer, the decomposed lattice has the characteristics of less lattice and regular shape, which greatly reduces the difficulty of designing and processing the diffractive optical element, obtains high-performance beam splitting, and maintains a good effect of the two-dimensional lattice. Beam splitting uniformity.

In addition, it can be understood that the diffractive optical element and its manufacturing method and the design method of the master diffraction pattern of the present application are reproducible and can be used in various industrial applications. For example, the diffractive optical element of the present application, its preparation method, and the design method of the master diffraction pattern can be used in the technical field of diffractive optics.

Claims

A preparation method of a diffractive optical element, characterized in that the preparation method comprises:

providing a transparent base;

forming a first grating structure layer on one side surface of the transparent substrate through a first master;

A second grating structure layer is formed on the transparent substrate formed with the first grating structure layer through a second master, wherein the first preset diffraction pattern on the first master and the first preset diffraction pattern on the second master Different from the second preset diffraction pattern, at least one of the first grating structure layer and the second grating structure layer is a one-dimensional grating structure layer.
The preparation method according to claim 1, characterized in that the one-dimensional grating structure layer is configured as a strip-shaped periodic grating pattern.
The preparation method according to claim 1 or 2, characterized in that a filling layer is formed between the first grating structure layer and the second grating structure layer.
The preparation method according to claim 3, characterized in that first, the first grating structure layer is embossed on the transparent substrate through the first master, and then the first grating structure layer is covered. The filling layer is spin-coated and leveled.
The preparation method according to claim 3 or 4, characterized in that the refractive index difference between the first grating structure layer and the filling layer is greater than or equal to 0.2, and the second grating structure layer There is a refractive index difference greater than or equal to 0.2 between the filling layer and the filling layer.
The preparation method according to any one of claims 1 to 5, characterized in that an optical film is coated between the transparent substrate and the first grating structure layer, and/or, an optical film is coated on the transparent substrate An optical film is coated on the side away from the first grating structure layer.
A kind of design method of master plate diffraction pattern, it is characterized in that, the design method of described master plate diffraction pattern comprises:

Substitute the input light intensity I 0 and the input phase φ 0 into the formula
Perform Fourier transform to obtain the output light intensity I t and output phase φ t ; where, the input light intensity is 1, the input phase is randomly selected between 0 and π, and i is the coefficient

Calculate the difference I c between the output light intensity I t and the target light intensity I m ;

the formula
Fourier transform and binarize to obtain target input light intensity I 0m and target input phase φ 0m ;

When the difference I c between the output light intensity I t and the target light intensity I m is less than the light intensity preset value, according to the formula
Calculate the binarized phase φ t0 of each coordinate point to obtain the preset diffraction pattern.
The method for designing a master plate diffraction pattern according to claim 7, wherein the formula
Fourier transform and binarization, after obtaining the target input light intensity I 0m and the target input phase φ 0m , the method also includes:

When the difference I c between the output light intensity I t and the target light intensity I m is greater than or equal to the light intensity preset value, the formula
Fourier transform to obtain the corrected input light intensity I r and the corrected input phase φ r ;

Binarize the corrected input phase φ r to obtain the cyclic input light intensity I n and the cyclic input phase φ n ;

Substitute the cyclic input light intensity I n and the cyclic input phase φ n into the formula
Fourier transform to obtain output light intensity I t and output binarized phase φ t ; wherein, i is a coefficient

Calculate the difference I c between the output light intensity I t and the target light intensity I m ;

When the difference I c between the output light intensity I t and the target light intensity I m is less than the light intensity preset value, the formula
Fourier transform, obtain target input light intensity I 0m and target input phase φ 0m ;

According to the formula
Calculate the binarized phase φ t0 of each coordinate point to obtain the preset diffraction pattern.
According to the design method of the master plate diffraction pattern described in claim 7 or 8, it is characterized in that, according to the formula
After calculating the binarized phase φ t0 of each coordinate point and obtaining the preset diffraction pattern, the method further includes:

comparing the light intensity distribution of each coordinate point of the preset diffraction pattern with the light intensity distribution of each coordinate point corresponding to the target diffraction pattern;

When the light intensity distribution of the coordinate point of the preset diffraction pattern exceeds the light intensity distribution threshold of the coordinate point corresponding to the target diffraction pattern, the target light intensity Im is corrected to obtain the light intensity distribution of each coordinate point plan.
The method for designing a master diffraction pattern according to claim 9, wherein when the light intensity distribution of the coordinate point of the preset diffraction pattern exceeds the light intensity distribution of the corresponding coordinate point of the target diffraction pattern When the threshold is reached, the target light intensity I m is corrected to obtain the light intensity distribution scheme of each coordinate point including:

Adjust the target light intensity I m =I 0 ×1/cos(θ), where θ is the angle between the direction of each point in the target lattice and the propagation direction of the light beam.
A diffractive optical element, prepared by the method for preparing a diffractive optical element according to any one of claims 1 to 6, characterized in that, the diffractive optical element comprises: a transparent substrate on which are sequentially formed The first grating structure layer and the second grating structure layer, at least one of the first grating structure layer and the second grating structure layer is a one-dimensional grating structure layer, and the light beam incident on the transparent substrate passes through the first grating structure layer After the first grating structure layer and the second grating structure layer, a preset array diffraction spot is emitted.
The diffractive optical element according to claim 11, wherein the surface pattern of the one-dimensional grating structure layer is a stripe periodic grating pattern.
The diffractive optical element according to claim 11 or 12, characterized in that a filling layer is formed between the first grating structure layer and the second grating structure layer.
The diffractive optical element according to claim 13, characterized in that there is a refractive index difference greater than or equal to 0.2 between the first grating structure layer and the filling layer, and the second grating structure layer and the There is a refractive index difference greater than or equal to 0.2 between the filled layers.
The diffractive optical element according to any one of claims 11 to 14, characterized in that an optical film is coated between the transparent substrate and the first grating structure layer, and/or the transparent substrate The side away from the first grating structure layer is coated with an optical film.