CN112099228B

CN112099228B - RCWA-based polarizer grating diffraction ray tracing simulation system and method

Info

Publication number: CN112099228B
Application number: CN202011145007.4A
Authority: CN
Inventors: 张宇宁; 刘皓天
Original assignee: Southeast University
Current assignee: Southeast University
Priority date: 2020-10-23
Filing date: 2020-10-23
Publication date: 2023-02-21
Anticipated expiration: 2040-10-23
Also published as: CN112099228A

Abstract

The invention discloses a system and a method for simulating RCWA-based polarizer grating (PVG) diffraction ray tracing. The method utilizes RCWA analysis theory to expand the anisotropic periodic grating structure into Fourier series, utilizes boundary conditions to solve the diffraction characteristic of incident light, and then combines a Monte Carlo method to optimize the light tracing algorithm, thereby improving the simulation precision and the operation speed. The model can rapidly calculate the diffraction characteristics of the grating under given parameters, comprises diffraction orders, a propagation direction, diffraction efficiency and polarization state analysis, has good portability, can be applied to commercial optical simulation software ZEMAX through a Dynamic Link Library (DLL), and realizes light ray tracing simulation.

Description

RCWA-based polarizer grating diffraction light ray tracing simulation system and method

Technical Field

The invention relates to a system and a method for simulating a polarizer grating diffraction light trace based on RCWA, belonging to the technical field of optical communication.

Background

In recent years, near-eye display technology has received much attention from the market, and among them, holographic waveguide display technology applied to Augmented Reality (AR) has made a great progress and has received wide attention at home and abroad. In order to achieve a high-performance slim design, a Diffractive Optical Element (DOE), typified by a grating, has been widely adopted and studied as a coupling element of a waveguide near-eye display. In recent years, related researchers have proposed a polarizer grating (PVG) which has a two-dimensional anisotropic periodicity by periodically rotating liquid crystal molecules in two-dimensional directions, retains the efficient single-order diffraction characteristics of a Volume Holographic Grating (VHG), has a large angular bandwidth, and has selectivity for the polarity of incident light, as shown in fig. 1, which can give a near-eye display holographic waveguide system a larger design optimization dimension. Experiments show that the grating can realize full-color near-to-eye display of holographic waves as a novel diffraction element. In order to apply the PVG to near-eye display and realize optimization of near-eye display imaging, simulation of the PVG and diffraction efficiency thereof is of great importance in the design process of an optical imaging system.

At present, the finite element method of COMSOL Multiphysics is adopted by domestic and foreign research institutions to simulate the diffraction characteristics of gratings with complex structures, the method can realize high-precision numerical simulation, however, COMSOL does not have a geometrical imaging optimization system of a system and is not suitable for design and optimization of an imaging system. Common optical simulation software such as Zemax and TracePro can realize the design, analysis, optimization and other auxiliary functions of the optical imaging system, but only support the simulation of simple surface gratings and bulk gratings, and lack the simulation model of the polarizer gratings. Compared with COMSOL, the design optimization of any-shape grating holographic waveguide display can be realized by a strong ray tracing algorithm and an optical design optimization function of Zemax as long as a simulation model of the grating is established in Zemax. Therefore, it is important to design an arbitrary-shaped grating simulation system based on Zemax.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a system and a method for simulating the diffraction ray trace of a polarizer grating based on RCWA, in order to overcome the defects in the prior art, which can perform imaging simulation and optimization functions of the polarizer grating in combination with the ray trace simulation algorithm of Zemax, and optimize the RCWA algorithm, so as to reduce the calculation time, improve the simulation accuracy, and enable the grating to be applied to the simulation optimization design of the holographic waveguide display.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

a polarizer grating diffraction ray tracing simulation system based on RCWA comprises a polarization state detection module, a Monte Carlo tracing module and a dynamic link library interface; wherein

The polarization state detection module is used for decomposing incident light into s-wave and p-wave, obtaining the polarization state of incident light by calculating the phase difference of the s-wave and the p-wave, and transmitting light information with the polarization state and the incident direction to the Monte Carlo tracking module;

the Monte Carlo tracking module is combined with a PVG diffraction model based on RCWA, and calculates the diffraction characteristics of light rays in each polarization state and incidence direction by using a Monte Carlo numerical calculation method, constructs a probability distribution interval, generates a random number in the light ray tracking process, and determines the diffraction direction of the light rays according to the interval where the random number is positioned;

the dynamic link library interface is used for defining a data communication interface between the RCWA-based PVG diffraction model and optical simulation software ZEMAX, embedding the RCWA-based PVG diffraction model into the ZEMAX, and realizing the light tracing simulation of the polarizer grating by using a light tracing algorithm of the ZEMAX.

Furthermore, the polarization state detection module obtains an incident plane where a p wave is located and a plane which is perpendicular to the incident plane and contains the s wave of the incident light according to the direction of the incident light and the normal line of a diffraction interface, and decomposes the incident light into the s wave and the p wave.

Furthermore, in the RCWA-based polarizer grating diffraction ray tracing simulation system provided by the present invention, when the monte carlo tracing module is used for calculation, the RCWA-based PVG diffraction model is an RCWA theoretical model using a three-dimensional anisotropic medium, and the propagation distribution of the electromagnetic wave is directly solved according to the diffraction characteristics of incident light with different polarization characteristics, and according to maxwell equation set and boundary condition limitation.

Furthermore, the dynamic link library interface comprises an input/output interface of a grating simulation model with any shape, the ZEMAX supports a self-defined dynamic link library, the grating simulation model with any shape is compiled into the dynamic link library, and the dynamic link library is imported into the ZEMAX through the self-defined diffraction model function of the ZEMAX, so that the light tracing simulation of the grating with any shape in the ZEMAX is realized.

The invention also provides a polarizer grating diffraction ray tracing method based on RCWA, which comprises the steps of expanding the anisotropic periodic grating structure into Fourier series by using RCWA analysis theory, solving the diffraction characteristic of incident rays by using boundary conditions, and optimizing a ray tracing algorithm by combining a Monte Carlo method to realize the ray tracing simulation of the polarizer grating.

Further, the method for tracing the diffraction light of the polarizer grating based on the RCWA provided by the invention specifically comprises the following steps:

step 1, polarization state detection: decomposing incident light into s-wave and p-wave, and calculating the phase difference between the s-wave and the p-wave to obtain the polarization state of the incident light;

step 2, monte Carlo tracking: calculating the diffraction characteristics of the light rays in each polarization state and incidence direction by combining a PVG diffraction model based on RCWA and utilizing a Monte Carlo numerical calculation method; constructing a probability distribution interval, generating a random number in the light ray tracing process, and determining the diffraction direction of the light ray according to the interval of the random number;

and 3, compiling the processes in the step 1 and the step 2 into a dynamic link library DLL file, importing the DLL file into optical simulation software ZEMAX, embedding the RCWA-based PVG diffraction model into the ZEMAX, and realizing the light tracing simulation of the polarizer grating by using a light tracing algorithm of the ZEMAX.

Further, in the RCWA-based polarizer grating diffraction ray tracing method provided by the present invention, in step 2, based on the PVG diffraction model of RCWA, the monte carlo numerical calculation method is used to calculate the diffraction characteristics of the ray in each polarization state and incident direction, specifically as follows:

(1) Assuming that a medium of the grating is an anisotropic material, defining the grating as an infinite plane with periodic variation, wherein PVG is periodically distributed in an xy plane, and the relative dielectric tensor of the PVG is expanded into a Fourier series form;

(2) Performing Fourier expansion on the electromagnetic waves, and deducing expressions of electromagnetic fields in the incident dielectric layer and the substrate layer by combining a Maxwell equation set;

(3) Deriving a coupled wave partial differential equation set by the dielectric tension series and the electromagnetic field series, and converting the problem of the partial differential equation into a solving problem of an eigenmode field;

(4) And solving the amplitude coefficient of the eigenmode field by a mathematical method at the boundary of different areas by using periodic boundary conditions so as to solve the expressions of the electric field and the magnetic field and further solve the diffraction efficiency.

Furthermore, the method for tracing the diffraction light of the polarizer grating based on the RCWA, provided by the invention, is characterized in that a probability distribution interval is constructed, a random number is generated in the light tracing process, and the diffraction direction of the light is determined according to the interval where the random number is located; the process is as follows:

incident light rays can be incident on the PVGGenerating a plurality of diffraction orders, and setting the diffraction efficiency of each diffraction order as follows: t is a unit of ₀ ,T ₁ ,…,T _n The range of the interval consisting of diffraction efficiencies is then:

each time the beam and PVG are acted upon, a random number R needs to be generated, taking the above range as the probability distribution of occurrence of diffracted light of each order.

Compared with the prior art, the technical scheme adopted by the invention has the following technical effects:

the invention provides a RCWA-based polarizer grating diffraction ray tracing simulation system, which can realize the ray tracing simulation of a polarizer grating in optical simulation software Zemax.

Drawings

Fig. 1 is a schematic diagram of a polarizer grating structure according to the present invention.

FIG. 2 is a flow chart of a simulation system.

FIG. 3 is a three-dimensional diffraction diagram of PVG.

Fig. 4 is a top view of PVG.

FIG. 5 is a schematic diagram of a Monte Carlo method for optimizing PVG tracking.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in detail below with reference to the accompanying drawings and embodiments.

Referring to fig. 2, the present invention provides a RCWA-based polarizer grating diffraction ray tracing simulation system, including a polarization state detection module, a PVG diffraction model based on RCWA, a monte carlo tracing module, and a dynamic link library interface, wherein:

after the incident light and the grating parameters are input into the system, the polarization state detection module obtains an incident plane (a plane where p waves are located) and a plane (a plane where s waves are located) which is perpendicular to the incident plane and contains the incident light according to the direction of the incident light and the normal line of a diffraction interface, the incident light is decomposed into the s waves and the p waves, and the polarization state of the incident polarized light is obtained by calculating the phase difference between the s waves and the p waves; and transmitting the light ray information with the polarization state and the incident direction to a Monte Carlo tracking module, wherein the module combines a PVG diffraction model based on RCWA, utilizes a Monte Carlo numerical calculation method to construct a random number meeting the conditions to optimize the calculation speed, and calculates the diffraction characteristics of the light rays with each polarization state and incident direction.

The RCWA-based PVG diffraction model assumes that the medium of the grating is an anisotropic material, i.e. the dielectric constant of the grating is a 3 x 3 tensor. To simplify the calculation, the grating is defined as a plane of infinite periodic variation. As shown in fig. 4, the PVG has a periodic distribution in the xy plane, and thus the relative dielectric tensor of the PVG can be expanded into the fourier series. Then, fourier series expansion is carried out on the electromagnetic waves, and expressions of electromagnetic fields in the incident dielectric layer (REGION 2) and the substrate layers (REGION 1 and REGION 3) are deduced by combining Maxwell equations. And deducing a coupled wave partial differential equation set from the dielectric tension series and the electromagnetic field series, and converting the problem of the partial differential equation into a solution problem of the eigenmode field. And finally, solving the amplitude coefficient of the eigen-mode field by using a mathematical method on the boundary of different areas by using a periodic boundary condition so as to obtain the expressions of the electric field and the magnetic field and further solve the diffraction efficiency.

The process is compiled into a Dynamic Link Library (DLL) file, the DLL file is imported into Zemax, and ray tracing simulation of PVG can be achieved by using the powerful ray tracing function of Zemax.

The dynamic link library interface defines a data communication interface between the PVG simulation model and Zemax, the model is embedded into Zemax, the Zemax supports a customized dynamic link library, the grating simulation model with any shape is compiled into the dynamic link library, and the Zemax is imported through the customized diffraction model function of the Zemax, so that the light ray tracing simulation of the PVG can be realized in the Zemax.

In the non-sequential mode of Zemax, the light is split through a reflective or transmissive surface and the split light continues to propagate. In the present invention, the light is not split into a plurality of light rays after passing through a surface, but the propagation direction is randomly changed according to a probability distribution proportional to the diffraction efficiency of each diffraction order.

The RCWA-based PVG diffraction model adopts an RCWA theoretical model of a three-dimensional anisotropic medium. The calculation process will be explained in detail below with the structure of the polarizer grating PVG shown in fig. 1.

The structure of the polarizer grating PVG is shown in fig. 1, in which the direction of the gray rod-shaped object is the direction of the optical axis, the optical axis directions of the anisotropic material are periodically distributed in the x direction and the y direction, and the optical axis presents a spiral structure on the y axis. This structure produces a series of tilted and periodic refractive index planes, the tilt angles

And is

If the included angle between the optical axis direction of a certain point (x, y) in the grating and the z axis is α, the following are included:

wherein Λ _x And Λ _y The periods of the optical axis direction in the x direction and the y direction, respectively. Let the grating period be Λ _B Then, there are:

connecting the points with the same direction of the optical axis of the medium to obtain the PVG three-dimensional diffraction shown in figure 3In the schematic view, the region1 is an incident region, the region2 is a grating region formed by anisotropic liquid crystal molecules, and the region3 is a transmission region. Incident light wave vector direction k ₁ The angle between the x and y plane is theta, k ₁ The included angle between the plane formed by the grating and the z axis and the y axis is delta, the included angle of the incident light polarization electric field direction in the incident plane is psi, and the grating period is lambda.

For better illustration, a top view is used to aid in the illustration, as shown in fig. 4. For holographic waveguide near-to-eye display systems, the present invention only considers the case where both

regions

1 and 3 are isotropic materials. The relative dielectric constants of the

regions

1 and 3 are respectively epsilon ₁ And ε ₃ Region2 is the anisotropic grating modulation region with a relative dielectric tensor of

It is represented by a 3 x 3 matrix.

Assuming that the refractive indexes of ordinary light and extraordinary light of the liquid crystal are n respectively under the condition that the material has no absorption and no optical rotation _o And n _e Then, when the rotation angle of the optical axis around the y-axis is α, the relative dielectric tensor matrix of PVG can be expressed as:

wherein the rotation angle α of the optical axis of the liquid crystal molecules is represented by formula (1).

The relative dielectric tensor of the modulation region2 can be expanded in the form of a fourier series:

wherein

Is the h-th fourier tensor component of the relative dielectric tensor,

r represents a position. The raster vector K is expressed as:

wherein K =2 pi/Λ, Λ is the grating period, and phi is the included angle between the grating vector K and the negative direction of the y axis.

The normalized electric field vector of the incident monochromatic plane wave is expressed as:

wherein

Is the unit vector of the incident electric field direction, and is represented by:

in formula (7)

The default incident ray is linearly polarized. If the incident light is in other polarization states, u can be modified _x ，u _y And u _z The real and imaginary components achieve the purpose of defining the polarization state of incident light.

k ₁ Is the direction of the wave vector of the incident light, and can be expressed as follows:

where | k ₁ |＝2πn ₁ /λ，n ₁ Is the refractive index of region1 and λ is the wavelength of the incident light in vacuum.

The fourier series form of the electric field for zone 1 and zone 3 after diffraction was written separately:

where s is the thickness of region2, this is set to facilitate the subsequent simplification of the boundary conditions. E _inc Defined by formula (6), R _i ，R _i ′，T _i ，T _i ' are unknown parameters that represent the magnitude vector of each diffraction order. According to Floquet theorem, k _1i ，k _1i ′，k _3i ，k _3i ' is defined by the formula:

where q =1,3,i =1,2,.. The subscript i corresponds to the i-th order reflected or transmitted wave.

k _qi The wave vector component is the propagation direction of the O light in the diffracted wave, and the magnitude is given by:

(k _qi ·k _qi )＝k ₀ ² n _Oq ² ，q＝1，3#(13)

wherein n is _Oq Is the optical refractive index of O light of the region q, k ₀ ＝2π/λ。k _qi ' the wavevector component is the propagation direction of the O light in the diffracted wave, and the magnitude is given by:

wherein n is _Eq Is the optical refractive index of O light of region q,

is a unit vector in the optical axis direction in the region q, and can be expressed as:

since both region1 and region3 are isotropic materials, c is assumed _qx ＝c _qz ＝0，c _qy ＝1，n _Eq ＝n _Oq ＝n _q . The above hypothesis is substituted for the formulae (10), (11), (12) and (14), k _qi ＝k _qi ', i.e., under the condition that the

regions

1 and 3 are isotropic materials, there is no distinction between the reflected wave and the transmitted wave for the O light and the E light. Thus, R in formula (9) can be represented by _i And R _i ' incorporation, T in formula (10) _i And T _i ' combine, then equation (9) and equation (10) are respectively reduced to the following equations:

wherein R is _ci ＝R _i +R _i ′，T _ci ＝T _i +T _i ′。

In the diffraction region2 shown in fig. 4, the electric and magnetic field components can be represented in the form of fourier series with respect to spatial harmonics:

where i is the ith diffraction order,

normalized amplitudes of the i-th order spatial harmonic electric and magnetic fields, respectively.

In the modulation region2, the electromagnetic field satisfies the maxwell equation set:

where ω is the angular frequency, μ ₀ Is the vacuum magnetic permeability ∈ ₀ Is a dielectric constant of a vacuum, and,

is defined by formula (4).

Substituting (4), (18) and (19) into (20) and (21) eliminates the y components of the electric field and the magnetic field, and the tangential components of the electric field and the magnetic field in the grating area can be represented in a matrix form:

wherein

M =2m +1, M is the infinite number of stages truncated to a finite number of stages.

Definition of parameters and

similarly.

Is a 4M × 4M matrix, which is defined as follows:

wherein

Are M × M matrices, which are defined as follows:

wherein k is ₀ ＝2π/λ，

Is an MxM organic pigment

Form of a symmetric submatrix (epsilon) _uv ) _i-j Is the dielectric tensor element ε _uv Fraction i-j of the fourier series, i, j = -m,1-m, · 1,0,1,. M-1, m, u, v = -x, y, z.

Are all M × M symmetric sub-matrices of the form:

wherein

Is an M × M identity matrix, k _xi (i = -m., 0., m) is defined by formula (11), K _y See formula (5), k _1z See formula (8).

Equation (23) can be solved by a state-variable method involving the matrix in the region of the de-grating

Eigenvalue and eigenvector problems. The solution of formula (20) is generally of the form:

wherein

Is a 4M × 4M containing matrix

Is calculated from the matrix of feature vectors of (1). Sub-matrix

Is a matrix of M x 4M with their k row n column elements denoted as W _p，kn 。

Is a 4M x 4M diagonal matrix whose diagonal elements are matrices

Characteristic value λ of _n (n＝1，2，3，...，4M)。

Is a 4M x 1 unknown constant vector whose values are solved by a boundary condition problem.

Solving the electric field amplitude vector R in the formulas (16) and (17) _ci ，T _ci And C, the boundary conditions of the tangential electric and magnetic fields need to be matched, resulting in the following matrix form:

wherein

Are M × 4M sub-matrices, and their respective elements are defined as follows:

wherein ω is _n ＝exp(-λ _n s), k =1,2, · M, n =1,2,. · 4M, i = k-M-1, where M =2m +1.α in the formula (24) _i ，β _i ，γ _i ，θ _i ，μ _i ，ν _i Is defined as follows:

is a 4 mx 1 column vector, which is defined as follows:

wherein:

p _m+1 ＝(k _1z k _x0 /k _y10 )u _x +k _1z u _y +[(k _1z ² /k _y10 )+k _y10 -k _1y ]u _z ，

p _3m+2 ＝[(k _x0 ² /k _y10 )+k _y10 -k _1y ]u _x +k _1x u _y +(k _x0 k _1z /k _y10 )u _z

the diffraction efficiency of the i-th order diffracted wave, defined as the ratio of the effective power of the diffracted wave perpendicular to the boundary (y-component) to the effective power of the corresponding incident wave, is:

DE _1i is the diffraction efficiency, DE, of the i-th order reflected wave _3i Is the diffraction efficiency of the i-th order transmitted wave. k is a radical of _y1i ，k _y3i ，k _1y ，k _3y See the formulas (8) to (13),

see formula (7).

From the above derivation, it can be known to calculate the i-th order diffraction parameter R _ci ，T _ci ，DE _1i And DE _3i Comprises the following steps:

1) Solving equation (25) to find the unknown parameters

2) Obtaining S by equation (24) _xi (0)、S _zi (0)、U _xi (0)、U _zi (0) And S _xi (-s)、S _zi (-s)、U _xi (-s)、U _zi (-s), where i = -m.

3) From the boundary conditions it follows:

R _cxi ＝S _xi (0)-u _x δ _i0

R _czi ＝S _zi (0)-u _z δ _i0

T _cxi ＝S _xi (-s)exp(-jiK _y s)

T _czi ＝S _zi (-s)exp(-jiK _y s)

4) Calculating R from the formula _cyi And T _cyi ：

R _cyi ＝-(l _xi1 /l _yi1 )R _cxi -(l _zi1 /l _yi1 )R _czi

T _cyi ＝-(l _xi3 /l _yi3 )T _cxi -(l _zi3 /l _yi3 )T _czi

Wherein l _wiq ＝k _xi ε _xwq +k _yqi ε _ywq +k _1z ε _zwq ，w＝x，y，z，q＝1，3。

5) R is to be _cxi ，R _czi ，R _cyi And T _cxi ，T _czi ，T _cyi The reflection wave diffraction efficiency DE can be obtained by substituting equations (29) and (30) _1i And transmitted wave diffraction efficiency DE _3i 。

The above RCWA computational model can be implemented using C + + programming, with the code being compiled into a dynamic link library DLL. Because a large number of matrix operations are needed in the calculation, a C + + matrix operation library Eigen3 is called in the system, and the library effectively supports linear algebra, matrix and vector operations, numerical analysis and related algorithms thereof, and can meet various matrix operation functions of the algorithm.

The Monte Carlo tracking module is a numerical calculation method which takes probability statistics theory as guidance, and generally comprises the following three steps: first, a probabilistic process is constructed or described; then, random sampling is carried out on the known probability distribution; finally, various estimates are established. The monte carlo method solves the complex problems of mathematically similar error estimation, numerical integration and optimization by constructing random numbers satisfying certain conditions. The following describes the operation of monte carlo tracking in detail by taking a transmissive grating as an example.

Before being optimized, incident light rays striking the PVG will generate a plurality of diffraction orders, each diffraction order having a diffraction efficiency: t is ₀ ，T ₁ ，…，T _n Then the range of the interval consisting of diffraction efficiencies is:

after optimization, each time the beam and PVG are acted upon, a random number R is generated, the range of the interval is used as the probability distribution of each level of diffraction light, if T is ₀ ＜R＜T ₀ +T ₁ It means that the diffraction direction of the light is the direction of the 1 st order diffraction light, and the energy of the light is the same as that of the incident light. The specific process of optimization using the monte carlo method is shown in fig. 5. Suppose thatThe diffraction efficiencies at each stage of PVG were:

T ₀ ＝0.5，T ₁ ＝0.15，T ₂ ＝0.25，T ₃ ＝0.1#(32)

the range of intervals under the above assumption is:

[0，0.5，0.65，0.9，1]#(32)

if the light ray hits the PVG for the first time, R =0.4, the light ray continues to advance in the direction of 0 th order diffracted light; when the second action is carried out, R =0.6, the light rays advance in the direction of 1 st-order diffraction light; in the third action, R =0.85, the light beam advances in the direction of the 2 nd order diffracted light, but the energy of the light beam is not changed at all times. It should be noted that the monte carlo method is only highly accurate when N is large, i.e. the number of incident light rays is large, and therefore the number of light rays emitted by the light source is generally defined to be more than one million.

From the above optimization process, it can be seen that the main role of the monte carlo method is to prevent ray splitting, and thus infinite increase in the number of rays and infinite decrease in the energy of the rays, but at the same time it comes at the cost of a huge number of samples. In the monte carlo method, there is a very important process to generate random numbers. In C + + syntax, randf) functions can be used to generate random numbers, but in practice it is not a truly chaotic random number, but a pseudo random number obtained using linear congruence. Since the period of the pseudo random number is particularly long, a number obtained within a certain range is random. Typically this function must be used with the srand () function to obtain a different random number at each execution. Since the PVG is inserted into Zemax in the form of a DLL, which means that each ray calls the DLL at the time of computation, the seed change speed of the srand () function must be fast. Based on the reasons, the nanosecond number of the current clock is selected as the seed in the system to generate the random number.

The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention, and such modifications and adaptations are intended to be within the scope of the invention.

Claims

1. A polarizer grating diffraction ray tracing simulation system based on RCWA is characterized by comprising a polarization state detection module, a Monte Carlo tracing module and a dynamic link library interface; wherein

The polarization state detection module is used for decomposing incident light into s-wave and p-wave, obtaining the polarization state of the incident light by calculating the phase difference of the s-wave and the p-wave, and transmitting light information with the polarization state and the incident direction to the Monte Carlo tracking module;

the Monte Carlo tracking module is combined with a PVG diffraction model based on RCWA, and utilizes a Monte Carlo numerical calculation method to calculate the diffraction characteristics of the light in each polarization state and incident direction, construct a probability distribution interval, generate a random number in the light tracking process, and determine the diffraction direction of the light according to the interval of the random number; the RCWA-based PVG diffraction model is an RCWA theoretical model adopting a three-dimensional anisotropic medium, and the propagation distribution of electromagnetic waves is directly solved according to the diffraction characteristics of incident light with different polarization characteristics and the limitation of Maxwell equations and boundary conditions;

2. The RCWA-based polarizer grating diffraction ray tracing simulation system of claim 1, wherein: the polarization state detection module obtains an incident plane where the p wave is located and an s wave plane which is perpendicular to the incident plane and contains the incident light according to the direction of the incident light and the normal line of the diffraction interface, and decomposes the incident light into the s wave and the p wave.

3. The RCWA-based polarizer grating diffraction ray tracing simulation system of claim 1, wherein: dynamic link storehouse interface contains the input/output interface of arbitrary shape grating simulation model, and ZEMAX supports customized dynamic link storehouse, writes into the dynamic link storehouse with arbitrary shape grating simulation model to ZEMAX is leading-in to self-defined diffraction model function through ZEMAX, realizes realizing the light ray trace emulation of arbitrary shape grating in ZEMAX.

4. A polarizer grating diffraction ray tracing method based on RCWA is characterized in that the method utilizes RCWA analysis theory to expand an anisotropic periodic grating structure into Fourier series, utilizes boundary conditions to solve diffraction characteristics of incident rays, and then combines a Monte Carlo method to optimize a ray tracing algorithm to realize ray tracing simulation of the polarizer grating; the method specifically comprises the following steps:

step 2, monte Carlo tracking: combining a PVG diffraction model based on RCWA, and calculating the diffraction characteristics of the light rays in each polarization state and the incident direction by using a Monte Carlo numerical calculation method; constructing a probability distribution interval, generating a random number in the light ray tracing process, and determining the diffraction direction of the light ray according to the interval of the random number;

step 3, compiling the processes in the step 1 and the step 2 into a Dynamic Link Library (DLL) file, importing the DLL file into optical simulation software ZEMAX, embedding the PVG diffraction model based on RCWA into the ZEMAX, and realizing the light ray tracing simulation of the polarizer grating by using a light ray tracing algorithm of the ZEMAX;

in step 2, based on the PVG diffraction model of RCWA, the diffraction characteristics of the light in each polarization state and incident direction are calculated by using a monte carlo numerical calculation method, specifically as follows:

(3) Deducing a coupled wave partial differential equation set according to the dielectric tension series and the electromagnetic field series, and converting the problem of the partial differential equation into a solution problem of the eigenmode field;

(4) Solving the amplitude coefficient of the eigenmode field by a mathematical method at the boundary of different areas by using periodic boundary conditions so as to solve the expressions of the electric field and the magnetic field and further solve the diffraction efficiency;

in step 2, a probability distribution interval is constructed, a random number is generated in the light tracing process, and the diffraction direction of the light is determined according to the interval of the random number, wherein the process is as follows:

after incident light rays strike the polarizer grating PVG, a plurality of diffraction orders can be generated, and the diffraction efficiency of each diffraction order is respectively set as follows: t is a unit of ₀ ,T ₁ ,…,T _n Then the range of the interval consisting of diffraction efficiencies is:

each time the beam and the PVG are acted upon, a random number R needs to be generated, and the range of the interval is used as the probability distribution of occurrence of each level of diffracted light.