Optimization design method for variable pitch grating recording structure

Abstract

The present invention provides a variable pitch grating recording structure optimization design method for optimizing the variable pitch grating recording structure, comprising: S1, determining the coordinates of the recording light source C, solving the recording light source C to the characteristic point P i Direction vector; S2, solve the feature point P i The corresponding incident light ray P in the aspherical wave recording arm is i Q i direction and optical path function difference I; S3, solve the characteristic point P i Corresponding to point Q on the auxiliary reflector i coordinates and calculate Q on the auxiliary reflector i The normal line at the point; S4, obtain the auxiliary reflector surface information by fitting method; S5, analyze the residual error of the auxiliary reflector after fitting, and when the discrete degree is greater than the set threshold, repeat the above steps S1-S4; when the discrete degree is less than the set threshold, output the design result. Compared with the traditional method, the present invention can realize the optimization design of the variable pitch grating recording structure more quickly and accurately.

Description

Technical Field

[0001] The invention relates to the technical field of optical design, and in particular to a method for optimizing the design of a variable-pitch grating recording structure. Background Art

[0002] A grating is an optical element with periodic microscopic lines distributed on the optical surface. It can achieve angular dispersion of light of different wavelengths in space and is widely used in spectrometers. A variable pitch grating is a special grating in which the grating line spacing varies with the spatial position of the grating surface. The variable spacing grating line distribution feature enables the grating to have specific aberration correction and beam focusing capabilities in addition to the dispersion capability, thus realizing the design of a high-resolution spectrometer with a single element. It is widely used in synchrotron radiation light sources, earth imaging spectral remote sensing, biomedical imaging and other fields. The current mainstream production method of variable pitch gratings is to obtain them through the interference of two non-plane waves and recording the interference fringes through photoresist. Figure 1 As shown, the commonly used recording structures include three types: using two spherical waves, interfering a spherical wave and a non-spherical wave, and interfering two non-spherical waves.

[0003] In terms of design optimization of variable pitch grating recording structures, the traditional method is to use the optical path function theory to establish an expansion model for the grating line distribution on the grating substrate surface, and optimize the recording parameters through a suitable optimization algorithm. However, the whole set of models is based on series expansion. The default of high-order terms in the series expansion leads to differences in the design results compared to the actual situation, and the grating line distribution error of the variable pitch grating made according to the design parameters is large. At the same time, since the grating line distribution expansion coefficient is relatively complex, the designer needs to have rich design experience and adjust the weight factors of each coefficient repeatedly during the optimization process, which makes the design process more complicated and inefficient. Therefore, an efficient and accurate design method for variable pitch grating recording structures is very important.

[0004] There are many related solutions at home and abroad for the design of variable pitch grating recording structures.

[0005] The journal article [Takeshi, Namioka, Masato, et al. Aspheric wave-front recording optics for holographic gratings [J]. Applied Optics, 1995.] presents a variable pitch grating design method with an auxiliary reflector. This method uses series expansion to obtain an expanded solution describing the grating line distribution, and optimizes the recording parameters to achieve a design that is closest to the target grating line distribution coefficient. However, the high-order expansion terms that are ignored in the design may have a serious impact on the grating design in some cases, making the grating line distribution generated by the designed recording structure inconsistent with the actual situation. In addition, this method requires designers to adjust the weights of each target back and forth, which makes the design difficult.

[0006] Invention patent CN201410521344.7 uses a similar method, also solving the record parameters through an expansion model, and also has the problem of low design accuracy caused by the neglect of high-order expansion terms. Summary of the invention

[0007] In view of the above problems, the purpose of the present invention is to propose a method for optimizing the design of variable-pitch grating recording structures, using ray tracing to achieve precise design without expansion errors, and there is no difference between the design result and the actual result; the tolerance design of various design goals is automatically brought into the design, and the whole method is more automated and intelligent. Compared with traditional methods, the present invention can achieve the optimized design of variable-pitch grating recording structures more quickly and accurately. The problem of multi-objective weight distribution is avoided by converting the design goals, and the inherent high-order expansion errors caused by the expansion method are avoided by using the ray tracing method.

[0008] To achieve the above object, the present invention adopts the following specific technical solutions:

[0009] The present invention provides a variable pitch grating recording structure optimization design method for optimizing the variable pitch grating recording structure, wherein the recording structure comprises: a recording light source C, a recording light source D, and an auxiliary reflector;

[0010] The coherent light beam emitted by the recording light source C directly irradiates the variable pitch grating substrate;

[0011] The coherent light beam emitted by the recording light source D is incident on the grating substrate after being reflected by the auxiliary reflector;

[0012] in,

[0013] Point O is the center point on the grating base, and point P is one of the characteristic points on the grating base;

[0014] Point O1 is the center point on the auxiliary reflector, and point Q is the reflection point on the auxiliary reflector;

[0015] CP is the optical path from light source C to point P;

[0016] DQP is the optical path of the coherent light beam emitted by the recording light source D from point Q to point P;

[0017] CO is the optical path from light source C to point O;

[0018] DO1O is the optical path of the coherent light beam emitted by the recording light source D passing through point O1 and intersecting point O;

[0019] The recording arm RC is used to record the distance from the light source C to the point O;

[0020] The recording arm RD is used to record the distance from the light source D to the point O1;

[0021] Record arm RQ as the distance from point O1 to point O;

[0022] Recording angle θ C is the angle between RC and the normal at the center of the grating base;

[0023] Recording angle θ D is the angle between RQ and the normal at the center of the grating substrate;

[0024] Recording angle θ Q is the angle between RD and the normal at the center of the auxiliary reflector;

[0025] It is characterized by comprising the following steps:

[0026] Preprocessing step S0: sampling feature points P on the grating base i , get each feature point P i The corresponding grating line function n i And the grating line density component n xi and n zi ;

[0027] The calculation process is:

[0028] Record a ray emitted by light source D that is reflected from point Q and intersects at point P. According to the optical path function theory, the grating line function n at point P is:

[0029]

[0030] in,

[0031] λ is the wavelength of recording light source C and recording light source D;

[0032] x p is the sagittal coordinate of point P;

[0033] z pis the meridian coordinate of point P;

[0034] n ij is the expansion coefficient of the grating base line distribution;

[0035] According to formula (1), the grating line function is obtained with respect to the sagittal coordinate x of point P: p and the meridian coordinate z p The partial derivative of the grating line density at point P is the sagittal component n x and the meridian component n z :

[0036]

[0037]

[0038] in,

[0039] α CP , β CP , γ CP Respectively represent the components of the direction cosines of CP in the X, Y, and Z directions;

[0040] α QP , β QP , γ QP Respectively represent the components of the direction cosines of QP in the X, Y, and Z directions;

[0041] x p ,y p , z p They represent the coordinates of point P in the three-dimensional rectangular coordinate system respectively;

[0042] δy p / δx p and δy p / δz p They represent the partial derivatives of the base surface at point P of the grating base respectively;

[0043] δn / δx p and δn / δz p They represent the partial derivatives of the optical path function with respect to the sagittal coordinate and the meridian coordinate of point P, i.e., the sagittal component n of the grating line density. x and the meridian component n z .

[0044] S1. Determine the coordinates of the recorded light source C and solve the distance from the recorded light source C to the feature point P. i The direction vector of

[0045] S2. Solve the characteristic point P according to formulas (1 to 3) i The corresponding incident light ray P in the aspherical wave recording arm is i Q iThe direction and optical path function difference I;

[0046] S3, according to the incident light P i Q i direction, record the coordinates of the light source D and the lengths of the recording arms RD and RQ, and solve for the characteristic point P i Corresponding to point Q on the auxiliary reflector i The coordinates of the auxiliary reflector are calculated according to the reflection law. i Normal at the point;

[0047] S4, according to the auxiliary reflector Q i Point coordinates and normal information, and auxiliary reflector surface information are obtained through fitting method;

[0048] S5. Analyze the residual error of the auxiliary reflector after fitting. When the discrete degree is greater than the set threshold, repeat the above steps S1-S4; when the discrete degree is less than or equal to the set threshold, output the design result.

[0049] Preferably, step S1 comprises:

[0050] According to the feature point P i The coordinates (x pi ,y pi ,z pi ) and record the coordinates of light source C (x c ,y c ,z c );

[0051] Corresponding to the feature point P i The direction vector at can be described as (x pi -x c ,y pi -y c ,z pi -z c );

[0052] Normalize the vector to get the feature point P i The direction vector of the incident light ray in the recording arm RC.

[0053] Preferably, the surface shape of the auxiliary reflector is a spherical surface, an ellipsoidal surface, a quadratic surface or a free-form surface.

[0054] Preferably, the optical path function difference I is:

[0055] I=DQ i P i -DO1O.

[0056] Preferably, the threshold is set to the upper limit of the number of iterations of the genetic algorithm. When the threshold is set to the upper limit of the number of iterations, the threshold is set to 20 times;

[0057] When the number of iterations reaches the set upper limit, the iteration process ends and the design results are output.

[0058] Preferably, the threshold value is set to be the root mean square value of the auxiliary reflector surface type fitting residual error. When the threshold value is set to be the root mean square value of the auxiliary reflector surface type fitting residual error, the threshold value is set to be less than one recording wavelength.

[0059] When the degree of discreteness is less than the set threshold, the iteration process ends and the design results are output.

[0060] Preferably, the threshold is set as a manual input control and is manually adjusted according to different requirements.

[0061] Compared with the prior art, the present invention has the following advantages:

[0062] (1) The present invention uses ray tracing to reconstruct the variable pitch grating recording structure, avoiding the errors caused by the high-order expansion terms inherent in the expansion method. Therefore, the solved recording structure can produce a more accurate variable pitch grating line distribution.

[0063] (2) The present invention uses a genetic algorithm to optimize the design of the entire structure, achieving global optimization within a set range, and the design result is more accurate.

[0064] (3) The present invention is more intelligent and does not require designers to have rich design experience to carry out the design of variable pitch grating recording structure.

[0065] (4) The present invention can quickly switch between different types of variable pitch grating recording structure designs by selecting different surface fitting targets, and no longer needs to establish corresponding expansion models for different recording structures and then perform optimization solutions separately. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 These are schematic diagrams of three typical variable pitch grating recording structures.

[0067] Figure 2 It is a schematic diagram of the recording structure of spherical waves versus aspherical waves provided according to an embodiment of the present invention.

[0068] Figure 3 It is a flow chart of a method for optimizing the design of a variable pitch grating recording structure provided according to an embodiment of the present invention.

[0069] Figure 4 It is a schematic diagram of the design process of the variable pitch grating recording structure optimization design method provided according to an embodiment of the present invention.

[0070] Figure 5 It is an algorithm flow chart of a variable pitch grating recording structure optimization design method provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0071] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same modules are represented by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, the detailed description thereof will not be repeated.

[0072] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0073] Figure 2 A schematic diagram of a recording structure of a spherical wave versus an aspherical wave provided in accordance with an embodiment of the present invention is shown.

[0074] like Figure 2 As shown, the spherical wave to aspherical wave recording structure provided by the embodiment of the present invention includes two coherent light sources (recording light source C and recording light source D), an auxiliary reflector with a specific surface shape, and a grating substrate coated with a photoresist film layer.

[0075] The light beam emitted by the recording light source C is directly incident on the grating substrate; the light beam emitted by the recording light source D is incident on the grating substrate after being reflected by the auxiliary reflector.

[0076] set up:

[0077] Point O is the center point on the grating base, and point P is one of the characteristic points on the grating base;

[0078] Point O1 is the center point on the auxiliary reflector, and point Q is a point on the auxiliary reflector;

[0079] CP is the optical path from light source C to point P;

[0080] DQP is the optical path of the light source D reflected from point Q on the auxiliary reflector to point P;

[0081] CO is the optical path from the recording light source C to the center of the grating substrate, point O;

[0082] DO1O is the optical path emitted by the recording light source D, passing through the center point O1 on the auxiliary reflector and finally intersecting with the center point O of the grating substrate.

[0083] The recording arm RC is the distance from the recording light source C to the center point O of the grating substrate;

[0084] The recording arm RD is the distance from the recording light source D to the center point O1 of the auxiliary reflector;

[0085] The recording arm RQ is the distance from the center point O1 of the auxiliary reflector to the center point O of the grating substrate.

[0086] Recording angle θ C is the angle between RC and the normal at the center of the grating base;

[0087] Recording angle θ D is the angle between RQ and the normal at the center of the grating substrate;

[0088] Recording angle θ Q It is the angle between RD and the normal at the center of the auxiliary reflector.

[0089] Figure 3 A schematic flow chart of a method for optimizing the design of a variable pitch grating recording structure provided according to an embodiment of the present invention is shown.

[0090] Figure 4 A schematic diagram of the design process of a variable pitch grating recording structure optimization design method provided in accordance with an embodiment of the present invention is shown.

[0091] like Figure 3 and Figure 4 As shown, the variable pitch grating recording structure optimization design method provided by the embodiment of the present invention comprises the following steps:

[0092] Preprocessing step S0: sampling a series of feature points P on the grating base i , obtain each feature point P according to the target grating line distribution i The corresponding grating line function n i And the grating line density component n xi and n zi .

[0093] The solution process is:

[0094] A ray of light emitted by the recording light source D is reflected by a point Q on the curved reflector and intersects with a point P on the grating substrate. According to the optical path function theory, the grating line function n of point P can be expressed as:

[0095]

[0096] in,

[0097] λ is the wavelength of recording light source C and recording light source D;

[0098] x p is the sagittal coordinate of point P;

[0099] z p is the meridian coordinate of point P;

[0100] n ij is the expansion coefficient of the variable pitch grating line distribution.

[0101] Usually, due to the complexity of the optical path function, it is represented as the sagittal coordinate x of point P p and the meridian coordinate z p The fourth-order polynomial form of each term has a coefficient n ij They respectively represent the expansion coefficients of the variable pitch grating line distribution.

[0102] The design of variable pitch grating recording structure is based on the coefficient n ij The design goal is to solve the appropriate recording parameters, including the recording arm length, recording angle and the surface shape of the auxiliary reflector.

[0103] At the same time, by further deducing equation (1), we can obtain the grating line function of point P with respect to the sagittal coordinate x of point P: p and the meridian coordinate z p The partial derivative of the grating line density at point P is the sagittal component n x and the meridian component n z :

[0104]

[0105]

[0106] in,

[0107] α CP , β CP , γ CP Respectively represent the components of the direction cosine of the light CP in the X, Y, and Z directions;

[0108] α QP , β QP , γ QP Respectively represent the components of the direction cosines of the light ray QP in the X, Y, and Z directions;

[0109] x p ,y p , z p They represent the coordinates of point P in the three-dimensional rectangular coordinate system respectively;

[0110] δy p / δx p and δy p / δz p They represent the partial derivatives of the base surface at point P of the grating base respectively;

[0111] δn / δx p and δn / δz p They represent the partial derivatives of the optical path function with respect to the sagittal coordinate and the meridian coordinate of point P, i.e., the sagittal component n of the grating line density. x and the meridian component nz The density component is used to sample feature points P on a known raster basis. i When recording the incident light direction in arm C, solve the incident light direction of the feature point in arm D. That is, solve α in formulas (2) and (3) when other quantities are known. QP , β QP , γ QP .

[0112] It can be seen that for this variable pitch grating recording structure, there are two ways to describe the grating lines at any point on the grating. One is the grating line function described by the optical path function, and the other is the meridian component and sagittal component of the grating line density defined by two incident light rays and the surface partial derivatives.

[0113] S1. Determine the coordinates of the recorded light source C and solve the coordinates of the recorded light source C to each feature point P i The direction vector of

[0114] The recording arm length RC and the tilt angle θ of the recording arm C C Preset, record the X, Y, Z coordinates of light source C as (0, RC*cos(θ C ), RC*sin(θ C )).

[0115] According to the sampling obtained grating substrate surface feature point P i The coordinates (x pi ,y pi ,z pi ) and record the coordinates of light source C (x c ,y c ,z c );

[0116] Corresponding to the feature point P i The direction vector at can be described as (x pi -x c ,y pi -y c ,z pi -z c );

[0117] By normalizing the vector, the direction vector of the incident light at the required feature point in the recording arm C can be obtained.

[0118] S2. Solve each feature point P according to formulas (1 to 3) i The corresponding incident light ray P in the aspherical wave recording arm is i Q i The direction and optical path function difference I.

[0119] I=DQ i Pi -DO1O

[0120] The aspherical wave recording arm is composed of recording parameters RD, RQ, θ D and θ Q Determine, that is, calculate according to the geometric relationship Figure 2 The coordinates of the light source point D and the auxiliary reflector center point O1 are recorded in .

[0121] S3, according to the obtained P i Q i direction, record the coordinates of the light source D and the lengths of the recording arms RD and RQ, and solve for each feature point P i Corresponding to point Q on the auxiliary reflector i The coordinates of the auxiliary reflector are calculated according to the reflection law. i Normal at the point;

[0122] S4, according to the auxiliary reflector Q i Point coordinates and normal information are used to obtain auxiliary reflector surface information through fitting method.

[0123] The coordinates and normal information of the feature points on the auxiliary reflector directly obtained are the global coordinate system (i.e. Figure 2 To solve the surface shape of the auxiliary reflector, it is necessary to first transform the information of the global coordinate system according to the coordinate system transformation rules, and then use the least squares method to fit and obtain the surface description.

[0124] The surface shape of the auxiliary reflector can be a spherical surface, an ellipsoidal surface, a quadratic surface, a free-form surface, etc.

[0125] Due to the existence of the auxiliary reflector surface fitting participation error, the variable pitch grating line distribution corresponding to the recording structure obtained by the above design results is still different from the design target. Therefore, further design of the recording arm length and recording angle is needed to obtain the best surface characterization.

[0126] S5. Analyze the residual error of the auxiliary reflector after fitting. When the discrete degree is greater than the set threshold, repeat the above steps S1-S4; when the discrete degree is less than or equal to the set threshold, output the design result.

[0127] Figure 5 The flowchart of the algorithm of the variable pitch grating recording structure optimization design method provided by the embodiment of the present invention is shown.

[0128] Setting the threshold includes two aspects: one is the upper limit of the number of iterations of the genetic algorithm, and the other is the root mean square value of the residual error of the auxiliary reflector surface fitting. When the number of iterations reaches the set upper limit or a set of solutions corresponding to the surface fitting error is obtained, the iteration process is terminated and the design result is output.

[0129] Set the threshold value for manual input control and can be manually adjusted according to different needs; the current given threshold value is a maximum number of iterations of 20 times, and the root mean square of the surface fitting participation error is less than one recording wavelength.

[0130] like Figure 5 As shown, the genetic algorithm is used to complete the above global optimization design. The design parameters include three recording arm lengths RC, RD, and RQ and two recording angles θ C and θ Q , where the recorded angle θ D and record angle θ C And the equivalent line density n0 at the center of the grating substrate is uniquely determined:

[0131]

[0132] Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. A person of ordinary skill in the art may change, modify, replace and modify the above embodiments within the scope of the present invention. The above specific implementation methods of the present invention do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made according to the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A variable pitch grating recording structure optimization design method for optimizing the variable pitch grating recording structure, the recording structure comprising: Recording light source C, recording light source D, auxiliary reflector; The coherent light beam emitted by the recording light source C directly irradiates the variable pitch grating substrate; The coherent light beam emitted by the recording light source D is incident on the grating substrate after being reflected by the auxiliary reflector; in, Point O is the center point on the grating substrate, and point P is one of the characteristic points on the grating substrate; Point O1 is the center point on the auxiliary reflector, and point Q is the reflection point on the auxiliary reflector; CP is the optical path from the recording light source C to the point P; DQP is the optical path of the coherent light beam emitted by the recording light source D from the point Q to the point P; CO is the optical path from the recording light source C to the point O; DO1O is the optical path of the coherent light beam emitted by the recording light source D passing through the point O1 and intersecting the point O; The recording arm RC is the distance from the recording light source C to the point O; The recording arm RD is the distance from the recording light source D to the point O1; The recording arm RQ is the distance from the point O1 to the point O; Recording angle θ C is the angle between the RC and the normal at the center of the grating base; Recording angle θ D is the angle between the RQ and the normal at the center of the grating substrate; Recording angle θ Q is the angle between the RD and the normal at the center of the auxiliary reflector; It is characterized by comprising the following steps: Preprocessing step S0: sampling feature points P on the grating base i , obtain each of the feature points P i The corresponding grating line function n i And the grating line density component n xi and n zi ; The calculation process is: A ray emitted by the recording light source D is reflected by the point Q and intersects the point P. According to the optical path function theory, the grating line function n of the point P is: (1) in, λ is the wavelength of the recording light source C and the recording light source D; x p is the sagittal coordinate of the point P; z p is the meridian coordinate of the point P; n ij is the expansion coefficient of the grating line distribution of the grating substrate; According to the formula (1), the grating line function with respect to the sagittal coordinate x of point P is obtained: p and the meridian coordinate z p The partial derivative of the grating line density at point P is the sagittal component n x and the meridian component n z : (2) (3) in, α CP , β CP , γ CP Respectively represent the components of the direction cosines of CP in the X, Y, and Z directions; α QP , β QP , γ QP Respectively represent the components of the direction cosines of QP in the X, Y, and Z directions; x p ,y p , z p They represent the coordinates of point P in the three-dimensional rectangular coordinate system respectively; δy p / δx p and δy p / δz p They represent the partial derivatives of the base surface at point P of the grating base respectively; δn / δx p and δn / δz p They represent the partial derivatives of the optical path function with respect to the sagittal coordinates and the meridian coordinates of point P, i.e., the sagittal component n of the grating line density. x and the meridian component n z ; S1. Determine the coordinates of the recording light source C and solve the distance from the recording light source C to the feature point P. i The direction vector of the grating substrate surface is obtained according to the sampling feature point P i The coordinates (x pi ,y pi ,z pi ) and record the coordinates of light source C (x c ,y c ,z c ); corresponding to the feature point P i The direction vector at can be described as (x pi -x c ,y pi -y c ,z pi -z c ); The vector is normalized to obtain the incident light direction vector of the required feature point in the recording arm C; S2. Solve the characteristic point P according to the formula (1-3) i The corresponding incident light ray P in the aspherical wave recording arm is i Q i The direction and optical path function difference I; S3, according to the incident light P i Q i direction, the coordinates of the recording light source D and the lengths of the recording arms RD and RQ, and solve the feature point P i Corresponding to point Q on the auxiliary reflector i The coordinates of the auxiliary reflector are calculated according to the reflection law. i Normal at the point; S4, according to the auxiliary reflector Q i Point coordinates and normal information, and obtaining the auxiliary reflector surface information by a fitting method; S5, analyzing the residual error of the auxiliary reflector after fitting, and when the discrete degree is greater than the set threshold, repeating the above steps S1-S4; when the discrete degree is less than or equal to the set threshold, outputting the design result.

2. The variable pitch grating recording structure optimization design method according to claim 1, wherein step S1 comprises: According to the feature point P i The coordinates (x pi ,y pi ,z pi ) and the coordinates (x c ,y c ,z c ); Corresponding to the feature point P i The direction vector at can be described as (x pi -x c ,y pi -y c ,z pi -z c ); Normalize the vector to obtain the feature point P i The direction vector of the incident light ray in the recording arm RC.

3. According to the variable pitch grating recording structure optimization design method of claim 2, the surface shape of the auxiliary reflector is a sphere, an ellipsoid, a quadratic surface or a free-form surface.

4. According to the variable pitch grating recording structure optimization design method of claim 3, the optical path function difference I is: I= DQ i P i -DO1O。 5. The variable pitch grating recording structure optimization design method according to claim 4, wherein the set threshold is the upper limit of the number of iterations of the genetic algorithm, and when the set threshold is the upper limit of the number of iterations, the set threshold is 20 times; When the number of iterations reaches the set upper limit, the iteration process ends and the design results are output.

6. According to the variable pitch grating recording structure optimization design method of claim 4, the set threshold is the root mean square value of the auxiliary reflector surface fitting residual error, when the set threshold is the root mean square value of the auxiliary reflector surface fitting residual error, the set threshold is less than one recording wavelength; When the discrete degree is less than the set threshold, the iteration process is terminated and the design result is output.

7. According to the variable pitch grating recording structure optimization design method of claim 5 or 6, the set threshold is manually input controlled and manually adjusted according to different needs.

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