A polarization aberration compensation method based on DMD vector diffraction

Abstract

A polarization aberration compensation method based on DMD vector diffraction. The invention belongs to the technical field of optical information and polarization aberration processing, and specifically relates to the technical field of polarization aberration compensation based on DMD vector diffraction. The method comprises the following steps: designing a long-wave infrared polarization optical system containing DMD; constructing a polarization aberration transmission model of DMD under vector diffraction in the long-wave infrared polarization optical system, and simulating and analyzing the long-wave infrared polarization optical system containing DMD based on the polarization aberration transmission model, and compensating the simulation results; deriving the best diffraction order under the condition that the polarization aberration and polarization degree of DMD are minimized; determining the best incident angle of DMD; inputting the best diffraction order under the condition that the polarization aberration and polarization degree of DMD are minimized and the best incident angle of DMD into the design software for designing the long-wave infrared polarization optical system containing DMD; and compensating the polarization aberration of the optical system by tilting the projection objective lens group and the lens coating.

Description

Technical Field

[0001] The invention belongs to the technical field of optical information and polarization aberration processing, and in particular relates to the technical field of polarization aberration compensation based on DMD vector diffraction. Background Art

[0002] The DMD digital micromirror array is a square micromirror array manufactured on a semiconductor silicon wafer. The rotation of the micromirror is controlled by electrostatic drive. As a reflective spatial light modulator, it has the characteristics of high resolution and fast response, and is widely used in the field of imaging, such as snapshot spectral imaging, coded super-resolution imaging, etc. By placing the DMD on the primary image plane of the optical system, the intermediate image can be coded and modulated to achieve high-resolution image reconstruction. However, in the long-wave infrared optical system, the vector diffraction effect of the DMD will change the incident angle of the light, seriously affecting the amount of light entering the projection objective and the imaging quality. In addition, due to the working principle of the DMD, when the micromirror is turned on, incident light at different angles will introduce large polarization aberrations on the DMD, affecting the imaging accuracy. Therefore, it is crucial to find the best incident angle and diffraction order of diffraction, and to study and compensate for the polarization aberration of the optical system containing the DMD.

[0003] Previous studies have not explored the relationship between diffraction and polarization aberration, and the DMD polarization aberration model constructed has defects. In the past design of infrared polarization imaging optical systems containing DMD, the changes in the incident and reflection angles of light on the DMD surface due to the vector diffraction characteristics and the resulting changes in polarization aberration have not been considered. In the relevant research process, there is a lack of analysis on the impact of DMD diffraction characteristics on polarization aberration. Summary of the invention

[0004] In order to solve the problem mentioned above that in the past designs of infrared polarization imaging optical systems containing DMDs, the changes in the incident and reflection angles of light on the DMD surface due to the vector diffraction characteristics and the resulting changes in polarization aberration have not been taken into consideration, and at least one of the technical issues of analyzing the influence of DMD diffraction characteristics on polarization aberration has been missing in the relevant research process, the present invention provides a polarization aberration compensation method based on DMD vector diffraction.

[0005] The method is based on a long-wave infrared polarization optical system containing a DMD, the optical system comprising a telescope objective lens group, a DMD, a projection objective lens group and a polarization detector, the incident light reaches the DMD through the telescope objective lens group, enters the projection objective lens group after being reflected and modulated by the DMD, and forms an image on the polarization detector after passing through the projection objective lens group, the method comprising the following steps:

[0006] S1. Design of long-wave infrared polarization optical system with DMD;

[0007] S2, constructing a polarization aberration transmission model of DMD under vector diffraction in a long-wave infrared polarization optical system, and performing simulation analysis on the long-wave infrared polarization optical system containing DMD based on the polarization aberration transmission model, and compensating the simulation results;

[0008] S3, deriving the optimal diffraction order when the DMD polarization aberration and polarization degree are minimized;

[0009] S4, determining the optimal incident angle of the DMD;

[0010] S5, inputting the optimal diffraction order with the DMD polarization aberration and polarization degree minimized and the optimal incident angle of the DMD into the design software for the long-wave infrared polarization optical system containing the DMD;

[0011] S6. Compensate for the polarization aberration of the optical system by tilting the projection objective lens group and the lens coating.

[0012] Furthermore, when designing a long-wave infrared polarization optical system containing DMD, simulation software is used for design. First, the overall indicators of the long-wave infrared polarization optical system containing DMD are determined, and the initial structure including the telescope objective lens group, DMD, projection objective lens group and polarization detector is determined; the modeling method of DMD selects US_MEMS.dll in the sequence mode; the constraint condition that the landing position of the full-field light on the primary and secondary image planes is accurate to within 1 / 2 pixel is written into the optimization evaluation function, and the image plane of the telescope objective lens in the long-wave infrared polarization optical system containing DMD is set to DMD for optimization; the optical path of the projection objective lens group is inverted for design, so that the exit angle of the light reflected from the DMD becomes the incident angle, and it is judged whether this incident angle is consistent with the diffraction angle obtained by simulation calculation, until the design of the projection objective lens group is completed; finally, the telescope objective lens group and the projection objective lens group after setting the DMD incident azimuth and altitude angle are spliced ​​together to meet the pupil connection principle, thereby realizing the design of the entire long-wave infrared polarization optical system containing DMD.

[0013] Further, the polarization aberration transmission model is:

[0014] ;in, represents the two-way attenuation of the system, represents the maximum intensity transmittance of the system, represents the minimum intensity transmittance of the system, represents the s-light amplitude reflection coefficient of the DMD, represents the p-light amplitude reflection coefficient of the DMD.

[0015] Further, the step S3 is specifically as follows:

[0016] S31. By: DMD is equivalent to a two-dimensional blazed grating, where and are the incident and outgoing beam altitude angles, and are the incident and outgoing beam azimuths, is the grating constant, is the diffraction order, ± indicates the interface of the diffracted light on the same / different side of the normal line of the micromirror;

[0017] S32, calculating the diffraction order in which the diffraction efficiency of the diffracted light in the two-dimensional blazed grating exists and is greater than 0, as the retained diffraction order;

[0018] S33, performing polarization aberration and polarization degree simulation on the DMD under the retained diffraction order, and selecting the diffraction order with the smallest average polarization degree among the two retained diffraction orders with the smallest polarization aberration as the optimal diffraction order of the DMD.

[0019] Furthermore, the screening condition for the DMD optimal incident angle is: the determined optimal incident angle needs to ensure that the spatial azimuth angle of the diffracted beam after DMD modulation is consistent with the spatial azimuth angle of the incident beam and the altitude angle of the diffracted beam after DMD modulation is less than the beam aperture angle of the projection objective lens group in the long-wave infrared polarization optical system.

[0020] Furthermore, the method of compensating the polarization aberration of the optical system by tilting the projection objective lens group and the lens coating is specifically as follows: continue to adjust in the simulation software, tilt the projection objective lens group as a whole along the X-axis until it is orthogonal to the polarization aberration direction of the DMD surface, and coat the surface of each lens of the system with an anti-reflection film, wherein the thickness of the anti-reflection film is one quarter of the working wavelength of the system.

[0021] The beneficial effects of the method of the present invention are:

[0022] In view of the difference between the DMD polarization aberration tracing process under vector diffraction conditions and that under scalar diffraction conditions, a polarization aberration analysis method based on the vector diffraction-polarized light Jones vector theory is proposed, and a polarization aberration analysis model under DMD diffraction conditions is constructed. A physical model of DMD diffraction efficiency containing parameters such as DMD incident beam angle boundary conditions, polarization aberration and polarization degree is established, and the optimal diffraction order and incident height angle of DMD and their corresponding diffraction efficiency can be calculated, thereby guiding the design of polarization optical systems containing DMDs and facilitating the calibration and compensation of system polarization aberrations.

[0023] A polarization aberration compensation method by tilting the projection objective and lens coating is proposed to compensate for the polarization aberration of the long-wave infrared polarization optical system caused by the diffraction phenomenon of the DMD, thereby improving the polarization measurement accuracy. This method can be used not only in long-wave infrared optical systems containing DMD, but also in systems in near-infrared, visible light and other bands. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a structural diagram of a long-wave infrared polarization optical system containing a DMD;

[0025] Figure 2 It is a schematic diagram of the relationship between the reflection azimuth angle and the diffraction altitude angle of each diffraction order of DMD at a beam incident azimuth angle of 0° and an incident altitude angle of 24°~50° obtained by the grating equation of the DMD two-dimensional grating model;

[0026] Figure 3 The diagram is a schematic diagram of the relationship between the reflection azimuth angle and the diffraction height angle of each diffraction order of the DMD at a beam incident azimuth angle of 45° and an incident height angle of 24° to 50°, obtained by the grating equation of the DMD two-dimensional grating model;

[0027] Figure 4 The diagram is a diagram showing the relationship between the reflection azimuth angle and diffraction height angle of each diffraction order of the DMD at a beam incident azimuth angle of 90° and an incident height angle of 24° to 50°, obtained through the grating equation of the DMD two-dimensional grating model;

[0028] Figure 5 is the diffraction efficiency of TE and TM polarized light at the (0, -1) order With the incident altitude angle The relationship curve of

[0029] Figure 6 (a) shows the Dop distribution when the bidirectional attenuation on the DMD surface is 0.04 at the (-1,0) level, and (b) shows the Dop distribution when the bidirectional attenuation on the DMD surface is 0.04 at the (0,-1) level.

[0030] Figure 7 (a) shows the Dop distribution when the bidirectional attenuation on the DMD surface is 0.53 at the (-1,0) level, and (b) shows the Dop distribution when the bidirectional attenuation on the DMD surface is 0.53 at the (0,-1) level.

[0031] Figure 8 Represents the two-way attenuation distribution diagram of the system before compensation;

[0032] Fig. 9 Represents the two-way attenuation distribution diagram of the compensated system. DETAILED DESCRIPTION

[0033] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0034] This embodiment provides a polarization aberration compensation method based on DMD vector diffraction. The method is based on a long-wave infrared polarization optical system containing DMD. The structure of the optical system is shown in FIG. Figure 1 As shown, it includes a telephoto objective lens group, a DMD, a projection objective lens group and a polarization detector. The incident light reaches the DMD through the telephoto objective lens group, enters the projection objective lens group after being reflected and modulated by the DMD, and forms an image on the polarization detector after passing through the projection objective lens group. The method includes the following steps:

[0035] S1. Design of long-wave infrared polarization optical system with DMD;

[0036] S2, constructing a polarization aberration transmission model of DMD under vector diffraction in a long-wave infrared polarization optical system, and performing simulation analysis on the long-wave infrared polarization optical system containing DMD based on the polarization aberration transmission model, and compensating the simulation results;

[0037] S3, deriving the optimal diffraction order when the DMD polarization aberration and polarization degree are minimized;

[0038] S4, determining the optimal incident angle of the DMD;

[0039] S5, inputting the optimal diffraction order with the DMD polarization aberration and polarization degree minimized and the optimal incident angle of the DMD into the design software for the long-wave infrared polarization optical system containing the DMD;

[0040] S6. Compensate for the polarization aberration of the optical system by tilting the projection objective lens group and the lens coating.

[0041] When designing a long-wave infrared polarization optical system containing DMD, simulation software is used for design. First, the overall system indicators are determined, the focal length and aperture of the optical system are calculated, and a suitable initial structure is found. Since the reflection of s-polarized light reflected on the DMD surface is higher than that of p-polarized light, the direction of two-way attenuation is along the vibration direction of s light, and the transmission of p-polarized light on the transmission surface is higher than that of s-polarized light, and the direction of two-way attenuation is along the vibration direction of p light, the polarization aberration in the system can be compensated by tilting the DMD reflection surface and the transmission mirror at a certain angle. The modeling method of DMD selects US_MEMS.dll in the sequence mode, because the primary image on the DMD should be accurately mapped to the detector target surface, it must have good imaging quality, and optical distortion needs to be strictly controlled. Therefore, the constraint condition that the landing position of the full field of view light on the primary and secondary image planes is accurate to within 1 / 2 pixel should be written into the optimization evaluation function, and the image plane of the telescope objective in the DMD imaging optical system is set to DMD for optimization.

[0042] Since the DMD diffraction order is -1, in the optical design software, the light can only be reflected from the 0th order according to the law of reflection. Therefore, the optical path of the projection objective lens group in the optical system is inverted for design, so that the exit angle of the light reflected from the DMD becomes the incident angle, and it is judged whether this incident angle is consistent with the diffraction angle obtained by simulation calculation until the design of the projection objective lens group is completed. Finally, the telephoto objective lens group after setting the DMD incident azimuth and altitude angle is spliced ​​with the projection objective lens group to meet the pupil connection principle, thereby realizing the design of the entire long-wave infrared polarization optical system containing DMD.

[0043] After the optical system design is completed, the entire optical system is simulated and analyzed based on the polarization aberration transmission model constructed in step S2, and then compensation is performed based on the simulation results to ensure that the performance of the optical system can meet the expected standards and requirements.

[0044] DMD in each diffraction order The diffraction wave vector for:

[0045]

[0046] In the formula, is the diffraction height angle, is the diffraction azimuth.

[0047] According to the Fresnel formula, the amplitude reflection coefficient of the DMD s-light and p-light can be obtained by substituting the diffraction height angle into the following formula: , .

[0048] ;

[0049] ;

[0050] Three-dimensional Jones matrix on the DMD surface .

[0051] A polarization aberration transmission model of DMD under vector diffraction in a long-wave infrared polarization optical system is constructed, and the polarization aberration transmission model is:

[0052] ;in, represents the two-way attenuation of the system, represents the maximum intensity transmittance of the system, represents the minimum intensity transmittance of the system, represents the s-light amplitude reflection coefficient of the DMD, represents the p-light amplitude reflection coefficient of the DMD.

[0053] The step S3 is specifically as follows:

[0054] S31. By: DMD is equivalent to a two-dimensional blazed grating, where and are the incident and outgoing beam altitude angles, and are the incident and outgoing beam azimuths, is the grating constant, is the diffraction order, ± indicates the interface of the diffracted light on the same / different side of the normal line of the micromirror;

[0055] S32, calculating the diffraction order in which the diffraction efficiency of the diffracted light in the two-dimensional blazed grating exists and is greater than 0, as the retained diffraction order;

[0056] S33, performing polarization aberration and polarization degree simulation on the DMD under the retained diffraction order, and selecting the diffraction order with the smallest average polarization degree among the two retained diffraction orders with the smallest polarization aberration as the optimal diffraction order of the DMD.

[0057] Step S3 is explained by taking a specific example: the wavelength of the light wave of the system is 8-12 μm, the DMD pixel selected is 13.68 μm, the deflection angle in the switching state is ±12°, and the grating blaze angle is It is ±12°. From step S31, it can be concluded that the diffraction efficiency of the diffracted light exists and is greater than 0 in the main orders (0, 0), (0, -1), (-1, 0) and (-1, -1), and the other diffraction orders do not exist or the diffraction efficiency is close to 0. Take 10 μm wavelength as the central wavelength of the system, Figure 2 It is a schematic diagram of the relationship between the reflection azimuth angle and the diffraction altitude angle of each diffraction order of DMD at a beam incident azimuth angle of 0° and an incident altitude angle of 24°~50° obtained by the grating equation of the DMD two-dimensional grating model; Figure 3 The diagram is a schematic diagram of the relationship between the reflection azimuth angle and the diffraction height angle of each diffraction order of the DMD at a beam incident azimuth angle of 45° and an incident height angle of 24° to 50°, obtained by the grating equation of the DMD two-dimensional grating model; Figure 4 This is a schematic diagram of the relationship between the reflection azimuth angle and diffraction altitude angle of each diffraction order of the DMD at a beam incident azimuth angle of 90° and an incident altitude angle of 24°~50°, which is obtained by the grating equation of the DMD two-dimensional grating model.

[0058] When determining the optimal incident angle of DMD, the screening conditions for the optimal incident angle of DMD are: limited by the optical-mechanical structure of the long-wave infrared polarization optical system containing DMD, when the DMD micro-lens is in the on (off) state, the spatial azimuth angle of the diffracted beam modulated by DMD should be consistent with the spatial azimuth angle of the incident beam; the height angle of the diffracted beam modulated by DMD should be smaller than the beam aperture angle of the projection objective lens group . is the F number of the projection lens group. When the F number of the projection lens group is 1.8, the absolute value of the elevation angle of the outgoing light beam should be less than 15.5° to avoid the entry of stray light and ensure the normal operation of the DMD micro-lens.

[0059] The relationship between the polarization degree (Dop) of the outgoing light and the polarization aberration of the DMD is:

[0060] ;

[0061] In the formula, is the linear polarization degree of the incident light, is the polarization angle of the incident light, is the bidirectional attenuation of DMD, is the bidirectional attenuation direction of DMD.

[0062] Combined with the above boundary conditions, the polarization aberration and polarization degree on the DMD surface are comprehensively considered to finally determine the incident angle and the exit angle of the light on the DMD surface.

[0063] DMD diffraction efficiency With the incident altitude The relationship diagram of the changes is as follows Figure 5 shown.

[0064] From the screening conditions of the optimal incident angle of the DMD, it can be concluded that the light of the (0, 0) and (-1, -1) orders cannot enter the projection system, and only the (-1, 0) and (0, -1) orders can be selected. When the polarization aberration on the DMD surface changes, the polarization degree will also change. Therefore, the polarization aberration size and polarization degree of the DMD under these two orders are simulated to determine the optimal diffraction order of the DMD.

[0065] Polarization aberration comparison:

[0066] Through the polarization aberration transmission model in step 2, it is obtained that the bidirectional attenuation of the DMD at the (-1, 0) level is the same as the bidirectional attenuation of the DMD at the (0, -1) level, which is: .

[0067] Dop comparison:

[0068] When the incident light has unit intensity, the linear polarization degree , polarization angle When incident, the polarization degree is obtained from the maximum and minimum values ​​of the bidirectional attenuation of the DMD as follows: Figure 6 and Figure 7 As shown, Figure 6 (a) shows the Dop distribution when the bidirectional attenuation on the DMD surface is 0.04 at the (-1,0) level, and (b) shows the Dop distribution when the bidirectional attenuation on the DMD surface is 0.04 at the (0,-1) level. Figure 7(a) in the figure shows the Dop distribution when the bidirectional attenuation on the DMD surface is 0.53 at the (-1,0) order, and (b) shows the Dop distribution when the bidirectional attenuation on the DMD surface is 0.53 at the (0,-1) order.

[0069] The polarization degree has the same extreme value but different average values ​​in two different diffraction orders. Table 1 compares the average values ​​of Dop of (-1, 0) and (0, -1) orders.

[0070] Table 1:

[0071]

[0072] It can be seen from the table that the Dop average value of the (0, -1) order is 0.7% lower than that of the (-1, 0) order, so the (0, -1) order is finally determined as the best diffraction order of DMD.

[0073] In order to make the light have a higher light energy utilization rate and reduce the overall volume of the system, the light beam should be emitted along the center of the optical axis of the projection system as much as possible. Therefore, among the incident height angles of 44~50°, an incident angle with a diffraction height angle closer to 0° is selected as the system design condition.

[0074] In the calculation of grating diffraction efficiency using rigorous coupled wave theory, the number of layers and the number of Fourier modes are important factors affecting the calculation accuracy and efficiency. Although increasing these values ​​can improve the accuracy of the calculation, it will also increase the complexity and time of the calculation. In order to balance the above relationship, the DMD two-dimensional blazed grating is divided into 100 layers, the number of Fourier modes is set to 12, and the (0, -1) order obtained by software simulation is used. , The relationship between the diffraction efficiency and the incident height angle of TE polarized light with the electric field vector perpendicular to the grating lines and TM polarized light with the electric field vector parallel to the grating lines is as follows: Figure 5 As shown,

[0075] It can be seen that when the (0, -1) light diffraction order is selected, the incident height angle of the DMD is The diffraction height angle is 47° The angle is 0°, which meets the condition that the projection system is perpendicular to the optical axis and is used as the design parameter of the subsequent optical system. The diffraction efficiencies of TE and TM polarized light are 21.67% and 58.47% respectively.

[0076] There is a certain relationship between polarization aberration and field pupil, and the larger the incident angle of light, the larger the polarization aberration. The polarization aberration of the optical system is the smallest at the center field of view, and a larger polarization aberration will be generated at the edge field of view. Therefore, according to the polarization aberration modeling formula in step S2, the three-dimensional polarization ray tracing of the optical design software is used to simulate and analyze the polarization aberration of the entire system and the DMD surface under the normalized (0, 1) edge field of view. The two-way attenuation at the exit pupil is as follows: Figure 8 As shown, Figure 8 Represents the two-way attenuation of the system before compensation.

[0077] The length of the short line in the figure represents the bidirectional attenuation value, and the direction of the short line represents the maximum transmission axis in the bidirectional attenuation. The overall polarization aberration of the system is large, so compensation is required to reduce the impact on imaging resolution.

[0078] The polarization aberration distribution of the DMD surface is symmetrical along the Y axis. In order to compensate for the polarization aberration of the DMD surface, the maximum transmission axis of the projection objective lens group should be orthogonal to the maximum transmission axis of the DMD polarization aberration, that is, the entire projection objective lens group should be tilted along the X axis until it is orthogonal to the polarization aberration direction of the DMD surface. In addition, an AR (anti-reflection) film is coated on the surface of each lens of the system with a thickness of one-quarter of the system's operating wavelength to reduce optical surface reflection, increase transmittance and reduce the loss of reflected light, thereby improving the performance of the optical system. The two-way attenuation distribution of the compensated system is shown in the figure below: Fig. 9 shown.

[0079] By comparing the polarization aberration of the system, it can be seen that Figure 8 The maximum value of the two-way attenuation is 0.1059. Fig. 9 The maximum value of the two-way attenuation is 8.7842×10 -3 Therefore, after the system is tilted and the lens coating is compensated, the two-way attenuation is reduced to the original The polarization aberration compensation effect is obvious, and this method can improve the polarization aberration caused by DMD diffraction.

Claims

1. A polarization aberration compensation method based on DMD vector diffraction, the method is based on a long-wave infrared polarization optical system containing DMD, the optical system includes a telescope objective lens group, a DMD, a projection objective lens group and a polarization detector, the incident light reaches the DMD through the telescope objective lens group, enters the projection objective lens group after being reflected and modulated by the DMD, and forms an image on the polarization detector after passing through the projection objective lens group, characterized in that: The method comprises the following steps: S1. Design of long-wave infrared polarization optical system with DMD; S2, constructing a polarization aberration transmission model of DMD under vector diffraction in a long-wave infrared polarization optical system, and performing simulation analysis on the long-wave infrared polarization optical system containing DMD based on the polarization aberration transmission model, and compensating the simulation results; S3, deriving the optimal diffraction order when the DMD polarization aberration and polarization degree are minimized; S4, determining the optimal incident angle of the DMD; S5, inputting the optimal diffraction order with the DMD polarization aberration and polarization degree minimized and the optimal incident angle of the DMD into the design software for the long-wave infrared polarization optical system containing the DMD; S6. Compensate for the polarization aberration of the optical system by tilting the projection objective lens group and the lens coating.

2. The polarization aberration compensation method based on DMD vector diffraction according to claim 1, characterized in that: When designing a long-wave infrared polarization optical system containing DMD, simulation software is used for design. First, the overall indicators of the long-wave infrared polarization optical system containing DMD are determined, and the initial structure including the telescope objective group, DMD, projection objective group and polarization detector are determined; the modeling method of DMD selects US_MEMS.dll in the sequence mode; the constraint condition that the landing point position of the full-field light on the primary and secondary image planes is accurate to within 1 / 2 pixel is written into the optimization evaluation function, and the image plane of the telescope objective in the long-wave infrared polarization optical system containing DMD is set to DMD for optimization; the optical path of the projection objective group is inverted for design, so that the exit angle of the light reflected from the DMD becomes the incident angle, and it is judged whether this incident angle is consistent with the diffraction angle obtained by simulation calculation, until the design of the projection objective group is completed; finally, the telescope objective group and the projection objective group after setting the DMD incident azimuth and altitude angle are spliced ​​together to meet the pupil connection principle, thereby realizing the design of the entire long-wave infrared polarization optical system containing DMD.

3. The polarization aberration compensation method based on DMD vector diffraction according to claim 2, characterized in that: The polarization aberration transmission model is: ;in, represents the two-way attenuation of the system, represents the maximum intensity transmittance of the system, represents the minimum intensity transmittance of the system, represents the s-light amplitude reflection coefficient of the DMD, represents the p-light amplitude reflection coefficient of the DMD.

4. The polarization aberration compensation method based on DMD vector diffraction according to claim 3, characterized in that: The step S3 is specifically as follows: S31. By: DMD is equivalent to a two-dimensional blazed grating, where and are the incident and outgoing beam altitude angles, and are the incident and outgoing beam azimuths, is the grating constant, is the diffraction order, ± indicates the interface of the diffracted light on the same / different side of the normal line of the micromirror; S32, calculating the diffraction order in which the diffraction efficiency of the diffracted light in the two-dimensional blazed grating exists and is greater than 0, as the retained diffraction order; S33, performing polarization aberration and polarization degree simulation on the DMD under the retained diffraction order, and selecting the diffraction order with the smallest average polarization degree among the two retained diffraction orders with the smallest polarization aberration as the optimal diffraction order of the DMD.

5. The polarization aberration compensation method based on DMD vector diffraction according to claim 4, characterized in that: The screening conditions for the DMD optimal incident angle are: the determined optimal incident angle needs to ensure that the spatial azimuth angle of the diffracted beam after DMD modulation is consistent with the spatial azimuth angle of the incident beam and the altitude angle of the diffracted beam after DMD modulation is smaller than the beam aperture angle of the projection objective lens group in the long-wave infrared polarization optical system.

6. The polarization aberration compensation method based on DMD vector diffraction according to claim 5, characterized in that: The method of compensating the polarization aberration of the optical system by tilting the projection objective lens group and the lens coating is specifically as follows: continue to adjust in the simulation software, tilt the projection objective lens group as a whole along the X-axis until it is orthogonal to the polarization aberration direction of the DMD surface, and coat the surface of each lens of the system with an anti-reflection film, and the thickness of the anti-reflection film is one-quarter of the working wavelength of the system.

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