DMD-based pupil signal detection device and detection method

Abstract

The invention discloses a DMD-based pupil signal detection device and method, the device comprises a light source incident end, a beam shrinking lens group, a digital micromirror device DMD, a focusing lens group and an optical signal receiving end which are sequentially arranged along an optical path, parallel light beams emitted from a pupil are shrunk by the beam shrinking lens group and then are vertically irradiated to the surface of the DMD, and the DMD is irradiated to the optical signal receiving end; wherein each micromirror unit on the DMD corresponds to a specific spatial position on a pupil. By controlling the deflection angle of each micro-mirror, two states of + 12 degrees or-12 degrees can be selected to realize spatial selective light splitting of a pupil area to be detected: when the micro-mirror is at + 12 degrees, reflected light of the micro-mirror is converged by a PMT focus lens and then is received by a PMT, so that detection of a light signal at a corresponding position is realized; and when the micro-mirror is at-12 degrees, reflected light is converged by the light trap focusing mirror and then is absorbed by the light trap. According to the invention, by switching the state of each micromirror on the DMD point by point or as required, scanning type measurement of the whole pupil plane can be completed, and high-precision automatic pupil signal detection is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical system design, in particular to a pupil signal detection device and method based on a digital micro-mirror device (DMD). BACKGROUND

[0002] Pupil signal detection is a key technology in optical measurement and imaging systems, and its precision and efficiency directly affect system performance analysis and optimization. Traditional pupil detection methods mainly include mechanical scanning and direct imaging by a surface array detector. The mechanical scanning method collects light intensity at different positions of the pupil point by point by physically moving the detector or optical components, which is slow in measurement speed, poor in system stability, and difficult to achieve high spatial resolution and fast measurement. The method of directly imaging the pupil surface by using a CCD or CMOS surface array detector can obtain full-field information at one time, but it is limited by the dynamic range, pixel crosstalk and noise of the detector, and the signal-to-noise ratio is low in weak signal or high dynamic range scenarios, and the measurement accuracy is insufficient. In recent years, as a high-speed and programmable spatial light modulator, the digital micro-mirror device (DMD) has been widely used in spectral analysis, structured light projection and other fields. The micro-mirror array of the DMD can quickly and flexibly split and direct the incident light. However, how to efficiently and accurately apply it to high dynamic range and high signal-to-noise ratio detection of pupil signals, especially to achieve programmable partition measurement of the pupil area and efficient suppression of invalid light, is still a problem to be solved in the prior art. Therefore, it is necessary to provide a pupil signal detection device and method based on DMD to overcome the above limitations. SUMMARY

[0003] In view of the above problems, the present application aims to provide a pupil signal detection device and method based on a digital micro-mirror device (DMD) to accurately measure the incident light signal intensity at different positions of the pupil based on the light signal intensity received by a photomultiplier tube (PMT), with high spatial resolution, fast detection speed, and effective suppression of background noise, thereby significantly reducing the cost and development cycle of mask design, greatly improving the signal-to-noise ratio of the system, and ensuring the accuracy and reliability of the measurement results.

[0004] To achieve the above-mentioned application purposes, the present application adopts the following technical solutions: The pupil signal detection device based on DMD comprises a light source incident end, a beam-reducing lens group, a digital micro-mirror device (DMD), a focusing lens group and a light signal receiving end arranged in sequence along the optical path. The light source incident end is a pupil. The beam-reducing lens group comprises a beam-reducing front lens group and a beam-reducing rear lens group arranged in front of and behind the optical path and having positive optical power, and each of the beam-reducing front lens group and the beam-reducing rear lens group comprises at least one lens. The digital micro-mirror device DMD comprises a micro-mirror array composed of a plurality of micro-mirror units and is arranged at an exit pupil position behind the condensing lens group; the rotation axis of each micro-mirror is perpendicular to the incident optical axis; the position of each micro-mirror being perpendicular to the incident light beam is defined as the initial state, at which the rotation angle of each micro-mirror is 0°; the clockwise direction is positive and the counterclockwise direction is negative; in operation, each micro-mirror switches between a fixed tilt angle of +12° or 12°; The focusing lens group comprises a light trap focusing lens group and a PMT focusing lens group with the same structure and positive focal power, and the two correspond to different effective reflection directions of the micro-mirror array on the digital micro-mirror device DMD; the light trap focusing lens group and the PMT focusing lens group each comprise at least one lens; The light signal receiving end comprises a light trap for absorbing stray light and a photomultiplier tube PMT for high-sensitivity signal detection; Parallel light with a diameter larger than the effective photosensitive short side size of the digital micro-mirror device DMD emitted from the light source incident end is condensed by the condensing lens group to form parallel light with a diameter smaller than the effective photosensitive short side size of the digital micro-mirror device DMD, which is perpendicular to the surface of the digital micro-mirror device DMD, and by controlling the tilt angle of each micro-mirror unit on the digital micro-mirror device DMD, the parallel light from different regions of the light pupil is split, and the reflected light to be detected and a plurality of invalid reflected lights are obtained: When each micro-mirror unit is independently switched from the state of 0° rotation angle to 12°, the plurality of invalid reflected lights are received by the light trap after being condensed by the light trap focusing lens group; When each micro-mirror unit is independently switched from the state of 0° rotation angle to +12°, the reflected light to be detected is received by the photomultiplier tube PMT after being condensed by the PMT focusing lens group, and the intensity signal of the PMT is outputted to realize the measurement of the light signal intensity of the light pupil at different positions.

[0005] The DMD-based light pupil signal detection device also has the following characteristics: Step 1. The condensing ratio of the condensing lens group is designed as follows: As a target design index, wherein, f1 and f2 are the focal lengths of the condensing pre-lens group and the condensing post-lens group, respectively; Step 2. The field of view angle θ of the incident light beam and the entrance pupil diameter D are determined, so that the condensing ratio of the condensing lens group is designed according to the entrance pupil diameter D and the effective photosensitive short side size d of the digital micro-mirror device DMD , and satisfies D· <d; Step 3. In a typical condensing lens reference lens library, the condensing ratio closest to a reference design, and then performing size scaling and modifying the field of view angle θ of the selected reference design to obtain an initial structure of the beam-reducing lens group; Step 4. Optimizing the initial structure of the beam-reducing lens group under the constraints of the beam-reducing ratio, the lens length, the image distance, the spherical aberration correction, and the boundary condition to obtain a final beam-reducing lens group. Step 4. Optimizing the initial structure of the beam-reducing lens group under the constraints of the beam-reducing ratio, the lens length, the image distance, the spherical aberration correction, and the boundary condition to obtain a final beam-reducing lens group.

[0006] Further, the parameters of the digital micro-mirror device DMD are designed according to the following steps: Step 1. Determining the position parameters of the digital micro-mirror device DMD in the optical path according to the position of the exit pupil formed in the optical path after the light passes through the beam-reducing lens group by using optical software; Step 2. Keeping other structures in the pupil signal detection device unchanged, and obtaining the rotation parameters of the digital micro-mirror device DMD when the rotation angle of each micro-mirror is +12° and -12°, respectively.

[0007] Further, the focusing lens group is designed according to the following steps: Step A. Determining the focal length of the light trap focusing lens group according to the focal length of the reference lens group in the optical lens library; and the focal length of the PMT focusing lens group is Step B. Determining the focal length of the PMT focusing lens group according to the receiving characteristics of the photomultiplier tube PMT according to formula (1): ; Step B. Determining the focal length of the PMT focusing lens group according to the receiving characteristics of the photomultiplier tube PMT according to formula (1): (1) In formula (1), is the maximum field of view angle of the light beam incident to the PMT focusing lens group, and R is the effective receiving surface radius of the photomultiplier tube PMT; Step C. Determining the aperture size F1 of the PMT focusing lens group according to formula (2): (2) In formula (2), is the spot diameter of the light reflected by the digital micro-mirror device DMD and then incident to the focusing lens group; Step D. Selecting a reference lens with an aperture number closest to from the optical lens library as the initial structure, and adaptively adjusting the field of view of the initial structure according to the actual field of view requirement to obtain the initial optical structure of the PMT focusing lens group; ​​Step E. Determine the optimization variables, including: the radius of curvature of each lens surface, the thickness of the lens, and the air thickness between the lenses in the initial structure of the PMT focusing lens group, and optimize the initial structure of the PMT focusing lens group under the constraints of focal length, lens length, image distance, spherical aberration correction, and boundary conditions to obtain the final structure of the PMT focusing lens group. Step F. Obtain an optical trap focusing lens group identical to the final structure of the PMT focusing lens group, thereby forming the focusing lens group.

[0008] Further: the optical axis of the optical trap focusing lens group and the PMT focusing lens group is symmetrically arranged relative to the normal of the digital micro-mirror device DMD, and the symmetry angle is equal to the effective deflection angle of the micro-mirror of the digital micro-mirror device DMD.

[0009] The detection method of the DMD-based pupil signal detection device of the application has the characteristics that it comprises the following steps: Step one. Project the parallel light from the pupil with a diameter greater than the effective photosensitive short side size of the digital micro-mirror device DMD to the surface of the digital micro-mirror device DMD after beam shrinking, so that the parallel light from the pupil with a diameter greater than the effective photosensitive short side size of the digital micro-mirror device DMD is spatially corresponding to the micro-mirror array of the digital micro-mirror device DMD according to the area division; Step two. Select one or more micro-mirror units on the digital micro-mirror device DMD as the current unit to be tested, and control the rotation angle so that the light beam corresponding to the current unit to be tested is reflected to the PMT focusing lens group for convergence, and the remaining micro-mirror units reflect their corresponding light beams to the optical trap focusing lens group, so as to be received by the optical trap; Step three. Replace the selected current unit to be tested, and repeat step two to obtain the light signal intensity of the pupil at different positions.

[0010] Further, the detection method further comprises a background noise calibration step, which is to control all the micro-mirror units to be tested to point to the optical trap, and record the background noise value of the photomultiplier PMT output at this time, and subtract it in the subsequent measurement of the light signal intensity of the pupil.

[0011] Further, the original light signal intensity of the pupil at the i-th position Wherein, A is the gain coefficient of the photomultiplier PMT, B is the transmittance of the structure composed of the beam shrinking lens group, the digital micro-mirror device DMD, and the focusing lens group, is the original light signal intensity of the pupil at the i-th position The signal energy intensity received by the photomultiplier PMT; i=1,2,3...,N, N represents the total number of positions, and wherein, is the effective photosensitive area of the digital micro-mirror device DMD, is the micro-mirror unit area of the digital micro-mirror device DMD.

[0012] Compared with the prior art, the beneficial effects of the present application are embodied in: 1. The present application uses high-speed and programmable digital micro-mirror device DMD to replace traditional mechanical scanning components, and switches the micro-mirror angle through electrical control to realize fast beam splitting and pointing, which discards the mechanical movement link, avoids the stability problems caused by mechanical wear and vibration, and improves the detection speed to the microsecond level, significantly improving the detection efficiency.

[0013] 2. The present application guides the light beams in the non-detection area to the light trap for absorption, and only allows the light signals from the specific to-be-measured positions of the pupil to enter the PMT, effectively suppressing the background stray light and system noise, and greatly improving the signal-to-noise ratio of the detection, so as to ensure the measurement accuracy and reliability of the signal under weak light or high dynamic range conditions.

[0014] 3. The present application utilizes the spatial light modulation characteristics of the DMD to flexibly define the detection area and sampling mode on the pupil, supports random access and custom path scanning, breaks through the fixed mode of traditional point-by-point mechanical scanning or area array imaging, and greatly enhances the adaptability and functionality of the system in complex pupil analysis tasks.

[0015] 4. The present application combines high-sensitivity PMT for single-point signal acquisition, fully utilizes the advantages of high-gain and low-noise of PMT, and cooperates with the precise beam splitting of DMD to realize high-precision and high-linearity measurement of the pupil signal intensity, and provides accurate data basis for subsequent light field analysis and mask optimization. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a schematic diagram of the optical system of the present application; Figure 2 is a schematic diagram of the reflected light beams of the micro-mirror array inside the DMD; Figure label: 1 light; 21 pre-compression lens group; L1 first lens; L2 second lens; L3 third lens; 22 post-compression lens group; L4 fourth lens; L5 fifth lens; L6 sixth lens; 3 digital micro-mirror device DMD; T1 digital micro-mirror device DMD micro-mirror unit rotation +12°; T2 digital micro-mirror device DMD micro-mirror unit rotation-12°; 41 light trap focusing lens group; L7 seventh lens; 42, PMT focusing lens group; L8 eighth lens; 51 light trap; 52 photomultiplier tube PMT. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings.

[0018] In the embodiment, the pupil signal detection device based on the DMD can accurately obtain the light intensity distribution information at the pupil, provide reliable basis for subsequent mask design, and realize high-precision automatic pupil signal detection. Figure 1 As shown in the figure, the device comprises, in sequence along the light path, a light source incident end 1, a beam-reducing mirror group 2, a digital micro-mirror device DMD 3, a focusing mirror group 4, and a light signal receiving end 5. The light source incident end 1 is a pupil. The beam-reducing mirror group 2 comprises a beam-reducing front mirror group 21 and a beam-reducing rear mirror group 22 which are arranged in front of and behind each other along the light path and have positive optical power, and the beam-reducing front mirror group 21 and the beam-reducing rear mirror group 22 each contain at least one lens.

[0019] The digital micro-mirror device DMD 3 is arranged at the exit pupil position of the optical system formed after the pupil passes through the beam-reducing mirror group 2, the light beam is vertically incident to the digital micro-mirror device DMD 3, and the micro-mirror rotating axis of the digital micro-mirror device DMD 3 is perpendicular to the incident optical axis; each micro-mirror unit can be independently switched between a fixed tilt angle of +12° or -12°.

[0020] The focusing mirror group 4 comprises a light-trap focusing mirror group 41 and a PMT focusing mirror group 42 which have positive optical power and are completely identical in structure, and correspond to two effective reflection directions of the micro-mirrors on the digital micro-mirror device DMD 3; the light-trap focusing mirror group 41 and the PMT focusing mirror group 42 each contain at least one lens.

[0021] The light signal receiving end 5 comprises a light trap 51 and a photomultiplier tube PMT 52 corresponding to the two focusing mirror groups respectively; The parallel light with a diameter larger than the effective photosensitive short side size of the digital micro-mirror device DMD 3, which is emitted from the light source incident end 1, is beam-reduced by the beam-reducing mirror group 2 to form parallel light with a diameter smaller than the effective photosensitive short side size of the digital micro-mirror device DMD 3, and is vertically incident to the surface of the digital micro-mirror device DMD 3; by controlling the tilt angle of each micro-mirror unit on the digital micro-mirror device DMD 3, the parallel light from different regions of the pupil is split, and the reflection light to be detected and a plurality of invalid reflection lights are obtained: When each micro-mirror unit is independently switched from the state of 0° rotation angle to 12°, the plurality of invalid reflection lights are received by the light trap 51 after being converged by the light-trap focusing mirror group 41; When each micro-mirror unit is independently switched from the state of 0° rotation angle to +12°, the reflection light to be detected is received by the photomultiplier tube PMT 52 after being converged by the PMT focusing mirror group 42, and the intensity signal of the photomultiplier tube PMT 52 is outputted, so as to realize the measurement of the light signal intensity of the pupil at different positions.

[0022] The structural schematic diagram of the embodiment one of the present application is shown in Figure 1 .

[0023] In this embodiment, the parallel light size from the light source incident end 1 is ≥25mm, and after the beam-reducing by the beam-reducing lens group 2, the parallel light size is ≤8.1mm.

[0024] In this embodiment, the beam-reducing lens group includes a beam-reducing front lens group 21 and a beam-reducing rear lens group 22, wherein the beam-reducing front lens group 21 includes a first lens L1, a second lens L2 and a third lens L3, the first lens L1 and the second lens L2 are spherical lenses with positive focal power; the third lens L3 is a spherical lens with negative focal power; the beam-reducing rear lens group 22 includes a fourth lens L4, a fifth lens L5 and a sixth lens L6, the fourth lens L4 and the sixth lens L6 are spherical lenses with positive focal power; the fifth lens L5 is a spherical lens with negative focal power.

[0025] In this embodiment, the digital micromirror device DMD 3 contains a micromirror array composed of a plurality of micromirror units, and the effective photosensitive short side size is 8.1mm, and is arranged at the exit pupil position after the pupil of the beam-reducing lens group 2; and the rotation axis of each micromirror is perpendicular to the incident optical axis; the position of each micromirror perpendicular to the incident light beam is defined as the initial state, at this time the rotation angle of each micromirror is 0°; and the clockwise direction is positive and the counterclockwise direction is negative; in operation, the digital micromirror device DMD 3 contains two working states, state T1 is that the internal micromirror of the digital micromirror device DMD 3 rotates +12°, and state T2 is that the internal micromirror of the digital micromirror device DMD 3 rotates -12°.

[0026] In this embodiment, the focusing lens group 4 includes a light trap focusing lens group 41 and a PMT focusing lens group 42 with the same structure and positive focal power, wherein the light trap focusing lens group 41 includes a spherical lens L7 with positive focal power, and the PMT focusing lens group 42 includes a spherical lens L8 with positive focal power.

[0027] In this embodiment, the light signal receiving end 5 includes a light trap 51 and a PMT 52.

[0028] In this embodiment, the beam-reducing lens group 2 is designed according to the following steps: Step 1. The beam-reducing ratio of the beam-reducing lens group 2 is designed as a target design index, wherein , respectively, are the focal length of the beam-reducing front lens group 21 and the focal length of the beam-reducing rear lens group 22; Step 2. The field angle θ of the incident light beam and the entrance pupil diameter D are determined, and the beam-reducing ratio of the beam-reducing lens group is designed according to the entrance pupil diameter D and the effective photosensitive short side size d of the DMD , to ensure that D· d.​

[0029] Step 3. Select the lens with the closest reduction ratio from the typical beam shrinking reference lens library. A reference design is selected, and then the size of the selected reference design is scaled and the field of view θ is modified to obtain the initial structure of the beam shrinking lens group 2; Step 4. Analyze the obtained initial structure based on the radius of curvature of each lens surface, lens thickness, and air thickness between lenses, then analyze the beam reduction ratio. The initial structure of the beam shrinking lens group 2 was optimized from five aspects: constraint, lens length constraint, image distance constraint, spherical aberration correction and boundary condition constraint, to obtain the final "beam shrinking lens group 2".

[0030] In this embodiment, the parameters of the DMD in the detection device are designed according to the following process: Step 1. Based on the exit pupil position formed in the optical path after the tracking pupil passes through the constrictor lens group 2, determine the position parameters of the digital micromirror device (DMD3) in the optical path; Step 2. Keeping the other structures in the pupil signal detection device unchanged, obtain the rotation parameters of the digital micromirror device DMD3 when the rotation angle of each micromirror is +12° and -12° respectively.

[0031] In this embodiment, the focusing lens group 4 is designed according to the following steps: Step A. Focus the light trap focusing lens group 41 focal length and PMT focusing lens group 42 focal length As the same target design metric, i.e., satisfying = ; Step B. Based on the receiving characteristics of the PMT, determine the focal length of the PMT focusing lens group (42) according to formula (1). : (1) Where θ is the field of view of the incident beam, and R is the effective receiving surface radius of the PMT; Step C. Determine the aperture size F1 of the PMT focusing lens group (42) according to formula (2): (2) in, It is the diameter of the light spot that is incident on the focusing lens group after being reflected by the DMD.

[0032] Step D. Select the reference lens with the closest aperture number to F1 from the optical lens library as the initial structure, and make adaptive adjustments to the field of view of the initial structure according to the actual field of view requirements to obtain the initial optical structure of the PMT focusing lens group 42. Step E. Determine the optimization variables, including the initial structure of the PMT focusing lens group 42, the radius of curvature of each lens surface, the thickness of the lens, and the air thickness between the lenses, and then optimize the initial structure of the PMT focusing lens group 42 from five aspects of focal length constraint, lens length constraint, image distance constraint, spherical aberration correction, and boundary condition constraint to obtain the final structure of the PMT focusing lens group 42; Step F. Obtain the optical trap focusing lens group 41 consistent with the final structure of the PMT focusing lens group 42, thereby jointly forming the focusing lens group 4.

[0033] In this embodiment, a DMD-based pupil signal detection device is characterized in that the optical axes of the optical trap focusing lens group 41 and the PMT focusing lens group 42 are symmetrically arranged relative to the normal line of the digital micromirror device DMD 3, and the symmetry angle is equal to the effective deflection angle of the micromirror of the digital micromirror device DMD 3.

[0034] In this embodiment, a DMD-based pupil signal detection method includes the following detection steps: Step one. Project the parallel light with a diameter greater than the effective photosensitive short side size of the digital micromirror device DMD 3 to the surface of the digital micromirror device DMD 3 after beam reduction, so that the parallel light with a diameter greater than the effective photosensitive short side size of the digital micromirror device DMD 3 is spatially corresponding to the micromirror array of the digital micromirror device DMD 3 according to the region division; Step two. Select one or more micromirror units on the digital micromirror device DMD 3 as the current unit to be measured, and control the rotation angle so that the light beam corresponding to the current unit to be measured is reflected to the PMT focusing lens group 42 for convergence and received by the photomultiplier PMT 52, while controlling the remaining micromirror units to reflect their corresponding light beams to the optical trap focusing lens group 41 for reception by the optical trap 51; In this embodiment, the step of replacing the micromirror unit to be measured is performed according to a preset scanning program, which includes at least one of continuous point-by-point scanning, random point sampling, specific region key scanning, or adaptive adjustment of scanning order and density according to preliminary scanning results.

[0035] Step three. Replace the selected current unit to be measured and repeat step two to obtain the light signal intensity of the pupil at different positions.

[0036] In this embodiment, a DMD-based pupil signal detection method further includes a background noise calibration step: control all micromirror units to be measured to switch to a state pointing to the optical trap 51, record the background noise value output by the PMT 52 at this time, and subtract it from the subsequent signal measurement value to improve the signal-to-noise ratio of the device.

[0037] In this embodiment, the original light signal intensity of the pupil at the i-th position is obtained by formula (3) : (3) In formula (3), A is the gain coefficient of the photomultiplier PMT, B is the transmittance of the structure composed of the beam-reducing lens group 2, the digital micromirror device DMD 3, and the focusing lens group 4, is the original light signal intensity at the i-th position of the pupil corresponds to the signal energy intensity received by the corresponding photomultiplier PMT 52, i = 1, 2, 3,..., N, N represents the total number of positions, and has: (4) In formula (4), is the effective light-sensing area of the digital micromirror device DMD (3), is the micro-mirror unit area of the digital micromirror device DMD 3.

[0038] In this embodiment, in the light signal receiving end 5, the PMT 52 is the only photoelectric detection device for intensity quantification of the to-be-measured light signal from the pupil; the light trap 51 is a terminal absorber for receiving and absorbing all light beams that are not directed to the PMT 52 after being split by the DMD 3; through independent control of each micro-mirror state of the DMD 3, the to-be-measured pupil unit signal at any moment is guided to the PMT 52, while all non-to-be-measured unit signals are guided to the light trap 51, thereby realizing point-by-point or programmable scanning detection with high signal-to-noise ratio.

[0039] Based on the above embodiments, in a further embodiment, the center thickness of the first lens L1 is 6.5 mm, and the refractive index n1 satisfies 1.4 ≤ n1 ≤ 1.6. The air gap between the centers of the first lens L1 and the second lens L2 is 1.0 mm, the center thickness of the second lens L2 is 6.0 mm, and the refractive index n2 satisfies 1.4 ≤ n2 ≤ 1.6. The air gap between the centers of the second lens L2 and the third lens L3 is 3.0 mm, the center thickness of the third lens L3 is 5.0 mm, and the refractive index n3 satisfies 1.4 ≤ n3 ≤ 1.6. The air gap between the centers of the third lens L3 and the fourth lens L4 is 84.0 mm, the center thickness of the fourth lens L4 is 3.0 mm, and the refractive index n4 satisfies 1.4 ≤ n4 ≤ 1.6. The air gap between the centers of lens L4 and the fifth lens L5 is 3.5 mm, the center thickness of the fifth lens L5 is 3.0 mm, and the refractive index n5 satisfies 1.4 ≤ n5 ≤ 1.6. The air gap between the centers of the fifth lens L5 and the sixth lens L6 is 1.0 mm, the center thickness of the sixth lens L6 is 4.0 mm, and the refractive index n6 satisfies 1.4 ≤ n6 ≤ 1.6. The air gap between the centers of the sixth lens L6 and the seventh lens L7 is 81.9 mm, the air gap between the centers of the sixth lens L6 and the eighth lens L8 is 81.9 mm, the center thickness of the seventh lens L7 is 3.5 mm, and the refractive index n7 satisfies 1.4 ≤ n7 ≤ 1.6. The center thickness of the eighth lens L8 is 3.5 mm, and the refractive index n8 satisfies 1.4 ≤ n8 ≤ 1.6.

[0040] The specific parameters of each lens in the optical system of this embodiment are shown in Table 1: Table 1 like Figure 2 The diagram shows a micromirror array inside the DMD reflecting a light beam. When the light beam is incident perpendicularly on the DMD surface, the reflected beam can be directed to two different preset spatial positions by rotating the micromirrors to a working state of +12° or -12°.

Claims

1. A pupil signal detection device based on DMD, characterized in that, include: Along the optical path are arranged the light source incident end (1), the beam shrinking lens group (2), the digital micromirror device (DMD) (3), the focusing lens group (4), and the optical signal receiving end (5). The light source incident end (1) is the pupil; The beam shrinking lens group (2) includes a front beam shrinking lens group (21) and a rear beam shrinking lens group (22) arranged along the front and rear of the optical path, both with positive optical power. The front beam shrinking lens group (21) and the rear beam shrinking lens group (22) each contain at least one lens. The digital micromirror device (DMD) (3) includes a micromirror array composed of multiple micromirror units and is positioned at the exit pupil position after the pupil passes through the beam shrinking lens group (2); and the rotation axis of each micromirror is perpendicular to the incident light axis; the initial state is defined as each micromirror being in a position perpendicular to the incident light beam, at which time the rotation angle of each micromirror is 0°; and the clockwise direction is positive and the counterclockwise direction is negative; during operation, each micromirror switches between a fixed tilt angle +12° or 12°; The focusing lens group (4) includes: an optical trap focusing lens group (41) and a PMT focusing lens group (42) with positive optical power and identical structure, and the two correspond to different effective reflection directions of the micromirror array on the digital micromirror device (DMD) (3); both the optical trap focusing lens group (41) and the PMT focusing lens group (42) contain at least one lens. The optical signal receiver (5) includes: an optical trap (51) for absorbing stray light and a photomultiplier tube (PMT) (52) for high-sensitivity signal detection; Parallel light emitted from the light source incident end (1), with a diameter larger than the effective photosensitive short side size of the digital micromirror device (DMD) (3), is beam-constricted by the beam-constricting lens group (2) to form parallel light with a diameter smaller than the effective photosensitive short side size of the digital micromirror device (DMD) (3). This parallel light is then incident perpendicularly onto the surface of the digital micromirror device (DMD) (3). By controlling the tilt angle of each micromirror unit on the digital micromirror device (DMD) (3), the parallel light from different regions of the pupil is split, resulting in the reflected light to be detected and multiple invalid reflected lights. When each micromirror unit independently switches from a rotation angle of 0° to 12°, multiple invalid reflected lights are converged by the optical trap focusing lens group (41) and then received by the optical trap (51). When each micromirror unit independently switches from a rotation angle of 0° to +12°, the reflected light to be detected is converged by the PMT focusing lens group (42) and received by the photomultiplier tube PMT (52), and the intensity signal of the PMT is output to realize the measurement of the light signal intensity at different positions of the pupil.

2. The pupil signal detection device based on DMD according to claim 1, characterized in that, The beam shrinking lens group (2) is designed according to the following steps: Step 1. Adjust the beam-shrinking ratio of the beam-shrinking lens group (2). As a target design metric, among which... These are the focal lengths of the front-contraction lens group (21) and the rear-contraction lens group (22), respectively. Step 2. Determine the field of view θ and entrance pupil diameter D of the incident beam, and then design the beam-shrinking ratio of the beam-shrinking lens group (2) based on the entrance pupil diameter D and the effective photosensitive short side dimension d of the digital micromirror device DMD (3). And satisfy D· <d; Step 3. Select the lens with the closest reduction ratio from the typical beam shrinking reference lens library. A reference design is selected, and then the size of the selected reference design is scaled and the field of view θ is modified to obtain the initial structure of the beam shrinking lens group (2); Step 4. Using the radius of curvature of each lens surface, lens thickness, and air thickness between lenses in the initial structure of the beam-shrinking lens group (2) as optimization variables, the beam-shrinking ratio is optimized. The initial structure of the beam shrinking lens group (2) is optimized under constraints such as lens length constraint, image distance constraint, spherical aberration correction and boundary condition constraint, so as to obtain the final beam shrinking lens group (2).

3. The pupil signal detection device based on DMD according to claim 1, characterized in that, The parameters of the digital micromirror device (DMD) (3) are designed according to the following steps: Step 1. Based on the exit pupil position formed in the optical path after the tracking pupil passes through the constrictor lens group (2) by the optical software, determine the position parameters of the digital micromirror device (DMD) (3) in the optical path; Step 2. Keeping the other structures in the pupil signal detection device unchanged, obtain the rotation parameters of the digital micromirror device (DMD) (3) under the conditions of +12° and -12° rotation angle of each micromirror.

4. The pupil signal detection device based on DMD according to claim 1, characterized in that, The focusing lens group (4) is designed according to the following steps: Step A. Adjust the focal length of the light trap focusing lens group (41). The PMT focusing lens group (42) is the focal length As the same target design metric, i.e., satisfying = ; Step B. Based on the receiving characteristics of the photomultiplier tube PMT (52), determine the focal length of the PMT focusing lens group (42) according to equation (1). : (1) In equation (1), R is the maximum field of view of the beam incident on the PMT focusing lens group (42), and R is the effective receiving surface radius of the photomultiplier tube PMT (52); Step C. Determine the aperture size F1 of the PMT focusing lens group (42) according to formula (2): (2) In equation (2), The diameter of the light spot incident on the focusing lens group (42) after being reflected by the digital micromirror device (DMD) (3); Step D. Select the lens with the closest aperture number from the optical lens library. The reference lens is used as the initial structure, and the field of view of the initial structure is adaptively adjusted according to the actual field of view requirements to obtain the initial optical structure of the PMT focusing lens group (42); Step E. Determine the optimization variables, including: the radius of curvature of each lens surface, lens thickness and air thickness between lenses in the initial structure of the PMT focusing lens group (42), and optimize the initial structure of the PMT focusing lens group (42) under focal length constraints, lens length constraints, image distance constraints, spherical aberration correction and boundary condition constraints to obtain the final PMT focusing lens group (42) structure. Step F. Obtain an optical trap focusing lens group (41) that is completely identical to the final structure of the PMT focusing lens group (42), thereby jointly constituting the focusing lens group (4).

5. The pupil signal detection device based on DMD according to claim 1, characterized in that: The optical axes of the optical trap focusing lens group (41) and the PMT focusing lens group (42) are arranged symmetrically with respect to the normal of the digital micromirror device (DMD) (3), and the symmetry angle is equal to the effective deflection angle of the micromirror of the digital micromirror device (DMD).

6. A detection method based on the pupil signal detection device based on DMD as described in claim 1, characterized in that, Includes the following steps: Step 1. The parallel light from the pupil, whose diameter is larger than the effective short side size of the digital micromirror device (DMD) (3), is bundled and projected onto the surface of the digital micromirror device (DMD) (3). This causes the parallel light from the pupil, whose diameter is larger than the effective short side size of the digital micromirror device (DMD) (3), to be divided into multiple beams according to the region, forming a spatial correspondence with the micromirror array of the digital micromirror device (DMD) (3). Step 2. Select one or more micromirror units on the digital micromirror device DMD (3) as the current unit under test, and control its rotation angle so that the beam corresponding to the current unit under test is reflected to the PMT focusing lens group (42) for convergence and then received by the photomultiplier tube PMT (52). At the same time, control the other micromirror units to reflect their corresponding beams to the optical trap focusing lens group (41) so that they are received by the optical trap (51). Step 3. Replace the selected current test unit and repeat Step 2 to obtain the light signal intensity at different positions of the pupil.

7. The detection method of the pupil signal detection device based on DMD according to claim 6, characterized in that, The detection method also includes a background noise calibration step, which involves controlling all micromirror units under test to switch to the state pointing to the light trap (51), recording the background noise value output by the photomultiplier PMT (52) at this time, and subtracting it from the subsequent light signal intensity measurement of the pupil.

8. The detection method of the pupil signal detection device based on DMD according to claim 6, characterized in that, The original light signal intensity of the pupil at position i Where A is the gain coefficient of the photomultiplier tube (PMT), and B is the transmittance of the structure composed of the beam shrinking mirror group (2), the digital micromirror device (DMD) (3), and the focusing mirror group (4). The original light signal intensity at the i-th position of the pupil. The corresponding signal energy intensity received by the photomultiplier PMT (52); i=1,2,3...,N, where N represents the total number of positions, and ,in, The effective photosensitive area of ​​the digital micromirror device (DMD) (3) denoted as the micromirror unit area of ​​the digital micromirror device (DMD(3)).

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