TIR prism system and dual-channel common-aperture medium-wave infrared projection optical system

Abstract

The invention relates to the technical field of infrared target simulation, in particular to a TIR prism system and a dual-channel common-caliber medium-wave infrared projection optical system. The TIR prism system comprises a first prism, a second prism and a third prism which are arranged in sequence, the side surfaces of the first prism are a beta 1 surface, a beta 2 surface, a beta 3 surface, a beta 4 surface and a beta 5 surface in sequence; the beta1 surface and the DMD micromirror are arranged in parallel; a first prism and a third prism are respectively arranged on the adjacent lambda1 surface and lambda3 surface in the second prism; the beta3 face is opposite to the lambda1 face, the mu1 face of the third prism is opposite to the lambda3 face, air gaps are formed between the beta3 face and the lambda1 face and between the mu1 face and the lambda3 face, and the three prisms are glued from the overall outer side face through a glass clamping plate. According to the invention, complete isolation of off-state and flat-state light beams of the DMD micromirror is realized under the condition that no light blocking device is arranged; meanwhile, the problem that a traditional method is difficult to adapt to large-range temperature changes is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of infrared target simulation, and particularly relates to a TIR prism system and a dual-channel common-aperture mid-wave infrared projection optical system. Background Art

[0002] Existing infrared target simulation systems mainly include three major cores, namely an illumination system, a scene generation device, and a projection system. Among them, the key components connecting the illumination system and the projection system are all TIR prisms. In the prior art, two-component TIR prisms are mostly used to separate the projection optical axis and the illumination optical axis to achieve the overall miniaturization of the system. However, the maximum angle between the effective on-state light beam reflected by the DMD mirror and the ineffective off-state light beam and the ineffective flat-state light beam is only 24°. The TIR prism can only effectively isolate the ineffective off-state light beam, and the ineffective flat-state light beam still needs to be assisted and suppressed by an externally attached light baffle. Therefore, it is inevitable that ineffective light beams enter the projection system and become stray light, reducing the imaging quality and performance of the projection system.

[0003] Moreover, since the infrared lens material used in the projection system is very susceptible to temperature changes and deforms, which in turn leads to a decline in the optical performance of the system. Especially when performing high-dynamic-range scene simulation, this thermally induced deformation can cause the target scene to be completely distorted. Therefore, the overall system is usually placed in a cold field environment during use to weaken the influence of the self-thermal radiation of the components. However, only by placing it at a low temperature, the optical performance of the projection system will decrease. Therefore, those skilled in the art have proposed various athermalization designs. Among them, based on excellent effects, the new generation of optical passive athermalization design ideas achieve temperature compensation through the combination of optical materials and structural materials, becoming the preferred idea for the athermalization design of optical systems. However, in actual applications, for example, in a Chinese patent with the publication number CN110031958A and the name of an improved three-component TIR prism, although athermalization can be partially achieved through material selection and structural design, in some cases, it is still difficult to completely eliminate the influence of temperature changes on the optical system.

[0004] Based on this, those skilled in the art urgently need to further improve the TIR prism to better adapt to the mid-wave infrared projection optical system. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects existing in the above-mentioned prior art, so as to provide a TIR prism system and a dual-channel common-aperture mid-wave infrared projection optical system.

[0006] A TIR prism system includes a first prism, a second prism, and a third prism arranged in sequence; The first prism has a pentaprism structure, and its sides are successively: β1 surface, β2 surface, β3 surface, β4 surface, and β5 surface; Among them, the β1 plane is arranged parallel to the DMD mirror, and the β1 plane is the incident plane of the DMD mirror; The first prism and the third prism are respectively arranged on the adjacent λ1 plane and λ3 plane in the second prism; moreover, the β3 plane is opposite to the λ1 plane, the μ1 plane of the third prism is opposite to the λ3 plane, there are air gaps between the β3 plane and the λ1 plane and between the μ1 plane and the λ3 plane, and the three prisms are glued together from the overall outer side by a glass splint; The light is vertically incident on the β5 plane and sequentially passes through the β5 plane, the β3 plane and the β1 plane inside the first prism and then is transmitted to the DMD mirror; When the DMD mirror is in the on state, the reflected light undergoes total internal reflection, sequentially passes through the first prism, the second prism and the third prism, and exits from the μ2 plane of the third prism; When the DMD mirror is in the off state, the reflected light undergoes total internal reflection on the β1 plane and sequentially passes through the first prism and the second prism, and exits from the λ3 plane of the second prism; When the DMD mirror is in the flat state, the reflected light undergoes total internal reflection on the β1 plane and sequentially passes through the first prism and the second prism, and exits from the λ3 plane of the second prism.

[0007] Preferably, the first incident angle α1 of the incident light on the β3 plane inside the first prism is greater than the critical angle; The third incident angle α3 of the light reflected from the DMD mirror to the β3 plane is less than the critical angle; The incident angle of the light incident from the β1 plane to the DMD mirror is θ DMD ; The second incident angle after being reflected from the β3 plane and incident on the β1 plane ; ; The refractive index n1 is 2.251 ± 0.05, and the critical angle is 24.9° - 26.025°; the first prism angle θ1 is the included angle between the β3 plane and the parallel axis of the β1 plane, and its value satisfies that the marginal light after being reflected by the DMD mirror does not undergo total internal reflection. The specific expression is ; in the expression of the value of the first prism angle θ1, the included angle between the marginal light and the principal optical axis becomes ; it is positive when the marginal light is above the principal optical axis of the TIR prism system; it is negative when the marginal light is below the principal optical axis.

[0008] Preferably, the second prism is of a triangular prism structure; and the λ2 plane of the second prism is parallel to the β2 plane of the first prism; The fourth incident angle α4 of the flat-state light beam and the off-state light beam incident on the λ3 plane is greater than the critical angle; The incident angle of the on-state light beam incident on the λ3 plane is less than the critical angle; The internal angle relationship of the second prism is: ; Where: After being reflected by the DMD mirror, the included angle between the flat-state and off-state light beams and the target surface of the DMD mirror is I, and I≥θ DMD ; The second prism angle θ2 is the included angle between the λ3 plane and the parallel axis of the β1 plane, and its value satisfies .

[0009] Preferably, the third prism is of a triangular prism structure; The widths of the λ3 plane of the second prism and the μ1 plane of the third prism are the same; The third prism angle θ3 is such that the included angle between the μ1 plane and the μ2 plane of the third prism is equal to the second prism angle θ2.

[0010] Preferably, when the light ray emitted from the lower edge of the DMD mirror target surface hits the β3 surface and the total reflection light ray is exactly reflected onto the upper edge of the DMD mirror, it is the minimum value of the thickness of the first prism ; Specifically: The thickness of the first prism The minimum value is the distance between the normal line at the center of the DMD mirror target surface and the intersection point of the β1 surface and the β3 surface. At this time, the thickness of the first prism = 19.17 mm; The length of the DMD mirror = 17.5 mm; The included angle between the normal line of the center of the DMD mirror target surface and the normal line of the incident light ray on the β3 surface is θ a , and θ a = θ1 = 20°.

[0011] Preferably, when the marginal light ray emitted by the DMD mirror is reflected from the β1 surface to the intersection point of the λ1 surface and the λ3 surface of the second prism, then the thickness of the second prism is the minimum value; Specifically: The thickness of the second prism The minimum value is the distance between the normal line at the center of the DMD mirror target surface and the intersection point of the λ1 surface and the λ3 surface. At this time 10.7124 mm; The distance between the DMD mirror and the first prism is d, d = 5 mm; The height between the incident point where the marginal light ray emitted by the DMD mirror is reflected onto the β1 surface and the intersection point of the λ1 surface and the λ3 surface of the second prism is y, y = 22.5504 mm. At this time, the included angle between the parallel axis of the normal line at the center of the DMD mirror target surface and the internally reflected light ray in the first prism is θ b , and θ b = 4.525°.

[0012] Preferably, the thickness of the third prism is the distance between the normal line at the center of the DMD mirror target surface and the intersection point of the μ1 surface and the μ2 surface; The minimum value of the thickness of the third prism is 7.4556 mm; The overall thickness of the TIR prism is 43.65 mm, and the first prism, the second prism, and the third prism are all made of ZnS material.

[0013] A dual-channel common-aperture mid-wave infrared projection optical system includes a first DMD micromirror, a first window glass, a first TIR prism system, a beam-combining prism, a first lens, a second lens, a third lens, a fourth lens, and a fifth lens that are sequentially optically connected on the same axis; it further includes: a second DMD micromirror, a second window glass, and a second TIR prism system that are sequentially optically connected on the same axis; and the central normal of the target surface of the first DMD micromirror is perpendicular to the central normal of the target surface of the second DMD micromirror. Both the first TIR prism system and the second TIR prism system adopt a TIR prism system as described in claim 7.

[0014] Preferably, the materials of the first lens and the third lens are silicon; The materials of the second lens and the fifth lens are germanium; The material of the fourth lens is zinc sulfide.

[0015] Preferably, the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are all spherical lenses; and the optical powers of the first lens and the second lens are in a positive-negative combination; The optical powers of the third lens, the fourth lens, and the fifth lens are all positive.

[0016] The technical solution of the present invention has the following advantages: The present invention provides a three-component TIR prism system, which can completely isolate the off-state beam and on-state beam of the DMD micromirror without setting any light-blocking devices; at the same time, it solves the problem that the mid-wave infrared projection optical system is difficult to adapt to large-range temperature changes, performs an athermal design on the projection system, and can maintain excellent projection quality in the range of -40°C to +60°C, enabling the projection system to always project high-precision infrared images. The two DMD micromirrors are connected to the same projection system by a beam-combining prism, and the optical performance of each optical path is exactly the same. The working state of the three-component TIR prism between the DMD micromirror and the projection system can be regarded as a parallel plate with the same thickness. Finally, the optical performance of the mid-wave infrared projection optical system approaches the diffraction limit, the MTF curve is better than 0.48 at 37 lp / mm, and the maximum distortion is less than 0.1%. The layout of the dual-channel common-aperture mid-wave infrared projection optical system is beneficial for use in scenarios with high integration requirements, and the combined modulation of the two DMD micromirrors has the potential to generate high-contrast and high-bit-depth infrared scene simulation images. Description of the Drawings

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0018] Figure 1 Schematic diagram of the relevant angle design within the first prism of the present invention; Figure 2 Schematic diagram of the relevant angle design within the second and third prisms of the present invention; Figure 3 Design drawing of the thickness of the first prism of the present invention; Figure 4 Design drawing of the thickness of the second prism of the present invention; Figure 5 Design drawing of the thickness of the third prism of the present invention; Figure 6 Schematic diagram of the verification test results when the DMD micromirror of Example 1 of the present invention is in the open state; Figure 7 Schematic diagram of the verification test results when the DMD micromirror of Example 1 of the present invention is in the closed state; Figure 8 Schematic diagram of the verification test results when the DMD micromirror of Example 1 of the present invention is in the flat state; Figure 9 Schematic diagram of the three-dimensional structure of a dual-channel common-aperture mid-wave infrared projection optical system of the present invention; Figure 10 Schematic diagram of the design results of a dual-channel common-aperture mid-wave infrared projection optical system of the present invention; Figure 11 MTF curve graph of the system of Example 2 at 20°C; Figure 12 MTF curve graph of the system of Example 2 at -40°C; Figure 13 MTF curve graph of the system of Example 2 at 60°C; Figure 14 Diffraction circle incident energy fraction graph of the system of Example 2 at 20°C; Figure 15 Diffraction circle incident energy fraction graph of the system of Example 2 at -40°C; Figure 16 Diffraction circle incident energy fraction graph of the system of Example 2 at 60°C; Figure 17Optical path diagram of the system in Example 2 when two DMD micromirrors are in the on state; Figure 18 Optical path diagram of the system in Example 2 when two DMD micromirrors are in the off state; Figure 19 Optical path diagram of the system in Example 2 when two DMD micromirrors are in the flat state.

[0019] Description of reference numerals: 1 - First prism, 2 - Second prism, 3 - Third prism, 4 - DMD micromirror, 5 - Window glass, 6 - Beam-combining prism, 7 - First lens, 8 - Second lens, 9 - Third lens, 10 - Fourth lens, 11 - Fifth lens, 12 - First DMD micromirror, 13 - First window glass, 14 - First TIR prism system, 15 - Second DMD micromirror, 16 - Second window glass, 17 - Second TIR prism system, S1 - Projection exit pupil plane, S2 - Fifth exit spherical surface, S3 - Fifth incident spherical surface, S4 - Fourth exit spherical surface, S5 - Fourth incident spherical surface, S6 - Third exit spherical surface, S7 - Third incident spherical surface, S8 - Second exit spherical surface, S9 - Second incident spherical surface, S10 - First exit spherical surface, S11 - First incident spherical surface, S12 - Beam-combining prism exit surface, S13 - Beam-combining prism incident spherical surface, S14 - First TIR prism system exit surface, S18 - Second TIR prism system exit surface, S15 - First TIR prism system incident spherical surface, S19 - Second TIR prism system incidence, S16 - First window glass exit surface, S20 - First window glass exit surface, S17 - First window glass incident spherical surface, S21 - Second window glass incident spherical surface. Detailed implementation manners

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0021] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0022] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0023] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0024] Embodiment 1 A TIR prism system includes a first prism 1, a second prism 2, and a third prism 3 arranged in sequence. The first prism 1 has a pentaprism structure, and its side surfaces are successively: β1 surface, β2 surface, β3 surface, β4 surface, and β5 surface. The second prism 2 has a triangular prism structure, and its side surfaces are successively: λ1 surface, λ2 surface, and λ3 surface. The third prism 3 has a triangular prism structure, and its side surfaces are successively: μ1 surface, μ2 surface, and μ3 surface. Among them, the β1 surface is arranged parallel to the DMD micromirror 4, and the β1 surface is the incident surface of the DMD micromirror 4. In the second prism 2, the first prism 1 and the third prism 3 are respectively arranged on the adjacent λ1 surface and λ3 surface; moreover, the β3 surface is opposite to the λ1 surface, the μ1 surface of the third prism 3 is opposite to the λ3 surface, an air gap is provided between the β3 surface and the λ1 surface and between the μ1 surface and the λ3 surface, and the three prisms are glued together by a glass splint from the overall outer side surface. Light is vertically incident on the β5 surface and successively passes through the β5 surface, β3 surface, and β1 surface inside the first prism 1 and then is transmitted to the DMD micromirror 4. When the DMD micromirror 4 is in the on state, the reflected light undergoes total internal reflection, successively passes through the first prism 1, the second prism 2, and the third prism 3, and is emitted from the μ2 surface of the third prism 3. When the DMD micromirror 4 is in the off state, the reflected light undergoes total internal reflection on the β1 surface and successively passes through the first prism 1 and the second prism 2, and is emitted from the λ3 surface of the second prism 2. When the DMD micromirror 4 is in the flat state, the reflected light undergoes total internal reflection on the β1 surface and successively passes through the first prism 1 and the second prism 2, and is emitted from the λ3 surface of the second prism 2.

[0025] Specifically: Regarding the design of the first prism 1: Main purpose: Since the first prism 1 of this embodiment is used in a dual-channel common-aperture mid-wave infrared projection optical system, the main purpose of the first prism 1 is to evenly illuminate the DMD mirror 4 with the light beam irradiated by the illumination system. The design requires that the first prism angle θ1 satisfies the following conditions: The first incident angle α1 of the incident light ray on the β3 surface in the first prism 1 is greater than the critical angle; The third incident angle α3 of the light ray reflected from the DMD mirror 4 to the β3 surface is less than the critical angle; The incident angle of the light ray from the β1 surface to the DMD mirror 4 is θ DMD , θ DMD The value is a pre-specified value; Such as Figure 1 , the incident illumination light ray enters the first prism 1 perpendicular to the β5 surface. To ensure that the illumination light beam hits the target surface of the DMD mirror 4 at θ DMD , the illumination light ray passes through the β5 surface, β3 surface and β1 surface in sequence inside the first prism 1 and then is transmitted to the DMD mirror 4. Among them, total internal reflection occurs on the β3 surface and the incident angle is the first incident angle α1, and it shoots towards the target surface of the DMD mirror 4. After exiting from the β1 surface, it enters the air and hits the target surface of the DMD mirror 4 at θ DMD . According to the triangle interior angle relationship, it can be known that the angles inside the first prism 1 should satisfy: ; According to Snell's law of refraction, the second incident angle after being reflected from the β3 surface and incident on the β1 surface; The material of the first prism 1 is selected as chalcogenide glass ZnS, which is more common in the mid-infrared band. The refractive index n1 is 2.251 ± 0.05, and the critical angle is 24.9° - 26.025°; The first prism angle θ1 is the angle between the parallel axes of the β3 surface and the β1 surface; Also, since there is a light cone angle of 12° for the light beam exiting from the DMD mirror 4 surface, considering factors such as spectral splitting accuracy and processing errors, the light cone angle is taken as 10° in the design of this embodiment. Therefore, the value of the first prism angle θ1 should also satisfy that the marginal light rays after being reflected by the DMD mirror 4 do not undergo total internal reflection. Actually, after the marginal light rays exiting along the main optical axis direction of the TIR prism system from the target surface of the DMD mirror 4 are offset by 10° up and down, they will not undergo total internal reflection on the surface of the first prism 1; The specific expression for the value of the first prism angle θ1 is ; In the expression for the value of the first prism angle θ1, the angle between the marginal light ray entering the first prism 1 and the main optical axis becomes ; When the marginal ray is above the principal optical axis, it is positive; when the marginal ray is below the principal optical axis, it is negative. According to the expression for the value of the first prism angle θ1, the maximum value of the first prism angle θ1 is 20.6°. Let the first prism angle θ1 be 20°, at this time, the first incident angle α1 is solved to be 32.55° - 33.13°, which is greater than the critical value, and the third incident angle α3 is solved to be 24.328° - 24.5251°, which is less than the critical angle, meeting the above requirements.

[0026] Regarding the design of the second prism 2: The λ2 surface of the second prism 2 is parallel to the β2 surface of the first prism 1; The main purpose: Modulate the light beam in the flat state and off state of the DMD mirror 4. Among them, the λ3 surface is responsible for modulating the light beam. Therefore, the second prism angle θ2 of the second prism 2 is designed to meet the following conditions: The fourth incident angle α4 of the flat state light beam and the off state light beam incident on the λ3 surface is greater than the critical angle; The incident angle of the on state light beam incident on the λ3 surface is less than the critical angle; Specifically: First, to ensure that the on state light beam can be transmitted inside the second prism 2, the second prism angle should be less than the critical angle ; Such as Figure 2 The second prism angle θ2 is the included angle between the λ3 surface and the parallel axis of the β1 surface; Secondly, after being reflected by the DMD mirror 4, the included angle between the flat state and off state light beams and the target surface of the DMD mirror 4 is I. According to the diffraction characteristics of the DMD mirror 4, I≥θ DMD , Through the triangle geometric relationship and Snell's law, the internal angle relationship of the second prism 2 is: ; Let the prism angle θ2 be 22.5°, at this time, α4 = 30.7061°, which is greater than the critical value angle, meeting the above requirements.

[0027] Regarding the design of the third prism 3: The third prism 3 is a triangular prism structure; the widths of the λ3 surface of the second prism 2 and the μ1 surface of the third prism 3 are the same; The main purpose: Ensure that the principal ray of the TIR prism system is parallel to the optical axis of the DMD mirror 4. Therefore, as Figure 4 The prism angle θ3 of the third prism 3 is equal to the included angle between the μ1 surface and the μ2 surface of the third prism 3 and the second prism angle θ2.

[0028] Regarding the design of the thickness: If the thickness of the TIR prism system is too thick, it will cause light energy loss and increase the working distance of the projection system; if the TIR prism system is too thin, the light rays cannot fully irradiate the DMD mirror 4, affecting the resolution. For this reason, the following technical solutions are proposed in this embodiment: 1) The thickness of the first prism 1 is determined based on the incident angle of the illumination light.

[0029] 2) The thickness of the second prism 2 needs to avoid affecting the imaging contrast, so it is designed based on the upper-edge light of the DMD micromirror 4 in the open state.

[0030] 3) The thickness of the third prism 3 is determined based on the geometric relationship and the spacing from other prisms.

[0031] These designs ensure that the light beam can accurately enter the projection optical system and effectively improve the contrast of the optical system.

[0032] Specifically: Design of the thickness of the first prism 1: Design is carried out using the middle wavelength. Specifically: When the light emitted from the lower edge of the target surface of the DMD micromirror 4 hits the β3 surface of the first prism 1 and the total reflection light is exactly reflected to the upper edge A of the DMD micromirror 4, it is considered that this is the minimum value of the thickness of the first prism 1 at this time. The minimum value; Specifically: The thickness of the first prism 1 The minimum value is the distance between the intersection point of the central normal of the target surface of the DMD micromirror 4 and the β1 surface and the β3 surface. At this time, the thickness of the first prism 1 = 19.17 mm; The length of the DMD micromirror 4 = 17.5 mm; The angle between the central normal of the target surface of the DMD micromirror 4 and the normal of the incident light on the β3 surface is θ a , and θ a = θ1 = 20°. The angle between the central normal parallel axis of the target surface of the DMD micromirror 4 and the internally reflected light of the first prism 1 is θ b ; See specifically Figure 3 The partial enlarged schematic diagram of the thickness of the first prism 1 and the following derivation formula for the thickness of the first prism 1: According to the law of reflection: ; ; Since AH / / CB / / FE, so there is ; ; Then ; From ; It can be known that: ; Similarly, ; That is: ; Since + == , is the length of the hypotenuse of the DMD, then: ; That is, it is obtained: ; For △BDE, ; Then: ; Since ; ; Therefore, it is obtained that ; Substituting it in, we get: ; Since = + = + ; Then ; Substituting θ a = θ 1 = 20°, the included angle between the marginal ray entering the first prism 1 and the normal of the center of the target surface of the DMD mirror 4 °, = 17.5mm is substituted into the calculation, and we can get = 19.17mm.

[0033] Design of the thickness of the second prism 2: When the marginal ray emitted by the DMD mirror 4 is reflected by the β1 surface to the intersection of the λ1 surface and the λ3 surface of the second prism 2, then the thickness of the second prism 2 at this time is the minimum value; Specifically: The thickness of the second prism 2 at its minimum value is the distance between the normal of the center of the target surface of the DMD mirror 4 and the intersection of the λ1 surface and the λ3 surface. At this time, is 10.7124mm; the distance between the DMD mirror 4 and the first prism 1 is d, d = 5mm; the height difference between the incident point of the marginal ray emitted by the DMD mirror 4 reflected by the β1 surface and the intersection of the λ1 surface and the λ3 surface of the second prism 2 is y, y = 22.5504mm. At this time, the included angle between the normal of the center of the target surface of the DMD mirror 4 parallel to the axis and the internally reflected ray in the first prism 1 is θ b = 4.525°, for details, please refer to Figure 4 the schematic diagram of the thickness of the second prism 2 and the following derivation formula for the thickness of the second prism 2: The marginal ray emitted from the DMD mirror 4 just enters the second prism 2 along the line segment WP as shown in Figure 4 . At this time, the second prism 2 is regarded as having the minimum thickness: (1); Since in ΔRPQ, there is (2); in ΔRPT, there is (3); Therefore, for the marginal ray reflected by the DMD mirror 4 inside the first prism 1, the relative movement from the incident point W to the exit point P is = y , since in ΔSWPy Denoted as (4); In ΔSUP, there is (5); So (6); Therefore, in the formula Denoted as (7); Let the distance between the DMD and the prism be d , then it is denoted as (8); Combining formulas (1) - (3) gives Denoted as: (9); Combining formulas (4) - (8), given that the distance between the target surface of the DMD micromirror 4 and the prism d = 5mm, θ θ1 = 20°, L1 = 19.17mm, θ b θ2 = 4.525°, obtaining L2 = 22.5504mm, substituting it into formula (9) to obtain L3 = 10.7124mm.

[0034] Design of the thickness of the third prism 3 The thickness of the third prism 3 is the distance from the center normal of the target surface of the DMD micromirror 4 to the intersection point of the μ1 surface and the μ2 surface; The minimum value of the thickness of the third prism 3 is 7.4556mm, specifically refer to Figure 5 the schematic diagram of the thickness of the third prism 3 and the following derivation formula for the thickness of the third prism 3: For ΔZQX, there is ; where ∠QZX is the second prism angle θ θ2, given θ θ2 = 22.5°, L = d 0; ; d L0 is for cooperation with the projection system and to ensure that the illumination beam can completely exit from the μ2 surface, taking 18mm; Lmin = 7.4556mm; In actual processing, sufficient margins should be reserved for the thicknesses of the second prism 2 and the third prism 3. And the second prism 2 is mainly used to deflect the flat-state beam and the off-state beam, making the non-on-state beam away from the projection optical axis. Therefore, the thickness value of the second prism 2 should be rounded up. For the third prism 3 to ensure the rationality of alignment and adjustment, the thickness of the third prism 3 should be appropriately increased following the second prism 2. The following table shows the final design results of the TIR prism system. The overall thickness of the TIR prism system is 43.65mm. The first prism 1, the second prism 2, and the third prism 3 all use ZnS material; Table 1 Design Results of TIR Prism System

[0035] Verification: Use LightTools software to perform ray tracing simulation on the designed TIR prism system, establish the model of DMD mirror 4 and the model of the three-component TIR prism system, and respectively test the propagation direction of the outgoing light when DMD mirror 4 is in the on state, off state, and flat state. The test results are as Figures 6 - 8 shown in the figure. DMD mirror 4 is optically connected to the TIR prism system through window glass 5: Analyzing the test results, it can be known that in the on state: the outgoing light is parallel to the main optical axis of the TIR prism system and exits from the exit surface of the TIR prism system: μ2 surface into the projection system; the outgoing light in the off state and flat state exits to the outside from the same surface: λ3 surface, and will not produce stray light effects on the projection system.

[0036] Embodiment 2 On the basis of Embodiment 1, this embodiment further discloses a dual-channel common-aperture mid-wave infrared projection optical system; in this embodiment, a dual-channel common-aperture mid-wave infrared projection optical system should meet the following conditions during design: 1) The projection exit pupil of the overall system should be pupil-matched with the entrance pupil of the device under test to avoid the device under test receiving information outside the target scene. At the same time, the exit pupil distance should be long enough to reserve space for alignment and adjustment.

[0037] 2) During design, the overall system should leave enough back focal length, specifically the distance from the center of the target surface of DMD mirror 4 to the center of the first lens of the projection system, to meet the alignment and adjustment space of the TIR prism system used by each of the two optical paths and the shared beam-combining prism 6.

[0038] 3) The thermal expansion coefficient of the infrared lens material is larger than that of the visible light lens material, and it is more likely to cause image quality changes in usage scenarios with a large temperature change range. It is necessary to perform thermal design on the projection system. It is required that the imaging effect of this infrared projection system is not affected by temperature changes within the range of -40°C to +60°C.

[0039] Design Indexes of Projection System The design indexes of the projection system should give appropriate margins. The field of view selection should be slightly larger than that of the device under test. Taking the full field of view 2 ω =±4° as the design value, the projection exit pupil diameter DIt is set to 50 mm. The focal length of the projection system is determined by the field of view size and the target surface size of the DMD mirror 4. The selected DMD mirror 4 has a resolution of 1024 * 768, and the size of a single DMD mirror 4 is 13.68 μm * 13.68 μm. From this, the size of the DMD mirror 4 is calculated to be 14 mm * 10.5 mm, and the diagonal image height is H = 17.5 mm. According to the field of view image height relationship formula: ; The focal length f is obtained as 125.13 mm, and the relative aperture F / # From this, it can be obtained that: = 2.5; ω represents the field of view angle.

[0040] Through the above analysis, the design indicators of the projection optical system are determined as shown in Table 2: Table 2 Design Indicators of the Projection System

[0041] In order to meet the requirements of athermal design and make the projection system have good stability within -40 °C to +60 °C, the projection system design needs to meet the total optical power equation, the axial chromatic aberration correction equation, and the thermal aberration correction equation: ; ; ; In the formula, is the total optical power of the projection system; is the optical power of a single lens; is the lens dispersion factor; is the incident height of the paraxial ray on the surface; is the thermal expansion coefficient of the lens; is the linear expansion coefficient of the structural member; L is the total length of the projection system; i is the lens serial number.

[0042] Due to the limitations in the selection of infrared materials, in this embodiment, conventional infrared materials such as germanium, silicon, and zinc sulfide are used for design. The material of the beam combining prism 6 is zinc sulfide, and the DMD window glass is sapphire. During the design process of this embodiment, the influence of the spherical aberration caused by the beam combining prism 6, the first TIR prism system 14, the second TIR prism system 17, and the window glass on the projection system always needs to be considered. Therefore, these four components are brought into the projection system for optimization.

[0043] Design results of this embodiment: As Figure 9The projection system designed in this embodiment is specifically a dual-channel common-aperture mid-wave infrared projection optical system, including a first DMD micromirror 12, a first window glass 13, a first TIR prism system 14, a beam-combining prism 6, a first lens 7, a second lens 8, a third lens 9, a fourth lens 10, and a fifth lens 11 that are optically connected in sequence on the same axis to form a first DMD projection optical path; it further includes: a second DMD micromirror 15, a second window glass 16, and a second TIR prism system 17 that are optically connected in sequence on the same axis to form a second DMD projection optical path; and the normal line of the target surface center of the first DMD micromirror 12 and the normal line of the target surface center of the second DMD micromirror 15.

[0044] Both the first TIR prism system 14 and the second TIR prism system 17 adopt a TIR prism system as described in claim 7.

[0045] The materials of the first lens 7 and the third lens 9 are silicon; The materials of the second lens 8 and the fifth lens 11 are germanium; The material of the fourth lens 10 is zinc sulfide.

[0046] The first lens 7, the second lens 8, the third lens 9, the fourth lens 10, and the fifth lens 11 are all spherical lenses; and the optical powers of the first lens 7 and the second lens 8 are in a positive and negative combination to ensure the back intercept of the overall system and leave enough space for the first TIR prism system 14 and the beam-combining prism 6; The optical powers of the third lens 9, the fourth lens 10, and the fifth lens 11 are all positive, making the overall system have a large enough exit pupil diameter; the total length of the projection system is 266.12 mm.

[0047] The two optical systems are completely consistent in parameters. The following gives the specific data of the projection system with the first DMD projection optical path, as shown in Table 3. Since the reverse design idea is adopted in the design, the first surface of the projection system is the projection exit pupil.

[0048] Table 3 Data Sheet of the Design Results of the Projection System

[0049] Image Quality Analysis of the Projection System The idea of reverse design is to design the projection system according to the imaging optical path, and focus on analyzing the MTF performance of the optical system and the energy entering the diffraction circle within one pixel of the DMD mirror 4. These two parameters can reflect the contrast of the projected image. Distortion and astigmatism should be kept at an extremely low level to ensure that the projected image has no obvious deformation. The design focus of the projection system lies in its working stability under cold field environment, normal temperature environment and high temperature environment from -40°C to +60°C. Therefore, the above image quality evaluation indicators should not have obvious differences within the entire temperature range.

[0050] In order to ensure that the influence of temperature changes on the components of the projection system can be accurately simulated within the full temperature range, structural parts are set between components such as lenses. The thermal expansion coefficient of aluminum alloy is used to simulate the opto-mechanical structure of the aluminum alloy shell. At the same time, 4 characteristic temperature values are set: 20°C, -40°C and 60°C, and the imaging quality under four temperature states is analyzed. As shown in the figure, the MTF curves corresponding to different temperatures are given respectively as Figures 11 - 13 and the energy fraction entering the diffraction circle as Figures 14 - 16 .

[0051] From the above Figures 11 - 16 and the actual test results, it can be known that under each temperature state, the optical performance differences of the projection system are tiny. In the case of 60°C, the RMS radius of the spot diagram of the projection system is at most 2.59μm, and it is less than 2μm under the other two temperature states; the MTF curve does not decrease with the change of temperature, and the projection system can always maintain optical performance close to the diffraction limit under the temperature change from -40°C to +60°C; within the radius of the Airy disk, the energy fraction entering the diffraction circle exceeds 80%, and the maximum distortion of the projection system is less than 0.1%, indicating that the projection system is not affected by distortion.

[0052] Overall projection system test The simulation test results have been shown in Example 1, and the results show that the TIR prism system in Example 1 can effectively separate the on-state optical path and stray light. In the LightTools software, continue to import the designed projection system data and analyze and test the overall projection system introduced in Example 1.

[0053] Analyze the optical path when a DMD mirror 4 is in the on-state, flat-state and off-state respectively, and verify that it is consistent with Zemax, as Figures 17 - 19 respectively show the trend of the outgoing light when a DMD mirror is in the on-state, off-state and flat-state, which is similar to the simulation results in Example 1. When a DMD mirror 4 is in the on-state, the light passes smoothly through the TIR prism system and the beam combining prism 6 in Example 1 and enters the projection system; when a DMD mirror 4 is in the off-state and flat-state, no light enters the projection system. The results show that by aligning the projection system according to the design parameters, stray light can be suppressed, and excellent optical performance can be maintained within a wide temperature range.

[0054] Obviously, the above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or alterations can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. And the obvious changes or alterations derived therefrom still fall within the protection scope of the present invention.

Claims

1. A TIR prism system, characterized in that, It includes a first prism (1), a second prism (2) and a third prism (3) arranged in sequence; The first prism (1) is a pentaprism structure, and its side faces are in sequence: β1 face, β2 face, β3 face, β4 face and β5 face; Among them, the β1 face is arranged parallel to the DMD micromirror (4), and the β1 face is the incident face of the DMD micromirror (4); The first prism (1) and the third prism (3) are respectively arranged on the adjacent λ1 face and λ3 face in the second prism (2); and the β3 face is opposite to the λ1 face, the μ1 face of the third prism (3) is opposite to the λ3 face, an air gap is provided between the β3 face and the λ1 face and between the μ1 face and the λ3 face, and the three prisms are glued together by a glass splint from the overall outer side; Light is vertically incident on the β5 face and sequentially passes through the β5 face, the β3 face and the β1 face inside the first prism (1) and then is transmitted to the DMD micromirror (4); When the DMD micromirror (4) is in the on state, the reflected light undergoes total reflection, sequentially passes through the first prism (1), the second prism (2) and the third prism (3), and is emitted from the μ2 face of the third prism (3); When the DMD micromirror (4) is in the off state, the reflected light undergoes total reflection on the β1 face and sequentially passes through the first prism (1) and the second prism (2), and is emitted from the λ3 face of the second prism (2); When the DMD micromirror (4) is in the flat state, the reflected light undergoes total reflection on the β1 face and sequentially passes through the first prism (1) and the second prism (2), and is emitted from the λ3 face of the second prism (2).

2. The TIR prism system according to claim 1, wherein The first incident angle α1 of the incident light on the β3 face in the first prism (1) is greater than the critical angle; The third incident angle α3 of the light reflected from the DMD micromirror (4) to the β3 face is less than the critical angle; The incident angle of the light on the DMD mirror (4) from the β1 surface is θ DMD ; The second incident angle that is reflected by the β3 plane and then incident on the β1 plane ; ; The refractive index n1 is 2.251 ± 0.05, and the critical angle is 24.9° to 26.025°; the first prism angle θ1 is the included angle between the β3 plane and the parallel axis of the β1 plane, and its value is such that the marginal rays reflected by the DMD mirror (4) do not undergo total internal reflection. The specific expression is ; in the expression for the value range of the first prism angle θ1, after the marginal rays enter the first prism (1), the included angle with the principal optical axis becomes ; Positive is taken when the marginal ray is above the principal optical axis of the TIR prism system; negative is taken when the marginal ray is below the principal optical axis.

3. The TIR prism system according to claim 2, wherein The second prism (2) is a triangular prism structure; and the λ2 face of the second prism (2) is parallel to the β2 face of the first prism (1); The fourth incident angle α4 of the flat-state light beam and the off-state light beam incident on the λ3 face is greater than the critical angle; The incident angle of the on-state light beam incident on the λ3 face is less than the critical angle; The internal angle relationship of the second prism (2) is as follows: ; Where: after being reflected by the DMD mirror (4), the angle between the flat and off-state light beam and the target surface of the DMD mirror (4) is I, and I ≥ θ DMD ; The second prism angle θ2 is the angle between the λ3 plane and the parallel axis of the β1 plane, and its value satisfies .

4. A TIR prism system according to claim 3, wherein, The third prism (3) is a triangular prism structure; The widths of the λ3 face of the second prism (2) and the μ1 face of the third prism (3) are the same; The angle θ3 of the third prism (3) is equal to the angle θ2, where the angle θ2 is the included angle between the μ1 face and the μ2 face of the third prism (3).

5. A TIR prism system according to claim 4, characterized in that, When the light emitted from the lower edge of the target surface of the DMD mirror (4) hits the β3 surface and the total reflection light is exactly reflected onto the upper edge of the DMD mirror (4), it is the minimum value of the thickness of the first prism (1). ; Specifically: The thickness of the first prism (1) The minimum value is the distance from the normal line of the target surface center of the DMD mirror (4) to the intersection point of the β1 plane and the β3 plane. At this time, the thickness of the first prism (1) = 19.17 mm; The length of the DMD mirror (4) = 17.5 mm; The included angle between the normal line of the target surface center of the DMD mirror (4) and the normal line of the incident light on the β3 plane is θ a , and θ a = θ1 = 20°.

6. The TIR prism system according to claim 5, characterized in that, When the marginal ray emitted by the DMD mirror (4) is reflected by the β1 surface to the intersection of the λ1 surface and the λ3 surface of the second prism (2), the thickness of the second prism (2) is at the minimum value; Specifically: the thickness of the second prism (2) The minimum value is the distance from the normal line at the center of the target surface of the DMD mirror (4) to the intersection point of the λ1 plane and the λ3 plane. At this time it is 10.7124 mm; the distance between the DMD mirror (4) and the first prism (1) is d, and d = 5 mm; the height difference between the incident point where the marginal ray emitted by the DMD mirror (4) is reflected onto the β1 plane and the intersection point of the λ1 plane and the λ3 plane of the second prism (2) is y, and y = 22.5504 mm. At this time, the angle between the normal line at the center of the target surface of the DMD mirror (4) parallel to the axis and the internally reflected ray in the first prism (1) is θ b , and θ b = 4.525°.

7. A TIR prism system according to claim 6, wherein Thickness of the third prism (3) is the distance between the normal at the center of the target surface of the DMD mirror (4) and the intersection point of the μ1 plane and the μ2 plane; thickness of the third prism (3) has a minimum value of 7.4556 mm; The overall thickness of the TIR prism is 43.65 mm, and the first prism (1), the second prism (2) and the third prism (3) are all made of ZnS material.

8. A dual-channel common-aperture mid-wave infrared projection optical system, characterized in that, It includes a first DMD micromirror (12), a first window glass (13), a first TIR prism system (14), a beam combining prism (6), a first lens (7), a second lens (8), a third lens (9), a fourth lens (10) and a fifth lens (11) that are sequentially optically connected on the same axis; it also includes: a second DMD micromirror (15), a second window glass (16) and a second TIR prism system (17) that are sequentially optically connected on the same axis; and the central normal of the target surface of the first DMD micromirror (12) is perpendicular to the central normal of the target surface of the second DMD micromirror (15); Both the first TIR prism system (14) and the second TIR prism system (17) adopt a TIR prism system as described in claim 7.

9. The dual-channel common-aperture mid-wave infrared projection optical system according to claim 8, wherein, The materials of the first lens (7) and the third lens (9) are silicon; The materials of the second lens (8) and the fifth lens (11) are germanium; The material of the fourth lens (10) is zinc sulfide.

10. A dual-channel common-aperture mid-wave infrared projection optical system according to claim 8, characterized in that, The first lens (7), the second lens (8), the third lens (9), the fourth lens (10), and the fifth lens (11) are all spherical lenses; and the optical powers of the first lens (7) and the second lens (8) are of positive and negative combination type; The optical powers of the third lens (9), the fourth lens (10), and the fifth lens (11) are all positive.

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