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

Abstract

The present invention relates to the field of infrared target simulation technology, and specifically to a TIR prism system and a dual-channel co-aperture medium-wave infrared projection optical system. One type of TIR prism system includes a first prism, a second prism, and a third prism arranged in sequence. The side surfaces of the first prism are sequentially: a β1 surface, a β2 surface, a β3 surface, a β4 surface, and a β5 surface. The β1 surface is arranged parallel to a DMD micromirror. The first prism and the third prism are arranged on adjacent λ1 and λ3 surfaces of the second prism, respectively. The β3 surface is opposite to the λ1 surface, and the μ1 surface of the third prism is opposite to the λ3 surface. Air gaps are provided between the β3 surface and the λ1 surface, and between the μ1 surface and the λ3 surface. The three prisms are glued together from the outer side surfaces of the whole by glass sandwich panels. The present invention achieves complete isolation of the off-state and flat-state light beams of the DMD micromirror without providing any light-blocking devices. At the same time, it solves the problem that traditional methods are difficult to adapt to large-scale temperature changes.

Description

Technical Field

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

[0002] Existing infrared target simulation systems mainly include three core components: the illumination system, the scene generation device, and the projection system. The key component connecting the illumination and projection systems is the TIR prism. Existing technologies often use a two-component TIR prism to separate the projection optical axis and the illumination optical axis to achieve overall system miniaturization. However, the maximum angle between the effective on-state beam, the invalid off-state beam, and the invalid flat-state beam reflected by the DMD micromirror is only 24°. The TIR prism can only effectively isolate the invalid off-state beam, and the invalid flat-state beam still requires external light shielding for auxiliary suppression. Therefore, it is inevitable that invalid beams will enter the projection system as stray light, reducing the imaging quality and performance of the projection system.

[0003] Furthermore, the infrared lens materials used in projection systems are highly susceptible to temperature changes, causing deformation, which in turn degrades the system's optical performance. This thermally induced deformation can lead to complete distortion of the target scene, particularly when simulating high-dynamic-range scenes. Therefore, the entire system is typically placed in a cold environment during use to mitigate the effects of the components' own thermal radiation. However, simply placing the projection system at low temperatures can degrade its optical performance. Consequently, those skilled in the art have proposed various athermalization designs. Among these, a new generation of optical passive athermalization designs, based on their superior performance, achieves temperature compensation through the combination of optical and structural materials, becoming the preferred approach for athermalization of optical systems. However, in practical applications, such as in the Chinese patent application CN110031958A, entitled "An Improved Three-Component TIR Prism," while athermalization can be partially achieved through material selection and structural design, in some cases, it is still difficult to completely eliminate the effects of temperature changes on the optical system.

[0004] Based on this, technicians in this field urgently need to further improve the TIR prism to better adapt it to the medium-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, thereby providing a TIR prism system and a dual-channel co-aperture medium-wave infrared projection optical system.

[0006] A TIR prism system includes a first prism, a second prism, and a third prism arranged in sequence;

[0007] The first prism is a pentaprism structure, and the side surfaces are: β1 surface, β2 surface, β3 surface, β4 surface and β5 surface;

[0008] Among them, the β1 surface is arranged parallel to the DMD micromirror, and the β1 surface is the incident surface of the DMD micromirror;

[0009] The first prism and the third prism are arranged on the adjacent λ1 and λ3 surfaces of the second prism, respectively; the β3 surface is opposite to the λ1 surface, and the μ1 surface of the third prism is opposite to the λ3 surface. Air gaps are provided between the β3 surface and the λ1 surface, and between the μ1 surface and the λ3 surface. The three prisms are glued together from the outer side of the whole by a glass sandwich panel;

[0010] The light is incident vertically on the β5 surface and passes through the β5 surface, β3 surface and β1 surface in the first prism before being transmitted to the DMD micromirror.

[0011] When the DMD micromirror is in the on state, the reflected light undergoes total internal reflection, passes through the first prism, the second prism, and the third prism in sequence, and is emitted from the μ2 surface of the third prism;

[0012] When the DMD micromirror is in the off state, the reflected light is fully reflected at the β1 surface, passes through the first prism and the second prism in sequence, and is emitted from the λ3 surface of the second prism;

[0013] When the DMD micromirror is in a flat state, the reflected light is fully reflected at the β1 surface, passes through the first prism and the second prism in sequence, and is emitted from the λ3 surface of the second prism.

[0014] Preferably, the first incident angle of the incident light on the β3 surface in the first prism is Greater than the critical angle;

[0015] The light is reflected by the DMD micromirror to the third incident angle of the β3 surface Less than the critical angle;

[0016] The incident angle of the light incident on the DMD micromirror from the β1 surface is ;

[0017] The second incident angle after being reflected from the β3 surface and incident on the β1 surface ; ;

[0018] Refractive index is 2.251±0.05, the critical angle is 24.9°~26.025°; the first prism angle is the angle between the β3 plane and the parallel axis of the β1 plane, and the value is selected so that the edge light reflected by the DMD micromirror does not undergo total reflection. The specific expression is: ; at the first prism angle In the angle value expression, the angle between the marginal light and the main optical axis after entering the first prism becomes ; When the marginal light is above the principal optical axis of the TIR prism system, it is positive; when the marginal light is below the principal optical axis, it is negative.

[0019] Preferably, the second prism is a triangular prism structure; and the λ2 surface of the second prism is parallel to the β2 surface of the first prism;

[0020] The fourth incident angle of the flat beam and the off-state beam incident on the λ3 surface Greater than the critical angle;

[0021] The incident angle of the open-state light beam incident on the λ3 surface is less than the critical angle;

[0022] The internal angle relationship of the second prism is: ;

[0023] Where: After being reflected by the DMD micromirror, the angle between the flat and off state light beams and the DMD micromirror target surface is , ; Second prism angle is the angle between the λ3 plane and the β1 plane parallel axis, and its value satisfies .

[0024] Preferably, the third prism is a triangular prism structure;

[0025] The λ3 surface of the second prism and the μ1 surface of the third prism have the same width;

[0026] Third prism angle The angle between the μ1 and μ2 faces of the third prism and the angle of the second prism equal.

[0027] Preferably, when the light emitted from the lower edge of the DMD micromirror target surface hits the β3 surface and the total reflected light is reflected to the upper edge of the DMD micromirror, the minimum value of the thickness of the first prism is ;

[0028] Specifically: the thickness of the first prism The minimum value is the distance between the center normal of the DMD micromirror target surface and the intersection of the β1 surface and the β3 surface. At this time, the thickness of the first prism is =19.17mm; DMD micromirror length =17.5mm; the angle between the normal line of the center of the DMD micromirror target surface and the normal line of the incident light on the β3 surface is ,and .

[0029] Preferably, when the edge light emitted by the DMD micromirror is reflected from the β1 surface to the intersection of the λ1 surface and the λ3 surface of the second prism, the thickness of the second prism is is the minimum value;

[0030] Specifically: the thickness of the second prism The minimum value is the distance between the center normal of the DMD micromirror target surface and the intersection of the λ1 surface and the λ3 surface. =10.7124mm; the distance between the DMD micromirror and the first prism is d, d=5mm; the incident point of the edge light emitted by the DMD micromirror reflected to the β1 surface and the intersection of the λ1 surface and λ3 surface of the second prism are at a height of y, y=22.5504mm. At this time, the angle between the axis parallel to the center normal of the DMD micromirror target surface and the reflected light from the first prism is ,and =4.525°.

[0031] Preferably, the thickness of the third prism is is the distance between the center normal of the DMD micromirror target surface and the intersection of μ1 surface and μ2 surface; the thickness of the third prism The minimum value is 7.4556mm;

[0032] 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.

[0033] A dual-channel common-aperture medium-wave infrared projection optical system comprises 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, all optically connected in sequence on the same axis; and further comprises a second DMD micromirror, a second window glass, and a second TIR prism system, all optically connected in sequence on the same axis; a target surface center normal of the first DMD micromirror is perpendicular to a target surface center normal of the second DMD micromirror;

[0034] The first TIR prism system and the second TIR prism system both adopt a TIR prism system.

[0035] Preferably, the material of the first lens and the third lens is silicon;

[0036] The second and fifth lenses are made of germanium.

[0037] The material of the fourth lens is zinc sulfide.

[0038] Preferably, the first lens, the second lens, the third lens, the fourth lens and the fifth lens are all spherical lenses; and the optical power of the first lens and the second lens is a combination of positive and negative;

[0039] The third lens, the fourth lens and the fifth lens all have positive refractive powers.

[0040] The technical solution of the present invention has the following advantages:

[0041] The present invention provides a three-component TIR prism system that completely isolates the off-state and flat-state beams of the DMD micromirrors without requiring any light-blocking devices. It also addresses the difficulty of medium-wave infrared projection optical systems in adapting to wide temperature fluctuations. The projection system is athermalized, maintaining excellent projection quality within a temperature range of -40°C to +60°C, enabling the projection system to consistently project high-precision infrared images. Two DMD micromirrors are connected to the same projection system via a beam-combining prism, with the optical performance of their respective optical paths completely consistent. The three-component TIR prisms, operating between the DMD micromirrors and the projection system, can be treated as parallel plates of equal thickness. Ultimately, the optical performance of the medium-wave infrared projection optical system approaches the diffraction limit, with an MTF curve exceeding 0.48 at 37 lp / mm and a maximum distortion of less than 0.1%. The dual-channel, co-aperture medium-wave infrared projection optical system layout is advantageous for use in scenarios requiring high integration. The joint modulation of the two DMD micromirrors has the potential to generate high-contrast, high-bit-depth simulated infrared scene images. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0043] Figure 1 Schematic diagram of the design of relevant angles within the first prism of the present invention;

[0044] Figure 2 Schematic diagram of the design of relevant angles within the second prism and the third prism of the present invention;

[0045] Figure 3 This is a design diagram of the thickness of the first prism of the present invention;

[0046] Figure 4 This is a design diagram of the thickness of the second prism of the present invention;

[0047] Figure 5 This is a thickness design diagram of the third prism of the present invention;

[0048] Figure 6 Schematic diagram of verification test results of the DMD micromirror in the on state according to Example 1 of the present invention;

[0049] Figure 7 Schematic diagram of verification test results of the DMD micromirror in the off state according to Example 1 of the present invention;

[0050] Figure 8Schematic diagram of verification test results of the DMD micromirror in a flat state according to Example 1 of the present invention;

[0051] Figure 9 This is a schematic diagram of the three-dimensional structure of a dual-channel common-aperture medium-wave infrared projection optical system of the present invention;

[0052] Figure 10 This is a schematic diagram of the design results of a dual-channel common-aperture medium-wave infrared projection optical system of the present invention;

[0053] Figure 11 This is the MTF curve of the system in Example 2 at 20°C;

[0054] Figure 12 This is the MTF curve of the system in Example 2 at -40°C;

[0055] Figure 13 This is the MTF curve of the system in Example 2 at 60°C;

[0056] Figure 14 The diffraction circle energy fraction diagram of the system in Example 2 at 20°C;

[0057] Figure 15 This is a diffraction circle energy fraction diagram of the system in Example 2 at -40°C;

[0058] Figure 16 The diffraction circle energy fraction diagram of the system in Example 2 at 60°C;

[0059] Figure 17 This is a light path diagram of the system in Example 2 when two DMD micromirrors are in the on state;

[0060] Figure 18 This is a light path diagram of the system in Example 2 when the two DMD micromirrors are in the off state;

[0061] Figure 19 This is the optical path diagram of the system in Example 2 when the two DMD micromirrors are in a flat state.

[0062] Description of reference numerals:

[0063] 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, S2-fifth exit sphere, S3-fifth incident sphere, S4-fourth exit sphere, S5-fourth incident sphere, S6-third exit sphere 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 incident, 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 DESCRIPTION

[0064] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0065] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0066] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0067] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0068] Example 1

[0069] A TIR prism system includes a first prism 1, a second prism 2, and a third prism 3 arranged in sequence;

[0070] The first prism 1 is a pentaprism structure, and the side surfaces are: β1 surface, β2 surface, β3 surface, β4 surface and β5 surface;

[0071] The second prism 2 is a triangular prism structure, and the side surfaces are: λ1 surface, λ2 surface and λ3 surface;

[0072] The third prism 3 is a triangular prism structure, and the side surfaces are: μ1 surface, μ2 surface and μ3 surface;

[0073] Wherein, the β1 surface is arranged parallel to the DMD micromirror 4, and the β1 surface is the incident surface of the DMD micromirror 4;

[0074] The first prism 1 and the third prism 3 are arranged on the adjacent λ1 and λ3 surfaces of the second prism 2, respectively; the β3 surface is opposite to the λ1 surface, and the μ1 surface of the third prism 3 is opposite to the λ3 surface. Air gaps are provided between the β3 surface and the λ1 surface, and between the μ1 surface and the λ3 surface. The three prisms are glued together from the outer side of the whole by glass sandwich panels;

[0075] The light is incident vertically on the β5 surface and passes through the β5 surface, β3 surface and β1 surface in the first prism 1 before being transmitted to the DMD micromirror 4;

[0076] When the DMD micromirror 4 is in the on state, the reflected light undergoes total internal reflection, passes through the first prism 1, the second prism 2 and the third prism 3 in sequence, and is emitted from the μ2 surface of the third prism 3;

[0077] When the DMD micromirror 4 is in the off state, the reflected light is fully reflected at the β1 surface, passes through the first prism 1 and the second prism 2 in sequence, and is emitted from the λ3 surface of the second prism 2;

[0078] When the DMD micromirror 4 is in a flat state, the reflected light is totally reflected at the β1 surface, passes through the first prism 1 and the second prism 2 in sequence, and is emitted from the λ3 surface of the second prism 2.

[0079] Specifically:

[0080] About the design of the first prism 1:

[0081] Main purpose: Since the first prism 1 of this embodiment is used in a dual-channel common aperture medium-wave infrared projection optical system, the main purpose of the first prism 1 is to evenly illuminate the DMD micromirror 4 with the light beam emitted by the illumination system. The design requires the first prism angle The following conditions are met:

[0082] The first incident angle of the incident light on the β3 surface in the first prism 1 Greater than the critical angle;

[0083] The light is reflected by DMD micromirror 4 to the third incident angle of β3 surface Less than the critical angle;

[0084] The incident angle of the light incident on the DMD micromirror 4 from the β1 surface is , The value is a pre-specified value;

[0085] like Figure 1 The incident illumination light enters the first prism 1 perpendicular to the β5 surface. To ensure that the illumination beam The illumination light hits the target surface of DMD micromirror 4, and then passes through β5 surface, β3 surface and β1 surface in the first prism 1 and then transmits to DMD micromirror 4. The total reflection incident angle at β3 surface is the first incident angle. , and shoots towards the target surface of DMD micromirror 4, and then enters the air after being emitted from the surface of β1, and Hitting the target surface of DMD micromirror 4, according to the relationship between the internal angles of the triangle, it can be seen that the angles in the first prism 1 should satisfy: ;

[0086] According to Snell's refraction law, the second incident angle after being reflected from the β3 surface and incident on the β1 surface is The first prism 1 is made of chalcogenide glass ZnS, which is more common in the mid-infrared band. Its refractive index is is 2.251±0.05, and the critical angle is 24.9°~26.025°;

[0087] First prism angle is the angle between the β3 plane and the axis parallel to the β1 plane;

[0088] Furthermore, since the light beam emitted from the surface of the DMD micromirror 4 has a light cone angle of 12°, and considering factors such as spectroscopic accuracy and processing errors, the light cone angle is set to 10° during design in this embodiment. Therefore, the value of the first prism angle θ1 should also be such that the marginal light reflected by the DMD micromirror 4 does not undergo total internal reflection. In fact, the marginal light emitted from the target surface of the DMD micromirror 4 along the main optical axis of the TIR prism system will not undergo total internal reflection on the surface of the first prism 1 after being deflected up and down by 10°.

[0089] First prism angle The specific expression for the value is ; at the first prism angle In the angle value expression, the angle between the marginal light and the main optical axis after entering the first prism 1 becomes ; When the marginal ray is above the main optical axis, it is positive; when the marginal ray is below the main optical axis, it is negative. Angle value expression to obtain the first prism angle The maximum value is 20.6°, so the first prism angle Take 20°, then the first incident angle The solution is 32.55°~33.13° which is greater than the critical value, and the third incident angle The solution is 24.328°~24.5251°, which is less than the critical angle and meets the above requirements.

[0090] About the design of the second prism 2:

[0091] The λ2 surface of the second prism 2 is parallel to the β2 surface of the first prism 1;

[0092] The main purpose is to modulate the light beam in the flat and off states of the DMD micromirror 4, where the λ3 surface is responsible for modulating the light beam, so the second prism angle of the second prism 2 is designed. The following conditions are met:

[0093] The fourth incident angle of the flat beam and the off-state beam incident on the λ3 surface Greater than the critical angle;

[0094] The incident angle of the open-state light beam incident on the λ3 surface is less than the critical angle;

[0095] Specifically:

[0096] First, to ensure that the open state light beam can be transmitted from the inside of the second prism 2, the second prism angle should be smaller than the critical angle ;like Figure 2 Second prism angle is the angle between the λ3 plane and the β1 plane parallel axis;

[0097] Secondly, after being reflected by the DMD micromirror 4, the angle between the flat and off state light beams and the target surface of the DMD micromirror 4 is I. According to the diffraction characteristics of the DMD micromirror 4, , through the triangle geometry and Snell's law, we know that the internal angle relationship of the second prism 2 is:

[0098] ; Let the second prism angle Take the value 22.5°, then =30.7061° is greater than the critical angle and meets the above requirements.

[0099] About the design of the third prism 3:

[0100] The third prism 3 is a triangular prism structure; the λ3 surface of the second prism 2 and the μ1 surface of the third prism 3 have the same width;

[0101] Main purpose: to ensure that the main light of the TIR prism system is parallel to the optical axis of the DMD micromirror 4, so that Figure 4 Third prism angle The angle between the μ1 and μ2 faces of the third prism 3 and the angle of the second prism equal.

[0102] About thickness design:

[0103] If 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 will not be able to fully illuminate the DMD micromirror 4, affecting the resolution. To this end, the following technical solutions are proposed in this embodiment:

[0104] 1) The thickness of the first prism 1 is determined based on the incident angle of the illumination light.

[0105] 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 on state.

[0106] 3) The thickness of the third prism 3 is determined based on the geometric relationship and the spacing between other prisms.

[0107] These designs ensure that the light beam can accurately enter the projection optical system and effectively improve the contrast of the optical system.

[0108] Specifically:

[0109] The thickness design of the first prism 1 is designed using the middle wavelength. Specifically, when the light emitted from the lower edge of the DMD micromirror 4 target surface is When the total reflected light hits the β3 surface of the first prism 1, it is considered that the thickness of the first prism 1 is The minimum value of

[0110] Specifically: the thickness of the first prism 1 The minimum value is the distance between the center normal of the DMD micromirror 4 target surface and the intersection of the β1 surface and the β3 surface. At this time, the thickness of the first prism 1 is =19.17mm; DMD micromirror 4 length =17.5mm; the angle between the normal line of the center of the DMD micromirror 4 target surface and the normal line of the incident light on the β3 surface is ,and The angle between the parallel axis of the center normal of the DMD micromirror 4 target surface and the reflected light of the first prism 1 is: ; For details, see Figure 3 A partially enlarged schematic diagram of the thickness of the first prism 1 and the following formula for deducing the thickness of the first prism 1:

[0111] According to the law of reflection: ; ;

[0112] Since AH / / CB / / FE, we have ; ;

[0113] but ;

[0114] Depend on ; It can be seen that: ;

[0115] same, ;

[0116] Right now: ; Because +== , is the length of the hypotenuse of DMD, then:

[0117] ; That is: ;

[0118] For △BDE, ;but: ;because ; ;

[0119] Therefore, we obtain ;

[0120] Will bring in: ;

[0121] because = + = + ;

[0122] but ;

[0123] Will θ a = θ 1=20°, the angle between the edge light entering the first prism 1 and the center normal of the DMD micromirror 4 target surface , =17.5mm into the calculation to get =19.17mm.

[0124] The thickness design of the second prism 2: When the edge light emitted by the DMD micromirror 4 is reflected from 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 is the minimum value;

[0125] Specifically: the thickness of the second prism 2 The minimum value is the distance between the center normal of DMD micromirror 4 target surface and the intersection of λ1 surface and λ3 surface. =10.7124mm; the distance between DMD micromirror 4 and the first prism 1 is d, d=5mm; the incident point of the edge light emitted by DMD micromirror 4 reflected to the β1 surface and the intersection of the λ1 surface and λ3 surface of the second prism 2 are at a height of y, y=22.5504mm. At this time, the angle between the axis parallel to the center normal of the target surface of DMD micromirror 4 and the reflected light of the first prism 1 is =4.525°, see Figure 4 Schematic diagram of the thickness of the second prism 2 and the following formula for deducing the thickness of the second prism 2:

[0126] The edge light emitted from the DMD micromirror 4 is exactly along the Figure 4 The line segment WP shown enters the second prism 2, at which point the second prism 2 is considered to have the minimum thickness: (1);

[0127] Since in ΔRPQ there is (2) In ΔRPT, there is (3);

[0128] Therefore, the lower edge light reflected by the DMD micromirror 4 inside the first prism 1 moves relatively from the incident point W to the exit point P. = y , since in ΔSWP y Expressed as (4); In ΔSUP there is (5); so (6); Therefore, Expressed as (7);

[0129] Let the distance between DMD and prism be d , then it is expressed as, (8);

[0130] Combining formulas (1) to (3), we can get Expressed as: (9);

[0131] Combining formulas (4) to (8), it is known that the distance between the DMD micromirror 4 target surface and the prism is d =5mm, =20°, 19.17mm, =4.525°, we get 22.5504 mm, which is substituted into formula (9) to obtain =10.7124mm.

[0132] The third prism 3 thickness design The third prism 3 thickness is the distance between the center normal of the DMD micromirror 4 target surface and the intersection of μ1 surface and μ2 surface; the thickness of the third prism 3 The minimum value is 7.4556mm. For details, see Figure 5 Schematic diagram of the thickness of the third prism 3 and the following formula for the thickness of the third prism 3:

[0133] For ΔZQX, we have ; where ∠QZX is the second prism angle θ 2. Known =22.5°, = d 0; ;

[0134] d 0 is to cooperate with the projection system and ensure that the illumination beam can be completely emitted from the μ2 surface, which is 18mm; =7.4556mm;

[0135] In actual processing, the thickness of the second prism 2 and the third prism 3 should be kept with sufficient margin, and the second prism 2 is mainly used to fold the flat state light beam and the off state light beam, so that the non-on state light beam is away from the projection optical axis, so the thickness of the second prism 2 The value should be taken upwards. To ensure the rationality of the third prism 3, the thickness of the third prism 3 should be appropriately increased following the second prism 2. The following table shows the final TIR prism system design results. The total thickness of the TIR prism system is 43.65mm. The first prism 1, the second prism 2 and the third prism 3 are all made of ZnS material.

[0136] Table 1 TIR prism system design results

[0137]

[0138] verify:

[0139] LightTools software is used to perform ray tracing simulation on the designed TIR prism system, and the model of DMD micromirror 4 and the three-component TIR prism system model are established. The propagation direction of the emitted light when the DMD micromirror 4 is in the on state, off state and flat state is tested respectively. The test results are as follows: Figure 6-8As shown in the figure, the DMD micromirror 4 is connected to the TIR prism system optical path through the window glass 5: Analysis of the test results shows that in the on state: the outgoing light is parallel to the main optical axis of the TIR prism system and enters the projection system through the TIR prism system exit surface: μ2 surface; the outgoing light in the off state and the flat state is emitted to the outside world through the same surface: λ3 surface, which will not cause stray light to the projection system.

[0140] Example 2

[0141] Based on Example 1, this example further discloses a dual-channel common-aperture medium-wave infrared projection optical system. In this example, the design of a dual-channel common-aperture medium-wave infrared projection optical system must meet the following conditions:

[0142] 1) The projection exit pupil of the entire system must match the entrance pupil of the device under test to prevent the device from receiving information outside the target scene. At the same time, the exit pupil distance must be long enough to reserve space for installation and adjustment.

[0143] 2) During the design process, the overall system must leave enough back intercept distance, specifically the distance from the center of the DMD micromirror 4 target surface to the center of the first lens of the projection system, to meet the adjustment space for the TIR prism systems used by the two optical paths and the shared beam combining prism 6.

[0144] 3) The thermal expansion coefficient of infrared lens materials is larger than that of visible light lens materials, which is more likely to cause changes in image quality in usage scenarios with a large temperature change range. It is necessary to perform physical thermal design on the projection system. The infrared projection system is required to be within the range of -40℃~+60℃, and the imaging effect is not affected by temperature changes.

[0145] Design indicators of projection system

[0146] The design indicators of the projection system should give appropriate margins, and the field of view should be slightly larger than the device under test, with a full field of view of 2 ω =±4° is the design value, projection pupil diameter D The focal length of the projection system is determined by the field of view and the target size of the DMD micromirror 4. The resolution of the selected DMD micromirror 4 is 1024*768, and the size of a single DMD micromirror 4 is 13.68μm*13.68μm. Based on this, the size of the DMD micromirror 4 is calculated to be 14mm*10.5mm, and the diagonal image height is H =17.5mm, according to the field of view image height relationship formula: ;

[0147] Get the focal length f The value is 125.13mm, the relative aperture F / # From this we can get: =2.5; ω represents the field of view.

[0148] After the above analysis, the design indicators of the projection optical system are determined as shown in Table 2:

[0149] Table 2 Design indicators of projection system

[0150]

[0151] In order to meet the requirements of athermal design and ensure good stability of the projection system within the temperature range of -40℃~+60℃, the projection system design must satisfy the total optical power equation, the axial chromatic aberration elimination equation, and the athermal difference elimination equation: ; ; Where, 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 component; L is the total length of the projection system; i is the lens number.

[0152] Due to the limitations of infrared material selection, this embodiment is designed using conventional infrared materials such as germanium, silicon, and zinc sulfide. The beam-combining prism 6 is made of zinc sulfide, and the DMD window glass is made of 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 must always be considered. Therefore, these four components are introduced into the projection system for optimization.

[0153] The design results of this embodiment are as follows:

[0154] like Figure 9 The projection system designed in this embodiment is specifically a dual-channel common-aperture medium-wave infrared projection optical system, including a first DMD projection optical path composed of 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 optically connected in sequence on the same axis; and also including: a second DMD projection optical path composed of a second DMD micromirror 15, a second window glass 16 and a second TIR prism system 17 optically connected in sequence on the same axis; and the target surface center normal of the first DMD micromirror 12 is the same as the target surface center normal of the second DMD micromirror 15.

[0155] The first TIR prism system 14 and the second TIR prism system 17 each employ a TIR prism system.

[0156] The material of the first lens 7 and the third lens 9 is silicon;

[0157] The second lens 8 and the fifth lens 11 are made of germanium;

[0158] The fourth lens 10 is made of zinc sulfide.

[0159] 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. The first lens 7 and the second lens 8 have a positive and negative power combination, which ensures the back focus of the overall system and leaves enough space for the first TIR prism system 14 and the beam combining prism 6.

[0160] The third lens 9, the fourth lens 10 and the fifth lens 11 all have positive optical powers, so that the entire system has a sufficiently large exit pupil diameter; the total length of the projection system is 266.12 mm.

[0161] The parameters of the two optical systems are exactly the same. The specific data of the projection system are given below based on the first DMD projection optical path, as shown in Table 3. Since the reverse design concept is adopted during the design, the first surface of the projection system is the projection exit pupil.

[0162] Table 3 Projection system design results data table

[0163]

[0164] Projection system image quality analysis

[0165] The reverse engineering approach involves designing the projection system based on the imaging optical path, focusing on analyzing the optical system's MTF performance and the diffraction energy within each pixel of the DMD micromirror. These two parameters reflect the contrast of the projected image. Distortion and astigmatism must be kept to extremely low levels to ensure no noticeable distortion of the projected image. The design of the projection system focuses on operational stability in cold, room, and high-temperature environments, from -40°C to +60°C. Therefore, the aforementioned image quality evaluation indicators should not vary significantly across the entire temperature range.

[0166] In order to ensure that the temperature changes of projection system components can be accurately simulated in the entire temperature range, the thermal expansion coefficient of the aluminum alloy of the structural parts is set between the lens and other components to simulate the optical and mechanical structure of the aluminum alloy shell. At the same time, four characteristic temperature values ​​are set: 20℃, -40℃ and 60℃, and the imaging quality under four temperature conditions is analyzed. The MTF curves corresponding to different temperatures are shown in the figure. Figure 11-13 and the diffraction circle energy fraction as Figure 14-16 .

[0167] From above Figure 11-16Actual test results show that the optical performance of the projection system varies slightly under various temperature conditions. At 60°C, the maximum RMS radius of the projection system's point diagram is 2.59μm, and less than 2μm at the other two temperature conditions. The MTF curve does not decrease with temperature changes, and the projection system can always maintain optical performance close to the diffraction limit when the temperature changes from -40°C to +60°C. Within the Airy disk radius, the diffraction circle energy fraction 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.

[0168] Overall projection system test

[0169] The simulation test results have been demonstrated in Example 1. The results show that the TIR prism system of Example 1 can effectively separate the off-state light path and stray light. The designed projection system data is further imported into the LightTools software to analyze and test the entire projection system introduced in Example 1.

[0170] The optical path is analyzed when a DMD micromirror 4 is in the on state, flat state and off state respectively, and it is verified that it is consistent with Zemax, such as Figure 17-19 The simulation results show the behavior of emitted light when a DMD micromirror is in the on, off, and neutral states. Similar to the simulation results in Example 1, when a DMD micromirror 4 is in the on state, light smoothly passes through the TIR prism system and beam-combining prism 6 of Example 1 and enters the projection system. When a DMD micromirror 4 is in the off and neutral states, no light enters the projection system. These results demonstrate that, when the projection system is adjusted according to the design parameters, stray light is suppressed and excellent optical performance is maintained over a wide temperature range.

[0171] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A TIR prism system, characterized in that: It comprises a first prism (1), a second prism (2) and a third prism (3) which are arranged in sequence; The first prism (1) is a pentaprism structure, and the side surfaces are: β1 surface, β2 surface, β3 surface, β4 surface and β5 surface; Wherein, the β1 surface is arranged parallel to the DMD micromirror (4), and the β1 surface is the incident surface of the DMD micromirror (4); The first prism (1) and the third prism (3) are arranged on adjacent λ1 surfaces and λ3 surfaces of the second prism (2), respectively; 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 from the outer side of the whole by a glass sandwich panel; The light is vertically incident on the β5 surface and passes through the β5 surface, the β3 surface and the β1 surface in sequence inside the first prism (1) before being transmitted to the DMD micromirror (4); When the DMD micromirror (4) is in an on state, the reflected light undergoes total internal reflection, passes through the first prism (1), the second prism (2), and the third prism (3) in sequence, and is emitted from the μ2 surface of the third prism (3); When the DMD micromirror (4) is in an off state, the reflected light is fully reflected at the β1 surface, passes through the first prism (1) and the second prism (2) in sequence, and is emitted from the λ3 surface of the second prism (2); When the DMD micromirror (4) is in a flat state, the reflected light is fully reflected at the β1 surface, passes through the first prism (1) and the second prism (2) in sequence, and is emitted from the λ3 surface 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 angle between the λ3 surface and the axis parallel to the β1 surface is obtained according to the diffraction characteristics: the angle of the second prism ; The fourth incident angle of the flat beam and the off-state beam incident on the λ3 surface =30.7061°.

2. A TIR prism system according to claim 1, characterized in that: The first incident angle of the incident light on the β3 surface in the first prism (1) Greater than the critical angle; The light is reflected by the DMD micromirror (4) to the third incident angle of the β3 surface Less than the critical angle; The incident angle of the light incident on the DMD micromirror (4) from the β1 surface is ; The second incident angle after being reflected from the β3 surface and incident on the β1 surface ; ; Refractive index is 2.251±0.05, the critical angle is 24.9°~26.025°; the first prism angle is the angle between the β3 plane and the parallel axis of the β1 plane, and the value is such that the edge light reflected by the DMD micromirror (4) does not undergo total reflection. The specific expression is: ; at the first prism angle In the angle value expression, the angle between the marginal light and the main optical axis after entering the first prism (1) becomes ; When the marginal light is above the principal optical axis of the TIR prism system, it is positive; when the marginal light is below the principal optical axis, it is negative.

3. A TIR prism system according to claim 2, characterized in that: The second prism (2) is a triangular prism structure; The fourth incident angle of the flat beam and the off-state beam incident on the λ3 surface Greater than the critical angle; The incident angle of the open-state light beam incident on the λ3 surface is less than the critical angle; The internal angle relationship of the second prism (2) is: ; Where: After being reflected by the DMD micromirror (4), the angle between the flat and off state light beams and the target surface of the DMD micromirror (4) is , ; Second prism angle is the angle between the λ3 plane and the β1 plane parallel axis, and its value satisfies .

4. A TIR prism system according to claim 3, characterized in that: The third prism (3) is a triangular prism structure; The λ3 surface of the second prism (2) and the μ1 surface of the third prism (3) have the same width; Third prism (3) angle The angle between the μ1 and μ2 faces of the third prism (3) and the angle of the second prism equal.

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 micromirror (4) hits the β3 surface and the total reflected light is reflected just to the upper edge of the DMD micromirror (4), the thickness of the first prism (1) is the minimum value. ; Specifically: the thickness of the first prism (1) The minimum value is the distance between the center normal of the DMD micromirror (4) target surface and the intersection of the β1 surface and the β3 surface. At this time, the thickness of the first prism (1) is =19.17mm; DMD micromirror (4) length =17.5mm; the angle between the normal line of the center of the DMD micromirror (4) target surface and the normal line of the incident light on the β3 surface is ,and .

6. A TIR prism system according to claim 5, characterized in that: When the edge light emitted by the DMD micromirror (4) is reflected from 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 is the minimum value; Specifically: the thickness of the second prism (2) The minimum value is the distance between the center normal of the DMD micromirror (4) target surface and the intersection of the λ1 surface and the λ3 surface. =10.7124mm; the distance between the DMD micromirror (4) and the first prism (1) is d, d=5mm; the incident point of the edge light emitted by the DMD micromirror (4) reflected to the β1 surface and the intersection of the λ1 surface and the λ3 surface of the second prism (2) are at a height of y, y=22.5504mm. At this time, the angle between the axis parallel to the center normal of the target surface of the DMD micromirror (4) and the internal reflection light of the first prism (1) is ,and =4.525°.

7. A TIR prism system according to claim 6, characterized in that: Thickness of the third prism (3) is the distance between the center normal of the target surface of the DMD micromirror (4) and the intersection of the μ1 surface and the μ2 surface; the thickness of the third prism (3) The minimum value is 7.4556mm; 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 medium-wave infrared projection optical system, characterized in that: The invention comprises 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) which are optically connected in sequence on the same axis; and further comprises a second DMD micromirror (15), a second window glass (16), and a second TIR prism system (17) which are optically connected in sequence on the same axis; and the target surface center normal of the first DMD micromirror (12) is perpendicular to the target surface center normal of the second DMD micromirror (15); The first TIR prism system (14) and the second TIR prism system (17) both adopt a TIR prism system as claimed in claim 7.

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

10. The dual-channel common-aperture medium-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 power of the first lens (7) and the second lens (8) is a positive and negative combination; The third lens (9), the fourth lens (10) and the fifth lens (11) all have positive optical powers.

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