Low-cost mid-wave refrigeration athermalized optical system based on silicon germanium material

Abstract

The application discloses a low-cost mid-wave refrigeration athermalization optical system based on a silicon germanium material, which sequentially comprises a fairing, a first lens, a second lens, a third lens, a detector protection glass, a cold light diaphragm and an image plane from outside to inside in the propagation direction of light. The first lens, the second lens, the third lens, the detector protection glass, the cold light diaphragm, the image plane and the fairing are coaxially arranged. The optical system is used for receiving infrared radiation inherent to a target and a background, and converging the infrared radiation onto a photosensitive surface of a refrigeration detector to realize photoelectric conversion, so that the target can be detected, identified and accurately positioned at night or under complex weather conditions. The application belongs to the technical field of optical imaging, can adapt to a harsh missile-borne working environment with a wide temperature range of 110 DEG C and high impact overload, has the characteristics of simple structure, excellent imaging quality, high resolution, strong environmental adaptability, good processing process, easy assembly and adjustment and high yield, is suitable for mass production, and can be widely applied to the fields of optical imaging guidance, search, tracking and reconnaissance.

Description

Technical Field

[0001] This invention belongs to the field of optical imaging technology, and more specifically, relates to a low-cost, mid-wave cooling and athermalized optical system based on silicon-germanium materials for imaging guidance. Background Technology

[0002] With the rapid development of infrared detectors, infrared imaging detection technology is being used more and more widely in fields such as aviation, aerospace, ground monitoring, and imaging guidance. In optical imaging terminal guidance systems, cooled infrared optical systems have outstanding advantages such as good imaging quality, high detection accuracy, strong anti-interference ability, and all-weather operation.

[0003] During the high-speed flight of a missile, the onboard operating environment is extremely harsh. It is necessary to ensure that the optical system can operate normally in a wide temperature range of 110°C and under high impact overload. Therefore, the system is required to have technical characteristics such as excellent imaging quality, strong environmental adaptability, high reliability, good manufacturability, easy assembly and adjustment, and high yield. At the same time, it is also necessary to reduce production and manufacturing costs to facilitate mass production. Summary of the Invention

[0004] The purpose of this invention is to achieve a low-cost, athermal, and high-resolution design for a mid-wave cooled infrared seeker. This invention provides a low-cost, athermalized mid-wave cooled optical system based on silicon-germanium materials.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A low-cost, athermochemically cooled mid-wave optical system based on silicon-germanium materials is characterized by the following components arranged sequentially from the outside to the inside along the light propagation direction: a radome, a first lens, a second lens, a third lens, a detector protective glass, a cold aperture, and an image plane. The first lens, second lens, third lens, detector protective glass, cold aperture, and image plane are coaxially aligned with the radome. The optical system receives infrared radiation inherent to the target and background and converges it onto the photosensitive surface of the cooled detector for photoelectric conversion. It exhibits high sensitivity and relatively low spatial resolution, enabling target detection, identification, and precise positioning at night or under complex weather conditions.

[0007] Furthermore, both the first and third lenses are spherical lenses; the outer surface of the second lens is a binary surface, and the inner surface is a sphere.

[0008] Furthermore, both the first and third lenses are spherical lenses; the outer surface of the second lens is a binary surface, and the inner surface is spherical. The equation of the binary surface (aspherical & diffractive surface) is:

[0009] The equation for an aspherical surface is (1):

[0010]

[0011] In the formula: H is the sum of the squares of the horizontal and vertical coordinates, H 2 =X 2 +Y 2 K is the constant of the quadratic surface; C is the curvature, a2, a4, a6, a8, a 10 a 12 It is the aspherical coefficient.

[0012] The equation of the diffraction plane is (2):

[0013]

[0014] In the formula: H is the sum of the squares of the horizontal and vertical coordinates, H 2 =X 2 +Y 2 m is the diffraction zone number; n0 is the material refractive index; C1 is the secondary phase coefficient.

[0015] Furthermore, the radius of curvature of the outer surface of the fairing is 110 mm, the radius of curvature of the inner surface is 105 mm, and the thickness is 5 mm; the radius of curvature of the outer surface of the first lens is 54.05 mm, the radius of curvature of the inner surface is 131.761 mm, and the thickness is 7.55 mm; the radius of curvature of the outer surface of the second lens is 171.582 mm, the radius of curvature of the inner surface is 62 mm, and the thickness is 4 mm; the radius of curvature of the outer surface of the third lens is 73.51 mm, the radius of curvature of the inner surface is 209.942 mm, and the thickness is 4 mm; the diffraction parameters of the outer surface of the second lens are quadratic surface constants K = 1.735051, C = 1 / 171.582, and the second, fourth, sixth, eighth, tenth, and twelfth order coefficients are a2 = 0, a4 = -1.4276888 × 10⁻⁶, and a₄ = -1.4276888 × 10⁻⁶, respectively. －7 a6 = -6.2881683 × 10 －12 a8 = 4.636342 × 10 －13 a 10 = -2.0717334 × 10 －15 a 12 = -6.5998157 × 10 －19 The diffraction order is 1, the diffraction ring number is 10, and C1 = 7.476985 × 10⁻⁶. -5 .

[0016] Furthermore, the fairing is a concentric convex lens made of sapphire; the first and third lenses are meniscus lenses made of silicon; and the second lens is a meniscus lens made of germanium.

[0017] Furthermore, the distance between the fairing and the first lens is 10 mm; the distance between the first lens and the second lens is 1.75 mm; the distance between the second lens and the third lens is 36.45 mm; the distance between the third lens and the detector protective glass is 10.45 mm; the distance between the detector protective glass and the cold aperture is 2.08 mm; and the distance between the cold aperture and the image plane is 19.8 mm.

[0018] Furthermore, the optical system operates in the wavelength range of 3.7μm to 4.8μm, has a focal length of 55mm, an F-number of 2, a field of view of 10°×8°, and at 33lp / mm, has an on-axis modulation transfer function value ≥0.6, an off-axis transfer function value ≥0.47, and a system distortion ≤1%.

[0019] Furthermore, the optical system is designed with a single-image, three-element structure, using silicon and germanium as lens materials. It achieves a wide-temperature, calorimetric design using only a single binary surface. Within a temperature range of -40℃ to +70℃, the maximum distortion of the optical system is -0.48%. At -40℃, at 33 lp / mm, the transfer function value for the 0 field of view is ≥0.58, and the transfer function values ​​for the other fields of view are ≥0.45. At 20℃, at 33 lp / mm, the transfer function value for the 0 field of view is ≥0.62, and the transfer function values ​​for the other fields of view are ≥0.45. At +70℃, at 33 lp / mm, the transfer function value for the 0 field of view is ≥0.60, and the transfer function values ​​for the other fields of view are ≥0.46.

[0020] Furthermore, the optical system exhibits a "cold reflection" effect, meaning that the image plane incoherent illuminance nonuniformity is <13%.

[0021] Furthermore, the external dimensions of the optical system (excluding the fairing) Total optical weight <90g.

[0022] The advantages of this invention over the prior art are:

[0023] 1. The optical system described in this invention operates in the wavelength range of 3.7μm to 4.8μm, has a focal length of 55mm, an F-number of 1.97, a full field-of-view distortion of ≤0.5%, a field of view of 10°×8°, and uses a Stirling cooled detector with a resolution of 640×512 and a pixel size of 15μm. It is a low F-number mid-wave infrared cooled optical system with high resolution, large relative aperture, and strong light-gathering ability.

[0024] 2. The optical system described in this invention adopts a single-image silicon-germanium-silicon three-chip optical structure, with external dimensions (excluding the fairing). With a total weight of less than 90g, it features a compact structure, good lens processing capabilities, simple assembly and calibration, and a high yield rate.

[0025] 3. The detector of the optical system described in this invention uses an optical system with a transfer function of ≥0.62 (33 lp / mm) for the field of view and ≥0.45 (33 lp / mm) for the full field of view. It has excellent imaging quality, a single pixel angle of less than 0.28 mrad, high resolution, long detection distance, and outstanding performance characteristics.

[0026] 4. The optical system uses silicon and germanium, two of the most commonly used, stable, and mature optical materials, as lens materials. It employs advanced aberration theory to effectively balance the contradiction between optical aberration and thermal difference. The optical system achieves a wide-temperature, calorimetric design using only a single binary surface. It has excellent imaging quality in the range of -40℃ to +70℃, requires fewer lenses, has high transmittance, strong environmental adaptability, and low cost, making it suitable for mass production.

[0027] 5. In cooled infrared optical systems, "cold reflection" is one of the important indicators for evaluating and calculating the performance of infrared systems, especially in guidance systems with radomes. Since the radome is a concentric circular lens, the cold reflection generated by residual reflection from the radome surface is particularly significant. The optical system described in this invention is specifically optimized by incorporating the radome curvature radius and employing a non-sequential mathematical simulation model for analysis. This effectively controls and reduces the "cold reflection" effect of the system, achieving an image plane incoherence illumination non-uniformity of <13%, improving the system's signal-to-noise ratio, enhancing its detection capability for weak, low-temperature targets, and meeting the usage requirements of infrared optical imaging guidance systems. Attached Figure Description

[0028] Figure 1 This is a structural diagram of a high-resolution long-wavelength cooled infrared imaging guidance optical system.

[0029] Figure 2 The modulation transfer function curve at +70℃;

[0030] Figure 3 The modulation transfer function curve is shown at +20℃.

[0031] Figure 4 The modulation transfer function curve at -40℃;

[0032] Figure 5 For optical system distortion and field curvature curves;

[0033] Figure 6 Diagram of non-sequence mathematical simulation model;

[0034] Figure 7 This is an incoherent grayscale image of the image plane of the optical system.

[0035] Figure 8 This represents the incoherent illuminance curve (X direction) of the image plane of the optical system.

[0036] Figure 9 This represents the incoherent illuminance curve (Y direction) of the image plane of the optical system.

[0037] In the diagram: 1. Fairing, 2. First lens, 3. Second lens, 4. Third lens, 5. Detector protective glass, 6. Cold aperture, 7. Image plane. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings.

[0039] Example 1

[0040] This embodiment describes a low-cost, athermochemically cooled mid-wave optical system based on silicon-germanium materials. The system comprises, from the outside in, a radome, a first lens, a second lens, a third lens, a detector protective glass, a cold aperture, and an image plane, arranged sequentially in the direction of light propagation. The first lens, second lens, third lens, detector protective glass, cold aperture, and image plane are coaxially aligned with the radome. The optical system receives the inherent infrared radiation from the target and background and converges it onto the photosensitive surface of the cooled detector for photoelectric conversion. It exhibits high sensitivity and relatively low spatial resolution, enabling target detection, identification, and precise positioning at night or under complex weather conditions.

[0041] The specific purpose of this technical solution is to achieve a low-cost, athermal design for a cooled infrared seeker. Based on silicon-germanium optical materials, it utilizes a three-element optical structure (Si-Ge-Si) for single-image imaging and selects a mid-wave infrared detector with a Stirling-cooled array size of 640×512 pixels and a size of 15μm as the receiving device. This design creates an athermal, high-resolution, and low-cost mid-wave cooled infrared imaging guidance optical system capable of detecting, identifying, and precisely locating targets.

[0042] Example 2

[0043] This embodiment describes a low-cost, athermochemically cooled mid-wave optical system based on silicon-germanium materials. The system comprises, from the outside in, a radome, a first lens, a second lens, a third lens, a detector protective glass, a cold aperture, and an image plane, arranged sequentially in the direction of light propagation. The first lens, second lens, third lens, detector protective glass, cold aperture, and image plane are coaxially aligned with the radome. The optical system receives the inherent infrared radiation from the target and background and converges it onto the photosensitive surface of the cooled detector for photoelectric conversion. It exhibits high sensitivity and relatively low spatial resolution, enabling target detection, identification, and precise positioning at night or under complex weather conditions.

[0044] The fairing 1 is made of sapphire; the first lens 2 is made of silicon; the second lens 3 is made of germanium; and the third lens 4 is made of silicon. The first and third lenses are both spherical lenses; the outer surface of the second lens is a binary surface, and its inner surface is spherical.

[0045] This technical solution defines the materials, quantity, and surface type of each lens. The design employs a single-image, three-element (silicon-germanium-silicon) structure, utilizing advanced aberration theory and considering the thermal expansion coefficients of optical and mechanical materials to effectively balance the contradiction between optical and thermal aberrations. Silicon and germanium, two of the most commonly used, stable, and technologically mature optical materials, are selected as lens materials, and aluminum is chosen as the lens barrel material. Using only a single binary diffraction surface, a wide-temperature, calorimetric design is achieved for the optical system. It exhibits excellent imaging quality within a temperature range of -40℃ to +70℃, a simple structure, a small number of lenses, high transmittance, a single-pixel angular diameter of 0.28 mrad, long detection distance, strong environmental adaptability, easy assembly and calibration, and low cost, making it suitable for mass production.

[0046] Example 3

[0047] This embodiment describes a low-cost, athermochemically cooled mid-wave optical system based on silicon-germanium materials. The system comprises, from the outside in, a radome, a first lens, a second lens, a third lens, a detector protective glass, a cold aperture, and an image plane, arranged sequentially in the direction of light propagation. The first lens, second lens, third lens, detector protective glass, cold aperture, and image plane are coaxially aligned with the radome. The optical system receives the inherent infrared radiation from the target and background and converges it onto the photosensitive surface of the cooled detector for photoelectric conversion. It exhibits high sensitivity and relatively low spatial resolution, enabling target detection, identification, and precise positioning at night or under complex weather conditions.

[0048] The optical system operates in the wavelength range of 3.7μm to 4.8μm, with a focal length of 55mm, an F-number of 1.97, and a field of view of 10°×8°. The detector used is a Stirling cooled detector with a resolution of 640×512 and a pixel size of 15μm. At 33lp / mm, the on-axis modulation transfer function (MTF) is ≥0.61, the off-axis transfer function (MTF) is ≥0.45, and the system distortion is ≤0.5%.

[0049] This technical solution defines the technical parameters of the optical system, including the operating band, focal length, F-number, field of view, detector resolution, and pixel size, and features high resolution, large relative aperture, and strong light-gathering capability.

[0050] Example 4

[0051] This embodiment describes a low-cost, athermochemically cooled mid-wave optical system based on silicon-germanium materials. The system comprises, from the outside in, a radome, a first lens, a second lens, a third lens, a detector protective glass, a cold aperture, and an image plane, arranged sequentially in the direction of light propagation. The first lens, second lens, third lens, detector protective glass, cold aperture, and image plane are coaxially aligned with the radome. The optical system receives the inherent infrared radiation from the target and background and converges it onto the photosensitive surface of the cooled detector for photoelectric conversion. It exhibits high sensitivity and relatively low spatial resolution, enabling target detection, identification, and precise positioning at night or under complex weather conditions.

[0052] The optical system has a maximum distortion design value of -0.48% within a temperature range of -40℃ to +70℃. At -40℃, the transfer function for the 0 field of view is ≥0.58 (33 lp / mm), and the transfer function for the other fields of view is ≥0.45 (33 lp / mm). At 20℃, the transfer function for the 0 field of view is ≥0.62 (33 lp / mm), and the transfer function for the other fields of view is ≥0.45 (33 lp / mm). At +70℃, the transfer function for the 0 field of view is ≥0.60 (33 lp / mm), and the transfer function for the other fields of view is ≥0.46 (33 lp / mm).

[0053] The optical system described in this technical solution has a modulation transfer function curve design value close to the diffraction limit within a temperature range of -40℃ to +70℃, exhibiting excellent imaging quality, good environmental adaptability, and outstanding performance characteristics.

[0054] Example 5

[0055] This embodiment describes a low-cost, athermochemically cooled mid-wave optical system based on silicon-germanium materials. The system comprises, from the outside in, a radome, a first lens, a second lens, a third lens, a detector protective glass, a cold aperture, and an image plane, arranged sequentially in the direction of light propagation. The first lens, second lens, third lens, detector protective glass, cold aperture, and image plane are coaxially aligned with the radome. The optical system receives the inherent infrared radiation from the target and background and converges it onto the photosensitive surface of the cooled detector for photoelectric conversion. It exhibits high sensitivity and relatively low spatial resolution, enabling target detection, identification, and precise positioning at night or under complex weather conditions.

[0056] The optical system fairing is a concentric circular lens made of sapphire. The outer surface has a radius of curvature of 110 mm, the inner surface has a radius of curvature of 105 mm, and the thickness is 5 mm. The optical system exhibits a "cold reflection" effect, meaning that the image plane incoherent illumination nonuniformity is <13%.

[0057] This technical solution defines the characteristic parameters of the radome and the requirements for cold reflection, i.e., the incoherent illumination non-uniformity of the image plane. Cold reflection is a crucial indicator for evaluating and calculating the performance of cooled infrared optical systems, especially in guidance systems containing radomes. Because the radome is a concentric circular lens, the "cold emission" phenomenon caused by residual reflection from the radome surface is particularly pronounced. The optical system described in this invention is specifically optimized based on the radome's radius of curvature and analyzed using a non-sequential mathematical simulation model. This effectively controls and reduces the cold reflection effect of the system, achieving an image plane incoherent illumination non-uniformity of <13%, improving the system's signal-to-noise ratio, enhancing its detection capability for weak, low-temperature targets, and meeting the application requirements of infrared optical imaging guidance systems.

[0058] Example 6

[0059] This embodiment describes a low-cost, athermochemically cooled mid-wave optical system based on silicon-germanium materials. The system comprises, from the outside in, a radome, a first lens, a second lens, a third lens, a detector protective glass, a cold aperture, and an image plane, arranged sequentially in the direction of light propagation. The first lens, second lens, third lens, detector protective glass, cold aperture, and image plane are coaxially aligned with the radome. The optical system receives the inherent infrared radiation from the target and background and converges it onto the photosensitive surface of the cooled detector for photoelectric conversion. It exhibits high sensitivity and relatively low spatial resolution, enabling target detection, identification, and precise positioning at night or under complex weather conditions.

[0060] The external dimensions of the optical system (excluding the fairing) Total weight < 90g.

[0061] This technical solution limits the external dimensions and total weight of the optical system, and features a compact structure, small size, and light weight.

[0062] Working principle of infrared imaging guidance system

[0063] The infrared imaging guidance system consists of three parts: a radome, an optical system, and a mid-wave cooled detector. The radome serves as the optical detection window, possessing high transmittance in the system's operating wavelength band. It forms a sealed space with other parts of the seeker head, protecting the internal components and ensuring their normal operation under thermal shock. The optical system receives the inherent infrared radiation from the target and background, focusing it onto the photosensitive surface of the mid-wave cooled detector for photoelectric conversion. It features high sensitivity and relatively low spatial resolution, enabling target detection, identification, and precise positioning at night or under complex weather conditions.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-cost, athermalized mid-wave cooling optical system based on silicon-germanium materials, characterized in that: A fairing (1), a first lens (2), a second lens (3), a third lens (4), a detector protective glass (5), a cold aperture (6), and an image plane (7) are arranged sequentially in the direction of light propagation. The first lens (2), the second lens (3), the third lens (4), the detector protective glass (5), the cold aperture (6), and the image plane (7) are arranged coaxially with the fairing (1). The optical system is used to receive the infrared radiation inherent to the target and the background and converge it onto the photosensitive surface of the cooled detector to achieve photoelectric conversion. It can detect, identify, and locate the target at night or under complex weather conditions. The outer surface of the fairing (1) has a radius of curvature of 110 mm, the inner surface has a radius of curvature of 105 mm, and a thickness of 5 mm; the outer surface of the first lens (2) has a radius of curvature of 54.05 mm, the inner surface has a radius of curvature of 131.761 mm, and a thickness of 7.55 mm; the outer surface of the second lens (3) has a radius of curvature of 171.582 mm, the inner surface has a radius of curvature of 62 mm, and a thickness of 4 mm; the outer surface of the third lens (4) has a radius of curvature of 110 mm, the inner surface has a radius of curvature of 105 mm, and a thickness of 5 mm; the outer surface of the third lens (4) has a radius of curvature of 110 mm, the inner surface has a radius of curvature of 105 mm, and a thickness of 5 mm; the outer surface of the third lens (4) has a radius of curvature of 54.05 mm, the inner surface has a radius of curvature of 131.761 mm, and a thickness of 7.55 mm; the outer surface of the second lens (3) has a radius of curvature of 171.582 mm, the inner surface has a radius of curvature of 62 mm, and a thickness of 4 mm; the outer surface of the third lens (4) has a radius of curvature of 110 mm, the inner surface has a radius of curvature of 105 ...5 mm. The radius of curvature of the outer surface is 73.51 mm, the radius of curvature of the inner surface is 209.942 mm, and the thickness is 4 mm; the outer surface of the second lens (3) is a binary surface, which is an aspherical surface and a diffraction surface, and the inner surface is a spherical surface. The parameters of the aspherical surface are as follows: the quadratic surface constant K = 1.735051, the curvature C = 1 / 171.582, and the coefficients of the second, fourth, sixth, eighth, tenth, and twelfth orders are a2 = 0, a4 = -1.4276888 × 10 －7 a6 = -6.2881683 × 10 －12 a8 = 4.636342 × 10 －13 a 10 = -2.0717334 × 10 －15 a 12 = -6.5998157 × 10 －19 ; The diffraction order in the diffraction plane is 1, the number of diffraction rings is 10, and the second phase coefficient C1 = 7.476985 × 10⁻⁶. －5 ; The distance between the fairing (1) and the first lens (2) is 10 mm; the distance between the first lens (2) and the second lens (3) is 1.75 mm; the distance between the second lens (3) and the third lens (4) is 36.45 mm; the distance between the third lens (4) and the detector protective glass (5) is 10.45 mm; the distance between the detector protective glass (5) and the cold aperture (6) is 2.08 mm; the distance between the cold aperture (6) and the image plane (7) is 19.8 mm. The fairing (1) is a concentric convex lens made of sapphire; the first lens (2) and the third lens (4) are meniscus lenses made of silicon; the second lens (3) is a meniscus lens made of germanium.

2. The low-cost, athermalized mid-wave cooling optical system based on silicon-germanium material according to claim 1, characterized in that: Both the first lens (2) and the third lens (4) are spherical lenses.

3. The low-cost, athermalized mid-wave cooling optical system based on silicon-germanium material according to claim 1, characterized in that: The optical system operates in the wavelength range of 3.7μm to 4.8μm, has a focal length of 55mm, an F-number of 2, a field of view of 10°×8°, and at 33lp / mm, has an on-axis modulation transfer function value ≥0.6, an off-axis transfer function value ≥0.47, and a system distortion ≤1%.

4. The low-cost, athermalized mid-wave cooling optical system based on silicon-germanium material according to claim 1, characterized in that: The optical system is designed with a single-image 3-element structure, using silicon and germanium as lens materials. It achieves a wide-temperature, calorimetric design using only one binary surface. Within the temperature range of -40℃ to +70℃, the maximum distortion of the optical system is -0.48%. At -40℃, the transfer function value at 33 lp / mm is ≥0.58 for the 0 field of view and ≥0.45 for the other fields of view; at 20℃, the transfer function value at 33 lp / mm is ≥0.62 for the 0 field of view and ≥0.45 for the other fields of view; at +70℃, the transfer function at 33 lp / mm is ≥0.60 for the 0 field of view and ≥0.46 for the other fields of view.

5. The low-cost, athermalized mid-wave cooling optical system based on silicon-germanium material according to claim 1, characterized in that: The "cold reflection" effect of the optical system refers to the image plane incoherent illumination nonuniformity of <13%.

6. The low-cost, athermalized mid-wave cooling optical system based on silicon-germanium material according to claim 1, characterized in that: The optical system, excluding the fairing, has the following dimensions: maximum outer diameter less than 53 mm, total optical length less than 54 mm, and total optical weight less than 90 g.

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