Monolithic passive athermalization medium-wave infrared imaging optical system

Abstract

The invention discloses a single-chip passive athermalization medium-wave infrared imaging optical system which comprises a chalcogenide glass lens, a detector window, a detector cold screen and a detector target surface which are arranged in sequence, the front surface of the chalcogenide glass lens is an aspheric surface, and the rear surface of the chalcogenide glass lens is an aspheric surface and a diffraction surface. The chalcogenide glass lens is an aspheric positive-focal-power meniscus lens made of Ge-As-Se-Te chalcogenide glass with a negative refractive index temperature coefficient. The focal length EFFL of the medium-wave infrared imaging optical system is 75 mm, the F # is 4, the view field is 8.8 degrees * 7 degrees, the optical distortion is smaller than or equal to 1%, the working spectral range is 3.7-4.8 micrometers, the passive heat elimination temperature range is-50 DEG C to + 70 DEG C, the total optical length TTL is smaller than or equal to 80 mm, and the optical rear intercept is larger than or equal to 43 mm. The passive athermalization medium-wave imaging system design under a wider temperature range is realized by adopting one lens, the structure of an optical system is simplified, the weight of the optical system is reduced, and the manufacturing cost of the optical system is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of infrared optical material technology and optical design, and in particular relates to a monolithic passively athermal medium-wave infrared imaging optical system. Background Art

[0002] Infrared imaging optical systems are often used in environments with large temperature fluctuations, such as those in military, aerospace, and outdoor surveillance equipment. Infrared imaging optical systems are often used in extreme temperature environments (such as space, deserts, polar regions, or high-speed aircraft), with temperatures ranging from -40°C to +70°C. Temperature fluctuations can cause materials to expand or contract, resulting in changes in the shape and position of optical components. Without heat dissipation, optical systems can fail at high and low temperatures. For example, at low temperatures, materials can become brittle, leading to mechanical structure seizure; at high temperatures, optical adhesives can soften, leading to lens debonding. Changes in the shape and position of optical components can lead to a sudden drop in system image quality. This is especially true in high-precision applications such as precision guidance or satellite remote sensing, where even minor changes can significantly degrade system performance. Heat dissipation design for infrared imaging optical systems is a key technology for ensuring optical performance, detection accuracy, and reliability in complex temperature environments. Ignoring heat dissipation can lead to blurred images, target loss, and even system failure. This is especially true in high-precision applications such as military and aerospace, where heat dissipation directly determines the system's practical value.

[0003] Athermal design for infrared imaging optical systems involves eliminating or compensating for the effects of temperature changes through active focusing or passive compensation, ensuring consistently clear images across a wide operating temperature range. Athermalization methods for infrared imaging optical systems are categorized as active or passive. Active athermalization uses temperature sensors and adjustment mechanisms to monitor temperature in real time and adjust lens position or shape. Feedback from the temperature sensor drives a motor to adjust the lens position to compensate for defocus. However, this approach cannot achieve lightweight and miniaturized infrared imaging optical systems, significantly limiting its application scenarios. Passive athermalization involves selecting appropriate material combinations, leveraging the thermal and mechanical properties of different materials to select material combinations with complementary thermal expansion coefficients. For example, aluminum alloy (high expansion) can be paired with titanium alloy (low expansion) to offset deformation through mechanical structure. Thermal defocus can also be offset by using lens combinations with opposite refractive index temperature coefficients (such as calcium fluoride and germanium). Optical system parameters (such as curvature and pitch) are optimized to minimize focus drift with temperature. Through an integrated design, lens deformation and aberrations caused by relative position shifts due to temperature changes are offset, achieving effective athermalization. Passive heat removal has become the preferred heat removal method for infrared imaging optical systems because it does not require a focusing mechanism.

[0004] The demand for miniaturization of infrared imaging optical systems stems from a combination of diverse application scenarios and technological developments, representing an inevitable trend driven by both technological evolution and market demand. In particular, miniaturization, with its low cost, low power consumption, and high integration, significantly enhances the adaptability of infrared imaging optical systems in various application scenarios, particularly in precision guidance, military individual equipment, consumer electronics, medical and industrial testing.

[0005] Existing infrared imaging optical systems are mainly based on infrared crystal materials such as silicon single crystal (Si), germanium single crystal (Ge), zinc sulfide (ZnS), zinc selenide (ZnSe), and fluoride. These infrared crystal materials are relatively expensive, hard, fragile, and have poor mechanical strength. Aspheric and diffraction surfaces must be obtained through single-point turning, which increases manufacturing costs and makes lens processing very inefficient. Mass production is difficult, resulting in high costs for infrared imaging optical systems, which greatly limits the civilian application of infrared imaging optical systems. At the same time, the refractive index of these infrared crystal materials will change significantly with temperature (called the dN / dT effect). For example, the temperature coefficient of the refractive index of germanium is approximately 4×10 -4 / °C, meaning that for every 1°C change in temperature, the refractive index changes, leading to a significant shift in the focal position (thermal defocus), resulting in blurred images. Current infrared crystal materials have relatively large dN / dT values. Traditional transmissive infrared passive athermalization optical systems often rely on combining multiple pieces of infrared crystal material to achieve passive athermalization. This results in a bulky and heavy optical system, causing more severe energy attenuation and compromising image quality, making it difficult to achieve lightweight and low-cost designs for infrared optical systems.

[0006] In contrast, new materials like chalcogenide glass offer a superior alternative. They not only offer high cost-performance but also possess a low refractive index temperature coefficient (dN / dT) in the infrared band, making them indispensable for passively athermalized mid-wave infrared imaging optical systems. As the only commercially available infrared-transparent glass material, chalcogenide glass exhibits a low refractive index temperature coefficient (dN / dT), making it an essential material for athermalized infrared optical systems. Furthermore, the low raw material cost of chalcogenide glass offers an effective approach to reducing the cost of infrared optical systems. However, despite over half a century of research and development as an infrared optical material, there are still only a dozen or so commercially available grades.

[0007] As listed in Table 1, the vast majority of chalcogenide glass materials are based on glass systems such as Ge-Sb-Se, Ge-As-Se, As-S, and As-Se. Their refractive index temperature coefficients, dN / dT, range from 17 to 168, and none of the chalcogenide glasses have a negative refractive index temperature coefficient. While infrared imaging optical systems that utilize a combination of traditional crystal materials and chalcogenide glasses for athermalization offer a reduction in overall price and lens count compared to systems relying solely on crystal materials for passive athermalization, they still require multiple lenses for athermalization, making it impossible to achieve a high-performance, low-cost, and compact passive athermalization mid-wave infrared imaging system.

[0008] Table 1 Properties and grades of commercial chalcogenide glass materials

[0009] Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a monolithic passively athermal medium-wave infrared imaging optical system in order to address the shortcomings of the existing technology and meet the application requirements of the new generation of infrared imaging optical systems. The medium-wave infrared imaging optical system has the characteristics of high sensitivity, wide temperature adaptability, light weight, negative refractive index temperature coefficient, low loss characteristics, and low cost.

[0011] The technical solution adopted by the present invention to solve the above technical problems is: a monolithic passively athermalized medium-wave infrared imaging optical system, the medium-wave infrared imaging optical system comprising a chalcogenide glass lens, a detector window, a detector cold shield, and a detector target surface arranged in sequence along the optical axis from the object side to the image side. The chalcogenide glass lens has an aspheric front surface and an aspheric and diffractive rear surface. The chalcogenide glass lens is an aspheric positive-power meniscus lens made of Ge-As-Se-Te chalcogenide glass, and the Ge-As-Se-Te chalcogenide glass has a negative refractive index temperature coefficient. The medium-wave infrared imaging optical system has a focal length (EFFL) of 75 mm, an F# of 4, a field of view of 8.8°×7°, optical distortion ≤1%, an operating spectrum range of 3.7 to 4.8 μm, a passive athermalization temperature range of -50°C to +70°C, a total optical length (TTL) ≤80 mm, and an optical back intercept ≥43 mm.

[0012] The medium-wave infrared imaging optical system of the present invention adopts a minimalist design and innovatively uses a new type of chalcogenide glass lens with a negative refractive index temperature coefficient dN / dT to form an infrared optical path, resulting in a monolithic passively athermal medium-wave infrared imaging optical system. This minimalist medium-wave infrared imaging optical system can achieve passive athermalization and ensure high imaging quality within a wide temperature range of the infrared band, while reducing the cost of the infrared imaging optical system, simplifying the structure, and improving the system integration. It effectively reduces the volume, length, weight, and power consumption of the system, and effectively improves the transmittance of the infrared imaging optical system, especially exhibiting high transmittance and low absorption characteristics in the medium and long-wave infrared bands. In addition, the medium-wave infrared imaging optical system of the present invention has stronger anti-interference capabilities and environmental adaptability, and can operate stably in various harsh environments. The medium-wave infrared imaging optical system of the present invention is of great significance in the development of infrared technology and industry. It not only improves the infrared imaging capability of the system, but also reduces costs, providing strong support for its application in the military and civilian markets.

[0013] Preferably, the molar composition formula of the Ge-As-Se-Te chalcogenide glass is Ge x -As y -Se z -Te w , wherein x, y, z, and w are all mole percentages, x=15-25, y=10-20, z=10-20, w=35-65, x+y+z+w=100.

[0014] Preferably, the thickness of the chalcogenide glass lens is 7 mm, and the optical back focus is 43 mm.

[0015] Preferably, both the front and rear surfaces of the chalcogenide glass lens are coated with an antireflection film.

[0016] Preferably, the detector adapted for the medium-wave infrared imaging optical system is a cooled medium-wave infrared detector, the F# of the cooled medium-wave infrared detector is 4, the cold screen height is 20.47 mm, the resolution is 640×512, and the pixel size is 15 μm.

[0017] Preferably, in the detector cold shield, the circular aperture serving as the aperture stop is made of aluminum alloy, and has an aperture of Φ10 mm.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) The present invention adopts a minimalist design to achieve minimalist passive thermal imaging using a single chalcogenide glass lens, thereby improving the utilization rate of thermal radiation and enhancing the target reconnaissance capability of the system.

[0020] (2) The present invention uses a new type of chalcogenide glass lens with a negative temperature coefficient of refractive index, which greatly reduces the number of lenses. The existing multi-lens combined passive athermalization medium-wave infrared imaging system requires at least three lenses to combine and image to achieve passive athermalization over a wide temperature range. The present invention uses only one lens to achieve the design of a passive athermalization medium-wave imaging system over a wider temperature range, which not only simplifies the structure of the optical system, reduces the weight of the optical system, but also reduces the manufacturing cost of the optical system.

[0021] (3) The operating temperature range of the medium-wave infrared imaging optical system of the present invention is -50°C to +70°C (i.e., the passive athermal temperature range), and within the temperature range of -50°C to +70°C, the full-field modulation transfer function is close to the diffraction limit at the Nyquist frequency (@33 cycles / mm) without moving any optomechanical components in the medium-wave infrared imaging optical system, and there is no obvious drop in the transfer function curve, thereby ensuring clear imaging within the full temperature operating range of -50°C to +70°C.

[0022] (4) The passive athermalization temperature range of the medium-wave infrared imaging optical system of the present invention is -50°C to +70°C, which is greater than the operating temperature range of the existing multi-lens combined passive athermalization medium-wave infrared imaging system, which is -45°C to +60°C. The applicable specifications of the focal plane of the adapted refrigerated medium-wave infrared detector are: 320×256 / 30μm, 640×512 / 15μm, 1280×1024 / 10μm, 1280×1024 / 15μm, and 1280×1024 / 25μm, which has a wider range of applicability;

[0023] (5) The medium-wave infrared imaging optical system of the present invention has the characteristics of high sensitivity, wide temperature adaptability, lightness and thinness, negative refractive index temperature coefficient, low loss characteristics, low cost, etc. It can realize all-weather observation of the target and meet the application needs of military and civilian industries such as precision guidance, border and coastal defense, night vision systems, environmental monitoring, key point monitoring and security, wildlife patrol, and industrial temperature measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the optical path structure of the mid-wave infrared imaging optical system in the embodiment;

[0025] Figure 2 : is a modulation transfer function diagram of the wave infrared imaging optical system in the embodiment at a temperature of 22° C. (room temperature);

[0026] Figure 3 : is a modulation transfer function diagram of the wave infrared imaging optical system in the embodiment at a temperature of -50°C (the lowest temperature);

[0027] Figure 4Graph showing the modulation transfer function of the infrared imaging optical system in the embodiment at a temperature of 70° C. (the highest temperature). DETAILED DESCRIPTION

[0028] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments. Components or structures not defined in the present invention are all based on conventional techniques in the art.

[0029] Example: A monolithic passive athermal mid-wave infrared imaging optical system, such as Figure 1 As shown, the medium-wave infrared imaging optical system includes a chalcogenide glass lens A, a detector window B, a detector cold screen C, and a detector target surface D, which are arranged in sequence from the object side to the image side along the optical axis. The front surface of the chalcogenide glass lens A is an aspherical surface, and the back surface is an aspherical surface and a diffraction surface. The chalcogenide glass lens A is an aspherical positive focal length meniscus lens made of Ge-As-Se-Te chalcogenide glass. The front and back surfaces of the chalcogenide glass lens A are both coated with antireflection coatings. The Ge-As-Se-Te chalcogenide glass has a negative refractive index temperature coefficient. The molar composition formula of the Ge-As-Se-Te chalcogenide glass is Ge x -As y -Se z -Te w (hereinafter referred to as TQNT), wherein x, y, z, and w are all mole percentages, x=20, y=18, z=17.5, and w=44.5.

[0030] In this embodiment, the MWIR imaging optical system has a focal length (EFFL) of 75mm, an F# of 4, a field of view of 8.8°×7°, optical distortion ≤1%, an operating spectral range of 3.7 to 4.8μm, a passive athermalization temperature range of -50°C to +70°C, a total optical length (TTL) of ≤80mm, and an optical back focus of 43mm. The detector compatible with this MWIR imaging optical system is a cooled MWIR detector with an F# of 4, a cold shield height of 20.47mm, a resolution of 640×512, and a pixel size of 15μm. The circular aperture stop in the detector cold shield is made of aluminum alloy and has a Φ10mm aperture.

[0031] In this embodiment, the chalcogenide glass lens A meets the parameter requirements of Table 2 and Table 3.

[0032] Table 2 Parameters of chalcogenide glass lens A

[0033]

[0034] Table 3 Data related to the aspheric and diffractive surfaces of chalcogenide glass lens A

[0035] <![CDATA[a4]]> <![CDATA[a6]]> <![CDATA[a8]]> <![CDATA[a 10 ]]> Aspheric 1.863E-005 2.609E-007 -4.727E-011 0 Diffraction surface 1.586E-004 2.223E-005 -8.989E-007 -3.954E-009

[0036] Note: En stands for “×10 -n ”.

[0037] The aspheric surfaces of the front and back surfaces of the chalcogenide glass lens A both satisfy the following formula:

[0038]

[0039] Where Z(r) is the distance from the vertex of the aspheric surface to the height r along the optical axis; c = 1 / R, R is the paraxial curvature fitting radius of the mirror, that is, the curvature radius; r is the semi-aperture of the lens perpendicular to the optical axis; k is the cone coefficient; a4, a6, a8, a 10 is the high-order aspheric coefficient.

[0040] The phase distribution function of the diffraction surface of the chalcogenide glass lens A in the zemax software is φ(r)=M(B1r 2 +B2r 4 , where M is the diffraction order coefficient, B1 and B2 are the diffraction surface coefficients respectively. The corresponding specific parameters are shown in Table 4.

[0041] Table 4 Data related to the diffraction surface of chalcogenide glass lens A

[0042] M <![CDATA[B1]]> <![CDATA[B2]]> Diffraction surface 1 -9.5 -2.1

[0043] Compared to passively athermalized infrared imaging optical systems that use a combination of traditional crystal materials and chalcogenide glass, the aforementioned medium-wave infrared imaging optical system utilizes a single TQNT aspheric positive-power meniscus lens, achieving a minimalist design for passively athermalized medium-wave infrared imaging. This system effectively reduces the system's size, length, weight, and power consumption, improves its transmittance, and achieves a lightweight and low-cost design. This medium-wave infrared imaging optical system boasts high sensitivity, wide temperature adaptability, a lightweight design, a negative refractive index temperature coefficient, low loss, and a low cost. It enables all-weather target observation and meets the needs of military and civilian applications such as precision guidance, border and coastal defense, night vision systems, environmental monitoring, key location surveillance and security, wildlife inspections, and industrial temperature measurement.

[0044] When the medium-wave infrared imaging optical system of the above embodiment is used, Figure 1 As shown, the light path is incident from the left side (i.e., the front surface) of the chalcogenide glass lens A, passes through the chalcogenide glass lens A, passes through the detector window B, matches the detector cold screen C, and reaches the detector target surface D, forming a medium-wave infrared light path, and a high-definition medium-wave infrared image is formed on the detector target surface D.

[0045] The modulation transfer function diagrams of the medium-wave infrared imaging optical system of the above embodiment at temperatures of 22°C (room temperature), -50°C (lowest temperature) and 70°C (highest temperature) are shown in FIG. Figure 2 、 Figure 3 and Figure 4 .

[0046] Figures 2 to 4 In the text, Diffraction MTF stands for the diffraction limit of the optical transfer function, Spatial Frequency (cycles / mm) stands for the spatial frequency (cycles / mm), Modulation stands for the modulation percentage, F1 to F6 stand for the six fields of view, RIH stands for the real image height, T stands for the sagittal plane, and R stands for the meridional plane. F1: Diff.Limit stands for the diffraction limit, F1: (RIH) 0.000mm stands for the real image height of 0.000mm, F2: T (RIH) 3.075mm stands for the real image height of 3.075mm in the sagittal plane, F2: R (RIH) 3.075mm stands for the real image height of 3.075mm in the meridional plane, F3: T (RIH) 4.348mm stands for the real image height of 4.348mm in the sagittal plane, F3: R (RIH) 4.348mm stands for the real image height of 4.348mm in the meridional plane, and F4: T (RIH) 5.22mm stands for the real image height of 5.22mm in the sagittal plane. 8mm means the real image height in the sagittal plane is 5.228mm, F4:R(RIH)5.228mm means the real image height in the meridional plane is 5.228mm, F5:T(RIH)6.150mm means the real image height in the sagittal plane is 6.150mm, F5:R(RIH)6.150mm means the real image height in the meridional plane is 6.150mm, F6:T(RIH)-6.150mm means the real image height in the sagittal symmetric plane is -6.150mm, and F6:R(RIH)-6.150mm means the real image height in the meridional symmetric plane is -6.150mm.

Claims

1. A monolithic passively athermalized mid-wave infrared imaging optical system, characterized in that: The medium-wave infrared imaging optical system includes a chalcogenide glass lens, a detector window, a detector cold screen, and a detector target surface, which are sequentially arranged along the optical axis from the object side to the image side. The front surface of the chalcogenide glass lens is aspherical, and the rear surface is aspherical and a diffraction surface. The chalcogenide glass lens is an aspherical positive-power meniscus lens made of Ge-As-Se-Te chalcogenide glass. The Ge-As-Se-Te chalcogenide glass has a negative refractive index temperature coefficient. The medium-wave infrared imaging optical system has a focal length EFFL of 75 mm, an F# of 4, a field of view of 8.8°×7°, an optical distortion of ≤1%, an operating spectrum range of 3.7 to 4.8 μm, a passive athermal temperature range of -50°C to +70°C, a total optical length TTL of ≤80 mm, and an optical back intercept of ≥43 mm.

2. The monolithic passively athermalized mid-wave infrared imaging optical system according to claim 1, characterized in that: The molar composition formula of the Ge-As-Se-Te chalcogenide glass is Ge x -As y -Se z -Te w , wherein x, y, z, and w are all mole percentages, x=15-25, y=10-20, z=10-20, w=35-65, x+y+z+w=100.

3. The monolithic passively athermalized mid-wave infrared imaging optical system according to claim 1, characterized in that: The thickness of the chalcogenide glass lens is 7 mm, and the optical back focus is 43 mm.

4. The monolithic passively athermalized mid-wave infrared imaging optical system according to claim 1, characterized in that: The front surface and the rear surface of the chalcogenide glass lens are both coated with antireflection films.

5. The monolithic passively athermalized mid-wave infrared imaging optical system according to claim 1, characterized in that: The detector adapted for the medium-wave infrared imaging optical system is a refrigerated medium-wave infrared detector. The F# of the refrigerated medium-wave infrared detector is 4, the cold screen height is 20.47 mm, the resolution is 640×512, and the pixel size is 15 μm.

6. The monolithic passively athermalized mid-wave infrared imaging optical system according to claim 1, characterized in that: In the detector cold shield, the circular aperture as the aperture stop is made of aluminum alloy, and its aperture is Φ10 mm.

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