A small F-number cooled athermalized mid-wave infrared optical system

Abstract

The invention relates to the technical field of infrared optical systems, and specifically discloses a small F-number refrigerated athermal medium-wave infrared optical system, comprising: seven coaxial lenses, wherein the seven lenses are divided into a front group and a rear group from the object side to the image side, wherein: the front group consists of a front lens group 1, a front lens group 2, and a front lens group 3; the rear group consists of a rear lens group 1, a rear lens group 2, a rear lens group 3, and a rear lens group 4; the invention adopts a secondary imaging structure to meet 100% cold aperture efficiency, and can effectively eliminate stray light in conjunction with a corresponding optical-mechanical structure design; through real-time monitoring of a temperature sensor and an intelligent temperature compensation algorithm, the system automatically adjusts the lens position to ensure that the optical system always maintains high-precision imaging within the temperature fluctuation range, avoiding image plane drift; and through accurate calculation and compensation of focal length changes, the optical system can adapt to a wide range of temperature fluctuations to ensure that the imaging quality is not affected.

Description

Technical Field

[0001] The invention belongs to the technical field of infrared optical systems, and in particular relates to a small F-number refrigeration type athermalized medium-wave infrared optical system. Background Art

[0002] Infrared imaging systems are not affected by adverse weather conditions such as fog and rain, can work all day long, and adopt a passive working mode with strong anti-interference ability. In recent years, they have made great progress in both military and civilian fields. The cooled infrared system has incomparable advantages over the uncooled infrared system, which are mainly reflected in the working distance and imaging effect. Therefore, in demanding use scenarios, such as the military and aerospace fields, cooled thermal imagers are widely used, and the detection degree of cooled detectors is 1 to 2 orders of magnitude higher than that of uncooled detectors.

[0003] As the temperature changes, the parameters of the optical system (r, d, n) will change and cause defocus, and the image quality will be significantly reduced. Therefore, for a wider temperature range, temperature compensation measures need to be adopted. In general, there are two ways of temperature compensation: one is temperature compensation through focusing. When the ambient temperature changes, the axial position of a group of lenses is manually or automatically adjusted by human eye observation or temperature sensor feedback to achieve temperature compensation; the other is optical passive athermal temperature compensation. This method uses the principle of different thermal coefficients of different materials to achieve mutual compensation of positive and negative thermal defocus of different parts of the optical system, and achieves unchanged image quality without focusing in a wide temperature range. This application combines focusing and optical passive athermal temperature compensation to accurately adjust the focal length at different temperatures.

[0004] Based on this, the inventors proposed a small F-number refrigerated athermal medium-wave infrared optical system to solve the above problems. Summary of the invention

[0005] The object of the present invention is to provide a small F-number refrigerated athermal medium-wave infrared optical system having the characteristics of small F-number, compactness and high resolution, and good imaging quality over the entire temperature range, so as to solve the problems raised in the above-mentioned background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A small F-number refrigerated athermalized medium-wave infrared optical system, comprising:

[0008] There are seven coaxial lenses, which are divided into a front group and a rear group from the object side to the image side and installed in an optical-mechanical structure. Spacers are arranged between adjacent lenses, and a precision motor is arranged in the spacer to adjust the position of the spacer to fine-tune the lens position and focal length, wherein:

[0009] The front group is composed of front lens group 1, front lens group 2, and front lens group 3;

[0010] The rear group consists of rear lens group 1, rear lens group 2, rear lens group 3 and rear lens group 4;

[0011] The object side imaging beam passes through the front lens group 1, the front lens group 2, and the front lens group 3 in sequence to form an image, and then passes through the rear lens group 1, the rear lens group 2, the rear lens group 3, and the rear lens group 4 to form a secondary image on the detector;

[0012] A digital temperature sensor TMP117 is embedded in the gap area between the front lens group 1 and the front lens group 2 in the optomechanical structure to monitor the operating temperature of the system in real time.

[0013] Preferably, the front lens group one is a meniscus silicon positive lens convex to the object side, the front lens group two is a biconvex germanium negative lens, and the front lens group three is a meniscus silicon positive lens convex to the object side; the rear lens group one is a zinc selenide negative lens convex to the image plane, the rear lens group two is a meniscus chalcogenide glass IRG101 negative lens convex to the image plane, the rear lens group three is a biconvex zinc selenide negative lens, and the rear lens group four is a biconvex chalcogenide glass IRG208 positive lens.

[0014] Preferably, the seven lenses are made of silicon, germanium, zinc selenide, Xinhuaguang's chalcogenide glass IRG101 and IRG208. The seven lenses include four conventional lenses and three aspherical lenses, which are used to compensate for the image plane drift of the optical system at different temperatures and achieve clear imaging in the full temperature range of -40°C to +60°C.

[0015] Preferably, the second surface of the front lens group 2 is an aspherical surface.

[0016] Preferably, the second surface of the rear lens group one, and the first surface and the second surface of the rear lens group three are aspherical surfaces.

[0017] Preferably, the focal length of the lens of the optical system is 165 mm, and the F number is as small as 1.65.

[0018] Preferably, the distance from the vertex of the first surface of the front lens group to the image plane is maintained at 180.00 mm, and the distance does not change within the temperature range of -40°C to +60°C.

[0019] Preferably, the optical system is suitable for a high-resolution large-target medium-wave cooling detector with a pixel number of 1024×1024 and a pixel size of 12×12 μm.

[0020] Preferably, temperature data is collected by a digital temperature sensor TMP117 and transmitted to a data processing unit, which uses a preset compensation model to calculate the required focal length or lens position adjustment. The calculated compensation amount is executed by a precision motor to make fine adjustments to the adjustable lens or displacement platform in the system to ensure athermal imaging at different temperatures.

[0021] Preferably, the total compensation amount of the system is calculated as follows: the total focal length f(T) of the system as a function of temperature T is affected by the change in the refractive index of the lens material and the change in the geometric size, and its expression is:

[0022]

[0023] Where: f0 is the focal length of the system at reference temperature T0;

[0024] αi is the linear expansion coefficient of the i-th lens material;

[0025] dni / dT is the coefficient of the refractive index of the i-th lens material changing with temperature;

[0026] n is the number of lenses in the system;

[0027] Real-time calculation of compensation:

[0028] According to the real-time temperature T, the compensation system needs to calculate the adjustment amount of the lens or focal length. Assuming the required adjustment amount is Δf(T), we have:

[0029]

[0030] By calculating Δf(T) in real time, the system can adjust the distance or focal length between lens groups according to the current temperature conditions, ensuring that the system can maintain athermal imaging within the design range even under extreme temperature changes. The intelligent temperature compensation algorithm effectively solves the problem of optical image drift caused by temperature changes.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The present invention adopts a secondary imaging structure. The secondary imaging component can compress the aperture of the front lens group to meet 100% cold aperture efficiency, and can effectively eliminate stray light in conjunction with the corresponding optical-mechanical structure design. The effective aperture of the first lens is 52.6 mm and the absolute length is 180 mm, which can achieve good imaging quality. The system includes a front group and a rear group, wherein the front group includes 3 lenses and the rear group includes 4 lenses. The lens materials are all commonly used materials for infrared optical systems. By matching different materials, conventional lenses and Q-type aspherical lenses, athermalization within the temperature range of -40°C to +60°C is achieved.

[0033] (2) The optical lens of the present invention has a focal length of 165 mm and an F number of 1.65. The lens is suitable for a high-resolution 1024×1024 medium-wave cooled detector. It has the characteristics of small F number, compactness, small size, athermalization and high resolution, and has good imaging quality over the entire temperature range.

[0034] (3) In the present invention, through real-time monitoring of the temperature sensor and intelligent temperature compensation algorithm, the system controls the precision motor to automatically adjust the lens position, ensuring that the optical system always maintains high-precision imaging within the temperature fluctuation range, avoiding image plane drift, and through accurate calculation and compensation of focal length changes, the optical system can adapt to a wide range of temperature fluctuations, ensuring that the imaging quality is not affected. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a schematic diagram of an optical system of the present invention;

[0036] Figure 2 A two-dimensional diagram of the optical path of the optical system of the present invention;

[0037] Figure 3 is an optical transfer function diagram of the optical system of the present invention at room temperature, with a cut-off resolution of 42 lp / mm;

[0038] Figure 4 is an optical transfer function diagram of the optical system of the present invention at a low temperature of -40°C, with a cut-off resolution of 42 lp / mm;

[0039] Figure 5 is an optical transfer function diagram of the optical system of the present invention at a high temperature of 60°C, with a cut-off resolution of 42 lp / mm;

[0040] Figure 6 is the diffuse spot size of each field of view of the optical system of the present invention at room temperature;

[0041] Figure 7 is the diffuse spot size of each field of view of the optical system of the present invention at a low temperature of -40°C;

[0042] Figure 8 is the size of the diffuse spot in each field of view of the optical system of the present invention at a low temperature of 60°C;

[0043] In the figure: 1, front lens group one; 2, front lens group two; 3, front lens group three; 4, rear group consists of rear lens group one; 5, rear lens group two; 6, rear lens group three; 7, rear lens group four. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] Embodiment 1:

[0046] See also Figures 1 to 8 As shown, a small F-number cooled athermalized medium-wave infrared optical system comprises:

[0047] There are seven coaxial lenses, which are divided into a front group and a rear group from the object side to the image side and installed in an optical-mechanical structure. Spacers are arranged between adjacent lenses, and a precision motor is arranged in the spacer to adjust the position of the spacer to fine-tune the lens position and focal length, wherein:

[0048] The front group is composed of front lens group one 1, front lens group two 2, and front lens group three 3;

[0049] The rear group is composed of rear lens group one 4, rear lens group two 5, rear lens group three 6, and rear lens group four 7;

[0050] The object side imaging light beam is formed once after passing through front lens group 1, front lens group 2, and front lens group 3 in sequence, and then formed a second image on the detector after passing through rear lens group 4, rear lens group 2, rear lens group 3, and rear lens group 4 7. In the optical-mechanical structure, a digital temperature sensor TMP117 is embedded in the gap area between front lens group 1 and front lens group 2 for real-time monitoring of the system's operating temperature.

[0051] Specifically, the front lens group 1 is a meniscus silicon positive lens convex to the object side, the front lens group 2 is a double convex germanium negative lens, and the front lens group 3 is a meniscus silicon positive lens convex to the object side; the rear lens group 4 is a zinc selenide negative lens convex to the image plane, the rear lens group 2 5 is a meniscus chalcogenide glass IRG101 negative lens convex to the image plane, the rear lens group 3 6 is a double convex zinc selenide negative lens, and the rear lens group 4 7 is a double convex chalcogenide glass IRG208 positive lens.

[0052] Specifically, the seven lenses are made of silicon, germanium, zinc selenide, Xinhuaguang's chalcogenide glass IRG101 and IRG208. The seven lenses include four conventional lenses and three aspherical lenses, which are used to compensate for the image plane drift of the optical system under different temperatures and achieve clear imaging in the full temperature range of -40℃ to +60℃.

[0053] Specifically, the second surface of the front lens group 2 is an aspherical surface.

[0054] Specifically, the second surface of the rear lens group 1 4 and the first surface and the second surface of the rear lens group 3 6 are aspherical surfaces.

[0055] Specifically, the focal length of the lens of the optical system is 165 mm, and the F number is as small as 1.65.

[0056] Specifically, the distance from the vertex of the first surface of the front lens group 1 to the image plane is maintained at 180.00 mm, and the distance does not change within the temperature range of -40°C to +60°C.

[0057] Specifically, the optical system is suitable for a high-resolution large-target medium-wave cooled detector with a pixel number of 1024×1024 and a pixel size of 12×12 μm.

[0058] Temperature data is collected by the digital temperature sensor TMP117 and transmitted to the data processing unit. The data processing unit uses a preset compensation model to calculate the required focal length or lens position adjustment. The calculated compensation is executed by a precision motor to make subtle adjustments to the adjustable lens or displacement platform in the system to ensure athermal imaging at different temperatures.

[0059] Preferably, the total compensation amount of the system is calculated as follows: the total focal length f(T) of the system as a function of temperature T is affected by the change in the refractive index of the lens material and the change in the geometric size, and its expression is:

[0060]

[0061] Where: f0 is the focal length of the system at reference temperature T0;

[0062] αi is the linear expansion coefficient of the i-th lens material;

[0063] dni / dT is the coefficient of the refractive index of the i-th lens material changing with temperature;

[0064] n is the number of lenses in the system;

[0065] Real-time calculation of compensation:

[0066] According to the real-time temperature T, the compensation system needs to calculate the adjustment amount of the lens or focal length. Assuming the required adjustment amount is Δf(T), we have:

[0067]

[0068] By calculating Δf(T) in real time, the system can adjust the distance or focal length between lens groups according to the current temperature conditions, ensuring that the system can maintain athermal imaging within the design range even under extreme temperature changes. The intelligent temperature compensation algorithm effectively solves the problem of optical image drift caused by temperature changes.

[0069] The design index requirements are shown in Table 1 below:

[0070]

[0071] Table 1

[0072] Initial parameter calculation and analysis:

[0073] 1) Focal length solution:

[0074] Known: Detector array: 1024×1024, pixel size: 12µm

[0075] Solving the focal length according to the formula:

[0076] Image height =

[0077] Solved image height = 8.689mm

[0078] Knowing that 2W=6°, we can solve the focal length according to the formula:

[0079]

[0080] The focal length is solved to be 165.8mm.

[0081] 2) Dewar flask calculation analysis

[0082] The cold screen (cold stop) has an aperture of 24.2mm at a distance of 40mm in front of the focal plane (image plane). There is a 0.8mm thick filter made of germanium (GERMANIUM) 4mm in front of the image plane, which improves the image quality by filtering out unnecessary wavelengths. There is a 2.5mm thick window made of silicon (SILICON) at a distance of 1.85mm in front of the cold screen, which protects the Dewar flask, and there is a cold finger behind the focal plane to cool the detector.

[0083] Embodiment 2:

[0084] See also Figures 1 to 8 As shown, from the object side to the image side, the first meniscus positive lens in the front group, the second meniscus negative lens in the front group, the third meniscus positive lens in the front group, the first meniscus negative lens in the rear group, the second meniscus negative lens in the rear group, the third meniscus negative lens in the rear group, the fourth meniscus negative lens in the rear group, the first detector protection window and the cold aperture are arranged in sequence.

[0085] The optical structure parameters are shown in Table 2 below:

[0086]

[0087] Table 2

[0088] From the above, we can see that the aspheric surfaces mentioned in the above 4 lenses are all Q-type aspheric surfaces, and their expressions are as follows:

[0089]

[0090] Where z is the distance vector height from the vertex of the aspheric surface when the aspheric surface is at a height of r along the optical axis, c represents the vertex curvature of the surface, k is the cone coefficient, , , is the high-order aspheric coefficient;

[0091] Table 3 shows the aspheric coefficients of surface S5:

[0092]

[0093] Table 3

[0094] As can be seen from the above, the present invention provides a small F-number refrigerated athermal medium-wave infrared optical system, which adopts high-order aspheric surfaces to improve the system image quality and uses five materials, namely silicon, germanium, zinc selenide, chalcogenide glasses IRG101 and IRG208, to correct chromatic aberration.

[0095] In the present invention, the effective focal length EFL of the small F-number refrigerated athermal medium-wave infrared optical system is 165 mm, the F-number is 1.65, the total length of the optical system is 180 mm, the adapted detector resolution is 1024×1024, and the pixel size is 12 μm.

[0096] Embodiment three:

[0097] This design is specifically used in the aerospace field. Infrared imaging technology can be used in applications such as aircraft navigation, rocket launches, and satellite monitoring. The system's athermal design and high-resolution imaging can cope with drastic temperature changes in outer space or high altitudes, and provide clear infrared images during long-distance detection missions of spacecraft, ensuring accurate detection and navigation support for aircraft or satellites of ground or space objects.

[0098] Furthermore, a small F-number refrigerated athermalized medium-wave infrared optical system, the temperature compensation is as follows:

[0099] Optical system focal length f0: 165mm (at reference temperature, T0=25℃)

[0100] F-number: 1.65

[0101] Operating temperature range: -40℃~+60℃

[0102] Sensor model: PT100 (accuracy ±0.1℃)

[0103] Lens Material:

[0104] The linear expansion coefficient of silicon lens is αSi=2.6×10 -6 / K

[0105] The linear expansion coefficient of the germanium lens is αGe=5.9×10 -6 / K

[0106] The linear expansion coefficient of zinc selenide lens is αZnSe=7.1×10 -6 / K

[0107] Refractive index temperature coefficient dn / dT:

[0108] Silicon lens: dnSi / dT=-1.2×10 -4 / K

[0109] Germanium lens: dnGe / dT=-4.0×10 -5 / K

[0110] Zinc selenide lens: dnZnSe / dT=-6.0×10 -5 / K

[0111] Sensor monitoring data and compensation calculation:

[0112] Assume that the system is at an ambient temperature of -20°C, the sensor measures the temperature and triggers the intelligent temperature compensation algorithm.

[0113] Temperature deviation: T = -20℃

[0114] Temperature deviation ΔT = T-T0 = -20℃-25℃ = -45℃

[0115] Focal length change calculation: Using the linear expansion coefficient and refractive index temperature coefficient of each lens material, calculate the impact of each lens on the focal length of the system. The total focal length change Δf(T) of the system is determined by the sum of the contributions of each lens. The specific formula is as follows:

[0116]

[0117] For silicon lens, germanium lens and zinc selenide lens, calculate respectively:

[0118] The influence of silicon lens (front lens 1 and 3):

[0119] ΔfSi=f0×(αSi×ΔT+dnSi / dT×ΔT)=165×(2.6×10 -6 ×(-45)+(-1.2×10 -4 )×(-45))=165×(-0.000117+0.0054)=165×0.005283=0.87 mm

[0120] The influence of the germanium lens (the second lens in the front group):

[0121] ΔfGe=165×(5.9×10 -6 ×(-45)+(-4.0×10 -5 )×(-45))=165×(-0.0002655+0.0018)=165×0.0015345=0.253 mm

[0122] The influence of zinc selenide lens (rear lens group one and three):

[0123] ΔfZnSe=165×(7.1×10 -6 ×(-45)+(-6.0×10 -5 )×(-45))=165×(-0.0003195+0.0027)=165×0.0023805=0.393 mm

[0124] Total focal length change: Add the focal length changes of each lens to get the total focal length change of the system Δf(T):

[0125] Δf(T)=ΔfSi+ΔfGe+ΔfZnSe=0.87+0.253+0.393=1.516 mm

[0126] Compensation execution: Based on the calculated focal length change Δf(T) = 1.516 mm, the intelligent temperature compensation system adjusts the position of the lens group, moving it by a precise distance of 1.516 mm to ensure that the system remains athermal at -20°C for optimal imaging quality.

[0127] From the above, we can see that when the temperature drops to -20℃, through real-time monitoring of the temperature sensor and intelligent temperature compensation algorithm, the system controls the precision motor to automatically adjust the lens position and compensate for the focal length change of 1.516mm, ensuring that the optical system always maintains high-precision imaging within the temperature fluctuation range and avoids image drift. By accurately calculating and compensating for focal length changes, the optical system can adapt to a wide range of temperature fluctuations and ensure that the imaging quality is not affected.

[0128] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples, unless they are contradictory.

[0129] In the drawings of the embodiments disclosed in the present invention, only the structures related to the embodiments disclosed in the present invention are involved, and other structures can refer to the general design. In the absence of conflict, the same embodiment and different embodiments of the present invention can be combined with each other.

Claims

1. A small F-number refrigerated athermalized medium-wave infrared optical system, characterized in that: include: There are seven coaxial lenses, which are divided into a front group and a rear group from the object side to the image side and installed in an optical-mechanical structure. Spacers are arranged between adjacent lenses, and a precision motor is arranged in the spacer to adjust the position of the spacer to fine-tune the lens position and focal length, wherein: The front group is composed of front lens group one (1), front lens group two (2), and front lens group three (3); The rear group is composed of rear lens group one (4), rear lens group two (5), rear lens group three (6), and rear lens group four (7); The object imaging beam passes through the front lens group one (1), the front lens group two (2), and the front lens group three (3) in sequence to form an image, and then passes through the rear lens group one (4), the rear lens group two (5), the rear lens group three (6), and the rear lens group four (7) to form a secondary image on the detector; in the optical-mechanical structure, a digital temperature sensor TMP117 is embedded in the gap area between the front lens group one (1) and the front lens group two (2) to monitor the working temperature of the system in real time; The front lens group one (1) is a positive meniscus silicon lens convex to the object side, the front lens group two (2) is a biconvex germanium negative lens, the front lens group three (3) is a positive meniscus silicon lens convex to the object side; the rear lens group one (4) is a negative zinc selenide lens convex to the image side, the rear lens group two (5) is a negative meniscus chalcogenide glass IRG101 lens convex to the image side, the rear lens group three (6) is a biconvex zinc selenide negative lens facing the image side, and the rear lens group four (7) is a biconvex chalcogenide glass IRG208 positive lens facing the object side; The focal length of the lens of the optical system is 165 mm, and the F number is relatively small, which is 1.

65.

2. The small F-number refrigerated athermalized medium-wave infrared optical system according to claim 1, characterized in that: The seven lenses are made of silicon, germanium, zinc selenide, Xinhuaguang's chalcogenide glass IRG101 and IRG208. The seven lenses include four conventional lenses and three aspherical lenses, which are used to compensate for the image drift of the optical system at different temperatures and achieve clear imaging in the full temperature range of -40°C to +60°C.

3. The small F-number refrigerated athermalized medium-wave infrared optical system according to claim 1, characterized in that: The second surface of the front lens group 2 (2) is an aspherical surface.

4. The small F-number refrigerated athermalized medium-wave infrared optical system according to claim 1, characterized in that: The second surface of the rear lens group one (4) and the first surface and the second surface of the rear lens group three (6) are aspherical surfaces.

5. The small F-number refrigerated athermalized medium-wave infrared optical system according to claim 1, characterized in that: The distance from the vertex of the first surface of the front lens group one (1) to the image plane is maintained at 180.00 mm, and the distance does not change within the temperature range of -40°C to +60°C.

6. A small F-number refrigerated athermalized medium-wave infrared optical system according to any one of claims 1 to 5, characterized in that: The optical system is suitable for a high-resolution large-target medium-wave cooling detector with a pixel number of 1024×1024 and a pixel size of 12×12 μm.

7. The small F-number refrigerated athermalized medium-wave infrared optical system according to claim 1, characterized in that: Temperature data is collected by the digital temperature sensor TMP117 and transmitted to the data processing unit. The data processing unit uses a preset compensation model to calculate the required focal length or lens position adjustment. The calculated compensation is executed by a precision motor to make subtle adjustments to the adjustable lens or displacement platform in the system to ensure athermal imaging at different temperatures.

8. The small F-number refrigerated athermalized medium-wave infrared optical system according to claim 7, characterized in that: For the compensation model, the total compensation of the system is calculated as follows: The total focal length f(T) of the system as a function of temperature T is affected by the change in the refractive index of the lens material and the change in the geometric size. Its expression is: Where: f0 is the focal length of the system at reference temperature T0; αi is the linear expansion coefficient of the i-th lens material; dni / dT is the coefficient of the refractive index of the i-th lens material changing with temperature; n is the number of lenses in the system; Real-time calculation of compensation: According to the real-time temperature T, the compensation system needs to calculate the adjustment amount of the lens or focal length. Assuming the required adjustment amount is Δf(T), we have: Δf(T)=f(T)-f0 By calculating Δf(T) in real time, the system can adjust the distance or focal length between lens groups according to the current temperature conditions.

Images