A normal temperature mirror spacing preset method and system for a transmission type low temperature optical system
By measuring the thermal expansion coefficients of the lens and structure, as well as the distance from the vertex to the surface, the mirror spacing at room temperature was calculated. This solved the problem of mismatched mirror spacing during the assembly and adjustment of low-temperature optical systems, enabling accurate preset of mirror spacing at low temperatures and improving imaging quality.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BEIJING UNIV OF POSTS & TELECOMM
- Filing Date
- 2026-03-30
- Publication Date
- 2026-06-19
AI Technical Summary
In existing technologies, when assembling and adjusting a low-temperature optical system at room temperature, the inter-mirror distance cannot be used as a valid reference, resulting in inconsistent changes in the inter-mirror distance under low-temperature conditions, which affects the imaging quality.
By measuring the thermal expansion coefficients of the lenses and the structure, as well as the distance from the vertex to the surface, the distance between the lenses at room temperature is calculated. Combined with the shrinkage due to temperature changes, this is converted into the distance between the lenses at low temperatures for assembly and adjustment.
It enables accurate pre-setting of the lens spacing in a low-temperature optical system at room temperature, ensuring that the lens spacing is consistent with the optical design at low temperatures and improving imaging quality.
Smart Images
Figure CN122239249A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of optical technology, and more specifically, to a method and system for presetting the mirror spacing at room temperature in a transmission-type low-temperature optical system. Background Technology
[0002] With the development of space infrared remote sensors, their spectral range has expanded from near-infrared (around 1 μm) to far-infrared (around 240 μm), and even to the submillimeter wave range (670 μm). However, since current infrared detection devices have approached or reached the background detection limit, the detection sensitivity and dynamic range of infrared remote sensors are mainly limited by the magnitude of radiated noise in the observation background. Even with good external stray light suppression, their detection capability is significantly affected because the internal radiation of the optical lens components has become the main source of background radiated noise. Therefore, to reduce internal thermal radiation, lower the background noise of the infrared detector, and effectively improve the detection sensitivity of infrared remote sensors, a cryogenic optical system with lens cooling must be adopted.
[0003] Lens spacing is a crucial factor affecting the imaging quality of an optical system. For cryogenic optical systems, assembly and adjustment are completed at room temperature. When operating in a cryogenic environment, the optical parameters of the lenses, such as refractive index, radius of curvature, and thickness, will change. Transmission-type cryogenic optical systems utilize the refractive index and other optical parameters of the lenses under cryogenic conditions for optical design, but assembly and adjustment must be performed at room temperature. Due to the influence of the coefficient of thermal expansion of materials, both optical and structural materials will experience dimensional shrinkage or expansion with changes in ambient temperature, leading to changes in lens spacing. Therefore, the cryogenic lens spacing of each lens in the optical design cannot be used as a valid basis for room temperature assembly and adjustment; it is necessary to convert the cryogenic lens spacing of the optical design to room temperature lens spacing for assembly and adjustment.
[0004] The change in lens spacing caused by temperature variations from low temperature to room temperature is related to the contact surface position of each lens in the lens structure design. However, the room temperature lens spacing calculated directly by optical software is derived from the air gap between the edges of two adjacent lenses, which does not match the actual change in lens spacing from low temperature to room temperature in the actual system. Therefore, this invention proposes a calculation method that can calculate the room temperature lens spacing using the distance from the lens vertex to the contact surface, the thermal expansion coefficient of the material, and the low temperature lens spacing. This allows for the preset room temperature lens spacing in low-temperature optical systems, ensuring that the lens spacing at low temperatures matches the optical design results and does not affect the imaging quality of the optical system. Summary of the Invention
[0005] This invention provides a method and system for presetting the mirror spacing at room temperature in a transmission-type low-temperature optical system, in order to overcome at least one technical problem existing in the prior art.
[0006] On one hand, the present invention provides a method for presetting the room temperature mirror spacing of a transmissive cryogenic optical system. The transmissive cryogenic optical system includes at least two lenses and a structure arranged alternately with each lens. Let two adjacent lenses be a front lens and a rear lens, the front lens corresponds to a first structure, and the rear lens corresponds to a second structure. The surface of the front lens that contacts the first structure is a first contact surface, and the surface of the rear lens that contacts the second structure is a second contact surface. Methods for presetting the mirror spacing at room temperature include: Measure the coefficients of thermal expansion of the front lens, the rear lens, and the structure; Measure the distance from the vertex of the exit surface of the front lens to the first contact surface, and the distance from the vertex of the incident surface of the rear lens to the second contact surface; Calculate the distance between the first and second contact surfaces at room temperature; Based on the coefficient of thermal expansion and distance, calculate the temperature-dependent shrinkage of the optical system from room temperature to low temperature; where assembly temperature represents room temperature and operating temperature represents low temperature. The cryogenic optical system was optically designed to obtain the cryogenic mirror spacing L. LT ; Based on the temperature shrinkage and the low-temperature mirror spacing L LT The distance L between the mirrors at room temperature was calculated. RT The value; According to the room temperature mirror spacing L RT The value is used to design the lens casing.
[0007] Optionally, the temperature shrinkage of the optical system includes the temperature shrinkage L of the rear lens. 后 Temperature shrinkage L of the front lens 前 Temperature shrinkage L of the structure 结构 .
[0008] Optionally, the temperature shrinkage of the front lens is expressed as L. 前 = L1·α1·△T, where L1 represents the distance from the vertex of the exit surface of the front lens to the first contact surface, α1 represents the thermal expansion coefficient of the front lens, and △T represents the temperature difference from room temperature to low temperature.
[0009] Optionally, the temperature-induced shrinkage of the rear lens is expressed as L. 后 = L2·α2·△T, where L2 represents the distance from the vertex of the exit surface of the rear lens to the first contact surface, α2 represents the thermal expansion coefficient of the rear lens, and △T represents the temperature difference from room temperature to low temperature.
[0010] Optionally, the temperature-induced shrinkage of the structure is expressed as L. 结构= L3·α3·△T, where L3 represents the distance from the first contact surface to the second contact surface at room temperature, L3=L RT - L1+ L2, α3 represents the thermal expansion coefficient of the structure, and ΔT represents the temperature difference from room temperature to low temperature.
[0011] Optionally, based on the temperature-induced shrinkage and the low-temperature mirror spacing L... LT The distance L between the mirrors at room temperature was calculated. RT The value is as follows: The relationship between the shrinkage of the front lens, rear lens, and structure and the inter-lens distance was analyzed from room temperature to low temperature. Specifically, the inter-lens distance decreased when the front lens shrank, the inter-lens distance decreased when the structure shrank, and the inter-lens distance increased when the rear lens shrank. Based on the aforementioned relationship, the cryogenic mirror spacing L is obtained. LT =Mirror spacing at room temperature L RT - Temperature shrinkage of the front lens L 前 - Temperature shrinkage of the structure L 结构 +Rear lens temperature shrinkage L 后 Then the distance between mirrors at room temperature, L RT =Low-temperature mirror spacing L LT +Temperature shrinkage of the front lens L 前 + Temperature shrinkage of the structure L 结构 - Temperature shrinkage L of the rear lens 后 .
[0012] Optionally, the cryogenic optical system is optically designed, specifically as follows: Measure the refractive index of the lens at low temperature; The low-temperature optical system is optically designed based on the refractive index of the lens.
[0013] On the other hand, the present invention also provides a room temperature mirror spacing preset system for a transmissive low-temperature optical system. The transmissive low-temperature optical system includes at least two lenses and a structure arranged alternately with each lens. Let two adjacent lenses be a front lens and a rear lens, the front lens corresponds to a first structure, and the rear lens corresponds to a second structure. The surface of the front lens that contacts the first structure is a first contact surface, and the surface of the rear lens that contacts the second structure is a second contact surface. The room temperature mirror spacing preset system includes: The first measurement module is used to measure the thermal expansion coefficients of the front lens, the rear lens, and the structure. The second measurement module is used to measure the distance from the vertex of the exit surface of the front lens to the first contact surface, and the distance from the vertex of the incident surface of the rear lens to the second contact surface. The first calculation module is used to calculate the distance between the first and second contact surfaces at room temperature; The second calculation module is used to calculate the temperature-dependent shrinkage of the optical system from room temperature to low temperature based on the coefficient of thermal expansion and distance; wherein, the assembly temperature represents room temperature and the operating temperature represents low temperature. The first design module is used to perform optical design on the cryogenic optical system and obtain the cryogenic mirror spacing L. LT ; The third calculation module is used to calculate the temperature-induced shrinkage and the low-temperature mirror spacing L. LT The distance L between the mirrors at room temperature was calculated. RT The value; The second design module is used to determine the normal temperature mirror spacing L. RT The value is used to design the lens casing.
[0014] Optionally, the temperature shrinkage of the optical system includes the temperature shrinkage L of the rear lens. 后 Temperature shrinkage L of the front lens 前 Temperature shrinkage L of the structure 结构 ; The third calculation module is specifically used for: The relationship between the shrinkage of the front lens, rear lens, and structure and the inter-lens distance was analyzed from room temperature to low temperature. Specifically, the inter-lens distance decreased when the front lens shrank, the inter-lens distance decreased when the structure shrank, and the inter-lens distance increased when the rear lens shrank. Based on the aforementioned relationship, the cryogenic mirror spacing L is obtained. LT =Mirror spacing at room temperature L RT - Temperature shrinkage of the front lens L 前 - Temperature shrinkage of the structure L 结构 +Rear lens temperature shrinkage L 后 Then the distance between mirrors at room temperature, L RT =Low-temperature mirror spacing L LT +Temperature shrinkage of the front lens L 前 + Temperature shrinkage of the structure L 结构 - Temperature shrinkage L of the rear lens 后 .
[0015] Optionally, the first design module is specifically used for: Measure the refractive index of the lens at low temperature; The low-temperature optical system is optically designed based on the refractive index of the lens.
[0016] The innovative aspects of this invention include: In this embodiment, addressing the issue that the optical processing and assembly of the lens in a low-temperature transmission optical system are carried out at room temperature and pressure, and the lens spacing provided after the optical design is a vacuum low-temperature lens spacing that cannot be used as the room-temperature assembly distance, a method is proposed to calculate the room-temperature lens spacing by using the distance from the lens vertex to the contact surface, the thermal expansion coefficient of the material, and the low-temperature lens spacing. This allows the low-temperature lens spacing to be converted into a room-temperature lens spacing for assembly, enabling the lens spacing change from room temperature to low temperature to be preset during the assembly process. This provides a reliable basis for the room-temperature assembly of the low-temperature optical system and is one of the innovative points of this embodiment. Attached Figure Description
[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0018] Figure 1 This is a schematic diagram of a transmission-type low-temperature optical system provided in an embodiment of the present invention; Figure 2 A flowchart of a method for presetting the distance between mirrors at room temperature provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of a room temperature mirror spacing preset system provided in an embodiment of the present invention. Detailed Implementation
[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0020] It should be noted that the terms "comprising" and "having," and any variations thereof, in the embodiments and drawings of this invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices.
[0021] This invention discloses a method and system for presetting the mirror spacing at room temperature in a transmission-type low-temperature optical system. These will be described in detail below.
[0022] Figure 1This is a schematic diagram of a transmission-type low-temperature optical system provided in an embodiment of the present invention. Figure 2 A flowchart of a room-temperature mirror spacing preset method provided in an embodiment of the present invention is provided below. Figure 1 and Figure 2 The present invention provides a method for presetting the room temperature mirror spacing of a transmissive cryogenic optical system. The transmissive cryogenic optical system 10 includes at least two lenses and a structure that is arranged alternately with each lens. Let two adjacent lenses be a front lens 11 and a rear lens 12. The front lens 11 corresponds to a first structure 13, and the rear lens 12 corresponds to a second structure 14. The surface of the front lens 11 that contacts the first structure 13 is the first contact surface 15, and the surface of the rear lens 12 that contacts the second structure 14 is the second contact surface 16. Methods for presetting the mirror spacing at room temperature include: Step 1: Measure the coefficients of thermal expansion of the front lens 11, the rear lens 12, and the structure; Step 2: Measure the distance from the vertex of the exit surface of the front lens 11 to the first contact surface 15, and the distance from the vertex of the incident surface of the rear lens 12 to the second contact surface 16. Step 3: Calculate the distance between the first contact surface 15 and the second contact surface 16 at room temperature; Step 4: Calculate the temperature shrinkage of the optical system from room temperature to low temperature based on the coefficient of thermal expansion and distance; where assembly temperature represents room temperature and operating temperature represents low temperature. Step 5: Perform optical design on the cryogenic optical system to obtain the cryogenic mirror spacing L. LT ; Step 6: Based on the temperature shrinkage and the low-temperature mirror spacing L LT The distance L between the mirrors at room temperature was calculated. RT The value; Step 7: Based on the room temperature mirror spacing L RT The value is used to design the lens mounting tube.
[0023] For details, please refer to Figure 1 The transmissive low-temperature optical system 10 includes at least two lenses and structures arranged alternately with each lens. To clearly illustrate the calculation method for the inter-lens distance at room temperature, this invention uses two lenses as an example, assuming two adjacent lenses are a front lens 11 and a rear lens 12. A structure is respectively provided for the front lens 11 and the rear transparent lens 12. The first structure 13 corresponds to the front lens 11, and the second structure 14 corresponds to the rear lens 12, as shown below. Figure 1 In the design, the first structure 13 is located between the front lens 11 and the rear lens 12, while the second structure 14 is located on the side of the rear lens 12 away from the front lens 11. The surface of the front lens 11 that contacts the first structure 13 is the first contact surface 15, and the surface of the rear lens 12 that contacts the second structure 14 is the second contact surface 16.
[0024] The inter-lens distance is the distance from the vertex of the exit surface of the front lens to the vertex of the incident surface of the rear lens, such as... Figure 1 As shown, L RT For the distance between mirrors at room temperature, L LT This refers to the distance between low-temperature mirrors. Normally, when the ambient temperature changes, the dimensions of a material change accordingly; this rate of change is called the coefficient of thermal expansion. Figure 1 In the low-temperature optical system shown, both the lens and the structure expand during the temperature change from low temperature to room temperature. Since the materials of the structure and the lens are different, their coefficients of thermal expansion are different, resulting in different dimensional changes. Therefore, it is necessary to calculate the changes in the structure and the lens with temperature separately.
[0025] Based on this, please refer to Figure 2 The method for presetting the distance between lenses in a low-temperature transmissive optical system provided in this embodiment of the invention involves measuring the coefficients of thermal expansion of the front lens 11, rear lens 12, and structure at low temperatures in step 1. The coefficients of thermal expansion are related to the selected materials. The lenses can be made of germanium or silicon, while the structure can be made of titanium alloy. In this embodiment, the measured low-temperature coefficients of thermal expansion for germanium are 1.98E-06, for silicon 5.37E-06, and for titanium alloy 8.76E-06.
[0026] When the temperature changes, for example, an assembly temperature of 293K represents room temperature, and an operating temperature of 200K represents a low temperature, the dimensional change of the material can be calculated using the formula ΔL = L0·α·ΔT. Therefore, in addition to the coefficient of thermal expansion α, the dimension L0 also needs to be obtained. From room temperature to low temperature, the contraction of both the front lens 11 and the rear lens 12 will cause the inter-lens distance to contract from room temperature to low temperature. (Refer to...) Figure 1 In this invention, the lens contraction mainly originates from the contraction of two distances: the distance L1 from the vertex of the exit surface of the front lens 11 to the first contact surface 15, and the distance L2 from the vertex of the incident surface of the rear lens 12 to the second contact surface 16. Therefore, after the lens is manufactured, step 2 is performed to measure the distance L1 from the vertex of the exit surface of the front lens 11 to the first contact surface 15, and the distance L2 from the vertex of the incident surface of the rear lens 12 to the second contact surface 16, in order to subsequently calculate the change in inter-lens distance caused by the lens.
[0027] Besides the lens, structural contraction can also cause changes in the inter-lens distance. (See reference...) Figure 1 In this invention, the structural shrinkage mainly originates from the shrinkage of the distance between the first abutment surface 15 and the second abutment surface 16. Therefore, in step 3, the distance between the first abutment surface 15 and the second abutment surface 16 at room temperature is calculated. Figure 1 It can be seen that the distance between the first contact surface 15 and the second contact surface 16 is related to the mirror spacing. Assuming the mirror spacing at room temperature is L...RT Then the distance L3 between the first contact surface 15 and the second contact surface 16 can be calculated as L = L RT - L1+ L2.
[0028] After obtaining the thermal expansion coefficients and distances of the structure and each lens, in step 4, the thermal shrinkage of the structure and each lens from room temperature to low temperature can be calculated based on the thermal expansion coefficients and distances. According to the dimensional change formula, the thermal shrinkage L of the front lens 11 is obtained. 前 = L1·α1·△T, the temperature-induced shrinkage L of the rear lens 12 后 = L²·α²·△T, the temperature-induced shrinkage of the structure, L 结构 = L3·α3·△T; where α1 represents the thermal expansion coefficient of the front lens 11, α2 represents the thermal expansion coefficient of the rear lens 12, α3 represents the structural thermal expansion coefficient, and △T represents the temperature difference from room temperature to low temperature.
[0029] Depend on Figure 1 The effects of temperature-induced shrinkage of the structure and individual lenses on the inter-lens distance can be analyzed from room temperature to low temperature. For example, shrinkage of the front lens 11 will decrease the inter-lens distance; structural shrinkage will also decrease the inter-lens distance; while shrinkage of the rear lens 12 will increase the inter-lens distance. Therefore, the overall temperature-induced shrinkage of the optical system from room temperature to low temperature can be calculated.
[0030] In this invention, the room-temperature mirror spacing is calculated by the overall temperature shrinkage of the optical system and the low-temperature mirror spacing. Therefore, after obtaining the overall temperature shrinkage of the optical system, the low-temperature optical system can be optically designed in step 5 to obtain the low-temperature mirror spacing L of the low-temperature optical system. LT .
[0031] In this embodiment, taking into account the system requirements of a working spectral range of 3μm~5μm, an object-side field of view of 8°×8°, an entrance pupil diameter of 265mm, a focal length of 525mm, and an operating temperature of 200K, as well as the requirement for compact structure due to the low-temperature cooling of the lens, the optical design of the low-temperature optical system is carried out by measuring the refractive index of the lens at low temperature. The optical design adopts an image-side telecentric transmission optical system.
[0032] The temperature shrinkage of the optical system and the low-temperature mirror spacing L were obtained. LT Then, in step 6, the temperature shrinkage of the optical system and the low-temperature mirror spacing L can be determined. LT The distance L between mirrors at room temperature was calculated. RT The value of .
[0033] As the distance between the front lens 11 and the mirrors decreases from room temperature to low temperature, the structural contraction also reduces the mirror spacing; conversely, the contraction of the rear lens 12 increases the mirror spacing. Therefore, the low-temperature mirror spacing L can be obtained. LT=Mirror spacing at room temperature L RT - Temperature shrinkage L of front lens 11 前 - Temperature shrinkage of the structure L 结构 +Temperature shrinkage L of rear lens 12 后 That is, L LT =L RT -(L RT -L1+L2)·α3·△T–L1·α1·△T+L2·α2·△T. Converting this formula yields L. RT =[L1·(α1·△T-α3·△T)-L2·(α2·△T-α3·△T)+L LT In practical applications, the room-temperature mirror spacing L can be calculated by substituting the measured values of each parameter into the formula. RT The value of .
[0034] When designing the lens structure, the results of tolerance analysis must be considered. Because tolerance analysis imposes strict requirements on the lens's eccentricity and tilt tolerances, each lens needs to be centered during subsequent assembly and adjustment. Each lens requires a frame during design, and a 2-4mm allowance is reserved on each side of each lens based on the lens's aperture diameter for edge-pressing design. After the lens frame design is completed, in step 7, the calculated room-temperature lens spacing L can be used... RT The value is used to design the lens mounting tube.
[0035] The present invention provides a method for presetting the lens spacing at room temperature in a low-temperature transmissive optical system. Addressing the issue that the optical processing and assembly of lenses in low-temperature transmissive optical systems are performed at room temperature and pressure, and the lens spacing provided after optical design is a vacuum low-temperature lens spacing that cannot be used as the room-temperature assembly distance, the present invention proposes a method to calculate the room-temperature lens spacing using the distance from the lens vertex to the contact surface, the material's thermal expansion coefficient, and the low-temperature lens spacing. This allows the low-temperature lens spacing to be converted to a room-temperature lens spacing for assembly, enabling the lens spacing change from room temperature to low temperature to be preset during the assembly process, providing a reliable basis for the room-temperature assembly of low-temperature optical systems.
[0036] Based on the same inventive concept, the present invention also provides a room-temperature mirror spacing preset system for a transmission-type low-temperature optical system. Figure 3 This is a schematic diagram of a room-temperature mirror spacing preset system provided in an embodiment of the present invention. Please refer to... Figure 3In the room temperature mirror spacing preset system of the transmissive low-temperature optical system provided by the present invention, the transmissive low-temperature optical system 10 includes at least two lenses and a structure that is alternately arranged with each lens. Let the two adjacent lenses be the front lens 11 and the rear lens 12, the front lens 11 corresponds to the first structure 13, and the rear lens 12 corresponds to the second structure 14; the surface of the front lens 11 that contacts the first structure 13 is the first contact surface 15, and the surface of the rear lens 12 that contacts the second structure 14 is the second contact surface 16. The ambient temperature mirror spacing preset system 100 includes: The first measurement module is used to measure the thermal expansion coefficients of the front lens 11, the rear lens 12, and the structure. The second measurement module is used to measure the distance from the vertex of the exit surface of the front lens 11 to the first contact surface 15, and the distance from the vertex of the incident surface of the rear lens 12 to the second contact surface 16. The first calculation module is used to calculate the distance between the first contact surface 15 and the second contact surface 16 at room temperature; The second calculation module is used to calculate the temperature-dependent shrinkage of the optical system from room temperature to low temperature based on the coefficient of thermal expansion and distance; where assembly temperature represents room temperature and operating temperature represents low temperature. The first design module is used for optical design of the cryogenic optical system to obtain the cryogenic mirror spacing L. LT ; The third calculation module is used to calculate the temperature-induced shrinkage and the low-temperature mirror spacing L. LT The distance L between the mirrors at room temperature was calculated. RT The value; The second design module is used to determine the mirror spacing L at room temperature. RT The value is used to design the lens mounting tube.
[0037] For details, please refer to Figure 1 The transmission-type low-temperature optical system 100 includes at least two lenses and structures arranged alternately with each lens. To clearly illustrate the calculation method for the inter-lens distance at room temperature, this invention uses two lenses as an example, assuming two adjacent lenses are a front lens 11 and a rear lens 12, with each lens 11 and rear lens 12 corresponding to a structure. Specifically, the front lens 11 corresponds to a first structure 13, and the rear lens 12 corresponds to a second structure 14, as shown below. Figure 1 In the design, the first structure 13 is located between the front lens 11 and the rear lens 12, while the second structure 14 is located on the side of the rear lens 12 away from the front lens 11. The surface of the front lens 11 that contacts the first structure 13 is the first contact surface 15, and the surface of the rear lens 12 that contacts the second structure 14 is the second contact surface 16.
[0038] Normally, when the ambient temperature changes, the dimensions of a material will change accordingly; this rate of change is called the coefficient of thermal expansion. Figure 1 In the low-temperature optical system shown, both the lens and the structure expand during the temperature change from low temperature to room temperature. Since the materials of the structure and the lens are different, their coefficients of thermal expansion are different, resulting in different dimensional changes. Therefore, it is necessary to calculate the changes in the structure and the lens with temperature separately.
[0039] Based on this, please refer to Figure 3 The room-temperature mirror spacing preset system 100 of the transmission-type low-temperature optical system provided in this embodiment of the invention measures the thermal expansion coefficients of the front lens 11, rear lens 12, and structure at low temperatures through a first measurement module. The thermal expansion coefficient is related to the selected materials. The lens can be made of germanium or silicon, while the structure can be made of titanium alloy. In this embodiment, the measured low-temperature thermal expansion coefficients of germanium are 1.98E-06, silicon is 5.37E-06, and titanium alloy is 8.76E-06.
[0040] When the temperature changes, for example, an assembly temperature of 293K represents room temperature, and an operating temperature of 200K represents a low temperature, the dimensional change of the material can be calculated using the formula ΔL = L0·α·ΔT. Therefore, in addition to the coefficient of thermal expansion α, the dimension L0 also needs to be obtained. From room temperature to low temperature, the contraction of both the front lens 11 and the rear lens 12 will cause the inter-lens distance to contract from room temperature to low temperature. (Refer to...) Figure 1 In this invention, the lens contraction mainly stems from the contraction of two distances: L1 from the vertex of the exit surface of the front lens 11 to the first contact surface 15, and L2 from the vertex of the incident surface of the rear lens 12 to the second contact surface 16. Therefore, after the lens is manufactured, the second measurement module measures the distance L1 from the vertex of the exit surface of the front lens 11 to the first contact surface 15, and the distance L2 from the vertex of the incident surface of the rear lens 12 to the second contact surface 16, in order to subsequently calculate the change in inter-lens distance caused by the lens.
[0041] Besides the lens, structural contraction can also cause changes in the inter-lens distance. (See reference...) Figure 1 In this invention, the structural shrinkage mainly originates from the shrinkage of the distance between the first resting surface 15 and the second resting surface 16. Therefore, the first calculation module calculates the distance between the first resting surface 15 and the second resting surface 16 at room temperature. Figure 1 It can be seen that the distance between the first contact surface 15 and the second contact surface 16 is related to the mirror spacing. Assuming the mirror spacing at room temperature is L... RT Then the distance L3 between the first contact surface 15 and the second contact surface 16 can be calculated as L = L RT - L1+ L2.
[0042] After obtaining the thermal expansion coefficients and distances of the structure and each lens, the second calculation module can calculate the temperature-induced shrinkage of the structure and each lens from room temperature to low temperature based on the thermal expansion coefficients and distances. According to the dimensional change formula, the temperature-induced shrinkage L of the front lens 11 can be obtained. 前 = L1·α1·△T, the temperature-induced shrinkage L of the rear lens 12 后 = L²·α²·△T, the temperature-induced shrinkage of the structure, L 结构 = L3·α3·△T; where α1 represents the thermal expansion coefficient of the front lens 11, α2 represents the thermal expansion coefficient of the rear lens 12, α3 represents the structural thermal expansion coefficient, and △T represents the temperature difference from room temperature to low temperature.
[0043] Depend on Figure 1 The effects of temperature-induced shrinkage of the structure and individual lenses on the inter-lens distance can be analyzed from room temperature to low temperature. For example, shrinkage of the front lens 11 will decrease the inter-lens distance; structural shrinkage will also decrease the inter-lens distance; while shrinkage of the rear lens 12 will increase the inter-lens distance. Therefore, the overall temperature-induced shrinkage of the optical system from room temperature to low temperature can be calculated.
[0044] In this invention, the room-temperature mirror spacing is calculated by combining the overall temperature-induced shrinkage of the optical system with the low-temperature mirror spacing. Therefore, after obtaining the overall temperature-induced shrinkage of the optical system, the first design module can be used to perform optical design on the low-temperature optical system, thereby obtaining the low-temperature mirror spacing L of the low-temperature optical system. LT .
[0045] In this embodiment, taking into account the system requirements of a working spectral range of 3μm~5μm, an object-side field of view of 8°×8°, an entrance pupil diameter of 265mm, a focal length of 525mm, and an operating temperature of 200K, as well as the requirement for compact structure due to the low-temperature cooling of the lens, the optical design of the low-temperature optical system is carried out by measuring the refractive index of the lens at low temperature. The optical design adopts an image-side telecentric transmission optical system.
[0046] The temperature shrinkage of the optical system and the low-temperature mirror spacing L were obtained. LT Then, the third calculation module can calculate the amount of thermal shrinkage of the optical system and the cryogenic mirror spacing L. LT The distance L between mirrors at room temperature was calculated. RT The value of .
[0047] As the distance between the front lens 11 and the mirrors decreases from room temperature to low temperature, the structural contraction also reduces the mirror spacing; conversely, the contraction of the rear lens 12 increases the mirror spacing. Therefore, the low-temperature mirror spacing L can be obtained. LT =Mirror spacing at room temperature L RT - Temperature shrinkage L of front lens 11 前 - Temperature shrinkage of the structure L 结构 +Temperature shrinkage L of rear lens 12后 That is, L LT =L RT -(L RT -L1+L2)·α3·△T–L1·α1·△T+L2·α2·△T. Converting this formula yields L. RT =[L1·(α1·△T-α3·△T)-L2·(α2·△T-α3·△T)+L LT In practical applications, the room-temperature mirror spacing L can be calculated by substituting the measured values of each parameter into the formula. RT The value of .
[0048] When designing the lens structure, the results of tolerance analysis must be considered. Because tolerance analysis imposes strict requirements on the lens's eccentricity and tilt tolerances, each lens needs to be centered during subsequent assembly and adjustment. Each lens requires a frame during design, and a 2-4mm allowance is reserved on each side of each lens based on the lens's aperture diameter for edge-pressing design. After the lens frame design is completed, the second design module uses the calculated room-temperature lens spacing L... RT The value is used to design the lens mounting tube.
[0049] The present invention provides a room-temperature lens spacing preset system for a transmissive low-temperature optical system. Addressing the issue that optical processing and assembly of lenses in low-temperature transmissive optical systems are performed at room temperature and pressure, and the lens spacing provided after optical design is a vacuum low-temperature lens spacing that cannot be used as the room-temperature assembly distance, the present invention proposes a method to calculate the room-temperature lens spacing using the distance from the lens vertex to the contact surface, the material's thermal expansion coefficient, and the low-temperature lens spacing. This allows the low-temperature lens spacing to be converted to a room-temperature lens spacing for assembly, enabling the preset of the lens spacing change from room temperature to low temperature during the assembly process, providing a reliable basis for room-temperature assembly of low-temperature optical systems.
[0050] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of one embodiment, and the modules or processes shown in the drawings are not necessarily essential for implementing the present invention.
[0051] Those skilled in the art will understand that the modules in the apparatus of the embodiments can be distributed in the apparatus of the embodiments as described in the embodiments, or they can be located in one or more devices different from this embodiment with corresponding changes. The modules of the above embodiments can be combined into one module, or they can be further divided into multiple sub-modules.
[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for presetting the mirror spacing at room temperature in a transmission-type low-temperature optical system, characterized in that, The transmissive cryogenic optical system includes at least two lenses and a structure that alternates with each lens. Let two adjacent lenses be a front lens and a rear lens, the front lens corresponds to a first structure, and the rear lens corresponds to a second structure; the surface of the front lens that contacts the first structure is a first contact surface, and the surface of the rear lens that contacts the second structure is a second contact surface. Methods for presetting the mirror spacing at room temperature include: Measure the coefficients of thermal expansion of the front lens, the rear lens, and the structure; Measure the distance from the vertex of the exit surface of the front lens to the first contact surface, and the distance from the vertex of the incident surface of the rear lens to the second contact surface; Calculate the distance between the first and second contact surfaces at room temperature; Based on the coefficient of thermal expansion and distance, calculate the temperature-dependent shrinkage of the optical system from room temperature to low temperature; where assembly temperature represents room temperature and operating temperature represents low temperature. The cryogenic optical system was optically designed to obtain the cryogenic mirror spacing L. LT ; Based on the temperature shrinkage and the low-temperature mirror spacing L LT The distance L between the mirrors at room temperature was calculated. RT The value; According to the room temperature mirror spacing L RT The value is used to design the lens casing.
2. The method for presetting the room-temperature mirror spacing of a transmission-type low-temperature optical system according to claim 1, characterized in that, The temperature shrinkage of the optical system includes the temperature shrinkage L of the rear lens. 后 Temperature shrinkage L of the front lens 前 Temperature shrinkage L of the structure 结构 .
3. The method for presetting the room-temperature mirror spacing of a transmission-type low-temperature optical system according to claim 2, characterized in that, The temperature shrinkage of the front lens is expressed as L. 前 = L1·α1·△T, where L1 represents the distance from the vertex of the exit surface of the front lens to the first contact surface, α1 represents the thermal expansion coefficient of the front lens, and △T represents the temperature difference from room temperature to low temperature.
4. The method for presetting the room-temperature mirror spacing of a transmission-type low-temperature optical system according to claim 3, characterized in that, The temperature-induced shrinkage of the rear lens is expressed as L. 后 = L2·α2·△T, where L2 represents the distance from the vertex of the exit surface of the rear lens to the first contact surface, α2 represents the thermal expansion coefficient of the rear lens, and △T represents the temperature difference from room temperature to low temperature.
5. The method for presetting the room-temperature mirror spacing of a transmission-type low-temperature optical system according to claim 4, characterized in that, The temperature shrinkage of the structure is expressed as L. 结构 = L3·α3·△T, where L3 represents the distance from the first contact surface to the second contact surface at room temperature, L3=L RT - L1+ L2, α3 represents the thermal expansion coefficient of the structure, and ΔT represents the temperature difference from room temperature to low temperature.
6. The method for presetting the room-temperature mirror spacing of a transmission-type low-temperature optical system according to claim 5, characterized in that, Based on the temperature shrinkage and the low-temperature mirror spacing L LT The distance L between the mirrors at room temperature was calculated. RT The value is as follows: The relationship between the shrinkage of the front lens, rear lens, and structure and the inter-lens distance was analyzed from room temperature to low temperature. Specifically, the inter-lens distance decreased when the front lens shrank, the inter-lens distance decreased when the structure shrank, and the inter-lens distance increased when the rear lens shrank. Based on the aforementioned relationship, the cryogenic mirror spacing L is obtained. LT =Mirror spacing at room temperature L RT - Temperature shrinkage of the front lens L 前 - Temperature shrinkage of the structure L 结构 +Rear lens temperature shrinkage L 后 Then the distance between mirrors at room temperature, L RT =Low-temperature mirror spacing L LT +Temperature shrinkage of the front lens L 前 + Temperature shrinkage of the structure L 结构 - Temperature shrinkage L of the rear lens 后 .
7. The method for presetting the room-temperature mirror spacing of a transmission-type low-temperature optical system according to claim 1, characterized in that, The optical design of the aforementioned low-temperature optical system is specifically as follows: Measure the refractive index of the lens at low temperature; The low-temperature optical system is optically designed based on the refractive index of the lens.
8. A room-temperature mirror spacing preset system for a transmission-type low-temperature optical system, characterized in that, The transmissive cryogenic optical system includes at least two lenses and a structure that alternates with each lens. Let two adjacent lenses be a front lens and a rear lens, the front lens corresponds to a first structure, and the rear lens corresponds to a second structure; the surface of the front lens that contacts the first structure is a first contact surface, and the surface of the rear lens that contacts the second structure is a second contact surface. The room temperature mirror spacing preset system includes: The first measurement module is used to measure the thermal expansion coefficients of the front lens, the rear lens, and the structure. The second measurement module is used to measure the distance from the vertex of the exit surface of the front lens to the first contact surface, and the distance from the vertex of the incident surface of the rear lens to the second contact surface. The first calculation module is used to calculate the distance between the first and second contact surfaces at room temperature; The second calculation module is used to calculate the temperature-dependent shrinkage of the optical system from room temperature to low temperature based on the coefficient of thermal expansion and distance; wherein, the assembly temperature represents room temperature and the operating temperature represents low temperature. The first design module is used to perform optical design on the cryogenic optical system and obtain the cryogenic mirror spacing L. LT ; The third calculation module is used to calculate the temperature-induced shrinkage and the low-temperature mirror spacing L. LT The distance L between the mirrors at room temperature was calculated. RT The value; The second design module is used to determine the normal temperature mirror spacing L. RT The value is used to design the lens casing.
9. The room-temperature mirror spacing preset system for a transmission-type low-temperature optical system according to claim 8, characterized in that, The temperature shrinkage of the optical system includes the temperature shrinkage L of the rear lens. 后 Temperature shrinkage L of the front lens 前 Temperature shrinkage L of the structure 结构 ; The third calculation module is specifically used for: The relationship between the shrinkage of the front lens, rear lens, and structure and the inter-lens distance was analyzed from room temperature to low temperature. Specifically, the inter-lens distance decreased when the front lens shrank, the inter-lens distance decreased when the structure shrank, and the inter-lens distance increased when the rear lens shrank. Based on the aforementioned relationship, the cryogenic mirror spacing L is obtained. LT =Mirror spacing at room temperature L RT - Temperature shrinkage of the front lens L 前 - Temperature shrinkage of the structure L 结构 +Rear lens temperature shrinkage L 后 Then the distance between mirrors at room temperature, L RT =Low-temperature mirror spacing L LT +Temperature shrinkage of the front lens L 前 + Temperature shrinkage of the structure L 结构 - Temperature shrinkage L of the rear lens 后 .
10. The method for presetting the room-temperature mirror spacing of a transmission-type low-temperature optical system according to claim 8, characterized in that, The first design module is specifically used for: Measure the refractive index of the lens at low temperature; The low-temperature optical system is optically designed based on the refractive index of the lens.