A two-stage zoom athermalized optical imaging system

Abstract

The application discloses a two-grade zooming athermalization optical imaging system, and belongs to the field of photoelectricity. The system comprises, in sequence from an object plane to an image plane along the direction of light incidence, a front fixed group with positive focal power, a variable magnification group with negative focal power, a compensation group with positive focal power, a rear fixed group with positive focal power and the image plane; wherein the variable magnification group and the compensation group can move axially along the optical axis to realize two-grade switching of focal length; the system further comprises at least one optical material with a positive refractive index temperature coefficient and at least one optical material with a negative refractive index temperature coefficient, which are used to compensate for the image plane drift caused by temperature change, and realize passive athermalization. The application can realize stable image plane position in the temperature range of-40 DEG C to 60 DEG C through passive athermalization design, and can realize efficient search, accurate identification and stable observation of a target through the same light path, and can meet the all-weather and high-reliability imaging use requirements without focusing.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic equipment technology, and more specifically to a two-level zoom calorimetric optical imaging system, particularly a miniaturized visible light imaging optical system with two-level switching zoom and calorimetric characteristics, suitable for imaging scenarios with stringent requirements for size and temperature adaptability, such as optoelectronic pods, security monitoring, vehicle imaging, and industrial inspection. Background Technology

[0002] With the rapid development of optoelectronic imaging technology, zoom optical systems have been widely adopted in fields such as security monitoring, UAV payloads, and industrial inspection. In practical applications, the system not only needs to have good observation capabilities for targets at different distances, but also needs to meet engineering requirements such as compact structure, miniaturization, and high adaptability.

[0003] However, with changes in altitude, climate, and season, the operating temperature of the optical system will vary within a wide range. As the refractive index of optical materials and the structure of the lens barrel are affected by temperature, the system's focal length drifts and the image plane position shifts, resulting in blurred or even out-of-focus images.

[0004] Currently, the commonly used heatless solutions to eliminate the effects of temperature employ mechanical compensation or active focusing. These methods require the addition of a motor and focusing mechanism. Although they can correct temperature drift, they significantly increase the system size, weight, and power consumption, which does not conform to the trend of lightweight and low-cost design. Summary of the Invention

[0005] In view of the above problems, this application provides a two-level zoom calorimetric optical imaging system to overcome the shortcomings of the prior art or at least partially solve the above problems.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a two-level zoom calorimetric optical imaging system. The system includes, in sequence from the object plane to the image plane along the light incident direction, a front fixed group (1) with positive optical power, a zoom group (2) with negative optical power, a compensation group (3) with positive optical power, a rear fixed group (4) with positive optical power, and an image plane (5). The zoom group (2) and the compensation group (3) can move axially along the optical axis to achieve two-stage switching of focal length; The optical imaging system includes at least one optical material with a positive refractive index temperature coefficient and at least one optical material with a negative refractive index temperature coefficient, so that the image plane drift caused by temperature change can be mutually compensated, thereby achieving passive calorimetry.

[0008] Furthermore, the optical material with a positive refractive index temperature coefficient is disposed in the front fixing group (1), and the optical material with a negative refractive index temperature coefficient is disposed in the rear fixing group (4).

[0009] Furthermore, the front fixing group (1) includes a first biconvex positive lens (1-1) made of H-FK61 material and a first meniscus negative lens (1-2) made of H-ZF88 material, and the rear fixing group (4) includes a fifth meniscus positive lens (4-4) made of PMMA material.

[0010] Furthermore, the object-side surface and image-side surface of the fifth meniscus lens (4-4) are both set as even-order aspherical surfaces.

[0011] Furthermore, the even-order aspherical surface type is defined by the following equation:

[0012] In the formula, For aspherical sag, It is the reciprocal of the radius of curvature. Radial coordinates, The conic coefficient, 、 、 、 It is the aspherical coefficient.

[0013] Furthermore, the optical imaging system also includes a controller and a drive mechanism. The controller has pre-stored the axial position data of the zoom group (2) and the compensation group (3) corresponding to the short focal length state and the long focal length state, respectively. The drive mechanism includes a stepper motor and a cam mechanism. The stepper motor is used to drive the zoom group (2) to move to a preset position. The cam mechanism is used to mechanically couple the compensation group (3) with the zoom group (2) and automatically move to the corresponding compensation position under the constraint of the cam groove profile.

[0014] Furthermore, the cam groove profile of the cam mechanism is pre-formed according to the zoom equation.

[0015] Furthermore, the zoom group (2) is composed of a second meniscus negative lens (2-1), a first double meniscus negative lens (2-2), and a second biconvex positive lens (2-3); the compensation group (3) is composed of a third biconvex positive lens (3-1), a third meniscus negative lens (3-2), and a fourth biconvex positive lens (3-3). The rear fixing group (4) also includes a second double meniscus positive lens (4-1), a fourth meniscus negative lens (4-2), and a fifth biconvex positive lens (4-3).

[0016] Furthermore, the second meniscus negative lens (2-1), the second biconvex positive lens (2-3), the third biconvex positive lens (3-1), and the second double meniscus positive lens (4-1) are all made of H-F52 material; The third meniscus negative lens (3-2) is made of H-ZF4A material; The fourth biconvex positive lens (3-3) is made of H-ZPK5 material; The fourth crescent negative lens (4-2) is made of H-ZF52 material; The fifth biconvex positive lens (4-3) is made of H-ZLAF55D material.

[0017] Furthermore, the operating wavelength is 0.45μm to 0.85μm, the focal length is 10mm in short focal length mode and 40mm in long focal length mode, and the operating temperature range is -40℃ to 60℃.

[0018] This invention provides a two-level zoom athermal optical imaging system. By combining passive athermalization with two-level switching zoom, the system can achieve miniaturization, high reliability, and stable imaging within the operating temperature range of -40℃ to 60℃. It can also effectively meet the engineering application requirements of rapid target search, accurate identification, and stable observation under complex working conditions.

[0019] The beneficial effects of the above-described technical solutions provided in the embodiments of the present invention include at least the following: 1. This invention employs a front fixed group, a zoom group, a compensation group, a rear fixed group, and an image plane to form a complete zoom optical path, creating a compact optical structure with two zoom levels of the same aperture. It achieves rapid switching between a short focal length with a large field of view and a long focal length with a small field of view through a single optical path. During zooming, the image plane position remains stable, and imaging is continuous, enabling continuous target locking, rapid search, and precise observation, thus improving the system's real-time detection and tracking stability. Simultaneously, the system boasts high overall integration and a unified structure, maintaining image plane position stability within a temperature range of -40℃ to 60℃, achieving clear imaging across the entire zoom range without active focusing.

[0020] 2. This invention has a wide range of applications: the optical system has a zoom ratio of 4×, a working focal length range of 10mm~40mm, and a working wavelength range of 0.45μm~0.85μm, and can be adapted to various detector specifications.

[0021] 3. This invention achieves high structural integration by sharing a zoom group. The zoom group and the compensation group work together to achieve two zoom levels and image plane position compensation. The rear fixed group is used for aberration correction and non-thermal compensation. Under this structure, there is no need to set up multiple independent zoom mechanisms, thereby reducing the system size, reducing structural complexity and improving assembly stability.

[0022] 4. The assembly process of this invention is simple, with strong engineering adaptability. The spacing and structural parameters of each component meet the requirements of conventional processing and assembly processes, and the processing and assembly accuracy requirements are suitable for conventional optical processing techniques. While ensuring imaging quality and thermal stability, it can reduce processing costs and improve mass production efficiency. Attached Figure Description

[0023] 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 embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the optical path structure of the optical imaging system of the present invention at a short focal length of f=10mm; Figure 2 This is a schematic diagram of the optical path structure of the optical imaging system of the present invention at a focal length of f=40mm; Figure 3 This is a dot plot of the optical imaging system of the present invention at a short focal length of f=10mm; Figure 4 This is a dot plot of the optical imaging system of the present invention at a focal length of f=40mm; Figure 5 The optical transfer function of the optical imaging system of the present invention at a short focal length of 10mm is shown in the figure. Figure 6 This is a graph showing the optical transfer function of the optical imaging system of the present invention at a focal length of 40mm.

[0025] Explanation of reference numerals in the attached figures: 1-Front fixed group, 1-1 is the first biconvex positive lens, 1-2 is the first meniscus negative lens; 2-Magnification group, 2-1 is the second meniscus negative lens, 2-2 is the first double meniscus negative lens, 2-3 is the second biconvex positive lens; 3-Compensation group, 3-1 is the third biconvex positive lens, 3-2 is the third meniscus negative lens, 3-3 is the fourth biconvex positive lens; 4-Rear fixed group, 4-1 is the second double meniscus positive lens, 4-2 is the fourth meniscus negative lens, 4-3 is the fifth biconvex positive lens, 4-4 is the fifth meniscus positive lens; 5-Image plane. Detailed Implementation

[0026] 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.

[0027] This invention discloses a two-level zoom calorimetric optical imaging system. The system comprises, from the object plane to the image plane along the light incident direction, a front fixed group (1) with positive optical power, a zoom group (2) with negative optical power, a compensation group (3) with positive optical power, a rear fixed group (4) with positive optical power, and an image plane (5). The front fixed group (1), zoom group (2), compensation group (3), and rear fixed group (4) are used to transmit and correct visible light in the 0.45μm–0.85μm band. The image plane (5) is used to receive the beam converged by the optical system and form an image. All components together constitute a single visible light common-aperture zoom optical path, eliminating the need for beam splitters or multi-band separation structures.

[0028] Specifically, the front fixed group (1) is used to receive the visible light spectrum information of the target and perform preliminary convergence and primary aberration correction; the zoom group (2) is used to change the focal length of the optical system by moving back and forth. In this embodiment, it is used to realize the zoom of the system focal length in the range of the shortest f=10mm to the longest f=40mm; the compensation group (3) is used to compensate for the image plane position change caused by the zoom group (2) during the zoom process; the rear fixed group (4) is used to correct the residual aberration of the system, improve the quality of the imaging beam, match the imaging requirements of the detector, and at the same time realize thermal compensation in the temperature range of -40℃ to 60℃ to ensure the imaging quality of the entire field of view, the entire zoom range and the entire temperature range; the image plane (5) is used to focus the beam after it has been converged and corrected by the optical system onto the photosensitive surface of the detector to realize photoelectric conversion and target detection.

[0029] In one embodiment, the front fixed group (1) and the rear fixed group (4) are fixedly arranged along the optical axis, and the zoom group (2) and the compensation group (3) can move axially along the optical axis. The zoom group (2) is used to switch the system between short focal length working state and long focal length working state. The compensation group (3) moves in the opposite direction to the zoom group during the zoom group movement and is used to compensate for the image plane position change caused by zoom.

[0030] In some implementations, the optical imaging system includes a controller and a drive mechanism. The controller has pre-stored axial position data of the zoom group (2) and the compensation group (3) corresponding to the short focal length state and the long focal length state, respectively. The drive mechanism includes a stepper motor and a cam mechanism. The stepper motor is used to drive the zoom group (2) to move to a preset position. The cam mechanism is used to mechanically couple the compensation group (3) with the zoom group (2) and automatically move to the corresponding compensation position under the constraint of the cam groove profile.

[0031] The pre-stored circumferential position data in this implementation plan is shown in Table 1 below; Table 1

[0032] In the table, D4 ​​is the distance between the front fixed group and the zoom group, D8 is the distance between the zoom group and the compensation group, D12 is the distance between the compensation group and the rear fixed group, and D14 is the distance between the rear fixed group and the image plane.

[0033] When the system switches from short focal length to long focal length, such as Figure 2 As shown, the controller drives the stepper motor to move the zoom group (2) along the optical axis from the object side to the image side to a preset position; the compensation group (3) is mechanically coupled to the zoom group through a cam mechanism, and automatically moves along the optical axis from the image side to the object side to the corresponding compensation position under the constraint of the cam groove profile. The cam groove profile is pre-processed according to the zoom equation to ensure that the compensation group can move synchronously during the movement of the zoom group to accurately compensate for the image plane offset. Conversely, when switching from long focal length to short focal length, such as Figure 1 As shown, the drive motor moves in the opposite direction, and the two components are reset under the constraint of the cam. The system achieves two-level zoom based on high-precision position control with mechanical preset, thereby ensuring the speed, repeatability, and reliability of the zoom action.

[0034] In one embodiment, the optical imaging system includes at least one optical material with a positive refractive index temperature coefficient and at least one optical material with a negative refractive index temperature coefficient, so that the image plane drift caused by each component when the temperature changes can compensate for each other, thereby achieving passive calorimetry. This allows the system to maintain a stable image plane position in both the short-focus and long-focus operating states within a predetermined temperature range, without the need for active focusing. In some embodiments, the optical material with a positive refractive index temperature coefficient is disposed in the front fixed group (1), and the optical material with a negative refractive index temperature coefficient is disposed in the rear fixed group (4).

[0035] As a preferred embodiment, the front fixing group (1) includes a coaxial first cemented doublet lens, specifically a first biconvex positive lens (1-1) made of H-FK61 material and a first meniscus negative lens (1-2) made of H-ZF88 material, and the rear fixing group (4) includes a fifth meniscus positive lens (4-4) made of PMMA material. The H-FK61 and H-ZF88 glass materials in the front fixing group (1) have high positive dn / dt, and their optical power increases with temperature, causing the image plane to drift backward; the PMMA material in the rear fixing group (4) has a dn / dt ≈ -1.2 × 10⁻⁶ m² / m ... -4 / ℃, the absolute value of which is about 10 times that of glass material) When the temperature increases, its optical power decreases, resulting in image plane drift in the opposite direction.

[0036] Meanwhile, to correct residual aberrations in the system, including astigmatism and higher-order chromatic aberration, both the object-side and image-side surfaces of the fifth meniscus lens (4-4) are set as even-order aspherical surfaces. This is used to correct higher-order aberrations in the system and improve imaging quality across the entire field of view and zoom range, ensuring clarity and stability of imaging within the full zoom range and the entire field of view. In this embodiment, the even-order aspherical surface shape is defined by the following equation:

[0037] In the formula, For aspherical sag, It is the reciprocal of the radius of curvature. Radial coordinates, The conic coefficient, 、 、 、 It is the aspherical coefficient.

[0038] In some specific embodiments, the aspheric coefficients of the object side and the phase side are shown in Table 2; Table 2

[0039] These coefficients determine the curvature of the aspherical surface at different apertures. By optimizing the aspherical surface to produce differentiated optical power in different radial regions of the lens, higher-order aberrations such as spherical aberration and astigmatism can be effectively corrected, and the overall chromatic aberration correction capability of the system can be improved, thereby enhancing image quality. Simultaneously, the introduction of aspherical surfaces reduces the reliance on multiple lens combinations for aberration correction, enabling a reduction in the number of lenses in the optical system and a smaller system size. Without an aspherical structure, the number of lenses typically needs to be increased to achieve aberration correction, leading to a more complex system structure, increased size, and increased light absorption and loss within the system, thus reducing the imaging capability for weak targets.

[0040] In one embodiment, the remaining components are configured as follows: The zoom group (2) consists of a coaxial second meniscus negative lens (2-1), a first double meniscus negative lens (2-2), and a second biconvex positive lens (2-3); The compensation group (3) consists of a third biconvex positive lens (3-1) and a second cemented doublet lens, wherein the cemented doublet lens includes a second and a third meniscus negative lens (3-2) and a fourth biconvex positive lens (3-3). The rear fixed assembly (4) also includes a coaxial second double meniscus positive lens (4-1), a fourth meniscus negative lens (4-2), and a fifth biconvex positive lens (4-3). The image plane (5) is the imaging plane of the system. After the light passes through each optical element, it finally converges on the image plane.

[0041] Furthermore, the second meniscus negative lens (2-1), the second biconvex positive lens (2-3), the third biconvex positive lens (3-1), and the second double meniscus positive lens (4-1) are all made of H-F52 material; The third meniscus negative lens (3-2) is made of H-ZF4A material; The fourth biconvex positive lens (3-3) is made of H-ZPK5 material; The fourth crescent negative lens (4-2) is made of H-ZF52 material; The fifth biconvex positive lens (4-3) is made of H-ZLAF55D material.

[0042] In this embodiment, the specific parameters of each optical element in the system are shown in Table 3; Table 3

[0043] Note: Along the direction of light incidence from the object plane to the image plane, each surface of the lens is sequentially labeled S1-S24.

[0044] This application achieves clear imaging across the entire temperature range without the need for active focusing by optimizing the matching of optical power and materials throughout the entire system. This allows the image plane defocus to be controlled within the detector's focal depth in both zoom states within a temperature range of -40℃ to 60℃ (in this embodiment, the detector pixel size is 6.5μm and the focal depth is approximately ±13μm).

[0045] The optical system of this invention, through a unified zoom structure design, can maintain consistent image quality at different focal lengths, meeting the requirements of high-precision imaging and recognition. The system requires no switching of the optical path during use, operates stably within a temperature range of -40℃ to 60℃, achieves clear imaging in the 0.45μm to 0.85μm visible light band, and also supports target search, recognition, and tracking functions.

[0046] In one exemplary embodiment, the system has a focal length of 10mm and a full field of view of 50° in short focal length mode (corresponding to the large field of view search mode); and a focal length of 40mm and a full field of view of 17° in long focal length mode (corresponding to the small field of view precise observation mode). The zoom ratio strictly meets the 4x requirement in both modes; the resulting image quality evaluation diagram is shown below. Figure 3 , Figure 4 As shown. From Figure 3 and Figure 4 It can be seen that all colors of light are enclosed by the Airy disk circle (the outermost black circle), and the RMS value of the full field-of-view dot plot is smaller than the size of a single pixel (the size of a single pixel is 6.5μm). This indicates that the visible light imaging system of the present invention has good imaging quality and high system resolution, meeting the requirements for high-precision target detection and recognition.

[0047] Figure 5 and Figure 6 These are the optical transfer function curves, respectively. Figure 5 and Figure 6 As can be seen, at the Nyquist frequency, the modulation transfer function value of this system is greater than 0.5 in both short and long focal length states, indicating that the system has high imaging resolution under different focal length conditions, thus ensuring the stability of imaging quality during zooming.

[0048] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0049] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A two-level zoom calorimetric optical imaging system, characterized in that, Along the incident direction of light, from the object plane to the image plane, it includes a front fixed group (1) with positive optical power, a zoom group (2) with negative optical power, a compensation group (3) with positive optical power, a rear fixed group (4) with positive optical power, and the image plane (5). The zoom group (2) and the compensation group (3) can move axially along the optical axis to achieve two-stage switching of focal length; The optical imaging system includes at least one optical material with a positive refractive index temperature coefficient and at least one optical material with a negative refractive index temperature coefficient, which are used to compensate for image plane drift caused by temperature changes and achieve passive calorimetry.

2. The two-level zoom calorimetric optical imaging system as described in claim 1, characterized in that, The optical material with a positive refractive index temperature coefficient is disposed in the front fixing group (1), and the optical material with a negative refractive index temperature coefficient is disposed in the rear fixing group (4).

3. The two-level zoom calorimetric optical imaging system as described in claim 2, characterized in that, The front fixing group (1) includes a first biconvex positive lens (1-1) made of H-FK61 material and a first meniscus negative lens (1-2) made of H-ZF88 material, and the rear fixing group (4) includes a fifth meniscus positive lens (4-4) made of PMMA material.

4. The two-level zoom calorimetric optical imaging system as described in claim 3, characterized in that, The object-side and image-side surfaces of the fifth meniscus lens (4-4) are both set as even-order aspherical surfaces.

5. The two-level zoom calorimetric optical imaging system as described in claim 4, characterized in that, The even-order aspherical surface shape is defined by the following equation: In the formula, For aspherical sag, It is the reciprocal of the radius of curvature. Radial coordinates, The conic coefficient, , , , It is the aspherical coefficient.

6. The two-level zoom calorimetric optical imaging system as described in claim 1, characterized in that, The optical imaging system also includes a controller and a drive mechanism. The controller has pre-stored the axial position data of the zoom group (2) and the compensation group (3) corresponding to the short focal length state and the long focal length state, respectively. The drive mechanism includes a stepper motor and a cam mechanism. The stepper motor is used to drive the zoom group (2) to move to a preset position. The cam mechanism is used to mechanically couple the compensation group (3) with the zoom group (2) and automatically move to the corresponding compensation position under the constraint of the cam groove profile.

7. The two-level zoom calorimetric optical imaging system as described in claim 6, characterized in that, The cam groove profile of the cam mechanism is pre-machined according to the zoom equation.

8. The two-level zoom calorimetric optical imaging system as described in claim 1, characterized in that, The zoom group (2) consists of a second meniscus negative lens (2-1), a first double meniscus negative lens (2-2), and a second biconvex positive lens (2-3); the compensation group (3) consists of a third biconvex positive lens (3-1), a third meniscus negative lens (3-2), and a fourth biconvex positive lens (3-3). The rear fixing group (4) also includes a second double meniscus positive lens (4-1), a fourth meniscus negative lens (4-2), and a fifth biconvex positive lens (4-3).

9. The two-level zoom calorimetric optical imaging system as described in claim 8, characterized in that, The second meniscus negative lens (2-1), the second biconvex positive lens (2-3), the third biconvex positive lens (3-1), and the second double meniscus positive lens (4-1) are all made of H-F52 material; The third meniscus negative lens (3-2) is made of H-ZF4A material; The fourth biconvex positive lens (3-3) is made of H-ZPK5 material; The fourth crescent negative lens (4-2) is made of H-ZF52 material; The fifth biconvex positive lens (4-3) is made of H-ZLAF55D material.

10. The two-level zoom calorimetric optical imaging system as described in claim 1, characterized in that, The operating wavelength range is 0.45μm to 0.85μm, the focal length is 10mm in short focal length mode and 40mm in long focal length mode, and the operating temperature range is -40℃ to 60℃.

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