Large aperture small field of view near infrared imaging lens

Abstract

The application discloses a large-aperture small-field-of-view near-infrared imaging lens and belongs to the technical field of coaxial aiming imaging optical systems of laser weapons, comprising a parabolic off-axis reflection beam-expanding component and a two-piece spherical imaging lens group; the parabolic off-axis reflection beam-expanding component comprises a first off-axis concave parabolic mirror and a second off-axis convex parabolic mirror, and the two mirrors form a common-path laser beam-expanding and imaging pre-optical path, thereby realizing the common aperture of a laser emission light path and a near-infrared imaging light path. The imaging lens group only comprises two standard spherical lenses, and the complex aspheric athermalization lenses are abandoned. The spherical lenses have low processing difficulty, the raw materials and processing costs are significantly reduced, the number of lenses is greatly reduced, the tolerance sensitivity of the optical system is reduced, the assembly and debugging procedures are simplified, the whole-machine production and debugging time is greatly shortened, the athermalization lens combination is cancelled, the working temperature of the lenses is stabilized through an independent temperature control module, the defocus and imaging blur problems caused by the change of the environmental temperature are completely solved, and the imaging quality is stable in the whole temperature range.

Description

Technical Field

[0001] This invention belongs to the technical field of coaxial aiming imaging optical systems for laser weapons, specifically referring to a large-aperture, small-field-of-view near-infrared imaging lens. Background Technology

[0002] To achieve precise laser targeting, the industry generally adopts a coaxial design with the laser beam path and imaging beam path sharing the same aperture. An imaging beam path is split off by a beam splitter and paired with a coaxial camera to identify and lock onto the target. Such systems uniformly use a parabolic off-axis reflective beam expander system to simultaneously expand the laser beam and the imaging beam path, increasing the imaging aperture and focal length, and improving the imaging resolution.

[0003] The current mainstream mature solution is a combination architecture of a parabolic off-axis reflection beam expander system and a multi-element athermal transmission imaging lens. This solution has obvious drawbacks:

[0004] The number of lenses in a thermal imaging lens is as high as 6 to 8, the lens structure is complex, and a large number of aspherical lenses are used. Aspherical processing technology is difficult, the production cycle is long, and the lens processing cost is high.

[0005] The large number of lenses, the stringent tolerances for optical system assembly and adjustment, the difficulty of assembling and debugging the whole machine, and the high time and labor costs for assembly and adjustment.

[0006] The athermalized lens relies on a complex combination of lenses to counteract the effects of temperature, resulting in redundant optical structure and a relatively large overall size.

[0007] Existing simplification and improvement approaches fall into two categories: one is to retain the athermalized structure and reduce the number of lenses to two spherical lenses, but after eliminating the athermalized design, changes in ambient temperature will cause the lens to defocus, resulting in a significant decrease in image quality; the other is to use a single aspherical lens to replace multiple athermalized lenses, which reduces the difficulty of assembly and adjustment, but the processing cost of aspherical lenses remains high.

[0008] Existing technologies lack a common aperture near-infrared imaging system that combines low-cost spherical lenses, minimal structure, temperature-controlled compensation for temperature drift, and compatibility with off-axis parabolic beam expanders. It cannot simultaneously solve the three major pain points of high processing costs, complex assembly and adjustment, and temperature drift defocusing. Summary of the Invention

[0009] In response to the above situation and to overcome the shortcomings of the prior art, the present invention provides a large-aperture, small-field-of-view near-infrared imaging lens, which effectively solves the problems currently on the market.

[0010] The technical solution adopted by the present invention is as follows: The present invention proposes a large-aperture, small-field-of-view near-infrared imaging lens, including a parabolic off-axis reflection beam expander assembly and a two-piece spherical imaging lens group;

[0011] Furthermore, the parabolic off-axis reflection beam expander includes a first off-axis concave parabolic mirror and a second off-axis convex parabolic mirror, which together form a common optical path for laser beam expansion and imaging pre-optical path, realizing that the laser emission optical path and the near-infrared imaging optical path share the same aperture.

[0012] Furthermore, the two-piece spherical imaging lens assembly includes a third crescent-shaped concave spherical lens and a fourth plano-convex spherical lens. The distance between the third crescent-shaped concave spherical lens and the fourth plano-convex spherical lens is fixed at 4mm. The two-piece spherical imaging lens assembly as a whole can move along the optical axis to complete the system focusing.

[0013] Furthermore, the optical path distance between the parabolic off-axis reflection beam expander and the two-piece spherical imaging lens group is adjustable and the maximum distance does not exceed 1m.

[0014] Furthermore, the two-piece spherical imaging lens assembly is equipped with an independent temperature control device to compensate for lens defocusing caused by changes in ambient temperature.

[0015] Furthermore, the parabolic off-axis reflection beam expander assembly can be used separately as a 4x laser beam expander.

[0016] Furthermore, the two-piece spherical imaging lens assembly can be independently detached and used separately as a near-infrared imaging lens.

[0017] Furthermore, the large-aperture, small-field-of-view near-infrared imaging optical system includes a parabolic off-axis reflection beam expander and a two-piece spherical imaging lens group. The parabolic off-axis reflection beam expander is located at the front end of the optical path, and the two-piece spherical imaging lens group is located at the rear end of the optical path. The optical path distance between the beam expander and the imaging lens is adjustable, and the maximum distance does not exceed 1m.

[0018] The entire optical system has an entrance pupil diameter of 200mm, a total focal length of 1500mm, an f / 7.5 aperture, an imaging field of view of 0.24° × 0.24°, and 5 adapter elements. A near-infrared photodetector with a resolution of 896×896.

[0019] Furthermore, the system assembly and debugging methods include:

[0020] S1. Individually calibrate the off-axis parabolic reflection beam expander: Use an interferometer to detect the transmitted wavefront and adjust the second off-axis convex parabolic reflector to make the RMS value of the transmitted wavefront less than 0.1.

[0021] S2. Individually adjust the two-piece spherical imaging lens group: the third crescent concave spherical lens and the fourth plano-convex spherical lens are coaxially installed, and the parallel light output by the collimator is used for adjustment so that the star point image is a complete circle and the imaging occupies no more than 2×2 pixels.

[0022] S3. Combine the calibrated beam expander and imaging lens group along the optical axis, and complete the overall focusing by translating the two-piece spherical imaging lens group as a whole.

[0023] Furthermore, all geometric speckles in the entire field of view fall within the Airy disk area, the system MTF value at 100 line pairs / mm is not less than 0.2, the maximum distortion is 0.4082%, and the energy ingress within a radius of 10 is higher than 80%.

[0024] The beneficial effects achieved by the present invention using the above structure are as follows:

[0025] (1) The imaging lens group has only two standard spherical lenses, eliminating 6 to 8 complex aspherical non-thermalized lenses. The spherical lens processing technology is mature and easy, the raw material and processing costs are significantly reduced, the number of lenses is greatly reduced, the tolerance sensitivity of the optical system is reduced, the assembly and debugging process is simplified, the production and debugging time of the whole machine is greatly shortened, the non-thermalized lens combination is eliminated, and the lens working temperature is stabilized through an independent temperature control module, which completely solves the defocus and imaging blur problems caused by changes in ambient temperature, and the imaging quality is stable in the whole temperature range.

[0026] (2) Both the parabolic off-axis beam expander and the two spherical imaging lens groups can be used separately. The beam expander can be used as a 4x laser beam expander, and the imaging lens groups can be used as near-infrared lenses. The equipment is highly versatile, and all geometric speckles in the entire field of view fall within the Airy disk. The MTF at 100 line pairs / mm is ≥0.2, and the maximum distortion is only 0.4082%. The energy within the radius is >80%, slight field curvature does not affect target recognition and laser aiming accuracy, the number of imaging optical path lenses is halved, the optical tube length is shortened, and it is suitable for installation in confined airborne and vehicle-mounted equipment compartments. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall optical path of the large-aperture, small-field-of-view near-infrared imaging lens proposed in this invention.

[0028] Figure 2 Diagram of a parabolic off-axis beam expander system;

[0029] Figure 3 Point diagram of the parabolic off-axis beam expander assembly;

[0030] Figure 4 Wavefront function plot of the parabolic off-axis beam expander component;

[0031] Figure 5 A point diagram of a two-piece spherical imaging lens assembly;

[0032] Figure 6 MTF curve for a two-piece spherical imaging lens assembly;

[0033] Figure 7This is a point array diagram of the entire system's field of view;

[0034] Figure 8 The MTF curve of the entire system;

[0035] Figure 9 The entire airport curve and distortion curve diagram;

[0036] Figure 10 This is a schematic diagram of the overall mesh distortion.

[0037] Figure 11 This is the overall energy curve of the machine.

[0038] Among them, lens 1 is an off-axis concave parabolic mirror, lens 2 is an off-axis convex parabolic mirror, lens 3 is a crescent-shaped concave spherical lens, and lens 4 is a plano-convex spherical lens.

[0039] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0040] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0041] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0042] like Figures 1-11 As shown, the present invention proposes a large-aperture, small-field-of-view near-infrared imaging lens, including a parabolic off-axis reflection beam expander assembly and a two-piece spherical imaging lens group.

[0043] The parabolic off-axis reflection beam expander includes a first off-axis concave parabolic mirror and a second off-axis convex parabolic mirror, which together form a common optical path for laser beam expansion and imaging pre-optical path, realizing that the laser emission optical path and the near-infrared imaging optical path share the same aperture.

[0044] The two-piece spherical imaging lens assembly includes a third crescent-shaped concave spherical lens and a fourth plano-convex spherical lens. The distance between the third crescent-shaped concave spherical lens and the fourth plano-convex spherical lens is fixed at 4mm. The two-piece spherical imaging lens assembly can be moved along the optical axis to complete the system focusing.

[0045] The optical path distance between the parabolic off-axis reflection beam expander and the two-piece spherical imaging lens group is adjustable and the maximum distance does not exceed 1m.

[0046] The two-piece spherical imaging lens assembly is equipped with an independent temperature control device to compensate for lens defocusing caused by changes in ambient temperature.

[0047] The parabolic off-axis reflection beam expander can be used separately as a 4x laser beam expander.

[0048] The two-piece spherical imaging lens group can be detached and used independently as a near-infrared imaging lens.

[0049] A large-aperture, small-field-of-view near-infrared imaging optical system includes a parabolic off-axis reflective beam expander and a two-piece spherical imaging lens group. The parabolic off-axis reflective beam expander is located at the front end of the optical path, and the two-piece spherical imaging lens group is located at the rear end of the optical path. The optical path distance between the beam expander and the imaging lens is adjustable, and the maximum distance does not exceed 1m.

[0050] The entire optical system has an entrance pupil diameter of 200mm, a total focal length of 1500mm, an F-number of 7.5, an imaging field of view of 0.24°×0.24°, and is compatible with a near-infrared photodetector with a surface area of ​​5μm and a resolution of 896×896.

[0051] System assembly and debugging methods include:

[0052] S1. Individually calibrate the off-axis parabolic reflector beam expander: Use an interferometer to detect the transmitted wavefront, and adjust the second off-axis convex parabolic reflector to make the RMS value of the transmitted wavefront less than 0.1. ;

[0053] S2. Individually adjust the two-piece spherical imaging lens group: the third crescent concave spherical lens and the fourth plano-convex spherical lens are coaxially installed, and the parallel light output by the collimator is used for adjustment so that the star point image is a complete circle and the imaging occupies no more than 2×2 pixels.

[0054] S3. Combine the calibrated beam expander and imaging lens group along the optical axis, and complete the overall focusing by translating the two-piece spherical imaging lens group as a whole.

[0055] All geometric speckles in the entire field of view fall within the Airy disk area; the system MTF value at 100 line pairs / mm is not less than 0.2; the maximum distortion is 0.4082%; and 10 The energy within the radius is higher than 80%.

[0056] Example 1

[0057] Off-axis concave parabolic mirrors and off-axis convex parabolic mirrors are fixedly mounted on the front beam expander tube, forming a 4x beam expander unit after interferometer calibration. A crescent-shaped concave spherical lens and a plano-convex spherical lens are fixedly mounted on the rear imaging tube at a 4mm spacing. The tube is externally covered with a temperature-controlled heating / cooling module. The front beam expander tube and the rear imaging tube are aligned along the same optical axis, with an adjustable distance between them, limited to a maximum of 1m. The overall entrance pupil is 200mm, the focal length is 1500mm, and the field of view is 0.24°×0.24°. The rear end is aligned with 896×896 and 5... Surface-mount near-infrared detector.

[0058] The laser emission and target imaging share the same front-stage parabolic beam expander optical path. The near-infrared beam reflected by the target is expanded by two stages of parabolic lenses and then enters two spherical imaging lens groups. The temperature control module maintains the lens operating temperature at 20~25℃ in real time to avoid defocusing due to high and low temperatures. After the beam is focused by the crescent concave lens and the plano-convex lens, it is imaged onto the detector target surface to complete target imaging and recognition. The coaxial optical path ensures that the laser strike point and the imaging target are completely coincident.

[0059] During combat, the entire unit can be focused by shifting the rear imaging lens barrel. In maintenance or multi-device reuse scenarios, the front beam expander and rear imaging lens group can be separated, with the beam expander serving as a 4x laser beam expander and the two spherical lens groups serving as near-infrared imaging lenses.

[0060] All speckles across the entire field of view are within the Airy disk; MTF ≈ 0.23 per 100 line pairs / mm; maximum distortion 0.4082%; 10 The energy within the radius is >80%, and slight field curvature does not affect target recognition, meeting the requirements for laser weapon aiming and imaging.

[0061] Example 2

[0062] The two spherical lens groups, the crescent concave spherical lens and the plano-convex spherical lens, in Embodiment 1 are replaced with a single aspherical lens, and an external temperature control device is provided for the lens; the assembly process of the two lenses is eliminated, and only the single lens is coaxially installed, further simplifying the assembly and adjustment process; the rest of the parabolic off-axis beam expander, the overall optical parameters, the temperature control logic, and the disassembly and use method are completely consistent with Embodiment 1, which is suitable for airborne lightweight small laser equipment, with the only difference being that the processing cost of the aspherical lens is slightly higher than that of the spherical lens.

[0063] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0064] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0065] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A near-infrared imaging lens with a large aperture and a small field of view, characterized in that: Includes a parabolic off-axis reflection beam expander and a two-piece spherical imaging lens assembly; The parabolic off-axis reflection beam expander includes a first off-axis concave parabolic reflector and a second off-axis convex parabolic reflector, which together form a common optical path for laser beam expansion and imaging pre-optical path, realizing that the laser emission optical path and the near-infrared imaging optical path share the same aperture.

2. The large-aperture, small-field-of-view near-infrared imaging lens according to claim 1, characterized in that: The two-piece spherical imaging lens assembly includes a third crescent-shaped concave spherical lens and a fourth plano-convex spherical lens. The distance between the third crescent-shaped concave spherical lens and the fourth plano-convex spherical lens is fixed at 4mm. The two-piece spherical imaging lens assembly can be moved along the optical axis to complete the system focusing.

3. The large-aperture, small-field-of-view near-infrared imaging lens according to claim 2, characterized in that: The optical path distance between the parabolic off-axis reflection beam expander and the two-piece spherical imaging lens group is adjustable and the maximum distance does not exceed 1m.

4. The large-aperture, small-field-of-view near-infrared imaging lens according to claim 3, characterized in that: The two-piece spherical imaging lens assembly is equipped with an independent temperature control device to compensate for lens defocusing caused by changes in ambient temperature.

5. The large-aperture, small-field-of-view near-infrared imaging lens according to claim 4, characterized in that: The parabolic off-axis reflection beam expander can be used separately as a 4x laser beam expander.

6. The large-aperture, small-field-of-view near-infrared imaging lens according to claim 5, characterized in that: The two-piece spherical imaging lens assembly can be independently separated and used as a near-infrared imaging lens.

7. A large-aperture, small-field-of-view near-infrared imaging optical system, characterized in that: It includes a parabolic off-axis reflection beam expander and a two-piece spherical imaging lens assembly. The parabolic off-axis reflection beam expander is located at the front end of the optical path, and the two-piece spherical imaging lens assembly is located at the rear end of the optical path. The optical path distance between the beam expander and the imaging lens is adjustable, and the maximum distance does not exceed 1m. The entire optical system has an entrance pupil diameter of 200mm, a total focal length of 1500mm, an f / 7.5 aperture, an imaging field of view of 0.24° × 0.24°, and 5 adapter elements. A near-infrared photodetector with a resolution of 896×896.

8. The large-aperture, small-field-of-view near-infrared imaging optical system according to claim 7, characterized in that: System assembly and debugging methods include: S1. Individually calibrate the off-axis parabolic reflector beam expander: Use an interferometer to detect the transmitted wavefront, and adjust the second off-axis convex parabolic reflector to make the RMS value of the transmitted wavefront less than 0.

1. ; S2. Individually adjust the two-piece spherical imaging lens group: the third crescent concave spherical lens and the fourth plano-convex spherical lens are coaxially installed, and the parallel light output by the collimator is used for adjustment so that the star point image is a complete circle and the imaging occupies no more than 2×2 pixels. S3. Combine the calibrated beam expander and imaging lens group along the optical axis, and complete the overall focusing by translating the two-piece spherical imaging lens group as a whole.

9. The large-aperture, small-field-of-view near-infrared imaging optical system according to claim 8, characterized in that: All geometric speckles in the entire field of view fall within the Airy disk area; the system MTF value at 100 line pairs / mm is not less than 0.2; the maximum distortion is 0.4082%; and 10 The energy within the radius is higher than 80%.

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