Long-pupil bichromatic infrared zoom projection optical system and infrared target simulator

Abstract

The present application relates to a kind of long pupil distance two-waveband infrared zoom projection optical system and infrared target simulator, belong to optical device technical field, solve the short pupil distance of existing zoom projection system exists Problem.The working waveband of the system is 3~5 and 8~12, adopts the inverted structure of diaphragm front, including the first fixed lens group, zoom lens group, compensation lens group, second fixed lens group being sequentially arranged along optical axis, optical power is respectively negative optical power, positive optical power, negative optical power, negative optical power;The first fixed lens group and second fixed lens group are fixed in position on optical axis, and zoom lens group, compensation lens group reciprocating moves along the direction of optical axis to realize the switching between short focus-130mm and long focus-260mm.The present application has long pupil distance, can realize the far field projection to mid-long wave infrared target while stabilizing zoom, avoid the interference between infrared target simulator and equipment to be measured.

Description

Technical Field

[0001] This invention relates to the field of optical device technology, and in particular to a dual-band infrared zoom projection optical system with a long exit pupil distance and an infrared target simulator. Background Technology

[0002] As a key component of infrared hardware-in-the-loop simulation, the infrared target simulator's core is the infrared optical system, which mainly includes an infrared light source, a beam splitting system, an illumination system, and a projection system. The infrared target simulator can realistically simulate target and background information in complex infrared environments, achieving a true representation of real-world scenarios. It is reusable, enabling indoor testing and evaluation of detectors, saving testing costs and time compared to field tests.

[0003] As research into infrared target simulators continues, infrared zoom technology is becoming increasingly mature. Applying continuous zoom characteristics to the design of infrared target simulator projection systems allows for obtaining high-quality images in different fields of view by changing the focal length. This enables the infrared target simulator to be compatible with detectors testing different fields of view. However, current zoom simulator projection systems do not consider the exit pupil distance, which is often short. This results in insufficient physical separation between the target simulator and the device under test (DUT), affecting the DUT's debugging and heat dissipation. In the paper "Design of Optical Engine for Dual-DMD Zoom Infrared Dual-Band Scene Simulator," Pan Yue et al., *Journal of Infrared and Millimeter Waves*, Vol. 37, No. 4, August 2018, a dual-channel, common-aperture, zoom optical system based on dual DMDs was designed. This system includes a projection optical system and two illumination optical systems. The projection optical system as a whole can achieve 2x zoom to adapt to different needs, but the problem of a short exit pupil distance still exists.

[0004] Therefore, it is necessary to provide a projection optical system that, while ensuring high imaging quality and continuous zoom capability, significantly increases the exit pupil distance and has greater adaptability, taking into account the application characteristics of infrared target simulators. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of existing technologies and provide a dual-band infrared zoom projection optical system with a long exit pupil distance and an infrared target simulator. By optimizing the optical path configuration and power distribution, this invention combines zoom with a long exit pupil distance. It achieves high-quality multi-field image output in both mid-wave and long-wave infrared bands, while also significantly increasing the exit pupil distance (i.e., the rear working distance). This provides sufficient space between the infrared target simulator and the device under test, effectively avoiding mutual interference between instruments.

[0006] To solve the above problems, the present invention adopts the following technical solution:

[0007] A dual-band infrared zoom projection optical system with extended interpupillary distance. The system adopts an inverted structure with the aperture in front. The inverted structure consists of a first fixed lens group, a zoom lens group, a compensation lens group, and a second fixed lens group arranged coaxially along the optical axis. The first fixed lens group, the compensation lens group, and the second fixed lens group all have negative optical power, while the zoom lens group has positive optical power.

[0008] The first fixed lens group and the second fixed lens group are fixed in position on the optical axis. The zoom lens group and the compensating lens group reciprocate along the optical axis to achieve switching between short focal length and long focal length. During the zooming process, the zoom lens group zooms while moving along the optical axis, and the compensating lens group focuses while moving along the optical axis. The short focal length is -130mm, the long focal length is -260mm, and the exit pupil distance is 400mm.

[0009] The operating wavelength is 3 ~5 and 8 ~12 The beam of light emitted by the infrared light source passes through the illumination optical system and digital micromirror device, then enters the second fixed lens group. After the focal length is adjusted by the compensation lens group and the zoom lens group, it exits from the first fixed lens group, completing the far-field projection of the infrared image.

[0010] Meanwhile, the present invention also provides an infrared target simulator, including the dual-band infrared zoom projection optical system with long exit pupil distance as described above, and further including an infrared light source, an illumination optical system, a beam splitting module, and a digital micromirror device, wherein the infrared light source operates at a wavelength of 3... ~5 and 8 ~12 ;

[0011] The light beam emitted by the infrared light source is incident on the beam splitting module after passing through the illumination optical system. The beam splitting module guides the light beam to the modulation surface of the digital micromirror device. The digital micromirror device spatially modulates the incident light according to the target image signal. Its open-state reflected light is then selectively redirected by the beam splitting module and enters the long exit pupil distance dual-band infrared zoom projection optical system. The long exit pupil distance dual-band infrared zoom projection optical system projects infrared images with different fields of view in the far field.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] (1) This invention provides a working wavelength band of 3 through the rational allocation of the optical power of the lens group and the systematic optimization of the optical parameters. ~5 and 8 ~12 A zoom projection optical system with a long exit pupil distance. This zoom projection optical system can achieve continuous and smooth zoom by adopting a specific "negative-positive-negative-negative" optical power allocation scheme and an inverted optical path configuration for secondary imaging. The image transition is smooth and it can stably output high-quality imaging effects.

[0014] (2) The zoom projection optical system of the present invention has a long exit pupil distance, extending the exit pupil distance to 400mm, which can realize far-field projection of infrared targets while maintaining stable zoom, avoid interference between infrared target simulator and device under test, and improve the testing accuracy of device under test. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of a dual-band infrared zoom projection optical system with long exit pupil distance according to one embodiment of the present invention;

[0016] Figure 2 The long exit pupil distance dual-band infrared zoom projection optical system provided in this embodiment of the invention is in 3 ~5 Modulation transfer function diagram for short focal length in mid-wave infrared band;

[0017] Figure 3 The long exit pupil distance dual-band infrared zoom projection optical system provided in this embodiment of the invention is in 3 ~5 Modulation transfer function diagram of the mid-focus area in the mid-wave infrared band;

[0018] Figure 4 The long exit pupil distance dual-band infrared zoom projection optical system provided in this embodiment of the invention is in 3 ~5 Modulation transfer function diagram of long focal length in mid-wave infrared band;

[0019] Figure 5 The long exit pupil distance dual-band infrared zoom projection optical system provided in the embodiments of the present invention is in 8 ~12 Modulation transfer function diagram for short focal length in long-wave infrared band;

[0020] Figure 6 The long exit pupil distance dual-band infrared zoom projection optical system provided in the embodiments of the present invention is in 8 ~12 Modulation transfer function diagram of the mid-focus area in the long-wave infrared band;

[0021] Figure 7 The long exit pupil distance dual-band infrared zoom projection optical system provided in the embodiments of the present invention is in 8 ~12 Modulation transfer function diagram of long focal length in long-wave infrared band.

[0022] Explanation of reference numerals in the attached diagram: G1, First fixed lens group; G2, Zoom lens group; G3, Compensating lens group; G4, Second fixed lens group; L1, First lens; L2, Second lens; L3, Third lens; L4, Fourth lens; L5, Fifth lens; L6, Sixth lens; L7, Seventh lens; L8, Eighth lens; L9, Ninth lens; L10, Tenth lens; L11, Eleventh lens; L12, Twelfth lens; L13, Thirteenth lens; L14, Fourteenth lens; L15, Fifteenth lens; L16, Sixteenth lens; L17, Seventeenth lens; L18, Eighteenth lens; L19, Prism replacing flat glass. Detailed Implementation

[0023] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and preferred embodiments.

[0024] like Figure 1 As shown, this embodiment provides a dual-band infrared zoom projection optical system with a long exit pupil distance for infrared target simulation. The operating band of this system is 3. ~5 and 8 ~12 The system employs an inverted structure with the aperture stop in front. This inverted structure specifically includes a first fixed lens group G1, a zoom lens group G2, a compensating lens group G3, and a second fixed lens group G4, arranged coaxially along the optical axis. The first fixed lens group G1 has negative optical power, the zoom lens group G2 has positive optical power, the compensating lens group G3 has negative optical power, and the second fixed lens group G4 has negative optical power. Optionally, the first fixed lens group G1, the zoom lens group G2, the compensating lens group G3, and the second fixed lens group G4 can be set separately or within the same lens barrel (not shown in the figure). The optical power distribution of the first fixed lens group G1, the zoom lens group G2, the compensating lens group G3, and the second fixed lens group G4 pushes the exit pupil of the entire projection optical system far back behind the system, effectively extending the exit pupil distance to 400mm, thus providing sufficient physical separation between the target simulator and the device under test.

[0025] The first fixed lens group G1 and the second fixed lens group G4 are fixedly positioned on the optical axis, so that the first fixed lens group G1 and the second fixed lens group G4 remain stationary relative to the image plane. The zoom lens group G2 and the compensation lens group G3 are movable along the optical axis, and they reciprocate along the optical axis to switch between short focal length and long focal length. During zooming, the zoom lens group G2 zooms while moving along the optical axis, and the compensation lens group G3 focuses while moving along the optical axis. By adjusting the positions of the zoom lens group G2 and the compensation lens group G3 on the optical axis, the focal length of the zoom projection optical system can be adjusted. The focal length adjustment range is -130mm (W) to -260mm (T), where W represents short focal length and T represents long focal length.

[0026] At the short focal length position, the ratio of the focal length of the first fixed lens group G1 to the focal length F of the entire projection optical system is 96.862, the ratio of the focal length of the zoom lens group G2 to the focal length F of the entire projection optical system is -1.572, the ratio of the focal length of the compensation lens group G3 to the focal length F of the entire projection optical system is 0.832, and the ratio of the focal length of the second fixed lens group G4 to the focal length F of the entire projection optical system is 1.016.

[0027] At the mid-focal position, the ratio of the focal length of the first fixed lens group G1 to the focal length F of the entire projection optical system is 72.794, the ratio of the focal length of the zoom lens group G2 to the focal length F of the entire projection optical system is -1.181, the ratio of the focal length of the compensation lens group G3 to the focal length F of the entire projection optical system is 0.618, and the ratio of the focal length of the second fixed lens group G4 to the focal length F of the entire projection optical system is 0.763.

[0028] At the telephoto position, the ratio of the focal length of the first fixed lens group G1 to the focal length F of the entire projection optical system is 48.431, the ratio of the focal length of the zoom lens group G2 to the focal length F of the entire projection optical system is -0.786, the ratio of the focal length of the compensation lens group G3 to the focal length F of the entire projection optical system is 0.411, and the ratio of the focal length of the second fixed lens group G4 to the focal length F of the entire projection optical system is 0.508.

[0029] By controlling the ratio of the focal length of the first fixed lens group G1, the zoom lens group G2, the compensation lens group G3, and the second fixed lens group G4 to the total focal length of the system within the range described above, the image plane position remains stable and the zooming is smoother when the projection optical system continuously zooms within the focal length range of -130mm to -260mm.

[0030] Because the zoom projection optical system employs an inverted structure design, the beam emitted by the infrared light source passes through the illumination optical system (not shown in the figure) and the digital micromirror device (DMD) (not shown in the figure), then enters the second fixed lens group G4. After the focal length is adjusted by the compensation lens group G3 and the zoom lens group G2, it exits from the first fixed lens group G1, completing the far-field projection of the infrared image. In this embodiment, the operating wavelength of the infrared light source is 360 nm. ~5 and 8 ~12 .

[0031] This embodiment proposes a projection optical system with a long exit pupil distance and continuous zoom, specifically designed for the application characteristics of long-wave infrared target simulators. By optimizing the optical path configuration and optical power allocation, it balances the long exit pupil distance and zoom capabilities. While ensuring high imaging quality and multi-field switching capabilities, it significantly increases the exit pupil distance, providing necessary space for equipment layout and heat dissipation, and making the infrared target simulator using this projection optical system more advantageous in complex testing environments.

[0032] Because the projection optics system employs an inverted structure design, the digital micromirror device can be considered as the image plane during design. In one specific implementation, the first fixed lens group G1 includes a first lens L1, a second lens L2, and a third lens L3 arranged sequentially from the aperture stop to the image plane. The first lens L1 has positive optical power, the second lens L2 has positive optical power, and the third lens L3 has negative optical power. The first lens L1 is aspherical glass, while the second lens L2 and the third lens L3 are both spherical glass, with glass grades ZNSE, ZNS_BROAD, and ZNS_BROAD, respectively. The parameters of the first fixed lens group G1 are shown in Table 1.

[0033] Table 1 Detailed parameters of the first fixed lens group G1

[0034]

[0035] In one specific implementation, the zoom lens group G2 includes a fourth lens L4, a fifth lens L5, and a sixth lens L6 arranged sequentially from the aperture stop to the image plane. The fourth lens L4 has positive optical power, the fifth lens L5 has negative optical power, and the sixth lens L6 has positive optical power. The fourth lens L4 and the fifth lens L5 are both spherical glass, with glass grades ZNSE, GERMANIUM, and GERMANIUM, respectively. The parameters of the zoom lens group G2 are shown in Table 2.

[0036] Table 2 Detailed parameters of zoom scope group G2

[0037]

[0038] In one specific implementation, the compensating lens group G3 includes a seventh lens L7, an eighth lens L8, and a ninth lens L9 arranged sequentially from the aperture stop to the image plane. The seventh lens L7 has negative optical power, the eighth lens L8 has positive optical power, and the ninth lens L9 has positive optical power. The seventh lens L7, the eighth lens L8, and the ninth lens L9 are all spherical glass, with glass grades ZNSE, GERMANIUM, and ZNS_BROAD, respectively. The parameters of the compensating lens group G3 are shown in Table 3.

[0039] Table 3 Detailed parameters of compensation lens group G3

[0040]

[0041] In one specific implementation, the second fixed lens group G4 includes a tenth lens L10, an eleventh lens L11, a twelfth lens L12, a thirteenth lens L13, a fourteenth lens L14, a fifteenth lens L15, a sixteenth lens L16, a seventeenth lens L17, an eighteenth lens L18, and a prism replacing the flat plate glass L19, arranged sequentially from the aperture stop to the image plane. The prism replacing the flat plate glass L19 mainly functions to deflect the light path during actual operation, deflecting the light emitted from the illumination optical system onto the DMD. The light beam reflected by the DMD then passes through the prism replacing the flat plate glass L19 again and enters the projection optical system. The tenth lens L10 has positive optical power, the eleventh lens L11 has positive optical power, the twelfth lens L12 has negative optical power, the thirteenth lens L13 has negative optical power, the fourteenth lens L14 has positive optical power, the fifteenth lens L15 has negative optical power, the sixteenth lens L16 has positive optical power, the seventeenth lens L17 has negative optical power, the eighteenth lens L18 has positive optical power, and the optical power of the prism replacing the flat glass L19 is 0. Lenses L10 (10th), L11 (11th), L12 (12th), L13 (13th), L14 (14th), L15 (15th), and L16 (16th) are all spherical glass, while lenses L17 (17th) and L18 (18th) are both aspherical glass. The glass grades for lenses L10 through L18 are GERMANIUM, GERMANIUM, GERMANIUM, ZNS_BROAD, ZNSE, GERMANIUM, ZNSE, GERMANIUM, and GERMANIUM, respectively. The parameters of the second fixed lens group G4 are shown in Table 4.

[0042] The prism replacing the flat glass L19 specifically includes a first total internal reflection prism, a first compensation prism, and a second compensation prism, all closely adjacent to each other. The lower side of the first total internal reflection prism is parallel to the upper side of the first compensation prism. The first total internal reflection prism is responsible for deflecting the light path of the illumination optical system to the DMD. The first and second compensation prisms are compensation plates responsible for compensating for optical path differences, i.e., the lower side of the first total internal reflection prism is parallel to the upper side of the first compensation prism. The second compensation prism is also responsible for deflecting the off-state light, keeping it away from the projection light path to avoid stray light interference. Light emitted from the infrared source enters from the left side of the first total internal reflection prism through the illumination optical system. After total internal reflection on the inclined surface of the first total internal reflection prism, it passes through the lower side of the first total internal reflection prism and enters the DMD. The on-state light reflected by the DMD passes through the lower side of the first total internal reflection prism again and sequentially through the first total internal reflection prism, the first compensation prism, and the second compensation prism before entering the projection system. This prism assembly is equivalently replaced by a single flat glass plate in the system design.

[0043] Table 4 Detailed parameters of the second fixed lens group G4

[0044]

[0045] Table 5. Coefficients of even-order aspherical surfaces

[0046]

[0047] S2, S34, and S35 represent the surface numbers of even-order aspherical surfaces in the first lens L1, the seventeenth lens L17, and the eighteenth lens L18, respectively.

[0048] The projection optical system for infrared target simulation provided by this invention adopts a zoom structure design, consisting of a first fixed lens group G1, a zoom lens group G2, a compensating lens group G3, and a second fixed lens group G4 in sequence. By rationally configuring the optical power distribution and lens surface parameters of each component, and by using existing mechanical structures such as a zoom cam mechanism (not shown in the figure) to precisely control the movement trajectory of the zoom lens group G2 and the compensating lens group G3, it can achieve performance in the mid-wave infrared band 3. ~5 Within a field of view of 3.94°–1.97° and in the long-wave infrared band 8 ~12 Continuous and smooth zoom within a field of view of 3.90°-1.98°.

[0049] This projection optical system employs an inverted structure with the aperture stop at the very front. Positioning the aperture stop at the very front ensures that the beam from the infrared light source, after passing through the illumination optical system, is reflected by the DMD and enters the projection optical system, completing the far-field projection of the infrared image. To achieve the requirements of image-side telecenty and long exit pupil distance, this projection optical system uses a secondary imaging structure: the first fixed lens group G1 and the zoom lens group G2 form the front zoom group, achieving 2x zoom; the second fixed lens group G4 serves as the magnification factor. The rear imaging group is stitched together with the front group to effectively achieve the image-side telecentric design and ensure a long exit pupil distance of 400mm.

[0050] The overall performance indicators of the dual-band infrared zoom projection optical system with long exit pupil distance of the present invention are as follows:

[0051] Operating band: 3 ~5 8 ~12 ;

[0052] Focal length: -130mm at short focal length (W) and -260mm at long focal length (T);

[0053] Field of view: 3 ~5 3.94° (W) - 1.97° (T);

[0054] 8 ~12 :3.90°(W)-1.98°(T);

[0055] Maximum aperture: 62.89mm;

[0056] Image size: 8.9mm;

[0057] Exit pupil distance: 400mm.

[0058] The long exit pupil distance dual-band infrared zoom projection optical system of the present invention operates at 3 ~5 and 8 ~12 Dual-band design enables the simulation of infrared target scenes with different fields of view, providing matching field-of-view conditions for the equipment under test. The components work collaboratively to achieve zoom functionality while ensuring image plane stability and optical performance.

[0059] Figures 2-4 To extend the interpupillary distance of the dual-band infrared zoom projection optical system in 3 ~5 Schematic diagrams of modulation transfer functions (MTFs) at short, medium, and long focal lengths in the mid-infrared band. As shown in the figures, at the on-axis, 0.7 field-of-view, and full field-of-view positions in the mid-infrared band, the system's MTF at a spatial frequency of 35 lp / mm is greater than 0.4, and it approaches the diffraction limit at low spatial frequencies. It maintains high contrast at high spatial frequencies, demonstrating good high-frequency response. Furthermore, the MTF curve changes smoothly from on-axis to full field of view, indicating that the system adequately corrects for off-axis aberrations such as astigmatism, coma, and field curvature, resulting in excellent image quality uniformity.

[0060] Figures 5-7 To extend the interpupillary distance of the dual-band infrared zoom projection optical system in 8 ~12 Schematic diagrams of modulation transfer functions (MTFs) at short, medium, and long focal lengths in the mid-infrared band. As shown in the figure, at the on-axis, 0.7 field-of-view, and full field-of-view positions in the long-wave infrared band, the system's MTF at a spatial frequency of 17 lp / mm is greater than 0.3, and it approaches the diffraction limit at low spatial frequencies. It maintains high contrast at high spatial frequencies, demonstrating good high-frequency response. Furthermore, the MTF curve changes smoothly from on-axis to full field of view, indicating that the system adequately corrects for off-axis aberrations such as astigmatism, coma, and field curvature, resulting in excellent image quality uniformity.

[0061] Another embodiment of the present invention provides an infrared target simulator, which includes the dual-band infrared zoom projection optical system with long exit pupil distance as described in the above embodiment, and also includes an infrared light source, an illumination optical system, a beam splitting module and a digital micromirror device.

[0062] Specifically, the beam emitted by the infrared light source, after passing through the illumination optics system, is incident on the beam-splitting module at a preset specific angle. The beam-splitting module guides the beam to the modulation surface of the digital micromirror device (DMM). The DMM spatially modulates the incident light according to the target image signal, and its open-state reflected light is then selectively redirected by the beam-splitting module before entering the long exit pupil distance dual-band infrared zoom projection optical system. In the long exit pupil distance dual-band infrared zoom projection optical system, the focal length is continuously adjusted through the zoom structure, ultimately projecting infrared images with different fields of view into the far field.

[0063] The infrared target simulator proposed in this embodiment operates at a wavelength of 3. ~5 and 8 ~12 Dual-band, capable of simulating infrared target scenes with different fields of view, providing matching field of view conditions for the equipment under test, while having continuous zoom function, and higher image plane stability and optical performance.

[0064] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0065] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A long eye relief dual band infrared zoom projection optical system characterized by, The inverted structure with a front aperture stop is composed of a first fixed lens group (G1), a zoom lens group (G2), a compensation lens group (G3), and a second fixed lens group (G4) arranged coaxially along the optical axis direction in sequence, and the first fixed lens group (G1), the compensation lens group (G3), and the second fixed lens group (G4) all have negative focal lengths, and the zoom lens group (G2) has a positive focal length; the compensation lens group (G3) is composed of a seventh lens (L7), an eighth lens (L8), and a ninth lens (L9) arranged in sequence from the aperture stop to the image plane; the seventh lens (L7) has a negative focal length, and the eighth lens (L8) and the ninth lens (L9) both have positive focal lengths; the seventh lens (L7), the eighth lens (L8), and the ninth lens (L9) are all spherical glasses, and the glass grades are ZNSE, GERMANIUM, and ZNS_BROAD respectively; The first fixed lens group (G1) and the second fixed lens group (G4) are fixed in position on the optical axis, the zoom lens group (G2) and the compensation lens group (G3) move reciprocally along the optical axis direction to realize switching between the short focus and the long focus, and in the zooming process, the zoom lens group (G2) is zoomed when moving along the optical axis direction, and the compensation lens group (G3) is focused when moving along the optical axis direction, wherein the short focus is -130 mm, the long focus is -260 mm, and the exit pupil distance is 400 mm; The working wavelength is 3 ~ 5 And 8 ~ 12 The light beams emitted by the infrared light source pass through the illumination optical system, the digital micromirror device, and then enter the second fixed lens group (G4), pass through the compensation mirror group (G3) and the variable focal length mirror group (G2) to adjust the focal length, and then exit from the first fixed lens group (G1), completing the far field projection of the infrared image.

2. The long-FL dual-band infrared zoom projection optical system according to claim 1, characterized in that, The first fixed lens group (G1) is composed of a first lens (L1), a second lens (L2), and a third lens (L3) arranged in sequence from the aperture stop to the image plane; the first lens (L1) and the second lens (L2) both have positive focal lengths, and the third lens (L3) has a negative focal length; the first lens (L1) is a non-spherical glass, and the second lens (L2) and the third lens (L3) are both spherical glasses with glass grades of ZNSE, ZNS_BROAD, and ZNS_BROAD respectively.

3. The long-FL dual-band infrared zoom projection optical system according to claim 1, characterized in that, The zoom lens group (G2) is composed of a fourth lens (L4), a fifth lens (L5), and a sixth lens (L6) arranged in sequence from the aperture stop to the image plane; the fourth lens (L4) and the sixth lens (L6) have positive focal lengths, and the fifth lens (L5) has a negative focal length; the fourth lens (L4), the fifth lens (L5), and the sixth lens (L6) are all spherical glasses with glass grades of ZNSE, GERMANIUM, and GERMANIUM respectively.

4. The long-FL dual-band infrared zoom projection optical system according to claim 1, characterized in that, The second fixed lens group (G4) is composed of a tenth lens (L10), an eleventh lens (L11), a twelfth lens (L12), a thirteenth lens (L13), a fourteenth lens (L14), a fifteenth lens (L15), a sixteenth lens (L16), a seventeenth lens (L17), an eighteenth lens (L18), and a prism-replaced flat glass (L19) arranged in sequence from the diaphragm to the image plane; the tenth lens (L10), the eleventh lens (L11), the fourteenth lens (L14), the sixteenth lens (L16), and the eighteenth lens (L18) all have positive refractive powers, the twelfth lens (L12), the thirteenth lens (L13), the fifteenth lens (L15), and the seventeenth lens (L17) all have negative refractive powers, and the refractive power of the prism-replaced flat glass (L19) is 0; the tenth lens (L10) to the sixteenth lens (L16) are all spherical glasses, the seventeenth lens (L17) and the eighteenth lens (L18) are both aspherical glasses, and the glass grades of the tenth lens (L10) to the eighteenth lens (L18) are GERMANIUM, GERMANIUM, GERMANIUM, ZNS_BROAD, ZNSE, GERMANIUM, ZNSE, GERMANIUM, and GERMANIUM, respectively.

5. The long-FL dual-band infrared zoom projection optical system according to claim 1, characterized in that, In the short-focus position, the ratio of the focal length of the first fixed lens group (G1) to the focal length F of the entire projection optical system is 96.862, the ratio of the focal length of the variable magnification lens group (G2) to the focal length F is -1.572, the ratio of the focal length of the compensation lens group (G3) to the focal length F is 0.832, and the ratio of the focal length of the second fixed lens group (G4) to the focal length F is 1.

106.

6. The long-FL dual-band infrared zoom projection optical system according to claim 1, characterized in that, In the mid-focus position, the ratio of the focal length of the first fixed lens group (G1) to the focal length F of the entire projection optical system is 72.794, the ratio of the focal length of the variable magnification lens group (G2) to the focal length F is -1.181, the ratio of the focal length of the compensation lens group (G3) to the focal length F is 0.618, and the ratio of the focal length of the second fixed lens group (G4) to the focal length F is 0.

763.

7. The long-FL dual-band infrared zoom projection optical system according to claim 1, characterized in that, In the long-focus position, the ratio of the focal length of the first fixed lens group (G1) to the focal length F of the entire projection optical system is 48.431, the ratio of the focal length of the variable magnification lens group (G2) to the focal length F is -0.736, the ratio of the focal length of the compensation lens group (G3) to the focal length F is 0.411, and the ratio of the focal length of the second fixed lens group (G4) to the focal length F is 0.

508.

8. The long-FL dual-band infrared zoom projection optical system according to claim 1, characterized in that, The first fixed lens group (G1), the variable magnification lens group (G2), the compensation lens group (G3), and the second fixed lens group (G4) are arranged in the same lens barrel.

9. An infrared target simulator characterized by, The long-throw double-band infrared zoom projection optical system as claimed in any one of claims 1 to 8, further comprising an infrared light source, an illumination optical system, a light splitting module, and a digital micromirror device, wherein the infrared light source has a working wavelength of 3 ~ 5 and 8 ~ 12 ; The light beam emitted by the infrared light source is incident on the illumination optical system and then on the light splitting module. The light splitting module guides the light beam to the modulation surface of the digital micromirror device. The digital micromirror device modulates the incident light according to the target image signal. The reflected light in the open state is selectively diverted by the light splitting module and then enters the long-standoff double-band infrared zoom projection optical system. The long-standoff double-band infrared zoom projection optical system projects infrared images of different fields of view in the far field.

Images