Common-aperture four-spectrum imaging optical system

Abstract

The invention discloses a common-caliber four-spectrum imaging optical system, and belongs to the technical field of optical design. The optical system sequentially comprises a four-spectrum-band common lens group unit, a diaphragm group, a spectroscope group unit, an imaging lens group unit and a focal plane detector unit along an optical axis. And the four-spectrum-band shared lens group unit is used for carrying out common-caliber collection and convergence on incident beams of R, G, B and near-infrared spectrum bands. The spectroscope group unit is located in the non-parallel light path and is used for splitting the light beam. The split light beams of each spectrum are subjected to independent aberration correction and imaging by the corresponding single-spectrum imaging lens group, and are received by respective focal plane detectors. The problem that the view field, the number of spectrum bands, the resolution and the system size are difficult to consider in a traditional scheme is solved.

Description

Technical Field

[0001] This application relates to the field of optical design technology, and more specifically to an optical system for common-aperture four-band imaging. Background Technology

[0002] With the rapid development of imaging optics technology, photographic objective lens optical system technology is gradually moving towards multispectral, large field of view and miniaturization. Traditional multispectral imaging technology often adopts a multi-lens system integration scheme with different apertures, which leads to a series of engineering application problems such as system optical axis mismatch, large size, and data spatiotemporal mismatch. Adopting a common aperture integration scheme can effectively avoid the above-mentioned engineering application problems and obtain multispectral data with high real-time performance and registration accuracy while significantly reducing the system size.

[0003] Traditional common-aperture multispectral imaging optical systems often employ a design scheme with coaxial primary and secondary mirrors followed by beam-splitter elements and a transmissive imaging subsystem. These systems are limited by the front-end cascade-like optical system, resulting in low energy utilization due to central obstruction, and the field of view is generally less than 3°, making large-field-of-view imaging impossible. Some researchers have proposed designing the front-end reflective system as a convex mirror followed by mirrors of different powers to form a front-reflective system, with a beam-splitter element and imaging subsystem to achieve wide-angle imaging. However, this type of system requires large-aperture convex aspherical mirrors, which are difficult to manufacture, test, and assemble, resulting in high costs and limited practical engineering applications. To achieve common-aperture multispectral large-field-of-view imaging, some researchers have proposed using a coaxial transmissive optical system, introducing a beam-splitter element into the transmissive optical system. This allows for simultaneous imaging of multiple spectral bands, but the field of view remains limited. While the maximum field of view from visible light to near-infrared bands has been significantly improved, it still cannot meet the requirements for ultra-wide-angle imaging.

[0004] Therefore, there is an urgent need for an optical system with a common aperture and four spectral bands for imaging to solve the technical problem of simultaneous imaging of multiple spectral bands under the condition of common aperture and ultra-wide angle in the existing technology. Summary of the Invention

[0005] The purpose of this application is to provide an optical system for four-band imaging with a common aperture, which can solve at least one of the technical problems mentioned above. The specific solution is as follows: An optical system for four-band imaging with a common aperture includes: a four-band common mirror group unit, an aperture stop, a beam splitter group unit, an imaging mirror group unit, and a focal plane detector unit arranged sequentially along the optical axis. The four-band shared lens unit is used to converge the incident beam with a common aperture; from the object side to the image side, it includes: a front negative lens group and a rear positive lens group; the front negative lens group includes at least one single lens with negative optical power; the rear positive lens group includes at least one cemented lens, each of which is formed by cementing a negative optical power lens and a positive optical power lens together. The aperture is located on the image side of the four-band common mirror group and is used to limit the light-transmitting aperture of the optical system and adjust the aberration distribution of the optical system. The beam splitter unit is disposed on the image side of the aperture and is used to split the light beam, including at least two beam splitters; The imaging lens group unit is disposed on each beam splitting optical path of the beam splitter group unit; The focal plane detector unit is positioned at the image plane of the imaging lens unit.

[0006] Furthermore, the front negative lens group includes: a first common lens, a second common lens, and a third common lens; The rear positive lens group includes: a first common cemented lens group and a second common cemented lens group; The first common cemented lens group is cemented together by a fourth common lens with negative optical power and a fifth common lens with positive optical power; The second common cemented lens group is cemented together by a sixth common lens with negative optical power and a seventh common lens with positive optical power.

[0007] Furthermore, in the first common lens, the second common lens, and the third common lens, the centers of curvature of the two optical surfaces of each single lens are located on the same side of the aperture stop.

[0008] Furthermore, the near-infrared imaging lens group includes, from the light incident side to the image side, a first near-infrared lens, a second near-infrared lens, a third near-infrared lens, and a fourth near-infrared lens; The first near-infrared lens is cemented to the second near-infrared lens; The first near-infrared lens, the third near-infrared lens, and the fourth near-infrared lens have positive optical power, and the second near-infrared lens has negative optical power; The image plane of the fourth near-infrared lens is aspherical.

[0009] Furthermore, the beam splitter unit includes: a first beam splitter prism, a second beam splitter prism, and a third beam splitter prism arranged sequentially; The first beam splitter is used to split the incident beam into two beams. The second and third beam splitters are used to further split the two beams to obtain beams in the R, G, B and near-infrared bands, respectively.

[0010] Furthermore, the imaging lens group includes: an independent R-band imaging lens group, a G-band imaging lens group, a B-band imaging lens group, and a near-infrared imaging lens group.

[0011] Furthermore, the focal plane detector unit includes an R-band detector, a G-band detector, a B-band detector, and a near-infrared spectral detector, which are respectively disposed at the image plane positions of the R-band imaging mirror group, the G-band imaging mirror group, the B-band imaging mirror group, and the near-infrared spectral imaging mirror group.

[0012] Furthermore, the beam splitter unit includes: an internal reflection right-angle prism and a fourth beam splitter prism; The internal reflection right-angle prism is used to fold and compress the axial dimension of the optical axis. The fourth beam splitter is used to separate the incident beam into an RGB spectral beam and a near-infrared spectral beam.

[0013] Furthermore, the imaging lens group includes: an RGB spectral imaging lens group and a near-infrared spectral imaging lens group, which respectively receive the RGB spectral beam and the near-infrared spectral beam split by the fourth beam splitter.

[0014] Furthermore, the focal plane detector unit includes an RGB spectral band detector and a near-infrared spectral band detector, which are respectively disposed at the image plane positions of the RGB spectral band imaging mirror group and the near-infrared spectral band imaging mirror group.

[0015] Compared with the prior art, the above-described solutions of this application have at least the following beneficial effects: 1. This application discloses a common-aperture four-band imaging optical system. By using a shared mirror group unit for all four spectral bands to collect all incident light rays with a common aperture and perform aberration pre-correction, it ensures ultra-wide-angle imaging capability from the source. Subsequently, a precise beam splitter group is used to accurately separate the composite light according to the working spectral bands, and an independent imaging mirror group is configured for each spectral band for targeted aberration optimization. This enables the system to achieve high-resolution imaging of the R, G, B, and near-infrared spectral bands while covering a field of view exceeding 120°, effectively solving the inherent contradiction in traditional solutions where wide-angle, multi-band, and high-definition imaging are difficult to achieve simultaneously.

[0016] 2. This application discloses a common-aperture four-band imaging optical system that incorporates several compaction measures in its optical path design. On one hand, by designing the optical surface of the negative lens in the shared lens group to bend towards the internal aperture, the light path and aberration distribution are optimized. On the other hand, particularly by employing a beam splitting scheme including an internally reflecting right-angle prism, the optical path can be folded 90°, thereby significantly compressing the overall axial dimension of the optical system. This design results in a flatter and more compact trinocular panoramic camera structure, facilitating integration and application on space-constrained mobile platforms, overcoming the drawbacks of traditional multispectral imaging systems, such as large size and difficult deployment.

[0017] 3. This application discloses a common-aperture four-band imaging optical system. Addressing the issue of near-infrared imaging being susceptible to advanced aberrations, a dedicated imaging lens group is designed for the near-infrared channel. Not only does it employ cemented lenses to effectively correct chromatic aberration, but it also utilizes an aspherical lens on the lens closest to the image plane to precisely eliminate residual astigmatism, field curvature, and other advanced aberrations generated by near-infrared light in a very wide field of view. This ensures that near-infrared images maintain the same high definition and high contrast as visible light images across the entire field of view. It achieves high-quality, all-day (day / night) monitoring capabilities, overcoming the shortcomings of traditional wide-angle systems where image quality deteriorates sharply in the near-infrared band. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings: Figure 1 This is a schematic diagram of the structure of an optical system for common aperture four-band imaging provided in Embodiment 1 of this application.

[0019] Figure 2 This is a schematic diagram of the MTF curve of the B band provided in Embodiment 1 of this application.

[0020] Figure 3 This is a schematic diagram of the MTF curve of the G band provided in Embodiment 1 of this application.

[0021] Figure 4 This is a schematic diagram of the MTF curve of the R-band provided in Embodiment 1 of this application.

[0022] Figure 5 This is a schematic diagram of the MTF curve of the near-infrared spectral band provided in Embodiment 1 of this application.

[0023] Figure 6This is a schematic diagram of the structure of an optical system for common aperture four-band imaging provided in Embodiment 2 of this application.

[0024] Figure 7 This is a schematic diagram of the MTF curve of the RGB spectrum provided in Embodiment 2 of this application.

[0025] Figure 8 This is a schematic diagram of the MTF curve of the near-infrared spectral band provided in Embodiment 2 of this application.

[0026] Figure 9 This is a first structural schematic diagram of a panoramic compact all-day surveillance camera composed of a common-aperture four-band imaging optical system stitched together, as provided in an embodiment of this application.

[0027] Figure 10 This is a second structural schematic diagram of a panoramic compact all-day surveillance camera composed of a common-aperture four-band imaging optical system stitched together, as provided in an embodiment of this application.

[0028] Explanation of reference numerals in the attached figures: First common lens 1, second common lens 2, third common lens 3, first common cemented lens group 4, fourth common lens 41, fifth common lens 42, second common cemented lens group 5, sixth common lens 51, seventh common lens 52, first beam splitter 6, second beam splitter 7, third beam splitter 8, first aperture 91, second aperture 92, third aperture 93, RGB spectral imaging lens group 10, first RGB lens 101, second RGB lens 102, third RGB lens 103, fourth RGB lens 104, RGB cemented lens 1012, near-infrared spectral imaging lens group 11, first near-infrared lens 111, second near-infrared lens 112, third near-infrared lens 113, fourth near-infrared lens 114, near-infrared cemented lens 1112, R-band detector 12, G-band detector 13, B-band detector 14, near-infrared spectral detector 15. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or device. Without further limitation, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the product or device that includes that element.

[0031] The embodiments of this application are described in detail below with reference to the accompanying drawings.

[0032] Example 1: like Figure 1 As shown, this application provides an optical system for four-band imaging with a common aperture. The optical system includes, along the optical axis, a four-band shared mirror group unit, an aperture group, a beam splitter group unit, an imaging mirror group unit, and a focal plane detector unit. In this application embodiment, the aperture in the aperture group located in the optical path direction of the GB band imaging mirror group is the first aperture 91, and the aperture in the aperture group located in the optical path direction of the R band and near-infrared band imaging mirror group 11 is the second aperture 92. The parameters of the first aperture 91 and the second aperture 92 are the same.

[0033] The four-band shared lens unit is used to converge the incident beams with a common aperture. From the object side to the image side, it includes a front negative lens group and a rear positive lens group. Located at the very front of the optical system, this unit serves as a shared front imaging unit for the R, G, B, and near-infrared bands. Under ultra-wide-angle incident conditions, it performs common-aperture collection and primary convergence of multi-band incident beams from different directions. Before beam splitting, it uniformly introduces and corrects the principal aberrations of each band: on-axis and off-axis spherical aberration, field curvature and distortion, and low-order chromatic aberration, providing subsequent beam splitting and imaging lens units with a controlled aberration distribution and consistent beam aperture. The front negative lens group diverges the incident beam through a negative optical power lens, enabling the optical system to achieve large field-of-view imaging under limited front aperture conditions. It controls the incident angle and height distribution of the principal rays, adjusting the propagation path of the principal rays at different field-of-view positions within the system, providing a reasonable height distribution for subsequent positive lens and beam splitting lens units. The rear positive lens group refocuses the diverged beams from the front negative lens group, forming a usable intermediate image or image-front beam state while maintaining a large field of view; it uniformly suppresses chromatic aberration and spherical aberration introduced by different spectral bands before beam splitting, reducing the correction burden of subsequent imaging lens groups for each spectral band.

[0034] In this embodiment, the four-band shared lens group unit includes seven lenses. The front negative lens group includes: a first shared lens 1, a second shared lens 2, and a third shared lens 3. The rear positive lens group includes: a first shared cemented lens group 4 and a second shared cemented lens group 5. The first shared lens 1 and the second shared lens 2 are both quasi-concentric, non-haloed meniscus lenses, which correct astigmatism and field curvature while introducing a small amount of spherical aberration and coma; the third shared lens 3 is used to correct the small amount of spherical aberration and coma generated by the first shared lens 1 and the second shared lens 2, so that the front negative lens group as a whole eliminates spherical aberration and coma, and corrects the astigmatism and field curvature of the entire optical system.

[0035] This application provides a preferred technical solution in which the curvature centers of the two optical surfaces of the first common lens 1, second common lens 2, and third common lens 3 of the front negative lens group are located on the same side of the aperture group. This technical solution, by designing the curved surface orientation of the negative lenses (not simply a repetition of the negative lenses), corrects aberrations before the light beam enters the rear positive lens group. This effectively reduces the incident angle of the light beam on the lens surface, optimizes the position and shape of the system pupil, and allows the light beams in each field of view to pass through the aperture group more uniformly and symmetrically. This results in more consistent illumination and aberration characteristics across the entire field of view, avoiding vignetting and sudden drops in image quality, and fundamentally reducing astigmatism and field curvature.

[0036] This application provides a preferred technical solution, in which the rear positive lens group includes: a first common cemented lens group 4 and a second common cemented lens group 5; the first common cemented lens group 4 is formed by cementing a fourth common lens 41 with negative optical power and a fifth common lens 42 with positive optical power; the second common cemented lens group 5 is formed by cementing a sixth common lens 51 with negative optical power and a seventh common lens 52 with positive optical power. The first common cemented lens group 4 plays a role in correcting off-axis aberrations in the optical system. Through the complementary aberrations of the positive and negative lenses and the continuous refraction setting of the cemented surface, it can effectively suppress the generation of higher-order spherical aberrations and higher-order coma, achieving an effective balance between system coma, astigmatism, and distortion. Simultaneously, it assists in correcting axial chromatic aberration, improving the consistency of image quality across the entire field of view. Choosing a cemented configuration with the negative lens group in front can effectively increase the field of view of the system. In this embodiment, there are two sets of the second common cemented lens group 5, both with identical parameter settings. They are respectively located in the optical path of the GB band imaging lens group and the optical path of the R band and near-infrared band imaging lens group 11. The first aperture 91 is located in the GB band imaging lens group optical path, and the second aperture 92 is located in the R band and near-infrared band imaging lens group 11 optical path. For ease of description, the one located in the GB band imaging lens group optical path is used as an example. The second common cemented lens group 5 is positioned near the first aperture 91, which helps to increase the relative aperture of the system and correct the system's magnification chromatic aberration. Choosing a negative group closer to the first aperture 91 and a positive group further away from the aperture 91 has the advantage of minimizing spherical aberration and coma while bearing the system's main optical power. Furthermore, the arrangement of the first common cemented lens group 4 and the second common cemented lens group 5 serves to correct off-axis aberrations and reduces the number of refractive surfaces in the system, thus improving the system's assembly stability and reducing eccentricity and tilt.

[0037] This application provides a preferred technical solution, in which the beam splitter unit includes: a first beam splitter 6, a second beam splitter 7, and a third beam splitter 8; the first beam splitter 6 is used to split the incident beam into two beams, and the second beam splitter 7 and the third beam splitter 8 are used to further split the two beams to obtain R-band, G-band, B-band, and near-infrared-band beams, respectively.

[0038] The incident beam is converged by the first common cemented lens group 4 and then incident on the first beam splitter 6. The first beam splitter 6 splits the beam into a transmitted beam and a reflected beam; the R-band and near-infrared band are transmitted beams, and the G-band and B-band are reflected beams. The reflected beams of the G-band and B-band are incident on the second beam splitter 7, where the G-band beam is transmitted and the B-band beam is reflected. The transmitted beams of the R-band and near-infrared band are incident on the third beam splitter 8, where the near-infrared beam is transmitted and the R-band beam is reflected. Finally, four beams of the R-band, G-band, B-band, and near-infrared bands are obtained.

[0039] The technical solution of this application embodiment enables the beam splitter unit to achieve the step-by-step separation of four spectral beams without introducing a complex folding structure, and ensures that there is a clear optical path distinction between each spectral beam.

[0040] This application provides a preferred technical solution, in which the imaging lens group includes: an independent R-band imaging lens group, a G-band imaging lens group, a B-band imaging lens group, and a near-infrared imaging lens group 11. The focal plane detector unit includes: an R-band detector 12, a G-band detector 13, a B-band detector 14, and a near-infrared detector 15, which are respectively disposed at the image plane positions of the R-band imaging lens group, the G-band imaging lens group, the B-band imaging lens group, and the near-infrared imaging lens group 11.

[0041] The G-band beam transmitted through the second beam splitter 7 enters an independent G-band imaging mirror group for aberration correction and imaging, and is finally received by the G-band detector 13. The B-band beam reflected by the second beam splitter 7 enters an independent B-band imaging mirror group for aberration correction and imaging, and is finally received by the B-band detector 14. The R-band beam reflected by the third beam splitter 8 enters an independent R-band imaging mirror group for aberration correction and imaging, and is finally received by the R-band detector 12. The near-infrared beam transmitted through the third beam splitter 8 enters an independent near-infrared imaging mirror group 11 for aberration correction and imaging, and is finally received by the near-infrared detector 15.

[0042] In this embodiment, four independent single-spectrum imaging lens groups include an R-band imaging lens group, a G-band imaging lens group, a B-band imaging lens group, and a near-infrared imaging lens group 11. The R-band, G-band, and B-band imaging lens groups adopt a standardized design with identical optical structural parameters, and are collectively referred to as the RGB-band imaging lens group 10. The RGB-band imaging lens group 10, from the light incident side to the image side, includes a first RGB lens 101, a second RGB lens 102, a third RGB lens 103, and a fourth RGB lens 104. The first RGB lens 101 and the second RGB lens 102 are cemented together. The first RGB lens 101, the third RGB lens 103, and the fourth RGB lens 104 have positive optical power, while the second RGB lens 102 has negative optical power. The second RGB lens 102 corrects the residual chromatic aberration and spherical aberration of the system, and the cemented lens is located near the aperture stop. The first RGB lens 101, the third RGB lens 103, and the fourth RGB lens 104 help to increase the relative aperture of the system on the image side, and reduce the size of optical elements and the overall system.

[0043] This application provides a preferred technical solution where the near-infrared imaging lens group 11, from the light incident side to the image side, includes: a first near-infrared lens 111, a second near-infrared lens 112, a third near-infrared lens 113, and a fourth near-infrared lens 114. The first near-infrared lens 111 and the second near-infrared lens 112 are cemented together to form a near-infrared cemented lens 1112. The first near-infrared lens 111, the third near-infrared lens 113, and the fourth near-infrared lens 114 have positive optical power, while the second near-infrared lens 112 has negative optical power. The image side of the fourth near-infrared lens 114 is aspherical. This technical solution avoids using too many cemented lenses, allowing a single lens to have more degrees of freedom for aberration correction and balancing the optical power of the system while correcting the Pitzervar field curvature.

[0044] This application provides a preferred technical solution where, in the near-infrared imaging lens group 11, the image-side optical surface of the lens closest to the image plane is aspherical, meaning the image plane of the fourth near-infrared lens 114 is aspherical. The expression for the aspherical elevation equation is: Where z represents the sag equation; r represents the half-aperture size; c represents the surface curvature, which is numerically equal to the reciprocal of the radius; k represents the conicity coefficient; and A, B, C, and D represent the aspheric coefficients, respectively. In the embodiments of this application, k=0, A=-1.3336E-5, B=-5.8951E-8, C=3.798E-10, and D=-7.9177E-12.

[0045] This application provides a preferred technical solution where the value of k is 0, which can effectively avoid the coupling problem between the conic coefficient and the aspherical coefficient. Taking the aspherical coefficient to the tenth power of the aperture can both enhance the ability to correct spherical aberration and balance the processing difficulty.

[0046] Although the four-band shared lens unit has been corrected, astigmatism and field curvature still remain in the edge light transmitted to each independent imaging channel, especially the near-infrared channel, under ultra-wide-angle conditions. The freeform shape of aspherical surfaces can eliminate these residual aberrations specific to the light characteristics of the near-infrared band, ensuring a flat near-infrared image with sharp edges. The aberration characteristics of the near-infrared band differ from those of the visible light band. Using an aspherical surface on the last lens, the fourth near-infrared lens 114, allows for the most effective fine-tuning of the convergence state of light in this band, correcting advanced spherical aberrations and off-axis coma that cannot be perfectly eliminated by ordinary spherical lenses, and improving the spot concentration across the entire field of view. Introducing an aspherical surface at the end of the imaging optical path ensures geometrically accurate registration between the near-infrared and visible light images.

[0047] This application provides a preferred technical solution in which the first common lens 1, the second common lens 2, the fifth common lens 42, the sixth common lens 51, the first RGB lens 101, the fourth RGB lens 104, the first near-infrared lens 111, and the fourth near-infrared lens 114 are made of lanthanum heavy flint glass with a refractive index n. d With the dispersion coefficient υ d Satisfy: 1.8 < n d <2.0, and 30 <υ d <45. The third common lens 3, the fourth common lens 41, the seventh common lens 52, the second RGB lens 102, and the second near-infrared lens 112 are made of heavy flint glass with a refractive index n. d With the dispersion coefficient υ d Satisfy: 1.8 < n d <2.0, and 15 <υ d <30. The third RGB lens 103 uses light crown glass with a refractive index n. d With the dispersion coefficient υ d Satisfy: 1.4 < n d <1.6, and 60 <υ d <75. The third near-infrared lens 113 is made of crown glass with a refractive index n. d With the dispersion coefficient υ d Satisfy: 1.6 < n d <1.8, and 50 <υ d <65. The first beam splitter 6, the second beam splitter 7, and the third beam splitter 8 are made of H-K9L glass or quartz glass.

[0048] In this embodiment, heavy lanthanum flint glass can introduce low dispersion while possessing a high refractive index, enabling it to handle most of the system's optical power without increasing the chromatic aberration burden. Heavy flint glass has medium-high refractive index and low Abbe number characteristics. It is the preferred material for the negative lens in the technical solution of this embodiment. The strong dispersion effect of heavy lanthanum flint glass can counteract the axial chromatic aberration of the light crown glass positive lens. Light crown glass is characterized by low refractive index and high Abbe number. The high Abbe number of light crown glass makes its dispersion effect weak. When used alone, it can reduce the axial chromatic aberration of the system. The low refractive index characteristic can reduce the incident angle of light on the lens surface and suppress the generation of higher-order spherical aberration and coma. The first common cemented lens group 4 adopts a cemented form with the heavy flint glass negative group in front and the heavy lanthanum flint glass positive group behind, which can correct axial chromatic aberration and suppress higher-order spherical aberration while handling most of the system's optical power. The second common cemented lens group 5 employs a cemented configuration with the heavy lanthanum flint glass negative group in front and the heavy flint glass positive group behind, and is positioned close to the aperture stop. This effectively corrects the second-order spectral chromatic aberration of the system and increases the relative aperture of the system. The RGB cemented lens 1012 and the near-infrared cemented lens 1112, also employing a cemented configuration with the heavy lanthanum flint positive group in front and the heavy flint negative group behind, effectively correct residual chromatic aberration and spherical aberration of the system, and optimize the system's optical power distribution.

[0049] The specific optical parameters of the common-aperture four-band imaging optical system in Example 1 are shown in Tables 1 and 2 below: Table 1. Specific optical parameters of the R-band, G-band, or B-band of the optical system for co-aperture four-band imaging. Table 2. Specific optical parameters of the near-infrared band of the optical system for common-aperture four-band imaging in Example 1. like Figures 2-5 The figure shows the variation of the optical system's transfer function as the half-field-of-view angle increases from 0° to 68.5°. The horizontal axis represents the spatial frequency, with units of line pairs per millimeter (lp / mm); the vertical axis represents the modulation transfer function (MTF) of the optical system. Figure 2 The MTF curve for the B band; Figure 3 The MTF curve for the G spectral band; Figure 4 The MTF curve for the R-band; Figure 5 The MTF curve is shown in the near-infrared spectral band.

[0050] The transfer function (MTF) of an optical system characterizes its imaging capability for objects with different spatial frequencies observed in different fields of view. As shown in the figure, at a spatial frequency of 200 lp / mm and a half-field of view from 0° to 68.5°, the common-aperture four-band imaging optical system provided in Embodiment 1 of this application exhibits an average MTF better than 0.2 in the R, G, B, and near-infrared bands, indicating good imaging quality. At a spatial frequency of 200 lp / mm, the average MTF values ​​for each band are all better than 0.2, demonstrating that the system maintains good imaging contrast and detail resolution even at high resolution. While the MTF curve decreases slightly from 0° to 68.5° in the half-field of view, it remains generally stable, indicating that the system maintains good image quality consistency even under ultra-wide-angle conditions. In most fields of view, the MTF curves in the T and R directions essentially overlap, indicating good astigmatism control and no significant directional differences in imaging.

[0051] The technical specifications of the optical system for co-aperture four-band imaging in Embodiment 1 of this application are shown in Table 3: As can be seen from the data in Table 3, the common-aperture four-band imaging optical system of this application embodiment simultaneously covers four spectral bands: visible light true color (0.45-0.67μm) and near-infrared (0.7-0.9μm), laying the spectral foundation for all-weather imaging. The optical system employs an ultra-short focal length of 3.6mm, which is an optical prerequisite for achieving an ultra-wide-angle field of view exceeding 120°. Combined with a relative aperture of 1:3.5, it balances system complexity and size while ensuring sufficient light throughput to support low-light, especially near-infrared, imaging.

[0052] The technical solution of this application embodiment utilizes a front-end shared unit: a four-band shared lens group unit with seven lenses, using a front-negative and rear-positive configuration as the sole entry point, to perform ultra-wide-angle collection, convergence, and primary aberration correction of light from all four spectral bands. The beam-splitting lens group unit is equipped with three beam-splitting prisms, and a rear-end parallel imaging lens group unit, precisely and purely separating the composite white light into four independent beams—R, G, B, and near-infrared—accurately and purely according to wavelength in a non-parallel optical path, i.e., a converging optical path. Each spectral band has a dedicated imaging lens group, which can perform optimized aberration correction and image plane shaping for a specific wavelength range of that spectral band. In particular, the final element of the near-infrared spectral band lens group uses an aspherical surface, effectively correcting higher-order aberrations. This ensures that each channel achieves high resolution across the entire field of view. Synchronous exposure by four detectors achieves strict temporal and spatial synchronization and high-precision registration of the four spectral band image information, enabling all-day monitoring.

[0053] Example 2: This application provides an optical system for four-band imaging with a common aperture. The optical system includes, along the optical axis, a four-band common mirror group unit, an aperture stop, a beam splitter group unit, an imaging mirror group unit, and a focal plane detector unit.

[0054] The structure, function, and material selection of the four-band shared mirror unit are exactly the same as in Example 1, and will not be repeated here.

[0055] The main difference between Example 2 and Example 1 lies in the structure of the beam splitter unit. For example... Figure 6 As shown, the beam splitter unit is located on the image side of the third aperture, including a first beam splitter 6 and a second beam splitter 7. In embodiment 2, the first beam splitter 6 is an internal reflection right-angle prism.

[0056] An internal reflection right-angle prism is positioned after the third aperture stop. Its main function is to fold the optical axis of the beam converged by the shared mirror group by 90°. The internal reflection right-angle prism is key to achieving a compact optical system, significantly reducing the axial dimensions of the system and making the overall structure flatter, facilitating integration on space-constrained platforms. A second beam splitter prism 7 is positioned after the internal reflection right-angle prism and receives the folded beam. The second beam splitter prism 7 separates the incident beam into two beams: a reflected beam in the RGB spectrum and a transmitted beam in the near-infrared spectrum. This scheme, where the second beam splitter prism 7 separates visible and near-infrared light in a single beam split, simplifies the beam splitting process.

[0057] In the technical solution of this application embodiment, due to the different structures of the beam splitter group units in the beam splitting scheme, the setting of the imaging lens group units is also adjusted accordingly, including two imaging lens groups: an RGB spectrum imaging lens group 10 and a near-infrared spectrum imaging lens group 11, which respectively receive the RGB spectrum beam and the near-infrared spectrum beam split by the second beam splitter 7.

[0058] An RGB spectral imaging mirror group 10 is used to receive and process the RGB composite beam reflected by the second beam splitter 7. This mirror group performs unified aberration correction and imaging on the R, G, and B spectral bands. A near-infrared spectral imaging mirror group 11 is used to receive and process the near-infrared beam transmitted by the second beam splitter 7.

[0059] In the technical solution of this application embodiment, the optical structure and function of each lens of the RGB spectral imaging lens group 10 are completely the same as the generalized design of the RGB spectral imaging lens group 10 in Embodiment 1. From the beam incident side to the image side, it includes, in sequence: a first RGB lens 101, a second RGB lens 102, a third RGB lens 103, and a fourth RGB lens 104. The first RGB lens 101 and the second RGB lens 102 are cemented together to form an RGB cemented lens 1012. The optical power of each lens is allocated as positive-negative-positive-positive to achieve compact and efficient visible light band aberration correction and accurate color reproduction.

[0060] In the technical solution of this application embodiment, the design of the near-infrared spectral imaging lens group 11 is consistent with that of the near-infrared spectral imaging lens group 11 in Embodiment 1, reflecting the versatility and optimality of the technical solution of this application embodiment. Specifically, from the light incident side to the image side, it includes a first near-infrared lens 111, a second near-infrared lens 112, a third near-infrared lens 113, and a fourth near-infrared lens 114 in sequence; wherein the first near-infrared lens 111 and the second near-infrared lens 112 are cemented together to form a near-infrared cemented lens 1112; the optical power distribution is positive-negative-positive-positive; and the image surface of the fourth near-infrared lens 114 is aspherical. The introduction of the aspherical surface, the sag equation and coefficients are the same as in Embodiment 1, which accurately corrects the high-level residual aberrations unique to the near-infrared band, ensuring high-resolution thermal imaging in the entire field of view. The division of labor of each lens, such as cementation correction of chromatic aberration, independent lens correction of monochromatic aberration, and fine correction of the aspherical surface of the last element, is the same as in Embodiment 1, and will not be described in detail here.

[0061] Similarly, the focal plane detector unit in this embodiment is also adjusted accordingly, including two detectors: an RGB spectral band detector 14, which is set at the image plane position of the RGB spectral band imaging lens group 10 and is used to receive true-color image information; and a near-infrared spectral band detector 15, which is set at the image plane position of the near-infrared spectral band imaging lens group 11 and is used to receive near-infrared image information.

[0062] In this embodiment, the material selection scheme for each lens in the four-band shared lens group unit, the RGB band imaging lens group 10, and the near-infrared band imaging lens group 11 is exactly the same as in Embodiment 1, to ensure excellent image quality in each band. The internal reflection right-angle prism and the second beam splitter prism 7 can be made of H-K9L glass or quartz glass.

[0063] The specific optical parameters of the common-aperture four-band imaging optical system in Example 2 are shown in Tables 4 and 5 below: Table 4. Specific optical parameters of the R-band, G-band, or B-band of the optical system for co-aperture four-band imaging. Table 5. Specific optical parameters of the near-infrared band of the optical system for common-aperture four-band imaging in Example 2. like Figure 7 , Figure 8 The figure shows the variation of the optical system's transfer function as the half-field-of-view angle increases from 0° to 68.5°. The horizontal axis represents the spatial frequency, with units of line pairs per millimeter (lp / mm); the vertical axis represents the modulation transfer function (MTF) of the optical system. Figure 7 The MTF curve for the RGB spectrum; Figure 8 The MTF curve is shown in the near-infrared spectral band.

[0064] The transfer function (MTF) of an optical system characterizes its imaging capability for objects with different spatial frequencies observed in different fields of view. As shown in the figure, at a spatial frequency of 200 lp / mm, with a half-field of view from 0° to 68.5°, the common-aperture four-band imaging optical system provided in Embodiment 2 of this application exhibits an average MTF better than 0.2 in both the RGB and near-infrared bands, indicating good imaging quality. At a spatial frequency of 200 lp / mm, the average MTF values ​​for each band are all better than 0.2, demonstrating that the system maintains good imaging contrast and detail resolution even at high resolution. While the MTF curve decreases slightly from 0° to 68.5° within the half-field of view, it remains generally stable, indicating that the system maintains good image quality consistency even under ultra-wide-angle conditions. In most fields of view, the MTF curves in the T and R directions essentially overlap, indicating good astigmatism control and no significant directional differences in imaging.

[0065] The technical specifications of the optical system for co-aperture four-band imaging in Embodiment 2 of this application are shown in Table 6: As can be seen from the data in Table 6, the common-aperture four-band imaging optical system of this application embodiment simultaneously covers four spectral bands: visible light true color (0.45-0.67μm) and near-infrared (0.7-0.9μm), laying the spectral foundation for all-weather imaging. The optical system employs an ultra-short focal length of 3.6mm, which is an optical prerequisite for achieving an ultra-wide-angle field of view exceeding 120°. Combined with a relative aperture of 1:3.5, it balances system complexity and size while ensuring sufficient light throughput to support low-light, especially near-infrared, imaging.

[0066] The detector parameters are approximately 26 megapixels, indicating that the optical system aims for ultra-high resolution detail acquisition. The 2.5μm pixel size is typical of current high-end, miniaturized industrial cameras, demonstrating that the technical solution of this application employs advanced sensor technology. The instantaneous field of view is greater than 60°×60°: i.e., the total field of view is >120°, indicating that in a wide scene covered by the optical system exceeding 120°, any 60°×60° local area possesses 26 megapixel detail resolution. The data proves that the optical system of this application's technical solution simultaneously possesses the ability to see both wide and clear images. The technical solution of this application successfully integrates key technical features such as ultra-wide angle, high resolution, four-band common aperture, and all-weather operation, resolving the inherent contradictions of these performance indicators in traditional solutions, marking a high-performance, engineered, compact multispectral imaging solution.

[0067] This application also provides a preferred technical solution, such as... Figure 9 and Figure 10 As shown, by stitching together the optical systems of the three common-aperture four-band imaging technologies in this application, it is possible to acquire four-band all-weather image information within a spatial range of 360° horizontally and 120° vertically.

[0068] Finally, it should be noted that 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 systems or apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and relevant parts can be referred to the method section.

[0069] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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. Such 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 this application.

Claims

1. An optical system for four-band imaging with a common aperture, characterized in that, include: The four-band shared mirror group unit, aperture group, beam splitter group unit, imaging mirror group unit and focal plane detector unit are arranged sequentially along the optical axis; The four-band shared mirror unit is used to converge the incident beam with a common aperture. From the object side to the image side, the lens group consists of a front negative lens group and a rear positive lens group. The front negative lens group includes at least one single lens with negative power. The rear positive lens group includes at least one cemented lens, and each cemented lens is formed by cementing a negative power lens and a positive power lens together. The aperture group is used to define the light-transmitting aperture of the optical system and adjust the aberration distribution of the optical system. The beam splitter unit, used to split a light beam, includes at least two beam splitters. The imaging lens group unit is disposed on each beam splitting optical path of the beam splitter group unit; The focal plane detector unit is positioned at the image plane of the imaging lens unit.

2. The optical system according to claim 1, characterized in that, The front negative lens group includes: a first common lens, a second common lens, and a third common lens; The rear positive lens group includes: a first common cemented lens group and a second common cemented lens group; The first common cemented lens group is cemented together by a fourth common lens with negative optical power and a fifth common lens with positive optical power; The second common cemented lens group is cemented together by a sixth common lens with negative optical power and a seventh common lens with positive optical power.

3. The optical system according to claim 1 or 2, characterized in that, In the first common lens, the second common lens, and the third common lens, the centers of curvature of the two optical surfaces of each single lens are located on the same side of the aperture group.

4. The optical system according to claim 1, characterized in that, The near-infrared imaging lens group includes, from the light incident side to the image side, a first near-infrared lens, a second near-infrared lens, a third near-infrared lens, and a fourth near-infrared lens. The first near-infrared lens is cemented to the second near-infrared lens; The first near-infrared lens, the third near-infrared lens, and the fourth near-infrared lens have positive optical power, and the second near-infrared lens has negative optical power; The image plane of the fourth near-infrared lens is aspherical.

5. The optical system according to claim 1, characterized in that, The beam splitter unit includes: a first beam splitter, a second beam splitter, and a third beam splitter arranged sequentially. The first beam splitter is used to split the incident beam into two beams. The second and third beam splitters are used to further split the two beams to obtain beams in the R, G, B and near-infrared bands, respectively.

6. The optical system according to claim 5, characterized in that, The imaging lens group includes: an independent R-band imaging lens group, a G-band imaging lens group, a B-band imaging lens group, and a near-infrared imaging lens group.

7. The optical system according to claim 6, characterized in that, The focal plane detector unit includes an R-band detector, a G-band detector, a B-band detector, and a near-infrared detector, which are respectively disposed at the image plane positions of the R-band imaging mirror group, the G-band imaging mirror group, the B-band imaging mirror group, and the near-infrared imaging mirror group.

8. The optical system according to claim 1, characterized in that, The beam splitter unit includes: a first beam splitter and a second beam splitter; The first beam splitter is used to fold and compress the axial dimension of the optical axis. The second beam splitter is used to separate the incident beam into an RGB spectral beam and a near-infrared spectral beam.

9. The optical system according to claim 8, characterized in that, The imaging lens group includes an RGB spectral band imaging lens group and a near-infrared spectral band imaging lens group, which respectively receive the RGB spectral band beam and the near-infrared spectral band beam split by the second beam splitter.

10. The optical system according to claim 9, characterized in that, The focal plane detector unit includes an RGB spectral band detector and a near-infrared spectral band detector, which are respectively disposed at the image plane positions of the RGB spectral band imaging lens group and the near-infrared spectral band imaging lens group.

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