Design method of airborne snapshot type hyperspectral polarization zoom imaging optical system

Abstract

The invention discloses a design method for an airborne snapshot type hyperspectral polarization zoom imaging optical system, and relates to the field of optics, and the method comprises the steps: calculating the focal length of a zoom group, the rear intercept of a front zoom telescoping system, the moving distance of the zoom group, the focal length of a front fixed group, and the focal length of a rear fixed group according to a focal power distribution model of a reverse long-distance zoom objective lens; setting the distance between the zoom group and the diaphragm according to the moving distance of the zoom group; the zoom group is arranged between the front fixed group and the diaphragm in a sliding manner; determining an optimal glass combination according to the total focal power corresponding to each glass combination, and setting the material of each lens according to the optimal glass combination; simulating each combination to obtain the distinguishable minimum wavelength difference of the polarization detector under each combination, calculating the focal length of the imaging mirror according to the minimum wavelength difference, and designing the zoom imaging optical system according to the combination corresponding to the minimum wavelength difference and the focal length of the imaging mirror. According to the invention, the snapshot type hyperspectral polarization imager with both high spatial resolution and high spectral resolution can be designed.

Description

Technical Field

[0001] The present application relates to the field of optical technology, and in particular to a design method for an airborne snapshot hyperspectral polarization zoom imaging optical system. Background Art

[0002] Imaging spectrometers can be used to obtain both the two-dimensional spatial image information of the observed target and the spectral information of each point in the space of the observed target, so as to achieve timing, quantitative, positioning and qualitative analysis of the observed target. After years of development, imaging spectrometers have been widely used in many fields such as modern production, resource development, environmental protection and monitoring, space exploration, aerospace remote sensing, geological analysis, medical testing and diagnosis, and military.

[0003] The imaging spectrometer introduces polarization technology, which can simultaneously obtain the target's polarization, spectrum, intensity and two-dimensional space four-dimensional data hypercube. Compared with traditional remote sensing technology, it obtains richer information and can have a deeper understanding of the target characteristics. Polarization spectral imaging technology is widely used in astronomical observation, cloud and atmospheric aerosol detection, earth environment monitoring, crop yield estimation, geological exploration, and military target detection and identification.

[0004] The existing design methods of airborne snapshot hyperspectral polarization imaging systems cannot design an airborne snapshot hyperspectral polarization imaging system with both high spatial resolution and high spectral resolution. Summary of the invention

[0005] The purpose of this application is to provide a method for designing an airborne snapshot hyperspectral polarization zoom imaging optical system, which can be used to design a snapshot hyperspectral polarization imager that takes into account both high spatial resolution and high spectral resolution.

[0006] To achieve the above objectives, this application provides the following solutions:

[0007] In a first aspect, the present application provides a method for designing an airborne snapshot hyperspectral polarization zoom imaging optical system, which is applied to an airborne snapshot hyperspectral polarization zoom imaging optical system, wherein the airborne snapshot hyperspectral polarization zoom imaging optical system comprises: a front zoom telescope system, a digital micromirror device arranged on an exit light path of the front zoom telescope system, a spectral imaging system arranged on an exit light path of the digital micromirror device, and a polarization detector arranged on an exit light path of the spectral imaging system; the front zoom telescope system comprises a front fixed group, a zoom group, an aperture, and a rear fixed group arranged in sequence from the object side to the image side; the front fixed group, the zoom group, and the rear fixed group are all composed of lenses; the spectral imaging system comprises a relay mirror and an imaging mirror, and the imaging mirror is arranged on the exit light path of the relay mirror; the method for designing an airborne snapshot hyperspectral polarization zoom imaging optical system comprises:

[0008] The focal length of the zoom group and the back intercept of the front zoom telescope system are calculated according to the optical power distribution model of the reverse telephoto zoom objective lens, and the zoom group is set according to the focal length of the zoom group, and the distance between the rear fixed group and the digital micromirror device is determined as the back intercept of the front zoom telescope system;

[0009] Calculate the moving distance of the zoom group and the focal length of the front fixed group when zooming according to the zoom group focal length; set the distance between the zoom group and the diaphragm to be greater than or equal to the moving distance of the zoom group when zooming; set the zoom group between the front fixed group and the diaphragm in a sliding manner to achieve zooming; set the front fixed group according to the focal length of the front fixed group;

[0010] Calculating the focal length of the rear fixed group according to the distance between the zoom group and the rear fixed group and the ratio of the back intercept of the front zoom telephoto system to the focal length of the front zoom telephoto system; and setting the rear fixed group according to the focal length of the rear fixed group;

[0011] For any glass combination, the total optical focal length of the front zoom telescope system corresponding to the glass combination at each wavelength is calculated according to the optical focal length of various glass materials in the glass combination at each wavelength; the glass combination includes n lens Type of glass material; n lens is the total number of lenses in the front zoom telephoto system;

[0012] Determine the optimal glass combination according to the total optical power of the front zoom telescope system corresponding to each glass combination at each wavelength, and set the material of each lens in the front fixed group, the variable magnification group and the rear fixed group of the front zoom telescope system according to the optimal glass combination; the glass materials and lenses in the glass combination are set one by one;

[0013] Set the distance between the aperture and the rear fixed group to be less than or equal to a set threshold;

[0014] Simulate each combination in the parameter set to obtain the minimum wavelength difference that the polarization detector can resolve under each combination, and calculate the focal length of the imaging mirror according to the combination corresponding to the minimum wavelength difference that the detector can resolve; the parameter set includes multiple combinations, each combination includes the focal length of the relay mirror and the pixel matching ratio of the digital micromirror device and the polarization detector; the pixel matching ratio of the digital micromirror device and the polarization detector is that one micromirror in the digital micromirror device corresponds to several pixels in the polarization detector;

[0015] According to the combination corresponding to the minimum wavelength difference that can be resolved by the smallest detector and the focal length of the imaging mirror, the focal length of the relay mirror, the focal length of the imaging mirror, and the pixel matching ratio between the digital micromirror device and the polarization detector, a designed airborne snapshot hyperspectral polarization zoom imaging optical system is obtained;

[0016] If the pixel evaluation index of the designed airborne snapshot hyperspectral polarization zoom imaging optical system does not meet the preset requirements, the process returns to the step of calculating the focal length of the zoom group and the back intercept of the front zoom telescope system according to the anti-telephoto zoom objective lens optical focal distribution model, setting the zoom group according to the focal length of the zoom group, and determining the distance between the rear fixed group and the digital micromirror device as the back intercept of the front zoom telescope system.

[0017] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0018] In the design process of the existing airborne snapshot hyperspectral polarization imaging system based on digital micromirror devices, the matching ratio of the digital micromirror device and the detector pixel, as well as the coupling mechanism of the matching ratio of the digital micromirror device and the detector pixel and the spatial resolution and the spectral resolution are ignored. When designing the front zoom telescope system, the influence of the focal length on the spatial resolution of the system is ignored, resulting in the inability to design an airborne snapshot hyperspectral polarization imaging system that takes into account both high spatial resolution and high spectral resolution. The present application provides a design method for an airborne snapshot hyperspectral polarization zoom imaging optical system. In the design process, the present application refers to the matching ratio of the digital micromirror device and the detector pixel, and sets the zoom group in a sliding form between the front fixed group and the aperture so that the spatial resolution is improved by switching the short focus state to the long focus state without changing the spectral resolution. The coupling mechanism of the matching ratio of the digital micromirror device and the detector pixel and the spatial resolution and the spectral resolution is considered, resulting in the final designed airborne snapshot hyperspectral polarization imaging system that takes into account both high spatial resolution and high spectral resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 A schematic structural diagram of an airborne snapshot hyperspectral polarization zoom imaging optical system to which the airborne snapshot hyperspectral polarization zoom imaging optical system design method provided in an embodiment of the present application is applied;

[0021] Figure 2 A general flow chart of a method for designing an airborne snapshot hyperspectral polarization zoom imaging optical system provided in an embodiment of the present application;

[0022] Figure 3 A specific flow chart of a method for designing an airborne snapshot hyperspectral polarization zoom imaging optical system provided in an embodiment of the present application;

[0023] Figure 4 A diagram showing the position of the zoom group in the long focus state and the short focus state;

[0024] Figure 5 A modulation transfer function diagram of the central wavelength in the short-focus state of the airborne snapshot hyperspectral polarization zoom imaging optical system applied by the airborne snapshot hyperspectral polarization zoom imaging optical system design method provided in an embodiment of the present application;

[0025] Figure 6 A modulation transfer function diagram of the central wavelength in the telephoto state of an airborne snapshot hyperspectral polarization zoom imaging optical system applied by the airborne snapshot hyperspectral polarization zoom imaging optical system design method provided in an embodiment of the present application.

[0026] Reference numerals: front zoom telescope system- 100 , digital micromirror device- 200 , spectral imaging system- 300 , polarization detector- 400 , aperture- 103 . DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0028] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0029] The present application provides a method for designing an airborne snapshot hyperspectral polarization zoom imaging optical system, which is applied to an airborne snapshot hyperspectral polarization zoom imaging optical system. Figure 1 The system shown in the figure includes: a front zoom telescope system 100, a digital micromirror device 200 arranged on the outgoing light path of the front zoom telescope system 100, a spectral imaging system 300 arranged on the outgoing light path of the digital micromirror device 200, and a polarization detector 400 arranged on the outgoing light path of the spectral imaging system 300; the front zoom telescope system 100 includes a front fixed group, a zoom group, an aperture 103 and a rear fixed group arranged in sequence from the object side to the image side; the front fixed group, the zoom group and the rear fixed group are all composed of lenses, and the digital micromirror device 200 is arranged on the outgoing light path of the rear fixed group; the spectral imaging system includes a relay mirror and an imaging mirror, and the imaging mirror is arranged on the outgoing light path of the relay mirror; the design method of the airborne snapshot hyperspectral polarization zoom imaging optical system is as shown in FIG. Figure 2As shown, the general idea includes: Step 1: Establish a mathematical model of the front zoom telescope system 100; Step 2: Glass matching to eliminate axial chromatic aberration of the front zoom telescope system 100; Step 3: Select the position of the aperture 103; Step 4: Establish a spectral resolution mathematical model to obtain the design parameters of the spectral imaging system 300; Follow steps 1 to 4 in sequence, and after completion, evaluate the image quality evaluation index of the optical system. If the image quality evaluation index meets the technical requirements, the design of the hyperspectral polarization zoom imaging optical system is completed, and the structural parameters of the optical system are obtained; if it does not meet the technical requirements, return to step 1 and repeat the steps to optimize the design. The method is as follows Figure 3 As shown, specifically including:

[0030] Step 201: Calculate the focal length of the zoom group and the back intercept of the front zoom telescope system according to the reverse telephoto zoom objective lens focal power distribution model, set the zoom group according to the focal length of the zoom group, and determine the distance between the rear fixed group and the digital micromirror device as the back intercept of the front zoom telescope system.

[0031] Step 202: Calculate the moving distance of the zoom group and the focal length of the front fixed group when zooming according to the zoom group focal length; set the distance between the zoom group and the diaphragm 103 to be greater than or equal to the moving distance of the zoom group when zooming; set the zoom group in a sliding form between the front fixed group and the diaphragm 103 to achieve zooming, Figure 4 Part (a) shows the position of the zoom group in the short focal state. Figure 4 The middle (b) part indicates the position of the zoom group in the telephoto state, and Δ indicates the moving distance of the zoom group when zooming; the front fixed group is set according to the focal length of the front fixed group.

[0032] Step 203: Calculate the focal length of the rear fixed group according to the distance between the zoom group and the rear fixed group and the ratio of the back intercept of the front zoom telescope system 100 to the focal length of the front zoom telescope system 100; and set the rear fixed group according to the focal length of the rear fixed group.

[0033] Step 204: For any glass combination, the total optical power of the front zoom telescope system 100 corresponding to the glass combination at each wavelength is calculated according to the optical power of various glass materials in the glass combination at each wavelength; the glass combination includes n lens Type of glass material; n lens is the total number of lenses in the front zoom telephoto system 100.

[0034] Step 205: Determine the optimal glass combination according to the total optical power of the front zoom telescope system 100 at each wavelength corresponding to each glass combination, and set the material of each lens in the front fixed group, the variable power group and the rear fixed group in the front zoom telescope system 100 according to the optimal glass combination; the glass materials and lenses in the glass combination are set one by one.

[0035] Step 206: Setting the distance between the aperture 103 and the rear fixing group to be less than or equal to a set threshold.

[0036] Step 207: Simulate each combination in the parameter set to obtain the minimum wavelength difference that the polarization detector 400 can resolve under each combination, and calculate the focal length of the imaging mirror according to the combination corresponding to the minimum wavelength difference that the detector can resolve; the parameter set includes multiple combinations, each combination includes the focal length of the relay mirror and the pixel matching ratio between the digital micromirror device 200 and the polarization detector 400; the pixel matching ratio between the digital micromirror device 200 and the polarization detector 400 is that one micromirror in the digital micromirror device corresponds to several pixels in the polarization detector.

[0037] Step 208: According to the combination corresponding to the minimum wavelength difference that can be resolved by the smallest detector and the focal length of the imaging mirror, the focal length of the relay mirror, the focal length of the imaging mirror, and the pixel matching ratio between the digital micromirror device 200 and the polarization detector 400 are set to obtain a designed airborne snapshot hyperspectral polarization zoom imaging optical system.

[0038] Step 209: If the pixel evaluation index of the designed airborne snapshot hyperspectral polarization zoom imaging optical system does not meet the preset requirements, return to the step of calculating the focal length of the zoom group and the back intercept of the front zoom telescope system according to the anti-telephoto zoom objective lens optical focal length distribution model, setting the zoom group according to the zoom group focal length, and determining the distance between the rear fixed group and the digital micromirror device as the back intercept of the front zoom telescope system.

[0039] In practical applications, before calculating the focal length of the zoom group and the back intercept of the front zoom telescope system according to the optical power distribution model of the reverse telephoto zoom objective lens, setting the zoom group according to the focal length of the zoom group, and determining the distance between the rear fixed group and the digital micromirror device as the back intercept of the front zoom telescope system, the following steps are also included:

[0040] Step 1001: Selecting a zoom mode of the front zoom telephoto system 100;

[0041] The airborne snapshot hyperspectral polarization zoom imaging optical system designed in the present application belongs to an airborne optical instrument. While switching the focal length, it needs to meet the characteristics of fast switching, high reliability, high precision, simple structure, and compactness. Therefore, as a preference, the present application selects two zoom modes, namely long focus and short focus, when designing the front zoom telescope system 100.

[0042] Step 1002: Select the zoom mode of the front zoom telephoto system 100. After the zoom mode is determined, a suitable zoom mode needs to be selected.

[0043] Preferably, the axial movement type is selected as the zoom mode. Compared with the switching type, it has the characteristics of small cross-sectional area and high imaging quality. Its principle is similar to the optical compensation continuous zoom system. The change of the system focal length is achieved by moving a group, while maintaining good image quality during zooming. When the zoom group moves along the axial direction, the focal length of the entire system changes accordingly.

[0044] In practical applications, after determining the zoom form and zoom mode, the corresponding mathematical model of the front zoom telescope system 100 (Formula (1) to Formula (4)) is established to design the initial structural parameters: Δ represents the moving distance of the zoom group when zooming, and when the airborne snapshot hyperspectral polarization zoom imaging optical system is in the short focus state or the long focus state, the lateral magnification of the zoom group is m respectively. zoom,S and m zoom,L , and they are reciprocals of each other, specifically:

[0045] Preferably, according to the formula or formula Calculate the focal length of the zoom group, where l represents the object distance of the zoom group (which is a preset value), and f zoom Indicates the focal length of the zoom group, m zoom,S represents the lateral magnification of the zoom group when the airborne snapshot hyperspectral polarization zoom imaging optical system is in the short-focus state, m zoom,L It indicates the lateral magnification of the zoom group when the airborne snapshot hyperspectral polarization zoom imaging optical system is in the telephoto state.

[0046] Preferably, according to the formula A = l / f obj,S / L (2) Calculate the back intercept of the front zoom telephoto system.

[0047] Preferably, according to the formula Δ=[(1-m zoom,L ) / m zoom,L -(1-m zoom,S ) / m zoom,S ]×f zoom (3) Calculate the moving distance of the zoom group when zooming, where Δ represents the moving distance of the zoom group when zooming, m zoom,S represents the lateral magnification of the zoom group when the airborne snapshot hyperspectral polarization zoom imaging optical system is in the short-focus state, m zoom,L represents the lateral magnification of the zoom group when the airborne snapshot hyperspectral polarization zoom imaging optical system is in the telephoto state, f zoom Indicates the focal length of the zoom group, m zoom,S and m zoom,L These are preset values.

[0048] Preferably, when the system is in a short-focus position, the distance between the zoom group and the front fixed group is d when the airborne snapshot hyperspectral polarization zoom imaging optical system is in a short-focus state. fz,S , then according to the formula ffront =(1-m zoom,S ) / m zoom,S ×f zoom +d fz,S (4) Calculate the front fixed group focal length, where f front Indicates the focal length of the front fixed group, m zoom,S represents the lateral magnification of the zoom group when the airborne snapshot hyperspectral polarization zoom imaging optical system is in the short focal state, f zoom Indicates the focal length of the zoom group.

[0049] The focal length of the zoom group directly affects the moving distance of the zoom group, and also directly affects the selection of the fixed group focal length. The shorter the zoom group focal length, the shorter the axial moving distance, and the smaller the fixed group focal length. The focal length of the zoom group directly affects the overall dimensions of the entire system. Therefore, if the image quality allows, minimizing the zoom group focal length is an effective way to shorten the lens's overall dimensions.

[0050] In practical applications, the calculation of the focal length of the rear fixed group according to the distance between the zoom group and the rear fixed group and the ratio of the back intercept of the front zoom telescope system 100 to the focal length of the front zoom telescope system 100 specifically includes:

[0051] The front group focal length is calculated according to the back focus of the front zoom telescope system 100 and the focal length ratio of the front zoom telescope system 100 and the distance between the variable power group and the rear fixed group; the front group includes: a front fixed group and a variable power group.

[0052] The rear fixed group focal length is calculated according to the back focus distance of the front zoom telephoto system 100, the focal length ratio of the front zoom telephoto system 100, and the front group focal length.

[0053] Based on the mathematical model of the front zoom telephoto system 100 established above and combined with the long back focus design index, the mathematical model formula (5) of the reverse telephoto optical group is established.

[0054] The front zoom telescope system 100 is connected to the digital micromirror device 200, and the light is reflected at an angle of 24° to enter the spectral imaging system 300. When designing the front zoom telescope system 100, it is necessary to have a long back intercept, and the front fixed group and the variable magnification group serve as the front group, and form an anti-telephoto optical group with the rear fixed group.

[0055] Because the ratio of the back focus distance of the front zoom telephoto system 100 to the focal length of the front zoom telephoto system 100 is A=l / f obj,S / L , where l is the front zoom telephoto system 100 back intercept, f obj,S / L is the front zoom telephoto system 100 focal length, is the preset value, then:

[0056]

[0057] In the formula, ffz,S / L is the focal length of the front group, d zp,S / L is the distance between the zoom group and the rear fixed group, f post is the focal length of the rear fixed group, d zp,S Indicates the distance between the zoom group and the rear fixed group in the short focal state, d zp,L Indicates the distance between the zoom group and the rear fixed group in the case of telephoto. According to the formula d zp,S -d zp,L =△ is calculated. According to formula (5), the focal length of the rear fixed group is determined.

[0058] Preferably, the front group focal length is calculated according to the ratio of the back focus of the front zoom telescope system 100 to the focal length of the front zoom telescope system 100 and the distance between the variable magnification group and the rear fixed group, specifically:

[0059] According to the formula Calculate the focal length of the front group, when d zp,S / L When the distance between the zoom group and the rear fixed group is taken into account in the short focal state, the f in A is obj,S / L The front focal length f obtained by taking the front zoom telephoto system 100 focal length into account in the short-focus state fz,S / L The front focal length is in the short focal state. The same is true for the long focal state and will not be described here.

[0060] Preferably, the rear fixed group focal length is calculated according to the rear intercept of the front zoom telephoto system 100, the focal length ratio of the front zoom telephoto system 100, and the front group focal length, specifically:

[0061] According to the formula Calculate the fixed group focal length, where f post is the focal length of the rear fixed group, A represents the ratio of the rear intercept of the front zoom telephoto system 100 to the focal length of the front zoom telephoto system 100, and f fz,S / L is the focal length of the front group, f obj,S / L For the front zoom telephoto system 100 short focal length or long focal length, when the front group focal length f fz,S / L When the front focal length is short focal length, f in A is obj,S / L The front zoom telephoto system is also brought into the short-focus state with a focal length of 100, f obj,S / L The focal length of the front zoom telephoto system 100 in the short focal state is also brought in, and the focal length of the rear fixed group in the short focal state is obtained. The same is true in the long focal state, but the focal length of the rear fixed group in the long focal state is the same as that in the short focal state.

[0062] In practical applications, first, the axial chromatic aberration analysis of the front zoom telescope system 100 is performed: each component of the front zoom telescope system 100 satisfies a differential equation of a component zoom process:

[0063]

[0064] By totally differentiating formula (6) with respect to the refractive index, we can obtain:

[0065]

[0066] In the formula, f′ front Denotes the differential of the front fixed group focal length, m zoom,S / L It represents the lateral magnification of the zoom group when the airborne snapshot hyperspectral polarization zoom imaging optical system is in the short-focus state or the long-focus state, f zoom Indicates the focal length of the zoom group, dm zoom,S Indicates m zoom,S Differentiate, dm zoom,L Indicates m zoom,L Differentiate, m zoom Indicates the horizontal magnification of the zoom group, which can be the horizontal magnification of the zoom group in the short focus state or the long focus state, m post is the lateral magnification of the posterior fixation group, Δf obj,c / f obj is the normalized chromatic aberration coefficient, which is equal to the inverse of the Abbe number and represents the dispersion capability of the mirror group in the system, Δf front,c / f front , Δf zoom,c / f zoom , Δf post,c / f post Similarly, in formula (7), (I) is the axial chromatic aberration within the fixed group and the zoom group, and (II) is the axial chromatic aberration caused by the movement of the zoom group. From formula (7), it can be found that the factors affecting the axial chromatic aberration of the zoom system are the dispersion ability of each lens group, the axial dispersion of the front fixed group, and the magnification of the zoom group. When the optical system is at a short focal length, m zoom,S Generally less than 1, the chromatic aberration between lens groups has little effect, and the dispersion of each component itself has a greater impact on the chromatic aberration of the system. When the optical system is at a telephoto position, m zoom,L Generally greater than 1.

[0067] Secondly, based on the above-mentioned axial chromatic aberration analysis of the front zoom telescope system 100, a glass matching and axial chromatic aberration elimination model of the front zoom telescope system 100 is established, including formula (8) to formula (10):

[0068] The glass material constituting the front zoom telephoto system 100 includes n lens The total optical power of the front zoom telephoto system 100 is expressed as:

[0069]

[0070] Therefore, according to the calculation of the optical focal length of various glass materials in the glass combination at various wavelengths, it is specifically:

[0071] According to the formula Calculate the total optical power of the front zoom telescope system 100 corresponding to the glass combination at each wavelength, where Φ obj (λ) represents the total optical power of the front zoom telephoto system 100 corresponding to the glass combination at wavelength λ, Indicates the central wavelength λ of the i-th glass material in the glass combination c The optical power under i (λ) represents the dispersion rate of the i-th glass material in the glass combination at input wavelength λ, λ c Indicates the central wavelength. If the system wavelength range is 400nm-650nm, then λ c It is 525nm, and the system wavelength range is determined according to the grating working band.

[0072] Determining the optimal glass combination according to the total optical power of the front zoom telescope system 100 at each wavelength corresponding to each glass combination specifically includes:

[0073] For any glass combination, if the total focal length of the front zoom telescope system 100 corresponding to the glass combination at two adjacent wavelengths is equal, that is, Φ obj (λ n -1)-Φ obj (λ n )=0 (9) indicates that the system has no axial chromatic aberration. Since there is no case where the axial chromatic aberration is zero, when designing a broadband optical system, the broadband chromatic aberration L′ is defined as 400,650 Considering the Airy criterion of the optical system, that is, when the wave aberration corresponding to the chromatic aberration of the spectrum lines at both ends of the wide band is less than a quarter wavelength, it can be considered that the optical system forms a perfect image in the wide band, and then it is determined whether the F number of the front zoom telephoto system 100 corresponding to the glass combination satisfies the formula |L′ 400,650 |≤2λ 400 (F / #) 2 +2λ 650 (F / #) 2 (10), if it satisfies, the glass combination is determined to be the optimal glass combination, where |L′ 400,650 | represents wide-band chromatic aberration, λ 400 Indicates the minimum wavelength in a wide band, λ 650 represents the maximum wavelength in a wide band, and F / # represents the F number of the front zoom telephoto system 100.

[0074] In practical applications, due to the special requirements of the detector used for the uniformity of image plane illumination, the existing solutions for improving image plane uniformity have the following disadvantages:

[0075] Each 2×2 units of the polarization detector 400 constitute a superpixel unit, and correspond to 0°, 45°, 90° and 135° transmission polarization directions respectively. The linear polarization degree, polarization angle and other information of the target can be calculated by obtaining the intensity information of the four corresponding polarization directions. If the illumination uniformity at the primary image plane, that is, the digital micromirror device 200, is too poor, it will affect the polarization detector 400's acquisition of the edge field polarization information. Solutions to improve the image plane illumination uniformity include the use of barrel distortion and image telecentricity.

[0076] The use of barrel distortion is beneficial to alleviate the decrease in off-axis image point illumination, thereby improving the uniformity of image plane illumination. However, the introduced aberrations will affect the final imaging quality, increase pixel alignment errors, and affect polarization and spectral measurements.

[0077] When using the image-side telecentric optical path, it is assumed that the brightness of the object plane is uniform, and the beam cross-sectional areas corresponding to the on-axis point and the off-axis point are equal, that is, there is no oblique beam vignetting. At this time, the illumination of the image plane can be improved to a certain extent, and finally the illumination of the entire image plane remains consistent. As the position of the aperture 103 approaches the object focal plane, the image-side half-field angle will decrease, and the uniformity of the image plane illumination will increase. When the aperture 103 is placed at the object focal plane, the optical path is the image-side telecentric optical path, and the illumination of the entire image plane is uniform. The image-side telecentric optical path requires the aperture 103 to be placed at the object focal plane position. At this time, the air gap between the aperture 103 and the rear fixed group is large, which does not meet the requirements of miniaturization of the optical system.

[0078] In order to prevent optical path interference with the subsequent optical system, the front zoom telephoto system 100 requires a long back focus. However, the generally used anti-long-distance image-side telecentric optical path configuration is difficult to achieve the long back focus required by the system designed in this application. If this optical path configuration is adopted, the difficulty of optical design will be increased, and additional aberrations will be generated to affect the imaging quality.

[0079] Since the front zoom telescope system 100 needs to have the characteristics of long back focus, large target surface, low distortion and low chromatic aberration, and high image plane illumination uniformity, the aperture 103 of the present application is placed in front of the fixed group behind the front zoom telescope system 100, and the spacing is controlled within 5 mm. At this time, the spacing is small and does not occupy too much space, which makes it easy to meet the long back focus index, and the primary image plane illumination uniformity is high. Since the field of view angle of the rear group lens is small, it will not have a significant impact on the illumination uniformity, so that the illumination of the upper edge field of view of the polarization detector 400 image plane can be almost consistent with the illumination of the center field of view, so as to meet the needs of polarization detection.

[0080] In practical applications, the spectral imaging system 300 further includes: a prism-grating-prism, wherein the prism-grating-prism is arranged between the imaging mirror and the relay mirror, and the output light of the relay mirror is incident on the imaging mirror through the prism-grating-prism.

[0081] In practical applications, firstly, according to step 4001 to step 4002, the parameters affecting the minimum wavelength difference that can be resolved by the detector are determined:

[0082] Step 4001: Establish the mathematical model formula (11) and formula (12) of the minimum resolution wavelength difference of the detector.

[0083] Assuming that the minimum spectral interval that the instrument can distinguish is Δλ, the distance between these two spectral lines on the image plane is Δx. From the geometric relationship, we can get:

[0084]

[0085] In the formula, f img is the focal length of the imaging mirror, dθ is the angular dispersion, m is the grating diffraction order, d is the grating constant, then the minimum resolution wavelength difference of the detector is:

[0086]

[0087] Where a is the pixel size and dλdl is the grating inverse linear dispersion.

[0088] Step 4002: Establishing a mathematical model of the relationship between the minimum resolution wavelength of the polarization detector 400 and the focal length of the spectral imaging system 300 and the pixel matching ratio between the digital micromirror device 200 and the polarization detector 400 includes formula (13) to formula (15):

[0089] For a transmission spectrometer, there are:

[0090]

[0091] In the formula, f total,S / L Indicates the overall focal length of the system in the short focus S or long focus L state, f rel represents the focal length of the spectral imaging system 300, f obj,S / L Indicates the front zoom telephoto system 100 focal length, when f obj,S / L When the front zoom telephoto system is in the short-focus S state with a focal length of 100, f total,S / L is the overall focal length of the system in the short-focus S state. The same is true for the long-focus state. DMD represents the size of the digital micromirror device 200, w MPA represents the pixel size of the polarization detector 400, and r represents the matching ratio between the digital micromirror device 200 and the polarization detector 400 pixels.

[0092] Combining equation (12) and equation (13), we can get:

[0093]

[0094] Simplified to matrix form:

[0095]

[0096] In the formula, the constant constant f rel,n represents the focal length of the relay lens in the nth spectral imaging system 300, f obj,S / L,n represents the focal length value of the nth front zoom telephoto system 100, r n It represents the pixel matching ratio between the nth digital micromirror device 200 and the polarization detector 400.

[0097] Step 4003: According to formula (13), the focal length of the relay lens in the spectral imaging system 300 and the pixel matching ratio between the digital micromirror device 200 and the polarization detector 400 have an impact on the minimum wavelength difference that the polarization detector 400 can distinguish, so a suitable focal length of the relay lens and the pixel matching ratio between the digital micromirror device 200 and the polarization detector 400 are selected. Specifically, from formula (13), it can be seen that the pixel matching ratio r between the digital micromirror device 200 and the polarization detector 400 and the focal length of the relay lens f rel The difference between the wavelength and the minimum resolution wavelength of the detector is Δλ MPA Inversely proportional, that is, r and f rel The larger the value, the smaller the minimum wavelength difference that the detector can distinguish, that is, the higher the spectral resolution. The selected polarization detector 400 pixels are 3.45um, and the digital micromirror device 200 micromirror size is 7.6um. Generally, the pixel matching ratio is a positive integer between 1 and 5. When the matching ratio is greater than 5, the detector with a resolution of 2448×2048 will be reduced to 408×342, and the spatial resolution is too low, making it difficult to form a high-resolution image of the target object.

[0098] The relay lens entrance pupil diameter is selected as the prism-grating-prism diameter of 16mm. When the relay lens F / # is greater than 5, the energy passing through is too small, and the focal length of the relay lens is 80mm at this time; when the focal length is less than 30mm, the smaller focal length will result in greater distortion and reduced edge illumination.

[0099] In practical applications, the focal length of the imaging mirror is calculated based on the combination corresponding to the smallest detector resolvable minimum wavelength difference. Specifically, according to the formula Calculate the focal length of the imaging mirror.

[0100] In practical applications, the digital micromirror device 200 performs spatial encoding modulation on the primary image plane formed by the front zoom telescope system 100 and then reflects it into the subsequent optical system. It is required to have high reflectivity within the working band and high resolution. Preferably, the digital micromirror device 200 adopts ViALUX's V-9001 spatial light modulator with a resolution of 2560×1600. In the range of 400nm-650nm, the micromirror reflectivity exceeds 90%, which meets the system's high-resolution imaging requirements and reduces light energy loss within the working band.

[0101] Due to the problems of complex optical path structure of amplitude-divided polarization imaging, low spatial resolution of aperture-divided polarization imaging, and difficulty in calibrating polarization information of spatial modulation polarization imaging, it is preferred that the focal plane polarization imaging form, i.e., the focal plane polarization detector, is used to obtain polarization information; preferably, the detector uses the Daheng Image MER-502-79U3M POL visible light polarization industrial camera, and the image plane is composed of multiple super-pixel tiles, in which one super-pixel is formed by a combination of 2×2 single pixels, and the two pixels on its diagonal differ by 90°. When the incident light passes through the MPA and is imaged on the detector, the intensity information of the four polarization transmission axis directions is obtained simultaneously according to the division of the super-pixels, thereby realizing the polarization information solution, and the polarization information of the target array can be obtained in real time, which is suitable for imaging dynamic targets.

[0102] The present application also provides more specific embodiments to explain the above method in detail:

[0103] Step A: The front zoom telephoto system 100 obtains initial structural parameters according to step 1:

[0104] The focal length of the front fixed group is 194.9mm, the focal length of the zoom group is -68.4mm, the focal length of the rear fixed group is 63.8mm, the moving distance of the zoom group is 63.3mm, and the front zoom telephoto system has a rear focus of 100 and 100mm.

[0105] Step B: The front zoom telephoto system 100 obtains the achromatic glass material matching according to step 2:

[0106] The front fixed group adopts a group of double-glued lens structure, using materials HZF39 and HZPK5 combination; the zoom group adopts a group of double-glued lens and two single lens structure, using materials H-LAK5A and ZF6 combination, and H-ZBAF21, H-BAK4; the rear fixed group adopts 5 single lenses and a group of double-glued lens structure, using materials D-ZK2L, ZF6 and H-ZK8 combination, H-LAF10LA, D-FK95, H-ZK6, D-ZLAF61.

[0107] Step C: The front zoom telephoto system 100 obtains the position of the aperture 103 according to step 3:

[0108] The position of the aperture 103 is 2.2 mm in front of the rear fixing group.

[0109] Step D: The spectral imaging system 300 obtains the pixel matching ratio between the digital micromirror device 200 and the polarization detector 400 and the focal length of the spectral imaging system 300 according to step 4:

[0110] The pixel matching ratio between the digital micromirror device 200 and the polarization detector 400 is 2, the focal length of the relay mirror is 66 mm, and the focal length of the imaging mirror is 60 mm.

[0111] Step E: Based on the above steps A to D, a subsystem modular design is performed, and after the design is completed, a snapshot hyperspectral polarization zoom imaging optical system is spliced ​​and recorded according to the pupil connection principle.

[0112] Combination Figure 5 and Figure 6 It shows that the designed snapshot hyperspectral polarization zoom imaging optical system has good imaging quality in short-focus or long-focus state, and the MTF at the Nyquist frequency of 144lp / mm at the central wavelength is higher than 0.2, which is close to the diffraction limit.

[0113] In summary, the technical indicators of the snapshot hyperspectral polarization zoom imaging optical system designed in this application are:

[0114] Short focus state focal length: 36mm, long focus state focal length: 109mm, short focus state field of view: 13.38°, long focus state field of view: 4.44°, working band: 400-650nm, short focus state spatial resolution: RS S =0.75m / pixel@5km, telephoto state spatial resolution: RS L =0.19m / pixel@5km, the spectral resolution in short focus / long focus state is 1nm.

[0115] The beneficial effects of this application are:

[0116] 1. In the design process of existing airborne snapshot hyperspectral polarization imaging systems based on digital micromirror devices, the matching ratio between the micromirror of the digital micromirror device and the detector pixel and the coupling mechanism of spatial resolution and spectral resolution are ignored. This application makes the imaging system suitable for the visible light band by using a prism-grating-prism whose working band is in the visible light band.

[0117] 2. The present application aims to solve the problem that the spatial resolution and spectral resolution of the existing airborne snapshot hyperspectral polarization imaging optical system cannot be improved at the same time, which makes it difficult to quickly discover and finely detect the target. By setting the zoom group in a sliding form between the front fixed group and the aperture, the short-focus-telephoto state can be quickly switched to solve the above problem.

[0118] 3. The airborne snapshot hyperspectral polarization zoom imaging optical system designed by this application is a single optical path, single detector, which can obtain spectral and polarization multi-dimensional images in one shot, and obtain multi-dimensional information of dynamic targets in real time. It can adapt to fast-moving targets, accurately, quickly and in real time to find and lock targets, and realize variable zoom to obtain data cubes of target space, spectrum and polarization information, which is conducive to target detection.

[0119] 4. This application can design a snapshot hyperspectral polarization imager that takes into account both high spatial resolution and high spectral resolution, realizing large-area search for ground targets in the short-focus state and fine imaging of points of interest in the long-focus state.

[0120] 5. This application can realize two-speed zoom of the hyperspectral imager, and achieve optical magnification without changing the target distance, making it more flexible to use; while the spectral resolution does not change, the short-focus state is switched to the long-focus state to improve the spatial resolution and achieve refined identification of the target; the drone can search for ground targets over a large area in the short-focus state, and for points of interest, it can quickly zoom and use the long-focus state to distinguish the ground area.

[0121] 6. The airborne snapshot hyperspectral polarization imaging system designed in this application not only obtains the two-dimensional image information of the target object, but also obtains the spectral information of each object point and the polarization information at each wavelength, which can understand the target more comprehensively, accurately and meticulously.

[0122] 7. Most of the existing designs are integrated designs. The present application adopts a modular design including four modules: a front zoom telescope system, a digital micromirror device, a spectral imaging system, and a polarization detector. This is of great benefit to the later maintainability and upgradeability of the system. The front zoom telescope system and the spectral imaging system are two independently designed subsystems. The optical design can be performed by changing the different parameters of the individual subsystems according to different application indicators, thereby improving design efficiency, improving product maintainability and upgradeability, and reducing costs.

[0123] The technical features of the above embodiments may be arbitrarily combined. To make the description concise, 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.

[0124] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A design method for an airborne snapshot hyperspectral polarization zoom imaging optical system, characterized in that: Applied to an airborne snapshot hyperspectral polarization zoom imaging optical system, the airborne snapshot hyperspectral polarization zoom imaging optical system comprises: a front zoom telescope system, a digital micromirror device arranged on the exit light path of the front zoom telescope system, a spectral imaging system arranged on the exit light path of the digital micromirror device, and a polarization detector arranged on the exit light path of the spectral imaging system; the front zoom telescope system comprises a front fixed group, a zoom group, an aperture and a rear fixed group arranged in sequence from the object side to the image side; the front fixed group, the zoom group and the rear fixed group are all composed of lenses; the spectral imaging system comprises a relay mirror and an imaging mirror, and the imaging mirror is arranged on the exit light path of the relay mirror; the design method of the airborne snapshot hyperspectral polarization zoom imaging optical system comprises: The focal length of the zoom group and the back intercept of the front zoom telescope system are calculated according to the optical power distribution model of the reverse telephoto zoom objective lens, and the zoom group is set according to the focal length of the zoom group, and the distance between the rear fixed group and the digital micromirror device is determined as the back intercept of the front zoom telescope system; Calculate the moving distance of the zoom group and the focal length of the front fixed group when zooming according to the zoom group focal length; set the distance between the zoom group and the diaphragm to be greater than or equal to the moving distance of the zoom group when zooming; set the zoom group between the front fixed group and the diaphragm in a sliding manner to achieve zooming; set the front fixed group according to the focal length of the front fixed group; Calculating the focal length of the rear fixed group according to the distance between the zoom group and the rear fixed group and the ratio of the back intercept of the front zoom telephoto system to the focal length of the front zoom telephoto system; and setting the rear fixed group according to the focal length of the rear fixed group; For any glass combination, the total optical focal length of the front zoom telescope system corresponding to the glass combination at each wavelength is calculated according to the optical focal length of various glass materials in the glass combination at each wavelength; the glass combination includes n lens Type of glass material; n lens is the total number of lenses in the front zoom telephoto system; Determine the optimal glass combination according to the total optical power of the front zoom telescope system corresponding to each glass combination at each wavelength, and set the material of each lens in the front fixed group, the variable magnification group and the rear fixed group of the front zoom telescope system according to the optimal glass combination; the glass materials and lenses in the glass combination are set one by one; Set the distance between the aperture and the rear fixed group to be less than or equal to a set threshold; Simulate each combination in the parameter set to obtain the minimum wavelength difference that the polarization detector can resolve under each combination, and calculate the focal length of the imaging mirror according to the combination corresponding to the minimum wavelength difference that the detector can resolve; the parameter set includes multiple combinations, each combination includes the focal length of the relay mirror and the pixel matching ratio of the digital micromirror device and the polarization detector; the pixel matching ratio of the digital micromirror device and the polarization detector is that one micromirror in the digital micromirror device corresponds to several pixels in the polarization detector; According to the combination corresponding to the minimum wavelength difference that can be resolved by the smallest detector and the focal length of the imaging mirror, the focal length of the relay mirror, the focal length of the imaging mirror, and the pixel matching ratio between the digital micromirror device and the polarization detector, a designed airborne snapshot hyperspectral polarization zoom imaging optical system is obtained; If the pixel evaluation index of the designed airborne snapshot hyperspectral polarization zoom imaging optical system does not meet the preset requirements, the process returns to the step of calculating the focal length of the zoom group and the back intercept of the front zoom telescope system according to the anti-telephoto zoom objective lens optical focal distribution model, setting the zoom group according to the focal length of the zoom group, and determining the distance between the rear fixed group and the digital micromirror device as the back intercept of the front zoom telescope system.

2. The method for designing an airborne snapshot hyperspectral polarization zoom imaging optical system according to claim 1, characterized in that: The focal length of the zoom group is calculated according to the focal power distribution model of the reverse telephoto zoom objective lens, specifically: According to the formula or formula Calculate the focal length of the zoom group, where l represents the object distance of the zoom group, and f zoom Indicates the focal length of the zoom group, m zoom,S represents the lateral magnification of the zoom group when the airborne snapshot hyperspectral polarization zoom imaging optical system is in the short-focus state, m zoom,L It indicates the lateral magnification of the zoom group when the airborne snapshot hyperspectral polarization zoom imaging optical system is in the telephoto state.

3. The method for designing an airborne snapshot hyperspectral polarization zoom imaging optical system according to claim 1, characterized in that: The back intercept of the front zoom telephoto system is calculated according to the focal power distribution model of the reverse telephoto zoom objective lens, specifically: According to the formula A = l / f obj，S / L Calculate the back intercept of the front zoom telephoto system, where l is the back intercept of the front zoom telephoto system, and f obj,S / L is the focal length of the front zoom telephoto system, and A represents the ratio of the back focus distance of the front zoom telephoto system to the focal length of the front zoom telephoto system.

4. The method for designing an airborne snapshot hyperspectral polarization zoom imaging optical system according to claim 1, characterized in that: Calculate the distance the zoom group moves when zooming based on the zoom group focal length, specifically: According to the formula Δ=[(1-m zoom,L ) / m zoom,L -(1-m zoom,S ) / m zoom,S ]×f zoom Calculate the distance the zoom group moves when zooming, where Δ represents the distance the zoom group moves when zooming, m zoom,S represents the lateral magnification of the zoom group when the airborne snapshot hyperspectral polarization zoom imaging optical system is in the short-focus state, m zoom,L represents the lateral magnification of the zoom group when the airborne snapshot hyperspectral polarization zoom imaging optical system is in the telephoto state, f zoom Indicates the focal length of the zoom group.

5. The method for designing an airborne snapshot hyperspectral polarization zoom imaging optical system according to claim 1, characterized in that: Calculate the front fixed group focal length based on the zoom group focal length, specifically: According to the formula f front =(1-m zoom,S ) / m zoom,S ×f zoom +d fz,S Calculate the front fixed group focal length, where f front Indicates the focal length of the front fixed group, m zoom,S It represents the lateral magnification of the zoom group when the airborne snapshot hyperspectral polarization zoom imaging optical system is in the short focal state, d fz,S represents the distance between the zoom group and the front fixed group when the airborne snapshot hyperspectral polarization zoom imaging optical system is in the short focal state, f zoom Indicates the focal length of the zoom group.

6. The method for designing an airborne snapshot hyperspectral polarization zoom imaging optical system according to claim 1, characterized in that: The calculating the focal length of the rear fixed group according to the distance between the zoom group and the rear fixed group and the ratio of the back intercept of the front zoom telescope system to the focal length of the front zoom telescope system specifically includes: Calculate the front group focal length according to the ratio of the front zoom telescope system back intercept to the front zoom telescope system focal length and the distance between the zoom group and the rear fixed group; the front group includes: a front fixed group and a zoom group; The rear fixed group focal length is calculated according to the ratio of the front zoom telephoto system back focus distance to the front zoom telephoto system focal length and the front group focal length.

7. The method for designing an airborne snapshot hyperspectral polarization zoom imaging optical system according to claim 6, characterized in that: The front group focal length is calculated based on the ratio of the front zoom telephoto system back intercept to the front zoom telephoto system focal length and the distance between the zoom group and the rear fixed group: According to the formula Calculate the front focal length, where f fz,S / L is the focal length of the front group, d zp,S / L is the distance between the zoom group and the rear fixed group, and A represents the ratio of the back intercept distance of the front zoom telephoto system to the focal length of the front zoom telephoto system.

8. The method for designing an airborne snapshot hyperspectral polarization zoom imaging optical system according to claim 6, characterized in that: The rear fixed group focal length is calculated according to the rear intercept length of the front zoom telephoto system, the focal length ratio of the front zoom telephoto system, and the front group focal length, specifically: According to the formula Calculate the fixed group focal length, where f post is the focal length of the rear fixed group, A represents the ratio of the front zoom telephoto system back intercept to the front zoom telephoto system focal length, f fz,S / L is the focal length of the front group, f obj,S / L This is the focal length of the front zoom telephoto system.

9. The method for designing an airborne snapshot hyperspectral polarization zoom imaging optical system according to claim 1, characterized in that: The total optical focal length of the front zoom telescope system corresponding to the glass combination at each wavelength is calculated according to the optical focal length of various glass materials in the glass combination at each wavelength, specifically: According to the formula Calculate the total optical power of the front zoom telescope system corresponding to the glass combination at each wavelength, where Φ obj (λ) represents the total optical power of the front zoom telephoto system corresponding to the glass combination at wavelength λ, Indicates the central wavelength λ of the i-th glass material in the glass combination c The optical power under i (λ) represents the dispersion rate of the i-th glass material in the glass combination at wavelength λ.

10. The method for designing an airborne snapshot hyperspectral polarization zoom imaging optical system according to claim 1, characterized in that: The optimal glass combination is determined according to the total optical power of the front zoom telescope system corresponding to each glass combination at each wavelength, specifically including: For any glass combination, if the total optical power of the front zoom telephoto system corresponding to the glass combination at two adjacent wavelengths is equal, it is determined whether the F number of the front zoom telephoto system corresponding to the glass combination satisfies the formula |L′ 400,650 |≤2λ 400 (F / #) 2 +2λ 650 (F / #) 2 , if it satisfies, the glass combination is determined to be the optimal glass combination, where |L′ 400,650 | represents wide-band chromatic aberration, λ 400 Indicates the minimum wavelength in a wide band, λ 650 It indicates the maximum wavelength in a wide band, and F / # indicates the F number of the front zoom telephoto system.

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