CN110631701A - Converging Light Split Aperture Multispectral Imaging Optical System - Google Patents

Abstract

In order to solve the problem that the existing sub-aperture spectral imaging optical system has a large volume and a small field of view, the present invention proposes a converging light sub-aperture multi-spectral imaging optical system, including the front group imaging objective lens and lens array; the front group imaging objective lens It is used to compress the light beam, form a converging light beam, and eliminate field curvature and chromatic aberration within the spectral range required by the design; the lens array is located in the converging light beam, including N lenses, and N is an integer greater than or equal to 2; N lenses are close to the front imaging objective lens The mirrors are coplanar and vertical to the optical axis of the front group imaging objective lens; N lenses are coated with filter films with different spectral bands to form N spectral splitting modules; the distance between adjacent spectral splitting modules ensures that they are on the detector The images formed do not interfere with each other; the imaging quality of the N spectral spectroscopic modules is close to the diffraction limit. The invention omits the eyepiece, compresses infinitely distant parallel light into a telecentric converging light beam by using the front group imaging objective lens, reduces the volume of the lens array, and the volume of the overall optical system is small.

Description

Converging Light Split Aperture Multispectral Imaging Optical System

technical field

The invention belongs to the technical field of snapshot multispectral imaging, and relates to a converging light sub-aperture multispectral imaging optical system.

Background technique

Spectral imaging technology is a high-tech fusion of optics, spectroscopy, electronic technology, computer technology and precision machinery that emerged in the 1980s. Because it can obtain rich information on the space and spectrum of the measured target, it has important application value in aerospace remote sensing, reconnaissance mapping, environmental monitoring, resource surveying, etc.

Spectral imaging remote sensing integrates the traditional image dimension and spectral dimension information. While acquiring the target space image, the continuous spectral information of the target is obtained, so that different targets can be identified according to different spectral characteristics. In the spectral image, each pixel or group of pixels of each object contains a unique continuous light (wave) spectrum, and it is this light (wave) spectrum that can be used as an indicator to identify this object after atmospheric correction. Characteristic parameters can quantitatively describe when, where, what attributes, and what changes have taken place in the observation target, so it has attracted more and more attention from various countries.

At present, spectral imaging technologies mainly include temporal pushbroom, spatial pushbroom and snapshot without pushbroom. The snapshot spectral imaging technology is to simultaneously acquire the two-dimensional spatial information and one-dimensional spectral information of the target within the time when the detector collects one frame of image. As a research hotspot, snapshot spectral imaging technologies of various principles emerge in an endless stream.

Due to the different principles of snapshot spectral imaging technologies, the optical systems used in them also have different structural types according to different principles. For the snapshot spectral imaging technology based on the principle of aperture multiplexing, there are currently two types of optical systems:

One is to directly form a lens array with multiple lenses. There are two types of detectors connected to the rear end of the lens array. One is to connect a large area array detector. The disadvantage of this structure is that the lens is limited by the target surface of the detector. Size, under the condition of a certain focal length, its relative aperture can only be made very small; the other is that each lens in the lens array is connected to a detector, this structure forms a camera array, the overall volume is large, and each camera The synchronization and image matching technology between them are very complicated.

Another type of optical system is shown in Figure 1, which consists of a simple series connection of a telescopic system and a lens array. The light beam is imaged onto the detector 105; since the telescopic system is composed of the front imaging objective lens 101 and the front imaging eyepiece 102, the structure is complex, the field of view is small, and the entire optical system is large in size, so there are certain requirements for the volume applications are limited.

Contents of the invention

In order to solve the technical problems of the existing sub-aperture spectral imaging optical system with large volume and small viewing angle, the present invention proposes a converging light sub-aperture multi-spectral imaging optical system.

Technical solution of the present invention is:

The converging light sub-aperture multi-spectral imaging optical system is special in that it includes the front group imaging objective lens and lens array;

The imaging objective lens of the front group is used to compress the light beam, form a converging light beam, and eliminate field curvature and chromatic aberration within the spectrum range required by the design;

The lens array is located in the converging light beam and is the aperture stop of the overall optical system;

The lens array includes independent N lenses, N is an integer greater than or equal to 2; the N lenses are coplanar near the mirror surfaces of the front group imaging objective lens, and are perpendicular to the optical axis of the front group imaging objective lens; the N lenses The filter film is coated on the lens, and the filter film spectrum on each lens is different, forming N spectrum splitting modules;

There is a sufficient distance between two adjacent spectrum splitting modules to ensure that the images formed on the detector do not interfere with each other;

The imaging qualities of the N spectrum splitting modules are all close to the diffraction limit, where close to the diffraction limit means that the MTF of the spectrum splitting modules is not lower than 95% of the MTF diffraction limit of the overall optical system.

Furthermore, the imaging objective lens of the front group is integrated with the lens array to form an imaging objective lens.

Further, the N spectrum splitting modules are evenly distributed.

Further, the N lenses have the same structure.

Further, the materials of the N lenses are the same.

Further, the imaging objective lens of the front group includes a first imaging lens, a second imaging lens, a third imaging lens and a fourth imaging lens arranged in sequence along the same optical axis; the first imaging lens and the second imaging lens form a doublet lens .

Further, the imaging objective lens of the front group also includes a protective glass arranged at the front end of the first imaging lens.

Further, the first imaging lens, the third imaging lens and the lens array are all made of ZK11 material, and the second imaging lens and the fourth imaging lens are all made of ZF3 material.

Further, among the N spectral light-splitting modules, one of the spectral light-splitting modules is coaxial with the imaging objective lens of the front group, and is located at the center of the meridian plane and the lone vector plane of the optical system, and the remaining N-1 spectral light-splitting modules are all relative to the The front group imaging objectives have different off-axis.

Further, the filter film is a narrow bandpass filter film, which is plated by Fabry-Perot interference principle.

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

1. The optical system of the present invention combines the lens array with the front group imaging objective lens, realizes aperture multiplexing, realizes snapshot type spectral imaging, and can image moving target spectrum; Compared with the structure of existing telescope+lens array, the present invention saves The eyepiece in the telephoto system is removed, and the front group imaging objective lens and the lens array are integrated to realize the imaging function, which reduces the volume of the optical system; the present invention uses the front group imaging objective lens to compress infinite parallel light into telecentric convergence The light beam ensures that the lens array has a relatively large relative aperture, and at the same time reduces the volume of the lens array, thereby reducing the volume of the overall device.

2. Since the lens array of the present invention directly forms an image in the converging beam of the imaging objective lens of the front group, it has the advantage of a large field of view.

3. The N lenses of the lens array of the present invention have the same material and structure, which reduces the difficulty of processing and assembly; if the spectrum needs to be changed, only one of the N lenses needs to be replaced, and the overall system has a strong Flexibility.

4. The present invention directly coats the filter film on the lens of the lens array, which eliminates the problem of matching precision between the lens and the filter, and eliminates the structure of fixing the filter, and the overall precision is higher.

5. The optical system of the present invention cooperates with ordinary detectors to achieve spectral imaging of the target within the time it takes for the detector to collect one frame of image, and there is no special requirement for the stability of the carrying platform.

6. The present invention can select a suitable spectral segment according to different application occasions of the spectral camera. If the spectral segment needs to be replaced, only the lens in the lens array needs to be replaced, and these lenses are installed and fixed separately, so the replacement is very convenient.

7. Since the mirror surface of the lens array close to the front group imaging objective acts as the aperture stop of the overall optical system, the light rays of all fields of view are imaged simultaneously through N lenses, so the image formed by N lenses is the same field of view, ensuring The consistency of image spatial positions of different spectral bands is ensured, and the feature images can be directly fused without complicated image processing.

8. In the optical system of the present invention, only two common materials are used to make the lens, the cost is low, and the engineering realization is good.

Description of drawings

FIG. 1 is a schematic diagram of the principle of an existing sub-aperture spectral imaging optical system.

Fig. 2 is a schematic diagram of the optical system of the present invention.

Fig. 3 is a schematic structural diagram of an embodiment of the optical system of the present invention.

Fig. 4 is a distribution diagram of nine lenses in the lens array in the embodiment of the optical system of the present invention.

Fig. 5 shows the imaging quality of intermediate lenses in the lens array in the embodiment of the optical system of the present invention.

Fig. 6 shows the imaging quality of the edge lens in the lens array in the embodiment of the optical system of the present invention.

Fig. 7 is an imaging spot diagram of the peripheral lens in the lens array in the embodiment of the optical system of the present invention.

Explanation of reference signs:

101-front imaging objective lens; 102-front imaging eyepiece; 103-lens; 104-filter; 105-detector;

201-protective glass; 202-first imaging lens; 203-second imaging lens; 204-third imaging lens; 205-fourth imaging lens, 206-lens array, 207-aperture stop, 208-detector, 209 - Front group imaging objective lens.

Detailed ways

Below in conjunction with accompanying drawing, the present invention will be further described.

Referring to Fig. 2 and Fig. 3, the optical system provided by the embodiment of the present invention includes setting a front group imaging objective lens 209 and a lens array 206;

The front group imaging objective lens 209 is mainly used to compress parallel light beams and form converging light beams to ensure that the lens array 206 has a larger relative aperture, while reducing the volume of the lens array 206; the front group imaging objective lens 209 can also eliminate the 400nm-1000nm spectral band Chromatic aberration within the range; in this embodiment, the front group imaging objective lens 209 includes protective glass 201, first imaging lens 202, second imaging lens 203, third imaging lens 204 and fourth imaging lens 205 arranged in sequence along the same optical axis , wherein the first imaging lens 202 and the second imaging lens 203 form a doublet lens;

In order to utilize the target surface of detector 208 as much as possible, lens array 206 is made of nine independent lenses (in other embodiments, lens array 6 also can be made of four or other numbers of lenses); The material and structure are the same, and the corresponding fields of view are exactly the same, so as to reduce the difficulty of processing and assembly; the nine lenses are coated with filter films, and the filter films on different lenses have different spectral bands, forming nine spectrum splitting modules, nine The incident surfaces of each spectrum splitting module serve as the aperture stop 207 of the entire optical system, thereby forming nine identical images of the field of view; specifically, the filter films plated on each lens are narrow bandpass filter films, each The filter films are plated on the principle of Fabry-Perot interference, which combines spectral and spatial light splitting;

Among the nine spectral light-splitting modules, one spectral light-splitting module is located on the main optical axis and is coaxial with the front group imaging objective lens, and is located at the center of the meridian plane and the lone vector plane of the front group imaging objective optical system. The optical axis has off-axis at different positions, and the amount of off-axis mainly depends on the size of the target surface of the detector 208. If the target surface of the detector 208 is large, the amount of off-axis will be large; if the target surface of the detector 208 is small, the amount of off-axis will be small; In this embodiment, the eight spectrum splitting modules have two kinds of off-axis parameters, which are 6 mm and 8.5 mm respectively, and their specific positions and off-axis values are shown in Fig. 4 .

The imaging quality of the nine spectral spectroscopic modules can reach 0.4 at the MTF (modulation transfer function) of 90lp/mm, which is close to the diffraction limit, so as to ensure that each spectral segment has the same field of view and imaging quality, thereby making the subsequent restoration algorithm simple, as Post data processing brings convenience;

The nine spectral splitting modules correspond to nine imaging channels respectively, and the nine imaging channels can be simultaneously connected to one detector 208 [the detector 208 is not part of the optical system of the present invention, the optical system of the present invention + detector 8 + restoration algorithm can be composed together Spectral imaging on the spectral imager], so that different spectral segments of the same target can be formed at different positions of the detector 208 to realize video multi-spectral imaging; in specific applications, only the lens array 206 needs to be replaced when changing different spectral segments according to actual needs The lens in the corresponding spectrum band is enough.

Since the light of all spectral bands has to enter the optical system through the front group imaging objective lens, and the front group imaging objective lens has better achromatic ability in the range of 400nm-1000nm spectrum band, no matter which nine spectral spectroscopic modules are replaced by The overall optical system can guarantee good imaging quality in the 400nm-1000nm spectral range.

It can be seen from Fig. 5, Fig. 6, and Fig. 7 that although the lenses in the lens array 206 in the optical system of this embodiment are located in different positions and have different aberration characteristics, the imaging modulation transfer function of the middle lens is consistent with the edge The imaging modulation transfer function of the lens is close to the diffraction limit, and the imaging scatter points of the edge lens are all in the diffuse spot, the imaging quality is close to the diffraction limit, and the imaging quality is good.

The imaging range of the optical system in this embodiment is the visible near-infrared spectrum. In other embodiments, the imaging range can be extended to the mid-wave infrared and long-wave infrared spectra by changing the lens material and coating the filter film in the corresponding spectral range. part.

Considering factors such as cost, processing, and achromatic aberration, in the entire optical system, except for the protective glass 201, only two materials are used, among which: the first imaging lens 202, the third imaging lens 204 and the lens array 206 are all made of ZK11 material As a result, both the second imaging lens 203 and the fourth imaging lens 205 are made of ZF3 material.

Claims (10)

1. Converging light sub-aperture multi-spectral imaging optical system, characterized in that: it includes a front group imaging objective lens and a lens array; The imaging objective lens of the front group is used to compress the light beam to form a converging light beam, eliminating field curvature and chromatic aberration within the spectral range required by the design; A lens array is located in said converging light beam, acting as the aperture stop of the overall optical system; The lens array includes independent N lenses, N is an integer greater than or equal to 2; the N lenses are coplanar near the mirror surfaces of the front group imaging objective lens, and are perpendicular to the optical axis of the front group imaging objective lens; the N lenses The filter film is coated on the lens, and the filter film spectrum on each lens is different, forming N spectrum splitting modules; There is a sufficient distance between two adjacent spectrum splitting modules to ensure that the images formed on the detector do not interfere with each other; The imaging qualities of the N spectrum splitting modules are all close to the diffraction limit. 2. The converging light sub-aperture multi-spectral imaging optical system according to claim 1, characterized in that: the front imaging objective lens and the lens array are integrated to form an imaging objective lens. 3. The converging light-splitting aperture multi-spectral imaging optical system according to claim 1, characterized in that: the N spectral splitting modules are evenly distributed. 4. The converging light sub-aperture multi-spectral imaging optical system according to claim 1, 2 or 3, characterized in that: the structures of the N lenses are the same. 5. The converging light sub-aperture multi-spectral imaging optical system according to claim 4, characterized in that: the materials of the N lenses are the same. 6. The converging light sub-aperture multi-spectral imaging optical system according to claim 1, 2 or 3, characterized in that: the front group imaging objective lens comprises a first imaging lens and a second imaging lens arranged in sequence along the same optical axis , the third imaging lens and the fourth imaging lens; the first imaging lens and the second imaging lens form a doublet lens. 7. The converging light split aperture multi-spectral imaging optical system according to claim 6, characterized in that: the front imaging objective lens further comprises a protective glass arranged at the front end of the first imaging lens. 8. The converging light split aperture multispectral imaging optical system according to claim 7, characterized in that: the first imaging lens, the third imaging lens and the lens array are all made of ZK11 material, the second imaging lens and the fourth imaging lens The lenses are all made of ZF3 material. 9. The converging light sub-aperture multi-spectral imaging optical system according to claim 1, 2 or 3, characterized in that: the N spectral light-splitting modules, wherein one of the spectral light-splitting modules is coaxial with the front group imaging objective lens, Located at the center of the meridian plane and the lone sagittal plane of the optical system, the remaining N-1 spectral light splitting modules have different off-axis relative to the imaging objective lens of the front group. 10. The converging light sub-aperture multispectral imaging optical system according to claim 1, 2 or 3, characterized in that: the filter film is a narrow bandpass filter film, which is plated on the principle of Fabry-Perot interference .

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