CN210268902U

CN210268902U - Compact refraction and reflection type plane grating hyperspectral imager optical system

Info

Publication number: CN210268902U
Application number: CN201921070802.4U
Authority: CN
Inventors: 王欣
Original assignee: Shanghai Institute of Technical Physics of CAS
Current assignee: Shanghai Institute of Technical Physics of CAS
Priority date: 2019-07-10
Filing date: 2019-07-10
Publication date: 2020-04-07
Anticipated expiration: 2029-07-10

Abstract

The patent discloses a compact refraction and reflection formula plane grating high spectral imager optical system, a strip of scenery target assembles through objective and forms images on the slit, assembles back through aspheric surface speculum, plane grating and battery of lens again and images at the area array detector according to the wavelength difference, pushes away along with the platform and sweeps and obtain map unification image. The problem that an optical path is huge when the field of view is large and the high spectral resolution is high is solved; the optical fiber laser imaging device only comprises an aspheric reflector and a lens group, has simple and compact structure, has the characteristics of excellent image quality and small spectral bending and distortion, and is coaxially designed with a large relative aperture, so that the axial size of the instrument is greatly reduced; the plane grating has adjustable reflection angle, is easy to realize the layout of a reflector and a lens group, and reduces the size of the instrument in the width direction; the rear intercept is large, so that the detector is convenient to mount; and the lens groups made of different materials are selected to expand the full spectrum range. Therefore, the device is suitable for occasions requiring miniaturization in the fields of aerospace, industry and the like, and the difficulty in developing instruments is reduced.

Description

Compact refraction and reflection type plane grating hyperspectral imager optical system

Technical Field

The patent relates to a miniaturized imaging instrument with large visual field, high spectral resolution and high spatial resolution, in particular to a high spectral imaging instrument form combining an objective lens and a refraction and reflection type plane grating spectrometer.

Background

The spectrum can reflect the molecular structure information of substances, and plays an important role in the fields of biology, chemistry, medical materials, food industry, geological exploration, aerospace and the like. With the development of scientific technology and the interdigitation, infiltration and fusion of numerous frontier disciplines, a series of new requirements such as wide spectrum, high resolution, miniaturization and the like are put forward on the spectrometer, so that the micro spectrometer is greatly concerned.

Compared with the prism-based spectrometer and the fourier transform-based spectrometer, the grating-based spectrometer has obvious advantages in terms of spectral resolution and spatial resolution, and therefore is widely applied to the field of imaging spectroscopy. Spectrometers can be classified into flat grating spectrometers, concave grating spectrometers and convex grating spectrometers, depending on the grating type. Wherein the former two are produced earliest and applied most widely; convex grating spectrometers have gained favor in recent years in various applications due to their superior imaging quality and relatively compact volume.

The convex grating concentric imaging spectrometer is mostly in an OFFNER form, an optical path is composed of two spherical or non-spherical reflectors and a convex grating, the manufacturing cost of the convex grating is relatively high, and the implementation difficulty in engineering application is relatively high.

The concave grating imaging spectrometer is in a Dyson form, the system can also realize extremely high imaging quality, an incident slit and a detector focal plane of the traditional Dyson imaging system are both arranged on the plane of a single lens, so that the incident slit and the detector are difficult to mount, and the structural form is difficult to arrange.

The plane grating spectrometer adopts a Czerny-Turner form more, and is divided into an M-shaped structure and a cross-shaped structure, a light path uses spherical reflectors with coincident centers of curvature of two surfaces as a collimating mirror and a reflecting mirror respectively, a plane diffraction grating is used as a dispersion element, the cross-shaped structure has higher space utilization rate and is more compact than the M-shaped structure, but the structure has larger size in the layout directions of the two mirror surfaces, the intercept is short after a large relative aperture optical system, and a detector is difficult to layout.

From the development trend of large-field-of-view hyperspectral imagers at home and abroad, most of the commonly used spectrometers are in Czerny-Turner or Dyson form, and the optical systems have a plurality of problems and are mainly reflected in that:

in a Czerny-Turner plane grating spectrometer, the axial distance of an optical path is correspondingly increased in order to separate the relative positions of two reflecting mirrors in the radial direction, so that the appearance volume is larger. Both the cross structure and the M-type structure have light overlapping and crossing, so that the focal plane is too close to the effective light, and particularly, the detector is difficult to arrange due to short rear intercept under the conditions of large field of view and large relative aperture imaging.

An incident slit and a focal plane of a detector of the Dyson concave grating spectrometer are both arranged on a plane of a single lens, so that the detector and the single lens do not interfere with each other, the slit position is close to an image plane of a dispersion system, an aspherical mirror or a meniscus lens is added at the position close to the concave grating to correct aberration generated by the movement of the slit and the image plane, and the slit and the image plane are arranged on different planes by folding the position of the image plane, so that the light path is complex, and the assembly and adjustment difficulty is high. Meanwhile, the concave grating greatly increases the difficulty and cost of grating manufacture compared with the plane grating.

The optical scheme of the light splitting and combining of the catadioptric optical element and the planar grating is applied to a large-field-of-view high-resolution hyperspectral imager system, the spectrometer only comprises an aspheric reflector and a lens group, the structure is simple and compact, the processing difficulty is low, and the spectrometer has the characteristics of excellent image quality, small spectrum bending and distortion; by changing the reflection angle of the plane grating, the layout of the reflector and the lens group is easy to realize, and the appearance of the instrument in the width direction is reduced; the rear intercept is suitable for the distance of various detectors, so that the detectors can be conveniently installed; the combination of different focal ratios of the reflector and the lens group is selected, so that the focal length change with large zoom ratio can be realized, and the optical lens is suitable for various relative aperture light path environments; different materials of the lens group are selected, so that the wide-spectrum imaging range can be expanded and suitable. Therefore, the compact refraction and reflection type plane grating spectrometer solves the problems of complex and huge light path under the conditions of large field of view, wide spectrum and high spectral resolution, and is suitable for the fields of aerospace, industry and the like.

Disclosure of Invention

The application of the catadioptric optical element and the planar grating light splitting provides a novel optical system form for researching a miniaturized high-resolution hyperspectral imager. The technical idea of the patent is to design according to the principle of a push-broom hyperspectral imager, and the catadioptric plane grating spectrometer is composed of a slit 1, an aspheric reflector 2, a plane grating 3, a lens group 4 and an area array detector 5. A strip of an object to be watched is converged and imaged on a slit 1 at a focal plane position through an objective lens, a refraction and reflection plane grating spectrometer is used for carrying out dispersion imaging on the slit 1, imaging on different positions of a plane array detector 5 according to different wavelengths after sequentially reflecting through an aspheric reflector 2, reflecting, dispersing and light splitting through a plane grating 3 and transmitting and converging through a lens group 4, and then, sweeping along with the running direction of an instrument platform to obtain an image with integrated maps. The technical solution of this patent is therefore as follows:

the aspherical mirror 2 according to the patent is a metal or glass mirror, and the surface shape is a 10-order high-order aspherical surface. The plane grating 3 is a reflection diffraction blazed grating, and the reflection level is-1 level. The lens group 4 is a glass spherical lens and consists of three lenses, and materials can be flexibly selected according to spectrum bands.

This patent is owing to combine together catadioptric optical element and plane grating, has obviously promoted the function that the wave band was surveyed under the big visual field condition, and the advantage of system is as follows:

1. the compact refraction and reflection type plane grating hyperspectral imager optical system is simple and compact in structure, only comprises an aspheric reflector and a lens group, and has the advantages of excellent imaging performance, small spectrum bending and small spectrum distortion. Under the conditions that the visual field is larger than 5 degrees and the wave band range is 1-2.5 mu m, the spatial resolution of 0.27mrad and the spectral resolution of 5nm can be realized, the transfer function of each wavelength system is better than 0.6 at the Nyquist frequency of 20lp/mm, the off-axis visual field spectrum bending is less than one pixel, and the spectrum distortion is less than 3 percent.

2. The aspheric surface reflector of the spectrometer is designed coaxially, off-axis aberration does not exist, and the axial overall dimension of the spectrometer is greatly reduced due to the design of the large relative aperture of the reflector; by changing the reflection angle of the plane grating, the layout of the reflector and the lens group is easy to realize, and the appearance of the instrument in the width direction is reduced; the rear intercept is suitable for the distance of various detectors, so that the detectors can be conveniently installed; the combination of different focal ratios of the reflector and the lens group is selected, so that the focal length change with large zoom ratio can be realized, and the optical lens is suitable for various relative aperture light path environments; different materials of the lens group are selected, so that the wide-spectrum imaging range can be expanded and suitable.

3. The compact refraction and reflection type plane grating spectrometer has wide application, and can be applied to various hyperspectral imaging fields of aerospace, industry, biology, chemistry, medical materials, geological exploration and the like.

Drawings

FIG. 1 is a light path diagram of an optical system of a compact refraction and reflection type plane grating hyperspectral imager, (1) a slit, (2) an aspheric reflector, (3) a plane grating, (4) a lens group, and (5) a plane array detector.

Detailed Description

This patent has designed a compact refraction and reflection formula plane grating hyperspectral imager optical system, and main technical indicator is as follows:

1. the aperture of the entrance pupil is 25mm, and the focal length of the optical system is 90 mm;

2. spectral range: 1000-2500nm and the spectral resolution is 5 nm;

3. and (3) full field of view: 5 degrees;

4. the size of the pixels of the area array detector is 25 mu m, and the number of the pixels is 640 x 512;

5. spatial resolution: better than 0.27 mrad;

6. the full field transfer function is better than 0.6 at the Nyquist frequency of 20lp/mm, the spectral distortion is less than 3%, and the spectral curvature is less than one pixel.

The specific design parameters of the optical system are shown in table 1:

TABLE 1 optical System specific design parameters

Claims

1. The utility model provides a compact refraction and reflection formula plane grating hyperspectral imager optical system, includes two parts of objective and refraction and reflection formula plane grating spectrum appearance, its characterized in that:

the refraction and reflection type plane grating spectrometer comprises a slit (1), an aspheric surface reflector (2), a plane grating (3), a lens group (4) and a plane array detector (5);

a strip of an object of view is focused and imaged on a slit (1) at a focal plane position through an objective lens, a refraction and reflection plane grating spectrometer is used for performing dispersion imaging on the slit (1), imaging on different positions of a plane array detector (5) according to different wavelengths after reflection of an aspheric reflector (2), reflection of dispersion light splitting of a plane grating (3) and transmission convergence of a lens group (4) sequentially, and then pushing and scanning along the running direction of an instrument platform to obtain an image with integrated maps.

2. The compact catadioptric planar grating hyperspectral imager optical system of claim 1, wherein: the aspheric surface reflector (2) is a metal or glass reflector, and the surface shape is a 10-order high-order aspheric surface.

3. The compact catadioptric planar grating hyperspectral imager optical system of claim 1, wherein: the plane grating (3) is a reflection diffraction blazed grating, and the reflection level is-1 level.

4. The compact catadioptric planar grating hyperspectral imager optical system of claim 1, wherein: the lens group (4) is a spherical lens and consists of three lenses, and the materials are selected according to the working spectrum of the spectrometer.