CN104359553B - A kind of compact grating dispersion spectrum imager - Google Patents

Abstract

The invention relates to a compact grating dispersion spectrum imager, comprising a front telescopic objective lens system, a slit, a collimation-imaging system, a reflective grating and an area array detector; the front telescopic objective lens system realizes the function of imaging a target ; The slit is the field diaphragm, which limits the imaging range of the target; on the one hand, the collimation-imaging system collimates the outgoing light beam of the target slit image, and also images the parallel light of each wavelength after the dispersion of the reflection grating to the detector target The reflective grating is a dispersive element, which realizes the spectral separation of space objects; the area array detector acquires and records digital information through the photoelectric effect. The invention adopts the method of sharing the collimation and imaging system, which simplifies the structure of the traditional dispersion system.

Description

A Compact Grating Dispersion Spectral Imager

technical field

The invention relates to a compact grating dispersion spectrum imager, which belongs to the technical field of remote sensing.

Background technique

Spectral imaging technology is based on the spectral analysis theory of matter and combines spectral and imaging technologies. During the imaging process, continuous spectral information of dozens or hundreds of bands of ground objects can be obtained with nanoscale spectral resolution. The synchronous acquisition of target spatial information, radiation information, and spectral information forms a three-dimensional data cube. It can directly reflect the geometric image and physical and chemical information of the observed object, realize the comprehensive detection perception and recognition of the target characteristics, greatly expand the target recognition and monitoring capabilities of remote sensing detection technology, and have irreplaceable advantages of other remote sensing technologies. It is used in various fields such as resource exploration, environmental and disaster monitoring, and criminal evidence identification. Compared with traditional remote sensing technology, hyperspectral imaging technology has a wide range of working spectral bands and a large number of spectral bands. This puts forward higher requirements for the hyperspectral imaging optical system, and the general hyperspectral imaging system is divided into two parts: the front telescopic objective lens and the spectral imaging system, and the spectral imaging system is the core of the entire instrument. The way directly affects the optomechanical complexity of the system and the overall volumetric quality. According to different spectral methods, hyperspectral imagers are mainly divided into prism/grating dispersion type, interference imaging type, computational imaging type, etc.

Interferometric spectral imaging technology is to add an interferometer to the optical path. The Sagnac transverse shearing spectral imager shown in Figure 1 obtains spectral information through the Fourier transform relationship between the interference sampling results and spectral characteristics. It has multi-channel, The advantage of high throughput, but generally requires high attitude stability, so there are not many successful examples on airborne platforms.

Computational imaging introduces computing methods into the imaging process. The target information obtained by one exposure can be reconstructed through subsequent data processing to obtain the spatial and spectral information of the target. It mainly includes computed tomography imaging, coded aperture spectral imaging, and light field spectral imaging technologies. However, the acquisition of direct spectral or spatial information that is not the target through computational imaging requires corresponding inversion and reconstruction to calculate the final data cube, which brings great challenges to the design and processing of the instrument, and is susceptible to multiple The interference of these factors is still in the laboratory stage at this stage. However, due to the characteristics of fast spectral detection, no scanning, high throughput and high stability of computational spectroscopy technology, it has attracted more and more attention and is an important development direction of spectral imaging technology.

The prism spectroscopic imaging spectrometer mainly uses different deflection angles due to the difference in refractive index when different wavelengths pass through the prism. In this way, after imaging through the objective lens, the light of each spectral segment converges on different positions of the image plane, realizing spectral separation, as shown in Figure 2(a). Grating light splitting uses the principle of grating diffraction. The diffraction angle corresponding to the maximum value of the diffraction fringes of the same order is related to the wavelength. After the objective lens is imaged on the image plane, the required diffused spectral lines can be obtained, as shown in the figure 2(b). Dispersive spectral imaging technology has been widely used in remote sensing platforms because of its simple principle, no need for other processing, and spectral data can be directly obtained.

For the traditional dispersive hyperspectral imager, the dispersive element needs to work in the collimated optical path. After the target is imaged by the front telescopic objective lens to the slit of the primary image plane, it is first collimated by the collimation system and then split by the dispersive element. The entire optical system is divided into three parts after the imaging system is imaged to the detector target surface. The system is too complicated to reduce the volume and quality, and cannot meet the application requirements of light, small, fast and flexible carrying platforms.

Contents of the invention

The invention solves the problem by overcoming the deficiencies of the prior art, and provides a compact grating dispersive spectral imager, which can greatly reduce the volume and quality of the traditional dispersive spectral imaging system due to the light going back and forth, sharing the collimating mirror and the imaging mirror , the structure is more compact.

The technical solution of the present invention: a compact grating dispersion spectral imager, including a front telescopic objective lens system (1), a slit (2), a collimation-imaging system (3), a reflective grating (4) and an area array The detector (5), each part is fixedly connected through the overall structure of the camera; the front telescopic objective lens system realizes the function of imaging the target, and images the target to the position of the slit; at the same time, in order to achieve pupil matching, the front telescopic objective lens system ( 1) Design the telecentric system of the imaging side; the slit (2) is the field stop, which limits the target imaging range. In order to avoid interference with the position of the final area array detector (5), relative to the collimation-imaging system (3 ) should be set off-axis; the collimation-imaging system (3) is an object-space telecentric system in order to connect with the front telescopic objective lens system (1). On the one hand, it is necessary to image the parallel light of each wavelength after the grating dispersion to the target surface of the area array detector (5); the reflective grating (4) is a dispersion element to realize the spectral separation of the space target; the area array detector (5) passes The photoelectric effect acquires and records digital information; the light beam emitted from the slit (2) is collimated by the collimation-imaging system (3) and then incident on the reflective grating (4), after being reflected and split by the reflective grating (4), the separated The parallel light of each spectral segment returns to the collimation-imaging system (3) again, passes through the collimation-imaging system (3) for the second time and is finally imaged on the area array detector (5), parallel to the slit (2) The direction forms slit images of different spectral bands, and the entire area array detector (5) corresponds to a row of space targets and several spectral channels, and a complete data cube of the target is obtained through the movement of the push-broom platform.

A compact grating dispersion spectral imaging method, the implementation steps are:

(1) The light emitted by the target passes through the front telescopic objective lens system and is imaged on its focal plane to form a target image;

(2) The slit limits the scope of the target image, and only the light in the slit can exit into the collimation-imaging system to obtain the collimation of the collimation-imaging system. Since the slit is set off-axis relative to the collimation-imaging system, Make the collimated parallel beam obliquely incident on the reflective grating, the inclination angle depends on the off-axis distance from the slit, and can be determined according to the actual structural design needs;

(3) The oblique parallel light is incident on the reflective grating, and after being reflected and split by the reflective grating, it is different from the general dispersion spectrum imager directly incident on the independent imaging mirror. At this time, the parallel light of each wavelength returns to the incident collimation-imaging system again;

(4) The collimation-imaging system images the parallel light of each wavelength after the grating dispersion to the area array detector, and the parallel light is separated from the slit position due to its oblique angle;

(5) The area array detector acquires and records the information of the slit image of each wavelength of the target through the photoelectric effect.

Compared with prior art solutions, the advantages of the present invention are:

(1) Adopting a common collimation and imaging system overcomes the shortcomings of bulky and bloated structures caused by the traditional separate use of two sets of lenses to realize the two functions respectively, making the entire spectral imager system more compact and portable. Light and small carrying platform suitable for portable use and rapid development;

(2) The front telescopic objective lens system constitutes the telecentric optical path at the image side, which reduces a series of problems caused by the matching of the rear field lens;

(3) The slit is arranged off-axis relative to the collimation-imaging system, which avoids interference with the position of the image plane.

In a word, the present invention adopts the method of sharing the collimation and imaging system, which simplifies the structure of the traditional dispersion system.

Description of drawings

Fig. 1 is the schematic diagram of this interference type spectral imager of prior art;

Fig. 2 is a schematic diagram of a dispersive spectral imager in the prior art; wherein a is a schematic diagram of a traditional prism dispersive spectral imager, and b is a schematic diagram of a traditional interference dispersive spectral imager;

Fig. 3 is a schematic diagram of the present invention;

Fig. 4 is a structural diagram of the optical system of the present invention;

Fig. 5 is the collimation-imaging system design schematic diagram of the present invention

Fig. 6 is the full-system panchromatic light spot diagram among the present invention;

Fig. 7 is a spot diagram of each wavelength of the whole system in the present invention;

Fig. 8 is an MTF curve diagram of each wavelength of the whole system in the present invention.

detailed description

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings that need to be used in the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For Those of ordinary skill in the art can also obtain other drawings based on these drawings on the premise of not paying creative work.

As shown in Figures 3 and 4, the present invention includes a front telescopic objective lens system 1, a slit 2, a collimation-imaging system 3, a reflective grating 4 and an area array detector 5, and each part is fixedly connected by the overall structure of the camera; The telescopic objective lens system 1 is an improved double-Gaussian system, which realizes the function of imaging the target, and images the target to the position of the slit 2. At the same time, in order to achieve pupil matching, the front telescopic objective lens system 1 should be designed to image far center system; the slit 2 is the field diaphragm, which limits the target imaging range, in order to avoid interference with the position of the final area array detector 5, it should be set off-axis relative to the collimation-imaging system 3; the collimation-imaging system 3 On the one hand, the outgoing beam of the target slit 2 is collimated, and on the other hand, the parallel light of each wavelength after the reflection 4 grating dispersion is imaged to the target surface of the area array detector 5, and at the same time, in order to connect with the front telescopic objective lens system 3, it is An object-space telecentric system; the reflective grating 4 is a dispersive element, which realizes the spectral separation of space objects; the area array detector 5 obtains and records digital information through the photoelectric effect; the beam emitted from the slit 2 passes through the collimation-imaging system 3 After being directly incident on the reflective grating 4, after being reflected and split by the reflective grating 4, the separated parallel light of each spectral segment is returned to the collimation-imaging system 3 again, and finally imaged to the area array through the collimation-imaging system 3 for the second time On the detector 5, slit images of different spectral bands are formed in the direction parallel to the slit. The entire area array detector corresponds to a row of space targets and several spectral channels. Through the movement of the push-broom platform, a complete data cube of the target is obtained.

Table 1 Parameter assignment of optical system

In the present invention, because the slit and the area array detector are on the same side of the collimation-imaging system, in order to avoid interference between the two positions, the slit is set off-axis relative to the collimation-imaging system, resulting in collimated parallel light is the oblique incidence reflective grating, and this oblique angle depends on the off-axis distance from the slit. Obviously, due to the oblique incidence of the parallel beam, it is separated from the beam reflected by the reflective grating, and the light emitted by the slit and the converged light of the final image are also separated, ensuring that there is sufficient position margin between the slit and the area array detector . It can be considered to add a reflector in the optical path to bend the light exiting the slit by 90 degrees to further increase the structural design space margin.

Collimation-imaging system The key component of this solution is both a collimating mirror and an imaging mirror. When designing an optical system, it can be designed as an imaging system. As shown in Figure 5, it is a schematic diagram of the collimation-imaging system design, its collimation-imaging system 3, slit 2 and area array detector 5, in order to ensure that the collimation-imaging system has two functions of collimation and imaging For a good effect, it is necessary to use the slit image 2 position of the primary image plane and all the dispersed target images in the image plane position of the final area array detector 5 as collimation—the field of view of the imaging system 3 when it is designed To investigate, to ensure that the entire area has excellent image quality, the collimation-imaging system collimation and imaging functions can be realized.

In the present invention, the reflective grating is used as the dispersion element of the entire spectral imaging system. In order to avoid aliasing of short-wave high-order diffracted light and long-wave low-order diffracted light, its application range is limited. The negative first-order diffracted light of the grating is selected as the imaging beam, and the spectral range is 460-920nm.

The field of view of the front telephoto objective lens system is 18.32 degrees, the relative aperture is 1/4, and the focal length is 50mm. It adopts an improved double Gauss structure and is a transmission optical system, which can effectively correct spherical aberration, astigmatism, chromatic aberration, etc. Seven aberrations. The collimation-imaging system corresponds to a slit line field of view of 16 mm, a numerical aperture of 0.125, and a slit width of 10 μm. The spectral range of the whole system is 460-920nm, the spectral dispersion length is 1mm, and there are 100 spectral segments. The pixel size of the area array detector is 10μm×10μm, and the Nyquist frequency is 50lp/mm. To achieve pupil matching, the front telescopic objective lens system is an image-space telecentric system, and the collimation-imaging system is an object-space telecentric system.

Fig. 6 is a panchromatic spot diagram of the whole system of the grating dispersion spectral imager, it can be seen that in the spectral range of 460-920nm, the spectral dispersion length basically reaches 1mm.

Fig. 7 is three typical wavelength spot diagrams of the whole system of the grating dispersion spectral imager provided by the embodiment of the present invention. The three groups of diagrams respectively correspond to the wavelengths of 460/650/920nm. It can be seen from Fig. 6 that the maximum value of the light spot is located at the short wavelength of the full field of view At 460nm, the RMS diameter of the spot at this place is less than 10um, which is smaller than the pixel size of the detector; FIG. 8 is the three typical wavelength MTF curves of the whole system of the grating dispersion spectral imager provided by the embodiment of the present invention, and the three groups of graphs correspond to the wavelength 460/ 650/920nm, as can be seen from Figure 7, the MTF of each wavelength is close to the diffraction limit at the Nyquist frequency of 50lp/mm, and the imaging quality is good, which meets the requirements of use.

The mentioned embodiment is only used as an illustration of the technical solution of the present invention, and should not be construed as a limitation of the present invention. Any obvious partial modification to the present invention should be regarded as an alternative of the present invention. Such alternatives include the application of other types of front mirror systems, changing the eccentricity or inclination angle of the optical surfaces, the distance between the surfaces, and the optical materials used. These modifications and changes do not depart from the true scope of the present invention.

Claims (2)

1. a compact grating dispersion spectrum imager, it is characterised in that: include preposition telephotolens system (1), Slit (2), collimation-imaging system (3), reflecting grating (4) and planar array detector (5), each several part passes through camera Overall structure is connected；Preposition telephotolens system (1) realizes the function to target imaging, by target imaging to slit (2) Position, simultaneously in order to realize pupil coupling, preposition telephotolens system (1) is designed to image space telecentric system；Slit (2) it is field stop, limits target imaging scope, in order to avoid occurring dry with final planar array detector (5) position Relate to, relative to collimation-imaging system (3) located off-axis；Collimation-imaging system (3) in order to preposition telephotolens system System (1) linking, is thing side's telecentric system, on the one hand to be collimated by the outgoing beam of target slit picture, the opposing party Each wavelength directional light after grating dispersion is imaged onto planar array detector (5) target surface by face again；Reflecting grating (4) is color Dissipate element, it is achieved separate, the spectrum of extraterrestrial target in order to avoid senior diffraction light of shortwave and rudimentary diffraction light of long wave Aliasing, its spectrum of use segment limit is restricted, and selection grating negative one order diffraction light as imaging beam, spectral coverage scope is 460～920nm；Planar array detector (5) is obtained by photoelectric effect and records digital information；Target emergent ray is through front Put telephotolens system (1), be imaged onto on its focal plane, form target picture；Slit limits the scope of target picture, only In slit, light can go out to inject collimation-imaging system, from slit (2) as outgoing beam is through collimation-imaging system (3) Incide in reflecting grating (4) after collimation, after reflecting grating (4) reflection beam splitting, each spectral coverage directional light of separation Retroeflection is ultimately imaged face battle array detection to collimation-imaging system (3), second time through collimation-imaging system (3) again On device (5), forming the slit image of different spectral coverage with slit (2) parallel direction, whole planar array detector (5) is right Answer a line extraterrestrial target and some spectrum channels, by pushing away the motion putting down platform, it is thus achieved that the data cube that target is complete.

2. a compact grating dispersion spectrum formation method, it is characterised in that realizing step is:

(1) target emergent ray is through preposition telephotolens system, is imaged onto on its focal plane, forms target picture；

(2) in slit limits the scope of target picture, only slit, light can go out to inject collimation-imaging system, obtains The collimation of collimation-imaging system, owing to slit is relative to collimation-imaging system located off-axis so that collimated light beam after collimation Oblique incidence reflecting grating, this angle of inclination depends on and slit off-axis distance, can according to practical structures design it needs to be determined that；

(3) dip-parallel smooth incidence reflection grating, after being reflected optical grating reflection light splitting, is different from general dispersion spectrum As the most incident independent imaging lens of instrument, the most each wavelength directional light again returns to incident collimation-imaging system；In order to avoid Senior diffraction light of shortwave and rudimentary diffraction light aliasing of long wave, its spectrum of use segment limit is restricted, and selects grating negative one Order diffraction light is as imaging beam, and spectral coverage scope is 460～920nm；

(4) each wavelength directional light after grating dispersion is imaged onto on planar array detector, due to parallel by collimation-imaging system Light has angle of inclination so that separate with slit location；

(5) planar array detector is obtained by photoelectric effect and the information of record object each wavelength slit image.