CN114485936B - Spectrum imaging system and method based on MEMS grating reflector - Google Patents

Spectrum imaging system and method based on MEMS grating reflector Download PDF

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CN114485936B
CN114485936B CN202111659767.1A CN202111659767A CN114485936B CN 114485936 B CN114485936 B CN 114485936B CN 202111659767 A CN202111659767 A CN 202111659767A CN 114485936 B CN114485936 B CN 114485936B
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working surface
mems grating
grating reflector
micro
dmd
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CN114485936A (en
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虞益挺
苏扬
董雪
石颖超
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Ningbo Research Institute of Northwestern Polytechnical University
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Ningbo Research Institute of Northwestern Polytechnical University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/28—Investigating the spectrum
    • G01J3/2823—Imaging spectrometer
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/02—Details
    • G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
    • G01J3/0235—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using means for replacing an element by another, for replacing a filter or a grating

Abstract

The invention provides a spectrum imaging system and a method based on an MEMS grating reflector, and relates to the technical field of spectrum imaging, wherein the system comprises a target, an imaging subsystem, a DMD working surface, a collimation subsystem, an MEMS grating reflector working surface and a detector working surface; when each micromirror scanning unit in the DMD working face is in a deflection working state, reflecting the target images in the corresponding columns to the collimation subsystem for collimation, and enabling the obtained parallel light to be incident on the MEMS grating reflector working face for light splitting; and by changing the deflection angle of the working surface of the MEMS grating reflector, the dispersion spectrum which is split and reflected by the MEMS grating reflector is incident to the same area of the working surface of the detector. The system can solve the problems of excessive dependence on the surface type of the detector with a large length-width ratio and low integration level in a scanning type spectrum imaging system based on the DMD.

Description

Spectrum imaging system and method based on MEMS grating reflector
Technical Field
The invention relates to the technical field of spectral imaging, in particular to a spectral imaging system and method based on an MEMS grating reflector.
Background
The spectrum imaging technology can obtain the spectrum information representing the physicochemical property while acquiring the target space information, so that the scene photo and the molecular fingerprint are integrated, the dimension and the magnitude of the imaging information can be greatly improved, the spectrum imaging technology becomes the core and the front edge of the detection and identification field, and the spectrum imaging technology is widely applied to the military and civil fields such as accurate guidance, target detection, petroleum exploration, intelligent medical treatment, accurate agriculture and the like. The spectral resolution refers to the minimum width of the detector in the wavelength direction, and is one of important performance indexes of a spectral imaging system. In general, the higher the spectral resolution, the more the number of spectral bands acquired by the system, the narrower the spectral band width that is partitioned, the easier the information of the object is to distinguish and identify, and the higher the spectral resolution is enough to distinguish objects with diagnostic spectral features. Therefore, it is important for a spectral imaging system to obtain high spectral resolution.
With the rapid development of micro-electro-mechanical systems (MEMS) technology, a representative product, namely a digital micromirror device (digital micromirror device, DMD), has advantages of small size, light weight, low energy consumption, customizable and the like, and many limitations in the conventional spectral imaging method can be overcome. The DMD working surface is typically composed of millions of micromirrors, each micromirror unit having a size of about 10 μm, which can deflect the same angle about the hinge tilt axis, and which can be programmed to achieve opposite deflection states, positive and negative.
The scanning type spectrum imaging method based on the DMD can reduce the mass and the volume of the system and make the system more compact and portable. However, the column-by-column scanning of DMD micromirrors causes the corresponding dispersive spectrum to shift in one direction on the detector, requiring a large-area and expensive detector to be used to collect all of the dispersive spectrum.
The MEMS scanning grating arrays are controlled by programming to deflect column by any angle, so that dispersion spectrums corresponding to different micro-mirror scanning units can be reflected to the same position of a detector, the optical splitting elements such as gratings and prisms in a spectrum imaging system can be replaced, the size and weight of the spectrum imaging system are greatly reduced, the problem of spectrum deflection is expected to be solved, but the control circuit of the MEMS scanning grating arrays is complex, each scanning grating array needs to be independently controlled, the size and the number of array units need to be in one-to-one correspondence with the size and the number of the DMD micro-mirror scanning units, and the array cannot be changed, namely, the MEMS scanning grating arrays with one specification can only be matched with the size and the number of the fixed scanning units of the DMD micro-mirror scanning units, and the MEMS scanning grating arrays matched with the DMD micro-mirror scanning units need to be reprocessed if the size and the number of the DMD micro-mirror scanning units are changed.
Disclosure of Invention
The invention solves the problems of dispersion spectrum offset and low integration level due to excessive dependence on the surface type of a detector with a large length-width ratio in a scanning spectrum imaging system based on a DMD.
In order to solve the problems, the invention provides a spectrum imaging system based on an MEMS grating reflector, which comprises a target, an imaging subsystem, a DMD working surface, a collimation subsystem, an MEMS grating reflector working surface and a detector working surface;
the DMD working face consists of a plurality of groups of micro-mirror scanning units, wherein the DMD working face comprises a first micro-mirror scanning unit, a second micro-mirror scanning unit and a third micro-mirror scanning unit;
the target and the DMD working surface are respectively arranged at the object plane and the image plane of the imaging subsystem, a target image formed by the target passing through the imaging subsystem is divided by the micromirror scanning units of the DMD working surface according to columns, the collimation subsystem enables light reflected from the DMD working surface to be parallel light, and the MEMS grating reflector working surface is positioned in the light emergent direction of the collimation subsystem;
when each micromirror scanning unit in the DMD working face is in a deflection working state, reflecting the target images in the corresponding columns to the collimation subsystem for collimation, and enabling the obtained parallel light to be incident on the MEMS grating reflector working face for light splitting; by changing the deflection angle of the working surface of the MEMS grating reflector, the dispersion spectrum obtained by the light splitting and the reflection of the MEMS grating reflector is incident to the same area of the working surface of the detector, namely, the light rays with the minimum wavelength lambda 1 and the maximum wavelength lambda 2 in the dispersion spectrum are respectively incident to the start and end fixed points M and N of the dispersion spectrum area, and all the obtained dispersion spectrums are imaged on the same position of the working surface of the detector.
After the system is adopted, the phenomenon that a dispersion spectrum is offset on a detector due to the deflection of the DMD micro-mirror according to the columns is eliminated, and compared with the existing scanning type spectrum imaging method based on the DMD, the obtained dispersion spectrum position is unchanged in one working period of the DMD and the MEMS grating reflector, so that a special surface type detector is not required to be selected, a high system spectrum resolution can be obtained without customizing a large length-width ratio surface type detector, and the system cost is effectively reduced; the same MEMS grating reflector can be used for matching the sizes and the number of the scanning units of various DMD micromirrors, and the system has flexible and adjustable diversified scene adaptability and higher intelligent degree. The number of the DMD micro-mirror scanning units and the number of micro-mirror columns contained in each unit can be flexibly changed according to practical application, only the deflection angle of the MEMS grating reflector is needed to be recalculated, hardware such as the MEMS grating reflector is not needed to be replaced, and the system is more flexible in modulating the spatial resolution; the system has smaller mass and volume and higher integration degree. The MEMS grating reflector has the functions of light splitting and reflecting, and light splitting elements such as gratings and prisms are not needed.
Further, the micromirror scanning unit is formed by a micromirror array, the number of columns and the number of rows of the micromirror array are respectively a and b, the width of each micromirror is u, the image of the object is divided into 2k+1 columns by the micromirror scanning unit of the DMD working surface, each micromirror scanning unit comprises x columns of micromirrors, the width t=xu, and x (2k+1) is less than or equal to a;
the deflection state of each micromirror is divided into an ON working state and an OFF working state; when the micro-mirror scanning unit is in an ON working state, the micro-mirror scanning unit reflects the selected target image to the collimation subsystem; when in the OFF working state, the micromirror scanning unit reflects the selected target image out of the collimating subsystem.
Further, the MEMS grating mirror working surface comprises a first deflection state, a second deflection state, and a third deflection state;
the MEMS grating reflector can respectively split and reflect the first light passing through the center of the first opening micro-mirror scanning unit, the second light passing through the center of the second opening micro-mirror scanning unit and the third light passing through the center of the third opening micro-mirror scanning unit according to the first deflection state, the second deflection state and the third deflection state, so that the obtained dispersion spectrum is distributed in the same area of the detector.
Further, the collimating subsystem is composed of a lens group and is used for collimating the light reflected by the working surface of the DMD, so that the light is parallel to the working surface of the MEMS grating reflector.
Further, the working surface of the MEMS grating reflector is manufactured by carrying out grating ruling on the reflector, wherein the grating ruling width is d, the diffraction order is m, and the MEMS grating reflector is used for realizing dispersion light splitting and deflection simultaneously.
Further, the working surface of the MEMS grating reflector is defined to deflect clockwise, and the deflection angle is as followsi∈[1,2K+1]，β i The incidence angle of the working surface of the MEMS grating reflector corresponding to the value of (0) is alpha 0 ；
Diffraction angles corresponding to light rays with minimum wavelength lambda 1 and maximum wavelength lambda 2 in the dispersion spectrum are respectively theta i1 And theta i2 ，And respectively incident to start and end fixed points M and N of the dispersion spectrum region;
the spectral dispersion length on the working face of the detector is MN, and the wavelength lambda epsilon lambda 1 ，λ 2 ]The working surface of the MEMS grating reflector is parallel to the working surface of the detector when not deflected, and the extension line of the cross section of the working surface of the MEMS grating reflector and the perpendicular line of the working surface of the detector at the point M are intersected at the point H, the length of HM is H, the length of MN is s, and the length of OH is l;
the incidence point of the central ray of the ith row of light beams divided by the micro mirror on the MEMS grating reflector is O i Through point O i Parallel lines as OH cross MH to H i The distance between the first light passing through the DMD working face and the third light passing through the DMD working face after exiting from the collimation subsystem is PG, the PG length is q, the light passing through the centers of all the micromirror scanning units in the DMD working face is processed by the collimation subsystem and exits at equal intervals, and the distance between the light passing through the centers of any two adjacent micromirror scanning units in the DMD working face after exiting from the collimation subsystem is the same.
Further, according to the incident angle alpha 0 HM length h, MN length s, OH length l, micromirror scanning unit width t, period 2K+1, diffraction order m, PG length q, minimum wavelength λ1, andthe value of the maximum wavelength lambda 2 is determined by the intermediate variable +.MO i H i ＝γ i ，∠NO i H i ＝δ i ，OO i ＝p i Angle of deflection beta i Expressed as:
wherein:
d[sin(α 0 +β i )+sinθ i1 ]＝mλ 1 (3)
d[sin(α 0 +β i )+sinθ i2 ]＝mλ 2 (4)
equation (4) -equation (3) and substituting equation (1) and equation (2) to obtain:
expanding (5) and substituting it into equation cos 2 β i +sin 2 β i =1, resulting in:
2(1-sinγ i sinδ i -cosγ i cosδ i )sin 2 β i -2c(sinγ i -sinδ i )sinβ i +c 2 -(cosγ i -cosδ i ) 2 ＝0
obtain the deflection angle beta i 。
A spectrum imaging method based on MEMS grating reflector includes the following steps:
s1: the method comprises the steps that through controlling a 1 st micro-mirror scanning unit of a DMD working surface to be in an ON working state and controlling deflection angles of an MEMS grating reflector working surface, all other micro-mirror scanning units are in an OFF working state, light rays of a 1 st row of target images are reflected by the 1 st micro-mirror scanning unit to enter a collimation subsystem, are collimated by the collimation subsystem and then are emitted to the MEMS grating reflector working surface in parallel, and are split and reflected by the MEMS grating reflector with the deflection angles, so that an emergent dispersion spectrum is imaged ON a detector working surface;
s2: the 2 nd micro-mirror scanning unit of the DMD working surface is controlled to be in an ON working state, the deflection angles of the MEMS grating reflector working surface are controlled, the rest micro-mirror scanning units are all in an OFF working state, the light rays of the 2 nd row of target images are reflected by the 2 nd micro-mirror scanning unit to enter a collimation subsystem, are collimated by the collimation subsystem and then are emitted to the MEMS grating reflector working surface in parallel, and are split and reflected by the MEMS grating reflector with the deflection angles, so that an emergent dispersion spectrum is imaged ON the same position of the detector working surface;
s3: synchronously controlling the MEMS grating reflector working surfaces to deflect corresponding angles respectively by controlling the 3 rd micro mirror scanning unit to the 2 th micro mirror scanning unit of the DMD working surface to be in an ON working state in sequence, synchronously recording and storing corresponding dispersion spectrograms by the detector working surfaces, and completing the spectral imaging of the 3 rd column to the 2 nd column target images;
s4: the 2K+1 th micro-mirror scanning unit of the DMD working surface is controlled to be in an ON working state, the deflection angles of the MEMS grating reflector working surface are controlled, other micro-mirror scanning units are all in an OFF working state, the 2K+1 th row of light rays of the target image are reflected by the 2K+1 th micro-mirror scanning unit to enter a collimation subsystem, collimated by the collimation subsystem and then parallelly emitted to the MEMS grating reflector working surface, and then are split and reflected by the MEMS grating reflector with the deflection angles, so that the emergent dispersion spectrum is imaged ON the same position of the detector working surface;
s5: and carrying out data processing on 2K+1 dispersion spectrograms acquired by the detector working face to obtain two-dimensional space scene and one-dimensional spectrum information of the target, and thus obtaining the three-dimensional data cube.
The technical scheme adopted by the invention has the following beneficial effects:
according to the invention, the MEMS grating reflector is introduced between the collimation subsystem and the detector, so that the light rays which are reflected by each micromirror scanning unit of the DMD and processed by the collimation subsystem are incident on the MEMS grating reflector to be split and obtain the corresponding dispersion spectrum, and meanwhile, the deflection angle of the MEMS grating reflector is controlled, so that the dispersion spectrum corresponding to each micromirror scanning unit in the DMD is incident on the same position on the working surface of the detector. According to the invention, no light splitting elements such as blazed gratings and prisms are needed, the quality and the volume of the system are effectively reduced, the integration of the system is greatly improved, and the dispersion spectrum generated by deflection of each micromirror scanning unit of the DMD is reflected to the same position on the working surface of the detector by the MEMS grating reflector, so that the problem of dispersion spectrum deviation is solved, the total length of the dispersion spectrum is greatly reduced, higher spectral resolution can be obtained by only using the common detector surface type, the system cost can be effectively reduced, and the problems that the conventional scanning type spectrum imaging system based on the DMD excessively depends on the surface type of the detector with a large length-width ratio and the integration level is not high are solved.
Drawings
FIG. 1 is a graph showing the comparison of the dispersion spectral position changes in two prior art DMD-based scanning spectral imaging methods;
FIG. 2 is a schematic diagram of a driving scheme of a MEMS scanning grating array;
FIG. 3 is a schematic diagram of a driving mode of a MEMS grating mirror of a spectrum imaging system based on the MEMS grating mirror according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a spectral imaging system based on MEMS grating mirrors according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a DMD working surface of a spectral imaging system based on MEMS grating mirrors according to an embodiment of the present invention;
FIG. 6 is a schematic diagram showing the relative position distribution of the MEMS grating mirror and the fixed point M, N of the MEMS grating mirror-based spectral imaging system according to the first embodiment of the present invention;
FIG. 7 is a graph showing an incident point distribution diagram of outgoing light of a collimation subsystem of a spectral imaging system based on a MEMS grating mirror on the MEMS grating mirror according to an embodiment of the present invention;
FIG. 8 is a flowchart of a spectral imaging method based on MEMS grating mirrors according to a second embodiment of the present invention;
fig. 9 is a schematic diagram of spectrum acquisition principle of a spectrum imaging method based on a MEMS grating mirror according to a second embodiment of the present invention;
fig. 10 is a schematic diagram of a target image spectrum acquisition principle of a spectrum imaging method based on a MEMS grating mirror according to a second embodiment of the present invention;
reference numerals illustrate:
1-target, 2-imaging subsystem, 3-DMD working face, 3-1-first on micromirror scanning unit, 3-2-second on micromirror scanning unit, 3-3-third on micromirror scanning unit, 4-collimation subsystem, 5-MEMS grating reflector working face, 5-1-first deflection state, 5-2-second deflection state, 5-3-third deflection state, 6-detector working face, 7-first light ray, 8-second light ray, 9-third light ray.
Detailed Description
In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.
The following are specific embodiments of the present invention and the technical solutions of the present invention will be further described with reference to the accompanying drawings, but the present invention is not limited to these embodiments.
Example 1
The embodiment provides a spectrum imaging system based on a MEMS grating reflector, which comprises a target 1, an imaging subsystem 2, a DMD working surface 3, a collimation subsystem 4, a MEMS grating reflector working surface 5 and a detector working surface 6 as shown in figures 4 to 7;
the DMD working face 3 consists of a plurality of groups of micro-mirror scanning units, wherein the micro-mirror scanning units comprise a first micro-mirror scanning unit 3-1, a second micro-mirror scanning unit 3-2 and a third micro-mirror scanning unit 3-3;
the object 1 and the DMD working surface 3 are respectively arranged at the object plane and the image plane of the imaging subsystem 2, the object image formed by the object 1 passing through the imaging subsystem 2 is divided by micro-mirror scanning units of the DMD working surface 3 according to columns, the collimation subsystem 4 enables light reflected from the DMD working surface 3 to be parallel light, and the MEMS grating reflector working surface 5 is positioned in the light emitting direction of the collimation subsystem 4;
when each micromirror scanning unit in the DMD working face 3 is in a deflection working state, reflecting a target image of a corresponding column into a collimation subsystem 4 for collimation, and incidence of the obtained parallel light on the MEMS grating reflector working face 5 for light splitting; by changing the deflection angle of the MEMS grating mirror working surface 5, the dispersion spectrum obtained by the beam splitting and the reflection of the MEMS grating mirror is incident to the same area of the detector working surface 6, that is, the light with the minimum wavelength λ1=650 nm and the maximum wavelength λ2=800 nm in the dispersion spectrum is respectively incident to the start and end fixed points M and N of the dispersion spectrum area, and all the obtained dispersion spectra are imaged on the same position of the detector working surface 6.
Specifically, by introducing a MEMS grating reflector between the collimating subsystem 4 and the detector, the light reflected by each micromirror scanning unit of the DMD and processed by the collimating subsystem is incident on the MEMS grating reflector to be split and obtain a corresponding dispersion spectrum, and meanwhile, the MEMS grating reflector is controlled to deflect for a certain angle, so that the dispersion spectrum corresponding to each micromirror scanning unit in the DMD is incident on the same position on the detector working surface 6.
Specifically, the phenomenon that a dispersion spectrum is offset on a detector due to the deflection of the DMD micro mirror according to the columns is eliminated, and compared with the existing scanning type spectrum imaging method based on the DMD, the obtained dispersion spectrum position is unchanged in one working period of the DMD and the MEMS grating reflector, so that a special surface type detector is not required to be selected, a high system spectrum resolution can be obtained without customizing a large-length-width ratio surface type detector, and the system cost is effectively reduced; the same MEMS grating reflector can be used for matching the sizes and the number of the scanning units of various DMD micromirrors, and the system has flexible and adjustable diversified scene adaptability and higher intelligent degree. The number of the DMD micro-mirror scanning units and the number of micro-mirror columns contained in each unit can be flexibly changed according to practical application, only the deflection angle of the MEMS grating reflector is needed to be recalculated, hardware such as the MEMS grating reflector is not needed to be replaced, and the system is more flexible in modulating the spatial resolution; the system has smaller mass and volume and higher integration degree. The MEMS grating reflector has the functions of light splitting and reflecting, and light splitting elements such as gratings and prisms are not needed.
In particular, the imaging subsystem 2 is a telescopic lens responsible for converging the reduced image of the target 1 on the DMD working surface 3. The minimum wavelength is selected to be 650nm and the maximum wavelength is selected to be 800nm.
Referring to fig. 1, a mechanical slit push-broom motion in a conventional spectral imaging system can be replaced with a column-wise scanning of micromirrors.
Referring to fig. 2, the MEMS scanning raster array is controlled to deflect by any angle column by programming, but the control circuit of the MEMS scanning raster array is complex, each scanning raster array needs to be controlled independently, the size and the number of array units need to be in one-to-one correspondence with the size and the number of DMD micromirror scanning units, and the array units cannot be changed, i.e. the MEMS scanning raster array of one specification can only match the size and the number of fixed scanning units of the DMD, and if the size and the number of DMD micromirror scanning units are changed, the MEMS scanning raster array matched with the DMD is required to be reprocessed.
Referring to fig. 3, compared with the MEMS scanning grating array, the MEMS grating mirror has more reticles, better spectroscopic effect, simpler driving circuit, lower manufacturing difficulty and cost, and can adapt to different sizes and numbers of DMD micromirror scanning units.
Referring to fig. 5, wherein the micromirror scanning unit is composed of a micromirror array, the number of columns and rows of the micromirror array are selected to be a=1024 and b=768, respectively, the width of each micromirror is u=13.68 μm, the image of the object 1 is divided into 255 columns (k=127) by the micromirror scanning unit of the DMD working surface 3 by columns, each micromirror scanning unit includes x=4 columns of micromirrors, the width t=xu= 54.72 μm, and x (2k+1) +.a;
the deflection state of each micromirror is divided into an ON working state and an OFF working state; when in an ON working state, the micromirror scanning unit reflects the selected target image to the collimation subsystem 4; when in the OFF operating state, the micromirror scanning unit reflects the selected target image out of the collimating subsystem 4.
Specifically, the DMD working surface 3 is rectangular and is formed by a micromirror array, the columns and rows of the micromirror array are a=1024 and b=768, the width of each micromirror is u=13.68 μm, the image of the object 1 is divided into 255 columns (k=127) by columns by the micromirror scanning units of the DMD working surface 3, each micromirror scanning unit contains x=4 columns of micromirrors, the widths are t=xu= 54.72 μm, x (2k+1) +.a is satisfied, and the deflection angle of each micromirror is ±12°. Selecting a deflection state with a deflection angle of 12 degrees as an ON working state, and reflecting a selected target image to the collimation subsystem 4 by a micromirror scanning unit in the ON working state; the other deflection state is used as an OFF working state, and the micromirror scanning unit in the OFF working state is responsible for reflecting the selected target image out of the system.
Specifically, 255 micro-mirror scanning units are controlled to be in an ON working state in sequence, and simultaneously, the angle corresponding to the deflection of the MEMS grating reflector is controlledi∈[1,255]Thereby realizing the column scanning of the target image, further obtaining 255 dispersion spectrograms on the same area of the detector working face 6, and completing the acquisition of the target three-dimensional data cube.
The first light ray 7 passing through the center of the first on-micromirror scanning unit 3-1 of the DMD working surface 3 passes through the center of the first on-micromirror scanning unit 3-1 of the DMD working surface 3 and the collimating subsystem 4, and is split and reflected by the MEMS grating mirror in the first deflection state 5-1, and the light rays with the minimum wavelength λ1=650 nm and the maximum wavelength λ2=800 nm in the obtained dispersion spectrum are respectively incident to the fixed points M and N.
The second light beam 8 passing through the center of the second on-micromirror scanning unit 3-2 of the DMD working surface 3 passes through the center of the second on-micromirror scanning unit 3-2 of the DMD working surface 3 and the collimating subsystem 4, and is split and reflected by the MEMS grating mirror in the second deflection state 5-2, and the light beams with the minimum wavelength λ1=650 nm and the maximum wavelength λ2=800 nm in the obtained dispersion spectrum are respectively incident to the fixed points M and N.
The third light 9 passing through the center of the third on-micromirror scanning unit 3-3 of the DMD working surface 3 passes through the center of the third on-micromirror scanning unit 3-3 of the DMD working surface 3 and the collimating subsystem 4, and is split and reflected by the MEMS grating mirror in the third deflection state 5-3, and the light with the minimum wavelength λ1=650 nm and the maximum wavelength λ2=800 nm in the obtained dispersion spectrum is respectively incident to the fixed points M and N.
Wherein the MEMS grating reflector working surface 5 comprises a first deflection state 5-1, a second deflection state 5-2 and a third deflection state 5-3;
the MEMS grating mirror splits and reflects the first light 7 passing through the center of the first open micromirror scanning unit 3-1, the second light 8 passing through the center of the second open micromirror scanning unit 3-2, and the third light 9 passing through the center of the third open micromirror scanning unit 3-3 according to the first deflection state 5-1, the second deflection state 5-2, and the third deflection state 5-3, respectively, so that the obtained dispersion spectrum is distributed in the same area of the detector working surface 6.
Specifically, the detector working face 6 is responsible for collecting the dispersion spectrum emitted by the MEMS grating reflector working face 5, and the surface shape of the detector working face 6 is a common detector surface shape in the market.
The collimating subsystem 4 is composed of a lens group, and is used for collimating the light reflected by the DMD working surface 3, so that the light is parallel to the MEMS grating reflector working surface 5.
The MEMS grating mirror working surface 5 is manufactured by grating scribing on a mirror, wherein the grating scribing width is d=2.5 μm, and the diffraction order is m=1, so as to realize dispersion light splitting and deflection simultaneously.
Referring to FIG. 6, wherein a MEMS grating mirror is definedThe working surface 5 deflects clockwise by an angle ofi∈[1,255]，β i The corresponding incidence angle of the MEMS grating mirror working surface 5 at =0 is α 0 ＝20°；
The diffraction angles corresponding to the light rays with the minimum wavelength λ1=650 nm and the maximum wavelength λ2=800 nm in the dispersion spectrum are respectively θ i1 And theta i2 ，And respectively incident to start and end fixed points M and N of the dispersion spectrum region;
the spectral dispersion length on the detector working surface 6 is MN, the wavelength lambda epsilon [650nm,800nm ], the MEMS grating reflector working surface 5 is parallel to the detector working surface 6 when not deflected, the cross section extension line of the MEMS grating reflector working surface 5 when not deflected and the perpendicular line of the detector working surface 6 at the point M are intersected at the point H, the HM length is h=150 mm, the MN length is s=9.041 mm, and the OH length is l= 12.345mm;
the incidence point of the central ray of the ith row of light beams divided by the micro mirror on the MEMS grating reflector is O i Through point O i Parallel lines as OH cross MH to H i ；
Referring to fig. 7, a distance between a first light ray 7 passing through the DMD working surface 3 and a third light ray 9 passing through the DMD working surface 3 after exiting from the collimating subsystem 4 is PG, the PG length is q=14.85 mm, and light rays passing through the centers of all the micromirror scanning units in the DMD working surface 3 after being processed by the collimating subsystem 4 are emitted at equal intervals, and the distance between the light rays passing through the centers of any two adjacent micromirror scanning units of the DMD working surface 3 after exiting from the collimating subsystem 4 is the same.
Wherein, according to the incident angle alpha 0 Values of HM length h, MN length s, OH length l, micromirror scanning unit width t, period 2K+1, diffraction order m, PG length q, minimum wavelength λ1 and maximum wavelength λ2, by intermediate variable +. i H i ＝γ i ，∠NO i H i ＝δ i ，OO i ＝p i Angle of deflection beta i Expressed as:
wherein:
d[sin(α 0 +β i )+sinθ i1 ]＝mλ 1 (3)
d[sin(α 0 +β i )+sinθ i2 ]＝mλ 2 (4)
equation (4) -equation (3) and substituting equation (1) and equation (2) to obtain:
expanding (5) and substituting it into equation cos 2 β i +sin 2 β i =1, resulting in:
2(1-sinγ i sinδ i -cosγ i cosδ i )sin 2 β i -2c(sinγ i -sinδ i )sinβ i +c 2 -(cosγ i -cosδ i ) 2 ＝0
obtain the deflection angle beta i 。
The system introduces the MEMS grating reflector between the collimation subsystem and the detector, so that the light rays which are reflected by each micromirror scanning unit of the DMD and processed by the collimation subsystem are incident on the MEMS grating reflector to be split and obtain corresponding dispersion spectrums, and meanwhile, the deflection angles of the MEMS grating reflector are controlled, so that the dispersion spectrums corresponding to each micromirror scanning unit in the DMD are incident on the same position on the working surface of the detector. The system does not need light splitting elements such as blazed gratings and prisms, the quality and the volume of the system are effectively reduced, the integration of the system is greatly improved, and the dispersion spectrum generated by deflection of each micromirror scanning unit of the DMD is reflected to the same position on the working surface of the detector by the MEMS grating reflector, so that the problem of dispersion spectrum deviation is solved, the total length of the dispersion spectrum is greatly reduced, higher spectral resolution can be obtained only by using the common detector surface type, the system cost can be effectively reduced, and the problems that the conventional scanning type spectrum imaging system based on the DMD excessively depends on the surface type of the detector with a large length-width ratio and the integration level is not high are solved.
Example two
The embodiment provides a spectral imaging method based on a MEMS grating reflector, as shown in FIG. 8, the method comprises the following steps:
referring to fig. 9, step S1: the method comprises the steps that through controlling a 1 st micro-mirror scanning unit of a DMD working surface to be in an ON working state and controlling deflection angles of an MEMS grating reflector working surface, all other micro-mirror scanning units are in an OFF working state, light rays of a 1 st row of target images are reflected by the 1 st micro-mirror scanning unit to enter a collimation subsystem, are collimated by the collimation subsystem and then are emitted to the MEMS grating reflector working surface in parallel, and are split and reflected by the MEMS grating reflector with the deflection angles, so that an emergent dispersion spectrum is imaged ON a detector working surface;
referring to fig. 10, the direction of spectral dispersion is defined as the X-axis direction, and the Y-axis direction perpendicular to this direction is the spatial position direction. The spectrum of the 1 st column of target image is sequentially unfolded along the X-axis direction according to different wavelengths, and spectrum components corresponding to different space positions are obtained in the Y-axis direction. The detector working face 6 records and stores the dispersion spectrogram of the 1 st column of target image, and the reflection work of the 1 st micro-mirror scanning unit and the first light splitting and reflection work of the MEMS grating reflector are finished, so that the spectral imaging of the 1 st column of target image is completed.
Referring to fig. 9, step S2: the 2 nd micro-mirror scanning unit of the DMD working surface is controlled to be in an ON working state, the deflection angles of the MEMS grating reflector working surface are controlled, the rest micro-mirror scanning units are all in an OFF working state, the light rays of the 2 nd row of target images are reflected by the 2 nd micro-mirror scanning unit to enter a collimation subsystem, are collimated by the collimation subsystem and then are emitted to the MEMS grating reflector working surface in parallel, and are split and reflected by the MEMS grating reflector with the deflection angles, so that an emergent dispersion spectrum is imaged ON the same position of the detector working surface;
referring to fig. 10, although the target image is shifted in the horizontal direction, the position of the dispersion spectrum on the detector face 6 is not changed. The detector working face 6 records and stores the dispersion spectrogram at the moment, and the reflection work of the 2 nd micro-mirror scanning unit and the second light splitting and reflection work of the MEMS grating reflector are finished, so that the spectral imaging of the 2 nd column of target images is completed.
Referring to fig. 9, step S3: synchronously controlling the MEMS grating reflector working surfaces to deflect corresponding angles respectively by controlling the 3 rd micro mirror scanning unit to the 2 th micro mirror scanning unit of the DMD working surface to be in an ON working state in sequence, synchronously recording and storing corresponding dispersion spectrograms by the detector working surfaces, and completing the spectral imaging of the 3 rd column to the 2 nd column target images;
step S4: the 255 th micro mirror scanning unit of the DMD working surface is controlled to be in an ON working state, meanwhile, the deflection angle of the MEMS grating reflector working surface is controlled, other micro mirror scanning units are all in an OFF working state, light rays of the 255 th row of target images are firstly reflected by the 255 th micro mirror scanning unit to enter a collimation subsystem, are collimated by the collimation subsystem and then are parallelly emitted to the MEMS grating reflector working surface, and are split and reflected by the MEMS grating reflector with the deflection angle, so that an emergent dispersion spectrum is imaged ON the same position of the detector working surface;
referring to fig. 10, since the spatial positions of the target images in different columns are unchanged in the spectral position in the X-axis direction, spectral imaging of the entire target can be completed as long as the detector working surface 6 is ensured to be able to completely collect the dispersion spectrum of any one column of the target image. The detector working face 6 records and stores the dispersion spectrogram at the moment, and the 255 th light splitting and reflection deflection work of the 255 th micro mirror scanning unit and the 255 th light splitting and reflection deflection work of the MEMS grating reflector are finished, so that the 255 th spectrum imaging of the target image is completed.
S5: and carrying out data processing on 255 dispersion spectrograms acquired by the detector working face to obtain two-dimensional space scene and one-dimensional spectrum information of the target, and thus obtaining the three-dimensional data cube.
The method sequentially controls 255 micro-mirror scanning units to be in an ON working state, and simultaneously controls the angle corresponding to the deflection of the MEMS grating reflectori∈[1,255]Thereby realizing the column scanning of the target image, further obtaining 255 dispersion spectrograms on the same area of the working surface of the detector, and completing the acquisition of the target three-dimensional data cube.
Although the present disclosure is described above, the scope of protection of the present disclosure is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the scope of the invention.

Claims (5)

1. The spectrum imaging system based on the MEMS grating reflector is characterized by comprising a target (1), an imaging subsystem (2), a DMD working surface (3), a collimation subsystem (4), an MEMS grating reflector working surface (5) and a detector working surface (6);
the DMD working face (3) consists of a plurality of groups of micro-mirror scanning units, wherein the DMD working face comprises a first micro-mirror scanning unit (3-1) which is started, a second micro-mirror scanning unit (3-2) which is started and a third micro-mirror scanning unit (3-3) which is started;
the object (1) and the DMD working surface (3) are respectively arranged at the object plane and the image plane of the imaging subsystem (2), the object image formed by the object (1) passing through the imaging subsystem (2) is divided by the micro-mirror scanning units of the DMD working surface (3) according to columns, the collimation subsystem (4) enables light reflected from the DMD working surface (3) to be parallel light, and the MEMS grating reflector working surface (5) is positioned in the light emergent direction of the collimation subsystem (4);
when each micromirror scanning unit in the DMD working face (3) is in a deflection working state, reflecting the target images in the corresponding columns into the collimation subsystem (4) for collimation, and enabling the obtained parallel light to be incident on the MEMS grating reflector working face (5) for light splitting; by changing the deflection angle of the working surface (5) of the MEMS grating reflector, the dispersion spectrum obtained by the light splitting and the reflection of the MEMS grating reflector is incident to the same area of the working surface (6) of the detector, namely, the light rays with the minimum wavelength lambda 1 and the maximum wavelength lambda 2 in the dispersion spectrum are respectively incident to start and end fixed points M and N of the dispersion spectrum area, and all the obtained dispersion spectrums are imaged on the same position of the working surface (6) of the detector;
the MEMS grating reflector working surface (5) comprises a first deflection state (5-1), a second deflection state (5-2) and a third deflection state (5-3);
the MEMS grating reflector can respectively split and reflect a first light ray (7) passing through the center of the first opening micro-mirror scanning unit (3-1), a second light ray (8) passing through the center of the second opening micro-mirror scanning unit (3-2) and a third light ray (9) passing through the center of the third opening micro-mirror scanning unit (3-3) according to the first deflection state (5-1), the second deflection state (5-2) and the third deflection state (5-3), so that the obtained dispersion spectrum is distributed in the same area of the detector working surface (6);
the MEMS grating reflector working surface (5) is prepared by carrying out grating ruling on a reflector, wherein the grating ruling width is d, the diffraction order is m, and the MEMS grating reflector working surface is used for realizing dispersion light splitting and deflection simultaneously;
defining the clockwise deflection of the working surface (5) of the MEMS grating reflector, wherein the deflection angle is as followsβ i The incidence angle of the working surface (5) of the MEMS grating reflector corresponding to the value of (0) is alpha 0 ；
Diffraction angles corresponding to light rays with minimum wavelength lambda 1 and maximum wavelength lambda 2 in the dispersion spectrum are respectively theta i1 And theta i2 ，And respectively incident to start and end fixed points M and N of the dispersion spectrum region;
the spectral dispersion length on the detector working surface (6) is MN, and the wavelength lambda epsilon lambda 1 ，λ 2 ]The MEMS grating reflector working surface (5) is parallel to the detector working surface (6) when not deflected, and the cross section extension line of the MEMS grating reflector working surface (5) and the perpendicular line of the detector working surface (6) at the point M are intersected at the point H, the length of HM is H, the length of MN is s, and the length of OH is l;
the incidence point of the central ray of the ith row of light beams divided by the micro mirror on the MEMS grating reflector is O i Through point O i Parallel lines as OH cross MH to H i The distance between the first light ray (7) passing through the DMD working surface (3) and the third light ray (9) passing through the DMD working surface (3) after exiting from the collimation subsystem (4) is PG, the PG length is q, the light rays passing through the centers of all the micro-mirror scanning units in the DMD working surface (3) are processed by the collimation subsystem (4) and exit at equal intervals, and the distance between the light rays passing through the centers of any two adjacent micro-mirror scanning units in the DMD working surface (3) after exiting from the collimation subsystem (4) is the same.
2. The MEMS grating mirror-based spectroscopic imaging system according to claim 1, wherein the micromirror scanning units are comprised of an array of micromirrors, the columns and rows of the array of micromirrors being a and b, respectively, each of the micromirrors having a width u, the image of the object (1) being divided by the micromirror scanning units of the DMD working surface (3) into 2k+1 columns by columns, each micromirror scanning unit comprising x columns of micromirrors, the widths t = xu, and x (2k+1) +.;
the deflection state of each micromirror is divided into an ON working state and an OFF working state; when in an ON working state, the micromirror scanning unit reflects the selected target image to the collimation subsystem (4); when in the OFF working state, the micromirror scanning unit reflects the selected target image out of the collimating subsystem (4).
3. A MEMS grating mirror based spectroscopic imaging system according to claim 1, wherein the collimating subsystem (4) is constituted by a lens group for collimating the light reflected off the DMD working surface (3) for parallel incidence on the MEMS grating mirror working surface (5).
4. The MEMS grating mirror-based spectroscopic imaging system of claim 1, wherein, in accordance with the angle of incidence α 0 Values of HM length h, MN length s, OH length l, micromirror scanning unit width t, period 2K+1, diffraction order m, PG length q, minimum wavelength λ1 and maximum wavelength λ2, by intermediate variable +. i H i ＝γ i ，∠NO i H i ＝δ i ，OO i ＝p i Angle of deflection beta i Expressed as:
wherein:
d[sin(α 0 +β i )+sinθ i1 ]＝mλ 1 (3)
d[sin(α 0 +β i )+sinθ i2 ]＝mλ 2 (4)
equation (4) -equation (3) and substituting equation (1) and equation (2) to obtain:
expanding (5) and substituting it into equation cos 2 β i +sin 2 β i =1, resulting in:
2(1-sinγ i sinδ i -cosγ i cosδ i )sin 2 β i -2c(sinγ i -sinδ i )sinβ i +c 2 -(cosγ i -cosδ i ) 2 ＝0
obtain the deflection angle beta i 。
5. A MEMS grating mirror based spectroscopic imaging method as defined in any one of claims 1 to 4, comprising the steps of:
s1: the method comprises the steps that through controlling a 1 st micro-mirror scanning unit of a DMD working surface to be in an ON working state and controlling deflection angles of an MEMS grating reflector working surface, all other micro-mirror scanning units are in an OFF working state, light rays of a 1 st row of target images are reflected by the 1 st micro-mirror scanning unit to enter a collimation subsystem, are collimated by the collimation subsystem and then are emitted to the MEMS grating reflector working surface in parallel, and are split and reflected by the MEMS grating reflector with the deflection angles, so that an emergent dispersion spectrum is imaged ON a detector working surface;
s2: the 2 nd micro-mirror scanning unit of the DMD working surface is controlled to be in an ON working state, the deflection angles of the MEMS grating reflector working surface are controlled, the rest micro-mirror scanning units are all in an OFF working state, the light rays of the 2 nd row of target images are reflected by the 2 nd micro-mirror scanning unit to enter a collimation subsystem, are collimated by the collimation subsystem and then are emitted to the MEMS grating reflector working surface in parallel, and are split and reflected by the MEMS grating reflector with the deflection angles, so that an emergent dispersion spectrum is imaged ON the same position of the detector working surface;
s3: synchronously controlling the MEMS grating reflector working surfaces to deflect corresponding angles respectively by controlling the 3 rd micro mirror scanning unit to the 2 th micro mirror scanning unit of the DMD working surface to be in an ON working state in sequence, synchronously recording and storing corresponding dispersion spectrograms by the detector working surfaces, and completing the spectral imaging of the 3 rd column to the 2 nd column target images;
s4: the 2K+1 th micro-mirror scanning unit of the DMD working surface is controlled to be in an ON working state, the deflection angles of the MEMS grating reflector working surface are controlled, other micro-mirror scanning units are all in an OFF working state, the 2K+1 th row of light rays of the target image are reflected by the 2K+1 th micro-mirror scanning unit to enter a collimation subsystem, collimated by the collimation subsystem and then parallelly emitted to the MEMS grating reflector working surface, and then are split and reflected by the MEMS grating reflector with the deflection angles, so that the emergent dispersion spectrum is imaged ON the same position of the detector working surface;
s5: and carrying out data processing on 2K+1 dispersion spectrograms acquired by the detector working face to obtain two-dimensional space scene and one-dimensional spectrum information of the target, and thus obtaining the three-dimensional data cube.
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