CN114485935A - Spectral imaging system and method based on MEMS - Google Patents
Spectral imaging system and method based on MEMS Download PDFInfo
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Abstract
The invention discloses a spectral imaging system and method based on MEMS, belongs to the field of spectral imaging, and mainly relates to a micro-electromechanical system technology, an optical system design technology, a hyperspectral imaging technology and the like. According to the invention, the MEMS scanning grating mirror array is introduced between the collimation subsystem and the detector, so that light rays reflected by each micro mirror scanning unit of the DMD and processed by the collimation subsystem can be split on each MEMS scanning grating mirror unit and corresponding dispersion spectrums are obtained, and meanwhile, the dispersion spectrums corresponding to each micro mirror scanning unit in the DMD are incident on the working surface of the detector at the same position by controlling the deflection angle of each unit in the MEMS scanning grating mirror array. Therefore, the dispersion spectrum generated after being scanned by the DMD micro-mirror in columns does not deviate along one direction any more, but is distributed at the same position on the working surface of the detector, so that the total length of the dispersion spectrum is greatly reduced, and the requirement of the system on the working surface of the detector with a large length-width ratio is reduced.
Description
Technical Field
The invention belongs to the field of spectral imaging, and mainly relates to a micro-electro-mechanical system technology, an optical system design technology, a hyperspectral imaging technology and the like.
Prior Art
The spectral resolution refers to the minimum width recorded by the detector in the wavelength direction, and is one of important performance indexes of the spectral imaging system. Generally, the higher the spectral resolution, the more spectral bands are acquired by the system, the narrower the width of the divided spectral bands, the easier the information of the target is to distinguish and identify, the stronger the pertinence is, and the target with diagnostic spectral features can be distinguished more easily by the high enough spectral resolution. The data with high spectral resolution can particularly depict the spectral details of ground objects, support the waveform analysis technology, be widely applied to the fields of atmospheric remote sensing, vegetation detection, geological archaeology, military reconnaissance, pathological tissue identification and the like, and the ability of automatically distinguishing and identifying target properties and composition of the system can be improved by subdividing the spectrum and improving the spectral resolution. Therefore, it is important for spectral imaging systems to achieve high spectral resolution.
The slit push-broom type is a commonly used spectrum data acquisition method, compared with staring type, snapshot type and other methods, the spectrum data acquisition method has higher resolution ratio, and the principle of constructing a target three-dimensional data cube is simpler. However, the method needs to rely on mechanical motion to realize push-scanning of the spatial scene, so as to acquire spectral data of the spatial scene, which results in a large volume and mass of the system and high energy consumption.
With the rapid development of Micro-electro-mechanical systems (MEMS) technology, a representative product, Digital Micromirror Device (DMD), has the advantages of small size, light weight, low energy consumption, customization, etc., and can overcome many limitations in the conventional spectral imaging method. The working surface of the DMD is generally composed of up to 50 to 200 ten thousand micromirrors, each micromirror unit has a size of about 10 μm, can deflect at the same angle around the hinge tilt axis, and can realize the opposite deflection states of positive and negative directions through programming control. The scanning column by utilizing the micro-mirror can replace the mechanical slit push-scanning movement (CN105527021A, CN110132412A and the like) in the traditional spectral imaging system, and the scanning type spectral imaging method based on the DMD can reduce the mass and the volume of the system, so that the system is more compact and portable. However, the line-by-line scanning of the DMD micromirrors causes the corresponding dispersion spectrum to shift on the detector in one direction, and therefore, in order to collect all the dispersion spectra and obtain a higher spectral resolution, a detector with a large working surface length-width ratio needs to be used, and such an expensive detector greatly increases the system cost, which is not favorable for popularization and application of the DMD-based scanning spectral imaging system in the civil field. Aiming at the problem, a new spectral imaging system based on the DMD divides a micromirror array of a DMD working surface into an upper part and a lower part (CN112484857A), and changes the position of an optical axis of emergent light of each part by adding an image transfer subsystem, so that a dispersion spectrum on a detector does not shift along only one direction any more, but shifts along two directions, as shown in figure 1, compared with a scanning spectral imaging system based on the DMD (CN105527021A and CN110132412A), the method can reduce the requirement of the system on the surface type of a detector with a large length-to-width ratio; at the same time, this method allows the spread of the dispersion spectrum produced by the deflection of each column of micromirrors to be wider, using the same detector, and the spectral resolution provided by the system is increased. However, the method only reduces the total length of the dispersion spectrum by 50%, does not fundamentally solve the problem of dispersion spectrum shift, still needs to select a special plane detector, and has limited improvement on spectral resolution.
In addition to DMD, the rapid development of optical MEMS technology opens up imagination for the development of new spectral imaging systems. The grating structure and the MEMS scanning mirror structure are integrated, the function of dynamic spectrum scanning can be realized, the size and the weight of a spectrum imaging system are expected to be greatly reduced, the flexible and adjustable diversified scene adaptability is realized, and the intelligent degree is higher.
Disclosure of Invention
Object of the Invention
The invention provides a spectral imaging system and a method based on a DMD (digital micromirror device) and an MEMS (micro-electromechanical system) scanning grating mirror array. Therefore, the dispersion spectrum generated after the DMD micro-mirror is scanned in columns does not deviate along one direction any more, but is distributed at the same position on the working surface of the detector, so that the total length of the dispersion spectrum is greatly reduced, and the requirement of the system on the working surface of the detector with large length-width ratio is reduced. Compared with the existing DMD-based scanning type spectral imaging method, the method has the advantage that wider dispersion spectrum and higher spectral resolution can be obtained under the condition that the same detector is used. The invention does not need blazed grating, prism and other light splitting elements, effectively reduces the quality and volume of the system, greatly improves the integration of the system, can obtain higher spectral resolution by using common detector surface types, can effectively reduce the system cost, and solves the problems that the existing scanning type spectral imaging system based on DMD excessively depends on the detector surface type with large length-width ratio and the integration level is not high enough.
Technical scheme
The technical scheme adopted by the invention is that the invention relates to a spectral imaging system and a method based on MEMS (micro-electromechanical system), referring to figure 2, the system mainly comprises a target 1, an imaging subsystem 2, a DMD working surface 3, a DMD working surface 1 st micro-mirror scanning unit 3-1, a DMD working surface middle micro-mirror scanning unit 3-2, a DMD working surface last 1 micro-mirror scanning unit 3-3, a collimation subsystem 4, an MEMS scanning grating mirror array working surface 5, an MEMS scanning grating mirror array working surface 1 st MEMS scanning grating mirror unit 5-1, an MEMS scanning grating mirror array working surface middle MEMS scanning grating mirror unit 5-2, an MEMS scanning grating mirror array working surface last 1 MEMS scanning grating mirror unit 5-3, a detector working surface 6, a light ray 7 passing through the DMD working surface 1 st micro-mirror scanning unit center, a light ray 8 passing through the DMD working surface middle micro-mirror scanning unit center and a DMD working surface last 1 micro-mirror scanning unit center Light rays 9. The target 1 and the DMD working surface 3 are respectively arranged on the imaging subsystemAt the object plane and the image plane of the system 2, a target image formed by the target 1 through the imaging subsystem 2 is divided into columns by the micro-mirror scanning units of the DMD working surface 3. The collimation subsystem 4 changes the light reflected from the DMD working surface 3 into parallel light, the MEMS scanning grating mirror array working surface 5 is located in the light exit direction of the collimation subsystem 4, the number of MEMS scanning grating mirror units in the MEMS scanning grating mirror array working surface 5 is the same as the number of micromirror scanning units in the DMD working surface 3, it is required that each micromirror scanning unit in the DMD working surface 3 must reflect the corresponding column of target images into the collimation subsystem 4 for collimation when in the deflection working state, the obtained parallel light is incident on the corresponding MEMS scanning grating mirror unit in the MEMS scanning grating mirror array working surface 5 for light splitting, and simultaneously, it is required that the light passing through the center of each micromirror scanning unit in the DMD working surface 3 also passes through the center of the corresponding MEMS scanning grating mirror unit in the MEMS scanning grating mirror array working surface 5, for example, the light 7 passing through the center of the 1 st micromirror scanning unit in the DMD working surface, The light 8 passing through the center of the middle micro-mirror scanning unit of the DMD working surface and the light 9 passing through the center of the last 1 micro-mirror scanning unit of the DMD working surface respectively pass through the centers of the 1 st, 5-1, 5-2 and 5-3 MEMS scanning grating mirror units of the MEMS scanning grating mirror array working surface 5. By changing the deflection angle of each MEMS scanning grating mirror unit in the MEMS scanning grating mirror array working surface 5, the dispersed spectrum which is split and emitted by each MEMS scanning grating mirror unit is incident to the same area of the detector, namely the minimum wavelength lambda in the dispersed spectrum1And maximum wavelength lambda2The light is incident to the beginning and end fixed points M and N of the dispersion spectrum region, and all the finally obtained dispersion spectra are imaged at the same position of the working face 6 of the detector.
The imaging subsystem 2 may be a telescope lens or a microscope head, and is responsible for converging the reduced or enlarged image of the target 1 on the DMD working surface 3.
The DMD working surface 3 is rectangular, referring to FIG. 3, it is composed of micromirror arrays, the number of columns and rows of the micromirror arrays are a and b respectively, the width of each micromirror is u, the image of the target 1 is divided into 2K +1 columns (K is a positive integer) by the micromirror scanning unit of the DMD working surface 3, each micromirror scanning unit comprises x columns of micromirrors, the width of each micromirror scanning unit is xu, and x (2K +1) is less than or equal to a, the deflection angle of each micromirror is only positive or negative, mostly +/-12 degrees, also +/-10 degrees, +/-17 degrees, etc. One of the deflection states is selected as an 'ON' working state, and the micromirror scanning unit in the state can reflect the selected target image to the collimation subsystem 4; the other deflection state is the "OFF" state, in which the micromirror scanning unit is responsible for reflecting the selected target image out of the system.
The collimation subsystem 4 may be composed of a lens group or a concave spherical reflector and other components, and is responsible for collimating the light reflected from the DMD working surface 3 and making the light incident in parallel on the MEMS scanning grating mirror array working surface 5.
The MEMS scanning grating mirror array working surface 5 is formed by grating lines on a long scanning micro mirror array by utilizing an MEMS technology, and can realize two functions of dispersion light splitting and scanning deflection at the same time. Referring to fig. 4, the MEMS scanning grating mirror array working surface 5 includes 2K +1 MEMS scanning grating mirror units, the grating groove width is d, the diffraction order is m, the width of each MEMS scanning grating mirror unit is t, the central point of the ith MEMS scanning grating mirror unit is Oi(i is a positive integer, i belongs to [1,2K +1 ]]). Referring to FIG. 5, the spectral dispersion length on the detector face 6 is MN, and the wavelength λ ∈ [ λ ]1,λ2]The MEMS scanning grating mirror array working surface 5 and the detector working surface 6 are required to be parallel to each other, the cross section extension line of the MEMS scanning grating mirror array working surface 5 and the perpendicular line of the detector working surface 6 at the N point are intersected at the O point, the ON length is h, the MN length is s, OO2K+1Length l, l > s, each MEMS scanning grating mirror unit can deflect only clockwise, and when the ith MEMS scanning grating mirror unit is in working state "ON", the deflection angle is betai，
βiWhen the incidence angle of the corresponding MEMS scanning grating mirror unit is 0, the incidence angle is alpha0Dispersion wavelength is λ1And λ2Of (2) a lightThe diffraction angles corresponding to the lines are respectively thetai1And thetai2They are incident to fixed points M and N, respectively. By reasonably selecting h, s, l, t, d and lambda1、λ2So that the dispersion spectrum obtained by the dispersion and reflection of the ith MEMS scanning grating mirror unit can be incident on a fixed region MN, i.e. beta, on the detectoriThere is a solution. Introducing an intermediate variable & lt NO according to the known parametersiO＝γi，∠MOiO＝δiGiving betaiThe solving method of (1):
βisatisfies the following formula:
wherein:
d(sin(α0+βi)+sinθi1)＝mλ1 (3)
d(sin(α0+βi)+sinθi2)＝mλ2 (4)
(4) - (3) and substituting the formulas (1) and (2) into the formula:
the equation (5) is expanded and substituted into the equation cos2βi+sin2βiGet 1, the quadratic equation of one element:
2(1-sinγisinδi-cosγicosδi)sin2βi+2c(sinγi-sinδi)sinβi
+c2-(cosγi-cosδi)2＝0
get it solved
Namely, it is
If there are two solutions, the smaller value is taken, wherein:
A＝2(1-sinγi sinδi-cosγi cosδi)
B＝2c(sinγi-sinδi)
D＝c2-(cosγi-cosδi)2
the detector working face 6 is used for collecting the dispersion spectrum emitted by the MEMS scanning grating mirror array working face 5, and the face type of the detector working face 6 is a common detector face type in the market.
The light 7 passing through the center of the 1 st micro-mirror scanning unit of the DMD working surface 3 passes through the center of the 1 st micro-mirror scanning unit 3-1 of the DMD working surface 3, the collimation subsystem 4 and the center of the 1 st MEMS scanning grating mirror unit 5-1 of the MEMS scanning grating mirror array working surface 5 respectively, and after the light is dispersed and deflected by the 1 st MEMS scanning grating mirror unit 5-1 of the MEMS scanning grating mirror array working surface 5, the obtained dispersion spectrum has the wavelength of lambda1、λ2Are incident to the fixed points M and N, respectively.
The light 8 passing through the center of the middle micro-mirror scanning unit of the DMD working surface 3 passes through the center of the middle micro-mirror scanning unit 3-2 of the DMD working surface 3, the center of the collimation subsystem 4 and the center of the middle MEMS scanning grating mirror unit 5-2 of the MEMS scanning grating mirror array working surface 5 respectively, and after the light is dispersed and deflected by the middle MEMS scanning grating mirror unit 5-2 of the MEMS scanning grating mirror array working surface 5, the dispersed light is obtainedWavelength in the spectrum is λ1、λ2Respectively, are incident to the fixed points M and N.
The light 9 passing through the center of the last 1 micromirror scanning unit of the DMD working surface 3 passes through the center of the last 1 micromirror scanning unit 3-3 of the DMD working surface 3, the collimation subsystem 4 and the center of the last 1 MEMS scanning grating mirror unit 5-3 of the MEMS scanning grating mirror array working surface 5 respectively, and after the light is dispersed and deflected by the last 1 MEMS scanning grating mirror unit 5-3 of the MEMS scanning grating mirror array working surface 5, the obtained dispersion spectrum has the wavelength of lambda1、λ2Are incident to the fixed points M and N, respectively.
The spectrum acquisition principle of the spectral imaging system and method based on MEMS provided by the invention is shown in FIG. 6. By controlling the 2K +1 micro-mirror scanning units and the 2K +1 MEMS scanning grating mirror units to be in an ON working state simultaneously in sequence, the target image is scanned in rows, and then 2K +1 dispersive spectrograms are obtained ON the same area of the working surface 6 of the detector, so that the acquisition of a target three-dimensional data cube is completed. The spectrum acquisition principle process of the MEMS-based spectrum imaging system and method provided by the invention specifically comprises the following steps of:
step 1: referring to fig. 6, the 1 st micromirror scanning unit of the DMD working surface 3 and the 1 st MEMS scanning grating mirror unit of the MEMS scanning grating mirror array 5 are controlled to be simultaneously in an "ON" working state, the other micromirror scanning units and the other MEMS scanning grating mirror units are in an "OFF" state, light of the 1 st column of target images is firstly reflected by the 1 st micromirror scanning unit to enter the collimation subsystem 4, is collimated by the collimation subsystem 4 and then parallelly emitted to the MEMS scanning grating mirror array working surface 5, and is then dispersed and reflected by the 1 st MEMS scanning grating mirror unit, and the obtained emergent dispersion spectrum is imaged ON the detector working surface 6. Referring to fig. 7, the direction of the spectral dispersion is defined as the X-axis direction, and the Y-axis direction perpendicular to the X-axis direction is the spatial position direction. The spectrum of the 1 st column target image is sequentially expanded along the X-axis direction according to different wavelengths, and the spectral components corresponding to different spatial positions are obtained in the Y-axis direction. The detector working surface 6 records and stores a dispersion spectrogram of a 1 st column of target images, and the reflection work of a 1 st micro-mirror scanning unit and the dispersion deflection work of a 1 st MEMS scanning grating mirror unit are finished, so that the spectral imaging of the 1 st column of target images is completed;
step 2: referring to fig. 6, the 2 nd micromirror scanning unit of the DMD working surface 3 and the 2 nd MEMS scanning grating mirror unit of the MEMS scanning grating mirror array working surface 5 are controlled to be simultaneously in an "ON" working state, the other micromirror scanning units and the other MEMS scanning grating mirror units are in an "OFF" state, light of the 2 nd row of target images is firstly reflected by the 2 nd micromirror scanning unit to enter the collimation subsystem 4, is collimated by the collimation subsystem 4 and then parallelly emitted to the MEMS scanning grating mirror array working surface 5, and is then dispersed and reflected by the 2 nd MEMS scanning grating mirror unit, and the obtained emergent dispersion spectrum is imaged ON the detector working surface 6. Referring to fig. 7, although the target image is shifted in the horizontal direction, the position of the dispersed spectrum on the detector working surface 6 is not changed. The working surface 6 of the detector records and stores the dispersive spectrogram at the moment, the reflection work of the 2 nd micro-mirror scanning unit and the dispersive deflection work of the 2 nd MEMS scanning grating mirror unit are finished, and the spectral imaging of the 2 nd row of target images is finished;
and step 3: controlling the 3 rd and 4 … … 2K micromirror scanning units of the DMD working surface 3 and the 3 rd and 4 … … 2K MEMS scanning grating mirror units of the MEMS scanning grating mirror array working surface 5 to be in an ON working state at the same time in sequence, synchronously recording and storing corresponding dispersion spectrograms by the detector working surface 6, and finishing spectral imaging of the 3 rd and 4 … … 2K row target images;
and 4, step 4: referring to fig. 6, the 2K +1 st micromirror scanning unit of the DMD working surface 3 and the 2K +1 st MEMS scanning grating mirror unit of the MEMS scanning grating mirror array working surface 5 are controlled to be simultaneously in an "ON" working state, the other micromirror scanning units and the other MEMS scanning grating mirror units are in an "OFF" state, light of the 2K +1 th row of target images is firstly reflected by the 2K +1 st micromirror scanning unit to enter the collimation subsystem 4, is collimated by the collimation subsystem 4 and then parallelly emitted to the MEMS scanning grating mirror array working surface 5, is then dispersed and reflected by the 2K +1 st MEMS scanning grating mirror unit, and the obtained emission dispersion spectrum is imaged ON the detector working surface 6. Referring to fig. 7, since the spectral positions of the spatial positions of the target images in different rows in the X-axis direction are not changed, the spectral imaging of the entire target can be completed as long as the detector working surface 6 is ensured to completely acquire the dispersive spectrum of any row of target images. The working surface 6 of the detector records and stores the dispersive spectrogram at the moment, the reflection work of the 2K +1 micro-mirror scanning unit and the dispersive deflection work of the 2K +1 MEMS scanning grating mirror unit are finished, and the spectral imaging of the 2K +1 row target image is completed;
and 5: and (3) carrying out data processing on the 2K +1 dispersive spectrograms acquired by the working face 6 of the detector to obtain two-dimensional space scene and one-dimensional spectral information of the target 1, namely a complete three-dimensional data cube.
Advantageous effects
1. The dispersion spectrum deviation phenomenon caused by 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 position of the dispersion spectrum obtained by the method is fixed in the working period of the DMD and the MEMS scanning grating mirror array;
2. compared with the existing scanning type spectral imaging method based on the DMD, the MEMS scanning grating mirror array has the functions of dispersion light splitting and deflection at the same time, and extra light splitting elements such as blazed gratings are not needed.
3. And a special surface detector is not required to be selected, a surface detector with a large length-width ratio is not required to be customized, the system cost is effectively reduced, and the spectral resolution of the system is improved. The invention can greatly reduce the total length of the dispersion spectrum, and the length of the working surface of the detector only needs to accommodate the dispersion spectrum generated by a certain micromirror scanning unit of the DMD, thereby allowing the dispersion spectrum to be spread more widely and obtaining higher spectral resolution.
Drawings
FIG. 1: comparison graph of position change of dispersive spectrum in two existing scanning type spectral imaging methods based on DMD
FIG. 2: spectral imaging system composition schematic diagram based on MEMS
FIG. 3: the target image is divided by the micro-mirror scanning unit of the DMD working surface according to the column
FIG. 4: MEMS scanning grating mirror array composition schematic diagram
FIG. 5: relative position distribution schematic diagram of MEMS scanning grating mirror array and fixed point M, N
FIG. 6: spectrum acquisition principle schematic diagram of spectrum imaging system and method based on MEMS
FIG. 7: target image spectrum collection principle schematic diagram
Wherein: 1. a target; 2. an imaging subsystem; 3, DMD working surface; 3-1. scanning unit of the 1 st micro mirror on the working surface of the DMD; 3-2, scanning unit of a middle micro mirror of the working surface of the DMD; 3-3, scanning units of the last 1 micro mirror on the working surface of the DMD; 4. a collimation subsystem; 5, scanning the grating mirror array working surface by the MEMS; 5-1, scanning the 1 st MEMS scanning grating mirror unit of the array working surface of the MEMS scanning grating mirror; 5-2, scanning the middle MEMS scanning grating mirror unit of the working surface of the MEMS scanning grating mirror array; 5-3, the last 1 MEMS scanning grating mirror unit on the working surface of the MEMS scanning grating mirror array; 6. a detector working surface; 7. light passing through the center of the 1 st micro-mirror scanning unit of the DMD working surface; 8. light passing through the center of a scanning unit of a middle micro mirror of the working surface of the DMD; 9. and light passing through the center of the last 1 micro-mirror scanning unit of the DMD working surface.
Detailed Description
Example 1
A MEMS-based spectral imaging system and method of the present embodiment, referring to fig. 2, the system mainly comprises a target 1, an imaging subsystem 2, a DMD working surface 3, a 1 st micro-mirror scanning unit 3-1 of the DMD working surface, a middle micro-mirror scanning unit 3-2 of the DMD working surface, a last 1 micro-mirror scanning unit 3-3 of the DMD working surface, a collimation subsystem 4, a MEMS scanning grating mirror array working surface 5, a 1 st MEMS scanning grating mirror unit 5-1 of the MEMS scanning grating mirror array working surface, a middle MEMS scanning grating mirror unit 5-2 of the MEMS scanning grating mirror array working surface, a last 1 MEMS scanning grating mirror unit 5-3 of the MEMS scanning grating mirror array working surface, a detector working surface 6, light 7 passing through the center of the 1 st micro-mirror scanning unit of the DMD working surface, light 8 passing through the center of the middle scanning micro-mirror unit of the DMD working surface and light 9 passing through the center of the last 1 scanning unit of the DMD working surface. Eyes of a userThe target 1 and the DMD working surface 3 are respectively arranged at the object plane and the image plane of the imaging subsystem 2, and a target image formed by the target 1 through the imaging subsystem 2 is divided by the micro-mirror scanning units of the DMD working surface 3 in columns. The collimation subsystem 4 changes the light reflected from the DMD working surface 3 into parallel light, the MEMS scanning grating mirror array working surface 5 is located in the light exit direction of the collimation subsystem 4, the number of MEMS scanning grating mirror units in the MEMS scanning grating mirror array working surface 5 is the same as the number of micromirror scanning units in the DMD working surface 3, it is required that each micromirror scanning unit in the DMD working surface 3 must reflect the corresponding column of target images into the collimation subsystem 4 for collimation when in the deflection working state, the obtained parallel light is incident on the corresponding MEMS scanning grating mirror unit in the MEMS scanning grating mirror array working surface 5 for light splitting, and simultaneously, it is required that the light passing through the center of each micromirror scanning unit in the DMD working surface 3 also passes through the center of the corresponding MEMS scanning grating mirror unit in the MEMS scanning grating mirror array working surface 5, for example, the light 7 passing through the center of the 1 st micromirror scanning unit in the DMD working surface, The light 8 passing through the center of the middle micro-mirror scanning unit of the DMD working surface and the light 9 passing through the center of the last 1 micro-mirror scanning unit of the DMD working surface respectively pass through the centers of the 1 st, 5-1, 5-2 and 5-3 MEMS scanning grating mirror units of the MEMS scanning grating mirror array working surface 5. By changing the deflection angle of each MEMS scanning grating mirror unit in the MEMS scanning grating mirror array working surface 5, the dispersed spectrum which is split and emitted by each MEMS scanning grating mirror unit is incident to the same area of the detector, namely the minimum wavelength lambda in the dispersed spectrum1And maximum wavelength lambda2The light is incident to the beginning and end fixed points M and N of the dispersion spectrum region, and all the finally obtained dispersion spectra are imaged at the same position of the working face 6 of the detector.
The imaging subsystem 2 is a telescopic lens and is responsible for converging the reduced image of the target 1 on the DMD working surface 3.
The DMD working surface 3 is rectangular, and referring to fig. 3, it is composed of a micromirror array, the number of columns and rows of the micromirror array are a 1024 and b 768, respectively, the width of each micromirror is u 13.68 μm, the image of the target 1 is divided into 251 columns by the micromirror scanning unit of the DMD working surface 3, K125, each micromirror scanning unit contains x 4 columns of micromirrors, the width of each micromirror scanning unit is xu 54.72 μm, x (2K +1) is equal to or less than a, 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, wherein the micromirror scanning unit in the state can reflect a selected target image to the collimation subsystem 4; the other deflection state is the "OFF" state, in which the micromirror scanning unit is responsible for reflecting the selected target image out of the system.
The collimation subsystem 4 is composed of a lens group and is responsible for collimating the light reflected by the DMD working surface 3, so that the light is incident on the MEMS scanning grating mirror array working surface 5 in parallel.
The MEMS scanning grating mirror array working surface 5 is formed by grating lines on a long scanning micro mirror array by utilizing an MEMS technology, and can realize two functions of dispersion light splitting and scanning deflection at the same time. Referring to fig. 4, the MEMS scanning grating mirror array working surface 5 includes 251 MEMS scanning grating mirror units, a grating line width d is 3.5 μm, a diffraction order m is 1, a width t of each MEMS scanning grating mirror unit is 100 μm, and a center point of the ith MEMS scanning grating mirror unit is Oi(i is a positive integer, i ∈ [1,251 ]]). Referring to FIG. 5, the spectral dispersion length on the detector face 6 is MN, and the wavelength λ is 400nm,600nm]The MEMS scanning grating mirror array working surface 5 and the detector working surface 6 are required to be parallel to each other, the cross section extension line of the MEMS scanning grating mirror array working surface 5 and the perpendicular line of the detector working surface 6 at the point N are intersected at the point O, the length h of ON is 100mm, the length s of MN is 30mm, OO251Is 200mm, satisfies l > s, requires that each MEMS scanning grating mirror unit can only deflect clockwise, and has a deflection angle beta when the ith MEMS scanning grating mirror unit is in an operating state of' ONi，
βiIncidence angle alpha of MEMS scanning grating mirror unit corresponding to 0020 DEG, the diffraction angles corresponding to the light rays having dispersion wavelengths of 400nm and 600nm, respectivelyIs thetai1And thetai2They are incident to fixed points M and N, respectively. Introducing an intermediate variable & lt NO according to the known parametersiO＝γi，∠MOiO＝δi，βiThe solving method of (2) is as follows:
βisatisfies the following formula:
wherein:
d(sin(α0+βi)+sinθi1)＝mλ1 (3)
d(sin(α0+βi)+sinθi2)＝mλ2 (4)
(4) - (3) and substituting the formulas (1) and (2) into the formula:
the equation (5) is expanded and substituted into the equation cos2βi+sin2βi Get 1, one-dimensional quadratic equation:
2(1-sinγisinδi-cosγicosδi)sin2βi+2c(sinγi-sinδi)sinβi
+c2-(cosγi-cosδi)2＝0
get it solved
Namely, it is
If there are two solutions, the smaller value is taken, wherein:
A＝2(1-sinγi sinδi-cosγi cosδi)
B＝2c(sinγi-sinδi)
D＝c2-(cosγi-cosδi)2
the detector working surface 6 is responsible for collecting the dispersion spectrum emitted by the MEMS scanning grating mirror array working surface 5, and the surface type of the detector working surface 6 is a common detector surface type in the market.
The light 7 passing through the center of the 1 st micro-mirror scanning unit of the DMD working surface 3 passes through the center of the 1 st micro-mirror scanning unit 3-1 of the DMD working surface 3, the collimation subsystem 4 and the center of the 1 st MEMS scanning grating mirror unit 5-1 of the MEMS scanning grating mirror array working surface 5 respectively, and after the light is dispersed and deflected by the 1 st MEMS scanning grating mirror unit 5-1 of the MEMS scanning grating mirror array working surface 5, the light with the wavelength of 400nm and the light with the wavelength of 600nm in the obtained dispersion spectrum are incident to the fixed points M and N respectively.
The light 8 passing through the center of the middle micromirror scanning unit of the DMD working surface 3 passes through the center of the middle micromirror scanning unit 3-2 of the DMD working surface 3, the collimation subsystem 4 and the center of the middle MEMS scanning grating mirror unit 5-2 of the MEMS scanning grating mirror array working surface 5 respectively, and after the light is dispersed and deflected by the middle MEMS scanning grating mirror unit 5-2 of the MEMS scanning grating mirror array working surface 5, the light with the wavelength of 400nm and the light with the wavelength of 600nm in the obtained dispersion spectrum are incident to the fixed points M and N respectively.
The light 9 passing through the center of the last 1 micromirror scanning unit of the DMD working surface 3 passes through the center of the last 1 micromirror scanning unit 3-3 of the DMD working surface 3, the collimation subsystem 4 and the center of the last 1 MEMS scanning grating mirror unit 5-3 of the MEMS scanning grating mirror array working surface 5, respectively, and after being dispersed and deflected by the last 1 MEMS scanning grating mirror unit 5-3 of the MEMS scanning grating mirror array working surface 5, the light with the wavelength of 400nm and the light with the wavelength of 600nm in the obtained dispersion spectrum are respectively incident to the fixed points M and N.
The spectrum acquisition principle of the spectral imaging system and method based on MEMS provided by the invention is shown in FIG. 6. By controlling 251 micromirror scanning units and 251 MEMS scanning grating mirror units to be in an ON working state simultaneously in sequence, the object image is scanned in rows, 251 dispersive spectrograms are obtained ON the same area of the working surface 6 of the detector, and the acquisition of the object three-dimensional data cube is completed. The spectrum acquisition principle process of the MEMS-based spectrum imaging system and method provided by the invention specifically comprises the following steps of:
step 1: referring to fig. 6, the 1 st micromirror scanning unit of the DMD working surface 3 and the 1 st MEMS scanning grating mirror unit of the MEMS scanning grating mirror array 5 are controlled to be simultaneously in an "ON" working state, the other micromirror scanning units and the other MEMS scanning grating mirror units are in an "OFF" state, light of the 1 st column of target images is firstly reflected by the 1 st micromirror scanning unit to enter the collimation subsystem 4, is collimated by the collimation subsystem 4 and then parallelly emitted to the MEMS scanning grating mirror array working surface 5, and is then dispersed and reflected by the 1 st MEMS scanning grating mirror unit, and the obtained emergent dispersion spectrum is imaged ON the detector working surface 6. Referring to fig. 7, the direction of the spectral dispersion is defined as the X-axis direction, and the Y-axis direction perpendicular to the X-axis direction is the spatial position direction. The spectrum of the 1 st column target image is sequentially expanded along the X-axis direction according to different wavelengths, and the spectral components corresponding to different spatial positions are obtained in the Y-axis direction. The detector working surface 6 records and stores a dispersion spectrogram of a 1 st column of target images, and the reflection work of a 1 st micro-mirror scanning unit and the dispersion deflection work of a 1 st MEMS scanning grating mirror unit are finished, so that the spectral imaging of the 1 st column of target images is completed;
step 2: referring to fig. 6, the 2 nd micromirror scanning unit of the DMD working surface 3 and the 2 nd MEMS scanning grating mirror unit of the MEMS scanning grating mirror array working surface 5 are controlled to be simultaneously in an "ON" working state, the other micromirror scanning units and the other MEMS scanning grating mirror units are in an "OFF" state, light of the 2 nd row of target images is firstly reflected by the 2 nd micromirror scanning unit to enter the collimation subsystem 4, is collimated by the collimation subsystem 4 and then parallelly emitted to the MEMS scanning grating mirror array working surface 5, and is then dispersed and reflected by the 2 nd MEMS scanning grating mirror unit, and the obtained emergent dispersion spectrum is imaged ON the detector working surface 6. Referring to fig. 7, although the target image is shifted in the horizontal direction, the position of the dispersed spectrum on the detector working surface 6 is not changed. The working surface 6 of the detector records and stores the dispersive spectrogram at the moment, the reflection work of the 2 nd micro-mirror scanning unit and the dispersive deflection work of the 2 nd MEMS scanning grating mirror unit are finished, and the spectral imaging of the 2 nd row of target images is finished;
and step 3: controlling the 3 rd and 4 … … 250 th micromirror scanning units of the DMD working surface 3 and the 3 rd and 4 … … 250 th MEMS scanning grating mirror units of the MEMS scanning grating mirror array working surface 5 to be in an ON working state at the same time in sequence, synchronously recording and storing corresponding dispersive spectrograms by the detector working surface 6, and finishing the spectral imaging of the 3 rd and 4 … … 250 th row target images;
and 4, step 4: referring to fig. 6, the 251 th micromirror scanning unit of the DMD working surface 3 and the 251 th MEMS scanning grating mirror unit of the linear MEMS scanning grating mirror array working surface 5 are controlled to be simultaneously in an "ON" working state, other micromirror scanning units and other MEMS scanning grating mirror units are in an "OFF" state, light of the 251 th column of target images is firstly reflected by the 251 th micromirror scanning unit to enter the collimation subsystem 4, is collimated by the collimation subsystem 4 and then parallelly emitted to the MEMS scanning grating mirror array working surface 5, and is then dispersed and reflected by the 251 th MEMS scanning grating mirror unit, and the obtained emergent dispersion spectrum is imaged ON the detector working surface 6. Referring to fig. 7, since the spectral positions of the spatial positions of different columns of target images in the X-axis direction are not changed, the spectral imaging of the whole target can be completed as long as the detector working surface 6 is ensured to completely acquire the dispersive spectrum of any one column of target images. The working surface 6 of the detector records and stores the dispersive spectrogram at the moment, the reflection work of the 251 th micro-mirror scanning unit and the dispersive deflection work of the 251 th MEMS scanning grating mirror unit are finished, and the spectral imaging of the 251 th row target image is completed;
and 5: and (3) carrying out data processing on 251 dispersive spectrograms acquired by the working face 6 of the detector to obtain two-dimensional space scene and one-dimensional spectral information of the target 1, namely a complete three-dimensional data cube.
Example 2
A MEMS-based spectral imaging system and method of the present embodiment, referring to fig. 2, the system mainly comprises a target 1, an imaging subsystem 2, a DMD working surface 3, a 1 st micro-mirror scanning unit 3-1 of the DMD working surface, a middle micro-mirror scanning unit 3-2 of the DMD working surface, a last 1 micro-mirror scanning unit 3-3 of the DMD working surface, a collimation subsystem 4, a MEMS scanning grating mirror array working surface 5, a 1 st MEMS scanning grating mirror unit 5-1 of the MEMS scanning grating mirror array working surface, a middle MEMS scanning grating mirror unit 5-2 of the MEMS scanning grating mirror array working surface, a last 1 MEMS scanning grating mirror unit 5-3 of the MEMS scanning grating mirror array working surface, a detector working surface 6, light 7 passing through the center of the 1 st micro-mirror scanning unit of the DMD working surface, light 8 passing through the center of the middle scanning micro-mirror unit of the DMD working surface and light 9 passing through the center of the last 1 scanning unit of the DMD working surface. The target 1 and the DMD working surface 3 are respectively arranged at the object plane and the image plane of the imaging subsystem 2, and a target image formed by the target 1 through the imaging subsystem 2 is divided by the micro-mirror scanning units of the DMD working surface 3 in columns. The collimation subsystem 4 changes the light reflected from the DMD working surface 3 into parallel light, the MEMS scanning grating mirror array working surface 5 is positioned in the light emergent direction of the collimation subsystem 4, the number of MEMS scanning grating mirror units in the MEMS scanning grating mirror array working surface 5 is the same as that of the micromirror scanning units in the DMD working surface 3, when each micromirror scanning unit in the DMD working surface 3 is in a deflection working state, a corresponding column of target images must be reflected to the collimation subsystem 4 for collimation, the obtained parallel light enters the corresponding MEMS scanning grating mirror unit in the MEMS scanning grating mirror array working surface 5 for light splitting, and meanwhile, the light passing through the center of each micromirror scanning unit in the DMD working surface 3 is required to pass through the MEMS scanning grating mirror units for light splitting as wellThe center of the corresponding MEMS scanning grating mirror unit in the array working surface 5, for example, a light ray 7 passing through the center of the 1 st micromirror scanning unit of the DMD working surface, a light ray 8 passing through the center of the middle micromirror scanning unit of the DMD working surface, and a light ray 9 passing through the center of the last 1 micromirror scanning unit of the DMD working surface pass through the centers of the 1 st MEMS scanning grating mirror unit 5-1, the middle MEMS scanning grating mirror unit 5-2, and the last 1 MEMS scanning grating mirror unit 5-3 of the MEMS scanning grating mirror array working surface, respectively. By changing the deflection angle of each MEMS scanning grating mirror unit in the MEMS scanning grating mirror array working surface 5, the dispersed spectrum which is split and emitted by each MEMS scanning grating mirror unit is incident to the same area of the detector, namely the minimum wavelength lambda in the dispersed spectrum1And maximum wavelength lambda2The light is incident to the beginning and end fixed points M and N of the dispersion spectrum region, and all the finally obtained dispersion spectra are imaged at the same position of the working face 6 of the detector.
The imaging subsystem 2 is a telescopic lens and is responsible for converging the reduced image of the target 1 on the DMD working surface 3.
The DMD working surface 3 is rectangular, and referring to fig. 3, it is composed of a micromirror array, the number of columns and rows of the micromirror array are a 1024 and b 768, respectively, the width of each micromirror is u 13.68 μm, the image of the target 1 is divided into 169 columns by the micromirror scanning unit of the DMD working surface 3, K84, each micromirror scanning unit contains x 6 columns of micromirrors, the width of each micromirror scanning unit is xu 82.08 μm, x (2K +1) is equal to or less than a, 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, wherein the micromirror scanning unit in the state can reflect a selected target image to the collimation subsystem 4; the other deflection state is the "OFF" state, in which the micromirror scanning unit is responsible for reflecting the selected target image out of the system.
The collimation subsystem 4 is composed of a lens group and is responsible for collimating the light reflected by the DMD working surface 3, so that the light is incident on the MEMS scanning grating mirror array working surface 5 in parallel.
The MEMS scanning grating mirror array working surface 5 is in a strip shape by using MEMS technologyThe grating ruling is carried out on the scanning micro-mirror array, and two functions of dispersion light splitting and scanning deflection can be simultaneously realized. Referring to fig. 4, the MEMS scanning grating mirror array working surface 5 includes 169 MEMS scanning grating mirror units, the width of the grating lines is d equal to 4 μm, the width of the diffraction order m is 1, the width of each MEMS scanning grating mirror unit is t equal to 160 μm, and the central point of the ith MEMS scanning grating mirror unit is Oi(i is a positive integer, i ∈ [1,169 ]]). Referring to FIG. 5, the spectral dispersion length on the detector face 6 is MN, and the wavelength λ ∈ [650nm,780nm ]]The MEMS scanning grating mirror array working surface 5 and the detector working surface 6 are required to be parallel to each other, the cross section extension line of the MEMS scanning grating mirror array working surface 5 and the perpendicular line of the detector working surface 6 at the point N are intersected at the point O, the length h of ON is 50mm, the length s of MN is 30mm, and OO169Is 200mm, satisfies l > s, requires that each MEMS scanning grating mirror unit can only deflect clockwise, and has a deflection angle beta when the ith MEMS scanning grating mirror unit is in an operating state of' ONi，
βiIncidence angle alpha of MEMS scanning grating mirror unit corresponding to 0020 DEG, and the diffraction angles corresponding to the light rays having dispersion wavelengths of 650nm and 780nm are respectively thetai1And thetai2They are incident to fixed points M and N, respectively. Introducing an intermediate variable & lt NO according to the known parametersiO＝γi，∠MOiO＝δi，βiThe solving method of (2) is as follows:
βisatisfies the following formula:
wherein:
d(sin(α0+βi)+sinθi1)＝mλ1 (3)
d(sin(α0+βi)+sinθi2)＝mλ2 (4)
(4) - (3) and substituting the formulas (1) and (2) into the formula:
the equation (5) is expanded and substituted into the equation cos2βi+sin2βi Get 1, one-dimensional quadratic equation:
2(1-sinγisinδi-cosγicosδi)sin2βi+2c(sinγi-sinδi)sinβi
+c2-(cosγi-cosδi)2＝0
get it solved
Namely that
If there are two solutions, the smaller value is taken, wherein:
A＝2(1-sinγi sinδi-cosγi cosδi)
B＝2c(sinγi-sinδi)
D＝c2-(cosγi-cosδi)2
the detector working surface 6 is responsible for collecting the dispersion spectrum emitted by the MEMS scanning grating mirror array working surface 5, and the surface type of the detector working surface 6 is a common detector surface type in the market.
The light 7 passing through the center of the 1 st micro-mirror scanning unit of the DMD working surface 3 passes through the center of the 1 st micro-mirror scanning unit 3-1 of the DMD working surface 3, the collimation subsystem 4 and the center of the 1 st MEMS scanning grating mirror unit 5-1 of the MEMS scanning grating mirror array working surface 5 respectively, and after the light is dispersed and deflected by the 1 st MEMS scanning grating mirror unit 5-1 of the MEMS scanning grating mirror array working surface 5, light with the wavelength of 650nm and light with the wavelength of 780nm in the obtained dispersion spectrum are incident to fixed points M and N respectively.
The light 8 passing through the center of the middle micromirror scanning unit of the DMD working surface 3 passes through the center of the middle micromirror scanning unit 3-2 of the DMD working surface 3, the collimation subsystem 4 and the center of the middle MEMS scanning grating mirror unit 5-2 of the MEMS scanning grating mirror array working surface 5 respectively, and after the light is dispersed and deflected by the middle MEMS scanning grating mirror unit 5-2 of the MEMS scanning grating mirror array working surface 5, the light with the wavelength of 650nm and the light with the wavelength of 780nm in the obtained dispersion spectrum are respectively incident to the fixed points M and N.
The light 9 passing through the center of the last 1 micromirror scanning unit of the DMD working surface 3 passes through the center of the last 1 micromirror scanning unit 3-3 of the DMD working surface 3, the collimation subsystem 4 and the center of the last 1 MEMS scanning grating mirror unit 5-3 of the MEMS scanning grating mirror array working surface 5, respectively, and after being dispersed and deflected by the last 1 MEMS scanning grating mirror unit 5-3 of the MEMS scanning grating mirror array working surface 5, the light with the wavelength of 650nm and 780nm in the obtained dispersion spectrum is incident to the fixed points M and N, respectively.
The spectrum acquisition principle of the spectral imaging system and method based on MEMS provided by the invention is shown in FIG. 6. The 169 micro-mirror scanning units and the 169 MEMS scanning grating mirror units are controlled to be in an ON working state simultaneously in sequence, so that the target image is scanned in rows, 169 dispersive spectrograms are obtained ON the same area of the working surface 6 of the detector, and the acquisition of a target three-dimensional data cube is completed. The spectrum acquisition principle process of the MEMS-based spectral imaging system and method provided by the invention specifically comprises the following steps of:
step 1: referring to fig. 6, the 1 st micromirror scanning unit controlling the DMD working surface 3 and the 1 st MEMS scanning grating mirror unit controlling the MEMS scanning grating mirror array 5 are simultaneously in an "ON" working state, the other micromirror scanning units and the other MEMS scanning grating mirror units are in an "OFF" state, light of the 1 st column of target images is reflected by the 1 st micromirror scanning unit first to enter the collimation subsystem 4, is collimated by the collimation subsystem 4 and then is emitted in parallel to the MEMS scanning grating mirror array working surface 5, and is dispersed and reflected by the 1 st MEMS scanning grating mirror unit, and the obtained emergent dispersion spectrum is imaged ON the detector working surface 6. Referring to fig. 7, the direction of the spectral dispersion is defined as the X-axis direction, and the Y-axis direction perpendicular to the X-axis direction is the spatial position direction. The spectrum of the 1 st column target image is sequentially expanded along the X-axis direction according to different wavelengths, and the spectral components corresponding to different spatial positions are obtained in the Y-axis direction. The detector working surface 6 records and stores a dispersion spectrogram of a 1 st column of target images, and the reflection work of a 1 st micro-mirror scanning unit and the dispersion deflection work of a 1 st MEMS scanning grating mirror unit are finished to finish the spectral imaging of the 1 st column of target images;
step 2: referring to fig. 6, the 2 nd micromirror scanning unit of the DMD working surface 3 and the 2 nd MEMS scanning grating mirror unit of the MEMS scanning grating mirror array working surface 5 are controlled to be simultaneously in an "ON" working state, the other micromirror scanning units and the other MEMS scanning grating mirror units are in an "OFF" state, light of the 2 nd row of target images is firstly reflected by the 2 nd micromirror scanning unit to enter the collimation subsystem 4, is collimated by the collimation subsystem 4 and then parallelly emitted to the MEMS scanning grating mirror array working surface 5, and is then dispersed and reflected by the 2 nd MEMS scanning grating mirror unit, and the obtained emergent dispersion spectrum is imaged ON the detector working surface 6. Referring to fig. 7, although the target image is shifted in the horizontal direction, the position of the dispersed spectrum on the detector working surface 6 is not changed. The working surface 6 of the detector records and stores the dispersive spectrogram at the moment, the reflection work of the 2 nd micro-mirror scanning unit and the dispersive deflection work of the 2 nd MEMS scanning grating mirror unit are finished, and the spectral imaging of the 2 nd row of target images is finished;
and step 3: controlling the 3 rd and 4 … … 168 th micromirror scanning units of the DMD working surface 3 and the 3 rd and 4 … … 168 th MEMS scanning grating mirror units of the MEMS scanning grating mirror array working surface 5 to be in an ON working state simultaneously in sequence, synchronously recording and storing corresponding dispersion spectrograms by the detector working surface 6, and finishing the spectral imaging of the 3 rd and 4 … … 168 th row target images;
and 4, step 4: referring to fig. 6, the 169 th micromirror scanning unit of the DMD working surface 3 and the 169 th MEMS scanning grating mirror unit of the linear MEMS scanning grating mirror array working surface 5 are controlled to be simultaneously in an "ON" working state, the other micromirror scanning units and the other MEMS scanning grating mirror units are in an "OFF" state, the light of the 169 th row of target images is firstly reflected by the 169 th micromirror scanning unit to enter the collimation subsystem 4, is collimated by the collimation subsystem 4, then is emitted in parallel to the MEMS scanning grating mirror array working surface 5, is then dispersed and reflected by the 169 th MEMS scanning grating mirror unit, and the obtained emission dispersion spectrum is imaged ON the detector working surface 6. Referring to fig. 7, since the spectral positions of the spatial positions of the target images in different rows in the X-axis direction are not changed, the spectral imaging of the entire target can be completed as long as the detector working surface 6 is ensured to completely acquire the dispersive spectrum of any row of target images. The working surface 6 of the detector records and stores the dispersive spectrogram at the moment, the reflection work of the 169 th micro-mirror scanning unit and the dispersive deflection work of the 169 th MEMS scanning grating mirror unit are finished, and the spectral imaging of the 169 th row of target images is finished;
and 5: and (3) carrying out data processing on the 169 dispersive spectrograms acquired by the working surface 6 of the detector to obtain two-dimensional space scene and one-dimensional spectral information of the target 1, namely a complete three-dimensional data cube.
Claims (2)
1. A spectral imaging system based on MEMS is characterized by mainly comprising a target 1, an imaging subsystem 2, a DMD working surface 3, a 1 st micro-mirror scanning unit 3-1 of the DMD working surface, a middle micro-mirror scanning unit 3-2 of the DMD working surface, a last 1 micro-mirror scanning unit 3-3 of the DMD working surface, a collimation subsystem 4, an MEMS scanning grating mirror array working surface 5, a 1 st ME of the MEMS scanning grating mirror array working surface5-1 of MS scanning raster mirror units, 5-2 of MEMS scanning raster mirror units in the middle of the working surface of the grating mirror array, 5-3 of the last 1 of the MEMS scanning raster mirror units of the working surface of the grating mirror array, 6 of the detector, 7 of light passing through the center of the 1 st micro-mirror scanning unit of the DMD working surface, 8 of light passing through the center of the middle micro-mirror scanning unit of the DMD working surface and 9 of light passing through the center of the last 1 micro-mirror scanning unit of the DMD working surface. The target 1 and the DMD working surface 3 are respectively arranged at the object plane and the image plane of the imaging subsystem 2, and a target image formed by the target 1 through the imaging subsystem 2 is divided by the micro-mirror scanning units of the DMD working surface 3 in columns. The collimation subsystem 4 changes the light reflected from the DMD working surface 3 into parallel light, the MEMS scanning grating mirror array working surface 5 is located in the light exit direction of the collimation subsystem 4, the number of MEMS scanning grating mirror units in the MEMS scanning grating mirror array working surface 5 is the same as the number of micromirror scanning units in the DMD working surface 3, it is required that each micromirror scanning unit in the DMD working surface 3 must reflect the corresponding column of target images into the collimation subsystem 4 for collimation when in the deflection working state, the obtained parallel light is incident on the corresponding MEMS scanning grating mirror unit in the MEMS scanning grating mirror array working surface 5 for light splitting, and simultaneously, it is required that the light passing through the center of each micromirror scanning unit in the DMD working surface 3 also passes through the center of the corresponding MEMS scanning grating mirror unit in the MEMS scanning grating mirror array working surface 5, for example, the light 7 passing through the center of the 1 st micromirror scanning unit in the DMD working surface, The light 8 passing through the center of the middle micro-mirror scanning unit of the DMD working surface and the light 9 passing through the center of the last 1 micro-mirror scanning unit of the DMD working surface respectively pass through the centers of the 1 st, 5-1, 5-2 and 5-3 MEMS scanning grating mirror units of the MEMS scanning grating mirror array working surface 5. By changing the deflection angle of each MEMS scanning grating mirror unit in the MEMS scanning grating mirror array working surface 5, the dispersed spectrum which is split and emitted by each MEMS scanning grating mirror unit is incident to the same area of the detector, namely the minimum wavelength lambda in the dispersed spectrum1And maximum wavelength lambda2The light is incident to the initial and final fixed points M and N of the dispersion spectrum area, and all finally obtained dispersion spectrums are imaged to work in a detectorThe same position of the face 6.
The imaging subsystem 2 is responsible for converging the reduced or enlarged image of the target 1 on the DMD working surface 3.
The DMD working surface 3 is rectangular and is composed of a micromirror array, the number of columns and rows of the micromirror array are a and b respectively, the width of each micromirror is u, the image of a target 1 is divided into 2K +1 columns (K is a positive integer) by the micromirror scanning unit of the DMD working surface 3 according to the columns, each micromirror scanning unit comprises x columns of micromirrors, the width of each micromirror scanning unit is xu, x (2K +1) is less than or equal to a, the deflection angle of each micromirror is only positive or negative, most of the deflection angles are +/-12 degrees, +/-10 degrees, +/-17 degrees and the like. One of the deflection states is selected as an 'ON' working state, and the micromirror scanning unit in the state can reflect the selected target image to the collimation subsystem 4; the other deflection state is the "OFF" state, in which the micromirror scanning unit is responsible for reflecting the selected target image out of the system.
The collimation subsystem 4 may be composed of a lens group or a concave spherical reflector and other components, and is responsible for collimating the light reflected from the DMD working surface 3 and making the light incident in parallel on the MEMS scanning grating mirror array working surface 5.
The MEMS scanning grating mirror array working surface 5 is formed by grating lines on a long scanning micro mirror array by utilizing an MEMS technology, and can realize two functions of dispersion light splitting and scanning deflection at the same time; the MEMS scanning grating mirror array working surface 5 comprises 2K +1 MEMS scanning grating mirror units, the width of a grating groove is d, the diffraction order is m, the width of each MEMS scanning grating mirror unit is t, and the central point of the ith MEMS scanning grating mirror unit is Oi(i is a positive integer, i is an element [1,2K +1 ]]). The length of spectral dispersion on the working surface 6 of the detector is MN, and the wavelength lambda belongs to lambda1,λ2]The MEMS scanning grating mirror array working surface 5 and the detector working surface 6 are required to be parallel to each other, the cross section extension line of the MEMS scanning grating mirror array working surface 5 and the perpendicular line of the detector working surface 6 at the N point are intersected at the O point, the ON length is h, the MN length is s, OO2K+1Length l, l > s, requires that each MEMS scanning grating mirror unit can deflect only clockwise when the ith MEMS scanning grating mirror unit is in the first positionWhen the mirror unit is in the working state 'ON', the deflection angle is betai，
βiWhen the incidence angle of the corresponding MEMS scanning grating mirror unit is 0, the incidence angle is alpha0Dispersion wavelength is λ1And λ2The diffraction angles corresponding to the light rays are respectively thetai1And thetai2They are incident to fixed points M and N, respectively. By reasonably selecting h, s, l, t, d and lambda1、λ2So that the dispersion spectrum obtained by the dispersion and reflection of the ith MEMS scanning grating mirror unit can be incident on a fixed region MN, i.e. beta, on the detectoriThere is a solution. Introducing an intermediate variable & lt NO according to the known parametersiO＝γi，∠MOiO＝δiGiving betaiThe solving method of (1):
βisatisfies the following formula:
wherein:
d(sin(α0+βi)+sinθi1)＝mλ1 (3)
d(sin(α0+βi)+sinθi2)＝mλ2 (4)
(4) and substituting the formulas (1) and (2) into (3):
the equation (5) is expanded and substituted into the equation cos2βi+sin2βiGet 1, one-dimensional quadratic equation:
2(1-sinγisinδi-cosγicosδi)sin2βi+2c(sinγi-sinδi)sinβi+c2-(cosγi-cosδi)2＝0
get it solved
Namely, it is
If there are two solutions, the smaller value is taken, wherein:
A＝2(1-sinγisinδi-cosγicosδi)
B＝2c(sinγi-sinδi)
D＝c2-(cosγi-cosδi)2
the detector working surface 6 is responsible for collecting the dispersion spectrum emitted by the MEMS scanning grating mirror array working surface 5, and the surface type of the detector working surface 6 is a common detector surface type in the market.
The light 7 passing through the center of the 1 st micro-mirror scanning unit of the DMD working surface 3 passes through the center of the 1 st micro-mirror scanning unit 3-1 of the DMD working surface 3, the collimation subsystem 4 and the center of the 1 st MEMS scanning grating mirror unit 5-1 of the MEMS scanning grating mirror array working surface 5 respectively, and after the light is dispersed and deflected by the 1 st MEMS scanning grating mirror unit 5-1 of the MEMS scanning grating mirror array working surface 5, the obtained dispersion spectrum has the wavelength of lambda1、λ2Light beam splitting ofRespectively incident on fixed points M and N.
The light 8 passing through the center of the middle micro-mirror scanning unit of the DMD working surface 3 passes through the center of the middle micro-mirror scanning unit 3-2 of the DMD working surface 3, the collimation subsystem 4 and the center of the middle MEMS scanning grating mirror unit 5-2 of the MEMS scanning grating mirror array working surface 5 respectively, and after the light is dispersed and deflected by the middle MEMS scanning grating mirror unit 5-2 of the MEMS scanning grating mirror array working surface 5, the obtained dispersion spectrum has the wavelength of lambda1、λ2Are incident to the fixed points M and N, respectively.
The light 9 passing through the center of the last 1 micromirror scanning unit of the DMD working surface 3 passes through the center of the last 1 micromirror scanning unit 3-3 of the DMD working surface 3, the collimation subsystem 4 and the center of the last 1 MEMS scanning grating mirror unit 5-3 of the MEMS scanning grating mirror array working surface 5 respectively, and after the light is dispersed and deflected by the last 1 MEMS scanning grating mirror unit 5-3 of the MEMS scanning grating mirror array working surface 5, the obtained dispersion spectrum has the wavelength of lambda1、λ2Are incident to the fixed points M and N, respectively.
2. A method of spectral imaging in accordance with the system of claim 1, comprising the steps of:
step 1: the 1 st micro-mirror scanning unit for controlling the DMD working surface 3 and the 1 st MEMS scanning grating mirror unit of the MEMS scanning grating mirror array 5 are simultaneously in an 'ON' working state, other micro-mirror scanning units and other MEMS scanning grating mirror units are in an 'OFF' state, light of a 1 st column of target images is firstly reflected by the 1 st micro-mirror scanning unit to enter the collimation subsystem 4, is collimated by the collimation subsystem 4 and then parallelly emitted to the MEMS scanning grating mirror array working surface 5, and is then dispersed and reflected by the 1 st MEMS scanning grating mirror unit, and the obtained emergent dispersion spectrum is imaged ON the detector working surface 6. 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 target image is sequentially expanded along the X-axis direction according to different wavelengths, and the spectral components corresponding to different spatial positions are obtained in the Y-axis direction. The detector working surface 6 records and stores a dispersion spectrogram of a 1 st column of target images, and the reflection work of a 1 st micro-mirror scanning unit and the dispersion deflection work of a 1 st MEMS scanning grating mirror unit are finished, so that the spectral imaging of the 1 st column of target images is completed;
step 2: the 2 nd micro-mirror scanning unit for controlling the DMD working surface 3 and the 2 nd MEMS scanning grating mirror unit of the MEMS scanning grating mirror array working surface 5 are in an ON working state at the same time, other micro-mirror scanning units and other MEMS scanning grating mirror units are in an OFF state, light of a 2 nd row of target images is firstly reflected by the 2 nd micro-mirror scanning unit to enter the collimation subsystem 4, is collimated by the collimation subsystem 4 and then parallelly emitted to the MEMS scanning grating mirror array working surface 5, is then subjected to dispersion and reflection by the 2 nd MEMS scanning grating mirror unit, and the obtained emergent dispersion spectrum is imaged ON the detector working surface 6. Although the target image is shifted in the horizontal direction, the position of its dispersed spectrum on the detector face 6 does not change. The working surface 6 of the detector records and stores the dispersive spectrogram at the moment, the reflection work of the 2 nd micro-mirror scanning unit and the dispersive deflection work of the 2 nd MEMS scanning grating mirror unit are finished, and the spectral imaging of the 2 nd row of target images is finished;
and step 3: controlling the 3 rd and 4 … … 2K micromirror scanning units of the DMD working surface 3 and the 3 rd and 4 … … 2K MEMS scanning grating mirror units of the MEMS scanning grating mirror array working surface 5 to be in an ON working state at the same time in sequence, synchronously recording and storing corresponding dispersion spectrograms by the detector working surface 6, and finishing spectral imaging of the 3 rd and 4 … … 2K row target images;
and 4, step 4: the 2K +1 micro-mirror scanning unit for controlling the DMD working surface 3 and the 2K +1 MEMS scanning grating mirror unit for controlling the MEMS scanning grating mirror array working surface 5 are simultaneously in an 'ON' working state, other micro-mirror scanning units and other MEMS scanning grating mirror units are in an 'OFF' state, light of a 2K +1 row of target images is firstly reflected by the 2K +1 micro-mirror scanning unit to enter the collimation subsystem 4, is collimated by the collimation subsystem 4 and then parallelly emitted to the MEMS scanning grating mirror array working surface 5, is then dispersed and reflected by the 2K +1 MEMS scanning grating mirror unit, and the obtained emitted dispersion spectrum is imaged ON the detector working surface 6. Because the spectral positions of the spatial positions of the target images in different rows in the X-axis direction are unchanged, the spectral imaging of the whole target can be completed as long as the working surface 6 of the detector can completely acquire the dispersion spectrum of any row of target images. The working surface 6 of the detector records and stores the dispersive spectrogram at the moment, the reflection work of the 2K +1 micro-mirror scanning unit and the dispersive deflection work of the 2K +1 MEMS scanning grating mirror unit are finished, and the spectral imaging of the 2K +1 row target image is completed;
and 5: and (3) carrying out data processing on the 2K +1 dispersive spectrograms acquired by the working face 6 of the detector to obtain two-dimensional space scene and one-dimensional spectral information of the target 1, namely a complete three-dimensional data cube.
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