CN115183870A - Broadband coding optical filter array and snapshot type hyperspectral camera - Google Patents
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Abstract
The invention relates to a broadband coding optical filter array which is used for modulating incident light from a target object and then emitting the modulated incident light to an image detector and comprises a plurality of periodic minimum repeating units formed by M filters, wherein each filter comprises a glass substrate, a first metal layer, a dielectric layer and a second metal layer which are sequentially arranged from bottom to top, the dielectric layer comprises a plurality of dielectric layer blocks with different film thicknesses, and the second metal layer is correspondingly arranged on the plurality of dielectric layer blocks. Compared with the prior art, the invention has the advantages of strong spectrum regulation and control capability, insensitivity to incident light angle and simple preparation.
Description
Technical Field
The invention relates to the technical field of optical imaging, in particular to a broadband coding optical filter array and a snapshot type hyperspectral camera.
Background
Spectral imaging techniques have wide applications in various fields of scientific research and daily life. For example, the method can be used in the aspects of life and production, such as printed matter authenticity monitoring, medicine component analysis, fruit and vegetable sorting, natural disaster monitoring and early warning, and the like.
There are many technical routes to achieve spectral imaging, for example: grating type spectral imager, interference type spectral imager, coded aperture snapshot type spectral imager, and filter type spectral imager, etc. The traditional spectral imaging system has large volume and strict requirements on working environment, and greatly limits the use of the traditional spectral imaging system in the fields of light and small unmanned aerial vehicles, consumer electronics products and the like. Therefore, light and small spectral imaging systems have been receiving wide attention. The on-chip spectral imaging system integrates the optical element and the detector on one chip, has compact structure and research prospect, and is expected to be popularized in daily life of people. However, the spatial resolution of conventional narrow-band filter-type spectral imaging techniques is limited by the nyquist sampling of the filter spectral array. In order to improve the spectral resolution of the spectral imager, filters with narrower pass bands and more filters need to be used, so that the spatial resolution of the target scene is reduced, and the contradiction that the spatial resolution and the spectral resolution of the target scene are mutually restricted exists.
The calculation type spectral imaging system based on the broadband coding optical filter receives spectral information of coded multi-wavelength aliasing through a detector, and the aliasing information is decoded by combining a compressed sensing algorithm, so that original spectral data can be recovered. According to the compressive sensing theory, the spectral curve of the filter can be properly designed to recover the sparse spectrum with high probability, and the number of the filters is far less than the expected number of spectral channels. The contradiction that the spatial resolution and the spectral resolution of the traditional optical filter type spectral imaging technology are mutually restricted can be broken.
The design of the broadband coding filter type spectral imaging system has two core elements: 1. designing a broadband coding filter; 2. in the form of a broadband encoding filter. In recent years, many researches have been made on the design of broadband coding filters, and from the past step-by-step design to the present end-to-end joint design, many research results have been obtained. However, the prior art still has the following problems:
(1) In the prior art, a pixel-level optical filter array for a snapshot-type hyperspectral camera needs to be obtained by electron beam direct writing processing, the thickness of a middle spacing layer needs to be changed in order to generate different spectrums, an alignment technology is used, multiple times of alignment needs to be carried out, the processing error is large, and the process is complex.
(2) In the prior art, the broadband coding filter with quantum dots and a Fabry-Perot structure is poor in spectrum regulation and control capability, so that the super-resolution reconstruction is low in precision.
(3) In the prior art, a broadband coding filter with a super-surface structure is adopted, and due to the abnormal angle sensitivity, the spectral transmittance changes greatly in a very small angle range, so that the characteristic of insensitivity to incident light angles is difficult to satisfy.
(4) In the prior art, the broadband coding optical filter adopting a thin film structure needs a practical overlay technology and is difficult to meet the characteristic of simple preparation.
In summary, the prior art lacks a broadband coding filter array which can simultaneously satisfy the requirements of strong spectrum regulation and control capability, insensitivity to incident light angle and simple preparation.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a broadband coding optical filter array and a snapshot type hyperspectral camera.
The purpose of the invention can be realized by the following technical scheme:
according to one aspect of the present invention, the present invention provides a wideband coding filter array, configured to modulate incident light from a target object and make the modulated incident light incident on an image detector, where the array includes a plurality of periodic minimum repeating units formed by M filters, each of the filters includes a glass substrate, a first metal layer, a dielectric layer, and a second metal layer, the dielectric layer includes a plurality of dielectric layer blocks with different film thicknesses, the second metal layer includes a plurality of second metal layer blocks, each of the second metal layer blocks is disposed on a corresponding dielectric layer block, and the dielectric layer blocks and the second metal layer blocks are in one-to-one correspondence.
Preferably, in each of the periodic minimum repeating units, the film thicknesses of all the dielectric layer blocks are different, the film thicknesses of the first metal layers of all the filters are equal, and the film thicknesses of the second metal layers of all the filters are equal.
Preferably, the glass substrate is a K9 layer, the first metal layer and the second metal layer are both Ag layers, and the dielectric layer is SiO 2 A layer.
Preferably, the film thickness of each layer in the optical filter is obtained by an optimal design method, and the optimal design method includes the following steps:
acquiring and calculating original data detected by the image detectors corresponding to the optical filters according to original spectral information of the target object and a spectral response function of each pixel of the image detector, and further acquiring the original data detected by the image detectors corresponding to each periodic repetition unit;
reconstructing a spectral curve of the target object through a spectral reconstruction algorithm based on the original data detected by the image detector corresponding to each periodic repetition unit;
and determining and solving an optimization problem according to the reconstructed spectral curve of the target object and the original spectral information of the target object, and obtaining the film thickness of each layer in the optical filter.
Preferably, the raw data detected by the image detector corresponding to each filter is:
I j =∫ λ S(λ)T j (λ)η(λ)dλ
in the formula, λ is wavelength, and S (λ) is original spectral information of the target object; t is j (λ) is the spectral transmittance response of the jth filter in each minimal repeating unit; η (λ) is a spectral response function of each pixel of the image detector, j =1,2, …, M; i is j Is the raw data detected by the image detector corresponding to the jth filter.
Preferably, the expression of the optimization problem is:
in the formula (I), the compound is shown in the specification,in order to optimize the film thickness of the obtained broadband coding filter,in order to optimize the parameters of the obtained spectral reconstruction algorithm, S (λ) is the original spectral information of the target object, decode (·) is a symbol representing the spectral reconstruction algorithm used, and I is the original data detected by the image detector.
Preferably, the first metal layer is arranged on the surface of the glass substrate by a magnetron sputtering method; arranging the dielectric layer on the second metal layer by a gray scale photoetching method; and arranging the second metal layer on the dielectric layer by a magnetron sputtering method.
Preferably, the wavelength range of the target object modulated by the broadband coding filter array is 400-700 nm.
According to another aspect of the present invention, the present invention provides a snapshot-type hyperspectral camera, which includes an image detector, and further includes the broadband coding optical filter array as described in any one of the above claims, where the broadband coding optical filter array modulates incident light from a target object and then emits the modulated incident light onto the image detector, and the image detector acquires aliasing information of space and spectrum of the target object, and then acquires information of space and spectrum of an original target object through a spectrum reconstruction algorithm.
Compared with the prior art, the invention has the following beneficial effects:
1. according to the broadband coding optical filter array, the medium layer blocks with different film thicknesses are arranged, so that the degree of freedom of the optical filter array is increased, the complexity of a spectral transmittance curve of the optical filter array is increased, and the characteristic that the optical filter array has strong spectral modulation capability is further met.
2. The broadband coding optical filter array provided by the invention processes all dielectric layer blocks with different film thicknesses at one time by a gray scale photoetching preparation technology, greatly reduces the preparation difficulty and can realize batch production.
3. The broadband coding filter array provided by the invention is improved on the basis of the Fabry-Perot structure, and the characteristic that the Fabry-Perot structure is insensitive to the incident light angle is continued, so that the broadband coding filter array provided by the invention has the characteristic that the broadband coding filter array is insensitive to the incident light angle.
Drawings
Fig. 1 is a schematic structural diagram of a wideband coding filter array provided in this embodiment.
Fig. 2 is a schematic structural diagram of a filter in the embodiment shown in fig. 1.
Fig. 3 is a schematic flow chart of an optimization design method of each filter segment in the embodiment shown in fig. 1.
FIG. 4 is a diagram showing the results of the embodiment shown in FIG. 1 for spectral imaging.
Labeled in the figure as: 1. the glass substrate, 2, the first metal layer, 3, the dielectric layer, 4, the second metal layer.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.
The embodiment provides a broadband coding filter array, including a plurality of periodic minimum repeating unit that constitute by a plurality of filters of M, every filter all includes by lower supreme glass substrate 1 that sets gradually, first metal level 2, dielectric layer 3 and second metal level 4, dielectric layer 3 includes the dielectric layer piece that a plurality of rete thicknesses differ, second metal level 4 includes a plurality of second metal level pieces, each second metal level piece all sets up on the dielectric layer piece that corresponds, dielectric layer piece and second metal level piece one-to-one.
The broadband coding optical filter array modulates incident light from a target object and then emits the modulated incident light to the image detector, the image detector directly obtains the space and spectrum aliasing information of the target object, and the space and spectrum information of the original target object can be obtained through a spectrum reconstruction algorithm.
Preferably, the first metal layer 2 is deposited on the surface of the glass substrate 1 by a magnetron sputtering technique, and the film thickness of the first metal layer 2 is h 1 A plurality of dielectric layer blocks are processed at one time by a gray level photoetching technology, and the film thickness of the dielectric layer blocks is h 2,j =[d 1,j ,d 2,j ,d 3,j ,d 4,j ,…,d n,j ](ii) a Depositing a second metal layer 4 on the dielectric layer 3 by a magnetron sputtering technology, wherein the film thickness of the second metal layer 4 is h 3 Where j =1,2, …, M.
As an optional implementation manner, in the periodic minimum repeating unit, the film thicknesses of all the dielectric layer blocks are different, the film thicknesses of the first metal layers 2 of all the optical filters are equal, and the film thicknesses of the second metal layers 4 of all the optical filters are equal.
As an optional implementation mode, the glass substrate 1 is a K9 layer, the first metal layer 2 is an Ag layer, and the dielectric layer 3 is SiO 2 Layer, the second metal layer 4 is an Ag layer.
Preferably, the band of the target object suitable for the broadband coding filter array is 400-700 nm, and the target object belongs to the visible light range.
Preferably, the spectral transmittance curve of the broadband coding filter array is almost constant in the incidence angle range of 0-6 degrees, i.e. the broadband coding filter array has the characteristic of being insensitive to the incident light angle.
Preferably, the thickness h of each layer in the optical filter 1 、h 2 And h 3 Are all obtained by an optimized design method,
as an alternative embodiment, the optimization design method includes a neural network algorithm.
Referring to FIG. 3, assuming that each minimal repeating unit has M filters, the spectral transmittance response of the jth filter is T j (λ), wherein j =1,2, …, M; the structure of the jth filter in the minimum repeating unit is as described above, and the thickness of the first metal layer 2 is h 1 The dielectric layer 3 comprises n different thicknesses h 2 The thickness of the second metal layer 4 is h 3 。
Acquiring and acquiring original data I detected by a detector corresponding to a jth optical filter according to original spectral information S (lambda) of a target object and a spectral response function eta (lambda) of each pixel of an image detector j 。
I j =∫ λ S(λ)T j (λ)η(λ)dλ
Where λ is wavelength, j =1,2, …, M.
Based on the raw data [ I ] detected by the image detector corresponding to each periodic minimum repeating unit 1 ,I 2 ,…,I M ]And reconstructing a spectral curve S of the target object by a spectral reconstruction algorithm * (λ);
And determining and solving an optimization problem according to the reconstructed spectral curve of the target object and the original spectral information of the target object, and obtaining the film thickness of each layer in the optical filter.
The solved optimization problem expression is as follows:
in the formula (I), the compound is shown in the specification,in order to optimize the film thickness of the obtained broadband coding filter,in order to optimize the parameters of the obtained spectral reconstruction algorithm, S (λ) is the original spectral information of the target object, decode (·) is a symbol representing the spectral reconstruction algorithm used, and I is the original data detected by the image detector.
Specifically, the whole optimization design process is a process from encoding to decoding, the optical filter encodes incident light information of the target object, the original data detected by the image detector corresponding to the optical filter is encoded information, and the detected information is restored to the original information of the target object through a decoding algorithm, such as a spectral reconstruction algorithm.
According to another aspect of the present embodiment, the present embodiment provides a snapshot-type hyperspectral camera, which includes an image detector, and further includes the broadband encoding optical filter array as described above, where the broadband encoding optical filter array modulates incident light from a target object and then emits the modulated incident light onto the image detector, and the image detector obtains information of aliasing of space and spectrum of the target object, and then obtains space and spectrum information of an original target object through a spectrum reconstruction algorithm.
Any combination of the above alternative embodiments can be used to obtain a better embodiment, and all the alternative embodiments are combined to obtain a best embodiment.
Assuming a periodic minimal repeating unit with 4 filters, the spectral transmittance response of the jth filter is T j (λ), wherein j =1,2,3,4;
the j filter in the periodic minimum repetition unit of the broadband coding filter array realizes the coding of the spectral information of the target scene, wherein j =1,2,3,4;
the structural parameters of each broadband coding filter are obtained by optimization design, the optimization design method refers to the method shown in fig. 2, and spatial and spectral information of the filter structure and the reconstructed target scene are optimized and designed jointly by a neural network method;
the structure of the first filter in the periodic minimum repeating unit is as follows: selecting a material K9 as a glass substrate 1, selecting a material Ag as a first metal layer 2 and a second metal layer 4, and selecting a material SiO2 as a dielectric layer 3; depositing a first metal layer 2 on a glass substrate 1 by a magnetron sputtering technology, wherein the thickness of the first metal layer 2 is 11.01nm; dividing the medium layer 3 into 4 medium layer blocks, wherein the 4 medium layer blocks correspond to 4 different film layer thicknesses h 2,j =[1886,1165,1735,2003]nm, preparing a dielectric layer 3 above the first metal layer 2 by a gray scale photoetching technology; finally, a second metal layer 4 with the thickness of 9.74nm is deposited on the dielectric layer 3 through a magnetron sputtering technology.
The structure of the second filter in the periodic minimum repeating unit is as follows: the material K9 was chosen as a glass liningThe method comprises the following steps of 1, selecting Ag as a first metal layer 2 and a second metal layer 4, and selecting SiO2 as a dielectric layer 3; depositing a first metal layer 2 on a glass substrate 1 by a magnetron sputtering technology, wherein the thickness of the deposited second metal layer 2 is 11.01nm; dividing the medium layer 3 into 4 medium layer blocks, wherein the 4 medium layer blocks correspond to 4 different film layer thicknesses h 2,j =[2480,764.9,1085,2510]nm, preparing a dielectric layer 3 above the first metal layer 2 by a gray scale photoetching technology; finally, a second metal layer 4 with the thickness of 9.74nm is deposited on the dielectric layer 3 through a magnetron sputtering technology.
The structure of the third filter in the periodic minimum repeating unit is as follows: selecting a material K9 as a glass substrate 1, selecting a material Ag as a first metal layer 2 and a second metal layer 4, and selecting a material SiO2 as a dielectric layer 3; depositing a first metal layer 2 on a glass substrate 1 by a magnetron sputtering technology, wherein the thickness of the deposited second metal layer 2 is 11.01nm; dividing the medium layer 3 into 4 medium layer blocks, wherein the 4 medium layer blocks correspond to 4 different film layer thicknesses h 2,j =[2401,1105,1105,713]nm, preparing a dielectric layer 3 above the first metal layer 2 by a gray scale photoetching technology; finally, a second metal layer 4 with the thickness of 9.74nm is deposited on the dielectric layer 3 through a magnetron sputtering technology.
The structure of the fourth filter in the periodic minimum repeating unit is: selecting a material K9 as a glass substrate 1, selecting a material Ag as a first metal layer 2 and a second metal layer 4, and selecting a material SiO2 as a dielectric layer 3; depositing a first metal layer 2 on a glass substrate 1 by a magnetron sputtering technology, wherein the thickness of the deposited second metal layer 2 is 11.01nm; dividing the medium layer 3 into 4 medium layer blocks, wherein the 4 medium layer blocks correspond to 4 different film layer thicknesses h 2,j =[1527,1787,693.5,978.9]nm, preparing a dielectric layer 3 above the first metal layer 2 by a gray scale photoetching technology; finally, a second metal layer 4 with the thickness of 9.74nm is deposited on the dielectric layer 3 through a magnetron sputtering technology.
The dielectric layer 3 adopts a gray level photoetching technology, and dielectric layer blocks with different film thicknesses are directly processed at one time, so that the precise manufacturing of the optical filter array is realized.
The prepared broadband coding optical filter array is directly integrated on an image detector, so that the one-to-one correspondence relationship between the broadband coding optical filter and the image detector pixels is realized, and the snapshot hyperspectral camera is formed.
The hyperspectral camera is adopted to shoot a target object, and if an unknown spectrum curve of the target object is S (lambda) and a spectrum response function of each pixel of an image detector is eta (lambda), original data detected by the image detector corresponding to the jth optical filter are as follows:
I j =∫ λ S(λ)T j (λ)η(λ)dλ
reconstructing the target spectrum curve by using a neural network algorithm, wherein the intensity I detected by the detector corresponding to each minimum repeating unit can be obtained 1 ,I 2 ,I 3 ,I 4 ]Reconstructing the spectral curve of the target object as S * (λ), the reconstruction results are shown in fig. 4.
According to the comparison result of the root mean square error between the target spectrum and the reconstructed spectrum, the broadband coding filter array for the snapshot-type hyperspectral camera is improved by 97% and 56% respectively compared with a Fabry-Perot structure and a super-surface structure.
The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations can be devised by those skilled in the art in light of the above teachings. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.
Claims (9)
1. The utility model provides a broadband coding filter array for incide the image detector after will coming from the incident light modulation of target object on, its characterized in that, the array includes a plurality of periodic minimum repeating unit that constitute by a plurality of filters of M, every the filter all includes glass substrate (1), first metal level (2), dielectric layer (3) and second metal level (4) that set gradually, dielectric layer (3) are including the dielectric layer piece that a plurality of rete thickness differ, second metal level (4) are including a plurality of second metal layer pieces, and each second metal layer piece all sets up on the dielectric layer piece that corresponds, dielectric layer piece and second metal layer piece one-to-one.
2. A broadband coded filter array according to claim 1, wherein in each of said periodic minimal repeating units, the film thickness of all said blocks of dielectric layers is unequal, the film thickness of the first metal layers (2) of all said filters is equal, and the film thickness of the second metal layers (4) of all said filters is equal.
3. The broadband coding filter array of claim 1, wherein the glass substrate (1) is a K9 layer, the first metal layer (2) and the second metal layer (4) are both Ag layers, and the dielectric layer (3) is SiO 2 And (3) a layer.
4. The array of claim 1, wherein the thicknesses of the layers of the filter are obtained by an optimal design method, and the optimal design method comprises the following steps:
acquiring and calculating original data detected by the image detectors corresponding to the optical filters according to original spectral information of the target object and a spectral response function of each pixel of the image detector, and further acquiring the original data detected by the image detectors corresponding to each periodic repetition unit;
reconstructing a spectral curve of the target object through a spectral reconstruction algorithm based on the original data detected by the image detector corresponding to each periodic repetition unit;
and determining and solving an optimization problem according to the reconstructed spectral curve of the target object and the original spectral information of the target object, and obtaining the film thickness of each layer in the optical filter.
5. The array of claim 4, wherein the raw data detected by the image detector corresponding to each filter is:
I j =∫ λ S(λ)T j (λ)η(λ)dλ
in the formula, λ is wavelength, and S (λ) is original spectral information of the target object; t is j (λ) is the spectral transmittance response of the jth filter in each minimal repeating unit; η (λ) is a spectral response function of each pixel of the image detector, j =1,2, …, M; i is j Is the raw data detected by the image detector corresponding to the jth filter.
6. A wideband coding filter array according to claim 5, wherein the optimization problem is expressed by:
in the formula (I), the compound is shown in the specification,in order to optimize the film thickness of the obtained broadband coding filter,in order to optimize the parameters of the obtained spectral reconstruction algorithm, S (λ) is the original spectral information of the target object, decode (·) is a symbol representing the spectral reconstruction algorithm used, and I is the original data detected by the image detector.
7. A broadband coded filter array according to claim 1, wherein the first metal layer (2) is provided on the surface of the glass substrate (1) by a magnetron sputtering method; arranging the dielectric layer (3) on the second metal layer (2) by a gray scale photoetching method; and arranging the second metal layer (4) on the dielectric layer (3) by a magnetron sputtering method.
8. The array of claim 1, wherein the wavelength range of the object modulated by the array of broadband coding filters is 400-700 nm.
9. A snapshot-type hyperspectral camera is characterized by comprising an image detector and a broadband coding optical filter array according to any one of claims 1 to 8, wherein the broadband coding optical filter array modulates incident light from a target object and then emits the modulated incident light onto the image detector, the image detector acquires aliasing information of space and spectrum of the target object, and the aliasing information of space and spectrum of the original target object is acquired through a spectrum reconstruction algorithm.
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CN116164841A (en) * | 2023-04-26 | 2023-05-26 | 中国科学院长春光学精密机械与物理研究所 | Spectrum reconstruction method based on calculation enhanced pixel spectroscopic imaging chip |
CN118131382A (en) * | 2024-05-07 | 2024-06-04 | 佛山市博顿光电科技有限公司 | Monolithically integrated filter device and manufacturing equipment system thereof |
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CN116164841A (en) * | 2023-04-26 | 2023-05-26 | 中国科学院长春光学精密机械与物理研究所 | Spectrum reconstruction method based on calculation enhanced pixel spectroscopic imaging chip |
CN118131382A (en) * | 2024-05-07 | 2024-06-04 | 佛山市博顿光电科技有限公司 | Monolithically integrated filter device and manufacturing equipment system thereof |
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