Micromirror control method of DMD scanning type echelle grating spectrometer

Abstract

The invention relates to the technical field of spectrometers, and discloses a micro-reflector control method of a DMD scanning type echelle grating spectrometer, which comprises the following steps of: firstly, initially reducing the number of micro-reflectors required to be overturned, dividing the whole DMD image surface into sub-regions consisting of a plurality of micro-reflectors, and overturning the sub-regions according to a row sequence; then, further reducing the number of the micro-reflectors required to be overturned, and for the reserved sub-regions with signals, carrying out independent analysis by taking each sub-region as a target, so as to reduce the number of the micro-reflectors; the images of the corresponding sub-regions are recovered, the images of the sub-regions are placed according to the position sequence, the operation is repeated, and the complete spectral image is recovered. According to the invention, the number of times of overturning the micro-mirror of the DMD scanning type echelle grating spectrometer can be reduced, the time of modulating the optical signal by the micro-mirror device is greatly reduced, the imaging efficiency of the DMD scanning type echelle grating spectrometer is improved, and the time required for imaging is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of spectrometers, and in particular to a micro-mirror control method of a DMD scanning type echelle grating spectrometer. Background Art

[0002] The characteristic spectrum of a substance is as unique as its "fingerprint," capable of determining its composition and content. Spectrometers analyze spectra to identify and classify substances, finding widespread application in fields such as quality inspection and medicine. Spectral resolution is a crucial parameter for spectrometers; the higher the resolution, the clearer the ability to distinguish similar substances.

[0003] The échelle grating spectrometer is a spectrometer with ultra-high spectral resolution, boasting extremely high resolution, reaching tens or even several picometers. This is two orders of magnitude higher than the spectral resolution of conventional spectrometers of the same size. The core dispersion element of the échelle grating spectrometer is a grating with a large blaze angle and low line density. This grating enables the spectrometer to operate at high diffraction orders, exhibiting extremely high angular dispersion, thereby achieving high resolution. However, this also results in severe order overlap, necessitating the use of another dispersion element for secondary dispersion in different directions, forming a cross-dispersion optical path. Existing technology requires the use of an area array camera to receive the two-dimensional dispersion spectrum of the échelle grating spectrometer. Highly sensitive area array cameras are expensive, limiting the application and promotion of échelle grating spectrometers.

[0004] A DMD (micromirror array) consists of a series of tiny mirrors, each of which can be independently flipped by software. A DMD scanning échelle spectrometer uses a DMD (micromirror array) placed in the same position as an area array camera. By controlling the flipping of each micromirror, the back-end optical path is connected. High-sensitivity, low-cost single-point detectors, such as photomultiplier tubes, then receive the light. Through long-term scanning, the two-dimensional image, which could only be captured by an area array camera, is restored. This significantly reduces the cost of the échelle spectrometer. Although the DMD has an extremely high flipping frequency, generally exceeding MHz, it is limited by the large number of micromirrors (for example, a 1k*1k array would require 1 million flips). Each flip can be separated by a very short time interval, which can cumulatively increase the total capture time to tens of seconds or even longer. This prolongs the imaging time, making it unsuitable for applications requiring high real-time performance.

[0005] There are also some studies related to micro-mirrors and / or spectral restoration of medium-step grating spectrometers in the prior art, such as the invention patent with application number CN202510486513.6, entitled "Method and system for constructing a two-dimensional spectrum restoration model of a medium-step grating spectrometer". It calculates the light transmission path and imaging position through the principles of geometric optics, constructs a mapping relationship between the wavelength and the coordinate position of the detector pixel, and realizes accurate conversion of the spectrum. However, it is mainly used to solve the problem that the existing medium-step grating spectrometer spectrum restoration model exhibits large errors within the inflatable wide-band spectral detection range, and does not involve the improvement of imaging efficiency.

[0006] Another example is application number CN202422058679.1, filed by the applicant for a utility model patent for an echelle grating spectrometer based on a micromirror device. This patent uses a micromirror device and a photomultiplier tube instead of an area array camera, reducing instrument development costs. By segmenting the micromirror mirror surface, it achieves a rapid micromirror scanning mode, optimizes the micromirror flipping strategy, and significantly reduces the time required to acquire full spectral information. However, this patent does not address the micromirror control method and spectrum restoration model for the echelle grating spectrometer, and the research on these methods is not in-depth. Summary of the Invention

[0007] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a micro-mirror control method for a DMD scanning medium-step grating spectrometer. By matching the acquisition timing of a data acquisition card, the number of required flips is reduced, the time for the micro-mirror device to modulate the light signal is greatly reduced, the imaging efficiency of the DMD scanning medium-step grating spectrometer is improved, and the time required for imaging is reduced.

[0008] The present invention is implemented by the following technical solution: a micro-mirror control method for a DMD scanning echelle grating spectrometer, wherein the optical path structure of the scanning echelle grating spectrometer used includes the front part of the area array detector, the micro-mirror array, the reflective focusing mirror, the single point detector, the data acquisition card and the host computer. After the light is split by the front part of the area array detector of the echelle grating spectrometer, it is focused on the micro-mirror array. By controlling the flipping of the micro-mirror pixels, the light containing spectral information is reflected to the reflective focusing mirror; the reflective focusing mirror focuses the light to the single point detector. On the photosensitive surface of the device, the light signal is converted into an analog voltage signal and amplified and transmitted to the data acquisition card. The data acquisition card converts the collected analog voltage signal into a digital voltage signal and transmits it to the host computer. Synchronously, the host computer transmits the micromirror flipping information to the micromirror to control its flipping. At the same time, the micromirror transmits its flipping synchronization signal to the data acquisition card. The data acquisition card collects data according to the synchronization signal of the micromirror and transmits it to the host computer. The flipping of the micromirror array, the conversion of the single-point detector, and the data acquisition card are performed synchronously.

[0009] The process of the micro-mirror control method includes the following steps:

[0010] (1) Preliminary reduction of the number of micro-mirrors required for flipping; the entire DMD image plane is divided into several sub-regions composed of micro-mirrors, which are flipped in row order. The number of micro-mirrors constituting each sub-region is dynamically adjusted according to the actual situation; each sub-region is flipped in row order. At this time, the single-point detector outputs the voltage value corresponding to the light intensity of each sub-region. According to the voltage value, it is judged whether these sub-regions contain effective light spots. If so, they are retained, otherwise they are discarded; through the division of regions, a large number of sub-regions without signals in the image plane matrix are deleted;

[0011] (2) Reduce the number of micro-mirrors that need to be flipped; for the sub-regions with signals that are retained, each sub-region is analyzed separately, and the number of micro-mirrors is reduced by combining the spectrum restoration model;

[0012] (3) Filter out the invalid position area according to the spectrum restoration model, and correspond the invalid area to the position of the micro-mirror through coordinate transformation; take the intersection of the filtered sub-area and the spectrum restoration model to obtain the spectrum restoration model in the sub-area; quickly flip these micro-mirrors and record the current / voltage signals collected on the single-point detector to restore the image of the corresponding sub-area; place each sub-area image in order of position, repeat the above operation, and thus restore the complete spectral image.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1. A micro-mirror control method for a DMD scanning echelle grating spectrometer of the present invention first preliminarily reduces the number of micro-mirrors required to be flipped, divides the entire DMD image plane into sub-regions composed of several micro-mirrors, and flips them in row order; then, further reduces the number of micro-mirrors required to be flipped, and for the retained sub-regions with signals, performs separate analysis with each sub-region as a target to reduce the number of micro-mirrors; restores the image of the corresponding sub-region, places each sub-region image in position order, repeats the above operation, and restores the complete spectral image, thereby reducing the number of times the micro-mirrors of the DMD scanning echelle grating spectrometer need to be flipped, greatly reducing the time for the micro-mirror device to modulate the light signal, improving the imaging efficiency of the DMD scanning echelle grating spectrometer, and reducing the time required for imaging.

[0015] 2. The present invention provides a micro-mirror control method for a DMD scanning medium-step grating spectrometer. The method uses a spectrum restoration model to quickly screen out invalid position areas and accurately corresponds the invalid areas to the positions of the micro-mirrors through coordinate transformation. The intersection of the screened sub-areas and the spectrum restoration model is taken to obtain the spectrum restoration model within the sub-area, and the image of the corresponding sub-area is restored. Each sub-area image is placed in order of position, thereby restoring the complete spectrum image.

[0016] 3. The present invention provides a micro-mirror control method for a DMD scanning type medium-step grating spectrometer, which synchronizes the micro-mirror flipping and the data acquisition card acquisition through the synchronization signal of the micro-mirror, thereby realizing the synchronization between the spatial position of the micro-mirror and the time sequence of the data acquisition card. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the optical path structure of a scanning echelle grating spectrometer;

[0018] Figure 2 is a diagram of the flipping state of the micro-mirror in the micro-mirror array;

[0019] Figure 3 This is the corresponding diagram of the DMD synchronization signal and flip state of the micromirror;

[0020] Figure 4 It is a flow chart of the micro-mirror control method of the DMD scanning type echelle grating spectrometer of the present invention;

[0021] Figure 5 Schematic diagram of DMD image plane segmentation and flipping in the present invention;

[0022] Figure 6 Schematic diagram of the position of the micro-mirror that needs to be flipped;

[0023] Figure 7is the restored complete spectral image.

[0024] In the figure: 1. Front part of the area array detector; 2. Micro-mirror array; 3. Reflective focusing mirror; 4. Single-point detector; 5. Data acquisition card; 6. Host computer. DETAILED DESCRIPTION

[0025] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless they conflict.

[0026] The object of the present invention is to provide a micro-mirror control method for a DMD scanning type echelle grating spectrometer in view of the defects of the prior art.

[0027] Example 1

[0028] A micro-mirror control method for a DMD scanning echelle grating spectrometer, wherein the optical path structure diagram of the scanning echelle grating spectrometer is shown in FIG. Figure 1 As shown in the figure, the dotted line with an arrow indicates the direction of optical signal propagation; the solid line with an arrow indicates the direction of electrical signal propagation. The optical path structure of the scanning echelle spectrometer includes the front part of the array detector 1, the micro-mirror array 2, the reflective focusing mirror 3, the single point detector 4, the data acquisition card 5 and the host computer 6.

[0029] Light is split by the front detector section 1 of the echelle grating spectrometer and then focused onto a micromirror array 2. By controlling the flipping of the micromirror pixels, the light containing spectral information is reflected onto a reflective focusing mirror 3. The reflective focusing mirror 3 focuses the light onto the photosensitive surface of a single-point detector 4, converting the optical signal into an analog voltage signal, amplifying it, and transmitting it to a data acquisition card 5. The data acquisition card 5 converts the collected analog voltage signal into a digital voltage signal and transmits it to a host computer 6. Simultaneously, the host computer 6 transmits micromirror flipping information to the micromirrors to control their flipping. Simultaneously, the micromirrors transmit a synchronization signal indicating their flipping to the data acquisition card 5. The data acquisition card 5 collects data based on the micromirror synchronization signal and transmits it to the host computer 6. The flipping of the micromirror array 2, the conversion of the single-point detector 4, and the data acquisition by the data acquisition card 5 are all performed synchronously.

[0030] Each micro-mirror has three flip states: the off state (flipped -12°), the on state (flipped +12°), and the non-flip state. Since the micro-mirror flips along the diagonal of each square pixel, the entire micro-mirror needs to be rotated 45° and placed on a horizontal surface to ensure that light is reflected within the horizontal plane.

[0031] Through the optical path setting, when the micro-reflector is flipped to the off state, the light is reflected by the micro-reflector to the reflective focusing mirror 3, that is, when it is in the off state, it is in the working state.

[0032] Reference Figure 2 Figure 2 shows the flipping state of the micro-mirrors in the micro-mirror array. The small black squares in the figure represent the micro-mirrors in the off state in the micro-mirror array 2. In this state, the light signal on them is reflected to the reflective focusing mirror 3. Most of the other pixels are in the on state, reflecting the light in the opposite direction. The blank areas between the black lines are short-term non-flipping states.

[0033] Reference Figure 3 The figure shows the correspondence between the DMD synchronization signal and the flip state of the micro-mirror. The DMD synchronization signal of the micro-mirror is a set of high and low level signals, which are transmitted by the micro-mirror to the data acquisition card 5. At the beginning of the DMD flip state, the output is high and lasts for half a cycle. At the halfway point of each flip cycle (when the optical signal received by the single-point detector 4 is more stable), the output is low, waiting for the next flip of the micro-mirror. At the beginning of the next flip of the micro-mirror, the output becomes high again. When the data acquisition card 5 receives the low level, it collects data (the electrical signal converted by the single-point detector 4). The synchronization between the micro-mirror flip and the data acquisition card's data acquisition is achieved through the synchronization signal of the micro-mirror, achieving the synchronization between the spatial position of the micro-mirror and the time sequence of the data acquisition card.

[0034] A micro-mirror control method for a DMD scanning echelle grating spectrometer, referring to Figure 4 As shown, the process includes the following steps:

[0035] (1) First, the number of micro-mirrors required for flipping is initially reduced; the entire DMD image plane is divided into several sub-areas composed of micro-mirrors, which are flipped in row order. The number of micro-mirrors in each sub-area is dynamically adjusted according to the actual situation. The sub-area should not contain too many micro-mirrors, nor too few micro-mirrors. Figure 5 The figure shows the DMD image plane segmentation and flipping diagram in this embodiment, wherein the sub-area includes 6x6 micro-mirrors, and the black area in the figure is the sub-area that is flipped to the off state each time. When flipping for the first time, the first area of ​​the first row ( Figure 5The black area in the upper left corner of the figure is in the off state, and the rest of the areas are in the on state. At this time, the data collected by the data acquisition card 5 is the voltage value corresponding to the light intensity of the first area in the first row; each sub-area is flipped in order according to the row order. At this time, the single-point detector 4 outputs the voltage value corresponding to the light intensity of each sub-area. According to the voltage value, it is judged whether these sub-areas contain valid light spots. If so, they are retained, and if not, they are discarded. Through the division of the area, a large number of sub-areas without signals in the image plane matrix are deleted. Due to the extremely high spectral resolution of the medium-step grating spectrometer, its detection targets are mostly linear discrete spectra, that is, the two-dimensional image is distributed in discrete and messy spots. Generally, the selection of sub-areas should ensure that at least 50% of invalid micromirrors are excluded.

[0036] (2) Next, the number of micro-mirrors required to be flipped is further reduced; for the sub-regions with signals that are retained, each sub-region is analyzed separately, and the number of micro-mirrors is reduced by combining the spectrum restoration model;

[0037] (3) According to the spectrum restoration model, the invalid position area can be quickly screened out, and the invalid area can be accurately mapped to the position of the micro-mirror through coordinate transformation; the intersection of the screened sub-area and the spectrum restoration model is taken to obtain the spectrum restoration model in the sub-area, such as Figure 6 As shown in FIG, the final position of the micro-mirrors that need to be flipped is obtained; these micro-mirrors are quickly flipped and the current / voltage signals collected by the single-point detector 4 are recorded to restore the image of the corresponding sub-region. Each sub-region image is placed in order of position and the above operation is repeated to restore the complete spectral image, as shown in FIG. Figure 7 As shown in the figure, the complete spectrum image is restored. The spectrum restoration model represents the one-to-one correspondence between the image position and the wavelength information. Figure 6 The middle white area is the position of the center of the light spot corresponding to each wavelength on the image plane. This micro-mirror scanning control strategy can reduce the number of micro-mirrors required to flip in the DMD scanning echelle spectrometer, greatly reducing the time it takes for the micro-mirror device to modulate the light signal, improving the imaging efficiency of the DMD scanning echelle spectrometer and reducing the time required for imaging.

[0038] Example 2

[0039] A micro-mirror control method for a DMD scanning échelle spectrometer is proposed. The spectrum restoration model is constructed as follows: by analyzing the optical structural characteristics of the échelle spectrometer, when the pinhole diameter and system focal length are determined, the horizontal and vertical coordinates of the two-dimensional spectrum spot position are related to the performance parameters of the prism and échelle grating, respectively. After the performance parameters of the two dispersion elements are determined, they are only functions of wavelength. Considering the quasi-Litrow structure, the grating equation is written as follows:

[0040] (1)

[0041] In the formula is the offset angle of the echelle grating, and the diffraction angle in the above formula is replaced by the distance y from the center of the main dispersion direction. i After expressing it with focal length, we can get the relationship between wavelength and y i , the corresponding relationship of order m, and then the first matrix about wavelength is obtained:

[0042] (2)

[0043] According to the functional relationship between the spot coordinates and the wavelength, the second and third matrices about the horizontal and vertical coordinates can be obtained respectively:

[0044] (3)

[0045] (4)

[0046] The above three matrices can be used to establish the relationship between wavelength and horizontal and vertical coordinates:

[0047] (5)

[0048] The relationship between the spectrum restoration model and the transformation of each micro-mirror in the micro-mirror array is shown in the following formula:

[0049] (6)

[0050] where x DMD and y DMD are the micro-mirror numbers in the x and y directions of the micro-mirror array, M and Y M are the horizontal and vertical coordinates in the spectrum restoration model, pixelsize and DMDsize are the pixel size in the model and the interval between micro-mirrors in the micro-mirror array, respectively.

[0051] Finally, each sub-region image is placed into a large matrix in order of position to restore the complete spectral image.

[0052] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A micro-mirror control method for a DMD scanning echelle grating spectrometer, characterized by: The optical path structure of the scanning type medium-step grating spectrometer used therein includes a front part of a planar array detector (1), a micro-mirror array (2), a reflective focusing mirror (3), a single-point detector (4), a data acquisition card (5) and a host computer (6). Light is split by the front part of the planar array detector (1) of the medium-step grating spectrometer and then focused on the micro-mirror array (2). By controlling the flipping of the micro-mirror pixels, the light containing spectral information is reflected onto the reflective focusing mirror (3); the reflective focusing mirror (3) focuses the light onto the photosensitive surface of the single-point detector (4), and converts the light signal into an analog voltage. The signal is amplified and transmitted to the data acquisition card (5), the data acquisition card (5) converts the collected analog voltage signal into a digital voltage signal and transmits it to the host computer (6); synchronously, the host computer (6) transmits the micro-mirror flipping information to the micro-mirror to control its flipping, and at the same time, the micro-mirror transmits its flipping synchronization signal to the data acquisition card (5), and the data acquisition card (5) collects data according to the synchronization signal of the micro-mirror and transmits it to the host computer (6); the flipping of the micro-mirror array (2), the conversion of the single-point detector (4), and the collection of the data acquisition card (5) are synchronously performed; The process of the micro-mirror control method includes the following steps: (1) Preliminary reduction of the number of micro-mirrors required for flipping; the entire DMD image plane is divided into several sub-regions composed of micro-mirrors, which are flipped in row order, and the number of micro-mirrors constituting each sub-region is dynamically adjusted according to the actual situation; each sub-region is flipped in row order, and at this time, the single-point detector (4) outputs the voltage value corresponding to the light intensity of each sub-region, and judges whether these sub-regions contain effective light spots based on the voltage value. If so, they are retained, and if not, they are discarded; through the division of regions, a large number of sub-regions without signals in the image plane matrix are deleted; (2) Reduce the number of micro-mirrors that need to be flipped; for the sub-regions with signals that are retained, each sub-region is analyzed separately, and the number of micro-mirrors is reduced by combining the spectrum restoration model; (3) Invalid position areas are screened out according to the spectrum restoration model, and the invalid areas are mapped to the positions of the micro-mirrors through coordinate transformation; the intersection of the screened sub-areas and the spectrum restoration model is taken to obtain the spectrum restoration model within the sub-areas; accordingly, these micro-mirrors are quickly flipped and the current / voltage signals collected on the single-point detector (4) are recorded to restore the image of the corresponding sub-area; each sub-area image is placed in order of position, and the above operation is repeated to restore the complete spectral image.

2. The micro-mirror control method of the DMD scanning echelle spectrometer according to claim 1, wherein: The method for constructing the spectrum restoration model involves analyzing the optical structure characteristics of the échelle grating spectrometer. When the pinhole diameter and system focal length are determined, the horizontal and vertical coordinates of the two-dimensional spectrum spot position are related to the performance parameters of the prism and échelle grating, respectively. After the performance parameters of the two dispersion elements are determined, they are only functions of wavelength. Considering the quasi-Litrow structure, the grating equation is written as follows: In the formula is the offset angle of the echelle grating, and the diffraction angle in the above formula is replaced by the distance y from the center of the main dispersion direction. i After expressing it with focal length, we can get the relationship between wavelength and y i , the corresponding relationship of order m, and then the first matrix about wavelength is obtained: According to the functional relationship between the spot coordinates and the wavelength, the second and third matrices about the horizontal and vertical coordinates can be obtained respectively: The above three matrices can be used to establish the relationship between wavelength and horizontal and vertical coordinates: The relationship between the spectrum restoration model and the transformation of each micro-mirror in the micro-mirror array is shown in the following formula: where x DMD and y DMD are the micro-mirror numbers in the x and y directions of the micro-mirror array, M and Y M are the horizontal and vertical coordinates in the spectrum restoration model, pixelsize and DMDsize are the pixel size in the model and the interval between micro-mirrors in the micro-mirror array, respectively; Finally, each sub-region image is placed into a large matrix in order of position to restore the complete spectral image.

3. The micro-mirror control method of the DMD scanning echelle grating spectrometer according to claim 1, wherein: The selection of sub-regions should exclude more than 50% of invalid micromirrors.

4. The micro-mirror control method of a DMD scanning echelle spectrometer according to claim 1, wherein: Each micro-mirror has three flip states, namely, off state, on state, and non-flip state; when the micro-mirror is flipped to the off state, light is reflected by the micro-mirror to the reflective focusing mirror (3), which is in the working state; when flipped for the first time, the first area of ​​the first row is in the off state, and the remaining areas are in the on state. At this time, the data collected by the data acquisition card (5) is the voltage value corresponding to the light intensity of the first area of ​​the first row.

5. The micro-mirror control method of the DMD scanning echelle grating spectrometer according to claim 1, wherein: The DMD synchronization signal of the micro-mirror is a set of high and low level signals, which are transmitted from the micro-mirror to the data acquisition card (5); the output is high level at the beginning of the DMD flip state, which lasts for half a cycle; the output is low level at half of each flip cycle, waiting for the next flip of the micro-mirror; it becomes high level again at the beginning of the next flip of the micro-mirror; when the data acquisition card (5) receives the low level, it collects data once; the synchronization between the micro-mirror flip and the data acquisition card acquisition is achieved through the synchronization signal of the micro-mirror, and the synchronization between the spatial position of the micro-mirror and the time sequence of the data acquisition card is achieved.

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