Fourier transform spectral imaging device and spectral imaging method

Abstract

The invention provides Fourier transform spectral imaging equipment and a spectral imaging method, and relates to the field of spectral imaging, the Fourier transform spectral imaging equipment comprises a Michelson interferometer, the Michelson interferometer comprises a scanning galvanometer fixedly arranged on a rotating shaft, and the Michelson interferometer is used for carrying out spectral imaging when the scanning galvanometer does reciprocating rotation motion along the rotating shaft; generating first interference light, and guiding the first interference light to the sample to be detected; the digital micromirror is used for displaying a plurality of modulation patterns and carrying out intensity modulation on second interference light by utilizing the plurality of modulation patterns to obtain a plurality of beams of third interference light, and the second interference light is obtained after the first interference light and the sample to be detected act; the photoelectric detector is used for receiving the plurality of beams of third interference light to obtain a plurality of modulation interferograms; and the control host is used for performing compressed sensing imaging based on the plurality of modulation patterns and the plurality of modulation interferograms to obtain a spectral image.

Description

Technical Field

[0001] The present application relates to the field of spectral imaging, and in particular to a Fourier transform spectral imaging device and a spectral imaging method. Background Art

[0002] Fourier transform spectroscopy imaging (FTSI) is an optical detection technology that uses a Fourier transform imaging spectrometer to perform spectral analysis and imaging. It can simultaneously obtain spatial and spectral information of the target object. It has the advantages of high spectral resolution, high signal-to-noise ratio, and a wide spectral range, and is widely used in multiple fields.

[0003] Traditional Fourier transform imaging spectrometers use a Michelson interferometer to generate interference light, which is then combined with an array detector to collect the interference light signal transmitted through the sample. Finally, a control host executes a Fourier transform algorithm to convert the interference light signal into a frequency-domain spectrum, generating a three-dimensional data cube consisting of two spatial dimensions and one spectral dimension, enabling simultaneous analysis of the sample's spectral information and spatial distribution. However, due to the low frame rate of the array detector, to ensure that the resulting frequency-domain spectrum does not exhibit aliasing, the scanning speed of the Michelson interferometer must be significantly reduced, which in turn reduces the overall imaging speed of the Fourier transform imaging spectrometer, limiting the application of this technology in the field of dynamic, real-time spectral imaging. Summary of the Invention

[0004] In response to the above problems, the present application provides a Fourier transform spectral imaging device and a spectral imaging method.

[0005] On the one hand, the present application proposes a Fourier transform spectral imaging device, including: a Michelson interferometer, including a scanning galvanometer fixedly arranged on a rotating shaft, the Michelson interferometer is used to generate a first interference light and guide the first interference light to a sample to be measured when the scanning galvanometer performs reciprocating rotation along the rotating shaft; a digital micromirror, used to display multiple modulation patterns, and use the multiple modulation patterns to modulate the intensity of the second interference light to obtain multiple beams of third interference light, wherein the second interference light is obtained after the first interference light interacts with the sample to be measured; a photodetector, used to receive the multiple beams of third interference light and obtain multiple modulated interference patterns; and a control host, used to perform compressed sensing imaging based on the multiple modulation patterns and the multiple modulated interference patterns to obtain a spectral image.

[0006] According to an embodiment of the present application, the control host is also used to provide a driving signal to the Michelson interferometer, wherein the driving signal is composed of multiple identical driving sub-signals; the Michelson interferometer is used to drive the scanning galvanometer to perform reciprocating rotational motion based on the driving signal.

[0007] According to an embodiment of the present application, the control host is further used to provide a trigger signal to the digital micromirror and the photodetector at a first moment and a second moment of the driving sub-signal, respectively, wherein the time difference between the first moment and the second moment is half of the total duration of the driving sub-signal; the digital micromirror is used to switch the displayed modulation pattern in response to the trigger signal, so as to use the switched modulation pattern to perform intensity modulation on the second interference light to obtain a third interference light; the photodetector is used to perform photoelectric conversion on the third interference light in response to the trigger signal to obtain a modulated interference pattern.

[0008] According to an embodiment of the present application, the driving sub-signal is a triangular wave signal, and the duration of the rising edge of the triangular wave signal is equal to the duration of the falling edge.

[0009] According to an embodiment of the present application, the control host is also used to train a convolutional neural network using multiple spectral image samples, and generate multiple modulation patterns based on the model parameters of multiple convolution kernels included in the trained convolutional neural network, so as to send multiple modulation patterns to the digital micromirror when performing spectral imaging.

[0010] According to an embodiment of the present application, the control host is used to input the spectral image sample into the convolutional neural network to obtain multiple single-pixel measurement values, perform compressed sensing imaging based on the model parameters of the multiple convolution kernels included in the convolutional neural network and the multiple single-pixel measurement values ​​to obtain a reconstructed spectral image, and update the model parameters of the convolutional neural network based on the loss value between the reconstructed spectral image and the spectral image sample to obtain a trained convolutional neural network.

[0011] According to an embodiment of the present application, the first interference light includes a first scanning light and a first reference light, and the Michelson interferometer also includes a light source, a spectrometer, a grating, a lens module and a reflector; wherein the light source is used to provide detection light; the spectrometer is used to split the detection light into a second scanning light and a second reference light, and guide the second scanning light to the grating, and guide the second reference light to the reflector; the grating is used to diffract and split the second scanning light to obtain a first light beam; the lens module is used to converge the first light beam to the rotating axis; the scanning galvanometer is used to introduce a phase delay into the first light beam when performing reciprocating rotation along the rotating axis to obtain a second light beam, and use the second light beam as the first scanning light, and output the first scanning light through the lens module, the grating and the spectrometer; the reflector is used to reflect the second reference light to obtain the first reference light, so as to output the first reference light through the spectrometer.

[0012] According to an embodiment of the present application, the Fourier transform spectral imaging device further includes:

[0013] The beam expander is used to expand the first interference light so as to expand the area of ​​the light spot formed when the first interference light irradiates the sample to be measured.

[0014] The focusing lens is used to focus the third interference light onto the photodetector.

[0015] On the other hand, the present application proposes a Fourier transform spectral imaging method, including: obtaining a first interference light when the scanning galvanometer of the Fourier transform spectral imaging device is in a state of reciprocating rotation along the rotation axis; directing the first interference light to the sample to be measured so that the first interference light interacts with the sample to be measured to obtain a second interference light; using multiple modulation patterns to modulate the intensity of the second interference light to obtain multiple beams of third interference light; performing photoelectric detection on the multiple beams of third interference light to obtain multiple modulated interference patterns; and performing compressed sensing imaging based on the multiple modulation patterns and the multiple modulated interference patterns to obtain a spectral image.

[0016] The embodiment of the present application sets a digital micromirror in a Fourier transform spectrometer to display the modulation pattern required by the compressed sensing algorithm, so that the interference light after interacting with the sample is directly modulated by the modulation pattern outside the control host. The modulated interference pattern generated after modulation is further received by the photodetector. The modulated interference pattern is transmitted to the control host, which then performs spectrum reconstruction to ultimately obtain sample information. The setting of the digital micromirror makes the interference light modulation module in the imaging process independent and no longer relies on the control host to perform this operation. The control host only needs to perform the Fourier transform and compressed sensing algorithm to reconstruct the spectrum process, thereby simplifying the execution program of the control host. Compared with the technical solution of using the control host to execute the entire compressed sensing algorithm process, the imaging efficiency is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other objects, features and advantages of the present application will become more apparent through the following description of the embodiments of the present application with reference to the accompanying drawings, in which:

[0018] Figure 1 A schematic diagram of a Fourier transform spectral imaging device according to an embodiment of the present application is shown.

[0019] Figure 2 A schematic diagram of a process for reconstructing a spectral image from a modulated interferogram according to an embodiment of the present application is shown.

[0020] Figure 3 A schematic diagram of a Michelson interferometer according to an embodiment of the present application is shown.

[0021] Figure 4 A schematic diagram of the modulation interferogram acquisition process according to an embodiment of the present application is shown.

[0022] Figure 5 A flow chart of a modulation pattern customization method based on a convolutional neural network according to an embodiment of the present application is shown.

[0023] Figure 6The figure shows the imaging principle diagram of the Fourier transform spectrometer according to an embodiment of the present application.

[0024] Figure 7 A flow chart of a Fourier transform spectral imaging method according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of this application more clear, this application is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0026] The terms used herein are only for describing specific embodiments and are not intended to limit this application. The terms "comprise," "include," etc. used herein indicate the presence of the features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0027] All terms used herein, including technical and scientific terms, have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0028] Existing improved Fourier transform imaging spectrometers propose using a compressed sensing algorithm to overcome the limited scanning speed of the Michelson interferometer due to the sampling theorem. Compressed sensing algorithms are not subject to the sampling theorem's limitations. Instead, they collect a small amount of core information and combine it with algorithms to reconstruct the complete signal. This eliminates the need to sample at twice the maximum signal frequency. Therefore, using this algorithm can significantly reduce the amount of data required for reconstruction, saving storage resources.

[0029] However, spectral imaging using compressed sensing algorithms relies on a host computer to generate and display the modulation patterns required for the modulation process and modulate the interference light passing through the sample. Furthermore, the host computer is required to perform the compressed sensing algorithm calculations to obtain the final measurement results. This results in the host computer being overloaded with tasks, resulting in complex programs and slowed down performance. Therefore, it is imperative to employ technical means to offload some of these tasks from the host computer, allowing hardware to perform some of these tasks, thereby simplifying the host computer's execution process and improving imaging efficiency.

[0030] Figure 1 A schematic diagram of a Fourier transform spectral imaging device according to an embodiment of the present application is shown.

[0031] like Figure 1 As shown, the Fourier transform spectral imaging device may include: a Michelson interferometer 1, a digital micromirror 2, a photodetector 3 and a control host 4.

[0032] The Michelson interferometer 1 includes a scanning galvanometer fixedly mounted on a rotating shaft. The Michelson interferometer 1 is configured to generate a first interference light beam while the scanning galvanometer mirror is rotating back and forth along the rotating shaft, and to direct the first interference light beam toward the sample to be measured. A digital micromirror 2 is configured to display multiple modulation patterns and utilize the multiple modulation patterns to modulate the intensity of the second interference light beam to obtain multiple beams of third interference light beams, wherein the second interference light beams are obtained by the interaction of the first interference light beams with the sample to be measured. A photodetector 3 is configured to receive the multiple beams of third interference light beams to obtain multiple modulated interference patterns. Furthermore, a control host 4 is configured to perform compressed sensing imaging based on the multiple modulation patterns and multiple modulated interference patterns to obtain a spectral image.

[0033] In a Michelson interferometer, light from a light source is split into two beams propagating in different directions. Since these two beams originate from the same source, they have the same frequency, a stable phase relationship, and consistent vibration directions, satisfying the conditions for optical interference. After propagating along different paths, the two beams reunite and superimpose. When the two beams reunite, if the optical path difference between the two beams is an integer multiple of the wavelength, the superposition increases the intensity, forming bright fringes. If the optical path difference is an odd multiple of half the wavelength, the superposition decreases the intensity, forming dark fringes. By varying the path length of one of the beams, the optical path difference between the two beams changes, and the interference fringes shift or deform accordingly. The path length of one beam can be varied by the reciprocating rotation of a scanning mirror. When the scanning mirror is angularly deflected, the angle of reflection of the incident beam on it also changes, thereby altering the path length of the reflected beam through the interferometer's optical path.

[0034] After the interference light generated by the Michelson interferometer 1 passes through the sample, it is modulated by a digital micromirror 2. The digital micromirror 2 can be a light modulation device composed of an array of numerous tiny mirrors (hereinafter referred to as micromirrors), each of which can independently rotate around its own axis by a small angle. When light strikes the digital micromirrors 2, each micromirror corresponds to a pixel in the image. The modulation pattern displayed by the digital micromirrors 2 is essentially a specific combination of the micromirror's on and off states, which can be controlled by the control host 4 using binary signals. A micromirror receiving a "1" signal rotates to the on state, while a micromirror receiving a "0" signal rotates to the off state. When the incident light to be modulated reaches an on micromirror, it precisely enters the imaging optical path, such as the projection lens. However, when it reaches a closed micromirror, the incident light deviates from the imaging optical path. Based on this principle, the spatial intensity distribution of the incident light perfectly matches the brightness and darkness distribution of the modulation pattern, thereby modulating the light signal passing through the modulation pattern.

[0035] The modulated interference pattern obtained after modulation is further detected and converted into a signal by a photodetector 3. The photodetector 3 can be composed of a photosensitive element, a photoelectric signal conversion structure, and auxiliary circuits, which can convert the optical signal into an electrical signal. When light radiation irradiates the photosensitive material of the photodetector 3, the electrons in the material absorb the photon energy and undergo a state change, thereby causing changes in electrical properties, such as current, voltage, or resistance. The strength of these electrical signals is related to the intensity and wavelength of the incident light. Through subsequent circuit amplification and processing, the optical signal can be detected and converted into a signal.

[0036] The photodetector 3 transmits the received modulation interferogram to the control host 4 , and the control host 4 uses a compressed sensing algorithm to perform spectrum reconstruction based on the modulation pattern and the corresponding modulation interferogram.

[0037] Compressed sensing algorithms are not constrained by sampling theorems. They can acquire small amounts of measurement data at rates far lower than traditional sampling rates. Using mathematical optimization algorithms, they then accurately reconstruct the original high-dimensional signal from this low-dimensional data. The compressed sensing workflow consists of two steps: first, signal modulation, which modulates the original signal by designing a measurement matrix, converting the high-dimensional signal into low-dimensional measurements with far fewer dimensions. One form of the measurement matrix can be the modulation pattern displayed by a digital micromirror. Second, signal reconstruction, using algorithms to infer the original signal from the low-dimensional measurements.

[0038] Figure 2 A schematic diagram of a process for reconstructing a spectral image from a modulated interferogram according to an embodiment of the present application is shown.

[0039] like Figure 2 As shown in the figure, the reconstruction process is divided into two steps: Fourier transform and compressed sensing reconstruction. First, the modulated interference patterns I1, I2, ..., I n Perform Fourier transform to obtain the modulation spectrum. For Michelson interferometer 1, the modulation spectrum at the optical frequency ν The theoretical expression of is shown in formula (1). Indicates the sequence number of the modulation pattern; Represents the frequency of light incident on the rotation axis of the scanning galvanometer; Indicates the modulation pattern The corresponding modulation coefficient; represents the collected interference light signal; represents the group delay, and its expression is shown in formula (2), F represents the focal length of the 4F system, N represents the number of grating lines, represents the rotation speed of the scanning galvanometer, and t represents time.

[0040]

[0041] Secondly, the control host 4 runs the compressed sensing algorithm to reconstruct the spectrum image based on the modulation spectrum at the optical frequency ν and the corresponding modulation pattern. The general solution principle of compressed sensing is shown in formula (3), where: represents the reconstructed spectral image; φ represents the measurement matrix. The solution principle of the measurement matrix is ​​shown in formula (4). First, the modulation pattern Flattened to row vector , and then synthesize it according to the rows; is the measured value synthesized from n modulation spectra at optical frequency ν.

[0042]

[0043] The modulated spectrum at each ν is reconstructed by compressed sensing, and finally a spectral image, i.e. a three-dimensional data cube, is obtained.

[0044] This application proposes a Fourier transform spectral imaging device and spectral imaging method. The device comprises a Michelson interferometer 1, a digital micromirror 2, a photodetector 3, and a control host 4. After the interference light generated by the Michelson interferometer 1 passes through the sample, it is modulated by the modulation pattern displayed by the digital micromirror 2. The modulated interference light is received by the photodetector 3, and finally, the spectral image is reconstructed by running a compressed sensing algorithm using the control host 4. This application modulates the interference light by providing a digital micromirror in a Fourier transform spectrometer, using the digital micromirror to display the modulation pattern required by the compressed sensing algorithm, and implementing some of the execution tasks of the control host through external hardware, thereby simplifying the execution program of the control host. Compared with the technical solution of using the control host to perform the entire compressed sensing algorithm process, the imaging speed is improved.

[0045] Figure 3 A structural schematic diagram of a Michelson interferometer according to an embodiment of the present application is shown.

[0046] like Figure 3As shown, in this embodiment of the present application, the Michelson interferometer 1 includes a reflector 101, a beam splitter 102, a light source 103, a grating 104, a lens module 105, and a scanning galvanometer 106. The light source 103 is used to provide detection light, and the beam splitter 102 is used to split the detection light into a second scanning light and a second reference light, directing the second scanning light to the grating 104 and the second reference light to the reflector 101. The grating 104 is used to diffract and split the second scanning light to obtain a first light beam; the lens module 105 is used to converge the first light beam onto the rotation axis; the scanning galvanometer 106 is used to introduce a phase delay into the first light beam while performing reciprocating motion along the rotation axis to obtain a second light beam, and use the second light beam as the first scanning light, which is output as the first scanning light through the lens module 105, the grating 104, and the beam splitter 102. The reflector 101 is used to reflect the second reference light to obtain the first reference light, which is then output as the first reference light through the beam splitter 102.

[0047] According to an embodiment of the present application, in the Michelson interferometer 1, a grating 104, a lens module 105, and a scanning galvanometer 106 are arranged in sequence, wherein a 4F structure is formed between the grating 104 and the lens module 105, and between the lens module 105 and the scanning galvanometer 106, that is, the distance between the grating 104 and the lens module 105, and between the lens module 105 and the scanning galvanometer 106 is F. The total optical path of the incident light from the grating 104 through the lens module 105 to the scanning galvanometer 106, and after being reflected by the scanning galvanometer 106, returning to the grating 104 through the lens module 105 is 4F, wherein F is the focal length of the lens in the lens module 105.

[0048] According to an embodiment of the present application, the detection light emitted by the light source 103 first reaches the spectroscope 102. The spectroscope 102 can be a glass plate coated with a semi-transparent and semi-reflective film. When the incident light reaches the spectroscope 102, half of the light is reflected and the other half is transmitted. The light reflected by the spectroscope 102 is the second scanning light, which then reaches the grating 104. The grating 104 can be composed of a large number of parallel slits of equal width and equal spacing. It can diffract and split the second scanning light to obtain a first light beam. The first light beam is converged to the rotation axis of the scanning galvanometer 106 through the lens module 105. As the scanning galvanometer 106 rotates back and forth along the rotation axis, the reflected optical path of the first light beam continuously changes, thereby introducing a phase delay to obtain a second light beam. The second light beam is then output as the first scanning light through the lens module 105, the grating 104 and the spectroscope 102. Among them, the lens module 105 can be a combination of two biconvex lenses. The center of light divergence emitted by grating 104 coincides with the object-side focal point of the biconvex lens. Based on the imaging principle of convex lenses, the emitted light becomes parallel light parallel to the optical axis after passing through the biconvex lens. After being reflected by scanning galvanometer mirror 106, the parallel light returns along its original path. Upon re-entering the biconvex lens, the parallel light is focused back to its original object-side focal position. The detection light emitted by light source 103 is transmitted through beam splitter 102 to produce a second reference light beam. The second reference light beam is reflected by reflector 101 to produce a first reference light beam. The first reference light beam interferes with the first scanning light beam to produce a first interference light beam.

[0049] According to an embodiment of the present application, the above-mentioned Fourier transform spectral imaging device may further include a beam expander. The beam expander is used to expand the first interference light to expand the area of ​​the light spot formed by the first interference light irradiating the sample to be measured. The beam expander may be composed of an input lens and an output lens. The input lens may be a short-focal-length concave lens, which is responsible for receiving the incident original light beam (e.g., the first interference light) and diverging it. The output lens may be a long-focal-length convex lens, which re-collimates and amplifies the diverged light beam, ultimately outputting a parallel light beam with a larger diameter.

[0050] According to an embodiment of the present application, the Fourier transform imaging spectrometer may further include a focusing lens. The focusing lens is used to converge the third interference light onto the photodetector 3. The focusing lens may be a double-cemented achromatic focusing lens, which is composed of a convex lens and a concave lens. The convex lens deflects the incident light toward the optical axis, while the concave lens compensates for the deflection angle of the convex lens for light of different wavelengths. Ultimately, after the two lenses work together, light of different wavelengths can converge to the same focal point.

[0051] According to an embodiment of the present application, the control host 4 is further configured to provide a drive signal to the Michelson interferometer, wherein the drive signal is composed of multiple identical drive sub-signals. The Michelson interferometer 1 is configured to drive the scanning galvanometer 106 to perform reciprocating rotational motion based on the drive signal. The drive sub-signals may be triangular wave signals, wherein the duration of the rising edge of the triangular wave signal is equal to the duration of the falling edge.

[0052] According to an embodiment of the present application, the control host 4 is further used to provide trigger signals to the digital micromirror 2 and the photodetector 3 at the first moment and the second moment of the driving sub-signal, respectively, wherein the time difference between the first moment and the second moment is half of the total duration of the driving sub-signal; the digital micromirror 2 is used to switch the displayed modulation pattern in response to the trigger signal, so as to use the switched modulation pattern to modulate the intensity of the second interference light to obtain the third interference light; the photodetector 3 is used to perform photoelectric conversion on the third interference light in response to the trigger signal to obtain a modulated interference pattern.

[0053] Figure 4 A schematic diagram of the modulation interferogram acquisition process according to an embodiment of the present application is shown.

[0054] like Figure 4 As shown, in order to collect the data required for spectral imaging, the control host 4 outputs a triangular wave driving signal to the scanning galvanometer 106 of the Michelson interferometer 1, and ensures that the duration of the rising edge and the falling edge of the signal are equal, so that it performs a uniform reciprocating symmetrical scanning motion to generate stable interference light.

[0055] The control host 4 outputs a synchronous trigger signal to the digital micromirror 2 and the photodetector 3 at the beginning (first moment) and halfway through (second moment) of each scanning cycle of the scanning galvanometer 106. After detecting the trigger signal, the digital micromirror 2 immediately switches the modulation pattern, and the photodetector 3 immediately begins to collect the modulation interference pattern under this modulation pattern. In this way, two modulation patterns are switched in each scanning cycle of the scanning galvanometer 106, two intensity modulations are performed, and two modulation interference patterns are measured. Finally, after Scan cycle, n modulation patterns are all switched, and n modulation interference patterns I1, I2, ..., I are collected. n Since the scanning of the scanning galvanometer 106 is synchronized with the switching of the modulation pattern, and the scanning speed of the galvanometer can generally reach several hundred scanning cycles per second, the above solution can effectively improve the signal acquisition speed.

[0056] According to an embodiment of the present application, the control host 4 is also used to train a convolutional neural network using multiple spectral image samples, and generate multiple modulation patterns based on the model parameters of multiple convolution kernels included in the trained convolutional neural network, so as to send multiple modulation patterns to the digital micromirror 2 when performing spectral imaging.

[0057] According to an embodiment of the present application, the control host 4 is used to input the spectral image sample into the convolutional neural network to obtain multiple single-pixel measurement values, perform compressed sensing imaging based on the model parameters of the multiple convolution kernels included in the convolutional neural network and the multiple single-pixel measurement values ​​to obtain a reconstructed spectral image, and update the model parameters of the convolutional neural network based on the loss value between the reconstructed spectral image and the spectral image sample to obtain a trained convolutional neural network.

[0058] Figure 5 A flow chart of a modulation pattern customization method based on a convolutional neural network according to an embodiment of the present application is shown.

[0059] like Figure 5 As shown, the method includes operations S501 to S504.

[0060] In operation S501 , a plurality of spectral image samples are input into a convolutional neural network, and n single-pixel measurement values ​​of the plurality of spectral image samples are obtained by performing n convolution operations on the plurality of spectral image samples.

[0061] In this operation, the model parameters of the n convolution kernels can be converted into a data format supported by the digital micromirror 2. Therefore, the n convolution kernels correspond to n modulation patterns.

[0062] In operation S502 , n single-pixel measurement values ​​and corresponding n convolution kernels are input into a compressed sensing imaging algorithm to obtain a reconstructed spectral image.

[0063] In operation S503 , a loss value between the reconstructed spectral image and the plurality of spectral image samples is calculated.

[0064] In operation S504, the model parameters of the convolution kernel of the convolutional neural network are updated.

[0065] This iteration continues until the loss value converges and falls below the expected level. After the iteration is complete, the model parameters of the n convolution kernels are converted into a data format supported by the digital micromirror 2 and uploaded to the digital micromirror 2 for Fourier transform spectral imaging. The control host 4 inputs the spectral image samples into the convolutional neural network to obtain multiple single-pixel measurement values. Based on the loss value between the input and measured values, the convolution kernel model parameters are updated and optimized to customize the optimal modulation pattern for the compressed sensing imaging algorithm in the Fourier transform spectral imaging system. This pattern is then displayed through the digital micromirror 2 to achieve modulation of the interference light signal.

[0066] It should be pointed out that there are many types of compressed sensing imaging algorithms, and the above is only one of the cases according to the embodiments of the present application. However, no matter what algorithm is used to train the customized modulation pattern, the compressed sensing imaging algorithm mentioned here should be consistent with the compressed sensing imaging algorithm used to reconstruct the spectral image in the previous article. Similarly, the modulation pattern obtained by training should also be consistent with the modulation pattern uploaded to the digital micromirror 2 during the imaging process. In addition, the number n of convolution kernels needs to be adjusted according to the actual spectral image reconstruction effect, and n can usually be taken to be equal to 5% to 20% of the total number of pixels of the target spectral image. This method of customizing the modulation pattern improves the spectral imaging quality of the compressed sensing algorithm when the modulation pattern is small, thereby reducing the number of measurements of the modulation interferogram required to reconstruct a high-quality spectral image, which helps to improve the Fourier transform spectral imaging speed.

[0067] Figure 6 The figure shows the imaging principle diagram of the Fourier transform spectrometer according to an embodiment of the present application.

[0068] like Figure 6 As shown, according to an embodiment of the present application, the light emitted by the light source 103 in the Michelson interferometer 1 reaches the spectrometer 102 and is reflected and transmitted respectively. The reflected light reaches the grating 104 as the second scanning light and is diffracted and split. It is then emitted in parallel through the lens module 105 and finally reaches the reciprocating scanning galvanometer 106 and is reflected to obtain a second light beam. The second light beam is output as the first scanning light through the lens module 105, the grating 104 and the spectrometer 102. The transmitted light reaches the reflector 101 as the second reference light and is reflected to obtain the first reference light. The first reference light interferes with the first scanning light to obtain the first interference light. The first interference light is expanded by the beam expander 5 and interacts with the sample to be measured 6 to obtain the second interference light. After the second interference light is modulated by the modulation pattern displayed in the digital micromirror 2, a third interference light is obtained. After the third interference light is converged to the photodetector 3 through the focusing lens 7, it is received by the photodetector 3 to obtain a modulated interference pattern. After the control host 4 receives the modulated interference pattern from the photodetector 3, it reconstructs the spectral image based on the modulated interference pattern and the modulation pattern through the compressed sensing algorithm, and finally obtains the spatial and spectral information of the sample to be tested 6.

[0069] Figure 7 A flow chart of a Fourier transform spectral imaging method according to an embodiment of the present application is shown.

[0070] like Figure 7 As shown, the method includes operations S701 to S705.

[0071] In operation S701 , a scanning galvanometer of a Fourier transform spectral imaging device is in a state of reciprocating rotation along a rotation axis to obtain first interference light.

[0072] In operation S702 , the first interference light is directed to the sample to be measured, so that the first interference light interacts with the sample to be measured to obtain a second interference light.

[0073] In operation S703 , the second interference light is intensity-modulated using a plurality of modulation patterns to obtain a plurality of third interference lights.

[0074] In operation S704 , photoelectric detection is performed on the plurality of third interference lights to obtain a plurality of modulated interference patterns.

[0075] In operation S705 , compressed sensing imaging is performed based on the multiple modulation patterns and the multiple modulation interferograms to obtain a spectral image.

[0076] This application uses a digital micromirror in a Fourier transform spectral imaging device to display the modulation pattern required by the compressed sensing algorithm, thereby modulating the interference light signal. After using a photodetector to collect the modulated interference pattern, the control host performs a spectral reconstruction process to obtain the spatial position and spectral information of the target sample. The setting of the digital micromirror in this application makes the interference light modulation step in the compressed sensing algorithm independent of the control host. By executing part of the compressed sensing algorithm through external hardware, the control host's computing program is simplified. Compared with the solution of executing the entire compressed sensing algorithm process through the control host, the spectral imaging speed is improved.

[0077] The embodiments of the present application have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application. Although each embodiment has been described separately above, this does not mean that the measures in each embodiment cannot be advantageously used in combination. The scope of the present application is defined by the appended claims and their equivalents. Without departing from the scope of the present application, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present application.

Claims

1. A Fourier transform spectral imaging device, characterized in that: include: A Michelson interferometer, comprising a scanning galvanometer fixedly mounted on a rotating shaft, wherein the Michelson interferometer is configured to generate a first interference light when the scanning galvanometer performs reciprocating rotation along the rotating shaft, and to direct the first interference light toward a sample to be measured; a digital micromirror, configured to display a plurality of modulation patterns and to modulate the intensity of the second interference light using the plurality of modulation patterns to obtain a plurality of third interference lights, wherein the second interference light is obtained by the first interference light interacting with the sample to be measured; a photodetector, configured to receive the plurality of third interference lights to obtain a plurality of modulated interference patterns; and The control host is used to perform compressed sensing imaging based on the multiple modulation patterns and the multiple modulation interference patterns to obtain a spectral image.

2. The Fourier transform spectral imaging device according to claim 1, characterized in that: The control host is further used to provide a driving signal to the Michelson interferometer, wherein the driving signal is composed of a plurality of identical driving sub-signals; The Michelson interferometer is used to drive the scanning galvanometer to perform reciprocating rotational motion based on the driving signal.

3. The Fourier transform spectral imaging device according to claim 2, characterized in that: The control host is further configured to provide trigger signals to the digital micromirror and the photodetector at a first moment and a second moment of the driving sub-signal, respectively, wherein the time difference between the first moment and the second moment is half of the total duration of the driving sub-signal; The digital micromirror is configured to switch the displayed modulation pattern in response to the trigger signal, so as to perform intensity modulation on the second interference light using the switched modulation pattern to obtain the third interference light; The photodetector is configured to perform photoelectric conversion on the third interference light in response to the trigger signal to obtain the modulated interference pattern.

4. The Fourier transform spectral imaging device according to claim 2 or 3, characterized in that: The driving sub-signal is a triangular wave signal, and the duration of the rising edge of the triangular wave signal is equal to the duration of the falling edge.

5. The Fourier transform spectral imaging device according to claim 1, characterized in that: The control host is also used to train a convolutional neural network using multiple spectral image samples, and generate multiple modulation patterns based on the model parameters of multiple convolution kernels included in the trained convolutional neural network, so as to send multiple modulation patterns to the digital micromirror when performing spectral imaging.

6. The Fourier transform spectral imaging device according to claim 5, characterized in that: The control host is used to input the spectral image sample into the convolutional neural network to obtain multiple single-pixel measurement values, perform compressed sensing imaging based on the model parameters of the multiple convolution kernels included in the convolutional neural network and the multiple single-pixel measurement values ​​to obtain a reconstructed spectral image, and update the model parameters of the convolutional neural network based on the loss value between the reconstructed spectral image and the spectral image sample to obtain the trained convolutional neural network.

7. The Fourier transform spectral imaging device according to claim 1, characterized in that: The first interference light includes a first scanning light and a first reference light, and the Michelson interferometer further includes a light source, a spectroscope, a grating, a lens module and a reflector; Wherein, the light source is used to provide detection light; The beam splitter is used to split the detection light into a second scanning light and a second reference light, and guide the second scanning light to the grating and guide the second reference light to the reflecting mirror; The grating is used to diffract and split the second scanning light to obtain a first light beam; The lens module is used to converge the first light beam to the rotation axis; The scanning galvanometer is used to introduce a phase delay into the first light beam when performing reciprocating rotation along the rotation axis to obtain a second light beam, and use the second light beam as the first scanning light, and output the first scanning light through the lens module, the grating and the beam splitter; The reflector is used to reflect the second reference light to obtain the first reference light, so as to output the first reference light through the beam splitter.

8. The Fourier transform spectral imaging device according to claim 1, characterized in that: Also includes: The beam expander is used to perform beam expansion processing on the first interference light to expand the area of ​​the light spot formed when the first interference light irradiates the sample to be measured.

9. The Fourier transform spectral imaging device according to claim 1, characterized in that: Also includes: A focusing lens is used to converge the third interference light onto the photodetector.

10. A spectral imaging method, applied to the Fourier transform spectral imaging device according to any one of claims 1 to 9, characterized in that: The spectral imaging method comprises: Acquiring first interference light when the scanning galvanometer of the Fourier transform spectral imaging device is in a state of reciprocating rotation along the rotation axis; directing the first interference light to a sample to be measured, so that the first interference light interacts with the sample to be measured to obtain a second interference light; Using a plurality of modulation patterns, intensity modulate the second interference light to obtain a plurality of third interference lights; Performing photoelectric detection on the plurality of beams of the third interference light to obtain a plurality of modulated interference patterns; and Compressed sensing imaging is performed based on the multiple modulation patterns and the multiple modulation interference patterns to obtain a spectral image.

Images