Spectrometer based on fast adjustable filter

Abstract

The invention provides a spectrograph based on a fast adjustable filter, the spectrograph comprises the fast adjustable filter, a photoelectric detector, a data acquisition card and a spectrum reconstruction module which are connected in sequence, the fast adjustable filter successively filters spectral components of different wavelengths in the working bandwidth of the spectrograph in sequence, and after each filtering, the spectral components of different wavelengths in the working bandwidth of the spectrograph are obtained. The photoelectric detector detects an optical signal with corresponding light intensity and converts the optical signal into an electric signal, and when the wavelength of the filtered spectral component is within the wavelength range of the to-be-detected light, the light intensity of the optical signal and the current of the electric signal are reduced; the data acquisition card performs current acquisition on each electric signal in sequence to obtain a to-be-measured current vector; the spectrum reconstruction module reconstructs the light spectrum to be measured according to the collected current vector to be measured and a pre-stored spectrum transmission matrix. The spectrograph is high in detection speed, small in size and simple in detection method.

Description

Technical Field

[0001] The invention belongs to the field of spectrometers, and in particular relates to a spectrometer based on a fast tunable filter. Background Art

[0002] Spectrometers are widely used in fields such as food, environmental testing, industry, and astronomy. There are generally two types of traditional spectral systems. One uses optical fiber as a light-guiding element, separating all spectral components through dispersive elements such as gratings. The spectral information is then collected using a CCD camera detection array. To achieve separation of all spectral components, the dispersive element is relatively long, and all spectral components are collected simultaneously by the CCD camera, which places high demands on spectral resolution. Due to the long dispersive element and large size of the CCD camera, this type of spectrometer is also larger. The other type uses a slit and a single detector to achieve single-wavelength spectral detection. This type of spectrometer detects fewer spectra at a time, has low light utilization, and its detection speed is limited by the mechanical scanning speed of the slit. With the development of technology, spectrometers that combine multimode optical fibers with reconstruction algorithms have emerged. During use, interference occurs between the guided modes of the multimode optical fiber, forming a speckle pattern related to the wavelength. The reconstruction algorithm analyzes the speckle pattern to obtain a spectrum. However, the speckle pattern still needs to be recorded using a CCD camera, and the length of the multimode optical fiber is also long. Therefore, this type of spectrometer still has the problem of being large in size. In addition, the speckle pattern is difficult to process, the reconstruction algorithm is relatively complex, and the spectrometer is not suitable for fast and accurate spectral detection of short pulses. Summary of the Invention

[0003] The present invention provides a spectrometer based on a fast tunable filter to solve the problems of current spectrometers such as low detection speed, large size, complex method and unsuitability for short pulse detection.

[0004] According to a first aspect of an embodiment of the present invention, a spectrometer based on a fast tunable filter is provided, comprising a fast tunable filter, a photodetector, a data acquisition card, and a spectrum reconstruction module connected in sequence. The fast tunable filter sequentially filters out spectral components of different wavelengths within the working bandwidth of the spectrometer. After each filtering, the photodetector detects a light signal with a corresponding light intensity and converts the light signal into an electrical signal. When the wavelength of the filtered spectral component is within the wavelength range of the light to be measured, the light intensity of the light signal and the current of the electrical signal decrease. The data acquisition card sequentially collects current from each electrical signal to obtain a current vector to be measured. The spectrum reconstruction module reconstructs the spectrum of the light to be measured based on the collected current vector to be measured and a pre-stored spectral transmission matrix.

[0005] The process of obtaining the spectral transmission matrix is as follows: The spectral components of different wavelengths within the working bandwidth of the spectrometer are sequentially input to the fast tunable filter. For each spectral component within the working bandwidth of the spectrometer, after receiving the spectral component, the fast tunable filter sequentially filters out the spectral components of different wavelengths within the working bandwidth of the spectrometer one by one. After each filtering, the photodetector will detect an optical signal with a corresponding optical intensity and convert the optical signal into an electrical signal; the data acquisition card sequentially collects the currents of each electrical signal, thereby obtaining a reference current vector corresponding to the spectral component. The spectral transmission matrix is composed of reference current vectors corresponding to each spectral component within the working bandwidth of the spectrometer.

[0006] Optionally, the measured current vector and the reference current vector are both row vectors or column vectors.

[0007] The spectral reconstruction module reconstructs the measured optical spectrum based on the collected measured current vector and the pre-stored spectral transmission matrix, using an improved spectral matrix demodulation method. In the improved spectral matrix demodulation method, the measured optical spectrum vector is represented by the product of a Gaussian basis function matrix and a weight coefficient vector. When determining the weight coefficient vector, a Tikhonov regularization term is introduced.

[0008] Optionally, the spectral reconstruction module reconstructs the spectral vector of the measured light according to the following steps:

[0009] Step S110: Expand the spectral vector of the measured light using Gaussian basis functions: Where is the Gaussian basis function of the spectral component corresponding to the measured light at the corresponding wavelength, m is the number of spectral components of different wavelengths within the working broadband of the spectrometer, α j is the weight coefficient of the spectral component corresponding to the measured light at the corresponding wavelength, is the Gaussian basis function matrix, is the weight coefficient vector; σ is the standard deviation of the Gaussian function, λ is the wavelength of the spectral component corresponding to the measured light, λ j is the central wavelength of the Gaussian basis function;

[0010] Step S120: The relationship between the collected measured current vector the pre-stored spectral transmission matrix and the spectral vector S(λ) of the measured light is:

[0011] Step S130: Based on the least squares method, introduce a Tikhonov regularization term and determine the weight coefficient vector according to the following formula where first calculate The square of the Euclidean norm, and The square of the Euclidean norm multiplied by the square of the regularization coefficient γ, add the two calculated terms, and find the minimum value in the added result. The corresponding to this minimum value is the determined weight coefficient vector Υ is obtained by the generalized cross-validation method;

[0012] Step S140, according to this formula Determine the spectral vector S(λ) of the light to be measured.

[0013] Optionally, during the acquisition process of the spectral transmission matrix, for each spectral component within the working bandwidth of the spectrometer, when inputting this spectral component to the fast tunable filter, the filtering wavelength of the fast tunable filter is different, the optical responsivity is different, and the reference current vector corresponding to this spectral component consists of each optical responsivity;

[0014] Each optical responsivity R is calculated by the spectral reconstruction module ij =(I light -I dark ) / P, where I light represents the current collected by the data acquisition card when the i-th spectral component within the working bandwidth of the spectrometer is input to the fast tunable filter and the filtering wavelength of the fast tunable filter is the j-th wavelength within the working bandwidth of the spectrometer; I dark represents the current collected by the data acquisition card when no optical signal is input to the fast tunable filter and the filtering wavelength of the fast tunable filter is the j-th wavelength within the working bandwidth of the spectrometer, and P represents the power of the i-th spectral component.

[0015] Optionally, the fast tunable filter is an all-fiber acousto-optic tunable filter. The all-fiber acousto-optic tunable filter includes an acoustic wave generator and a single-mode fiber without a coating layer. The acoustic wave generator provides the acoustic wave signal it generates to the single-mode fiber, so that the acoustic wave signal propagates along the axis of the single-mode fiber. When the frequency of the acoustic wave signal is adjusted to the frequency band range of the light to be measured, a resonant wavelength corresponding to the frequency of the acoustic wave signal appears on the single-mode fiber. At this time, the spectral component corresponding to this resonant wavelength in the light to be measured propagating along the core jumps from the fundamental mode to the higher-order mode and propagates along the cladding, thereby filtering out the spectral component corresponding to this resonant wavelength to achieve fast tunable filtering.

[0016] Optionally, the fast tunable filter is an all-fiber acousto-optic tunable filter, which includes an acoustic wave generator and a dispersion compensation fiber with a reduced diameter. The acoustic wave generator supplies the acoustic wave signal it generates to the dispersion compensation fiber, enabling the acoustic wave signal to propagate along the axis of the dispersion compensation fiber. When the frequency of the acoustic wave signal is adjusted to the frequency band range of the light to be measured, a resonant wavelength corresponding to the frequency of the acoustic wave signal appears on the dispersion compensation fiber. At this time, the spectral component corresponding to the resonant wavelength in the light to be measured propagating along the core jumps from the fundamental mode to the higher-order mode and propagates along the cladding, thereby filtering out the spectral component corresponding to the resonant wavelength and achieving fast tunable filtering.

[0017] Optionally, the resonant wavelength satisfies phase matching: L B = Λ, where L B is the beat length between the fundamental mode and the higher-order mode, showing a monotonic increasing or decreasing relationship with the optical wavelength, and Λ represents the wavelength of the acoustic wave signal;

[0018] After the frequency of the acoustic wave signal, i.e., the wavelength of the acoustic wave signal, is adjusted in place, the resonant wavelength is determined according to the relationship between L B and the optical wavelength.

[0019] Optionally, the longer the filtering fiber section in the optical fiber, the smaller the 3dB bandwidth of the fast tunable filter, the smaller the working bandwidth of the corresponding spectrometer, and the higher the resolution; when adjusting the resonant wavelength, the duration of the acoustic wave signal corresponding to the adjusted frequency is greater than the length of the filtering fiber section divided by the propagation speed of the acoustic wave signal in the optical fiber.

[0020] Optionally, it further includes a refractive index matching liquid. The tail of the filtering fiber section in the optical fiber is placed in the refractive index matching liquid, and the higher-order mode propagating along the cladding is absorbed by the refractive index matching liquid.

[0021] Optionally, the acoustic wave generator includes a connected radio frequency signal generator and a piezoelectric transducer. The radio frequency signal generator sends the radio frequency signal it generates to the piezoelectric transducer, enabling the piezoelectric transducer to generate an acoustic wave signal with the same frequency. The piezoelectric transducer supplies the acoustic wave signal to the optical fiber;

[0022] The data acquisition card is connected to the radio frequency signal generator to collect the start and end times of the period corresponding to the radio frequency signal generated by the radio frequency signal generator. Completing filtering of all wavelength spectral components in the working bandwidth of the spectrometer in sequence is regarded as one period; the spectral reconstruction module determines a current vector corresponding to the period according to the start and end times of the period of the radio frequency signal collected.

[0023] The beneficial effects of the present invention are:

[0024] 1. When separating spectral components, the present invention uses a fast tunable filter. The fast filtering performance of the filter can improve the spectral detection speed of the spectrometer and enable the spectrometer of the present invention to be applicable to short pulse detection. Since the filter is a tunable filter, when the spectrometer performs spectral detection, spectral components of all different wavelengths within the working bandwidth of the spectrometer can be sequentially filtered out. When the filtered spectral components are within the wavelength range of the light to be measured, the collected current decreases. Based on the measured current vector used to characterize the current change after each filtering and the pre-stored spectral transmission matrix, the spectrum of the light to be measured can be reconstructed. The present invention only needs to collect the current multiple times and can reconstruct the spectrum of the light to be measured based on the current change without processing the speckle pattern. The reconstruction method is simple, thereby further improving the spectral detection speed. The present invention does not need to use a CCD camera to collect spectral information, so it has a small volume and low cost.

[0025] 2. The present invention adopts the spectral matrix demodulation method and improves the spectral matrix demodulation method, so as to ensure that different wavelengths of the light to be measured can be clearly identified after spectral reconstruction, that is, the resolution of the spectrometer can be improved. On the basis of a relatively high resolution of the spectrometer, a filter with a faster filtering speed and a faster filtering adjustment speed can be adopted, thereby further improving the spectral detection speed.

[0026] 3. When constructing the spectral transmission matrix of the present invention, the reference current vector corresponding to the spectral component is composed of each optical responsivity. The optical responsivity introduces the current collected by the data acquisition card when there is no optical signal input to the fast tunable filter and the power of the spectral component. Reconstructing the spectrum based on the spectral transmission matrix composed of the optical responsivity can ensure the accuracy of spectral reconstruction.

[0027] 4. The present invention uses an all-fiber acousto-optic tunable filter as the fast tunable filter. Compared with the multimode fiber length of about 100 m, the length of the filtering fiber section of the single-mode fiber or dispersion compensation fiber in the filter of the present invention only needs more than a dozen centimeters. The length of the filtering fiber section is very short, so its volume is small and it is easy to integrate. Moreover, the fast tunable filter is only composed of two components, an acoustic wave generator and an optical fiber, and the structure is very simple. Since the propagation speed C of the acoustic wave in the single-mode fiber or dispersion compensation fiber is very fast and the length L of the filtering fiber section AO is very short, according to the acoustic-optic response time calculation formula: It can be seen that the tuning speed of the all-fiber acousto-optic tunable filter is very fast; the filter of the present invention can use two types of optical fibers, single-mode optical fiber and dispersion compensation optical fiber, to construct a spectrometer. The characteristics of the spectrometers constructed by the two are compared as follows: when the filter uses a single-mode optical fiber, the resolution of the spectrometer constructed by it is relatively low, but the working bandwidth is relatively large. When the filter uses a dispersion compensation optical fiber, the resolution of the spectrometer constructed by it is relatively high, but the working bandwidth is relatively small. The tuning range of the dispersion compensation optical fiber is 1510 - 1700 nm, and the tuning range of the single-mode optical fiber is 1200 - 1700 nm. Therefore, compared with the dispersion compensation optical fiber, when the filter uses a single-mode optical fiber, the tuning range is higher. Generally speaking, the tuning range of the present invention is higher than that of the prior art;

[0028] 5. The present invention uses a radio frequency generator and a piezoelectric transducer as an acoustic wave generator. The amplitude-frequency characteristics of the piezoelectric transducer enable the all-fiber acousto-optic tunable filter of the present invention to have a high tunable coupling efficiency; and the present invention connects a data acquisition card to the radio frequency signal generator, which can ensure that each current vector corresponds to the period of the radio frequency signal, so as to ensure the accuracy of current vector acquisition. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic structural diagram of an embodiment of a spectrometer based on a fast tunable filter of the present invention;

[0030] Figure 2 are respectively the spectral comparison diagrams of the spectral matrix demodulation method improved by the present invention and the spectral reconstruction using the least squares method;

[0031] Figure 3 A schematic structural diagram of an embodiment of the fast tunable filter of the present invention;

[0032] Figure 4 is a schematic diagram of the frequency modulation curve of the acoustic wave signal and the collected optical current vector in the all-fiber acousto-optic tunable filter. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and make the above-mentioned objects, features, and advantages of the embodiments of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be further described in detail below with reference to the drawings.

[0034] In the description of the present invention, unless otherwise specified and defined, it should be noted that the term "connection" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the communication inside two components. It can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific situations.

[0035] See Figure 1, which is a schematic structural diagram of an embodiment of the spectrometer based on a fast tunable filter of the present invention. The spectrometer may include a fast tunable filter, a photodetector, a data acquisition card, and a spectral reconstruction module connected in sequence. The fast tunable filter sequentially filters out spectral components of different wavelengths within the working bandwidth of the spectrometer. After each filtering, the photodetector will detect an optical signal with corresponding optical intensity and convert the optical signal into an electrical signal. When the wavelength of the filtered spectral component is within the wavelength range of the optical signal to be measured, the optical intensity of the optical signal and the magnitude of the current of the electrical signal decrease; the data acquisition card sequentially collects the currents of each electrical signal to obtain a vector of the current to be measured; the spectral reconstruction module reconstructs the spectrum of the optical signal to be measured according to the collected vector of the current to be measured and the pre-stored spectral transmission matrix.

[0036] The process of obtaining the spectral transmission matrix is as follows: The spectral components of different wavelengths within the working bandwidth of the spectrometer are sequentially input to the fast tunable filter. For each spectral component within the working bandwidth of the spectrometer, after receiving the spectral component, the fast tunable filter sequentially filters out spectral components of different wavelengths within the working bandwidth of the spectrometer. After each filtering, the photodetector will detect an optical signal with corresponding optical intensity and convert the optical signal into an electrical signal; the data acquisition card sequentially collects the currents of each electrical signal, thereby obtaining a reference current vector corresponding to the spectral component. The spectral transmission matrix is composed of reference current vectors corresponding to each spectral component within the working bandwidth of the spectrometer.

[0037] In this embodiment, the fast tunable filter may be a band-stop filter, a band-pass filter, or a multi-wavelength filter. The vector of the current to be measured and the reference current vector may both be row vectors or column vectors, and each reference current vector in the spectral transmission matrix is an individual row vector or column vector. The filter of the present invention has fast filtering performance. If a general reconstruction method is used during spectral reconstruction, overfitting or underfitting is likely to occur, and the optical signals to be measured of different wavelengths reconstructed cannot be clearly identified. Therefore, the spectral reconstruction module of the present invention can reconstruct the spectrum of the optical signal to be measured based on an improved spectral matrix demodulation method according to the collected vector of the current to be measured and the pre-stored spectral transmission matrix. In the improved spectral matrix demodulation method, the spectral vector of the optical signal to be measured is represented by the product of a Gaussian function matrix and a weight coefficient vector, and a Tikhonov regularization term is introduced when determining the weight coefficient vector. Figure 2The following are the spectral comparison diagrams of using the improved spectral matrix demodulation method of the present invention and using the least squares method for spectral reconstruction. It can be seen from the above figure that in the spectrum reconstructed by using the improved spectral matrix demodulation method of the present invention, the spectra of the light to be measured at each different wavelength can be clearly identified; while the spectrum reconstructed by using the least squares method in the following figure is chaotic and difficult to distinguish. It can be seen that the present invention uses the spectral matrix demodulation method and improves the spectral matrix demodulation method, so as to ensure that the lights to be measured at each different wavelength can be clearly identified after spectral reconstruction, that is, the resolution of the spectrometer can be improved; on the basis of a higher resolution of the spectrometer, a filter with a faster filtering speed and a faster filtering adjustment speed can be used, thereby further improving the spectral detection speed.

[0038] When performing spectral reconstruction, the spectral reconstruction module reconstructs the spectral vector of the light to be measured according to the following steps: Step S110: Expand the spectral vector of the light to be measured by using a Gaussian basis function: Where is the Gaussian basis function of the spectral component corresponding to the wavelength in the light to be measured, m is the number of spectral components with different wavelengths within the working broadband of the spectrometer, and α j is the weight coefficient of the spectral component corresponding to the wavelength in the light to be measured, is the Gaussian basis function matrix, is the weight coefficient vector; σ is the standard deviation of the Gaussian function, λ is the wavelength of the spectral component corresponding to the light to be measured, and λ j is the central wavelength of the Gaussian basis function;

[0039] Step S120: The relationship between the measured current vector the pre-stored spectral transmission matrix and the spectral vector S(λ) of the light to be measured is:

[0040] Step S130: Based on the least squares method, introduce a Tikhonov regularization term and determine the weight coefficient vector according to the following formula Where first calculate the square of the Euclidean norm of, and the square of the Euclidean norm of multiplied by the square of the regularization coefficient Υ, add the two calculated items, and find the minimum value in the added result. The corresponding is the determined weight coefficient vector γ is obtained by the generalized cross-validation method;

[0041] Step S140: Determine the spectral vector S(λ) of the light to be measured according to this formula ​

[0042] In the process of acquiring the spectral transmission matrix, for each spectral component within the working bandwidth of the spectrometer, when the spectral component is input into the fast tunable filter, the fast tunable filter has different filtering wavelengths and different photoresponses, and the reference current vector corresponding to the spectral component is composed of the respective photoresponses;

[0043] The spectrum reconstruction module calculates the light response rate R ij =(I light -I dark ) / P, where I light I represents the current collected by the data acquisition card when the i-th spectral component within the working bandwidth of the spectrometer is input to the fast tunable filter and the filtering wavelength of the fast tunable filter is the j-th wavelength within the working bandwidth of the spectrometer; dark represents the current collected by the data acquisition card when no optical signal is input to the fast tunable filter, and the filtering wavelength of the fast tunable filter is the jth wavelength within the operating bandwidth of the spectrometer. P represents the power of the i-th spectral component. When constructing the spectral transmission matrix, the present invention uses a reference current vector corresponding to each spectral component as a component composed of individual photoresponses. The photoresponses incorporate the current collected by the data acquisition card and the power of the spectral component when no optical signal is input to the fast tunable filter. Spectral reconstruction based on the spectral transmission matrix composed of photoresponses ensures spectral reconstruction accuracy.

[0044] As can be seen from the above embodiments, the present invention utilizes a fast, tunable filter when separating spectral components. The fast filtering performance of the filter can improve the spectral detection speed of the spectrometer and make the spectrometer of the present invention suitable for short pulse detection. Since the filter is a tunable filter, it can sequentially filter out spectral components of all different wavelengths within the spectrometer's operating bandwidth during spectral detection. When the filtered spectral components are within the wavelength range of the light to be measured, the collected current decreases. Based on the measured current vector representing the current changes after each filtering and a pre-stored spectral transmission matrix, the spectrum of the light to be measured can be reconstructed. The present invention only requires multiple current acquisitions to reconstruct the spectrum of the light to be measured based on the current changes, without requiring any processing of the speckle pattern. This simplifies the reconstruction method and further improves the spectral detection speed. The present invention does not require a CCD camera to collect spectral information, resulting in a compact size and low cost.

[0045] See also Figure 3 , is a structural diagram of another embodiment of a spectrometer based on a fast tunable filter according to the present invention. Figure 3 and Figure 1The spectrometer based on the fast tunable filter is different in that the fast tunable filter can be an all-fiber acousto-optic tunable filter, which can include an acoustic wave generator and a single-mode fiber without a coating layer. The acoustic wave generator provides the generated acoustic wave signal to the single-mode fiber, so that the acoustic wave signal propagates along the axis of the single-mode fiber. When the frequency of the acoustic wave signal is adjusted to the frequency band range of the light to be measured, a resonant wavelength corresponding to the frequency of the acoustic wave signal appears on the single-mode fiber. At this time, the spectral component corresponding to the resonant wavelength in the light to be measured propagating along the core jumps from the fundamental mode to the high-order mode and propagates along the cladding, thereby filtering out the spectral component corresponding to the resonant wavelength and achieving fast tunable filtering.

[0046] Among them, the single-mode fiber can be replaced by a dispersion compensation fiber. At this time, the all-fiber acousto-optic tunable filter can include an acoustic wave generator and a dispersion compensation fiber with a reduced diameter (such as by etching or tapering). The acoustic wave generator provides the generated acoustic wave signal to the dispersion compensation fiber, so that the acoustic wave signal propagates along the axis of the dispersion compensation fiber. When the frequency of the acoustic wave signal is adjusted to the frequency band range of the light to be measured, a resonant wavelength corresponding to the frequency of the acoustic wave signal appears on the dispersion compensation fiber. At this time, the spectral component corresponding to the resonant wavelength in the light to be measured propagating along the core jumps from the fundamental mode to the high-order mode and propagates along the cladding, thereby filtering out the spectral component corresponding to the resonant wavelength and achieving fast tunable filtering.

[0047] In this embodiment, when the acoustic wave signal propagates along the axis of the single-mode fiber or the dispersion compensation fiber, the single-mode fiber or the dispersion compensation fiber can be used as a dynamic microbend grating with refractive index perturbation. The distribution of the acoustic-induced refractive index perturbation on the cross-section of the single-mode fiber or the dispersion compensation fiber can be Δn(x,y) = n0(1 + χ)K 2 u0y, where n0 is the refractive index of the core material (such as silica), χ = -0.22 is the elasto-optic coefficient of the core material, K and u0 are the wave vector and amplitude of the acoustic wave signal respectively, K = 2π / Λ, Λ represents the wavelength of the acoustic wave signal, and x and y are the coordinate systems on the cross-section of the fiber, which are perpendicular to the axis of the single-mode fiber or the dispersion compensation fiber respectively.

[0048] The resonant wavelength of the single-mode fiber or the dispersion compensation fiber needs to satisfy the following phase matching: L B = Λ, where L B = 2π / (β 01 -β 11 ) is the beat length between the fundamental mode and the high-order mode, which has a monotonic increasing or decreasing relationship with the optical wavelength. β 01 and β 11 are the propagation constants of the fundamental mode and the high-order mode corresponding to the optical signal wavelength respectively, represents the wavelength of the acoustic wave signal, where R is the radius of the single-mode fiber or the dispersion compensation fiber, C ext= 5760 m / s is the propagation speed of sound waves in fused silica, and f is the sound wave frequency. After the sound wave signal frequency, that is, the sound wave signal wavelength, is adjusted in place, according to the relationship between L B and the optical wavelength, the resonant wavelength of the single-mode fiber or dispersion compensation fiber is determined. In this embodiment, the spectrometer of the present invention may further include a polarizer located before the fast tunable filter. In addition, the spectrometer of the present invention may further include a refractive index matching liquid. The tail of the filtering fiber section in the single-mode fiber or dispersion compensation fiber is placed in the refractive index matching liquid, and the high-order modes propagating along the cladding are absorbed by the refractive index matching liquid.

[0049] The present invention uses an all-fiber acousto-optic tunable filter as the fast tunable filter. The longer the filtering fiber section in its single-mode fiber or dispersion compensation fiber, the smaller the 3dB bandwidth of the fast tunable filter, the smaller the working bandwidth of the corresponding spectrometer, and the higher the resolution. Compared with the multi-mode fiber length of about 100m, the length of the filtering fiber section of the single-mode fiber or dispersion compensation fiber in the filter of the present invention only needs more than a dozen centimeters, and the length of the filtering fiber section is very short. Therefore, its volume is small, it is easy to integrate, and it only consists of two components, an acoustic wave generator and an optical fiber, and its structure is very simple; since the propagation speed C of sound waves in the single-mode fiber or dispersion compensation fiber is very fast and the length L of the filtering fiber section AO is very short, according to the acoustic-optic response time calculation formula: it can be seen that the tuning speed of the all-fiber acousto-optic tunable filter is very fast; the filter of the present invention can use two types of optical fibers, single-mode fibers and dispersion compensation fibers, to construct a spectrometer, and compare the characteristics of the spectrometers constructed by the two: when the filter uses a single-mode fiber, the resolution of the spectrometer constructed by it is low, but the working bandwidth is large. When the filter uses a dispersion compensation fiber, the resolution of the spectrometer constructed by it is high, but the working bandwidth is small. Among them, the tuning range of the dispersion compensation fiber is 1510 - 1700nm, and the tuning range of the single-mode fiber is 1200 - 1700nm. Therefore, compared with the dispersion compensation fiber, when the filter uses a single-mode fiber, the tuning range is higher, but generally the tuning range of the present invention is higher than that of the prior art. When adjusting the resonant wavelength of the single-mode fiber or dispersion compensation fiber, the duration of the corresponding frequency acoustic wave signal after adjustment is greater than the length of the filtering fiber section in the single-mode fiber or dispersion compensation fiber divided by the propagation speed of the acoustic wave signal in the single-mode fiber or dispersion compensation fiber.

[0050] In addition, the working bandwidth of the spectrometer is usually within the working frequency band of the fast tunable filter. For example, if the filtering range of the filter is 1200 - 1700 nm, then 1500 - 1600 nm can be selected as the working wavelength band for spectral detection. The acoustic wave generator may include a connected radio frequency signal generator and a piezoelectric transducer. The radio frequency signal generator sends the radio frequency signal it generates to the piezoelectric transducer, so that the piezoelectric transducer generates an acoustic wave signal with the same frequency. The piezoelectric transducer provides the acoustic wave signal to a single-mode fiber or a dispersion compensation fiber, so that the piezoelectric transducer and the single-mode fiber or the piezoelectric transducer and the dispersion compensation fiber resonate at the same frequency. The data acquisition card is connected to the radio frequency signal generator to collect the start and end times of the period corresponding to the radio frequency signal generated by the radio frequency signal generator. Completing a filtering of all wavelength spectral components in the working bandwidth of the spectrometer in sequence is regarded as one period; the spectral reconstruction module determines a current vector corresponding to the period according to the start and end times of the period of the radio frequency signal collected. In the present invention, a radio frequency generator and a piezoelectric transducer are used as the acoustic wave generator. The amplitude-frequency characteristic of the piezoelectric transducer enables the tunable coupling efficiency of the all-fiber acousto-optic tunable filter of the present invention to be high; and in the present invention, the data acquisition card is connected to the radio frequency signal generator, which can ensure that each group of current vectors corresponds to the period of the radio frequency signal, thereby ensuring the accuracy of current vector acquisition. Combined with Figure 4 As shown, the upper left figure is the frequency modulation curve of the acoustic wave signal, and the lower figure is the collected photocurrent. As the resonant wavelength increases, the concave peak of the photocurrent will move to the right, and its shape depends on the degree of concavity of the tunable filtering peak at this tuning wavelength; Figure 4 The right figure of

[0051] is the waveform diagram of the acoustic wave signal. It can be seen from the figure that the frequency of the acoustic wave signal changes with negative chirp, and the waveform of the acoustic wave signal is the same as that of the radio frequency signal.

[0052] Other embodiments of the present invention will be readily apparent to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention following the general principles of the invention and including known or customary techniques in the art not disclosed herein. The specification and examples are only exemplary, and the true scope and spirit of the invention are pointed out by the following claims.

[0053] It should be understood that the present invention is not limited to the exact structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is only regulated by the appended claims.

Claims

1. A spectrometer based on a fast tunable filter, characterized in that, It includes a rapidly tunable filter, a photodetector, a data acquisition card, and a spectral reconstruction module connected in sequence. The rapidly tunable filter sequentially filters out spectral components of different wavelengths within the working bandwidth of the spectrometer. After each filtering, the photodetector detects an optical signal with corresponding optical intensity and converts the optical signal into an electrical signal. When the wavelength of the filtered spectral component is within the wavelength range of the optical signal to be measured, the optical intensity of the optical signal and the magnitude of the current of the electrical signal decrease. The data acquisition card sequentially collects the currents of each electrical signal to obtain a vector of the current to be measured. The spectral reconstruction module reconstructs the spectrum of the optical signal to be measured based on the collected vector of the current to be measured and the pre-stored spectral transmission matrix. The process of obtaining the spectral transmission matrix is as follows: The spectral components of different wavelengths within the working bandwidth of the spectrometer are sequentially input to the rapidly tunable filter. For each spectral component within the working bandwidth of the spectrometer, after receiving the spectral component, the rapidly tunable filter sequentially filters out spectral components of different wavelengths within the working bandwidth of the spectrometer. After each filtering, the photodetector detects an optical signal with corresponding optical intensity and converts the optical signal into an electrical signal. The data acquisition card sequentially collects the currents of each electrical signal to obtain a reference current vector corresponding to the spectral component. The spectral transmission matrix is composed of reference current vectors corresponding to each spectral component within the working bandwidth of the spectrometer.

2. The spectrometer based on a fast tunable filter according to claim 1, characterized in that, The vector of the current to be measured and the reference current vector are both row vectors or column vectors. The spectral reconstruction module reconstructs the spectrum of the optical signal to be measured based on the collected vector of the current to be measured and the pre-stored spectral transmission matrix using an improved spectral matrix demodulation method. In the improved spectral matrix demodulation method, the spectral vector of the optical signal to be measured is represented by the product of a Gaussian function matrix and a weight coefficient vector, and a Tikhonov regularization term is introduced when determining the weight coefficient vector.

3. The spectrometer based on a rapidly tunable filter according to claim 2, wherein The spectral reconstruction module reconstructs the spectral vector of the optical signal to be measured according to the following steps: Step S110: Expand the spectral vector of the light to be measured using Gaussian basis functions: where is the Gaussian basis function of the spectral component corresponding to the wavelength in the light to be measured, m is the number of spectral components with different wavelengths within the working broadband of the spectrometer, and α j is the weight coefficient of the spectral component corresponding to the wavelength in the light to be measured, is the Gaussian basis function matrix, is the weight coefficient vector; σ is the standard deviation of the Gaussian function, λ is the wavelength of the spectral component corresponding to the light to be measured, and λ j is the central wavelength of the Gaussian basis function; Step S120, the measured current vector to be measured Pre-stored spectral transmittance matrix The relationship between the spectral vector S(λ) of the light to be measured is as follows: Step S130: Based on the least squares method, introduce a Tikhonov regularization term and determine the weight coefficient vector according to the following formula where first calculate the square of the Euclidean norm of and the square of the Euclidean norm of multiplied by the square of the regularization coefficient γ, add the two calculated terms, find the minimum value in the added result, and the corresponding to the minimum value is the determined weight coefficient vector γ is obtained by the generalized cross-validation method; Step S140, according to this formula determine the spectral vector S(λ) of the light to be measured.

4. The spectrometer based on a fast tunable filter according to any one of claims 1 to 3, characterized in that, During the process of obtaining the spectral transmission matrix, for each spectral component within the working bandwidth of the spectrometer, when inputting the spectral component to the rapidly tunable filter, the filtering wavelength of the rapidly tunable filter is different, and the optical response rate is different. The reference current vector corresponding to the spectral component consists of each optical response rate. Each optical responsivity R is calculated by the spectral reconstruction module ij =(I light -I dark ) / P, where I light represents the current collected by the data acquisition card when the i-th spectral component within the working bandwidth of the spectrometer is input to the fast tunable filter and the filtering wavelength of the fast tunable filter is the j-th wavelength within the working bandwidth of the spectrometer; I dark represents the current collected by the data acquisition card when no optical signal is input to the fast tunable filter and the filtering wavelength of the fast tunable filter is the j-th wavelength within the working bandwidth of the spectrometer, and P represents the power of the i-th spectral component.

5. The spectrometer based on a fast tunable filter according to claim 2, wherein, The rapidly tunable filter is an all-fiber acousto-optic tunable filter, which includes an acoustic wave generator and a single-mode fiber without a coating layer. The acoustic wave generator provides the acoustic wave signal it generates to the single-mode fiber to make the acoustic wave signal propagate along the axial direction of the single-mode fiber. When the frequency of the acoustic wave signal is adjusted to the frequency band range of the optical signal to be measured, a resonant wavelength corresponding to the frequency of the acoustic wave signal appears on the single-mode fiber. At this time, the spectral component corresponding to the resonant wavelength in the optical signal to be measured propagating along the core jumps from the fundamental mode to the higher-order mode and propagates along the cladding, thereby filtering out the spectral component corresponding to the resonant wavelength and achieving rapidly tunable filtering.

6. The spectrometer based on a rapidly tunable filter according to claim 2, wherein, The fast tunable filter is an all-fiber acousto-optic tunable filter, which includes an acoustic wave generator and a dispersion compensation fiber with a reduced diameter. The acoustic wave generator provides the acoustic wave signal it generates to the dispersion compensation fiber, so that the acoustic wave signal propagates along the axis of the dispersion compensation fiber. When the frequency of the acoustic wave signal is adjusted to the frequency band range of the optical signal to be measured, a resonant wavelength corresponding to the frequency of the acoustic wave signal appears on the dispersion compensation fiber. At this time, the spectral component corresponding to the resonant wavelength in the optical signal to be measured propagating along the core jumps from the fundamental mode to the high-order mode and propagates along the cladding, thereby filtering out the spectral component corresponding to the resonant wavelength and realizing fast tunable filtering.

7. The spectrometer based on a fast tunable filter according to claim 5 or 6, characterized in that: The resonant wavelength satisfies phase matching: L B = Λ, where L B is the beat length between the fundamental mode and the higher-order mode, showing a monotonic increasing or decreasing relationship with the optical wavelength, and Λ represents the wavelength of the acoustic wave signal; After the frequency of the acoustic wave signal, i.e., the wavelength of the acoustic wave signal, is adjusted in place, determine the resonant wavelength according to the relationship between L B and the optical wavelength.

8. The spectrometer based on a fast tunable filter according to claim 7, characterized in that: The longer the filtering fiber section in the optical fiber, the smaller the 3dB bandwidth of the fast tunable filter, the smaller the working bandwidth of the corresponding spectrometer, and the higher the resolution; when adjusting the resonant wavelength, the duration of the acoustic wave signal corresponding to the adjusted frequency is greater than the length of the filtering fiber section divided by the propagation speed of the acoustic wave signal in the optical fiber.

9. The spectrometer based on a rapidly tunable filter according to claim 5 or 6, characterized in that, It further includes a refractive index matching liquid. The tail of the filtering fiber section in the optical fiber is placed in the refractive index matching liquid, and the high-order mode propagating along the cladding is absorbed by the refractive index matching liquid.

10. The spectrometer based on a rapidly tunable filter according to claim 5 or 6, characterized in that, The acoustic wave generator includes a connected radio frequency signal generator and a piezoelectric transducer. The radio frequency signal generator sends the radio frequency signal it generates to the piezoelectric transducer, so that the piezoelectric transducer generates an acoustic wave signal with the same frequency, and the piezoelectric transducer provides the acoustic wave signal to the optical fiber; The data acquisition card is connected to the radio frequency signal generator to collect the start and end times of the period corresponding to the radio frequency signal generated by the radio frequency signal generator. All the spectral components of all wavelengths within the working bandwidth of the spectrometer are filtered in sequence once as a period; the spectral reconstruction module determines a current vector corresponding to the period according to the start and end times of the period of the radio frequency signal collected.

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