CN114383527A - Multi-channel grating demodulation device and method for frequency multiplexing and demultiplexing - Google Patents
Multi-channel grating demodulation device and method for frequency multiplexing and demultiplexing Download PDFInfo
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- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
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- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
- G01K11/3206—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres at discrete locations in the fibre, e.g. using Bragg scattering
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Abstract
The invention discloses a frequency multiplexing and demultiplexing multi-channel grating demodulation device and a frequency multiplexing and demultiplexing multi-channel grating demodulation method. Based on a coherent detection technology, the multi-channel signal is subjected to frequency multiplexing, photoelectric signal conversion is realized on a single photoelectric detector, analog-to-digital conversion is carried out by using a single-channel acquisition card, FFT operation is realized by using an FPGA (field programmable gate array) inside the acquisition card, the physical position and the spectrum signal of the FBG to be detected are output, and finally a series of data processing operations such as window inverse Fourier transform and the like are carried out in the calculation to obtain rapid temperature and strain demodulation. The invention can realize multichannel rapid fiber grating demodulation, realizes frequency sweep light source multiplexing and single-channel acquisition, and greatly saves the cost of a demodulation device on the premise of meeting the performance.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to a frequency multiplexing and demultiplexing multi-channel grating demodulation device and method.
Background
The high-speed strain measurement and impact collision vibration test have wide requirements. The conventional means comprises an electronic strain gauge and a fiber grating; the electronic strain gauge is not suitable for special fields due to the problem of electric and electromagnetic compatibility. The fiber grating strain measurement has the characteristics of small volume, light weight, high sensitivity, strong anti-interference capability and the like, and is particularly suitable for monitoring high-speed strain, impact collision and the like.
Currently, the Fiber sensing demodulation technology is developed rapidly, wherein the attention of FBG (Fiber Bragg Grating) demodulation based on a tunable laser source is obviously improved due to the unique technical advantages of the FBG demodulation. The FBG demodulation technology of the tunable laser light source is mainly based on a fast frequency sweep laser, and temperature strain demodulation can be conveniently realized through spectral drift of a grating reflection spectrum only by the fiber grating in the spectral range of the frequency sweep laser. The scheme has the advantages of high demodulation speed, high signal-to-noise ratio, simple demodulation algorithm and the like, and has wide application prospect in the FBG sensing field.
FBG demodulation based on a frequency-sweeping laser is mainly characterized in that gratings with different reflection spectrums are connected in series in a single channel, and multiplexing of multiple FBGs is realized. The main problems faced by this conventional scheme are that the spatial resolution is not high and a large number of FBGs of different center wavelengths are required to make the sensor; in the multi-channel multiplexing, the optical power of the light source needs to be divided into multiple paths, and the power of the light source is sacrificed, so that the signal-to-noise ratio of the grating spectrum is reduced, and the measurement range and the measurement precision are further influenced.
Disclosure of Invention
In view of the above-mentioned drawbacks and needs of the prior art, the present invention provides a multi-channel grating demodulation apparatus and method for frequency multiplexing and demultiplexing. The invention adopts a linear frequency-sweeping laser as a light source, accurately positions the FBG position in each channel by utilizing a frequency-sweeping coherent detection technology, and secondarily shifts the frequency of each channel by utilizing an acousto-optic frequency shift technology, thereby realizing multi-channel parallel demodulation and obviously improving the demodulation speed.
According to one aspect of the present invention, the present invention provides a multi-channel grating demodulation apparatus for frequency multiplexing and demultiplexing, which includes a linear frequency-sweeping laser, a first optical fiber coupler, a second optical fiber coupler, an optical fiber circulator, an optical fiber beam splitter, a plurality of acousto-optic frequency shifters, an FBG optical fiber grating, a photodetector, a data acquisition card, and a computer; wherein:
the linear frequency-sweeping laser is used for emitting frequency-sweeping laser with linearly changed wavelength;
the input end of the first optical fiber coupler is connected with the output end of the linear frequency-sweeping laser and is used for dividing the frequency-sweeping laser into two paths, wherein one path is signal light, and the other path is reference light;
an input end of the second optical fiber coupler is connected with an output end of the first optical fiber coupler, so that the reference light enters the second optical fiber coupler;
the first port of the optical fiber circulator is connected with the other output end of the first optical fiber coupler, so that signal light enters the optical fiber circulator;
the optical splitter is connected with the second port of the optical fiber circulator and is used for splitting the signal light transmitted by the optical fiber circulator into a plurality of light beams, each light beam corresponds to one channel, and each channel corresponds to one end of an acousto-optic frequency shifter which is sequentially connected with the output port of the optical splitter;
the other end of each acousto-optic frequency shifter is used for being sequentially connected with an FBG fiber grating, and the acousto-optic frequency shifter is used for carrying out frequency shifting on the grating reflection spectrum of each channel so as to enable each channel to generate different frequency shifting quantities and realize frequency multiplexing; the optical beam splitter is also used for transmitting the light reflected by each channel to the optical beam splitter;
the third port of the optical fiber circulator is connected with the other input end of the second optical fiber coupler, so that the light reflected by each channel transmitted to the optical splitter is subjected to the second optical fiber coupler and interferes with the reference light to generate an interference signal;
the photoelectric detector is used for converting the interference signal into an electric signal;
the data acquisition card acquires a mixing interference signal in the electrical signal, performs FFT (fast Fourier transform) on the mixing interference signal, and demultiplexes the mixing interference signal to obtain a position signal and amplitude information of each FBG (fiber Bragg Grating);
and the computer is used for controlling the laser and the data acquisition card, and transmitting the data after the data acquisition card is subjected to FFT to a memory of the computer for secondary operation to obtain the spectral response information of each optical fiber.
Further, in the frequency-multiplexed and demultiplexed multi-channel grating demodulation apparatus of the present invention, half of the frequency shift amount of each channel is larger than the maximum sweep difference frequency of the previous channel.
Furthermore, in the frequency multiplexing and demultiplexing multi-channel grating demodulation device of the invention, the high-speed acquisition card is a single-channel acquisition card, and the inside of the acquisition card can be subjected to FFT (fast Fourier transform).
Further, in the frequency-multiplexed and demultiplexed multi-channel grating demodulation apparatus of the present invention, the quadratic operation includes a fast windowed inverse fourier transform.
Further, in the frequency multiplexing and demultiplexing multi-channel grating demodulating apparatus of the present invention, the photodetector is a single-channel photodetector.
According to another aspect of the present invention, to solve the technical problem, there is provided a multi-channel grating demodulation method for frequency multiplexing and demultiplexing, which is used in the multi-channel grating demodulation apparatus, and includes the following steps:
firstly, setting the frequency shift quantity of the acousto-optic frequency shifter in each channel by adopting a frequency multiplexing technology, so that the FBG fiber bragg grating carries out frequency shift on the spectrum reflected by the frequency-swept laser, and acquiring the interference signal of the second fiber coupler by utilizing an optical heterodyne detection technology to obtain the frequency shift quantity of the acousto-optic frequency shifter and the frequency-swept quantity of the frequency-swept laser;
secondly, performing fast Fourier transform operation on the mixed interference signals in the acquired interference signals in an acquisition card to obtain the spectral reflection intensity of each position of different channels, so as to realize the positioning of each FBG fiber grating;
thirdly, performing window inverse Fourier transform on the FBG fiber gratings at different positions to obtain spectral response information of each FBG fiber grating;
and fourthly, finding the abscissa corresponding to the maximum value of the reflection spectrum of each FBG based on the spectral response information, and quickly demodulating the temperature or the strain by combining a temperature strain demodulation formula.
Advantageous effects
Compared with the prior art, the invention has the beneficial effects that: the invention provides a frequency multiplexing and demultiplexing multi-channel grating demodulation device and method, which are based on a sweep frequency light source and a coherent detection technology, and realize the multi-channel high-capacity fast demodulation of a grating by adopting the frequency multiplexing and demultiplexing technology in the fast demodulation of the fiber grating. The invention only uses one sweep frequency laser, greatly saves the cost, and the invention adopts the coherent detection technology, can obviously improve the signal-to-noise ratio of the grating spectrum, thus obtaining the strain test with high precision and high measuring range; the invention only adopts a single-path photoelectric detector and a single-path acquisition card, the cost is obviously reduced, a large amount of parallel operations such as fast Fourier transform and the like are realized in the acquisition card, the demodulation rate is improved, and the invention is particularly suitable for high-speed strain and impact collision measurement.
Drawings
FIG. 1 is a schematic diagram of a frequency multiplexing and demultiplexing multi-channel fiber grating demodulation apparatus according to the present invention;
FIG. 2 is a schematic diagram of grating reflectivity-distance output after acquisition and transformation by the acquisition card of the present invention;
FIG. 3 is a flow chart of a grating demodulation method of the present invention;
in fig. 1, 1 is a linear frequency-sweeping laser 1, 2 is a first fiber coupler, 3 is a fiber circulator, 4 is a second fiber coupler, 5 is a fiber splitter, 6 is a first acousto-optic frequency shifter, 7 is a first FBG fiber grating, 8 is a second FBG fiber grating, 9 is a second acousto-optic frequency shifter, 10 is a third FBG fiber grating, 11 is a fourth FBG fiber grating, 12 is a photodetector, 13 is a data acquisition card, and 14 is a computer.
Detailed Description
In order to make the technical means, the original characteristics, the achieved purposes and the effects of the invention easily understood, the invention is further described below with reference to the specific embodiments and the attached drawings, but the following embodiments are only the preferred embodiments of the invention, and not all embodiments. Based on the embodiments in the implementation, other embodiments obtained by those skilled in the art without any creative efforts belong to the protection scope of the present invention.
Specific embodiments of the present invention are described below with reference to the accompanying drawings.
The multi-channel grating demodulating device for frequency multiplexing and demultiplexing of the embodiment of the invention totally adopts 2 channels, and comprises a linear frequency-sweeping laser 1, a first optical fiber coupler 2, an optical fiber circulator 3, a second optical fiber coupler 4, an optical fiber beam splitter 5, a first acousto-optic frequency shifter 6, a first FBG optical fiber grating 7, a second FBG optical fiber grating 8, a second acousto-optic frequency shifter 9, a third FBG optical fiber grating 10, a fourth FBG optical fiber grating 11, a photoelectric detector 12, a data acquisition card 13 and a computer 14.
The output end of the linear scanning laser 1 is connected with the input end of the first optical fiber coupler 2, and two output ends of the first optical fiber coupler 2 are respectively connected with the a port of the optical fiber circulator and one input end of the second optical fiber coupler 4.
The port b of the optical fiber circulator 3 is connected with the input end of the optical fiber beam splitter 5, and the port c of the optical fiber circulator 3 is connected with the other input end of the second optical fiber coupler.
The output end of the optical fiber splitter 5 is respectively connected with one end of a first acousto-optic frequency shifter 6 and one end of a second acousto-optic frequency shifter 9 in the two channels.
In the channel 1, the other end of the first acousto-optic frequency shifter 6 is respectively connected with the first FBG fiber bragg grating 7 and the second FBG fiber bragg grating 8 in sequence.
In the channel 2, the other end of the second acoustic-optical frequency shifter 9 is sequentially connected with a third FBG fiber grating 10 and a fourth FBG fiber grating 11 respectively.
The output end of the second fiber coupler 4, that is, the beam combining end, is connected to the photodetector 12, and after the photodetector 12 is connected to the data acquisition card 13, the data acquisition card 13 is connected to the computer 14.
The invention is based on the coherent detection technology, skillfully multiplexes the frequency of multi-channel signals, and realizes the conversion of photoelectric signals in a single detector. The coherent detection technology is as follows: the linear frequency-sweeping laser 1 emits frequency-sweeping laser with linearly changing wavelength, the frequency-sweeping laser enters the first optical fiber coupler 2, the frequency-sweeping laser is divided into two paths in the first optical fiber coupler 2, one path is signal light and enters the optical fiber circulator 3, and the other path is reference light and enters the second optical fiber coupler 4.
The signal light sequentially enters the optical fiber beam splitter 5 and then respectively enters each channel. In the channel 1, the signal light enters the first acousto-optic frequency shifter 6 and then continues to enter the first FBG fiber grating 7 and the second FBG fiber grating 8, and the FBG fiber grating reflects the spectrum with a specific wavelength. The reflected spectrum returns along the path, returns to the b port of the optical fiber circulator 3, and then exits from the c port to enter the second optical fiber coupler 4, and interferes with the reference light at the second optical fiber coupler 4. In the channel 2, the signal light enters the second acoustic frequency shifter 9 and then continues to enter the third FBG fiber grating 10 and the second FBG fiber grating 11, and the FBG fiber grating reflects the spectrum with a specific wavelength. The reflected spectrum returns along the path, returns to the b port of the optical fiber circulator 3, and then exits from the c port to enter the second optical fiber coupler 4, and interferes with the reference light at the second optical fiber coupler 4.
In each channel, the paths traveled by the signal light and the reference light are different, so that the two paths of light have a distance difference, the distance difference corresponds to a time difference, and the time difference corresponds to a frequency difference. Therefore, the second fiber coupler 4 generates mixed interference, and the photodetector 12 can detect the mixed interference by using an optical heterodyne coherent detection technology.
Taking channel 1 as an example:
after the first fiber coupler 2 is split, the reference light reaches the second fiber coupler 4, and the path is A0；
After the beam splitting of the first optical fiber coupler 2, the signal light is reflected back by the first acousto-optic frequency shifter 6 through the first optical fiber grating 7, and then reaches the second optical fiber coupler 4 through the optical fiber circulator 3, and the path is A1；
The difference between them is
△f1=γ(|A0-A1|. n)/c formula 1
Wherein gamma is the sweep frequency speed of the laser, and the unit is nm/s (or GHz/s); n is the refractive index of the fiber and c is the speed of light.
After the beam splitting of the first optical fiber coupler 2, the signal light passes through the first acousto-optic frequency shifter 6, is reflected back by the second optical fiber grating 8, passes through the optical fiber circulator 3 and reaches the second optical fiber coupler 4, and the path is A2;
the difference between them is
△f1=γ(|A0-A2|. n)/c formula 2
Wherein gamma is the sweep frequency speed of the laser, and the unit is nm/s (or GHz/s); n is the refractive index of the fiber and c is the speed of light.
Since the sweep speed of the laser is known, the refractive index of the fiber is known, and the speed of light is known, the frequency difference and the distance difference are in a linear relationship, i.e., the position of each grating can be known by demodulating the frequency difference.
Specifically, for convenience of description, we will refer to the difference frequency as a sweep difference.
The frequency multiplexing and demultiplexing multi-channel grating demodulation in the invention refers to: in each channel, an acousto-optic frequency shifter is introduced, so that a frequency shift difference is continuously added to grating reflection spectrum signals at all positions of each channel on the premise of containing a frequency sweep difference, and half of the frequency shift amount of the frequency shift difference is larger than the frequency sweep difference (maximum frequency sweep difference frequency) of the reflection spectrum at the position of the last grating of the previous channel, and the frequency is multiplexed.
Therefore, each FBG fiber grating contains a sweep frequency difference and a shift frequency difference relative to the reference light, after frequency mixing interference of the sweep frequency difference and the shift frequency difference, the signals are converted into electric signals in the single photoelectric detector 12 and collected by the data collection card 13, fast fourier transform is realized inside the data collection card 13, and the grating spectrum at each position of each channel is solved, which is frequency demultiplexing.
The core of the invention is that the multi-channel temperature and strain demodulation is realized by utilizing a single linear frequency-sweeping laser 1, a single photoelectric detector 12 and a single-channel acquisition card 13. The key means is to add an acousto-optic frequency shifter in each channel and set different frequency shift amount. And the frequency sections of each channel are staggered, each signal light is subjected to frequency modulation by different acousto-optic frequency shifters, the signal light processed by the different acousto-optic frequency shifters returns to the optical fiber circulator 3 along a path, and finally interferes with the reference light at the second optical fiber coupler 4.
Particularly, since the signal light passes through the acousto-optic frequency shifter twice, in order to ensure that the frequency difference of any two paths does not overlap, the invention requires that half of the frequency shift amount of each channel must be greater than the maximum sweep frequency difference frequency of the previous path, that is:
△mm>2△（fn）m-1 formula 3
Wherein m is a channel number,. DELTA.mmAnd n is the sweep frequency difference between the last grating reflection spectrum of any channel and the reference light.
Fig. 2 is a schematic diagram of grating reflectivity-distance obtained by fast fourier transform of data acquired by the data acquisition card 13. As shown in FIG. 2, the abscissa is distance, i.e., frequency difference, and the ordinate is reflectivity, 0- Δ m1Within the frequency difference of/2, the position information reflection signals of the first FBG fiber grating 7 and the second FBG fiber grating 8 in the first channel are within the range of Deltam1/2-△m2The frequency difference of/2 is the position information reflection signal of the third FBG fiber grating 10 and the fourth FBG fiber grating 11 of the second channel.
Therefore, the positions of all FBG fiber gratings of all channels are completely unfolded, each aliasing can demodulate all grating spectrums of all channels only by corresponding each grating to the obtained reflection spectrum through simple positioning, and the position precision positioning can reach millimeter magnitude.
The fiber grating demodulation is as follows: and taking the independent window as a unit for carrying out secondary data processing, namely, inverse Fourier transform on the FBG fiber bragg grating after each frequency is demultiplexed. As shown in fig. 3, taking the fourth FBG fiber grating 11 as an example, the distance domain information of the fourth FBG fiber grating 11 is subjected to window inverse fourier transform to obtain the spectrum information of the whole frequency-swept laser.
It is specifically noted here that the spectrum reflected by the linear swept-frequency laser 1 after entering the FBG fiber grating is the spectral information of the specific wavelength of the FBG fiber grating, and the spectral information may drift under the external temperature strain.
The purpose of performing a windowed inverse fourier transform on the range domain signal is to obtain a swept-frequency spectral signal.
The FBG fiber bragg gratings corresponding to different difference frequencies are accurately positioned through frequency multiplexing and demultiplexing and through two times of Fourier transformation, and spectrum inversion is realized.
After window Fourier transform, the spectrum signal of each FBG fiber grating is obtained, the drift of the abscissa corresponding to the highest point is only needed to be found for the spectrum information, the change amount of the temperature strain can be obtained according to the temperature strain and spectrum frequency shift formula, and the speed is remarkably improved. The strain can be demodulated in the same way.
The device remarkably improves the spectral signal-to-noise ratio through a coherent detection technology. The frequency multiplexing technology is applied to fiber bragg grating demodulation for the first time, signals after frequency mixing interference are converted into distance domain signals through fast Fourier transform, and the distance domain signals can be used for carrying out window inverse Fourier transform to obtain spectral information of each grating after the position of each fiber bragg grating is accurately positioned.
The device and the method can realize large-scale fiber grating array demodulation, the demodulation speed is obviously improved, and the coherent detection technology is adopted, so that the device and the method have the advantages of high grating spectrum signal-to-noise ratio, obviously improved accuracy and stability of temperature strain measurement, and are particularly suitable for high-accuracy collision vibration test.
The multichannel parallel grating demodulation device and method based on frequency multiplexing and demultiplexing specifically comprise several steps
Firstly, setting the frequency shift amount of an acousto-optic frequency shifter in each channel by adopting a frequency multiplexing technology, so that the FBG fiber bragg grating carries out frequency shift on the spectrum reflected by the frequency-swept laser, and acquiring an interference signal of a second fiber coupler by utilizing an optical heterodyne detection technology to obtain the frequency shift amount of the acousto-optic frequency shifter and the frequency-swept amount of the frequency-swept laser;
secondly, performing fast Fourier transform operation on the mixed interference signals in the acquired interference signals in an acquisition card to obtain the spectral reflection intensity of each position of different channels, so as to realize the positioning of each FBG fiber grating;
thirdly, performing window inverse Fourier transform on the FBG fiber gratings at different positions to obtain spectral response information of each FBG fiber grating;
and fourthly, finding the abscissa corresponding to the maximum value of the reflection spectrum of each FBG based on the spectral response information, and quickly demodulating the temperature or the strain by combining a temperature strain demodulation formula.
It should be noted that, for better explaining the apparatus and scheme, the present invention only gives an example of 2 FBG fiber gratings for 2 channels, and 4 FBG demodulators. It will be appreciated that the invention is equally applicable to channels greater than 2, 1 or greater than 2 FBG fibre gratings per channel.
In the present invention, unless otherwise expressly stated or limited, "above" or "below" a first feature means that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact with each other via another feature therebetween. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly under and obliquely below the second feature, or simply meaning that the first feature is at a lesser elevation than the second feature.
The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and the preferred embodiments of the present invention are described in the above embodiments and the description, and are not intended to limit the present invention. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (6)
1. A multi-channel grating demodulation device for frequency multiplexing and demultiplexing is characterized by comprising a linear frequency-sweeping laser, a first optical fiber coupler, a second optical fiber coupler, an optical fiber circulator, an optical fiber beam splitter, a plurality of acousto-optic frequency shifters, an FBG (fiber Bragg Grating) optical fiber grating, a photoelectric detector, a data acquisition card and a computer; wherein:
the linear frequency-sweeping laser is used for emitting frequency-sweeping laser with linearly changed wavelength;
the input end of the first optical fiber coupler is connected with the output end of the linear frequency-sweeping laser and is used for dividing the frequency-sweeping laser into two paths, wherein one path is signal light, and the other path is reference light;
an input end of the second optical fiber coupler is connected with an output end of the first optical fiber coupler, so that the reference light enters the second optical fiber coupler;
the first port of the optical fiber circulator is connected with the other output end of the first optical fiber coupler, so that signal light enters the optical fiber circulator;
the optical splitter is connected with the second port of the optical fiber circulator and is used for splitting the signal light transmitted by the optical fiber circulator into a plurality of light beams, each light beam corresponds to one channel, and each channel corresponds to one end of an acousto-optic frequency shifter which is sequentially connected with the output port of the optical splitter;
the other end of each acousto-optic frequency shifter is used for being sequentially connected with an FBG fiber grating, and the acousto-optic frequency shifter is used for carrying out frequency shifting on the grating reflection spectrum of each channel so as to enable each channel to generate different frequency shifting quantities and realize frequency multiplexing; the optical beam splitter is also used for transmitting the light reflected by each channel to the optical beam splitter;
the third port of the optical fiber circulator is connected with the other input end of the second optical fiber coupler, so that the light reflected by each channel transmitted to the optical splitter is subjected to the second optical fiber coupler and interferes with the reference light to generate an interference signal;
the photoelectric detector is used for converting the interference signal into an electric signal;
the data acquisition card acquires a mixing interference signal in the electrical signal, performs FFT (fast Fourier transform) on the mixing interference signal, and demultiplexes the mixing interference signal to obtain a position signal and amplitude information of each FBG (fiber Bragg Grating);
and the computer is used for controlling the laser and the data acquisition card, and transmitting the data after the data acquisition card is subjected to FFT to a memory of the computer for secondary operation to obtain the spectral response information of each optical fiber.
2. The frequency multiplexed and demultiplexed multi-channel grating demodulation apparatus according to claim 1, wherein half of the frequency shift amount of each channel is larger than the maximum swept difference frequency of the previous channel.
3. The frequency multiplexing and demultiplexing multi-channel grating demodulator according to claim 1, wherein said high speed acquisition card is a single channel acquisition card, and the inside of the acquisition card can be FFT transformed.
4. The frequency multiplexed and demultiplexed multi-channel grating demodulation device according to claim 1 wherein the quadratic operation comprises a fast windowed inverse fourier transform.
5. The frequency multiplexed and demultiplexed multi-channel grating demodulation device according to claim 1, wherein the photo detector is a single-channel photo detector.
6. A multi-channel grating demodulation method for frequency multiplexing and demultiplexing, for a multi-channel grating demodulation apparatus according to any one of claims 1 to 5, comprising the steps of:
firstly, setting the frequency shift amount of an acousto-optic frequency shifter in each channel by adopting a frequency multiplexing technology, so that the FBG fiber bragg grating carries out frequency shift on the spectrum reflected by the frequency-swept laser, and acquiring an interference signal of a second fiber coupler by utilizing an optical heterodyne detection technology to obtain the frequency shift amount of the acousto-optic frequency shifter and the frequency-swept amount of the frequency-swept laser;
secondly, performing fast Fourier transform operation on the mixed interference signals in the acquired interference signals in an acquisition card to obtain the spectral reflection intensity of each position of different channels, so as to realize the positioning of each FBG fiber grating;
thirdly, performing window inverse Fourier transform on the FBG fiber gratings at different positions to obtain spectral response information of each FBG fiber grating;
and fourthly, finding the abscissa corresponding to the maximum value of the reflection spectrum of each FBG based on the spectral response information, and quickly demodulating the temperature or the strain by combining a temperature strain demodulation formula.
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