CN110736708B - FBG high-precision demodulation method based on recovery in variable temperature environment - Google Patents
FBG high-precision demodulation method based on recovery in variable temperature environment Download PDFInfo
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- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
- G01D5/35309—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer
- G01D5/35316—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer using a Bragg gratings
Abstract
The invention discloses a recovery-based FBG high-precision demodulation method in a variable temperature environment, which comprises an ASE broadband light source (1), an optical fiber isolator (2), a tunable F-P filter (3), an optical fiber 1 multiplied by 2 coupler (4), first and second optical fiber circulators (5) and (6), an optical fiber Bragg grating string (7), an HCN air chamber (8), a photoelectric detector array (9), a data acquisition card (10), a processing unit (11) and a signal generation module (12); and processing the collected HCN gas chamber absorption signal by using a back convolution algorithm to obtain a recovered HCN absorption spectrum with a sharp absorption peak as an absolute wavelength reference, thereby realizing high-precision demodulation of the fiber bragg grating wavelength. The method does not need a redundant device structure, overcomes the influence of temperature change on the demodulation result, and can effectively improve the demodulation performance in constant-temperature and variable-temperature environments; the demodulation precision is improved by 49.4 percent on average. The range of accurate demodulation is extended to the entire C-band.
Description
Technical Field
The invention belongs to the technical field of fiber bragg grating sensing, and particularly relates to a FBG high-precision demodulation method based on a recovered HCN gas chamber absorption spectrum in a variable temperature environment.
Background
In recent years, the application of Fiber Bragg Grating (FBG) sensing in many fields has attracted much attention. To date, researchers have developed a number of demodulation schemes such as optical interferometry, edge filtering, tunable laser or tunable fabry-perot (F-P) filtering, and spectral analysis, among others. Among them, the fiber grating demodulation system based on tunable F-P filter has been widely researched and applied because of its high demodulation precision.
The ambient temperature in practical applications can sometimes vary greatly. For example, spacecraft are typically operated in harsh temperature swing conditions such as vacuum environments. In addition, monitoring of international oil pipelines by fiber optic sensing systems can also face serious temperature and humidity variation challenges. Approaches based on tunable F-P filters in combination with F-P etalons are susceptible to unpredictable temperature variations, which can lead to large errors. In order to stabilize the demodulation result of the sensing fiber grating, researchers have proposed several real-time calibration wavelength reference methods of tunable F-P filters. Acetylene (C)2H2) And Hydrogen Cyanide (HCN) are insensitive to temperature variations, so researchers use their absorption spectra to calibrate etalons. However, the additional calibration module causes a complicated structure and additional errors. There is a literature on the use of acetylene (C) alone2H2) As a reference for demodulating the wavelength of the system, but in the C band, C2H2The wavelength coverage of the gas cell is only 3nm, limiting the wavelength division multiplexing capability of the sensors in the system. There is another method that uses an HCN gas cell as an absolute wavelength reference. The method can only demodulate the Bragg wavelength grating near the wave band with a sharp HCN gas chamber absorption peak. The absorption peak is shallow at the C-band edge and the mark point, so the demodulation accuracy of this region is reduced. In addition, the method needs to adopt a tunable F-P filter to control the output of the ASE broadband light source. The bandwidth of the F-P filter can widen the absorption peak of the absorption spectrum of the HCN gas chamber, thereby making the determination of the peak position of the absorption peak difficult and reducingThe accuracy of the demodulation.
Therefore, a demodulation scheme based on deconvolution is proposed herein, which is used to recover the absorption spectrum from the broadening of the F-P filter, resulting in an HCN gas cell absorption spectrum with sharp absorption peaks for demodulation.
Disclosure of Invention
Aiming at the prior art and the defects thereof, the invention aims to provide a FBG high-precision demodulation device method based on recovery in a variable temperature environment, which recovers an absorption spectrum from the broadening of an F-P filter based on a deconvolution demodulation scheme to obtain an HCN gas chamber absorption spectrum with a sharp absorption peak for temperature demodulation based on fiber gratings, and is applied to variable temperature environments such as aerospace, petrochemical industry, civil power and the like.
The FBG high-precision demodulation method based on recovery in the variable temperature environment realizes demodulation by using an FBG high-precision demodulation device, wherein the FBG high-precision demodulation device comprises an ASE broadband light source 1, an optical fiber isolator 2, a tunable F-P filter 3, an optical fiber 1 multiplied by 2 coupler 4, a first optical fiber circulator 5, a second optical fiber circulator 6, an optical fiber Bragg grating string 7, an HCN air chamber (8), a photoelectric detector array 9, a data acquisition card 10, a processing unit 11 and a signal generation module 12; the ASE broadband light source 1, the optical fiber isolator 2, the tunable F-P filter 3 and the optical fiber 1 x 2 coupler 4 are sequentially connected, the output end of the optical fiber 1 x 2 coupler 4 is divided into two paths, one path is sequentially connected with the first optical fiber circulator 5, the optical fiber Bragg grating string 7 and the photoelectric detector array 9, and the other path is sequentially connected with the second optical fiber circulator 6, the HCN air chamber 8 and the photoelectric detector array 9; the output end of the photoelectric detector array 9 is sequentially connected with the data acquisition card 10 and the processing unit 11, and the data acquisition card 10 is connected with the tunable F-P filter 3 through a signal generation module (12); the broadband light emitted by the ASE broadband light source 1 enters the tunable F-P filter 3 after passing through the optical fiber isolator 2, the broadband light is converted into narrow-band light which is scanned back and forth, the scanned narrow-band light enters from the input port of the optical fiber 1 x 2 coupler 4 and is divided into two paths according to the ratio of 1:1 to be output: one path enters from an input port of the first optical fiber circulator 5, is input into the optical fiber Bragg grating string 7 from an output port, and reflects light with corresponding wavelength to enter the photodetector array 9; the other path enters from the input port of the first optical fiber circulator 5, and is input to the HCN gas chamber through the output port, and then is detected by the photodetector array 9 to obtain an absorption spectrum of the HCN gas chamber, the photodetector array 9 converts an optical signal into an electrical signal and amplifies the electrical signal, the amplified electrical signal is subjected to acquisition of all data in the temperature rise process by the data acquisition card 10, an analog voltage signal is converted into a digital signal, and the digital signal is sent to the processing unit 11 for signal processing, and the processing flow of the processing unit 11 specifically includes the following steps:
on one hand, the HCN gas chamber detected by the detector absorbs signals;
removing light source envelope from the HCN gas chamber absorption signal detected by the detector;
then eliminating random noise in the HCN air chamber absorption signal by using a low-pass filter;
performing FFT (fast Fourier transform) on the spectrum to obtain a spectrum of an absorption spectrum signal of the HCN gas chamber;
on the other hand, a transmissivity function signal h (t) of the F-P filter is measured by a wavelength tunable laser and a detector to carry out denoising processing;
carrying out FFT (fast Fourier transform) on the denoising treatment to obtain a frequency spectrum H (omega) of the F-P filter spectral signal;
in the time domain, expressing the HCN gas chamber absorption signal P (t) detected by the detector as a real HCN spectrum signal g (t), and convolving the real HCN spectrum signal g (t) with an F-P filtering transmission function signal h (t):
p(t)＝g(t)*h(t)
the frequency domain form of the formula is
p(ω)＝G(ω)H(ω)
Thus, the spectrum G (ω) of the true HCN absorption spectrum is represented as
Performing frequency domain division calculation according to the formula;
performing IFFT (inverse fast Fourier transform) on the obtained spectrum G (omega) of the real HCN absorption spectrum to obtain a recovered HCN gas chamber absorption spectrum signal G (t);
and (3) carrying out interpolation adjustment on the full width at half maximum of the F-P filtering transmission function signal h (t), repeating the steps until an optimal recovered HCN absorption signal with a sharp absorption peak is obtained and is used as an absolute wavelength reference to realize the demodulation of the Bragg wavelength.
Compared with the traditional demodulation method, the invention has the advantages that:
(1) the method does not need a redundant device structure, overcomes the influence of temperature change on a demodulation result, and can effectively improve the demodulation performance in constant-temperature and variable-temperature environments;
(2) the demodulation precision is improved by 49.4 percent on average. And extends the range of accurate demodulation to the entire C-band.
Drawings
FIG. 1 is a schematic structural diagram of a high-precision demodulation device based on recovered FBGs in a variable temperature environment according to the present invention;
FIG. 2 is a schematic flow chart of the deconvolution algorithm of the present invention;
FIG. 3 is a comparison graph of the absorption spectrum of the HCN gas cell collected by the detector and the absorption spectrum of the HCN gas cell recovered by the deconvolution algorithm.
Reference numerals:
1. the optical fiber sensor comprises an ASE broadband light source, 2, an optical fiber isolator, 3, a tunable F-P filter, 4, an optical fiber 1 multiplied by 2 coupler, 5, 6, a first optical fiber circulator, a second optical fiber circulator, 7, an optical fiber Bragg grating string, 8, an HCN air chamber, 9, a photoelectric detector array, 10, a data acquisition card, 11, a processing unit, 12 and a signal generation module.
Detailed Description
The technical solution of the present invention is clearly and completely described below with reference to the drawings in the present invention, and the described technical solution is only an embodiment of the present invention. All other related technical solution changes based on the embodiment of the present invention belong to the protection scope of the present invention.
Fig. 1 is a schematic structural diagram of a high-precision demodulation apparatus based on recovered FBG in a temperature-varying environment according to the present invention. The device comprises an ASE broadband light source 1, an optical fiber isolator 2, a tunable F-P filter 3, an optical fiber 1 multiplied by 2 coupler 4, a first optical fiber circulator 5, a second optical fiber circulator 6, an optical fiber Bragg grating string 7, an HCN air chamber 8, a photoelectric detector array 9, a data acquisition card 10, a processing unit 11 and a signal generation module 12; wherein:
the ASE broadband light source 1 provides broad spectrum light (such as a C-band ASE light source) for the device, the light source power is 30mw, and the spectral range is 1525-1565 nm;
the optical fiber isolator 2 is used for isolating return light and ensuring unidirectional transmission of the light;
the tunable F-P filter 3 filters out narrow-band spectrum signals with variable wavelengths from the ASE broadband light source 1 by controlling the driving voltage of the tunable F-P filter, so that wavelength scanning is realized, the spectral width of the tunable F-P filter is 10 pm-400 pm, and the free spectral range is 90 nm-200 nm;
the optical fiber 1 x 2 coupler 4 is used for dividing input light into two beams of light according to a certain proportion, and the optical fiber 1 x 2 coupler is used in the invention with a 1:1 splitting ratio;
the optical fiber circulator 5 is used for sending light to the grating string and collecting reflected signal light, and when the power of a light source is more than 1mW, the system cost is reduced by adopting an optical fiber coupler to replace the light source;
the optical fiber Bragg grating string 7 is used for sensing the external physical quantity change to be measured and encoding the external physical quantity change to the reflection wavelength of the optical fiber grating, and the central wavelengths are 1528nm, 1534nm, 1542nm, 1556nm and 1562nm respectively;
an HCN gas chamber 8, which is recovered by using a reverse convolution algorithm and is used as an absolute wavelength reference of the device, and the pressure is 25Torr, and the effective optical length is 16.5 cm;
the photoelectric detector array 9 is used for converting two paths of optical signals with pi phase difference into voltage analog signals;
a data acquisition card 10 for acquiring voltage analog signals obtained by the photodetector array;
the processing unit 11 is a computer system or an embedded computing system and is used for demodulating the wavelength of the sensing fiber grating to be detected;
the signal generating module 12 is configured to generate square wave signals and triangular wave signals with the same frequency, where the triangular wave signals are used to modulate the filter to enable the light source module to generate scanning light, the square wave signals are used as a trigger signal of the acquisition card, and the frequency is 200 hz.
The Bragg wavelength of the fiber grating can be accurately demodulated even in the vicinity of the mark points (1541.7nm and 1543.3nm) where the absorption peak of the HCN spectrum is shallow and in the vicinity of both ends (1525nm and 1565 nm).
The data processing program mainly comprises two parts of deconvolution of the spectrum signal of the HCN air chamber and demodulation of Bragg wavelength.
The broadband light emitted by the ASE broadband light source 1 enters the tunable F-P filter 3 after passing through the optical fiber isolator 2, and is converted into narrow-band light which is scanned back and forth. After scanning narrow-band light enters from the input port of the optical fiber 1 × 2 coupler 4, the ratio of 1:1, splitting into two paths to output: one path enters from an input port of the first optical fiber circulator 5, is input into the optical fiber Bragg grating string 7 from an output port, and reflects light with corresponding wavelength to enter into a photoelectric detector array 9; the other path enters from the input port of the first optical fiber circulator 5, is input into the HCN gas chamber from the output port, and is detected by the photoelectric detector array 9 to obtain the absorption spectrum of the HCN gas chamber. The photodetector array 9 converts the optical signal into an electrical signal and amplifies the electrical signal, the amplified electrical signal is used for acquiring all data in the temperature rise process by the data acquisition card 10, the analog voltage signal is converted into a digital signal, and the digital signal is sent to the processing unit 11 for signal processing.
Five fiber grating sensors were connected in series in a metrological well calibrator (Fluke 9170). The Bragg wavelengths of the sensors are 1528nm, 1534nm, 1542nm, 1556nm and 1562nm respectively. The reflectivity of each sensor is more than 80%. The calibrator temperature was maintained at 25 ℃ and the temperature stability was better than + -0.005 ℃. Since the FBG temperature sensitivity is 10 pm/DEG C, the wavelength drift caused by the corrector is less than +/-0.05 pm.
The ASE broadband light source 1, the F-P filter 3 and the HCN air chamber 8 are all placed in a constant temperature box. The temperature of the thermostat is set to 10 ℃, and after stabilization, the temperature is continuously raised until 60 ℃.
As shown in fig. 2, the flow chart of the deconvolution algorithm of the present invention is schematic. And processing the collected HCN gas chamber absorption signal by using a back convolution algorithm to obtain a recovered HCN absorption spectrum with a sharp absorption peak, and using the spectrum as an absolute wavelength reference of the system to realize high-precision demodulation of the fiber bragg grating wavelength. The process specifically includes the following processing:
on one hand, the HCN gas chamber detected by the detector absorbs signals;
removing light source envelope from the HCN gas chamber absorption signal detected by the detector;
then eliminating random noise in the HCN air chamber absorption signal by using a low-pass filter;
performing FFT (fast Fourier transform) on the spectrum to obtain a spectrum of an absorption spectrum signal of the HCN gas chamber;
on the other hand, a transmissivity function signal h (t) of the F-P filter is measured by a wavelength tunable laser and a detector to carry out denoising processing;
carrying out FFT (fast Fourier transform) on the denoising treatment to obtain a frequency spectrum H (omega) of the F-P filter spectral signal;
in the time domain, expressing the HCN gas chamber absorption signal P (t) detected by the detector as a real HCN spectrum signal g (t), and convolving the real HCN spectrum signal g (t) with an F-P filtering transmission function signal h (t):
p(t)＝g(t)*h(t)
the frequency domain form of the formula is
p(ω)＝G(ω)H(ω)
Thus, the spectrum G (ω) of the true HCN absorption spectrum is represented as
Performing frequency domain division calculation according to the formula;
performing IFFT (inverse fast Fourier transform) on the obtained spectrum G (omega) of the real HCN absorption spectrum to obtain a recovered HCN gas chamber absorption spectrum signal G (t);
the full width at half maximum of the F-P filter transmission function signal h (t) is interpolated. Repeating the steps until obtaining an optimal recovered HCN absorption signal with a sharp absorption peak as an absolute wavelength reference, and realizing the demodulation of the Bragg wavelength.
The deconvolution algorithm of the demodulation system adopts the same detector when measuring the absorption signal of the HCN air chamber and the signal of the F-P filter, so that the error caused by the resolution of the detector is avoided in the subsequent deconvolution process.
The deconvolution algorithm of the demodulation system is influenced by the amplification factor of the detector due to the full width at half maximum of the transmission function signal of the F-P filter.
The Bragg wavelength demodulation algorithm based on the recovered HCN gas chamber absorption spectrum utilizes deconvolution to obtain the recovered HCN absorption spectrum with sharp absorption peak and applies the spectrum to demodulation, thereby eliminating the influence of the bandwidth of an F-P filter on the absorption spectrum of the HCN gas chamber.
Claims (1)
1. A FBG high-precision demodulation method based on recovery in a variable temperature environment utilizes an FBG high-precision demodulation device to realize demodulation, and the FBG high-precision demodulation device comprises an ASE broadband light source (1), an optical fiber isolator (2), a tunable F-P filter (3), an optical fiber 1 multiplied by 2 coupler (4), a first optical fiber circulator (5), a second optical fiber circulator (6), an optical fiber Bragg grating string (7), an HCN air chamber (8), a photoelectric detector array (9), a data acquisition card (10), a processing unit (11) and a signal generation module (12); the ASE broadband light source (1), the optical fiber isolator (2), the tunable F-P filter (3) and the optical fiber 1 x 2 coupler (4) are sequentially connected, the output end of the optical fiber 1 x 2 coupler (4) is divided into two paths, one path is sequentially connected with the first optical fiber circulator (5), the optical fiber Bragg grating string (7) and the photoelectric detector array (9), and the other path is sequentially connected with the second optical fiber circulator (6), the HCN gas chamber (8) and the photoelectric detector array (9); the output end of the photoelectric detector array (9) is sequentially connected with the data acquisition card (10) and the processing unit (11), and the data acquisition card (10) is connected with the tunable F-P filter (3) through the signal generation module (12); the ASE broadband light source is characterized in that broadband light emitted by the ASE broadband light source (1) enters the tunable F-P filter (3) after passing through the optical fiber isolator (2), the broadband light is converted into narrow-band light which is scanned back and forth, the scanned narrow-band light enters from the input port of the optical fiber 1 x 2 coupler 4 and is divided into two paths for output according to 1:1 splitting: one path enters from an input port of the first optical fiber circulator (5), is input into the optical fiber Bragg grating string (7) from an output port, and reflects light with corresponding wavelength to enter the photoelectric detector array (9); the other path enters from an input port of the first optical fiber circulator (5), is input into an HCN air chamber from an output port, and is detected by the photoelectric detector array (9) to obtain an absorption spectrum of the HCN air chamber, the photoelectric detector array (9) converts an optical signal into an electric signal and amplifies the electric signal, the amplified electric signal is acquired by the data acquisition card (10) in the temperature rise process, an analog voltage signal is converted into a digital signal, and the digital signal is sent to the processing unit (11) for signal processing, and the processing flow of the processing unit (11) specifically comprises the following steps:
on one hand, the HCN gas chamber detected by the detector absorbs signals;
removing light source envelope from the HCN gas chamber absorption signal detected by the detector;
then eliminating random noise in the HCN air chamber absorption signal by using a low-pass filter;
performing FFT (fast Fourier transform) on the spectrum to obtain a spectrum of an absorption spectrum signal of the HCN gas chamber;
on the other hand, a transmissivity function signal h (t) of the F-P filter is measured by a wavelength tunable laser and a detector to carry out denoising processing;
carrying out FFT (fast Fourier transform) on the denoising treatment to obtain a frequency spectrum H (omega) of the F-P filter spectral signal;
in the time domain, expressing the HCN gas chamber absorption signal P (t) detected by the detector as a real HCN spectrum signal g (t), and convolving the real HCN spectrum signal g (t) with an F-P filtering transmission function signal h (t):
p(t)＝g(t)*h(t)
the frequency domain form of the formula is
p(ω)＝G(ω)H(ω)
Thus, the spectrum G (ω) of the true HCN absorption spectrum is represented as
Performing frequency domain division calculation according to the formula;
performing IFFT (inverse fast Fourier transform) on the obtained spectrum G (omega) of the real HCN absorption spectrum to obtain a recovered HCN gas chamber absorption spectrum signal G (t);
and (3) carrying out interpolation adjustment on the full width at half maximum of the F-P filtering transmission function signal h (t), repeating the steps until an optimal recovered HCN absorption signal with a sharp absorption peak is obtained and is used as an absolute wavelength reference to realize the demodulation of the Bragg wavelength.
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| CN113628700B (en) * | 2021-06-30 | 2024-02-09 | 北京空间机电研究所 | Absorption spectrum rapid acquisition method based on HITRAN database |
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| CN114414089B (en) * | 2022-03-29 | 2022-06-17 | 武汉奇测科技有限公司 | Method for simultaneously improving demodulation speed and measuring range of fiber bragg grating |
| CN117387673B (en) * | 2023-12-08 | 2024-02-23 | 山东星冉信息科技有限公司 | Fiber bragg grating demodulation method and device based on reference air chamber |
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