CN110082068B - Fiber grating wavelength demodulation system and method with wavelength correction function - Google Patents
Fiber grating wavelength demodulation system and method with wavelength correction function Download PDFInfo
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Abstract
The invention relates to a fiber grating wavelength demodulation system with a wavelength correcting function and a method thereof, aiming at a wavelength scanning fiber grating wavelength demodulation system, the method realizes the measurement of unknown fiber length by the time difference between an optical signal reflected by the tail end of a fiber grating sensor and a light source intensity signal of a reference light path. The wavelength correction demodulation method comprises a broadband light source, an adjustable filter, an etalon, a beam splitter, a photoelectric detector, a control and signal processing circuit and other modules, and realizes the calculation of the time delay of the reference and sensing optical signals by selecting the data of the optical signals of the reference optical path and the sensing optical signals and adopting methods such as a cross-correlation algorithm, a least mean square adaptive filter method and the like. Therefore, the problem that the demodulation wavelength value is deviated due to the fact that the length of the optical fiber of the connecting sensor in the wavelength scanning type fiber bragg grating wavelength demodulation system is solved, the demodulation accuracy of the wavelength demodulation system is guaranteed, the measurement accuracy of the sensor is improved, and the wavelength scanning type fiber bragg grating wavelength demodulation system has high engineering practical value.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensors, and mainly relates to an optical fiber grating wavelength demodulation system and method with a wavelength correction function.
Background
The fiber grating sensor has the advantages of small volume, light weight, corrosion resistance, high sensitivity, no electromagnetic interference, low cost, easy integration and the like, is applied to an optical fiber temperature and depth chain, an optical fiber temperature and depth section instrument, an optical fiber hydrophone and the like, and has wide application prospect in military and civil fields such as marine hydrology monitoring, underwater sound monitoring, non-acoustic anti-submarine detection and the like.
The fiber grating sensor utilizes the characteristic that the reflected light wavelength of the fiber grating changes along with temperature and stress to realize the measurement of physical quantity, so the measurement accuracy of the reflected light wavelength of the fiber grating determines the performance of the sensor, and the fiber grating wavelength demodulation method mainly comprises a spectroscopic spectrum detection method, a wavelength scanning method, an interferometry method and the like, wherein the wavelength scanning method has the advantages of simple system, high measurement accuracy, strong multiplexing capability, low price, high stability and the like, and has become a preferred mode for industrial use.
However, the wavelength scanning fiber grating wavelength demodulation method has a problem that the length of the optical fiber connected with the sensor causes the wavelength demodulation value to shift, that is, the longer the length of the connected optical fiber is, the larger the wavelength demodulation value is for the same fiber grating sensor. The deviation between the wavelength demodulation value and the actual value caused by the length of the sensor fiber will result in the reduction of the measurement accuracy of the fiber grating sensor. To solve the problem, the main method adopted at present is to measure the length of the optical fiber connected with the sensor in advance, and then correct the wavelength value of the demodulated fiber bragg grating according to the relationship between the length of the optical fiber of the sensor of the wavelength demodulation system and the wavelength deviation caused by corresponding factors. The method has complicated operation process and brings inconvenience to engineering application. Therefore, the method for wavelength demodulation of the wavelength scanning type fiber bragg grating capable of automatically correcting the wavelength demodulation value deviation caused by the length of the optical fiber has important application value.
Disclosure of Invention
Aiming at the problem that the wavelength demodulation value is shifted due to the fact that the length of an optical fiber connected with a sensor is used in a wavelength scanning type optical fiber grating wavelength demodulation method, the invention provides an optical fiber grating wavelength demodulation system with a wavelength correction function and a method thereof.
The object of the present invention is achieved by the following technical means. A fiber grating wavelength demodulation system with a wavelength correcting function comprises a broadband light source, a tunable filter, a beam splitter A, an etalon, a beam splitter B, a beam splitter C, a circulator, a fiber coil (an optical fiber to be detected with unknown length), a fiber grating sensor, a detector A, a detector B, a detector C, a detector D and a control and signal processing circuit; the broadband light source outputs a demodulation spectrum, the demodulation spectrum enters a tunable filter, a control and signal processing circuit outputs a triangular wave driving signal to the tunable filter, the tunable filter scans and outputs an input optical signal under the driving of the driving signal, the output optical signal enters a beam splitter A3, the beam splitter A divides the input optical signal into two paths, one path of the input optical signal is input to a beam splitter B to serve as a reference signal for wavelength demodulation, and the other path of the output optical signal is input to a circulator to serve as a sensing optical signal; the beam splitter B divides an input optical signal into two paths, one path enters the etalon to process the input signal, a comb-shaped spectral intensity signal is generated and enters the detector A0, and the other path is directly input to the detector B to serve as a light source intensity signal; the optical signal entering the circulator is input into the fiber grating sensor after passing through the fiber coil, and the optical signal reflected by the fiber grating sensor is output into the beam splitter C through the original path; the beam splitter C divides the sensing optical signal into two paths which respectively enter the detector C and the detector D.
The wavelength scanning range of the tunable filter is larger than the spectral range of the broadband light source.
A fiber grating wavelength demodulation method with a wavelength correction function comprises the following steps: the control and signal processing circuit synchronously collects four paths of signals after photoelectric conversion, wherein the first path and the third path are used for normally demodulating a wavelength data value of the sensor, the second path and the fourth path are used for calculating the length of the optical fiber coil, wavelength scanning is realized by using a tunable filter, when the wavelength of a wavelength scanning optical signal is the same as the wavelength of the sensing grating, the light with the wavelength is reflected, the light with the other wavelengths is transmitted, and the measurement of the length of the optical fiber is realized by the time difference of the optical signal reflected by the tail end of the optical fiber grating sensor and a light source intensity signal detected by a reference optical path through a wavelength correction algorithm.
The wavelength correction algorithm takes a light intensity signal collected by the detector B as a reference, under two conditions of no access of the optical fiber coil, the position of a signal reflected by the optical fiber grating sensor deviates relative to the light intensity signal, the deviation is introduced by the optical fiber coil, data processing operation is carried out on the signal, time delay of the reference and sensing optical signals is solved, and finally wavelength deviation is calculated according to wavelength scanning, so that the correction function is realized.
The invention has the beneficial effects that: the wavelength self-correction function of the invention conveniently and effectively solves the problem of offset of a demodulation wavelength value caused by the length of an optical fiber connected with a fiber grating sensor in a wavelength scanning fiber grating wavelength demodulation system, ensures the demodulation accuracy of the wavelength demodulation system and improves the measurement accuracy of the sensor.
Drawings
Fig. 1 is a block diagram showing the overall structure of the system of the present invention.
FIG. 2 is a graph showing the relative position of the light intensity signal and the sensor signal.
Description of reference numerals: the device comprises a broadband light source 1, a tunable filter 2, a beam splitter A3, an etalon 4, a beam splitter B5, a beam splitter C6, a circulator 7, an optical fiber coil 8, an optical fiber grating sensor 9, a detector A10, a detector B11, a detector C12, a detector D13 and a control and signal processing circuit 14.
Detailed Description
The invention will be described in detail below with reference to the following drawings:
as shown in fig. 1, a fiber grating wavelength demodulation system with a wavelength correction function includes a broadband light source 1, a tunable filter 2 (tunable F-P filter), a beam splitter A3, an etalon 4(F-P etalon), a beam splitter B5, a beam splitter C6, a circulator 7, a fiber coil 8, a fiber grating sensor 9, a detector a10, a detector B11, a detector C12, a detector D13, and a control and signal processing circuit 14; the wavelength scanning range of the tunable filter 2 is larger than the spectral range of the broadband light source 1.
Emitting a broadband optical signal with wavelength light by a broadband light source;
scanning the light wavelength output by the light source by the adjustable F-P filter under the drive of the stepped triangular wave voltage signal;
splitting the optical signal for multiple times by a beam splitter to achieve different functions;
an F-P etalon for generating a standard comb spectrum as a reference signal for wavelength demodulation;
the photodetector is used for a photoelectric conversion function, and converts an optical signal into an electric signal for subsequent processing;
the control and signal processing circuit realizes the functions of light path driving and control, data acquisition, wavelength correction algorithm realization, wavelength demodulation algorithm realization and the like.
The broadband light source 1 outputs a demodulation spectrum, the demodulation spectrum enters the tunable filter 2, the control and signal processing circuit 14 outputs a triangular wave driving signal to the tunable filter 2, the tunable filter 2 scans and outputs an input optical signal under the driving of the driving signal, and the output optical signal enters the beam splitter A3; the beam splitter A3 divides the input light into two paths, one path is input into the beam splitter B5 as a reference signal for wavelength demodulation, and the other path is input into the circulator 7 as a sensing light signal; the beam splitter B5 divides the input optical signal into two paths, one path enters the etalon 4 to process the input signal, the generated comb-shaped spectral intensity signal enters the detector A10, and the other path is directly input to the detector B11 to be used as a light source intensity signal; the optical signal entering the circulator 7 passes through the optical fiber coil 8 and then is input into the fiber grating sensor 9, and the optical signal reflected by the fiber grating sensor 9 is output into the beam splitter C6 through the primary path; the beam splitter C6 divides the sensing optical signal into two paths to enter the detector C12 and the detector D13 respectively, wherein the detector D13 has high gain, reflects the light intensity background amplitude of the sensing signal aiming at the characteristic that the reflected signal at the tail end of the optical fiber is weak, and facilitates the subsequent wavelength correction.
The invention also discloses a fiber grating wavelength demodulation method with a wavelength correction function, which comprises the steps of selecting data of a reference light path optical signal and a sensing optical signal (the spectrum edge of a broadband light source), calculating the time delay of the reference and sensing optical signals by adopting methods such as a cross-correlation algorithm, a least mean square self-adaptive filter method and the like, and calculating the wavelength offset according to the wavelength scanning speed. The method comprises the following specific steps: the control and signal processing circuit 14 synchronously acquires four photoelectric conversion signals, wherein the first path and the third path are used for normally demodulating the wavelength data value of the sensor, the second path and the fourth path are used for calculating the length of the optical fiber coil 8, the tunable filter is used for realizing wavelength scanning, when the wavelength of the wavelength scanning optical signal is the same as the wavelength of the sensing grating, the light with the wavelength is reflected, the light with the other wavelengths is transmitted, and the measurement of the length of the optical fiber is realized through the time difference between the optical signal reflected by the tail end of the optical fiber grating sensor and the light source intensity signal detected by the reference optical path through the wavelength correction algorithm. The wavelength correction algorithm takes a light intensity signal collected by a detector B11 as a reference, under two conditions that no optical fiber coil 8 is accessed, a signal reflected by the fiber grating sensor 9 has a position offset relative to the light intensity signal, the offset is introduced by the optical fiber coil 8, the signals are subjected to data processing operations such as a cross-correlation algorithm, a least mean square adaptive filter and the like, the time delay of the reference and sensing optical signals is calculated, and the wavelength offset is finally calculated according to wavelength scanning, so that the correction function is realized.
The specific working flow of the system is as follows:
1) the broadband light source outputs a demodulation spectrum, and the demodulation spectrum enters a tunable filter;
2) the control and signal processing circuit outputs a triangular wave driving signal to the tunable filter;
3) the tunable filter scans and outputs an input optical signal under the drive of a drive signal, the output optical signal enters the beam splitter A, and the wavelength scanning range of the tunable filter is larger than the spectral range of the wide-spectrum light source;
4) the beam splitter A divides input light into two paths, wherein one path of input light is input to the beam splitter B as a reference signal for wavelength demodulation, and the other path of input light is input to the circulator as a sensing light signal;
5) the beam splitter B divides an input optical signal into two paths, one path enters the etalon to process the input signal, a comb-shaped spectral intensity signal is generated and enters the detector A, and the other path is directly input to the detector B to serve as a light source intensity signal;
6) the optical signal entering the circulator is input into the FBG sensor after passing through an optical fiber coil (an optical fiber to be measured with unknown length), and the optical signal reflected by the FBG sensor is output into the beam splitter C through the original path;
7) the beam splitter C divides the sensing optical signal into two paths which respectively enter the detectors C and D, wherein the detector D has high gain, reflects the light intensity background amplitude of the sensing signal aiming at the characteristic that the reflected signal at the tail end of the optical fiber is weak, and is convenient for the subsequent wavelength correction;
8) the control and signal processing circuit synchronously collects four photoelectric conversion finished signals; the first path and the third path are used for normally demodulating the wavelength data value of the sensor, and the second path and the fourth path are used for calculating the length of the optical fiber coil;
FIG. 2 is a diagram showing the comparison of the relative positions of the light intensity signal and the sensor signal, and the optical fiber coil length calculation algorithm is described by comparing the diagram as follows:
1) the right picture in the figure is an enlarged view of the left picture at the position of algorithm implementation;
2) in the figure, a blue line is a light source intensity signal acquired by a detector B, a red line is a signal acquired by a detector D and acquired by a fiber grating sensor when no fiber coil is accessed, and a green line is a signal acquired by the detector D and acquired by the fiber grating sensor when the fiber coil is accessed;
3) the relative position of the light intensity signal is not changed because the light intensity signal is not influenced by the optical fiber coil, and the signal is taken as a reference, so that the sensor signal is backwards moved when the optical fiber coil is accessed compared with the relative position when the coil is not accessed, and the backwards moved position is the offset introduced by the optical fiber coil;
and performing data processing operations such as a cross-correlation algorithm, a least mean square adaptive filter and the like on the signals in the graph, solving time delays of the reference and sensing optical signals, and finally calculating a wavelength offset according to wavelength scanning so as to realize a correction function.
It should be understood that equivalent substitutions and changes to the technical solution and the inventive concept of the present invention should be made by those skilled in the art to the protection scope of the appended claims.
Claims (3)
1. A fiber grating wavelength demodulation system with a wavelength correction function is characterized in that: the device comprises a broadband light source (1), a tunable filter (2), a beam splitter A (3), an etalon (4), a beam splitter B (5), a beam splitter C (6), a circulator (7), an optical fiber coil (8), an optical fiber grating sensor (9), a detector A (10), a detector B (11), a detector C (12), a detector D (13) and a control and signal processing circuit (14); the circulator (7) is connected with a fiber grating sensor (9) through a fiber coil (8), and the detector A (10), the detector B (11), the detector C (12) and the detector D (13) are respectively connected with a control and signal processing circuit (14); the broadband light source (1) outputs a demodulation spectrum, the demodulation spectrum enters the tunable filter (2), the control and signal processing circuit (14) outputs a triangular wave driving signal to the tunable filter (2), the tunable filter (2) scans and outputs an input optical signal under the driving of the driving signal, and the output optical signal enters the beam splitter A (3); the beam splitter A (3) divides input light into two paths, one path of input light is input to the beam splitter B (5) to be used as a reference signal for wavelength demodulation, and the other path of input light is input to the circulator (7) to be used as a sensing light signal; the beam splitter B (5) divides an input optical signal into two paths, one path enters the etalon (4) to process the input signal, a comb-shaped spectral intensity signal is generated and enters the detector A (10), and the other path is directly input to the detector B (11) to serve as a light source intensity signal; the optical signal entering the circulator (7) passes through the optical fiber coil (8) and then is input into the optical fiber grating sensor (9), and the optical signal reflected by the optical fiber grating sensor (9) is output into the beam splitter C (6) through the original path; and the beam splitter C (6) divides the sensing optical signal into two paths which respectively enter the detector C (12) and the detector D (13).
2. The fiber grating wavelength demodulating system with wavelength correction function according to claim 1, wherein: the wavelength scanning range of the tunable filter (2) is larger than the spectral range of the broadband light source (1).
3. A method of using the fiber grating wavelength demodulation system with wavelength correction function of claim 1, characterized in that: the control and signal processing circuit (14) synchronously acquires four paths of signals subjected to photoelectric conversion, wherein the first path and the third path are used for normally demodulating a wavelength data value of the sensor, the second path and the fourth path are used for calculating the length of the optical fiber coil (8), a tunable filter is used for scanning the wavelength, when the wavelength of the wavelength scanning optical signal is the same as that of the sensing grating, the light with the wavelength is reflected, the light with the other wavelengths is transmitted, and the measurement of the length of the optical fiber is realized through the time difference of the optical signal reflected by the tail end of the optical fiber grating sensor and a light source intensity signal detected by a reference light path through a wavelength correction algorithm; the wavelength correction algorithm takes a light intensity signal collected by a detector B (11) as a reference, under two conditions that no optical fiber coil (8) is accessed, a signal reflected by the optical fiber grating sensor (9) has position deviation relative to the light intensity signal, the deviation is introduced by the optical fiber coil (8), data processing operation is carried out on the signal reflected by the optical fiber grating sensor (9) and the light intensity signal, time delay of reference light and the collected light intensity signal is calculated, and finally wavelength deviation is calculated according to wavelength scanning, so that a correction function is realized.
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| CN113252088B (en) * | 2021-05-18 | 2022-09-13 | 电子科技大学 | Multi-wavelength distributed optical fiber sensing system and method |
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| CN101586986B (en) * | 2009-07-07 | 2011-05-11 | 北京交通大学 | High precision optical fiber grating wave length demodulation system |
| CN102589588A (en) * | 2012-02-17 | 2012-07-18 | 南京师范大学 | Method for demodulating cavity length of Fabry-Perot cavity by utilizing fiber Bragg gratings |
| CN103196473B (en) * | 2013-03-26 | 2015-10-28 | 天津大学 | Multi-channel high-accuracy fiber grating sensing demodulation device and demodulation method thereof |
| CN105241482B (en) * | 2015-10-14 | 2018-02-23 | 中国船舶重工集团公司第七一五研究所 | A kind of Active Optical Fiber grating sensor Wavelength demodulation system and method |
| CN205981243U (en) * | 2016-08-11 | 2017-02-22 | 中国船舶重工集团公司第七一五研究所 | Fiber grating wavelength demodulation system with self -adaptation function |
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