CN110763324B - Fiber grating demodulation system - Google Patents
Fiber grating demodulation system Download PDFInfo
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- CN110763324B CN110763324B CN201911007043.1A CN201911007043A CN110763324B CN 110763324 B CN110763324 B CN 110763324B CN 201911007043 A CN201911007043 A CN 201911007043A CN 110763324 B CN110763324 B CN 110763324B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
Abstract
The invention provides a fiber grating demodulation system, when sawtooth wave voltage modulation is conducted on first piezoelectric ceramics in a tunable narrow-band light source, the spectrum of the tunable narrow-band light source can be scanned in a certain range, when the wavelength is just equal to the reflection wavelength of a sensing fiber grating, the output of a detector is strongest, and meanwhile, the measurement precision is improved; when the measured physical quantities such as stress, temperature and the like are changed, the interference fringes move, the phase also changes, the mismatching of the reflection wavelengths of the sensing fiber grating and the reference fiber grating is caused, the sawtooth wave generator generates sawtooth waves to overdrive the second piezoelectric ceramic, so that the sensing fiber grating and the reference fiber grating are matched again, the wavelength information is demodulated according to the voltage value of the sawtooth waves, and the measured changes such as temperature, stress and the like are obtained.
Description
Technical Field
The invention relates to the field of optical sensing, in particular to a fiber grating demodulation system.
Background
The fiber grating vibration sensing technology is generally applied in the field of security protection because of the advantages of no electromagnetic interference, no power supply on site, good long-term reliability and stability, long transmission distance and the like. The key of the fiber grating vibration sensing system is a light source. The light source is generally a tunable semiconductor laser, which is one of the key optoelectronic devices in the fields of next-generation optical fiber communication systems and novel testing and measuring. The tunable semiconductor laser adopts a laser principle, so that the spectral density of output laser is very high, the interferometer is easy to damage, and in the fiber grating vibration sensing technology, the measurement precision of the fiber grating demodulation system is easy to reduce due to the problem of a light source.
Disclosure of Invention
In view of this, the invention provides a fiber grating demodulation system, which can reduce the optical power of a tunable semiconductor laser, reduce the damage of laser to an interferometer, and introduce a reference signal when the phase of the grating changes due to demodulation temperature and stress, thereby improving the signal-to-noise ratio of the system and achieving higher resolution.
The technical scheme of the invention is realized as follows: the invention provides a fiber grating demodulation system, which comprises a tunable narrowband light source, a first 3db coupler, a sensing fiber grating, an interference unit, a detection unit and a reference unit, wherein the tunable narrowband light source comprises a semiconductor optical amplifier, a circulator, a tunable optical attenuator, an unbalanced M-Z interferometer, a first piezoelectric ceramic, a sawtooth wave generator and an isolator;
the semiconductor optical amplifier emits spontaneous radiation light, the spontaneous radiation light enters a port 3 from a port 2 of the circulator, an optical signal is attenuated by the tunable optical attenuator and filtered by the unbalanced M-Z interferometer, enters a 2 port through a 1 port of the circulator, is amplified by a semiconductor optical amplifier and isolated by an isolator and then is output to the input end of a first 3db coupler, the first 3db coupler divides an optical signal into two parts, the two optical paths are respectively marked as a first branch and a second branch, the optical signal of the first branch is output to the sensing fiber grating, the optical signal of the second branch is output to the matching fluid, the reflected signal of the optical signal at the sensing fiber grating is coupled to enter the unbalanced M-Z interferometer, one arm of the non-equilibrium M-Z interferometer is wound on the first piezoelectric ceramic driven by a sawtooth wave generator signal to change the optical path difference between the two arms, and an optical signal at the output end of the non-equilibrium M-Z interferometer is output to the detection unit through the reference unit.
On the basis of the above technical solution, preferably, the reference unit includes a second 3db coupler, a reference fiber grating, a first photodetector and a band-pass filter;
the output end of the unbalanced M-Z interferometer is connected with the input end of a second 3db coupler, the second 3db coupler divides an optical signal into two paths, one path of the optical signal is output to the reference fiber grating, the other path of the optical signal is output to the matching fluid, the output end of the second 3db coupler, which is output to the matching fluid, is electrically connected with the input end of the band-pass filter through the first photoelectric detector, and the output end of the band-pass filter is electrically connected with the detection unit.
Further preferably, the interference unit comprises a third 3db coupler, a first faraday rotator mirror, a second piezoelectric ceramic and a sawtooth wave generator;
the output end of the first 3db coupler outputs a reflected signal of the sensing fiber grating to the input end of a third 3db coupler, the third 3db coupler divides an optical signal into two optical paths which are respectively marked as a first optical path and a second optical path, the optical signal on the first optical path is output to a first Faraday rotator mirror, the optical fiber from the third 3db coupler to the first Faraday rotator mirror is wound on a second piezoelectric ceramic, the second piezoelectric ceramic is axially connected with the first Faraday rotator mirror, a sawtooth wave generator generates sawtooth waves and is loaded on the second piezoelectric ceramic to drive the second piezoelectric ceramic to generate telescopic deformation, the optical signal on the second optical path is output to the second Faraday rotator mirror, and the output end of the third 3db coupler outputs an optical signal to a detection unit.
Further preferably, the detection unit comprises a second photodetector, a signal amplifier, a filter and a phase meter which are electrically connected in sequence;
the output end of the third 3db coupler outputs optical signals which are detected by the second photoelectric detector, the second photoelectric detector converts the optical signals into electric signals, the electric signals are amplified by the signal amplifier and filtered by the filter in sequence and then reach the input end of the phase meter, the signals output by the output end of the band-pass filter serve as reference waves and are sent to the other input end of the phase meter, and the output end of the phase meter outputs phase signals.
Compared with the prior art, the fiber grating demodulation system has the following beneficial effects:
(1) when the first piezoelectric ceramic is modulated by sawtooth wave voltage, the spectrum of the tunable narrow-band light source can be scanned in a certain range, and when the wavelength is just equal to the reflection wavelength of the sensing fiber grating, the output of the detector is strongest, and the measurement precision is improved;
(2) the tunable narrow-band light source adopts a main amplifier framework, spontaneous radiation light of a semiconductor optical amplifier is modulated by an unbalanced M-Z interferometer and returns to the semiconductor optical amplifier for amplifying and outputting, the maximum output optical power is also determined by the saturated output power of the semiconductor optical amplifier and can be approximately equal to the saturated output power of the semiconductor optical amplifier, so that the output optical power of the tunable narrow-band light source and the optical power of a sweep laser are in one order of magnitude, the signal-to-noise ratio is about two orders of magnitude lower than that of the sweep laser, and the damage of laser to the unbalanced M-Z interferometer is reduced;
(3) under the condition that the temperature is not changed, the amplitude of a sawtooth wave signal generated by the sawtooth wave generator and the magnitude of a direct current level can be adjusted, so that the change frequency of an output signal of the interferometer is consistent with the frequency of a reference signal output by the band-pass filter, the value detected by the phase meter is in direct proportion to the strain to be detected applied to the sensing fiber grating, and the phase of the reference signal is irrelevant to the value, so that the phase change detected by the phase meter is actually the change of the phase of the signal to be detected;
(4) when the measured physical quantities such as stress, temperature and the like are changed, the interference fringes move, the phase also changes, the mismatching of the reflection wavelengths of the sensing fiber grating and the reference fiber grating is caused, the sawtooth wave generator generates sawtooth waves to overdrive the second piezoelectric ceramic, so that the sensing fiber grating and the reference fiber grating are matched again, the wavelength information is demodulated according to the voltage value of the sawtooth waves, and the measured changes such as temperature, stress and the like are obtained.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a structural diagram of a fiber grating demodulation system according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
As shown in FIG. 1, the fiber grating demodulation system of the present invention comprises a tunable narrowband optical source, a first 3db coupler, a sensing fiber grating, an interference unit, a detection unit and a reference unit.
Further preferably, the tunable narrowband light source comprises a semiconductor optical amplifier, a circulator, a tunable optical attenuator, an unbalanced M-Z interferometer, a first piezoelectric ceramic, a sawtooth wave generator and an isolator; specifically, a semiconductor optical amplifier emits spontaneous emission light, the spontaneous emission light enters a port 3 from a port 2 of a circulator, an optical signal is attenuated by a tunable optical attenuator and filtered by an unbalanced M-Z interferometer, then enters the port 2 through a port 1 of the circulator, is amplified by the semiconductor optical amplifier and isolated by an isolator and then is output to an input end of a first 3db coupler, the first 3db coupler divides the optical signal into two parts, two optical paths are respectively marked as a first branch and a second branch, the optical signal of the first branch is output to a sensing fiber grating, the optical signal of the second branch is output to matching liquid, a reflection signal of the optical signal on the sensing fiber grating is coupled to the unbalanced M-Z interferometer, one arm of the optical signal is wound on first piezoelectric ceramic driven by a sawtooth wave generator signal to change an optical path difference between the two arms, and because an optical path difference exists between the two arms of the unbalanced M-Z interferometer, therefore, the output end of the unbalanced M-Z interferometer has an optical signal output, and the optical signal is output to the detection unit through the reference unit.
When the first piezoelectric ceramic is modulated by sawtooth wave voltage, the spectrum of the tunable narrow-band light source can be scanned in a certain range, and when the wavelength is just equal to the reflection wavelength of the sensing fiber grating, the detector outputs the strongest light;
the tunable narrow-band light source adopts a main amplifier framework, spontaneous radiation light of a semiconductor optical amplifier is modulated by an unbalanced M-Z interferometer and returns to the semiconductor optical amplifier for amplifying and outputting, the maximum output optical power is also determined by the saturated output power of the semiconductor optical amplifier and can be approximately equal to the saturated output power of the semiconductor optical amplifier, so that the output optical power of the tunable narrow-band light source and the optical power of a sweep laser are in one order of magnitude, the signal-to-noise ratio is about two orders of magnitude lower than that of the sweep laser, and the damage of laser to the unbalanced M-Z interferometer is reduced.
Further preferably, the reference unit comprises a second 3db coupler, a reference fiber grating, a first photodetector and a band-pass filter; specifically, the output end of the unbalanced M-Z interferometer is connected with the input end of a second 3db coupler, the second 3db coupler divides an optical signal into two paths, one path of the optical signal is output to the reference fiber grating, the other path of the optical signal is output to the matching fluid, the output end of the second 3db coupler, which is output to the matching fluid, is electrically connected with the input end of the band-pass filter through the first photoelectric detector, and the output end of the band-pass filter is electrically connected with the detection unit.
Further preferably, the interference unit comprises a third 3db coupler, a first faraday rotator mirror, a second piezoelectric ceramic and a sawtooth wave generator; specifically, the output end of the first 3db coupler outputs a reflected signal of the sensing fiber grating to the input end of the third 3db coupler, the third 3db coupler divides an optical signal into two optical paths, which are respectively marked as a first optical path and a second optical path, the optical signal on the first optical path is output to the first faraday rotator, the optical fiber from the third 3db coupler to the first faraday rotator is wound on the second piezoelectric ceramic, the second piezoelectric ceramic is axially connected with the first faraday rotator, the sawtooth wave generator generates sawtooth waves and loads the sawtooth waves on the second piezoelectric ceramic to drive the second piezoelectric ceramic to generate telescopic deformation, the optical signal on the second optical path is output to the second faraday rotator, and the output end of the third 3db coupler outputs an optical signal to the detection unit. The optical signal output by the tunable narrow-band light source reaches the sensing fiber grating through the first 3db coupler, the optical signal is reflected in the sensing fiber grating, the reflected signal is coupled into the interferometer and the tunable narrow-band light source through the first 3db coupler, and the optical signal is modulated in the interferometer due to the optical path difference between the two arms of the interferometer, so that the polarization fading phenomenon of the interferometer is overcome, and the interference is ensured to only output the signal with high extinction ratio;
the detection unit detects the optical signal output by the interference unit, converts the optical signal into an electric signal, and outputs phase information after signal amplification and filtering processing. Further preferably, the detection unit comprises a second photodetector, a signal amplifier, a filter and a phase meter which are electrically connected in sequence; the output end of the third 3db coupler outputs optical signals which are detected by the second photoelectric detector, the second photoelectric detector converts the optical signals into electric signals, the electric signals are amplified by the signal amplifier and filtered by the filter in sequence and then reach the input end of the phase meter, the signals output by the output end of the band-pass filter serve as reference waves and are sent to the other input end of the phase meter, and the output end of the phase meter outputs phase signals.
Under the condition that the temperature is not changed, the amplitude of a sawtooth wave signal generated by the sawtooth wave generator and the magnitude of a direct current level can be adjusted, so that the change frequency of an output signal of the interferometer is consistent with the frequency of a reference signal output by the band-pass filter, the value detected by the phase meter is in direct proportion to the strain to be detected applied to the sensing fiber grating, and the phase of the reference signal is irrelevant to the phase change, so that the phase change detected by the phase meter is actually the change of the phase of the signal to be detected;
when the measured physical quantities such as stress, temperature and the like are changed, the interference fringes move, the phase is also changed, the reflection wavelength mismatch of the sensing fiber grating and the reference fiber grating is caused, the sawtooth wave generator generates sawtooth waves to overdrive the second piezoelectric ceramic, so that the sensing fiber grating and the reference fiber grating are matched again, the wavelength information is demodulated according to the voltage value of the sawtooth waves, and the measured changes such as temperature, stress and the like are obtained.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (4)
1. A fiber grating demodulation system comprises a tunable narrow-band light source, a first 3db coupler, a sensing fiber grating, an interference unit, a detection unit and a reference unit, and is characterized in that: the tunable narrow-band light source comprises a semiconductor optical amplifier, a circulator, a tunable optical attenuator, an unbalanced M-Z interferometer, a first piezoelectric ceramic, a sawtooth wave generator and an isolator;
the semiconductor optical amplifier emits spontaneous radiation light, and enters the 3 ports from the 2 ports of the circulator, after the optical signal is attenuated by the tunable optical attenuator and filtered by the unbalanced M-Z interferometer, enters a 2 port through a 1 port of the circulator, is amplified by a semiconductor optical amplifier and isolated by an isolator and then is output to the input end of a first 3db coupler, the first 3db coupler divides an optical signal into two parts, the two optical paths are respectively marked as a first branch and a second branch, the optical signal of the first branch is output to the sensing fiber grating, the optical signal of the second branch is output to the matching fluid, the reflected signal of the optical signal at the sensing fiber grating is coupled to enter the unbalanced M-Z interferometer, one arm of the non-equilibrium M-Z interferometer is wound on the first piezoelectric ceramic driven by a sawtooth wave generator signal to change the optical path difference between the two arms, and an optical signal at the output end of the non-equilibrium M-Z interferometer is output to the detection unit through the reference unit.
2. A fiber grating demodulation system as claimed in claim 1, wherein: the reference unit comprises a second 3db coupler, a reference fiber grating, a first photoelectric detector and a band-pass filter;
the output end of the unbalanced M-Z interferometer is connected with the input end of a second 3db coupler, the second 3db coupler divides an optical signal into two paths, one path of the optical signal is output to the reference fiber grating, the other path of the optical signal is output to the matching fluid, the output end of the second 3db coupler, which is output to the matching fluid, is electrically connected with the input end of the band-pass filter through the first photoelectric detector, and the output end of the band-pass filter is electrically connected with the detection unit.
3. A fiber grating demodulation system as claimed in claim 2, wherein: the interference unit comprises a third 3db coupler, a first Faraday rotator mirror, a second Faraday rotator mirror and second piezoelectric ceramics;
the output end of the first 3db coupler outputs a reflection signal of the sensing fiber grating to the input end of a third 3db coupler, the third 3db coupler divides an optical signal into two optical paths which are respectively marked as a first optical path and a second optical path, the optical signal on the first optical path is output to a first Faraday rotator mirror, the optical fiber from the third 3db coupler to the first Faraday rotator mirror is wound on a second piezoelectric ceramic, the second piezoelectric ceramic is axially connected with the first Faraday rotator mirror, a sawtooth wave generator generates sawtooth waves and is loaded on the second piezoelectric ceramic to drive the second piezoelectric ceramic to generate telescopic deformation, the optical signal on the second optical path is output to the second Faraday rotator mirror, and the output end of the third 3db coupler outputs an optical signal to a detection unit.
4. A fiber grating demodulation system as claimed in claim 3, wherein: the detection unit comprises a second photoelectric detector, a signal amplifier, a filter and a phase meter which are electrically connected in sequence;
and the output end of the third 3db coupler outputs an optical signal which is detected by the second photoelectric detector, the second photoelectric detector converts the optical signal into an electric signal, the electric signal is amplified by the signal amplifier and filtered by the filter in sequence and then reaches the input end of the phase meter, a signal output by the output end of the band-pass filter is used as a reference wave and is sent to the other input end of the phase meter, and the output end of the phase meter outputs a phase signal.
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