CN210268885U - Phase modulation type optical time domain reflectometer - Google Patents
Phase modulation type optical time domain reflectometer Download PDFInfo
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- CN210268885U CN210268885U CN201921066512.2U CN201921066512U CN210268885U CN 210268885 U CN210268885 U CN 210268885U CN 201921066512 U CN201921066512 U CN 201921066512U CN 210268885 U CN210268885 U CN 210268885U
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Abstract
The utility model discloses a phase modulation type optical time domain reflectometer, including phi-OTDR host computer and single mode fiber, phi-OTDR host computer comprises phi-OTDR demodulation module, optic fibre raman laser, two-way isopower raman spectroscopy module, isolator, optical divider and photoswitch. The phi-OTDR demodulation module is connected with a plurality of bidirectional equal-power Raman light splitting modules through an optical switch, so that the disturbance detection range is expanded, and multi-channel measurement is realized; the uniformity of the distribution of the detection pulse light in the test optical fiber is improved and the signal-to-noise ratio is improved by a first-order or second-order bidirectional equal-power Raman amplification technology; the fiber Raman laser and the isolator are connected with the splitter to provide a pumping source for the plurality of bidirectional equal-power Raman light splitting modules, so that the instrument integration level is improved, and the cost is reduced. The utility model discloses a method helps phi-OTDR technique wide application in vibration detection scheme such as railway line control, electric power system cable monitoring, the illegal excavation of oil gas pipeline detects, important facility perimeter security protection and mining disaster rescue location.
Description
Technical Field
The utility model relates to a distributed optical fiber sensing technical field, concretely relates to phase modulation type optical time domain reflectometer.
Background
The phase modulation type optical time domain reflectometer (phi-OTDR) is based on the interference effect of backward Rayleigh scattering light, when a single-mode fiber is disturbed along a certain position, the refractive index of a fiber core at the position can be changed due to the elastic light principle, so that the optical phase modulation is facilitated, the interference phenomenon of the backward Rayleigh scattering light, namely the intensity of light intensity, is influenced finally, and the external vibration can be positioned by injecting pulse light and detecting the intensity of the backward Rayleigh scattering light. The multichannel distributed measurement range, the signal-to-noise ratio and the spatial resolution of the sensor are superior to those of other sensing measurement technologies, so that the sensor is widely applied to vibration detection schemes such as railway line monitoring, electric power system cable monitoring, illegal excavation detection of oil and gas pipelines, perimeter security of important facilities, intelligent monitoring of urban pipe networks, mine disaster rescue positioning and the like.
The conventional phi-OTDR device is extended in measurement range by extending the measurement distance, and the solution of extending the measurement distance is generally based on enhancing the power of the test pulse light in the optical fiber and using optical amplification technology. The detection pulse light based on the EDFA centralized amplification type phi-OTDR which is generally adopted is weakened along with the increase of the distance of the optical fiber, the power of the pulse light entering the optical fiber is improved by improving the optical amplification effect of the pump power enhanced erbium-doped optical fiber, but the power of the front end of the optical fiber is far larger than that of the rear end of the optical fiber, and the following three design defects are introduced along with the front end power of the optical fiber: the front end of the optical fiber is easy to generate a nonlinear effect, and if the fiber entering power is larger than the stimulated Brillouin threshold value, the stimulated Brillouin scattering effect is caused; when the optical power is unevenly distributed in the optical fiber, the signal-to-noise ratio of the front end is higher than that of the rear end, so that the false alarm rate of the instrument is increased; enhancing spontaneous emission noise that affects performance.
Therefore, how to enlarge the measurement range of the phase modulation type optical time domain reflectometer, further improve the uniformity of the distribution of the detection pulse light in the test optical fiber, improve the signal to noise ratio, improve the performance development and utilization degree of the phase modulation type optical time domain reflectometer, and reduce the cost still remains to be solved urgently.
SUMMERY OF THE UTILITY MODEL
In order to overcome the above-mentioned defect of prior art, the utility model aims to solve the problem that a phase modulation type optical time domain reflectometer is provided, it can enlarge disturbance detection range, realize the multichannel measurement, improves phi-OTDR's performance development and utilization degree, improves the degree of consistency of probing the pulse light distribution in the test optic fibre, improves the SNR, realizes real full distributing type vibration location and measurement on a large scale.
In order to achieve the above purpose, the utility model adopts the following technical scheme:
the phi-OTDR host machine is composed of a phi-OTDR demodulation module, a fiber Raman laser, a bidirectional equal-power Raman light splitting module, an isolator, an optical splitter and an optical switch, the phi-OTDR demodulation module is connected with the bidirectional equal-power Raman light splitting module through the optical switch, and the fiber Raman laser and the isolator are sequentially connected with the optical splitter.
The phi-OTDR demodulation module is composed of a narrow line width laser, an acousto-optic modulator, an erbium-doped fiber amplifier, a waveform generator, a data acquisition module, a photoelectric detector, a band-pass filter, a circulator and an upper mechanism.
The bidirectional equipower Raman spectrum module is further divided into a first-order bidirectional equipower Raman spectrum module and a second-order bidirectional equipower Raman spectrum module.
The first-order bidirectional equal-power Raman optical splitting module is composed of an 50/50 coupler and a wavelength division multiplexer, and the second-order bidirectional equal-power Raman optical splitting module is composed of a 50/50 coupler, a wavelength division multiplexer and a fiber Bragg grating.
And further, the fiber Bragg grating in the second-order bidirectional equal-power Raman spectroscopy module is connected with the light emergent end of the wavelength division multiplexer.
Furthermore, the head end and the tail end of the single-mode optical fiber are respectively connected with two light emergent ends of the bidirectional equal-power Raman light splitting module to form an annular cavity.
Furthermore, the phi-OTDR demodulation module is connected with the light incidence end of the optical switch, and the light emergence end of the optical switch is connected with the light incidence end of the wavelength division multiplexer in the bidirectional equal-power Raman spectroscopy module.
The light emitting end of the optical splitter is connected with the light incident end of the 50/50 coupler in the bidirectional equipower Raman amplification module.
The utility model has the advantages that: the phi-OTDR demodulation module is connected with a plurality of bidirectional equal-power Raman spectroscopy modules through an optical switch, so that the disturbance detection range is expanded, multi-channel measurement is realized, and the performance development and utilization degree of the phi-OTDR is improved; the uniformity of the distribution of the detection pulse light in the test optical fiber is improved and the signal-to-noise ratio is improved by a first-order or second-order bidirectional equal-power Raman amplification technology; the fiber Raman laser and the isolator are connected with the splitter to provide a pumping source for the plurality of bidirectional equal-power Raman light splitting modules, so that the instrument integration level is improved, and the cost is reduced. The utility model discloses a method helps phi-OTDR technique wide application in vibration detection scheme such as railway line control, electric power system cable monitoring, the illegal excavation of oil gas pipeline detects, important facility perimeter security protection, city pipe network intelligent monitoring and mining disaster rescue location.
Drawings
FIG. 1 is a structural diagram of a multi-channel phase modulation type optical time domain reflectometer based on first-order bidirectional equal power Raman amplification;
fig. 2 is a structural diagram of a multichannel phase modulation type optical time domain reflectometer based on second-order bidirectional equal power raman amplification.
Detailed Description
The invention will be further described with reference to the accompanying drawings:
as an embodiment of the present invention, the multichannel phase modulation type optical time domain reflectometer based on the first-order bidirectional isopower raman amplification is, as shown in fig. 1, composed of a Φ -OTDR demodulation module 16, a 1 × N optical switch 5, a first-order bidirectional isopower raman splitting module 14, a single mode fiber 15, a 1 × N splitter 11, an isolator 12, and a fiber raman laser 13. The phi-OTDR demodulation module 16 is composed of a narrow linewidth laser 1, an acousto-optic modulator 2, an erbium-doped fiber amplifier 3, a circulator 4, a waveform generator 6, an upper computer 7, a data acquisition module 8, a photoelectric detector 9 and a 1550nm band-pass filter 10. The first order bidirectional equal power raman splitting module 14 is composed of 50/50 couplers 19, 1455nm/1550nm1 × 2 wavelength division multiplexers 17 and 18 and an isolator 20. The light emitting end of the phi-OTDR demodulation module 16 is connected with the light incident end of the 1 xN optical switch 5, the N light emitting ends of the 1 xN optical switch 5 are respectively connected with the light incident end of the 1455nm/1550nm1 x 2 wavelength division multiplexer 17 in the N first-order bidirectional equipower Raman optical splitting modules 14, the head end and the tail end of the single-mode optical fiber 15 are respectively connected with the two light emitting ends of the first-order bidirectional equipower Raman optical splitting module 14 to form an annular cavity, the light incident ends of the optical fiber Raman laser 13, the isolator 12 and the 1 xN optical splitter 11 are sequentially connected, the N light emitting ends of the 1 xN optical splitter 11 are connected with the light incident end of the 50/50 coupler 19 in the first-order bidirectional equipower Raman amplification module 14, and multichannel measurement is achieved.
The narrow linewidth laser 1 outputs 1550nm continuous light to the acousto-optic modulator 2 to be modulated into pulse light, and the acousto-optic modulator 2 is driven by the waveform generator 6; the pulse light is subjected to centralized light amplification by the erbium-doped optical fiber amplifier 3 and then is coupled into the light incidence end of the 1 × N optical switch 5 through the port 21 of the circulator 4, and then the pulse light is coupled into the light incidence end of the 1455nm/1550nm1 × 2 wavelength division multiplexer 17 in the first-order bidirectional equal-power Raman optical splitting module 14; the pump light with 1455nm wavelength output by the fiber raman laser 13 is first protected by the isolator 12 (preventing reflected light from damaging the fiber raman laser 13), and then divided into two paths with two-way equal power by the 50/50 coupler 19, and then the two paths of light are coupled into the single mode fiber 15 by the 1455nm/1550nm1 × 2 wavelength division multiplexers 17 and 18, respectively. Backward rayleigh scattered light transmitted back from the single mode fiber 15 enters through a port 22 and a port 23 of the circulator 4, then is subjected to elimination of redundant 1455nm first-order stokes light and 1455nm backward rayleigh scattered light through a 1550nm band-pass filter 10, and then enters into the photoelectric detector 9. The data acquisition module 8 acquires the output electric signal of the photoelectric detector 9 and sends the output electric signal into the upper computer 7 to complete data processing and position and measure external disturbance according to the change of a pulse light detection curve along with space, wherein the waveform generator 6 synchronously triggers the data acquisition module 8 to acquire signals, and the isolator 20 is used for preventing end face reflection.
The fiber Raman laser 13 outputs pump light with the wavelength of 1455nm, and first-order Stokes light with the wavelength of 1455nm is generated when the power of the pump light exceeds a stimulated Raman scattering threshold; in the single-mode optical fiber 15, 1550nm pulsed light and 1455nm first-order stokes light exist simultaneously, and the frequency difference of the two lights is within the gain bandwidth of the raman gain spectrum so that the pulsed light is distributively amplified by the raman gain.
The multi-channel phase modulation type optical time domain reflectometer based on first-order bidirectional equipower Raman amplification can obtain a relatively flat signal gain effect in the single-mode fiber 15, wherein if the output continuous optical power of the narrow-linewidth laser 1 is changed under the condition that the pump optical power output by the fiber Raman laser 13 is fixed, the fiber-entering optical power is too strong, so that the backward Rayleigh scattering light interference intensity at the rear end of the single-mode fiber 15 is weakened, and the sensing distance is reduced; if the pump light power output by the fiber raman laser 13 is changed under the condition that the output continuous light power of the narrow linewidth laser 1 is fixed, the pump light power is too low to amplify the signal light at the rear end of the fiber, and if the pump light power is too high, the signal-to-noise ratio of the backward rayleigh scattered light interference signal at the rear end is reduced, so that the output continuous light power of the narrow linewidth laser 1 and the pump light power output by the fiber raman laser 13 need to be changed and optimized simultaneously, and the instrument works in an optimal state.
As an embodiment of the present invention, the second-order bi-directional equipower raman amplification-based multi-channel phase modulation type optical time domain reflectometer is, as shown in fig. 2, composed of a Φ -OTDR demodulation module 16, a 1 × N optical switch 5, a second-order bi-directional equipower raman splitting module 14, a single-mode fiber 15, a 1 × N splitter 11, an isolator 12, and a fiber raman laser 13. The phi-OTDR demodulation module 16 is composed of a narrow linewidth laser 1, an acousto-optic modulator 2, an erbium-doped fiber amplifier 3, a circulator 4, a waveform generator 6, an upper computer 7, a data acquisition module 8, a photoelectric detector 9 and a 1550nm band-pass filter 10. The second-order bidirectional equipower Raman spectroscopy module 14 consists of an 50/50 coupler 19, 1366nm/1550nm1 × 2 wavelength division multiplexers 17 and 18, an isolator 20 and two fiber Bragg gratings 24. The light emitting end of the phi-OTDR demodulation module 16 is connected with the light incident end of the 1 xN optical switch 5, N light emitting ends of the 1 xN optical switch 5 are respectively connected with the light incident end of a 1366nm/1550nm1 x 2 wavelength division multiplexer 17 in the N second-order bidirectional equipower Raman optical splitting modules 14, the head end and the tail end of the single-mode optical fiber 15 are respectively connected with two light emitting ends of the second-order bidirectional equipower Raman optical splitting module 14 to form an annular cavity, the light incident ends of the optical fiber Raman laser 13, the isolator 12 and the 1 xN optical splitter 11 are sequentially connected, N light emitting ends of the 1 xN optical splitter 11 are connected with the light incident end of a 50/50 coupler 19 in the second-order bidirectional equipower Raman amplification module 14, and multichannel measurement is achieved.
The narrow linewidth laser 1 outputs 1550nm continuous light to the acousto-optic modulator 2 to be modulated into pulse light, and the acousto-optic modulator 2 is driven by the waveform generator 6; the pulsed light is subjected to centralized light amplification by the erbium-doped optical fiber amplifier 3 and then is coupled into the light incidence end of the 1 × N optical switch 5 through the port 21 of the circulator 4, and then the pulsed light is coupled into the light incidence end of the 1366nm/1550nm1 × 2 wavelength division multiplexer 17 in the second-order bidirectional equal-power Raman optical splitting module 14; the pumping light with the wavelength of 1366nm output by the fiber raman laser 13 is firstly protected by the isolator 12 (preventing reflected light from damaging the fiber raman laser 13), and then divided into two paths with two-way equal power by the 50/50 coupler 19, and then the two paths of light are respectively coupled into the single mode fiber 15 by the 1366nm/1550nm1 × 2 wavelength division multiplexers 17 and 18 and the fiber bragg grating pair 24. Backward rayleigh scattered light transmitted back from the single mode fiber 15 enters through a port 22 and a port 23 of the circulator 4, and then enters into the photoelectric detector 9 after redundant 1366nm pump light, 1455nm second-order stokes light and 1455nm backward rayleigh scattered light are eliminated through the 1550nm band-pass filter 10. The data acquisition module 8 acquires the output electric signal of the photoelectric detector 9 and sends the output electric signal into the upper computer 7 to complete data processing and position and measure external disturbance according to the change of a pulse light detection curve along with space, wherein the waveform generator 6 synchronously triggers the data acquisition module 8 to acquire signals, and the isolator 20 is used for preventing end face reflection.
The fiber Raman laser 13 outputs pumping light with the wavelength of 1366nm, and first-order Stokes light with the wavelength of 1455nm is generated when the power of the pumping light exceeds a stimulated Raman scattering threshold; the central reflection wavelength 1455nm of the fiber Bragg grating pair 24 is respectively welded at the light emergent ends of the 1366nm/1550nm1 x 2 wavelength division multiplexers 17 and 18, and the head end and the tail end of the single mode fiber 15 are respectively connected with the two light emergent ends of the second-order bidirectional equal-power Raman spectroscopy module 14, so that a distributed annular laser resonant cavity is formed and is used for lasing 1455nm second-order Stokes light. In the single-mode optical fiber 15, 1550nm pulse light and 1455nm second-order stokes light exist simultaneously, and the frequency difference of the two lights is within the gain bandwidth of the raman gain spectrum, so that the pulse light is subjected to distributed amplification due to the raman gain.
The multi-channel phase modulation type optical time domain reflectometer based on the second-order bidirectional equipower Raman amplification can obtain a flatter signal gain effect and larger signal intensity in the single mode fiber 15 than the multi-channel phase modulation type optical time domain reflectometer based on the first-order bidirectional equipower Raman amplification, wherein if the output continuous optical power of the narrow-linewidth laser 1 is changed under the condition that the pump optical power output by the optical fiber Raman laser 13 is fixed, the backward Rayleigh scattering light interference intensity at the rear end of the single mode fiber 15 can be weakened and the sensing distance can be reduced if the fiber-entering optical power is too strong; if the pump light power output by the fiber raman laser 13 is changed under the condition that the output continuous light power of the narrow linewidth laser 1 is fixed, the pump light power is too low to amplify the signal light at the rear end of the fiber, and if the pump light power is too high, the signal-to-noise ratio of the backward rayleigh scattered light interference signal at the rear end is reduced, so that the output continuous light power of the narrow linewidth laser 1 and the pump light power output by the fiber raman laser 13 need to be changed and optimized simultaneously, and the instrument works in an optimal state.
Claims (8)
1. Phase modulation type optical time domain reflectometer, including phi-OTDR host computer and single mode fiber, its characterized in that: the phi-OTDR host machine is composed of a phi-OTDR demodulation module, a fiber Raman laser, a bidirectional equipower Raman spectroscopy module, an isolator, an optical splitter and an optical switch, wherein the phi-OTDR demodulation module is connected with the bidirectional equipower Raman spectroscopy module through the optical switch, and the fiber Raman laser, the isolator and the optical splitter are sequentially connected.
2. The phase modulation type optical time domain reflectometer according to claim 1, characterized in that: the phi-OTDR demodulation module is composed of a narrow line width laser, an acousto-optic modulator, an erbium-doped fiber amplifier, a waveform generator, a data acquisition module, a photoelectric detector, a band-pass filter, a circulator and an upper mechanism.
3. The phase modulation type optical time domain reflectometer according to claim 2, characterized in that: the bidirectional equipower Raman spectroscopy module is divided into a first-order bidirectional equipower Raman spectroscopy module and a second-order bidirectional equipower Raman spectroscopy module.
4. The phase modulation type optical time domain reflectometer according to claim 3, characterized in that: the first-order bidirectional equal-power Raman optical splitting module is composed of an 50/50 coupler and a wavelength division multiplexer, and the second-order bidirectional equal-power Raman optical splitting module is composed of a 50/50 coupler, a wavelength division multiplexer and a fiber Bragg grating.
5. The phase modulation type optical time domain reflectometer according to claim 4, wherein: and the fiber Bragg grating in the second-order bidirectional equipower Raman spectroscopy module is connected with the light emergent end of the wavelength division multiplexer.
6. The phase modulation type optical time domain reflectometer according to claim 5, wherein: the head end and the tail end of the single-mode optical fiber are respectively connected with two light emergent ends of the bidirectional equal-power Raman light splitting module to form an annular cavity.
7. The phase modulation type optical time domain reflectometer according to claim 6, wherein: the phi-OTDR demodulation module is connected with the light incidence end of the optical switch, and the light emergence end of the optical switch is connected with the light incidence end of the wavelength division multiplexer in the bidirectional equal-power Raman light splitting module.
8. The phase modulation type optical time domain reflectometer as in claim 7, wherein: the light emitting end of the optical splitter is connected with the light incident end of the 50/50 coupler in the bidirectional equipower Raman amplification module.
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