Hybrid Distributed Optical Fiber Sensing System

Abstract

To provide a fiber optic sensing system which enable measurement of temperature of an object under test at any position.SOLUTION: A hybrid distributed fiber optic sensing system based on the Brillouin optical time-domain analysis method and a phase-sensitive optical time-domain reflectometer is disclosed, the system being configured to perform sensing using the Rayleigh scattering principle and Brillouin phase shift characteristics so as to measure temperature, tension, and vibration parameters of a location under test.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to optical fiber sensing systems, and more particularly to a hybrid distributed optical fiber sensing system based on Brillouin Optical Time Domain Analysis and Phase-sensitive Optical Time Domain Reflectometry. [Background technology]

[0002] In the field of traditional measurement technology, when a measurement is required, a certain length needs to be measured, and when optical fiber sensing is used alone for measurement, it is difficult to measure the exact position because the temperature change or topography is different for each length, and it is difficult to determine whether the adverse effect is caused by temperature or other factors such as other stresses.

[0003] 1 shows a prior art Brillouin optical time domain analysis and measurement system, which includes, for example, the following elements: First, the system light source 1001 is a laser light source, then the coupler 1002 splits it into a pump light source and a probe light source, and the first all-fiber component polarization controller 1003 and the second all-fiber component polarization controller 1004 adjust the light polarization state to maximize the output power.

[0004] Also, as shown in FIG. 1, a signal generator 1005 is used to generate a continuous wave signal and sense the Brillouin frequency of the fiber under test, a first electro-optic modulator 1006 and a second electro-optic modulator 1007 are used to convert the electrical signal to an optical signal, and a pulse pattern generator 1008 and an arbitrary waveform generator 1009 are used to generate the pulse wave signals required by the system.

[0005] 1, a variable optical attenuator 1010 is connected to the isolator 1014, and the variable optical attenuator 1010 adjusts the optical power, and the isolator 1014 restricts the optical path to be connected to the fiber under test 1015 in only one direction. A modulator bias controller 1011 can automatically adjust the bias voltage to generate a stable pulse wave signal output, and the modulator bias controller 1011 is connected to the computer 1012.

[0006] 1, the computer 1012 is electrically connected to a digital fluorescent oscilloscope 1013, the modulator bias controller 1011 is connected to a first erbium-doped fiber amplifier 1016, and the first erbium-doped fiber amplifier 1016 is connected to a polarization scrambler 1017. The polarization scrambler 1017 can suppress polarization noise.

[0007] Also, as shown in FIG. 1, the polarization scrambler 1017 is connected to a variable optical attenuator 1018, which is connected to an optical circulator 1019 and a second erbium-doped fiber amplifier 1020, which is connected to a tunable filter 1021 for filtering the required Brillouin scattering light band using a tunable filter 1021.

[0008] Finally, as shown in FIG. 1, the tunable filter 1021 is connected to a photodetector 1022, which is connected to a DC block 1023.

[0009] Conventional known technologies such as optical fiber sensing technology can be used as sensing measurement in any measurement target area ranging from several kilometers to tens of kilometers, and the sensing range is quite wide, but the more sensing heads there are, the higher the sensing cost is, and the more likely the light energy insertion loss of the light source occurs. On the other hand, point-by-point optical fiber sensing has a high accuracy in a short distance and can determine the correct position of the disturbance, but when used for long-distance measurement, the fiber under test is prone to have a break point, and the system cannot detect when the probe light and the pump laser cannot communicate. That is, the Brillouin optical time domain analysis measurement system of the prior art cannot be used for long-distance measurement.

[0010] As can be seen from the above, the existing prior art distributed optical fiber sensing and point-by-point optical fiber sensing still need improvement, need further review, and feasible solutions are required, therefore research and progress on new types of optical fiber measurement systems are needed to be implemented in practice. Furthermore, there is still a need to update and commercialize optical fiber measurement systems. Summary of the Invention

[0011] The disclosed hybrid distributed optical fiber sensing system based on Brillouin optical time domain analysis and phase-sensitive optical time domain reflectometry uses Brillouin scattering and Brillouin frequency shift for sensing, thereby measuring the temperature of an object under test at any position.

[0012] The hybrid distributed optical fiber sensing system based on Brillouin optical time domain analysis and phase-sensitive optical time domain reflectometer in the first embodiment of the present disclosure includes the following elements: a narrow linewidth fiber laser connected to a coupler connected to a first all-fiber component polarization controller and a second all-fiber component polarization controller, an electro-optic modulator connected through a signal generator, the first all-fiber component polarization controller connected to the electro-optic modulator, the electro-optic modulator further connected to a first variable optical attenuator, an isolator, a switch and a fiber under test, the second all-fiber component polarization controller connected to an acousto-optic modulator, and configured to be sequentially connected to a first erbium-doped fiber amplifier, a second variable optical attenuator, an optical circulator, a second erbium-doped fiber amplifier, a tunable filter, a photodetector, a DC block and a digital phosphor oscilloscope, the acousto-optic modulator connected to a driver and a pulse generator.

[0013] The hybrid distributed optical fiber sensing system based on Brillouin optical time domain analysis and phase-sensitive optical time domain reflectometer in the second embodiment of the present disclosure includes the following elements: A narrow linewidth fiber laser connected to a coupler, a first coupler splits a pump light source and a probe light source, the first coupler is connected to a first all-fiber component polarization controller and a second all-fiber component polarization controller, and is connected to an electro-optic modulator through a signal generator, the first all-fiber component polarization controller is connected to an electro-optic modulator, the electro-optic modulator is sequentially connected to a first variable optical attenuator, an isolator, a switch, and a fiber under test, the second all-fiber component polarization controller is configured to be connected to an acousto-optic modulator, and is sequentially connected to a first erbium-doped fiber amplifier, a second variable optical attenuator, an optical circulator, a second erbium-doped fiber amplifier, a second coupler, and a first tunable filter, the first tunable filter is connected to a first photodetector, and finally connected to a digital phosphor oscilloscope, the second tunable filter is connected to a second photodetector, and finally connected to a digital phosphor oscilloscope, the acousto-optic modulator is connected to a driver and connected to a pulse generator.

[0014] In order to make the above-mentioned features of the present disclosure more clear and understandable, the following embodiments are set forth in detail. [Brief description of the drawings]

[0015] The foregoing and many other advantages of the present disclosure will become more clearly apparent in the following detailed description of the preferred embodiments of the present disclosure, the drawings of which are given below. [Figure 1] FIG. 1 shows a prior art Brillouin optical time domain analysis and measurement system. [Diagram 2] FIG. 2 shows a schematic diagram of a hybrid distributed optical fiber sensing system based on Brillouin optical time domain analysis and phase-sensitive optical time domain reflectometer according to a first embodiment of the present disclosure. [Diagram 3]FIG. 3 shows a schematic diagram of a hybrid distributed optical fiber sensing system based on Brillouin optical time domain analysis and phase-sensitive optical time domain reflectometer according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The various aspects and embodiments are illustrative and non-limiting only, and after reading this specification, a person skilled in the art may have other aspects and embodiments without departing from the scope of the present disclosure. The features and advantages of these embodiments will become more apparent from the following detailed description and claims.

[0017] The disclosed hybrid distributed optical fiber sensing system based on Brillouin optical time domain analysis and phase-sensitive optical time domain reflectometry uses Brillouin scattering and Brillouin frequency shift to measure the temperature of an object under test at any location.

[0018] First, please refer to the schematic diagram of a hybrid distributed optical fiber sensing system based on Brillouin optical time domain analysis and phase-sensitive optical time domain reflectometer of the first embodiment 200 of the present disclosure shown in Figure 2. As shown, first, a narrow linewidth fiber laser (NLFL) 2001 provides a laser light source, and the narrow linewidth fiber laser 2001 is connected to a coupler (coupler) 2002, which splits a pump light source (pump light) and a probe light source. The coupler 2002 is connected to a first all-fiber component polarization controller (PC) 2003, and at the same time, a second all-fiber component polarization controller (PC) 2004, and the first all-fiber component polarization controller 2003 and the second all-fiber component polarization controller 2004 can adjust the light polarization state to maximize the output power.

[0019] Continuing with the schematic diagram of the hybrid distributed optical fiber sensing system based on Brillouin optical time domain analysis and phase-sensitive optical time domain reflectometer of the first embodiment 200 of the present disclosure shown in FIG. 2, a signal generator (SG) 2005 is connected to an electro-optic modulator (EOM) 2006, and a first all-fiber component polarization controller 2003 is connected to the electro-optic modulator (EOM) 2006 to generate a continuous wave signal. The Brillouin frequency of the fiber under test can then be detected. The electro-optic modulator (EOM) 2006 is then sequentially connected to a first variable optical attenuator (VOA) 2007, an isolator (ISO) 2008, a switch 2009, and a fiber under test (FUT) 2010.

[0020] Continuing with the schematic diagram of the hybrid distributed optical fiber sensing system based on Brillouin optical time domain analysis and phase-sensitive optical time domain reflectometer of the first embodiment 200 of the present disclosure shown in FIG. 2, the second all-fiber component polarization controller 2004 is sequentially connected to an acousto-optic modulator (AOM) 2011, a first erbium-doped fiber amplifier (EDFA) 2012, a second variable optical attenuator (VOA) 2013, an optical circulator (OC) 2014, a second erbium-doped fiber amplifier (EDFA) 2017, a tunable filter 2018, a photodetector (PD) 2019, a direct current (DC) block 2020, and a digital fluorescence oscilloscope (DPO) 2021.

[0021] Continuing with the schematic diagram of the hybrid distributed optical fiber sensing system based on Brillouin optical time domain analysis and phase sensitive optical time domain reflectometer of the first embodiment 200 of the present disclosure shown in FIG. 2, an acousto-optic modulator (AOM) 2011 is in turn connected to a driver 2015 and a pulse generator (PG) 2016 to load the sinusoidal signal required to generate the probe light. A computer 2022 performs signal communication with the driver 2015 and the tunable filter 2018.

[0022] In addition, please refer to the schematic diagram of a hybrid distributed optical fiber sensing system based on Brillouin optical time domain analysis and phase-sensitive optical time domain reflectometer of the second embodiment 300 of the present disclosure shown in Figure 3. It includes the following elements as shown. First, a narrow-linewidth fiber laser 3001 provides a laser light source, the narrow-linewidth fiber laser 3001 is connected to a coupler 3002, the first coupler 3002 splits the pump light source and the probe light source, the first coupler 3002 is connected to a first all-fiber component polarization controller 3003 and simultaneously connected to a second all-fiber component polarization controller 3004, the first all-fiber component polarization controller 3003 and the second all-fiber component polarization controller 3004 can adjust the optical polarization state to maximize the input power to the electro-optic modulator 3006 and the acousto-optic modulator 3011.

[0023] Continuing with the schematic diagram of the hybrid distributed optical fiber sensing system based on Brillouin optical time domain analysis and phase-sensitive optical time domain reflectometer of the second embodiment 300 of the present disclosure shown in Figure 3, a signal generator 3005 is connected to an electro-optic modulator 3006, and a first all-fiber component polarization controller 3003 is connected to the electro-optic modulator 3006 to generate a continuous wave signal for subsequent sensing of the Brillouin frequency of the fiber under test. The electro-optic modulator 3006 is then sequentially connected to a first variable optical attenuator 3007, an isolator 3008, a switch 3009, and a fiber under test 3010.

[0024] Continuing with the schematic diagram of the hybrid distributed optical fiber sensing system based on Brillouin optical time domain analysis and phase-sensitive optical time domain reflectometer of the second embodiment 300 of the present disclosure shown in FIG. 3, the second all-fiber component polarization controller 3004 is sequentially connected to an acousto-optic modulator 3011, a first erbium-doped fiber amplifier 3012, a second variable optical attenuator 3013, an optical circulator 3014, a second erbium-doped fiber amplifier 3017, and a second coupler 3018, and then simultaneously connected to a first tunable filter 3019 and a second tunable filter 3020, the first tunable filter 3019 is connected to a first photodetector 3021, and finally to a digital phosphor oscilloscope 3023. The second tunable filter 3020 is connected to a second photodetector 3022, and finally to a digital phosphor oscilloscope 3023.

[0025] Continuing with the schematic diagram of the hybrid distributed optical fiber sensing system based on Brillouin optical time domain analysis and phase-sensitive optical time domain reflectometer of the second embodiment 300 of the present disclosure shown in Figure 3, the acousto-optic modulator 3011 is connected to a driver 3015, which is then connected to a pulse generator 3016, thereby loading the sinusoidal signal required to generate the probe light. A computer 3024 controls the signal sent from the driver 3015 to the acousto-optic modulator 3011.

[0026] The hybrid distributed optical fiber sensing system based on the Brillouin optical time domain analysis method and phase-sensitive optical time domain reflectometer of the present disclosure can have the effect of the electro-optic modulator 3006. Since the electro-optic modulator 3006 has a good lightwave frequency shift effect, the present disclosure requires fitting the frequency difference of the two lightwaves through the Brillouin gain, and therefore the characteristics of the lightwave frequency shift effect can be realized by using the electro-optic modulator 3006 to perform the optical path modulation of the laser carrier. At this time, the desired pulse can be generated in the pulse waveform generator 3016 and sent to the acousto-optic modulator 3011 through the driver 3015. The pulse is supplied to one path of the pump laser, then passes through the first erbium-doped fiber amplifier 3012, passes through the optical attenuator 3013 to adjust the power ratio between the pump laser and the probe light, passes through the isolator to be limited, and prevents it from being transmitted to the non-test area. Additionally, the other path of the pump laser 3001 as the probe light can pass through an electro-optic modulator 3006 that is loaded with the required sinusoidal signal from a sinusoidal signal generator 3005 .

[0027] The hybrid distributed optical fiber sensing system based on the Brillouin optical time-domain analysis method and phase-sensitive optical time-domain reflectometer of the present disclosure can observe the optical signal-to-noise ratio (OSNR) of the Brillouin scattered light and Rayleigh scattered light under each channel, as well as the gain of the Brillouin scattered light by adjusting the filter channel. In addition, since both the incident pump power and the probe optical power are better, by allowing the interaction between the two, the gain of the Brillouin scattered light can be increased and the signal-to-noise ratio can be increased. Therefore, when changing the probe optical power, it is necessary to pay attention to the amplitude of the pulse of the electrical signal at the same time, as shown in Table 1. The present disclosure proposes to fix the pump optical power. The gain of the Brillouin scattered light can be observed with the change of the probe optical power, thereby improving the sensing distance. Table 1 below shows the experimental data.

[0028] Table 1: Probe light adjustments

Table 1

[0029] For the basic operation principle of the hybrid distributed optical fiber sensing system based on the Brillouin optical time domain analysis method and phase-sensitive optical time domain reflectometer of the present disclosure, when the switch 3009 is set as an open circuit, it is the framework of Brillouin optical time domain analysis. This framework uses excited Brillouin scattering with electrostrictive effect in the single mode fiber 103. That is, the interference between the pump light and the backward Brillouin scattered light estimates the beat frequency electric field. When the power of the Brillouin scattered light is smaller, the backward incident continuous probe light can pass to interact with the pump light, thereby ensuring that both the probe light and the pump light maintain a specific frequency and polarization, and when the probe light and the pump light encounter each other, excited Brillouin scattering is generated and energy transfer is carried out. The optical signal is received through the first photodetector 3021, and the signal is observed through the oscilloscope 3023. When the switch 3009 is shorted, the probe light path of the BOTDA is blocked, and this framework is the framework of phase-sensitive optical time domain reflectometry. Using the narrow linewidth fiber laser 3001 as the light source, the pulse wave signal required for the experiment is loaded by entering the acousto-optic modulator 3011. Because the modulated signal has a significant power loss, the optical signal is amplified for the first time through the first erbium-doped fiber amplifier 3012. The probe principle of phase-sensitive optical time-domain reflectometry uses Rayleigh backscattering, and the Rayleigh scattered light is the elastic collision of light to make the incident light and the scattered light coherent. The scattered light is received for signal processing. When the incident light enters the fiber under test 3010, the excessive power will lead to the excited Brillouin scattered light effect and other unnecessary nonlinear effects, making the processing of the scattered signal difficult and reducing the SNR of the system. Therefore, the optical attenuator can adjust the power of the incident light, and the quality of the incident light can be observed by the optical spectrum analyzer. After the light enters the fiber under test 3010, the Rayleigh backscattered light is output from port 3 of the optical circulator 3014, and after the optical spectrum analyzer does not observe any Brillouin scattered light, it enters the second Erbium-doped fiber amplifier 3017. The second amplification is performed on the optical signal that has loss after long-distance transmission.However, the optical signal is amplified by the optical amplifier 3017 so that the optical signal contains a broad spectrum light source and is filtered to the required Rayleigh scattered light by the tunable optical filter 3020. Finally, it is received by a second photodetector 3022 and a digital phosphor oscilloscope 3023 is used to extract the signal for final signal processing.

[0030] The advantages of the hybrid distributed optical fiber sensing system based on the Brillouin optical time domain analysis and phase-sensitive optical time domain reflectometer of the above embodiment are different from conventional detection technology. The optical fiber sensing technology is easy to measure the precise position and can be used alone for the measurement, which can avoid the influence of other factors. In addition, the optical fiber sensing technology allows the above embodiment to be extended to any interval of several kilometers to tens of kilometers as a sensing measurement, and has a wide sensing range. In addition, according to the above embodiment, the sensing cost can be reduced and the optical energy insertion loss of the light source can be reduced. The optical fiber detection system of the above embodiment has a reasonably accurate accuracy over a long distance and can also determine the precise location of the disturbance.

[0031] One of the advantages of the above embodiment is that it uses the increase and decrease of the Brillouin frequency of the optical fiber itself. This phenomenon is caused by the change in the diameter of the optical fiber and the change in the density of the optical fiber. The above description is only the preferred embodiment of the present disclosure, and is not intended to limit the scope of the present disclosure, and all other equivalent changes or modifications that do not depart from the spirit disclosed in the present disclosure should be included in the following claims. [Explanation of symbols]

[0032] 101: Distributed Optical Fiber Sensing System 102: Dispersion shifted fiber 103: Single mode fiber 1001: System light source 1002: Coupler 1003: All Fiber Component Polarization Controller 1004: All Fiber Component Polarization Controller 1005: Signal generator 1006: First electro-optic modulator 1007: second electro-optic modulator 1008: Pulse pattern generator 1009: Arbitrary Waveform Generator 1010: Variable optical attenuator 1011: Modulator Bias Controller 1012: Computer 1013: Digital phosphor oscilloscope 1014: Isolator 1015: Fiber under test 1016: First Erbium-doped Fiber Amplifier 1017: Polarization scrambler 1018: Variable optical attenuator 1019: Optical Circulator 1020: Second Erbium-doped Fiber Amplifier 1021: Tunable filter 1022: Photodetector 1023:DC Block 200: A hybrid distributed optical fiber sensing system based on Brillouin optical time-domain analysis and phase-sensitive optical time-domain reflectometry 2001: Narrow linewidth fiber laser 2002: Capra 2003: First all-fiber component polarization controller 2004: Second all-fiber component polarization controller 2005: Signal generator 2006: Electro-optic modulator 2007: First variable optical attenuator 2008: Isolator 2009: Switch 2010: Fiber under test 2011: Acousto-optic modulator 2012: First erbium-doped fiber amplifier 2013: 2nd variable optical attenuator 2014: Light Circulator 2015: Driver 2016: Pulse generator 2017: Second Erbium-doped Fiber Amplifier 2018: Tunable filters 2019: Photodetectors 2020:DC Block 2021: Digital fluorescent oscilloscope 2022: Computers 300: A hybrid distributed optical fiber sensing system based on Brillouin optical time-domain analysis and phase-sensitive optical time-domain reflectometry 3001: Narrow linewidth fiber laser 3002: Kapla 3003: The first all-fiber component polarization controller 3004: 2nd All-Fiber Component Polarization Controller 3005: Signal Generator 3006: Electro-optic modulator 3007: First variable optical attenuator 3008: Isolator 3009: Switch 3010: Fiber under test 3011: Acousto-optic modulator 3012: First Erbium-doped Fiber Amplifier 3013: 2nd variable optical attenuator 3014: Optical Circulator 3015: Driver 3016: Pulse generator 3017: Second Erbium-doped Fiber Amplifier 3018: 2nd coupler 3019: 1st tunable filter 3020: 2nd tunable filter 3021: First photodetector 3022: Second photodetector 3023: Digital phosphor oscilloscope 3024: Computer

Claims

1. A hybrid distributed optical fiber sensing system based on Brillouin Optical Time Domain Analysis and Phase-sensitive Optical Time Domain Reflectometry, comprising: a narrow linewidth fiber laser coupled to a coupler coupled to at least a first all-fiber component polarization controller and a second all-fiber component polarization controller; an electro-optic modulator is connected through a signal generator, the first all-fiber component polarization controller is connected to the electro-optic modulator, the electro-optic modulator is further connected to a first variable optical attenuator, an optical isolator, a switch and a fiber under test; the second all-fiber component polarization controller is configured to couple the acousto-optic modulator, the first erbium-doped fiber amplifier, the second variable optical attenuator, the optical circulator, the second erbium-doped fiber amplifier, the tunable filter, the photodetector, the DC block, and the digital phosphor oscilloscope; The acousto-optic modulator is connected to a driver and a pulse generator, forming a hybrid distributed fiber optic sensing system.

2. 10. The fiber optic sensing system of claim 1, wherein the first all-fiber component polarization controller and the second all-fiber component polarization controller are capable of adjusting the optical polarization state to maximize output power.

3. 2. The fiber optic sensing system of claim 1, wherein the acousto-optic modulator is connected to the driver and to the pulse generator for loading a sinusoidal signal required to generate the probe light.

4. A hybrid distributed optical fiber sensing system based on Brillouin Optical Time Domain Analysis and Phase-sensitive Optical Time Domain Reflectometry, comprising: a narrow linewidth fiber laser coupled to a coupler coupled to at least a first all-fiber component polarization controller and a second all-fiber component polarization controller; an electro-optic modulator is connected through a signal generator, the first all-fiber component polarization controller is connected to the electro-optic modulator, the electro-optic modulator is connected to a first variable optical attenuator, an optical isolator, a switch and a fiber under test; a second all-fiber component polarization controller configured to couple the acousto-optic modulator, the first erbium-doped fiber amplifier, the second variable optical attenuator, the optical circulator, the second erbium-doped fiber amplifier, the second coupler, the first tunable filter, and the second tunable filter; the first tunable filter is connected to the first photodetector and the digital fluorescent oscilloscope; a second tunable filter coupled to the second photodetector and to the digital fluorescent oscilloscope; The acousto-optic modulator is coupled to a driver and a pulse generator, forming a hybrid distributed fiber optic sensing system.

5. 5. The fiber optic sensing system of claim 4, wherein the first all-fiber component polarization controller and the second all-fiber component polarization controller are capable of adjusting the optical polarization state to maximize output power.

6. 5. The fiber optic sensing system of claim 4, wherein the acousto-optic modulator is connected to the driver and to the pulse generator for loading a sinusoidal signal required to generate the probe light.

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