CN117092715A - Optical fiber sensing system and detection method - Google Patents

Abstract

The embodiments of the present application relate to the field of optical fiber sensing technology, and disclose an optical fiber sensing receiving system and a detection method. The system includes: a first signal generation unit, a second signal generation unit, a first signal modulation unit, a second signal modulation unit, a circulator unit and a coherent detection unit; the first signal modulation unit is used to generate the signal generated by the second signal generation unit. The detection modulation signal modulates the detection signal generated by the first signal generation unit to generate a target detection signal; the second signal modulator is used to modulate the local oscillation signal generated by the first signal generation unit according to the local oscillation modulation signal generated by the second signal generation unit. Modulation is performed to generate a target local oscillator signal that is negatively correlated with the power of the backscattered signal; the circulator unit is used to send the target detection signal and output the backscattered signal; the coherent detection unit is used to achieve the integration of the target local oscillator signal and the backscattered signal. Coherent detection to obtain sensing data. This improves the signal-to-noise ratio and reduces cost and implementation difficulty.

Description

Optical fiber sensing system and detection method

Technical field

The embodiments of the present application relate to the field of optical fiber sensing technology, and in particular to an optical fiber sensing system and detection method.

Background technique

When optical signals are transmitted in optical fibers, changes in vibration, temperature, pressure and other factors will affect the phase, amplitude, polarization state, etc. of the optical signal. Therefore, changes in vibration, temperature, pressure, etc. can be reflected by changes in the phase, amplitude, polarization state and other information of the optical signal transmitted in the optical fiber. In other words, optical fibers can be used for sensing and detection. Moreover, because the optical fiber itself has the advantages of continuous sensing space, integrated synaesthesia, anti-electromagnetic interference, and low cost, it has been applied in earthquake early warning, bridge health monitoring, security monitoring and other fields, especially in long-distance and large-scale Sensing is more widely used in sensor monitoring scenarios. The optical fiber sensing system currently used for optical fiber sensing detection is mainly based on the backscattering principle and the coherent detection principle.

However, the signal-to-noise ratio of current optical fiber sensing systems becomes worse when used in long-distance scenarios. In order to solve this problem, higher-performance receiver devices need to be used. For example, if the noise coefficient of the optoelectronic device is required to be better, the signal power range can be input. Larger, higher resolution, etc., but this will make the cost of the receiver higher and the implementation more complicated and difficult.

Contents of the invention

The main purpose of the embodiments of the present application is to propose an optical fiber sensing system and detection method. By generating a local oscillator signal that is negatively correlated with the power of the backscattered signal, the backscattered signal and the local oscillator signal are mixed during coherent detection. The signal power is more stable, which reduces the requirements for the input power range and resolution of the device. That is to say, the functional characteristics requirements of these devices are reduced, thereby reducing the cost and implementation difficulty.

To achieve the above objectives, embodiments of the present application provide an optical fiber sensing system, including: a first signal generating unit, a second signal generating unit, a first signal modulation unit, a second signal modulation unit, a circulator unit and coherent detection unit; the first signal generating unit is used to generate a detection signal and a local oscillator signal; the second signal generation unit is used to generate a detection modulation signal and a local oscillator modulation signal; the first signal modulator is used to generate a detection signal according to the detection signal. The modulation signal performs pulse modulation on the detection signal to generate a target detection signal; the second signal modulator is used to perform intensity modulation on the local oscillator signal according to the local oscillator modulation signal to generate a signal that is negatively correlated with the backscattered signal power. The target local oscillator signal, the backscattered signal is the signal generated by backscattering when the target detection signal is transmitted in the optical fiber; the circulator unit is used to send the target detection signal through the first port to the optical fiber and output the backscattered signal through the third port; the coherent detection unit is used to achieve coherent detection of the target local oscillator signal and the backscattered signal to obtain sensing detection data.

In order to achieve the above purpose, embodiments of the present application also propose a detection method, which is applied to the optical fiber sensing system as described above. The method includes: generating a detection signal, a local oscillator signal, a detection modulation signal and a local oscillator modulation signal; The detection signal is pulse modulated according to the detection modulation signal to generate a target detection signal; the local oscillator signal is intensity modulated according to the local oscillator modulation signal to generate a target local oscillator that is negatively correlated with the backscattered signal power. signal, the backscattered signal is a signal generated by backscattering when the target detection signal is transmitted in the optical fiber; sending the target detection signal to the optical fiber and acquiring the backscattered signal; to the target The local oscillator signal and the backscattered signal are coherently detected to obtain sensing detection data.

In the optical fiber sensing system proposed in the embodiment of the present application, after the detection signal and the local oscillator signal are generated in the first signal generation unit, and the detection modulation signal and the local oscillator modulation signal are generated in the second signal generation unit, the first signal modulator The detection signal is pulse modulated according to the detection modulation signal in the second signal modulator to generate a target detection signal, and the local oscillator signal is intensity modulated according to the local oscillator modulation signal in the second signal modulator to generate a target local oscillator signal that is negatively correlated with the backscattered signal power. , that is, a low-power target local oscillator signal is provided for the high-power backscattered signal, and a high-power target local oscillator signal is provided for the low-power backscattered signal, so that the backscattered signal is consistent with the modulated local oscillator signal during coherent detection. The signal obtained after mixing the oscillator signal can be maintained within a certain power range, making the signal power after mixing the backscattered signal and the target local oscillator signal more stable during coherent detection, reducing the input power range of some devices and The resolution requirements reduce the functional characteristics requirements of these devices, thereby reducing the cost and implementation difficulty.

Description of the drawings

One or more embodiments are exemplified by the pictures in the corresponding drawings, and these exemplary illustrations do not constitute limitations to the embodiments.

Figure 1 is a schematic structural diagram of the optical fiber sensing system provided in the embodiment of the present application;

Figure 2 is a schematic diagram of the signal flow of the optical fiber sensing system provided in the embodiment shown in Figure 1 of the present application;

Figure 3 is a schematic structural diagram of another optical fiber sensing system provided in the embodiment of the present application;

Figure 4 is the intensity trace diagram of the signal after coherent detection and mixing of the existing optical fiber sensing system;

Figure 5 is a signal intensity trace diagram after coherent detection of the optical fiber sensing system provided in the embodiment of the present application;

Figure 6 is a flow chart of the detection method provided in the embodiment of the present application;

Figure 7 is a comparison chart of the local oscillator signal power provided by the existing optical fiber sensing system provided in the embodiment of the present application and the target local oscillator signal power of the optical fiber sensing system provided in the embodiment of the present application;

Figure 8 is a signal synchronization diagram of the target local oscillator signal, backscattered signal and target detection signal provided in the embodiment of the present application.

Detailed ways

It can be seen from the background technology that the current optical fiber sensing system has the problems of high cost and high implementation difficulty.

After analysis, it was found that one of the reasons for the above problems is that in the distributed optical fiber sensing system, the inherent transmission loss of the optical fiber channel will cause the attenuation of the sensing signal power, because the optical fibers at different locations correspond to different transmission distances, that is, Signals experience varying transmission losses. Therefore, sensing signals at different locations in the optical fiber will have different optical powers. That is, when the receiving end performs direct detection or coherent detection of signals, the detector must have a larger input optical power range. Moreover, the amplitude of the electrical signal output by the detector will also fluctuate greatly. For example, when a phase-sensitive optical time-domain reflectometer (φOTDR) is used to monitor an optical fiber channel with a length of 100 km, in the sensing signal strength trace after coherent detection, the signal power fluctuation range is caused by the transmission loss of the optical fiber. reaches about 35dB. Considering the random power fluctuation of the sensing signal itself, the overall power fluctuation range is as high as nearly 70dB. Such a large signal power fluctuation range places higher requirements on the components of optical fiber sensing receivers, such as: detectors must have a larger input power range and higher receiving sensitivity; analog to digital converters (Analog to Digital) Converter, ADC), etc. must have a wide input voltage range, and the ADC needs to have a higher resolution, otherwise relatively large quantization noise will be introduced to small signals, seriously affecting system performance. Therefore, there is an urgent need for an optical fiber sensing system that can control the fluctuation range of signal intensity traces within a smaller range.

In order to solve the above problems, embodiments of the present application provide an optical fiber sensing system, including: a first signal generation unit, a second signal generation unit, a first signal modulation unit, a second signal modulation unit, a circulator unit and coherent detection unit; the first signal generating unit is used to generate a detection signal and a local oscillator signal; the second signal generation unit is used to generate a detection modulation signal and a local oscillator modulation signal; the first signal modulator is used to generate a detection signal according to the detection signal. The modulation signal performs pulse modulation on the detection signal to generate a target detection signal; the second signal modulator is used to perform intensity modulation on the local oscillator signal according to the local oscillator modulation signal to generate a signal that is negatively correlated with the backscattered signal power. The target local oscillator signal, the backscattered signal is the signal generated by backscattering when the target detection signal is transmitted in the optical fiber; the circulator unit is used to send the target detection signal through the first port to the optical fiber and output the backscattered signal through the third port; the coherent detection unit is used to achieve coherent detection of the target local oscillator signal and the backscattered signal to obtain sensing detection data.

The optical fiber sensing system provided by the embodiment of the present application can use the local oscillator modulation signal generated by the second signal generator to perform intensity modulation on the local oscillator signal generated by the first signal generator, so that the modulated target local oscillator signal It can be negatively correlated with the power of the backscattered signal, thereby using target local oscillator signals of different powers to non-equivalently amplify the backscattered signal, so that it can provide different power loss compensation for backscattered signals of different powers, thereby reducing The power fluctuation range of the signal generated after mixing the backscattered signal and the target local oscillator signal after coherent detection is reduced, and the requirements for related devices are reduced. That is, the optical fiber sensing system can be constructed using devices with less high functional characteristics, which reduces the cost.

In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, each embodiment of the present application will be described in detail below with reference to the accompanying drawings. However, those of ordinary skill in the art can understand that in each embodiment of the present application, many technical details are provided to enable readers to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solution claimed in this application can also be implemented. The division of the following embodiments is for the convenience of description and should not constitute any limitation on the specific implementation of the present application. The various embodiments can be combined with each other and referenced with each other on the premise that there is no contradiction.

On the one hand, embodiments of the present application provide an optical fiber sensing system, which is used in the process of sensing and detecting using optical fibers. As shown in Figure 1, the optical fiber sensing system at least includes: a first signal generation unit 101, a second signal generation unit 102, a first signal modulation unit 103, a second signal modulation unit 104, a circulator unit 105 and a coherent detection unit 106 . Among them, the first signal generation unit 101 is used to generate a detection signal and a local oscillator signal; the second signal generation unit 102 is used to generate a detection modulation signal and a local oscillator modulation signal; the first signal modulator 103 is used to generate detection signals according to the detection modulation signal. The signal is pulse modulated to generate a target detection signal; the second signal modulator 104 is used to perform intensity modulation on the local oscillator signal according to the local oscillator modulation signal to generate a target local oscillator signal that is negatively correlated with the power of the backscattered signal. The backscattered signal is The signal generated by backscattering when the target detection signal is transmitted in the optical fiber; the circulator unit 105 is used to send the target detection signal to the optical fiber through the first port and output the backscattered signal through the third port; the coherent detection unit 106 uses It is used to achieve coherent detection of target local oscillator signals and backscattered signals to obtain sensing detection data.

It should be emphasized that the circulator unit is introduced to better extract the backscattered signal. The first signal modulation unit is mainly used to be driven by the detection modulation signal generated by the first signal generation unit to achieve electro-optical conversion and modulation of the signal. In order to achieve better effects, a sensor with high extinction ratio, good waveform quality, etc. can also be used. Acoustic-Optic Modulator (AOM).

As shown in Figure 2, when the optical fiber sensing system is used for sensing and detection, the first signal generating unit 101 will generate the detection signal 1 and the local oscillator signal 2. Compared with directly sending the detection signal 1 into the optical fiber 107, The detection signal 1 is pulse modulated to generate a target pulse light signal with specific intensity, pulse width, frequency and other parameters. That is, the second signal generating unit 102 will also generate the detection modulation signal 3 used to pulse modulate the detection signal 1, so that the first signal generation unit 101 sends the generated detection signal 1 to the first signal modulation unit 103 and the second signal After the generating unit 102 sends the generated detection modulation signal 3 to the first signal modulation unit 103, the first signal modulation unit 103 pulse modulates the detection signal 1 according to the detection modulation signal 3 to generate a pulse light signal - target detection signal 4, Then, the target detection signal 4 generated by the first signal modulation unit 103 is sent into the optical fiber 107 through the first port of the circulator unit 105 . In this way, the target detection signal 4 will be transmitted in the optical fiber 107 and backscattered, and a backscattered signal 5 opposite to the propagation direction of the target detection signal 4 will be obtained, and will be output from the third port of the circulator unit 105 and sent into Coherent detection unit 106. Among them, according to different backscattering principles, the backscattering signal 5 may be a backscattering signal based on Rayleigh scattering, a backscattering signal based on Brillouin scattering, a backscattering signal based on Raman scattering, etc. At the same time, in order to perform non-equivalent amplification of the backscattered signal 5, it is necessary to provide a target local oscillator signal 7 that is negatively correlated with the backscattered signal 5. Therefore, the second signal generating unit 102 also generates a local oscillator signal 7 used to modulate the local oscillator signal 2. The local oscillator modulated signal 6 is sent to the second signal modulation unit 104, so that the second signal modulation unit 104 can send the first signal generating unit 101 to the second signal modulation unit according to the local oscillator modulated signal 6. The local oscillator signal 2 of 104 is intensity modulated to obtain the target local oscillator signal 7, so as to provide the target local oscillator signal 7 with relatively low power when the power of the backscattered signal 5 is high, and when the power of the backscattered signal 5 is low, The purpose is to provide a target local oscillator signal 7 with relatively high power. Then the second signal modulation unit 104 sends the target local oscillator signal 7 to the coherent detection unit 106. The coherent detection unit 106 realizes coherent detection of the backscattered signal 5 and the target local oscillator signal 7. During the coherent detection process, the target local oscillator is controlled. Signal 7 results in a signal whose power range stabilizes within a relatively small fluctuation range.

It should be noted that when the target detection signal enters the optical fiber from one end of the optical fiber, it will begin to generate a backscattered signal until the target detection signal reaches the other end of the optical fiber, and during this process, the target detection signal has been experiencing power loss. . Correspondingly, the power loss of the backscattered signal obtained by backscattering is also constantly accumulating. That is, in the process of the target detection signal entering the optical fiber from one end to leaving the optical fiber from the other end, the power of the backscattered signal gradually decreases. That is to say, in order to keep the mixed signal power within a certain range without large fluctuations, the target local oscillator signal that is negatively correlated with the backscattered signal power should gradually increase during the above process. Therefore, this embodiment does not specifically limit the power change of the local oscillator modulated signal generated by the second signal generating unit. When the power of the local oscillator signal generated by the first signal transmitting unit is stable, the power change of the local oscillator modulated signal generated by the second signal generating unit is stable. The power of the local oscillator modulated signal can be dynamically modulated as long as it gradually increases as the target detection signal enters the fiber and the backscattered signal completely returns and exits the fiber. By setting a reasonable power of the target local oscillator signal, the power of the signal obtained after mixing the target local oscillator signal and the back detection signal during the coherent detection process is flexibly controlled within a small reasonable fluctuation range.

In order to ensure that the signal obtained after mixing the target local oscillator signal and the backscattered signal during the coherent detection process is more stable, in some examples, the relationship between the target local oscillator signal and the backscattered signal can be further constrained as Inverse relationship between power.

In order to keep the signal obtained by mixing the target local oscillator signal and the back detection signal in the minimum range during the coherent detection process, that is, the signal trace obtained by mixing the target local oscillator signal and the back detection signal during the coherent detection process is required. The line is flat, and the target local oscillator signal can be set to exactly compensate for the power loss of the back detection signal on the basis that the target local oscillator signal and the back detection signal are inversely proportional. Therefore, in some other examples, when the power of the backscattered signal is determined based on the fiber attenuation, the power trace of the backscattered signal should be related to the loss coefficient and transmission time of the fiber, as: The power trace of the target local oscillator signal can be: Among them, t∈[0,T], T is the length of a detection cycle of the target detection signal, t ₀ is the starting time of the detection cycle of the target detection signal, p _s (t ₀ +t) is the time t ₀ +t The power of the backscattered signal, p _LO (t ₀ +t) is the power of the target local oscillator signal at time t ₀ +t, P ₀ is the power of the target detection signal when it enters the optical fiber, α is the loss coefficient of the optical fiber, and c is the speed of light , n is the refractive index of the optical fiber, r(t ₀ +t) is the backscattering intensity at each position in the optical fiber at time t ₀ +t, and P _Lo is the preset target local oscillator signal power constant. It should be noted that the detection period can be understood as the period during which the target detection signal is sent into the optical fiber.

It should be noted that the amplitude, frequency, phase, etc. of the local oscillator modulation signal are generated by a controller to achieve the purpose of controlling the power of the target local oscillator signal.

In some examples, the modulation period of the local oscillator signal is the same as the transmission period of the target detection signal.

In particular, the modulation period of the local oscillator signal should be no less than the time required for the target detection signal to travel from one end of the optical fiber to the other end plus the backscattered signal to travel from the other end of the optical fiber to one end, that is, it should not be less than the time required for the optical signal to travel from one end of the optical fiber to the other. The time it takes to transmit one round trip in an optical fiber. Specifically, the modulation period of the local oscillator signal should be no less than (2*n*L)/c, where n is the refractive index of the optical fiber, c is the speed of light, and L is the radial length of the optical fiber.

And, in some examples, the local oscillator modulation signal is synchronized with the target detection signal, so that the backscattered signal returned close to the position where the target detection signal enters the optical fiber is synchronized with the target detection signal away from the target detection signal. The backscattered signals returned from the position where the signal enters the optical fiber correspond to different target local oscillator signal powers.

It can be understood that in coherent detection, the local oscillator signal and the received detection signal are optically mixed to realize down-conversion of the signal from the optical carrier frequency to the microwave carrier frequency, and then the center frequency of the signal is detected by the photodetector, which is The difference in frequency between the detection signal and the local oscillator signal, and then the intermediate frequency signal is demodulated and compensated by the algorithm to obtain the baseband signal output. Specifically, when the detection signal is And the local oscillator signal is/> In the case of , the heterodyne signal after coherent reception is/> Among them, P _s is the power of the detection signal, and P _lo is the power of the local oscillator signal. It can be seen from this that the output signal i(t) can be amplified by increasing the power P _lo of the local oscillator signal. That is to say, the optical fiber sensing system provided in this embodiment also realizes the amplitude adjustment of the coherent received signal by performing intensity modulation on the local oscillator signal, thereby increasing the signal power, reducing the requirements on the system receiving sensitivity, and achieving a high signal-to-noise ratio.

It can also be understood that using the second signal modulation unit to perform intensity modulation of the local oscillator signal will not affect the phase of the local oscillator signal. The details are as follows: Taking the Mach-Zehnder Modulator (MZM) as an example to modulate the local oscillator signal Analyze the modulation process: the transfer function of MAM can be expressed as Among them, φ ₁ (t) and φ ₂ (t) represent the phase shift of the upper arm and lower arm of the MZM respectively, E _out is the output, and E _in is the input. When the phase shift between the arms is opposite, the signal obtained at the output end is the intensity-modulated target local oscillator signal. At this time, the local oscillator signal (E _in (t)) and the target local oscillator signal (E _out (t)) The relationship between It can be seen that there is only an amplitude change from the local oscillator signal to the target local oscillator signal, that is, the coefficient/> There is no phase change, that is, intensity modulation of the local oscillator signal will not affect the phase of the local oscillator signal. Therefore, the optical fiber sensing system provided in this embodiment can implement phase-based optical fiber sensing detection.

In order to facilitate those skilled in the art to better understand the optical fiber sensing system provided in this embodiment, specific examples of different components of the optical fiber sensing system will be described below.

As shown in Figure 3, the first signal generating unit 101 may include a laser 1011 and a coupler 1012, where the coupler 1012 is used to branch the continuous laser light generated by the laser 1011 to generate a detection signal and a local oscillator signal. That is to say, the laser generates a continuous laser signal and sends it to the coupler 1012. The coupler 1012 divides the laser signal into two paths to obtain a detection signal and a local oscillator signal. Among them, the power occupied by different signals during splitting can be flexibly set according to needs. Furthermore, in order to provide a highly coherent light source, the laser can be configured as a narrow linewidth laser.

The second signal generating unit 102 may include a signal generator 1021 and a controller 1022. The signal generator 1021 generates a detection modulation signal and a local oscillator modulation signal respectively, wherein the signal generator 1021 is under the control of the controller 1022 to generate a signal capable of controlling the local oscillator. The signal is modulated to obtain a local oscillator modulated signal of the target local oscillator signal that is inversely correlated with the backscattered signal.

The first signal modulation unit 103 may be an AOM, thereby obtaining a target detection signal with a high extinction ratio and good waveform quality.

The second signal modulation unit 104 may be an intensity modulator, and is driven by the local oscillator modulation signal generated by the second signal generation unit 102 to generate a target local oscillator signal.

The circulator unit 105 may be an optical circulator. The target detection signal will be input into the optical circulator from the first port and output from the second port and sent into the sensing fiber. From the time when the target detection signal is sent into the sensing fiber until Until the target detection signal is transmitted to the other end of the optical fiber, it will continuously generate backscattered signals in the opposite propagation direction of the target detection signal, and the optical circulator will receive the backscattered signal through the second port and output the backscattered signal through the third port. The scattered signal is sent to the coherent detection unit 106 to extract the backscattered signal.

The coherent detection unit 106 may include a coupler 1061, a coherent detector 1062 and an ADC 1063, where the coupler 1061 is used to combine the target local oscillator signal and the backscattered signal to obtain a mixed frequency signal. That is to say, the target local oscillator signal and the backscattered signal will be mixed and received by the coupler 1061 to achieve variable gain amplification of the backscattered signal; the coherent detector 1062 is used to coherently detect the target sensing signal and Perform photoelectric conversion to obtain sensing analog electrical signals. ADC1063 is used to perform analog-to-digital conversion on the sensing analog electrical signals to obtain sensing detection data.

In particular, the optical fiber sensing system also includes: an amplifier 108, which is used to amplify the target detection signal generated by the first signal modulator. At this time, the circulator unit 105 is used to send the amplified target detection signal into the optical fiber.

It should be noted that in scenarios where optical fibers that provide communication services are used for sensing and detection, since the use of Raman amplifiers in communication optical fiber cables will have a certain impact on the business signals in the channel, the amplifier cannot be directly set. for Raman amplifiers. The difference is that the amplifier can use an Erbium-doped Optical Fiber Amplifier (EDFA) at this time, which directly amplifies the optical signal at a single end, and the signal is no longer affected by the amplifier once it is output.

As can be seen from the above description, the optical fiber sensing system provided in this embodiment is based on optical frequency domain reflectometry (OFDR), phase-sensitive optical time domain reflectometry (φOTDR), coherent optical time domain reflectometry (COTDR), Brillouin light On the basis of time domain reflectometer (BOTDR), Brillouin optical time domain analyzer (BOTDA), Raman optical time domain reflectometer (ROTDR), etc., an additional intensity modulation function for the local oscillator signal is introduced, that is, an intensity modulator is introduced and The signal generator not only provides the detection modulation signal generation function, but also adds the local oscillator modulation signal generation function, thereby providing the backscattered signal with a target local oscillator signal that is negatively related to its power, so as to stabilize the power variation range of the mixed signal within Within a relatively small range, specifically: when using an optical fiber with a length of 100km for sensing, the intensity trace of the signal after the traditional optical fiber sensing system mixes the backscattered signal and the local oscillator signal without intensity modulation As shown in Figure 4, the signal power fluctuation range caused by the transmission loss of the optical fiber reaches approximately 35dB. Superimposed on the amplitude fluctuation of the signal itself, the overall amplitude fluctuation range is as high as nearly 70dB; and using the optical fiber provided in this embodiment The power trace of the target local oscillator signal in the sensing system is the aforementioned expression In the case of , which is about 35dB.

On the other hand, the embodiment of the present application also provides a detection method, as shown in Figure 6, which is applied to the optical fiber sensing system described in the above embodiment. The detection method at least includes the following steps:

Step 601: Generate a detection signal, a local oscillator signal, a detection modulation signal and a local oscillator modulation signal.

In some examples, the detection signal and the local oscillator signal are obtained by splitting a laser beam according to a certain power distribution ratio.

Step 602: Pulse modulate the detection signal according to the detection modulation signal to generate a target detection signal.

Step 603: Perform intensity modulation on the local oscillator signal according to the local oscillator modulation signal to generate a target local oscillator signal that is negatively correlated with the power of the backscattered signal. The backscattered signal is the backscattered signal that occurs when the target detection signal is transmitted in the optical fiber. The signal generated by scattering.

In some examples, a target local oscillator signal is generated that is inversely proportional to the power of the backscattered signal.

In some other examples, the power trace of the backscattered signal within one detection period of the target detection signal is Accordingly, the power trace generated is/> _The target local _oscillator signal _of The power of the backscattered signal at time t ₀ +, P ₀ is the power of the target detection signal when it enters the optical fiber, α is the loss coefficient of the optical fiber, c is the speed of light, n is the refractive index of the optical fiber, r(t ₀ +t) is The backscattering intensity at each position in the optical fiber at time t ₀ +t, P _Lo is the preset power constant. At this time, as shown in Figure 7, compared with the traditional optical fiber sensing receiving method shown in the solid line, the local oscillator signal maintains 0dB, the power of the target local oscillator signal provided by the present embodiment shown in the dotted line increases logarithmically linearly. state. Furthermore, the signal obtained after coherent detection mixing is:/> At this time, the target local oscillator signal can just compensate for the power loss of the backscattered signal.

Moreover, in some examples, the local oscillator signal is periodically modulated according to the transmission period of the target detection signal, that is, the transmission period of the target detection signal is the same as the modulation period of the local oscillator signal.

Among them, the local oscillator signal is periodically modulated with the period length not less than (2*n*L)/c as the modulation period, n is the refractive index of the optical fiber, c is the speed of light, and L is the radial length of the optical fiber.

In some examples, step 601 generates a local oscillator modulation signal that is synchronized with the target detection signal, so as to determine the local oscillator modulation signal used for the local oscillator signals at different times and improve the accuracy of modulation.

For example, the signals can be synchronized as shown in Figure 8. The solid line represents the backscattered signal, the dotted line represents the target local oscillator signal, and the filled area represents the pulse target detection signal. The synchronization period of the three is (2*n*L)/ c, and as the transmission time of the backscattered signal in the optical fiber increases during the period, the power of the backscattered signal gradually decreases, and the generated target local oscillator signal gradually increases. Among them, τ is the impulse response duration of the target local oscillator signal, T = (2*n*L)/c, and t ₀ is the starting time of the cycle.

Step 604: Send the target detection signal to the optical fiber and obtain the backscattered signal.

In some cases, the target detection signal is amplified before being sent into the optical fiber to increase the power after backscattering.

Step 605: Perform coherent detection on the target local oscillator signal and backscattered signal to obtain sensing detection data.

In some examples, coherent detection of the target local oscillator signal and the backscattered signal can be achieved by combining the target local oscillator signal and the backscattered signal to obtain the target sensing signal after interference, and then The target sensing signal is photoelectrically detected to obtain the sensing analog electrical signal, and then the sensing analog electrical signal is analog-to-digital converted to obtain sensing detection data.

In addition, it should be understood that the division of steps in the various methods above is only for the purpose of clear description. During implementation, they can be combined into one step or some steps can be split into multiple steps. As long as they include the same logical relationship, all Within the protection scope of this patent; adding insignificant modifications or introducing insignificant designs to the algorithm or process, but not changing the core design of the algorithm and process are all within the protection scope of this patent.

It is not difficult to find that the embodiments of the present invention are method embodiments corresponding to the system embodiments, and the embodiments of the present invention can be implemented in cooperation with the system embodiments. The relevant technical details mentioned in the system embodiment are still valid in this embodiment. In order to reduce duplication, they will not be described again here. Correspondingly, the relevant technical details mentioned in this embodiment can also be applied to the system embodiment.

The above embodiments are provided for those of ordinary skill in the art to implement and use the present invention. Those of ordinary skill in the art can make various modifications or changes to the above embodiments without departing from the inventive concept of the present invention. Therefore, the present invention The scope of protection is not limited by the above embodiments, but should comply with the maximum scope of the innovative features mentioned in the claims.

Claims (10)

1. A fiber optic sensing system, comprising: the device comprises a first signal generation unit, a second signal generation unit, a first signal modulation unit, a second signal modulation unit, a circulator unit and a coherent detection unit;

the first signal generation unit is used for generating a detection signal and a local oscillation signal;

the second signal generation unit is used for generating a detection modulation signal and a local oscillation modulation signal;

the first signal modulator is used for carrying out pulse modulation on the detection signal according to the detection modulation signal to generate a target detection signal;

the second signal modulator is configured to perform intensity modulation on the local oscillation signal according to the local oscillation modulation signal, and generate a target local oscillation signal that is inversely related to a backscattering signal power, where the backscattering signal is a signal generated by backscattering when the target detection signal is transmitted in an optical fiber;

the circulator unit is used for sending the target detection signal to an optical fiber through a first port and outputting the back scattering signal through a third port;

the coherent detection unit is used for realizing coherent detection of the target local oscillation signal and the back scattering signal so as to obtain sensing detection data.

2. The fiber optic sensing system of claim 1, wherein the power of the target local oscillator signal is inversely proportional to the power of the backscatter signal.

3. The fiber optic sensing system of claim 2, wherein the power trace at the backscattered signal isIn the case of (a), the power trace of the target local oscillator signal isWherein t is [0, T ]]T is the duration of one detection period of the target detection signal, T ₀ For the start time, p, of the detection period of the target detection signal _s (t ₀ +t) is t ₀ The power of the back-scattered signal at +t, p _LO (t ₀ +t) is t ₀ The power of the target local oscillation signal at +t moment, P ₀ For the power of the target detection signal when entering the optical fiber, alpha is the loss coefficient of the optical fiber, c is the speed of light, n is the refractive index of the optical fiber, r (t ₀ +t) is t ₀ Back scattering intensity, P, at each position in the fiber at +t _Lo For the object ofAnd a local oscillation power constant preset when the detection signal enters the optical fiber.

4. A fibre optic sensing system as claimed in any one of claims 1 to 3, wherein the modulation period of the local oscillator signal is the same as the transmission period of the target probe signal.

5. The optical fiber sensing system according to claim 4, wherein the modulation period of the local oscillation signal is not less than (2 x n x L)/c, where n is the refractive index of the optical fiber, c is the speed of light, and L is the radial length of the optical fiber.

6. A fibre optic sensing system according to any of claims 1 to 3, wherein the local oscillator modulation signal is synchronised with the target detection signal.

7. A fibre optic sensing system according to any one of claims 1 to 3, wherein the first signal generating unit comprises a laser and a coupler for splitting the continuous laser light generated by the laser to generate the probe signal and the local oscillator signal.

8. A fibre optic sensing system according to any one of claims 1 to 3, further comprising: the amplifier is used for amplifying the target detection signal generated by the first signal modulator, and the circulator unit is used for sending the amplified target detection signal to an optical fiber through the first port.

9. A fibre optic sensing system according to any one of claims 1 to 3, wherein the coherent detection unit comprises a coupler for combining the target local oscillator signal and the backscatter signal to obtain a target sensing signal, a coherent detector for coherently detecting and photoelectrically converting the target sensing signal to obtain a sensing analogue electrical signal, and an analogue to digital converter ADC for analogue to digital converting the sensing analogue electrical signal to obtain sensing detection data.

10. A detection method applied to the optical fiber sensing system according to any one of claims 1 to 9, the method comprising:

generating a detection signal, a local oscillation signal, a detection modulation signal and a local oscillation modulation signal;

performing pulse modulation on the detection signal according to the detection modulation signal to generate a target detection signal;

performing intensity modulation on the local oscillation signal according to the local oscillation modulation signal to generate a target local oscillation signal which is inversely related to the power of a back scattering signal, wherein the back scattering signal is a signal generated by back scattering when the target detection signal is transmitted in an optical fiber;

transmitting the target detection signal to an optical fiber and acquiring the back scattering signal;

and performing coherent detection on the target local oscillation signal and the back scattering signal to obtain sensing detection data.