CN117092715A - Optical fiber sensing system and detection method - Google Patents
Optical fiber sensing system and detection method Download PDFInfo
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Abstract
The embodiment of the application relates to the technical field of optical fiber sensing, and discloses an optical fiber sensing receiving system and a detection method. The system comprises: 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 modulation unit is used for modulating the detection signal generated by the first signal generation unit according to the detection modulation signal generated by the second signal generation unit to generate a target detection signal; the second signal modulator is used for modulating 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, and generating a target local oscillation signal which is inversely related to the back scattering signal power; the circulator unit is used for sending a target detection signal and outputting a back scattering signal; 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 data. So that the signal-to-noise ratio is improved, and the cost and the implementation difficulty are reduced.
Description
Technical Field
The embodiment of the application relates to the technical field of optical fiber sensing, in particular to an optical fiber sensing system and a detection method.
Background
When an optical signal is transmitted in an optical fiber, changes in factors such as vibration, temperature, pressure and the like affect the phase, amplitude, polarization state and the like of the optical signal. Therefore, variations in vibration, temperature, pressure, etc. can be reflected by variations in information such as phase, amplitude, polarization state, etc. of the optical signal transmitted in the optical fiber. That is, the optical fiber may be used for sensing detection. In addition, the optical fiber has the advantages of continuous sensing space, integrated sensing, electromagnetic interference resistance, low cost and the like, and is applied to the fields of earthquake early warning, bridge health monitoring, security monitoring and the like, and particularly has wider application in sensing monitoring scenes of long-distance and large-range sensing. The current optical fiber sensing system for optical fiber sensing detection is mainly realized based on a back scattering principle and a coherent detection principle.
However, the signal-to-noise ratio of the current optical fiber sensing system applied in a long distance scene is poor, and in order to solve the problem, a receiver device with higher performance is needed, for example, the noise coefficient of an optical-electrical device is required to be better, the power range of an input signal is larger, the resolution ratio is higher, and the like, but the cost of the receiver is higher, and the complexity of implementation is higher.
Disclosure of Invention
The embodiment of the application mainly aims to provide an optical fiber sensing system and a detection method, which enable the signal power after the backscattering signal and the local oscillation signal are mixed to be more stable during coherent detection by generating the local oscillation signal which is inversely related to the power of the backscattering signal, thereby reducing the requirements on the range and the resolution of the device which can be input. The requirements on the functional characteristics of the devices are reduced, and the cost and the implementation difficulty are further reduced.
To achieve the above object, an embodiment of the present application provides an optical fiber sensing system, including: 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.
In order to achieve the above object, an embodiment of the present application further provides a detection method, which is applied to the optical fiber sensing system as described above, and the method includes: 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.
The optical fiber sensing system provided by the embodiment of the application generates the detection signal and the local oscillation signal in the first signal generating unit, generates the detection modulation signal and the local oscillation modulation signal in the second signal generating unit, carries out pulse modulation on the detection signal according to the detection modulation signal in the first signal modulator, generates the target detection signal, carries out intensity modulation on the local oscillation signal according to the local oscillation modulation signal in the second signal modulator, generates the target local oscillation signal which is inversely related to the power of the back scattering signal, namely, provides the low-power target local oscillation signal for the high-power back scattering signal, and provides the high-power target local oscillation signal for the low-power back scattering signal, so that the signal power obtained by mixing the back scattering signal and the modulated local oscillation signal during coherent detection can be kept in a certain power range, the signal power obtained by mixing the back scattering signal and the target local oscillation signal during coherent detection is more stable, the requirements on the range and the resolution of the input power of partial devices are reduced, namely, the functional characteristic requirements on the devices are reduced, and the cost and the implementation difficulty are further reduced.
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One or more embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings.
FIG. 1 is a schematic diagram of a fiber optic sensing system provided in an embodiment of the present application;
FIG. 2 is a schematic signal flow diagram of a fiber optic sensing system provided in the embodiment of FIG. 1 of the present application;
FIG. 3 is a schematic diagram of another optical fiber sensing system provided in an embodiment of the present application;
FIG. 4 is a plot of the intensity of a signal after coherent detection mixing of a prior art fiber optic sensing system;
FIG. 5 is a plot of the intensity of a signal after coherent detection by an optical fiber sensing system provided in an embodiment of the present application;
FIG. 6 is a flow chart of a detection method provided in an embodiment of the present application;
fig. 7 is a graph comparing the local oscillation signal power provided by the existing optical fiber sensing system provided in the embodiment of the present application with the target local oscillation signal power of the optical fiber sensing system provided in the embodiment of the present application over time;
fig. 8 is a schematic diagram of signal synchronization of a target local oscillator signal, a backscatter signal, and a target probe signal provided in an embodiment of the present application.
Detailed Description
As known from the background art, the existing optical fiber sensing system has the problems of high cost and high implementation difficulty.
It was found by analysis that one of the reasons for the occurrence of the above problems is: in a distributed optical fiber sensing system, the inherent transmission loss of the optical fiber channel can cause attenuation of the power of the sensing signal, and the signal can experience different transmission loss due to the fact that the optical fibers at different positions correspond to different transmission distances. Therefore, the sensing signals at different positions in the optical fiber have different optical powers, that is, the detector has a larger range of optical power capable of being input when the receiving end directly detects or coherently detects the signals. And the amplitude of the electric signal output by the detector also has larger amplitude fluctuation. For example, when a phase sensitive Optical Time-domain reflectometer (Φoptical Time-Domain Reflectometer, Φotdr) is used to monitor a fiber channel with a length of 100km, the signal power fluctuation range caused by the transmission loss of the fiber reaches about 35dB in the sensed signal intensity trace after coherent detection. And then, considering the random power fluctuation of the sensing signal, the whole power fluctuation range is up to nearly 70dB. Such a large signal power fluctuation range places higher demands on the constituent devices of the optical fiber sensing receiver, such as: the detector has a larger input power range and higher receiving sensitivity; the analog-to-digital converter (Analog to Digital Converter, ADC) and the like have a wide range of voltage range, and the ADC needs to have higher resolution, otherwise, a relatively large quantization noise is introduced to the small signal, which seriously affects the system performance. Accordingly, there is a need for a fiber optic sensing system that enables control of the signal strength trace fluctuation range to a smaller extent.
To solve the above problems, an embodiment of the present application provides an optical fiber sensing system, including: 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.
The optical fiber sensing system provided by the embodiment of the application can utilize the local oscillation modulation signal generated by the second signal generator to carry out intensity modulation on the local oscillation signal generated by the first signal generator, so that the modulated target local oscillation signal can be inversely related to the power of the back scattering signal, and thus, the back scattering signal can be subjected to non-equivalent amplification by utilizing the target local oscillation signals with different power, and the loss compensation of different powers can be provided for the back scattering signals with different powers, thereby reducing the power fluctuation range of the signals generated after the back scattering signal and the target local oscillation signal are subjected to mixing, reducing the requirements on related devices, namely, the optical fiber sensing system can be constructed by using devices with low functional characteristics, and reducing the cost.
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present application more apparent, the embodiments of the present application will be described in detail below with reference to the accompanying drawings. However, it will be understood by those of ordinary skill in the art that in various embodiments of the present application, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, the claimed technical solution of the present application can be realized without these technical details and various changes and modifications based on the following embodiments. The following embodiments are divided for convenience of description, and should not be construed as limiting the specific implementation of the present application, and the embodiments can be mutually combined and referred to without contradiction.
An aspect of the present application provides an optical fiber sensing system, which is applied to a sensing and detecting process using an optical fiber. As shown in fig. 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. The first signal generating unit 101 is configured to generate a detection signal and a local oscillation signal; the second signal generating unit 102 is configured to generate a detection modulation signal and a local oscillation modulation signal; the first signal modulator 103 is configured to pulse-modulate a detection signal according to the detection modulation signal, and generate a target detection signal; the second signal modulator 104 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 inversely related to the power of the backscatter signal, where the backscatter signal is a signal generated by backscatter generated when the target detection signal is transmitted in the optical fiber; the circulator unit 105 is used for sending the target detection signal to the optical fiber through the first port and outputting the back scattering signal through the third port; the coherent detection unit 106 is configured to perform coherent detection on the target local oscillation signal and the backscatter signal, so as to obtain sensing detection data.
It is emphasized that the circulator unit is introduced for better extraction of the back-scattered signal. The first signal modulation unit is mainly used for being driven by the detection modulation signal generated by the first signal generation unit to realize the electro-optical conversion and modulation of the signal, and an acousto-Optic Modulator (AOM) with advantages of high extinction ratio, good waveform quality and the like can be used for realizing better effect.
As shown in fig. 2, when the optical fiber sensing system is used for sensing detection, the first signal generating unit 101 generates the detection signal 1 and the local oscillation signal 2, and compared with directly sending the detection signal 1 into the optical fiber 107, the optical fiber sensing system also modulates the pulse of the detection signal 1 to generate a target pulse optical signal with specific intensity, pulse width, frequency and other parameters. That is, the second signal generating unit 102 also generates the probe modulation signal 3 for pulse-modulating the probe signal 1, so that the first signal generating unit 101 sends the generated probe signal 1 to the first signal modulating unit 103, and the second signal generating unit 102 sends the generated probe modulation signal 3 to the first signal modulating unit 103, and then the first signal modulating unit 103 pulse-modulates the probe signal 1 according to the probe modulation signal 3 to generate a pulse optical signal, namely, the target probe signal 4, and then the target probe signal 4 generated by the first signal modulating unit 103 is sent to the optical fiber 107 through the first port of the circulator unit 105. The object detection signal 4 will thus be transmitted in the optical fiber 107 and back-scattered, resulting in a back-scattered signal 5 opposite to the direction of propagation of the object detection signal 4, which is output from the third port of the circulator unit 105 and fed to the coherent detection unit 106. The backscatter signal 5 may be a backscatter signal based on rayleigh scattering, a backscatter signal based on brillouin scattering, a backscatter signal based on raman scattering, or the like, depending on the principle of backscatter. Meanwhile, in order to perform non-equivalent amplification on the backscatter signal 5, a target local oscillation signal 7 inversely related to the backscatter signal 5 needs to be provided, so that the second signal generating unit 102 also generates a local oscillation modulation signal 6 for modulating the local oscillation signal 2, and sends the local oscillation modulation signal 6 to the second signal modulating unit 104, so that the second signal modulating unit 104 can perform intensity modulation on the local oscillation signal 2 sent to the second signal modulating unit 104 by the first signal generating unit 101 according to the local oscillation modulation signal 6, thereby obtaining the target local oscillation signal 7, and achieving the purpose of providing the target local oscillation signal 7 with relatively low power when the power of the backscatter signal 5 is high and providing the target local oscillation signal 7 with relatively high power when the power of the backscatter signal 5 is low. The second signal modulation unit 104 then sends the target local oscillator signal 7 to the coherent detection unit 106, and coherent detection of the backscatter signal 5 and the target local oscillator signal 7 is achieved by the coherent detection unit 106, and a signal with a power range stable in a relatively small fluctuation range is obtained by controlling the target local oscillator signal 7 in the coherent detection process.
It should be noted that, the target detection signal starts to enter the optical fiber from one end of the optical fiber, and a back scattering signal starts to be generated until the target detection signal reaches the other end of the optical fiber, and in this process, the power loss of the target detection signal occurs. Accordingly, the power loss of the back-scattered signal obtained by back-scattering is continuously accumulated, that is, the power of the back-scattered signal gradually decreases in the process that the target detection signal enters the optical fiber from one end to leaves the optical fiber from the other end. That is, in order to keep the mixed signal power within a certain range without large fluctuation, the target local oscillation signal inversely related to the back-scattered signal power should be gradually increased in the above process. Therefore, the power change of the local oscillation modulated signal generated by the second signal generating unit is not specifically limited in this embodiment, and under the condition that the local oscillation signal generated by the first signal transmitting unit is stable in power, the power of the local oscillation modulated signal generated by the second signal generating unit can be dynamically modulated, so long as the requirement of gradually increasing in the process from entering the optical fiber to completely returning the backscatter signal from the target detection signal to leaving the optical fiber is satisfied. The method and the device have the advantages that the power of the target local oscillator signal is reasonably set, and the power of the signal obtained by mixing the target local oscillator signal and the back detection signal in the coherent detection process is flexibly controlled within a smaller reasonable fluctuation range.
In order to ensure that the signals obtained after mixing the target local oscillator signal and the back detection signal in the coherent detection process can be more stable, in some examples, the relationship between the target local oscillator signal and the back scattering signal can be further constrained to be a power inverse relationship.
In order to keep the signal obtained by mixing the target local oscillator signal and the back detection signal in the coherent detection process within a minimum range, namely, the signal trace obtained by mixing the target local oscillator signal and the back detection signal in the coherent detection process is required to be flat, the target local oscillator signal can be set to exactly compensate 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. Thus, in still other examples, where the power of the back-scattered signal is determined based on fiber attenuation, the power trace of the back-scattered signal should be related to the loss factor and transmission time of the fiber as: the power trace of the target local oscillator signal may be:wherein 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 Power of backscattered signal at +t moment, p LO (t 0 +t) is t 0 Power of 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 Is a preset target local oscillator signal power constant. The detection period is understood to be the period during which the target detection signal is fed into the optical fiber.
It should be noted that, the amplitude, frequency, phase, etc. of the local oscillation modulating signal are generated by a controller, so as to achieve the purpose of controlling the power of the target local oscillation signal.
In some examples, the modulation period of the local oscillator signal is the same as the transmission period of the target probe signal.
Specifically, the modulation period of the local oscillation signal should be not less than the time required for the target detection signal to pass from one end of the optical fiber to the other end plus the back-scattered signal to pass from the other end of the optical fiber to one end, i.e., not less than the time required for the optical signal to travel back and forth in the optical fiber. Specifically, the modulation period of the local oscillation signal should be not 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.
In some examples, the local oscillator modulation signal is synchronized with the target detection signal, so that the backscattering signal transmitted back close to the position where the target detection signal enters the optical fiber and the backscattering signal transmitted back far from the position where the target detection signal enters the optical fiber respectively correspond to different target local oscillator signal powers through synchronization of the target detection signal and the local oscillator modulation signal.
It can be understood that in coherent detection, the local oscillation signal and the received detection signal are subjected to optical frequency mixing to realize down-conversion of the signal from the optical carrier frequency to the microwave carrier frequency, then the center frequency of the signal, namely the difference between the frequencies of the detection signal and the local oscillation signal, is detected by the photoelectric detector, and then the intermediate frequency signal is subjected to demodulation and compensation algorithm to obtain the baseband signal output. Specifically, when the detection signal isAnd the local oscillation signal is +.>In the case of (2), the heterodyne signal after coherent reception is +.>Wherein P is s To detect the power of the signal, P lo Is the power of the local oscillator signal. From this, it can be seen that by increasing the power P of the local oscillation signal lo Amplification of the output signal i (t) can be achieved. That is, the optical fiber sensing system provided in this embodiment further modulates the intensity of the local oscillation signal, so as to adjust the amplitude of the coherent received signal, improve the signal power, reduce the requirement on the receiving sensitivity of the system, and realize a high signal-to-noise ratio.
It can be further understood that intensity modulation of the local oscillation signal by the second signal modulating unit does not affect the phase of the local oscillation signal, which is specifically as follows: taking a Mach-Zehnder modulator (Mach-Zehnder Modulator, MZM) as an example, the modulation process of the local oscillation signal is analyzed: the transfer function of the MAM can be expressed asWherein phi is 1 (t) and phi 2 (t) phase shifts of the upper and lower arms of the MZM, E out For output, E in Is input. When the phase shift between the two arms is opposite, the signal obtained by the output end is the target local oscillation signal after the intensity modulation, and the local oscillation signal is @ at the momentE in (t)) and a target local oscillator signal (E) out The relationship between (t)) can be expressed as It can be seen that only the amplitude changes from the local oscillator signal to the target local oscillator signal, i.e., the coefficient +.>And no phase change exists, namely, the intensity modulation of the local oscillation signal does not influence the phase of the local oscillation signal. Therefore, the optical fiber sensing system provided by the embodiment can realize optical fiber sensing detection based on phase.
In order to facilitate a better understanding of the optical fiber sensing system provided by the present embodiment, the following will specifically exemplify the different constituent devices of the optical fiber sensing system.
As shown in fig. 3, the first signal generating unit 101 may include a laser 1011 and a coupler 1012, wherein the coupler 1012 is configured to split continuous laser light generated by the laser 1011 to generate a detection signal and a local oscillation signal. That is, the laser generates a continuous laser signal and feeds the laser signal into the coupler 1012, and the coupler 1012 splits the laser signal into two paths, thereby obtaining a detection signal and a local oscillator signal. The power occupied by different signals during branching can be flexibly set according to the needs. Still further, to provide a high coherence light source, the laser may be configured as a narrow linewidth laser.
The second signal generating unit 102 may include a signal generator 1021 and a controller 1022, where the signal generator 1021 generates a detection modulation signal and a local oscillation modulation signal, respectively, and the signal generator 1021 generates the local oscillation modulation signal capable of modulating the local oscillation signal to obtain a target local oscillation signal negatively correlated with the backscatter signal under the control of the controller 1022.
The first signal modulation unit 103 may be an AOM, so as to obtain a target detection signal with high extinction ratio and good waveform quality.
The second signal modulation unit 104 may be an intensity modulator, and generates the target local oscillation signal after being driven by the local oscillation modulation signal generated by the second signal generation unit 102.
The circulator unit 105 may be an optical circulator, the target detection signal is input into the optical circulator from the first port and output from the second port and is fed into the sensing optical fiber, and the backscattering signal opposite to the propagation direction of the target detection signal is continuously generated from the time when the target detection signal is fed into the sensing optical fiber until the target detection signal is transmitted to the other end of the optical fiber, and the optical circulator receives the backscattering signal through the second port and outputs the backscattering signal from the third port and is fed into the coherent detection unit 106, so as to extract the backscattering signal.
The coherent detection unit 106 may include a coupler 1061, a coherent detector 1062, and an ADC1063, where the coupler 1061 is configured to combine the target local oscillator signal and the backscatter signal to obtain a mixed signal. That is, the target local oscillator signal and the backscatter signal will be mixed and received by the coupler 1061, so as to implement variable gain amplification of the backscatter signal; the coherent detector 1062 is configured to perform coherent detection and photoelectric conversion on a target sensing signal to obtain a sensing analog electrical signal, and the ADC1063 is configured to perform analog-to-digital conversion on the sensing analog electrical signal to obtain sensing detection data.
In particular, the optical fiber sensing system further comprises: and an amplifier 108, wherein the amplifier 108 is configured to amplify the target detection signal generated by the first signal modulator. At this time, the circulator unit 105 is used to feed the amplified target detection signal into the optical fiber.
In the case of sensing by an optical fiber providing a communication service, the use of a raman amplifier in a communication optical fiber cable has a certain influence on a traffic signal in a channel, and therefore, it is not possible to directly set the amplifier as a raman amplifier. In contrast, the amplifier may be an Erbium-doped fiber amplifier (Erbium-doped Optical Fiber Amplifier, EDFA) which directly amplifies a single-ended optical signal, which is no longer affected by the amplifier once it has been output.
As can be seen from the foregoing description, the optical fiber sensing system provided in this embodiment additionally introduces an intensity modulation function to the local oscillation signal based on an Optical Frequency Domain Reflectometer (OFDR), a phase sensitive optical time domain reflectometer (Φotdr), a Coherent Optical Time Domain Reflectometer (COTDR), a Brillouin Optical Time Domain Reflectometer (BOTDR), a Brillouin Optical Time Domain Analyzer (BOTDA), a Raman Optical Time Domain Reflectometer (ROTDR), and the like, that is, introduces an intensity modulator and the signal generator provides a detection modulation signal generating function, and also increases the local oscillation modulation signal generating function, so as to provide a target local oscillation signal inversely related to the power of the backscattering signal, so as to stabilize the power variation range of the mixed signal within a relatively small range, specifically: when sensing is carried out by using an optical fiber with the length of 100km, the intensity trace of a signal after the back scattering signal and the local oscillation signal without intensity modulation are mixed by a traditional optical fiber sensing system is shown as a graph in fig. 4, the signal power fluctuation range caused by the transmission loss of the optical fiber is about 35dB, the amplitude fluctuation of the signal is superimposed, and the overall amplitude fluctuation range is as high as nearly 70dB; the optical fiber sensing system provided by the embodiment is used for determining the target local oscillation signal power trace as the expressionIn the case of the resulting mixed signal, the signal power fluctuation range due to the transmission loss of the optical fiber is still about 35dB, as shown in fig. 5, but the floating fluctuation range as a whole is substantially consistent with the fluctuation range thereof, i.e., about 35dB.
In another aspect, the embodiment of the present application further provides a detection method, as shown in fig. 6, which is applied to the optical fiber sensing system described in the foregoing embodiment, where the detection method at least includes the following steps:
in step 601, a detection signal, a local oscillation signal, a detection modulation signal and a local oscillation modulation signal are generated.
In some examples, the probe signal and the local oscillator signal are obtained by splitting a laser beam according to a certain power splitting ratio.
Step 602, pulse modulating the detection signal according to the detection modulation signal to generate a target detection signal.
And 603, 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 the back scattering signal, wherein the back scattering signal is a signal generated by back scattering when the target detection signal is transmitted in the optical fiber.
In some examples, a target local oscillator signal is generated that is inversely proportional to the power of the backscatter signal.
In still other examples, the back-scattered signal has a power trace ofCorrespondingly, it is generated that the power trace is +.> Wherein t is [0, T]T is the duration of the 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 Power of back-scattered signal at +time, 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 Is a preset power constant. At this time, as shown in fig. 7, compared with the conventional optical fiber sensing receiving method shown by the solid line in which the local oscillation signal is maintained at 0dB, the target local oscillation signal power provided by the embodiment shown by the dotted line is in a logarithmic linear increasing state. Further, the signals obtained after coherent detection and mixing are: /> At this time, the target local oscillation signal can just compensate the power loss of the back scattering signal.
Also, in some examples, the local oscillation signal is modulated periodically according to the transmission period of the target detection signal, that is, such that the transmission period of the target detection signal is the same as the modulation period of the local oscillation signal.
And (2) periodically modulating the local oscillation signal by taking the period duration not smaller than (2 x n x L)/c as a modulation period, wherein n is the refractive index of the optical fiber, c is the light velocity, and L is the radial length of the optical fiber.
In some examples, step 601 generates a local oscillation modulation signal synchronous with the target detection signal, so as to determine local oscillation modulation signals adopted by the local oscillation signals at different moments, thereby improving the accuracy of modulation.
For example, the signals may be synchronized as shown in fig. 8, where the solid line represents the backscatter signal, the dashed line represents the target local oscillator signal, the filled region represents the pulsed target probe signal, and the synchronization period of the three is (2×n×l)/c, and the power of the backscatter signal gradually decreases and the generated target local oscillator signal gradually increases as the transmission time of the backscatter signal in the optical fiber increases in the period. Wherein τ is the impulse response time of the target local oscillation signal, t= (2×n×l)/c, T 0 Is the starting time of the cycle.
Step 604, a target detection signal is sent to the optical fiber and a backscatter signal is acquired.
In some examples, the target detection signal is further amplified before being fed into the fiber to increase the back-scattered power.
Step 605, performing coherent detection on the target local oscillation signal and the backscatter signal to obtain sensing detection data.
In some examples, coherent detection of the target local oscillator signal and the backscatter signal may be achieved by: and combining the target local oscillation signal and the back scattering signal to obtain an interfered target sensing signal, then carrying out photoelectric detection on the interfered target sensing signal to obtain a sensing analog electric signal, and then carrying out analog-to-digital conversion on the sensing analog electric signal to obtain sensing detection data.
Moreover, it should be understood that the above steps of the various methods are divided, for clarity of description, and may be combined into one step or split into multiple steps when implemented, so long as they include the same logic relationship, and all the steps are within the scope of protection of the present patent; it is within the scope of this patent to add insignificant modifications to the algorithm or flow or introduce insignificant designs, but not to alter the core design of its algorithm and flow.
It is to be appreciated that the embodiments of the present application are method embodiments corresponding to system embodiments, and that the embodiments of the present application may be implemented in conjunction with system embodiments. The related technical details mentioned in the system embodiment are still valid in this embodiment, and in order to reduce repetition, they are not described here again. Accordingly, the related technical details mentioned in the present embodiment can also be applied to the system embodiment.
The embodiments described hereinabove are intended to provide those of ordinary skill in the art with a variety of modifications and variations that would make it possible to the embodiments without departing from the inventive concept, and thus the scope of the application is not limited by the embodiments described hereinabove but is to be accorded the broadest scope consistent with the innovative features recited 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.
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| CN202210523849.1A CN117092715A (en) | 2022-05-13 | 2022-05-13 | Optical fiber sensing system and detection method |
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| CN107769858A (en) * | 2016-08-22 | 2018-03-06 | 中兴通讯股份有限公司 | A kind of optical signal processing method and device |
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| EP3916365A1 (en) * | 2020-05-25 | 2021-12-01 | Aragon Photonics Labs, S.L.U. | Method and system for interrogating optical fibers |
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