CN112762970A - High-performance distributed optical fiber sensing system and method - Google Patents
High-performance distributed optical fiber sensing system and method Download PDFInfo
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Abstract
The invention discloses a high-performance distributed optical fiber sensing system and a method, wherein the system comprises: the device comprises a multi-wavelength narrow-linewidth light source, a modulation unit, a splitter, a wavelength division multiplexer, a wavelength division demultiplexer, a circulator, a sensing optical fiber, a demodulation module and an upper computer; the invention utilizes the sweep-frequency filter or the multi-channel signal generator to modulate the continuous light emitted by the multi-wavelength narrow linewidth laser, realizes the asynchronous modulation among all wavelengths by controlling the sweep-frequency rate of the sweep-frequency filter or the parallel time delay trigger modulator of the multi-channel signal generator, and has the advantages of flexible and adjustable pulse interval, pulse width and pulse repetition frequency. And the demultiplexer and the wavelength division multiplexer are utilized to realize multi-path synchronous sensing, so that the measurement efficiency is improved. Pulse light with multiple wavelengths is used as detection light to enter the sensing optical fiber, information carried by Rayleigh scattering signals under each wavelength is demodulated respectively, and the signals are comprehensively processed. The invention reduces the complexity of the system and improves the performance of the system.
Description
Technical Field
The invention relates to the technical field of distributed optical fiber sensing systems, in particular to a high-performance distributed optical fiber sensing system and a method.
Background
The optical fiber sensing technology has been successfully applied to a plurality of fields such as structural health monitoring, oil and gas exploration and the like through the vigorous development for decades. In a distributed optical fiber sensing system, an optical fiber can be used as a transmission medium of the optical fiber, and when light propagates in the optical fiber, characteristic parameters (amplitude, phase, polarization state, wavelength and the like) representing light waves are indirectly or directly changed due to the action of external factors (such as temperature, pressure, magnetic field, electric field, displacement and the like), and a demodulation module demodulates the external action.
The fiber sensing system can be classified into a distributed type and a point type according to different measurement modes. The distributed optical fiber sensing system has the capability of seamless measurement, can make up the defects of a point type sensor, and solves a plurality of problems in the engineering field. For example, the distributed optical fiber acoustic wave sensor can realize single full-well section seismic signal acquisition in the field of oil and gas exploration, and the acquisition cost is reduced.
After years of research, a large number of scholars propose various optical fiber sensing systems such as DTS, DVS, DAS and the like aiming at various application environments, and each system has own characteristics. For example, a distributed optical fiber sensing system and method (CN109282839B) based on multiple pulses and multiple wavelengths utilize multiple pulse lasers and optical fiber delay lines with different center wavelengths to realize optical fiber sensing of multiple pulses and multiple wavelengths, thereby improving the performance of the sensing system to a certain extent, but the scheme requires multiple lasers with different wavelengths and has a high cost, and the use of the optical fiber delay line also has a great disadvantage, one of which is to use optical fibers with different lengths to perform pulse delay, which requires precise control of the length of the optical fiber, thereby making it difficult to ensure accurate pulse delay intervals, and the other of which is to use optical fiber delay optical pulses to limit the pulse delay time in hardware, thereby reducing the flexibility of the system.
Disclosure of Invention
The invention aims to solve the technical problems that the existing distributed optical fiber sensing system needs a plurality of lasers with different wavelengths, has higher cost and low performance, and has larger defects by using an optical fiber delay line, wherein one is to utilize optical fibers with different lengths to carry out pulse delay, the length of the optical fiber needs to be accurately controlled, the pulse delay interval is difficult to ensure to be accurate, and the other is to use the optical fiber to delay optical pulses to limit the pulse delay time on hardware, thereby reducing the flexibility of the system. The invention aims to provide a high-performance distributed optical fiber sensing system and a high-performance distributed optical fiber sensing method, and provides a high-performance low-cost real-time optical fiber sensing system which is subjected to multi-wavelength asynchronous modulation and has flexibly adjustable pulse interval, pulse width and pulse repetition frequency aiming at the problems.
The invention is realized by the following technical scheme:
in a first aspect, the present invention provides a high performance distributed optical fiber sensing system, comprising: the device comprises a multi-wavelength narrow-linewidth light source, a modulation unit, a splitter, a wavelength division multiplexer, a wavelength division demultiplexer, a circulator, a sensing optical fiber, a demodulation module and an upper computer;
the multi-wavelength narrow linewidth light source emits continuous light containing n wavelengths (the multi-wavelength narrow linewidth light source simultaneously emits light with the wavelength of lambda)1、λ2、……、λnThe continuous light) is divided into two paths by a first splitter, one path is used as reference light, and the other path is used as signal light to be subjected to asynchronous modulation of each wavelength by the modulation unit to form probe light;
the input end of the modulation unit is connected with the multi-wavelength narrow linewidth light source, and the output end of the modulation unit is connected with the second shunt; the second splitter is correspondingly connected with the first ports of the m-path circulators, the second ports of the m-path circulators are connected with the corresponding m-path sensing optical fibers, and the second ports of the m-path circulators are connected with the corresponding wavelength division multiplexers; each wavelength division multiplexer is correspondingly connected with n demodulation modules, and the demodulation modules are connected with an upper computer;
the detection light is divided into m paths of detection light by the second splitter, and the m paths of detection light enter m paths of sensing optical fibers connected to the second port of the circulator through the first port of the circulator; the detection light is propagated in the sensing optical fiber to generate backward Rayleigh scattering light, and the backward Rayleigh scattering light returns along the sensing optical fiber and then enters the wavelength division multiplexer through a third port of the circulator; the wavelength division demultiplexer demultiplexes Rayleigh scattered light generated by the detection light containing n wavelengths into n paths of Rayleigh scattered light; the n paths of Rayleigh scattering light and the reference light with the corresponding wavelengths enter a demodulation module, the external information which is carried by the Rayleigh scattering light generated by the detection light with each wavelength and acts on the sensing optical fiber is demodulated by the demodulation module, and the external information is transmitted to an upper computer; the upper computer processes the information acquired by the n demodulation modules to acquire high-quality sensing signals; and the upper computer processes the signals of the m paths of sensing optical fibers and acquires the signals monitored by the m paths of sensing optical fibers.
The working principle is as follows: in the prior art, a distributed optical fiber sensing system and a distributed optical fiber sensing method based on multiple pulses and multiple wavelengths utilize a plurality of pulse lasers and optical fiber delay lines with different central wavelengths to realize optical fiber sensing of multiple pulses and multiple wavelengths, and improve the performance of the sensing system to a certain extent.
According to the technical scheme, the continuous light emitted by the multi-wavelength narrow linewidth laser is modulated by the sweep frequency filter or the multi-path signal generator, the asynchronous modulation among wavelengths is realized by controlling the sweep frequency rate of the sweep frequency filter or the parallel time delay trigger modulator of the multi-path signal generator, and the pulse interval, the pulse width and the pulse repetition frequency are flexibly adjustable. And the demultiplexer and the wavelength division multiplexer are utilized to realize multi-path synchronous sensing, so that the measurement efficiency is improved. Pulse light with multiple wavelengths is used as detection light to enter the sensing optical fiber, information carried by Rayleigh scattering signals under each wavelength is demodulated respectively, and the signals are comprehensively processed.
The invention utilizes the characteristic of the sweep frequency filter to carry out asynchronous pulse modulation on multi-wavelength continuous light emitted by the multi-wavelength narrow linewidth light source, and can flexibly control the width of the light pulse and the delay between the light pulses with different wavelengths by setting the sweep frequency rate of the filter. The invention adopts a mode of asynchronous modulation of multiple wavelengths, only pulse light with one wavelength enters the optical fiber at each moment, and avoids the nonlinear effect caused by overhigh total optical power of the entering optical fiber when the multiple wavelengths simultaneously enter the optical fiber, thereby improving the optical power of the entering optical fiber under each wavelength and improving the system performance. The invention can control the sweep frequency speed and flexibly control the pulse width by controlling the sweep frequency speed of the sweep frequency filter, and can flexibly adjust the spatial resolution of the system because the spatial resolution of the system is related to the pulse width.
As a further preferred scheme, the modulation unit performs asynchronous pulse modulation on each wavelength of the signal light in two modes, the first mode is modulation by selecting a sweep-frequency filter, and the multi-wavelength continuous light is subjected to asynchronous pulse modulation into detection light by setting the scanning rate of the sweep-frequency filter;
and the second mode is that a multi-channel signal generator and a modulator are selected for modulation, signal lights with different wavelengths enter different modulators, and the modulators are triggered by delay among control signals of each channel of the multi-channel signal generator to realize asynchronous modulation.
As a further preferable scheme, when a frequency sweep filter is selected for modulation, the modulation unit comprises a frequency sweep filter and an erbium-doped fiber amplifier EDFA, the input end of the frequency sweep filter is connected with a first splitter, the output end of the frequency sweep filter is connected with the erbium-doped fiber amplifier EDFA, and the erbium-doped fiber amplifier EDFA is connected with a second splitter;
recording the bandwidth of the frequency sweep filter as delta lambda and the frequency sweep rate of the frequency sweep filter as delta lambda1In seconds, the wavelength is λnHas an optical pulse width of
Two adjacent wavelengths lambdaqAnd λq-1With a delay of light pulses in between
As a further preferred scheme, when a multi-channel signal generator and a modulator are selected for modulation, the modulation unit includes a first wavelength division multiplexer, a splitter, a multi-channel signal generator, a modulator, and a second wavelength division multiplexer, an input end of the first wavelength division multiplexer is connected to the input of the multi-wavelength narrow linewidth light source, an output end of the first wavelength division multiplexer is connected to the corresponding splitter, and the splitter is connected to the corresponding modulator; the multi-path signal generator is connected with each modulator, each modulator is connected with a second wavelength division multiplexer, and the second wavelength division multiplexer is connected with a second splitter through an erbium-doped fiber amplifier (EDFA);
the multi-channel signal generator controls the modulators in parallel by multi-channel control signals, the delay time between each channel of control signals is flexibly adjustable by setting parameters of the multi-channel signal generator, the number of light wavelengths entering each modulator is q, and q is more than or equal to 1.
As a further preferable mode, when the modulation unit modulates the signal light to generate a frequency shift, a frequency shift device is added to the reference optical path so that there is no frequency difference between the reference light and the probe light generated by the modulation unit and corresponding to the wavelength of the reference light.
As a further preferred scheme, the modulator may work in a pulse modulation mode, a continuous wave modulation mode or the like.
As a further preferable scheme, the multi-wavelength narrow linewidth light source is continuous light with n wavelengths formed by laser light emitted by a multi-wavelength narrow linewidth laser, and the wavelength of the multi-wavelength narrow linewidth laser is matched with the pass band of the devices such as the wavelength division multiplexer, the wavelength division demultiplexer, the splitter, the circulator, the erbium-doped fiber amplifier and the like, so as to ensure that the laser light normally passes through the modules or the devices.
As a further preferable scheme, the m sensing optical fibers are respectively cabled separately, or m sensing optical fibers are integrated in one optical cable to form a multi-core optical fiber. When m paths of optical fibers are integrated in one optical cable, a plurality of optical fibers can measure the same signal at the same time, and the signal-to-noise ratio is further improved.
As a further preferred solution, the system is adapted for demodulating optical fibers, FBG strings, fiber fabry-perot sensors, etc.
As a further preferred solution, the multi-wavelength narrow linewidth laser may be replaced by a plurality of narrow linewidth lasers having different center wavelengths.
As a further preferable scheme, the demodulation module may select an I/Q demodulation method, a heterodyne demodulation method, a homodyne demodulation method, a distributed optical fiber sensing demodulation method based on a 2 × 4 coupler, a distributed optical fiber sensing demodulation method based on a 3 × 3 coupler, and the like.
When the demodulation module adopts a distributed optical fiber sensing demodulation method based on a 3-by-3 coupler, reference light is not needed, namely, a multi-wavelength narrow-linewidth laser emits a beam of continuous light containing n wavelengths and then directly enters the modulator.
On the other hand, the invention also provides a high-performance distributed optical fiber sensing method, which comprises the following steps:
s1, a multi-wavelength narrow linewidth light source emits continuous light containing multiple wavelengths, the continuous light is divided into two paths through a splitter, one path is used as reference light, and the other path is used as signal light to be subjected to asynchronous modulation of each wavelength through the modulation unit to form detection light;
s2, dividing the detection light into m paths of detection light through a splitter, wherein the m paths of detection light enter m paths of sensing optical fibers connected to the second port of the circulator through the first port of the circulator;
s3, transmitting the detection light in the sensing optical fiber to generate backward Rayleigh scattering light, and returning the backward Rayleigh scattering light along the sensing optical fiber to enter the wavelength division multiplexer through a third port of the circulator;
s4, the wavelength division multiplexer demultiplexes Rayleigh scattered light generated by the probe light containing n wavelengths into n paths of Rayleigh scattered light;
s5, enabling n paths of Rayleigh scattering light and reference light with corresponding wavelengths to enter a demodulation module, and demodulating external information which is carried by Rayleigh scattering light and acts on the sensing optical fiber and is generated by the detection light with each wavelength by the demodulation module;
s6, the upper computer processes the information obtained by the n demodulation modules to obtain high-quality sensing signals;
and S7, processing the signals of the m paths of sensing optical fibers by the upper computer, and acquiring the signals monitored by the m paths of sensing optical fibers.
Compared with the prior art, the invention has the following advantages and beneficial effects:
the invention provides a high-performance optical fiber sensing system, which utilizes the characteristic of a sweep frequency filter to carry out asynchronous pulse modulation on multi-wavelength continuous light emitted by a multi-wavelength narrow linewidth light source, and can flexibly control the width of an optical pulse and the delay between optical pulses with different wavelengths by setting the sweep frequency rate of the filter. The invention utilizes the sweep frequency filter for modulation, can generate ultra-narrow pulse by controlling the sweep frequency speed of the sweep frequency filter, realizes high spatial resolution of the system, can control the sweep frequency period of the sweep frequency filter, improves the pulse repetition frequency and improves the response bandwidth of the system. The invention adopts a mode of asynchronous modulation of multiple wavelengths, only pulse light with one wavelength enters the optical fiber at each moment, and avoids the nonlinear effect caused by overhigh total optical power of the entering optical fiber when the multiple wavelengths simultaneously enter the optical fiber, thereby improving the optical power of the entering optical fiber under each wavelength, improving the system performance, and ensuring that the spatial resolution is not reduced under the condition of ensuring more wavelength of the entering optical fiber by utilizing the characteristic of larger interval of different wavelengths. The invention can control the sweep frequency speed and flexibly control the pulse width by controlling the sweep frequency speed of the sweep frequency filter, and can flexibly adjust the spatial resolution of the system because the spatial resolution of the system is related to the pulse width. The frequency shift device is added in the reference light path, so that no frequency difference exists between the reference light and the detection light, homodyne detection is realized, the requirement on a demodulation module detector is reduced, and the system cost is reduced.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
fig. 1 is a schematic structural diagram of a high-performance distributed optical fiber sensing system according to the present invention.
Fig. 2 is a schematic structural diagram of a high-performance distributed optical fiber sensing system according to the present invention.
Fig. 3 is a schematic structural diagram of a distributed optical fiber sensing system according to embodiment 2 of the present invention.
Fig. 4 is a schematic diagram of waveform movement of a high-performance distributed optical fiber sensing method according to embodiment 2 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that: it is not necessary to employ these specific details to practice the present invention. In other instances, well-known structures, circuits, materials, or methods have not been described in detail so as not to obscure the present invention.
Throughout the specification, reference to "one embodiment," "an embodiment," "one example," or "an example" means: the particular features, structures, or characteristics described in connection with the embodiment or example are included in at least one embodiment of the invention. Thus, the appearances of the phrases "one embodiment," "an embodiment," "one example" or "an example" in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable combination and/or sub-combination in one or more embodiments or examples. Further, those of ordinary skill in the art will appreciate that the illustrations provided herein are for illustrative purposes and are not necessarily drawn to scale. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
In the description of the present invention, the terms "front", "rear", "left", "right", "upper", "lower", "vertical", "horizontal", "upper", "lower", "inner", "outer", etc. indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and therefore, should not be construed as limiting the scope of the present invention.
Example 1
As shown in fig. 1 to 3, the present invention provides a high performance distributed optical fiber sensing system, including: the device comprises a multi-wavelength narrow-linewidth light source, a modulation unit, a splitter, a wavelength division multiplexer, a wavelength division demultiplexer, a circulator, a sensing optical fiber, a demodulation module, an upper computer and the like;
the multi-wavelength narrow linewidth light source emits continuous light containing n wavelengths (the multi-wavelength narrow linewidth light source emits wavelengths simultaneouslyIs λ1、λ2、……、λnThe continuous light) is divided into two paths by a first splitter, one path is used as reference light, and the other path is used as signal light to be subjected to asynchronous modulation of each wavelength by the modulation unit to form probe light;
the input end of the modulation unit is connected with the multi-wavelength narrow linewidth light source, and the output end of the modulation unit is connected with the second shunt; the second splitter is correspondingly connected with the first ports of the m-path circulators, the second ports of the m-path circulators are connected with the corresponding m-path sensing optical fibers, and the second ports of the m-path circulators are connected with the corresponding wavelength division multiplexers; each wavelength division multiplexer is correspondingly connected with n demodulation modules, and the demodulation modules are connected with an upper computer;
the detection light is divided into m paths of detection light by the second splitter, and the m paths of detection light enter m paths of sensing optical fibers connected to the second port of the circulator through the first port of the circulator; the detection light is propagated in the sensing optical fiber to generate backward Rayleigh scattering light, and the backward Rayleigh scattering light returns along the sensing optical fiber and then enters the wavelength division multiplexer through a third port of the circulator; the wavelength division demultiplexer demultiplexes Rayleigh scattered light generated by the detection light containing n wavelengths into n paths of Rayleigh scattered light; the n paths of Rayleigh scattering light and the reference light with the corresponding wavelengths enter a demodulation module, the external information which is carried by the Rayleigh scattering light generated by the detection light with each wavelength and acts on the sensing optical fiber is demodulated by the demodulation module, and the external information is transmitted to an upper computer; the upper computer processes the information acquired by the n demodulation modules to acquire high-quality sensing signals; and the upper computer processes the signals of the m paths of sensing optical fibers and acquires the signals monitored by the m paths of sensing optical fibers.
Specifically, the modulation unit performs asynchronous pulse modulation on signal light with each wavelength in two modes, the first mode is modulation by selecting a sweep-frequency filter, and the multi-wavelength continuous light is subjected to asynchronous pulse modulation into detection light by setting the scanning rate of the sweep-frequency filter;
and the second mode is that a multi-channel signal generator and a modulator are selected for modulation, signal lights with different wavelengths enter different modulators, and the modulators are triggered by delay among control signals of each channel of the multi-channel signal generator to realize asynchronous modulation.
Specifically, when a frequency sweep filter is selected for modulation, as shown in fig. 1, the modulation unit includes a frequency sweep filter and an erbium-doped fiber amplifier EDFA, an input end of the frequency sweep filter is connected to a first splitter, an output end of the frequency sweep filter is connected to the erbium-doped fiber amplifier EDFA, and the erbium-doped fiber amplifier EDFA is connected to a second splitter;
recording the bandwidth of the frequency sweep filter as delta lambda and the frequency sweep rate of the frequency sweep filter as delta lambda1In seconds, the wavelength is λnHas an optical pulse width of
Two adjacent wavelengths lambdaqAnd λq-1With a delay of light pulses in between
Specifically, when a multi-channel signal generator and a modulator are selected for modulation, as shown in fig. 2, the modulation unit includes a first wavelength division multiplexer, a splitter, a multi-channel signal generator, a modulator, and a second wavelength division multiplexer, an input end of the first wavelength division multiplexer is connected to the input of the multi-wavelength narrow linewidth light source, an output end of the first wavelength division multiplexer is connected to the corresponding splitter, and the splitter is connected to the corresponding modulator; the multi-path signal generator is connected with each modulator, each modulator is connected with a second wavelength division multiplexer, and the second wavelength division multiplexer is connected with a second splitter through an erbium-doped fiber amplifier (EDFA);
the multi-channel signal generator controls the modulators in parallel by multi-channel control signals, the delay time between each channel of control signals is flexibly adjustable by setting parameters of the multi-channel signal generator, the number of light wavelengths entering each modulator is q, and q is more than or equal to 1.
Specifically, when the modulation unit modulates the signal light to generate a frequency shift, a frequency shift device is added to the reference optical path so that there is no frequency difference between the reference light and the probe light generated by the modulation unit and corresponding to the wavelength of the reference light.
In practice, the modulator may operate by pulse modulation or continuous wave modulation.
In implementation, the multi-wavelength narrow linewidth light source is continuous light with n wavelengths formed by laser emitted by a multi-wavelength narrow linewidth laser, and the wavelength of the multi-wavelength narrow linewidth laser is matched with the pass band of the wavelength division multiplexer, the wavelength demultiplexing multiplexer, the splitter, the circulator, the erbium-doped fiber amplifier and other devices, so as to ensure that the laser normally passes through the modules or the devices.
When the optical fiber is implemented, the m paths of sensing optical fibers are respectively and independently cabled, or m sensing optical fibers are integrated in one optical cable to form a multi-core optical fiber. When m paths of optical fibers are integrated in one optical cable, a plurality of optical fibers can measure the same signal at the same time, and the signal-to-noise ratio is further improved.
When in implementation, the system is suitable for demodulating optical fibers, FBG strings, optical fiber Fabry-Perot sensors and the like.
In implementation, the multi-wavelength narrow linewidth laser can be replaced by a plurality of narrow linewidth lasers with different central wavelengths.
In implementation, the demodulation module can adopt an I/Q demodulation method, heterodyne demodulation, homodyne demodulation, a distributed optical fiber sensing demodulation method based on a 2 x 4 coupler, a distributed optical fiber sensing demodulation method based on a 3 x 3 coupler and the like.
When the demodulation module adopts a distributed optical fiber sensing demodulation method based on a 3-by-3 coupler, reference light is not needed, namely, a multi-wavelength narrow-linewidth laser emits a beam of continuous light containing n wavelengths and then directly enters the modulator.
When in implementation: according to the technical scheme, the continuous light emitted by the multi-wavelength narrow linewidth laser is modulated by the sweep frequency filter or the multi-path signal generator, the asynchronous modulation among wavelengths is realized by controlling the sweep frequency rate of the sweep frequency filter or the parallel time delay trigger modulator of the multi-path signal generator, and the pulse interval, the pulse width and the pulse repetition frequency are flexibly adjustable. And the demultiplexer and the wavelength division multiplexer are utilized to realize multi-path synchronous sensing, so that the measurement efficiency is improved. Pulse light with multiple wavelengths is used as detection light to enter the sensing optical fiber, information carried by Rayleigh scattering signals under each wavelength is demodulated respectively, and the signals are comprehensively processed.
The invention utilizes the characteristic of the sweep frequency filter to carry out asynchronous pulse modulation on multi-wavelength continuous light emitted by the multi-wavelength narrow linewidth light source, and can flexibly control the width of the light pulse and the delay between the light pulses with different wavelengths by setting the sweep frequency rate of the filter. The invention adopts a mode of asynchronous modulation of multiple wavelengths, only pulse light with one wavelength enters the optical fiber at each moment, and avoids the nonlinear effect caused by overhigh total optical power of the entering optical fiber when the multiple wavelengths simultaneously enter the optical fiber, thereby improving the optical power of the entering optical fiber under each wavelength and improving the system performance. The invention can control the sweep frequency speed and flexibly control the pulse width by controlling the sweep frequency speed of the sweep frequency filter, and can flexibly adjust the spatial resolution of the system because the spatial resolution of the system is related to the pulse width.
Example 2
As shown in fig. 1 to 4, the present embodiment is different from embodiment 1 in that the present embodiment provides a high-performance distributed optical fiber sensing method, which is applied to a high-performance distributed optical fiber sensing system described in embodiment 1; the method comprises the following steps:
s1, a multi-wavelength narrow linewidth light source emits continuous light containing multiple wavelengths, the continuous light is divided into two paths through a splitter, one path is used as reference light, and the other path is used as signal light to be subjected to asynchronous modulation of each wavelength through the modulation unit to form detection light;
s2, dividing the detection light into m paths of detection light through a splitter, wherein the m paths of detection light enter m paths of sensing optical fibers connected to the second port of the circulator through the first port of the circulator;
s3, transmitting the detection light in the sensing optical fiber to generate backward Rayleigh scattering light, and returning the backward Rayleigh scattering light along the sensing optical fiber to enter the wavelength division multiplexer through a third port of the circulator;
s4, the wavelength division multiplexer demultiplexes Rayleigh scattered light generated by the probe light containing n wavelengths into n paths of Rayleigh scattered light;
s5, enabling n paths of Rayleigh scattering light and reference light with corresponding wavelengths to enter a demodulation module, and demodulating external information which is carried by Rayleigh scattering light and acts on the sensing optical fiber and is generated by the detection light with each wavelength by the demodulation module;
s6, the upper computer processes the information obtained by the n demodulation modules to obtain high-quality sensing signals;
and S7, processing the signals of the m paths of sensing optical fibers by the upper computer, and acquiring the signals monitored by the m paths of sensing optical fibers.
As shown in fig. 3, the implementation is as follows:
s1, a multi-wavelength narrow linewidth light source emits continuous light containing 3 wavelengths, the continuous light is divided into two paths through a splitter, one path is used as reference light, and the other path is used as signal light and enters a frequency sweeping filter to be subjected to asynchronous modulation of each wavelength to be detection light;
s2, dividing the detection light into 2 paths of detection light through a splitter, and enabling the 2 paths of detection light to enter a 2-path sensing optical fiber connected to a second port of the circulator through a first port of the circulator;
s3, transmitting the detection light in the sensing optical fiber to generate backward Rayleigh scattering light, and returning the backward Rayleigh scattering light along the sensing optical fiber to enter the wavelength division multiplexer through a third port of the circulator;
s4, the wavelength division multiplexer demultiplexes Rayleigh scattered light generated by the detection light containing 3 wavelengths into 3 paths of Rayleigh scattered light;
s5, enabling n paths of Rayleigh scattering light and reference light with corresponding wavelengths to enter a demodulation module, and demodulating external information which is carried by Rayleigh scattering light and acts on the sensing optical fiber and is generated by the detection light with each wavelength by the demodulation module;
s6, the upper computer processes the information acquired by the 3 demodulation modules to acquire high-quality sensing signals;
and S7, processing the signals of the 2-path sensing optical fibers by the upper computer, and acquiring the signals monitored by the 2-path sensing optical fibers.
As shown in fig. 4, the specific implementation manner of asynchronously modulating different wavelengths by the swept-frequency filter in step S1 is as follows: the passband Delta lambda of the swept filter is swept along the wavelength axis, i.e., the wavelengths passing through the passband of the swept filter at different times are different, and at time t1, the wavelength lambda is1Entering the passband of the frequency sweep filter, and passing the frequency sweep filter along with the change of timeWith band at Δ λ1Velocity in/sec towards wavelength λ2Direction shift, time t2, wavelength λ1Just away from the passband of the swept filter, a center wavelength λ is formed1Pulse width of
When the filter passband is located at λ1And λ2In between, no light pulse is formed, and the time length of no light pulse is
When the passband of the sweep frequency filter is lambda2Then, a central wavelength is formed as lambda2Pulse width of
The optical pulses of (2) form optical pulse trains with different central wavelengths, the same pulse widths and the same pulse intervals by analogy.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. A high performance distributed optical fiber sensing system, comprising: the device comprises a multi-wavelength narrow-linewidth light source, a modulation unit, a splitter, a wavelength division multiplexer, a wavelength division demultiplexer, a circulator, a sensing optical fiber, a demodulation module and an upper computer;
the multi-wavelength narrow linewidth light source emits continuous light containing n wavelengths, the continuous light is divided into two paths through a first splitter, one path is used as reference light, the other path is used as signal light, and the signal light is subjected to asynchronous modulation on each wavelength through the modulation unit to form detection light;
the input end of the modulation unit is connected with the multi-wavelength narrow linewidth light source, and the output end of the modulation unit is connected with the second shunt; the second splitter is correspondingly connected with the first ports of the m-path circulators, the second ports of the m-path circulators are connected with the corresponding m-path sensing optical fibers, and the second ports of the m-path circulators are connected with the corresponding wavelength division multiplexers; each wavelength division multiplexer is correspondingly connected with n demodulation modules, and the demodulation modules are connected with an upper computer;
the detection light is divided into m paths of detection light by the second splitter, and the m paths of detection light enter m paths of sensing optical fibers connected to the second port of the circulator through the first port of the circulator; the detection light is propagated in the sensing optical fiber to generate backward Rayleigh scattering light, and the backward Rayleigh scattering light returns along the sensing optical fiber and then enters the wavelength division multiplexer through a third port of the circulator; the wavelength division demultiplexer demultiplexes Rayleigh scattered light generated by the detection light containing n wavelengths into n paths of Rayleigh scattered light; the n paths of Rayleigh scattering light and the reference light with the corresponding wavelengths enter a demodulation module, the external information which is carried by the Rayleigh scattering light generated by the detection light with each wavelength and acts on the sensing optical fiber is demodulated by the demodulation module, and the external information is transmitted to an upper computer; the upper computer processes the information acquired by the n demodulation modules to acquire high-quality sensing signals; and the upper computer processes the signals of the m paths of sensing optical fibers and acquires the signals monitored by the m paths of sensing optical fibers.
2. The high-performance distributed optical fiber sensing system according to claim 1, wherein the modulating unit performs asynchronous pulse modulation on the signal light with different wavelengths in two ways, the first way is to select a frequency sweep filter for modulation, and the multi-wavelength continuous light is subjected to asynchronous pulse modulation into the probe light by setting the scanning rate of the frequency sweep filter;
and the second mode is that a multi-channel signal generator and a modulator are selected for modulation, signal lights with different wavelengths enter different modulators, and the modulators are triggered by delay among control signals of each channel of the multi-channel signal generator to realize asynchronous modulation.
3. The high-performance distributed optical fiber sensing system according to claim 2, wherein when a frequency sweep filter is selected for modulation, the modulation unit comprises a frequency sweep filter and an erbium-doped fiber amplifier EDFA, the input end of the frequency sweep filter is connected with a first splitter, the output end of the frequency sweep filter is connected with the erbium-doped fiber amplifier EDFA, and the erbium-doped fiber amplifier EDFA is connected with a second splitter;
recording the bandwidth of the frequency sweep filter as delta lambda and the frequency sweep rate of the frequency sweep filter as delta lambda1In seconds, the wavelength is λnHas an optical pulse width of
Two adjacent wavelengths lambdaqAnd λq-1With a delay of light pulses in between
4. The system according to claim 2, wherein when the multiple signal generators and the modulators are selected for modulation, the modulation unit includes a first wavelength division multiplexer, a splitter, multiple signal generators, a modulator, and a second wavelength division multiplexer, an input end of the first wavelength division multiplexer is connected to the input of the multi-wavelength narrow linewidth light source, an output end of the first wavelength division multiplexer is connected to the corresponding splitter, and the splitter is connected to the corresponding modulator; the multi-path signal generator is connected with each modulator, each modulator is connected with a second wavelength division multiplexer, and the second wavelength division multiplexer is connected with a second splitter through an erbium-doped fiber amplifier (EDFA);
the multi-channel signal generator controls the modulators in parallel by multi-channel control signals, the delay time between each channel of control signals is flexibly adjustable by setting parameters of the multi-channel signal generator, the number of light wavelengths entering each modulator is q, and q is more than or equal to 1.
5. The system according to claim 4, wherein when the modulation unit modulates the signal light to generate a frequency shift, a frequency shift device is added to the reference optical path to make no frequency difference between the reference light and the probe light generated by the modulation unit corresponding to the wavelength of the reference light.
6. A high performance distributed optical fiber sensing system according to claim 4, wherein said modulator operates using pulse modulation or continuous wave modulation.
7. The high-performance distributed optical fiber sensing system according to claim 1, wherein m sensing optical fibers are individually cabled or integrated in one optical cable to form a multi-core optical fiber;
the multi-wavelength narrow linewidth light source is continuous light with n wavelengths formed by laser emitted by a multi-wavelength narrow linewidth laser, and the wavelength of the multi-wavelength narrow linewidth laser is matched with the pass band of the wavelength division multiplexer, the wavelength demultiplexing multiplexer, the branching unit, the circulator and the erbium-doped optical fiber amplifier.
8. A high performance distributed optical fiber sensing system according to claim 1, wherein the system is adapted for demodulating optical fiber, FBG string, optical fiber fabry-perot sensors.
9. The system according to claim 1, wherein the demodulation module is selected from an I/Q demodulation method, a heterodyne demodulation method, a homodyne demodulation method, a distributed optical fiber sensing demodulation method based on a 2 x 4 coupler, and a distributed optical fiber sensing demodulation method based on a 3 x 3 coupler.
10. A method for an optical fiber sensing system according to any of claims 1 to 9, the method comprising the steps of:
s1, a multi-wavelength narrow linewidth light source emits continuous light containing multiple wavelengths, the continuous light is divided into two paths through a splitter, one path is used as reference light, and the other path is used as signal light to be subjected to asynchronous modulation of each wavelength through the modulation unit to form detection light;
s2, dividing the detection light into m paths of detection light through a splitter, wherein the m paths of detection light enter m paths of sensing optical fibers connected to the second port of the circulator through the first port of the circulator;
s3, transmitting the detection light in the sensing optical fiber to generate backward Rayleigh scattering light, and returning the backward Rayleigh scattering light along the sensing optical fiber to enter the wavelength division multiplexer through a third port of the circulator;
s4, the wavelength division multiplexer demultiplexes Rayleigh scattered light generated by the probe light containing n wavelengths into n paths of Rayleigh scattered light;
s5, enabling n paths of Rayleigh scattering light and reference light with corresponding wavelengths to enter a demodulation module, and demodulating external information which is carried by Rayleigh scattering light and acts on the sensing optical fiber and is generated by the detection light with each wavelength by the demodulation module;
s6, the upper computer processes the information obtained by the n demodulation modules to obtain high-quality sensing signals;
and S7, processing the signals of the m paths of sensing optical fibers by the upper computer, and acquiring the signals monitored by the m paths of sensing optical fibers.
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