CN110440838B - Multi-parameter optical fiber sensing instrument and sensing method based on multi-core optical fiber - Google Patents

Abstract

The invention relates to the technical field of optical fiber sensing, in particular to a multi-parameter optical fiber sensing instrument and a multi-parameter optical fiber sensing method based on a multi-core optical fiber, wherein the method comprises the following steps: the polarization and Raman light source is turned on at the time of T1, the fiber bragg grating light source is turned off, the Raman optical time domain reflection technology is used for sensing a first fiber core in the multi-core fiber, and the polarization light technology is used for sensing the first fiber core and a second fiber core; turning on a fiber bragg grating light source at the time of T2, turning off a polarization and Raman light source, and sensing a first fiber core in the multi-core fiber by using a grating technology; and comprehensively processing the data acquired by the three technologies, determining whether the whole optical fiber link has disturbance or not, and obtaining the current temperature value, strain value and vibration frequency value of the multi-core optical fiber. The invention simultaneously utilizes fiber grating, Raman and polarized light technologies to realize the simultaneous sensing of strain, temperature and vibration, and only two fiber cores can meet the quasi-synchronous acquisition requirements of the three technologies through wavelength division multiplexing and time division multiplexing.

Description

Multi-parameter optical fiber sensing instrument and sensing method based on multi-core optical fiber

[ technical field ] A method for producing a semiconductor device

The invention relates to the technical field of optical fiber sensing, in particular to a multi-parameter optical fiber sensing instrument and a multi-parameter optical fiber sensing method based on multi-core optical fibers.

[ background of the invention ]

The multi-core fiber is an optical fiber with a single cladding and a plurality of fiber cores, and by utilizing the space division multiplexing technology based on the multi-core fiber, higher-density data transmission can be realized in the aspect of optical communication, and a new use method can be expanded in the aspect of optical sensing. As is well known, the fiber sensing technology can generally realize continuous measurement at each point on the fiber link due to the use of fiber as a sensor, and the sensing distance can reach tens of kilometers. In addition to the common advantages with other fiber optic sensing technologies, fiber optic sensors have several specific advantages: spatial structure advantages, parametric compensation advantages and channel integration advantages. For example, the multiple cores of the multi-core optical fiber have the advantage of a spatial structure, so that the curvature and torsion rate information of the optical fiber can be inverted through the bending strain and the torsion strain of the spatial geometry structure by virtue of the difference of the relative geometric positions and structures of the multiple cores in one optical fiber, and the three-dimensional shape sensing of spatial bending and torsion can be realized through reconstruction; for another example, since the cores of the multi-core fiber are integrated in a cladding of several hundred micrometers, the ambient temperature at each point can be considered to be approximately the same, and thus the change of the optical path formed by the cores is also approximately the same, and the temperature compensation of multiple optical paths is automatically realized.

At present, in the aspect of mechanical parameters, the multi-core optical fiber can be used for measuring bending, strain, acceleration and the like, wherein the multi-core optical fiber is most widely used for bending sensing; the multi-core optical fiber also has very important application in the temperature sensing aspect, and a temperature sensing scheme based on the multi-core optical fiber with double cores, seven cores, nineteen cores and the like is proposed at present; in addition to this, there has been a study on refractive index sensing.

The traditional distributed optical fiber sensing technology mainly comprises an optical fiber grating technology, an optical fiber Brillouin sensing technology, a Raman optical time domain reflection technology, a polarized light time domain reflection technology, a phase sensitive optical time domain reflection technology, an optical frequency domain reflection technology and the like, and different physical quantities such as temperature, strain, vibration and the like can be measured by using optical fibers according to different measurement principles through corresponding optical fiber sensing instruments. However, the existing optical fiber sensing instruments are generally based on a single measurement principle, the measured physical quantity is single, and simultaneous measurement of multiple physical quantities cannot be realized, so that the application scenarios are limited. In addition, some measurement technologies, such as the fiber grating technology or the fiber brillouin sensing technology, have response to both temperature and strain, and are difficult to distinguish in practical application, so that the use is limited.

For example, for most of the devices with cables laid, it is necessary to prevent external forces from damaging the cables on the one hand and to monitor the working conditions of the cables on the other hand, so that it is necessary to be able to measure and distinguish between external disturbances and temperature simultaneously. For another example, in the field of bridge monitoring and building monitoring, on one hand, vibration events (such as earthquakes) need to be sensed, and on the other hand, fire and the like need to be warned, so that vibration and temperature need to be measured simultaneously. In the application scenarios, it is difficult to meet the use requirement by using the conventional optical fiber sensing technology.

In view of the above, it is an urgent problem in the art to overcome the above-mentioned drawbacks of the prior art.

[ summary of the invention ]

The technical problems to be solved by the invention are as follows:

the traditional optical fiber sensing technology is generally realized based on a single measurement principle, the measured physical quantity is single, the synchronous sensing measurement of multiple parameters cannot be realized, and the application scene is limited; in practical application, it is difficult to distinguish and quantitatively analyze different parameters for a sensing technology with a measurement result responding to a plurality of parameters.

The invention achieves the above purpose by the following technical scheme:

in a first aspect, the invention provides a multi-parameter optical fiber sensing instrument based on a multi-core optical fiber, which comprises a grating demodulator, a Raman temperature measuring instrument, a polarization analyzer and a processor; in three devices, namely a grating demodulator, a Raman thermometer and a polarization analyzer, wavelength division multiplexing is performed between the Raman thermometer and the polarization analyzer, and time division multiplexing is performed between the grating demodulator and the other two devices;

the grating demodulator, the Raman thermometer and the polarization analyzer are externally connected with the front end of a first fiber core a1 in the multi-core optical fiber through a first optical fiber interface b1, the polarization analyzer is also externally connected with the front end of a second fiber core a2 in the multi-core optical fiber through a second optical fiber interface b2, and the tail end of the first fiber core a1 is connected with the tail end of the second fiber core a 2;

the processor is respectively connected with the grating demodulator, the Raman temperature measuring instrument and the polarization analyzer and is used for comprehensively analyzing and processing data acquired by the three devices, judging whether disturbance exists on the whole optical fiber link and obtaining the current temperature value, the strain value and the vibration frequency value of the multi-core optical fiber.

In a second aspect, the invention also provides a multi-parameter optical fiber sensing instrument based on the multi-core optical fiber, which comprises a Raman light source, a polarization light source, an optical fiber grating light source, a polarizer, a coupler, a circulator, a beam splitter, an analyzer, a polarization light detector, a stokes light detector, an anti-stokes light detector, a grating demodulation device, an acquisition card and a processor; among the three light sources, the signals to be detected generated after the emission of the Raman light source and the polarization light source are distributed in different frequency bands, the signals are respectively detected after the demultiplexing by the wavelength division demultiplexing technology, and the time division multiplexing is performed between the fiber bragg grating light source and the other two light sources;

the Raman light source, the polarization light source and the fiber grating light source are respectively connected with the coupler, and the coupler, the circulator, the analyzer and the polarization light detector are sequentially connected; the circulator is also connected with the optical splitter, the optical splitter is respectively connected with the grating demodulation device, the stokes photodetector and the anti-stokes photodetector, the grating demodulation device, the stokes photodetector, the anti-stokes photodetector and the polarized photodetector are respectively connected with the acquisition card, and the acquisition card is connected with the processor;

the circulator is externally connected with the front end of a first fiber core a1 in the multi-core optical fiber through a first optical fiber interface b1, the analyzer is externally connected with the front end of a second fiber core a2 in the multi-core optical fiber through a second optical fiber interface b2, and the tail end of the first fiber core a1 is connected with the tail end of the second fiber core a 2;

the processor is used for carrying out comprehensive analysis processing on the data acquired by the acquisition card, judging whether the whole optical fiber link is disturbed or not, and obtaining the current temperature value, strain value and vibration frequency value of the multi-core optical fiber.

Preferably, the multi-parameter optical fiber sensing instrument further comprises a synchronous trigger circuit, wherein the synchronous trigger circuit is connected with the raman light source, the polarized light source and the acquisition card respectively, and is used for triggering the raman light source and the polarized light source to transmit light pulses and triggering the acquisition card to acquire data, so that synchronization of light pulse transmission and data acquisition is maintained.

In a third aspect, the present invention provides a multi-parameter optical fiber sensing method based on a multi-core optical fiber, which can be performed by the sensing apparatus of the first aspect or the second aspect, and includes:

turning on a polarized light source and a Raman light source at the time of T1, turning off a fiber bragg grating light source, so as to perform sensing measurement on a first fiber core a1 in the multi-core fiber by using a Raman optical time domain reflection technology, and perform sensing measurement on a first fiber core a1 and a second fiber core a2 in the multi-core fiber by using a polarized light technology;

turning on a fiber grating light source at the time of T2, turning off a polarized light source and a Raman light source so as to carry out sensing measurement on a first fiber core a1 in the multi-core optical fiber by using a grating technology;

and comprehensively processing data acquired by a Raman optical time domain reflection technology, a polarized light technology and a fiber grating technology, determining whether the whole optical fiber link has vibration or strain, and obtaining the current temperature value, strain value and vibration frequency value of the multi-core optical fiber.

Preferably, after the first fiber core a1 in the multicore fiber is subjected to sensing measurement by using the grating technology, the wavelength variation Δ λ of the fiber bragg grating in the multicore fiber is obtained_B。

After the first fiber core a1 in the multi-core fiber is subjected to sensing measurement by using a Raman optical time domain reflection technology, the luminous flux psi of Stokes scattering light in the multi-core fiber is obtained_s(T) and anti-Stokes scattered light luminous flux ψ_as(T)；

After the first fiber core a1 and the second fiber core a2 in the multi-core fiber are subjected to sensing measurement by utilizing a polarized light technology, the change condition of the light intensity in the multi-core fiber is obtained, and the vibration frequency is extracted.

Preferably, the comprehensively processing data acquired by the raman optical time domain reflection technology, the polarized light technology and the fiber bragg grating technology to determine whether the whole optical fiber link has vibration or strain, and obtaining the current temperature value, strain value and vibration frequency value of the multi-core fiber specifically includes:

comprehensively processing data acquired by a fiber grating technology and a Raman optical time domain reflection technology to obtain a temperature value and a strain value in the current environment parameter of the multi-core fiber;

and comprehensively processing data acquired by the fiber bragg grating technology and the polarized light technology, determining whether the whole optical fiber link has vibration or strain, and obtaining the current vibration frequency value of the multi-core optical fiber.

Preferably, the data acquired by the fiber grating technology and the raman optical time domain reflectometry technology are processed comprehensively to obtain the temperature value and the strain value of the multi-core fiber in the current environmental parameter, and the method specifically comprises the following steps:

psi detected from Raman optical time domain reflectometry_s(T) and psi_as(T), demodulating a temperature value T in the current environment parameters of the multi-core optical fiber by using a Raman formula;

temperature value T demodulated based on Raman formula and delta lambda detected by fiber grating technology_BAnd demodulating a strain value epsilon in the current environment parameters of the multi-core optical fiber by using a grating formula.

The invention has the beneficial effects that:

in the multi-parameter optical fiber sensing instrument and the sensing method provided by the invention, the fiber grating technology, the Raman optical time domain reflectometer technology and the polarized light technology are utilized, and the multi-path parallel optical link of the multi-core optical fiber is matched to synchronously measure different fiber cores in the multi-core optical fiber, so that the strain, temperature and vibration of the optical fiber can be simultaneously sensed, and the application scene is wider; and wavelength division multiplexing and time division multiplexing are adopted, so that the number of fiber cores required by detection in the multi-core fiber can be reduced, the quasi-synchronous acquisition requirements of three detection devices can be met only by any two fiber cores in the multi-core fiber, and the connection setting is more convenient.

[ description of the drawings ]

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments of the present invention will be briefly described below. It is obvious that the drawings described below are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.

Fig. 1 is a schematic structural diagram of a multi-parameter optical fiber sensing instrument based on a multi-core optical fiber according to an embodiment of the present invention;

fig. 2 is a schematic diagram illustrating a demodulation principle of a fiber grating technology according to an embodiment of the present invention;

fig. 3 is a schematic structural diagram of a grating demodulator based on a spectrometer demodulation method according to an embodiment of the present invention;

fig. 4 is a schematic structural diagram of a grating demodulator based on an edge filtering demodulation method according to an embodiment of the present invention;

fig. 5 is a schematic structural diagram of a grating demodulator based on a tunable F-P filter demodulation method according to an embodiment of the present invention;

fig. 6 is a schematic structural diagram of a grating demodulator based on a tunable narrowband light source demodulation method according to an embodiment of the present invention;

fig. 7 is a schematic structural diagram of a raman thermometer according to an embodiment of the present invention;

fig. 8 is a schematic structural diagram of a polarization analyzer according to an embodiment of the present invention;

FIG. 9 is a schematic structural diagram of another multi-core fiber-based multi-parameter optical fiber sensing apparatus according to an embodiment of the present invention;

fig. 10 is a schematic structural diagram of a multi-parameter optical fiber sensing apparatus based on a multi-core optical fiber according to an embodiment of the present invention;

fig. 11 is a flowchart of a multi-parameter optical fiber sensing method based on a multi-core optical fiber according to an embodiment of the present invention.

[ detailed description ] embodiments

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

In the description of the present invention, the terms "inside", "outside", "longitudinal", "lateral", "upper", "lower", "top", "bottom", "left", "right", "front", "rear", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of describing the present invention but do not require that the present invention must be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

As described in the background art, the conventional distributed optical fiber sensing technology mainly includes an optical fiber grating technology, an optical fiber brillouin sensing technology, a raman optical time domain reflection technology, a polarized light time domain reflection technology, and the like. In the invention, the optical fiber sensing technology mainly utilized is the fiber grating technology, the Raman optical time domain reflection technology and the polarized light technology, and the introduction of each optical fiber sensing technology is as follows:

the sensing principle of the Raman optical time domain reflection technology is as follows: when a laser pulse is transmitted in an optical fiber, Stokes Raman scattered light and anti-Stokes Raman scattered light are generated, the intensity of the two kinds of scattered light is influenced by temperature (and is insensitive to other parameters), but the modulation coefficients are different; by analyzing the modulation coefficients of the scattered light at two different frequencies and the measured luminous flux, the temperature change can be judged. This technique is capable of sensing temperature and performing quantitative analysis, but has a disadvantage in that only temperature parameters can be measured.

The sensing principle of the fiber grating technology is as follows: a plurality of Fiber Bragg Gratings (FBGs) are written in the optical fiber in a point-type or quasi-distributed manner, when external factors capable of responding change, parameters such as the effective refractive index and the Grating period of the optical fiber change, and further the resonant wavelength of the FBGs changes; the sensing of the ambient environment parameters can be realized by measuring the change of the resonance wavelength. However, for the multi-parameter sensing task, since the resonance wavelength of the sensing fiber can be changed by both temperature and strain, when only the fiber grating technology is used (i.e. only the grating demodulator is used), only the temperature or strain event can be judged to occur, the temperature and strain cannot be distinguished, and the quantitative analysis of the temperature and strain is more difficult to be carried out respectively. Meanwhile, the fiber grating technology can only realize point and quasi-distributed sensing, namely, whether vibration, strain or temperature change exists at the position where the FBG is located can only be detected, and the vibration, strain or temperature change at other positions cannot be detected, so that the state of the whole optical fiber cannot be obtained only by utilizing the fiber grating technology, and only the state of a specific position can be obtained.

According to the characteristics of the fiber grating technology and the Raman optical time domain reflection technology (namely, the fiber grating technology can sense temperature and strain at the same time but is difficult to distinguish and analyze quantitatively respectively, while the Raman optical time domain reflection technology can only analyze quantitatively the temperature), the invention considers the combination of the two technologies, expects to realize the simultaneous sensing of the temperature and the strain, and can distinguish and analyze quantitatively the temperature and the strain respectively.

The sensing principle of the polarized light technology is as follows: when light propagates in the optical fiber, the polarization state changes continuously; when the state of the fiber is stable, the change of the polarization state is relatively stable and slowly changed; when vibration or stress occurs, the polarization state changes suddenly, and the change is visually expressed as the change of light intensity after passing through the analyzer. The technology can realize the non-existent qualitative analysis on the disturbance, and if the vibration occurs, the vibration frequency can be demodulated according to the frequency of the detected pulse intensity change; the disadvantage is that when any point in the optical fiber has vibration or stress, the intensity of the optical pulse at the receiving end changes, so that the place of the event can not be determined.

Aiming at the defects of the polarized light technology, the polarized light time domain reflection technology can be directly used, and after the detection pulse is sent out, the time of arrival of the received signal is in proportional relation with the corresponding optical fiber position, so that the place of the occurrence of the event can be judged; however, the time domain reflection technique of polarized light utilizes scattered light in an optical fiber, the signal is weak, multiple averaging may be required to improve the signal-to-noise ratio, and the dynamic response capability is relatively low. Thus, the present invention contemplates combining polarized light technology with fiber grating technology: as mentioned above, the polarized light technology can sense the stress and vibration events at all points of the optical fiber, but cannot distinguish the position; and the fiber grating technology can monitor the state of the grating position. Combining the two techniques can create some degree of complementarity.

The invention will be described in detail below with reference to the figures and examples.

Example 1:

the embodiment of the invention provides a multi-parameter optical fiber sensing instrument based on a multi-core optical fiber, which comprises a grating demodulator 1, a Raman thermometer 2, a polarization analyzer 3, a synchronous trigger circuit 4 and a processor 5, wherein three detection devices, namely the grating demodulator 1, the Raman thermometer 2 and the polarization analyzer 3, are connected in parallel; among three devices, namely a grating demodulator 1, a raman thermometer 2 and a polarization analyzer 3, wavelength division multiplexing is performed between the raman thermometer 2 and the polarization analyzer 3, and time division multiplexing is performed between the grating demodulator 1 and the other two devices.

Referring to fig. 1, the grating demodulator 1, the raman thermometer 2, and the polarization analyzer 3 are all externally connected to the front end of a first fiber core a1 in the multicore fiber 7 through a first fiber interface b1, and the polarization analyzer is also externally connected to the front end of a second fiber core a2 in the multicore fiber through a second fiber interface b2, and the terminal of the first fiber core a1 is connected to the terminal of the second fiber core a2, so that two fiber cores in the multicore fiber 7 can be synchronously measured through a fiber grating technology, a raman optical time domain reflection technology, and a polarized light technology, and simultaneous sensing of temperature, strain, and vibration is realized.

The synchronous trigger circuit 4 is respectively connected with the grating demodulator 1, the raman thermometer 2 and the polarization analyzer 3 through electrical signal lines, and is used for triggering equipment at a specific moment to synchronously transmit light pulses and acquire data, and specifically comprises the following components: on one hand, the Raman temperature measuring instrument 2 and the polarization analyzer 3 are triggered to synchronously transmit light pulses at the time of T1, and the two devices are triggered to synchronously acquire data; and on the other hand, triggering the grating demodulator 1 to collect data at the time T2. For the raman thermometer 2 and the polarization analyzer 3, the pulse light source and the data acquisition inside need to be pulse synchronized; when the three detection devices are used in combination, except that the continuous light source used by the grating demodulator 1 does not need to be synchronized, the rest light sources and the light detection part not only need to be pulse-synchronized in each device, but also need to be synchronously triggered for light pulse and data acquisition among the three devices, so that a common synchronous trigger circuit 4 is introduced, and a sensing signal completely aligned in time can be obtained during signal processing, so that accurate compensation of cross sensitive signals is facilitated, and synchronous acquisition of the three devices is realized. However, due to the use of the time division multiplexing technology, Raman and polarization at the same time are synchronous; the grating is not acquired at the same time as the first two, so that the grating is not acquired synchronously; however, since the times T1 and T2 are short, the external conditions can be regarded as constant during the switching process, and thus quasi-synchronization can be regarded. The most common use of the synchronous trigger circuit 4 is to use a 555 timer, but in practical use, any circuit capable of stably outputting a periodic pulse electrical signal may be used, and the present invention is not limited thereto.

The processor 5 is connected with the grating demodulator 1, the raman thermometer 2 and the polarization analyzer 3 through electric signal lines, and is used for comprehensively analyzing and processing data acquired by the three devices, judging whether disturbance exists on the whole optical fiber link, and obtaining the current temperature value, strain value and vibration frequency value of the multi-core optical fiber. The current temperature value and the strain value of the multi-core optical fiber 7 can be obtained by complementary analysis (namely combining a fiber grating technology and a Raman optical time domain reflection technology) of the data collected by the grating demodulator 1 and the Raman thermometer 2; by complementary analysis (i.e. combining the fiber grating technology and the polarized light technology) of the data collected by the grating demodulator 1 and the polarization analyzer 3, whether the whole optical fiber link has disturbance can be judged, and the current vibration frequency value of the multi-core optical fiber 7 can be obtained. The processor 5 may be a computer or other device having an analysis processing function, and is not limited to a specific one, and the three detection devices may share one processor to perform data analysis.

During actual sensing measurement, the connection between each detection device and the optical fiber is external, that is, the connection is connected with the optical fiber through an external optical fiber interface. The grating demodulator 1 and the Raman thermodetector 2 are both reflective and are connected with any fiber core in the multi-core optical fiber 7 for sensing measurement; the polarization analyzer 3 is not reflective, and usually needs to connect any two cores in the multi-core fiber 7 for sensing measurement to obtain an output at a single end. Therefore, in the case where three detection devices are used in common, at least 4 cores in the multicore fiber 7 are generally required. In the embodiment of the present invention, wavelength division multiplexing is performed between the raman thermometer 2 and the polarization analyzer 3, and time division multiplexing is performed between the grating demodulator 1 and the other two devices, so that the number of the fiber cores can be reduced to two, and the fiber grating technology and the raman optical time domain reflection technology are both implemented by using the first fiber core a1, while the polarized light technology is implemented by using the two fiber cores of the first fiber core a1 and the second fiber core a 2.

The multi-parameter optical fiber sensing instrument integrates the grating demodulator, the Raman temperature measuring instrument and the polarization analyzer, can realize simultaneous sensing of strain, temperature and vibration of optical fibers by utilizing an optical fiber grating technology, a Raman optical time domain reflection technology and a polarized light technology, can reduce the number of fiber cores required by detection in a multi-core optical fiber by adopting wavelength division multiplexing and time division multiplexing, can meet the synchronous acquisition requirement of three detection devices only by any two fiber cores in the multi-core optical fiber, and is more convenient to connect and set.

The multi-core fiber 7 includes n cores, n is greater than or equal to 2, and may be a seven-core fiber, for example. The first fiber core a1 and the second fiber core a2 are two selected from n fiber cores, and are not specifically limited, and the rest fiber cores are used for normal optical signal transmission; therefore, the real-time detection of the environmental parameters of the signal transmission optical fiber (such as a seven-core optical fiber) can be realized. Referring to fig. 1, the front end of the core is the left end in the drawing, and the end of the core is the right end in the drawing.

For three detection devices, the grating demodulator 1 mainly senses temperature and strain by measuring the wavelength change of the FBGs, the raman thermometer 2 mainly senses temperature by measuring the light intensity change, and the polarization analyzer 3 mainly performs qualitative analysis on strain and vibration by measuring the polarization state change. With the above structure, the control process of time division multiplexing and wavelength division multiplexing is specifically as follows:

the time division multiplexing may specifically be controlled by the switching time of the corresponding light sources: turning on the light sources of the Raman thermometer 2 and the polarization analyzer 3 at the time of T1, and turning off the light source of the grating demodulator 1; and at the time of T2, turning on the light source of the grating demodulator 1, and turning off the light sources of the Raman thermometer 2 and the polarization analyzer 3, thereby realizing the time division multiplexing of the fiber grating technology and the other two technologies.

When the light sources of the raman thermometer 2 and the polarization analyzer 3 are turned on, on the one hand, the raman thermometer 2 can sense the temperature, and on the other hand, the polarization analyzer 3 can perform qualitative sensing analysis of strain and vibration. In the process, wavelength division multiplexing is performed between raman detection and polarization detection, specifically: the forward light is detected by the polarized light technology, the wavelength of the forward light is consistent with the wavelength of the light source and is 1550nm waveband; the Raman temperature measurement technology detects Stokes light and anti-Stokes light with wavelengths of 1660nm and 1450nm respectively, so that detection in different wavelength ranges can be performed.

When a light source of the grating demodulator 1 is turned on, the grating demodulator 1 can realize sensing of temperature and strain; in terms of the fiber grating technology, the fiber grating technology is wavelength division multiplexing, and the original resonant frequencies corresponding to a plurality of written FBG gratings in the optical fiber are different and are distributed between 1525nm and 1565 nm.

The detection principle and the structural design of the three detection devices are specifically described below.

First, regarding the fiber grating technology and the grating demodulator 1:

the strain sensing network of the fiber Bragg grating generally adopts a wavelength division multiplexing technology, and the principle of the strain sensing network is shown in fig. 2: the light from a light source (typically a continuous broadband light source) is transmitted through a coupler to an optical fiber on which a plurality of FBG sensors are distributed, each sensor having a different Bragg wavelength. After the broadband light passes through the FBGs, the transmitted light has a plurality of wave troughs on the spectrum, and the wave troughs correspond to the Bragg wavelengths of the FBGs respectively; the reflected light contains a plurality of peaks in the spectrum, also corresponding to the Bragg wavelengths of the respective FBGs. The spectrum of the reflected light passing through the coupler is detected by a wavelength signal demodulation device, so that the Bragg wavelength of the FBG can be obtained, and further the sensing signal of the FBG can be obtained. Wherein, FBG is inscribed in the multi-core optical fiber; it should be noted here that only the core (i.e. the first core a1) connected to the device of the grating demodulator 1 inscribes the grating FBG; after the grating demodulator 1 is externally connected with the multi-core fiber, the reflected light of the FBG can be used for sensing. The wavelength division multiplexing technique has an advantage in that a plurality of FBG sensors, which can measure a plurality of wavelengths at a time, can be compared with the time division multiplexing technique.

Based on the above demodulation principle, the grating demodulator 1 may have a plurality of implementation structures, specifically as follows:

(1) by adopting a spectrometer demodulation method, as shown in fig. 3, the grating demodulator 1 includes a first broadband light source 101, an optical circulator 102 and a spectrometer 103, which are connected in sequence, the optical circulator 102 is externally connected to the multi-core fiber 7 through a corresponding fiber interface, and the spectrometer 103 is connected to a common processor 5. The demodulation principle specifically comprises the following steps: after the continuous broadband light emitted by the first broadband light source 101 is transmitted to the fiber bragg grating FBG through the optical circulator 102, the reflected light passes through the optical circulator 102 and enters the spectrometer 103, and the offset of the wavelength is measured by the spectrometer 103, so that the processor 5 calculates the value of the physical quantity (temperature or strain) to be measured according to the wavelength change.

In order to ensure synchronous triggering of data acquisition, the spectrometer 103 is connected with the synchronous trigger circuit 4, and the synchronous trigger circuit 4 generates a pulse with a certain repetition frequency and sends a synchronous pulse to the spectrometer 103 to start data acquisition.

The spectrometer demodulation is the simplest and most direct demodulation method, and has the advantages of accurate detection, high sensitivity, convenient operation, high cost and large equipment volume. Therefore, the spectrometer demodulation method is not generally used in engineering environment, and is generally used as research in a laboratory.

(2) By using the edge filtering demodulation method, as shown in fig. 4, the grating demodulator 1 includes a second broadband light source 104, a first coupler 105, a first optical splitter 106, a first photodetector 107, an edge filter 108, a second photodetector 109, and a first data acquisition card 110, which are connected in sequence. The first coupler 105 is externally connected with the multi-core fiber 7 through a corresponding fiber interface, the first photodetector 107 is respectively connected with the first optical splitter 106 and the first data acquisition card 110, the second photodetector 109 is respectively connected with the edge filter 108 and the first data acquisition card 110, and the edge filter 108 is connected with the first optical splitter 106. The first data acquisition card 110 is embodied as a dual-channel data acquisition card and is connected to a common processor 5.

The demodulation principle specifically comprises the following steps: after the continuous broadband light emitted by the second broadband light source 104 is transmitted to the FBG through the first coupler 105, the reflected light passes through the first coupler 105 and enters the first optical splitter 106, and a part of the light is not attenuated, and is directly detected by the first photodetector 107 and then is subjected to data acquisition by the first data acquisition card 110; the other part of the light is attenuated after being filtered by the edge filter 108, and then is detected by the second photodetector 109 and then is subjected to data acquisition by the first data acquisition card 110. Therefore, the light intensity before and after the attenuation of the reflected light can be detected, the attenuation amount of the light intensity is determined, the offset of the wavelength is further obtained, and the processor 5 calculates the value of the physical quantity to be measured according to the wavelength change.

In order to ensure the synchronous triggering of data acquisition, the first data acquisition card 110 is connected to the synchronous trigger circuit 4, and the synchronous trigger circuit 4 generates a pulse with a certain repetition frequency, and sends a synchronous pulse to the first data acquisition card 110 to start data acquisition.

The edge filter demodulation method has the advantages that the signal processing is convenient and the price is low, but has the defect that the working area needs to be controlled, because the linear working area of the edge filter has a certain range, the Bragg condition needs to be specially set when the demodulation system is designed, and the central wavelength of the reflected light is in the linear working area of the edge filter.

(3) By adopting a tunable F-P filter demodulation method, as shown in fig. 5, the grating demodulator 1 includes a third broadband light source 111, a second coupler 112, an F-P tunable filter 113, a third photodetector 114, a second data acquisition card 115, an amplifier 116, a control system 117, and a signal generator 118, which are connected in sequence. The second coupler 112 is externally connected to the multi-core optical fiber 7 through a corresponding optical fiber interface, the amplifier 116 is respectively connected to the third photodetector 114 and the control system 117, the control system 117 is connected to the signal generator 118, and the signal generator 118 is connected to the F-P tunable filter 113, so as to load a scan voltage to the F-P tunable filter 113. The second data acquisition card 115 is connected to a common processor 5.

The demodulation principle specifically comprises the following steps: after the broadband light emitted from the third broadband light source 111 is transmitted to the FBG through the second coupler 112, the reflected light passes through the second coupler 112 and enters the F-P tunable filter 113, the F-P tunable filter 113 is loaded with a saw tooth scan voltage, and the center wavelength of the transmitted light of the F-P tunable filter 113 is back-scanned near the reflected wavelength. If the F-P tunable filter 113 just scans the reflection wavelength of the FBG at this time, since the reflection wavelengths of the F-P tunable filter 113 and the FBG are overlapped, the third photodetector 114 can detect the maximum intensity of the light intensity, and further obtain the offset of the wavelength, and the processor 5 calculates the value of the physical quantity to be measured according to the wavelength change.

In order to ensure the synchronous triggering of data acquisition, the second data acquisition card 115 is connected to the synchronous trigger circuit 4, and the synchronous trigger circuit 4 generates a pulse with a certain repetition frequency, and sends a synchronous pulse to the second data acquisition card 115 to start data acquisition.

The tunable F-P filter demodulation method has the advantages of wide demodulation wavelength range, high demodulation efficiency, small instrument and convenience in integration in a monitoring system, and is particularly suitable for a plurality of FBG detection systems (namely distributed fiber bragg grating sensing systems). The tunable F-P filter has the advantages that piezoelectric ceramics are adopted in the tunable F-P filter to control the cavity length of the F-P cavity and further control the transmission wavelength, so that the detection sensitivity can be influenced by the characteristics of the piezoelectric ceramics, such as temperature drift, zero drift and the like, the influence can be reduced by a certain external compensation measure, and the sensitivity of a detection system is improved.

(4) By adopting a tunable narrowband light source demodulation method, as shown in fig. 6, the grating demodulator 1 includes a tunable narrowband light source 119, a third coupler 120, and a digital oscilloscope 121, which are connected in sequence, where the tunable narrowband light source 119 is used to emit continuous narrowband light. The tunable narrow-band light source 119 is fixed on a lead zirconate titanate (PZT) piezoelectric ceramic (PZT) 122, and the PZT 122 is driven by a sawtooth wave or a sinusoidal voltage; the digital oscilloscope 121 is connected with the tunable narrow-band light source 119 and is also connected with a common processor 5; the third coupler 120 is externally connected to the multi-core fiber 7 through a corresponding fiber interface. Wherein an isolator 123 may also be disposed between the tunable narrowband optical source 119 and the third coupler 120.

The demodulation principle specifically comprises the following steps: the reflection spectrum of the photosensitive grating FBG is periodically scanned by said digital oscilloscope 121 with a narrow band spectrum of wavelengths. When the PZT 122 is driven by a sawtooth wave or a sinusoidal voltage, the spectrum of the tunable narrowband light source 119 changes within a certain range, and when the output wavelength of the tunable narrowband light source 119 is the same as the reflected wavelength of the sensing grating FBG, the signal intensity received by the digital oscilloscope 121 is the maximum; and then the offset of the FBG wavelength can be obtained through the tuning relation between the voltage and the wavelength of the PZT 122, and the processor 5 calculates the value of the physical quantity to be measured according to the wavelength change.

In order to ensure synchronous triggering of data acquisition, the digital oscilloscope 121 is connected to the synchronous trigger circuit 4, and the synchronous trigger circuit 4 generates a pulse with a certain repetition frequency and sends a synchronous pulse to the digital oscilloscope 121, so that the digital oscilloscope 121 starts data acquisition synchronously.

(5) And a matched grating filtering demodulation method is adopted. The matched grating filtering demodulation method is to use the wavelength of a known receiving grating to measure the wavelength of a sensing grating by a certain method, and the matched grating filtering demodulation method generally comprises two methods: the first mode is a reflection mode, namely, a sensing signal enters a matched grating through a sensing grating to detect the intensity of reflected light, and when a detector receives the maximum light intensity, the sensing grating is completely matched with the central wavelength of the matched grating; and the second mode is a transmission mode, which is similar to a reflection method for detecting the intensity of transmitted light, and when the detector receives the minimum light intensity, the central emission wavelength of the sensing grating can be obtained.

Second, regarding the raman optical time domain reflectometry technique and the raman thermometer 2:

referring to fig. 7, the raman thermometer 2 may generally include a pulse light source 201, a WDM coupler 202, a second optical splitter 203, a photo-detection module and a third data acquisition card 204, which are connected in sequence, wherein the photo-detection module includes a fourth photo-detector 205 and a fifth photo-detector 206 for detecting Stokes raman scattered light (Stokes light) and Anti-Stokes raman scattered light (Anti-Stokes light) reflected back from the optical fiber, respectively; the WDM coupler 202 is externally connected to the multicore fiber 7 through a corresponding fiber interface. The third data acquisition card 204 is a dual-channel data acquisition card and is connected to the common processor 5.

The demodulation principle specifically comprises the following steps: the optical pulse emitted by the pulsed light source 201 is coupled into a sensing optical fiber (i.e., a multi-core optical fiber in the embodiment of the present invention) through the WDM coupler 202 (bi-directional coupler), and interacts with molecules in an optical fiber medium during propagation to continuously generate back-raman scattered light (intensity of the scattered light is modulated by a temperature field along the optical fiber), the reflected back-raman scattered light is sent into the WDM coupler 202 for filtering, and then the separated Stokes scattered light and Anti-Stokes scattered light are respectively input into the fourth photodetector 205 and the fifth photodetector 206 through the second optical splitter 203 for photoelectric conversion, and a level signal is amplified into an effective collection range of the third data acquisition card 204. The third data acquisition card 204 acquires the scattering signals along the sensing optical fiber at a certain sampling frequency, the acquired data are sequentially stored in a designated memory or the processor 5, and the processor 5 calculates the temperature value to be measured according to the light intensity.

In order to ensure synchronous triggering of optical pulse and data acquisition, the pulse light source 201 and the third data acquisition card 204 are respectively connected with the synchronous trigger circuit 4, the synchronous trigger circuit 4 generates pulses with a certain repetition frequency, on one hand, the pulse light source 201 is modulated to generate narrow detection light pulses, and on the other hand, the synchronous pulses are sent to the third data acquisition card 204 to synchronously start data acquisition. After the process of acquiring temperature information is completed, the synchronous trigger circuit 4 controls the pulse light source 201 to emit the next detection pulse light. The system repeats the above process, and according to the system setting, the data in the memory or the processor 5 is subjected to accumulation average processing and the like, and finally the temperature measurement curve along the sensing optical fiber is obtained through temperature demodulation and graphic display.

Third, regarding the polarized light technique and the polarization analyzer 3:

referring to fig. 8, the polarization analyzer 3 includes a light source 301, a polarizer 302, an analyzer 303, a light detector 304 and a fourth data acquisition card 305, which are connected in sequence. The polarizer 302 and the analyzer 303 are respectively externally connected to the multi-core fiber 7 through corresponding fiber interfaces, wherein the polarizer 302 is externally connected to the front end of a first fiber core a1 in the multi-core fiber 7 through a first fiber interface b1, and the analyzer 303 is externally connected to the front end of a second fiber core a2 in the multi-core fiber 7 through a second fiber interface b 2.

The demodulation principle specifically comprises the following steps: the light source 301 emits a periodic light pulse signal, the light pulse signal is polarized by the polarizer 302 and then converted into linearly polarized light, the linearly polarized light enters the sensing fiber (i.e., the multi-core fiber 7 in the figure) and then enters the analyzer 303, the polarization information is converted into light intensity information, the signal is converted into an electrical signal through the optical detector 304, the electrical signal is collected and stored by the fourth data acquisition card 305, and the processor 5 performs further data processing.

In order to ensure the synchronous triggering of the optical pulse and the data acquisition, the light source 301 and the fourth data acquisition card 305 are respectively connected to the synchronous trigger circuit 4, the synchronous trigger circuit 4 generates a pulse with a certain repetition frequency, on one hand, the light source 301 is modulated to generate a detection optical pulse, and on the other hand, a synchronous pulse is sent to the fourth data acquisition card 305, so that the data acquisition is started synchronously.

The above-mentioned structures are designed for the grating demodulator 1, the raman thermometer 2 and the polarization analyzer 3, and other structures may be set as required during actual use, which is not repeated herein.

Example 2:

on the basis of the above embodiment 1, the embodiment of the present invention further integrates and simplifies the structures with the same function in the three detection devices, that is, the grating demodulator 1, the raman thermometer 2, and the polarization analyzer 3, and provides another multi-parameter optical fiber sensing apparatus based on a multi-core optical fiber, which has a simpler structure and a lower cost compared with the multi-parameter optical fiber sensing apparatus in the embodiment 1, and can realize the same function as the structure in the embodiment 1.

As shown in fig. 9, the multi-parameter optical fiber sensing instrument according to the embodiment of the present invention includes a raman light source 601, a polarization light source 602, a fiber grating light source 603, a polarizer 604, a coupler 605, a circulator 606, a beam splitter 607, an analyzer 608, a polarization light detector 609, a stokes light detector 610, an anti-stokes light detector 611, a grating demodulation device 612, an acquisition card 613, a synchronous trigger circuit 4, and a processor 5; among the three light sources, the signals to be detected generated after the emission of the raman light source 601 and the polarization light source 602 are distributed in different wave bands, and can be respectively detected after being demultiplexed by the wavelength division demultiplexing technology, and the time division multiplexing is performed between the fiber bragg grating light source 603 and the other two light sources.

The raman light source 601, the polarization light source 602, and the fiber grating light source 603 are respectively connected to the coupler 605, and the polarization light source 602 is connected to the coupler 605 through the polarizer 604. The coupler 605, the circulator 606, the analyzer 608 and the polarized light detector 609 are connected in sequence; the circulator 606 is further connected to the optical splitter 607, the optical splitter 607 is respectively connected to the grating demodulation device 612, the stokes photodetector 610 and the anti-stokes photodetector 611, the grating demodulation device 612, the stokes photodetector 610, the anti-stokes photodetector 611 and the polarization photodetector 609 are respectively connected to the acquisition card 613, and the acquisition card 613 is connected to the processor 5. The circulator is externally connected with the front end of a first fiber core a1 in the multi-core optical fiber through a first optical fiber interface b1, the analyzer is externally connected with the front end of a second fiber core a2 in the multi-core optical fiber through a second optical fiber interface b2, and the tail end of the first fiber core a1 is connected with the tail end of the second fiber core a 2.

The synchronous trigger circuit 4 is connected to the raman light source 601, the polarized light source 602 and the acquisition card 613 through electrical signal lines, and is configured to trigger the raman light source 601 and the polarized light source 602 to transmit light pulses, and simultaneously trigger the acquisition card 613 to perform data acquisition, so as to maintain synchronization between light pulse transmission and data acquisition. The most common use of the synchronous trigger circuit 4 is to use a 555 timer, but in practical use, any circuit capable of stably outputting a periodic pulse electrical signal may be used, and the present invention is not limited thereto.

The processor 5 is connected to the acquisition card 613 through an electrical signal line, and is configured to perform comprehensive analysis processing on multiple items of data acquired by the acquisition card 613, determine whether there is disturbance on the entire optical fiber link, and obtain a current temperature value, a current strain value, and a current vibration frequency value of the multi-core optical fiber. The current temperature value and the strain value of the multi-core optical fiber 7 can be obtained by collecting and analyzing the data detected by the grating demodulation device 612, the stokes optical detector 610 and the anti-stokes optical detector 611; by collecting and analyzing the data detected by the grating demodulation device 612 and the polarized light detector 609, whether the whole optical fiber link has disturbance can be judged, and the current vibration frequency value of the multi-core optical fiber 7 can be obtained.

The multi-parameter optical fiber sensing instrument provided by the invention further integrates and simplifies the grating demodulator, the Raman temperature measuring instrument and the polarization analyzer, can realize simultaneous sensing of strain, temperature and vibration of the optical fiber by utilizing the fiber grating technology, the Raman optical time domain reflection technology and the polarized light technology, can reduce the number of fiber cores required by detection in the multi-core optical fiber by reasonably adopting wavelength division multiplexing and time division multiplexing, can meet the requirement of quasi-synchronous acquisition of three detection devices by only needing any two fiber cores in the multi-core optical fiber, and is more convenient to connect and set.

With the above structure, the control process of time division multiplexing and wavelength division multiplexing is specifically as follows:

the time division multiplexing can be specifically controlled by the switching time of the light sources corresponding to different technologies, for example, the polarized light source 602 and the raman light source 601 are turned on at time T1, the fiber grating light source 603 is turned off, the fiber grating light source 603 is turned on at time T2, and the polarized light source 602 and the raman light source 601 are turned off, so that the time division multiplexing of the fiber grating technology and the other two technologies is realized.

When the polarized light source 602 and the raman light source 601 are turned on, on one hand, a light pulse generated by the raman light source 601 sequentially passes through the coupler 605 and the circulator 606 and then is coupled into a sensing fiber (i.e., a multi-core fiber in the embodiment of the present invention), and continuously generates back raman scattering light in the propagation process, the back raman scattering light reflected back reaches the optical splitter 607 after passing through the circulator 606, and the separated Stokes scattering light and Anti-Stokes scattering light are respectively input into the Stokes optical detector 610 and the Anti-Stokes optical detector 611 for photoelectric conversion, and finally data acquisition is performed by the acquisition card 613. On the other hand, the light pulse generated by the polarized light source 602 is polarized by the polarizer 604 and then converted into linearly polarized light, the linearly polarized light enters the sensing optical fiber through the circulator 606 and then enters the analyzer 608, the polarization information is converted into light intensity information, the light intensity information is converted into an electrical signal through the polarized light detector 609, and finally data acquisition is performed by the acquisition card 613.

In the above process, wavelength division multiplexing between raman detection and polarization detection specifically includes: the forward light is detected by the polarized light technology, the wavelength of the forward light is consistent with the wavelength of the light source and is 1550nm waveband; the Raman temperature measurement technology detects Stokes light and anti-Stokes light which are respectively detected by the stokes photodetector 610 and the anti-Stokes photodetector 611, and the detected wavelengths are respectively 1660nm waveband and 1450nm waveband, so that detection in different wavelength ranges can be performed.

When the fiber grating light source 603 is turned on, the continuous light emitted by the fiber grating light source 603 sequentially passes through the coupler 605 and the circulator 606 and enters the sensing fiber, the reflected light reaches the optical splitter 607 through the circulator 606, the separated light is subjected to signal demodulation of wavelength by the grating demodulation device 612, and finally data acquisition is performed by the acquisition card 613. In terms of the fiber grating technology, the fiber grating technology is wavelength division multiplexing, and the original resonant frequencies corresponding to a plurality of written FBG gratings in the optical fiber are different and are distributed between 1525nm and 1565 nm.

The specific structural composition of the grating demodulation device 612 can refer to embodiment 1, and when a spectrometer demodulation method is adopted, the grating demodulation device 612 is specifically the spectrometer 103; when the edge filtering demodulation method is adopted, the grating demodulation device 612 specifically includes a first photodetector 107, an edge filter 108, and a second photodetector 109; when a tunable F-P filter demodulation method is adopted, the grating demodulation device 612 specifically includes an F-P tunable filter 113, a third photodetector 114, an amplifier 116, a control system 117, and a signal generator 118; when a tunable narrowband light source demodulation method is adopted, the grating demodulation device 612 is specifically a digital oscilloscope 121. For each structural composition, the specific optical path structure and the detection principle can refer to embodiment 1, which is not described herein again.

Further referring to fig. 10, since the switching time of the raman light source 601 and the polarization light source 602 are the same and the emission wavelength is the same, the two light sources can be combined and referred to as a raman/polarization light source. In this structure, the raman/polarization light source is connected to the coupler 605 through the polarizer 604, and the synchronous trigger circuit 4 is connected to the raman/polarization light source and the acquisition card 613 through electrical signal lines, respectively, so as to maintain the synchronization of the emission of the optical pulses and the data acquisition. The rest of the structure is still the same as the structure shown in fig. 9, and is not described herein.

Example 3:

the embodiment of the invention provides a multi-parameter optical fiber sensing method based on a multi-core optical fiber, which can be completed by adopting the multi-parameter optical fiber sensing instrument in the embodiment 1 or the embodiment 2. Before the multi-parameter optical fiber sensing method of the embodiment of the invention is introduced, firstly, the calculation formula and the derivation of each sensing technology are introduced:

raman optical time domain reflection technology (Raman temperature measurement technology)

For the Raman optical time domain reflection technology, the temperature parameter is mainly responded. The anti-stokes scattered light is sensitive to temperature, and the intensity of the anti-stokes scattered light is modulated by temperature; the intensity of stokes scattered light also has a certain relation with temperature, but is slightly influenced by the temperature. Therefore, in the measurement, it is necessary to collect the intensities of the stokes scattered light and the anti-stokes scattered light, demodulate the anti-stokes light as the signal light and the stokes light as the reference light. At any temperature T, the relationship between the signal light and the reference light is:

by T₀As reference temperature, then at reference temperature T₀The lower signal light and the reference light have the following relationship:

dividing the formula (1) and the formula (2) to obtain the temperature T of the optical fiber at any point, which satisfies the following relation:

wherein psi_sIs the luminous flux, ψ, corresponding to the Stokes scattered light (i.e. reference light) in the optical fiber at temperature_asThe luminous flux of anti-stokes scattered light (namely signal light) in the optical fiber at the corresponding temperature can be obtained by actual measurement through a Raman optical time domain reflection technology. k is Boltzmann constant, h is Planckian constant, and Δ v is phonon frequency in the optical fiber. v. of_asAnd v_sAnti-stokes raman scattered photon frequency and stokes raman scattered photon frequency respectively; alpha is alpha_asAnd alpha_sOptical fiber transmission losses of the anti-stokes raman scattered light and the stokes raman scattered light, respectively; beta is a_asAnd beta_sWith anti-stokes and stokes raman scattering, respectivelyAnd L is the position of the point to be measured in the optical fiber, specifically the distance from the point to be measured to the front end of the optical fiber. The raman formula is obtained from equation (3) as follows:

wherein, mu_TIs a Raman temperature coefficient, and

in the case of temperature demodulation using Raman equation,. mu._TThe details may be determined by pre-fitting.

Second, optical fiber grating technology

For fiber grating technology, the response to temperature and strain parameters is dominant. The wavelength matching condition of the optical fiber Bragg grating is lambda_B＝2n_effLambda, which is a basic formula of the fiber grating and is the basis for carrying out sensing characteristic research; wherein λ is_BIs the center wavelength, n, of the Bragg grating_effAnd lambda is the effective refractive index of the fiber core, and lambda is the grating period. From this equation, the physical quantities that enable the effective refractive index or period of the grating to change affect its center wavelength, and stress and temperature are the most significant physical quantities that change the wavelength of the fiber Bragg grating. Before the calculation formula is given, it should be noted that research shows that the thermal effect generated by temperature and the force effect generated by strain can be considered to be relatively independent. From the above basic formula, the induced wavelength change is as follows:

Δλ_B＝2Λ·Δn_eff+2n_eff·ΔΛ (5)

assuming that the temperature is unchanged, the grating is only under the action of strain, and the central wavelength change Delta lambda of the fiber Bragg grating caused by strain is considered under the action of uniform axial stress_BAnd the strain epsilon satisfy the following relation:

modified from the above equation (6):

Δλ_B＝λ_B(1-P_e)ε＝α_εε (7)

wherein, P_eIs an effective elasto-optical coefficient, and

v is the cedar ratio of the core material; p₁₁And P₁₂The elastic-optical coefficient is any two values, related to the core material, and refers to a matrix containing many values, and P₁₁And P₁₂Is a fraction of the elasto-optic coefficient. Alpha is alpha_εIs the strain coefficient of the grating, and alpha_ε＝λ_B(1-P_e)。

From the above equation, it can be seen that when the grating material is determined, the strain ε and the change in the center wavelength Δ λ_BThe linear relation is formed, when the technology is actually used for strain measurement, only the Delta lambda needs to be determined through pre-fitting_BRelating to e, i.e. determining the strain coefficient a of the grating_ε. It should be noted that the above linear relationship should be applicable when the strain is small, since taylor expansion is performed and high-order terms are omitted in the formula derivation process. In the embodiment of the present invention, it is preferable that the corresponding linear relationship interval is obtained by calculation according to the measurement result, and the linear relationship interval may confirm the interval range by fitting a straight line, which is not described herein again. Therefore, in a specific application scene, the linear fitting interval and the fitting relation provided by the invention can directly feed back the stress value according to the linear relation when a specific detection value falls into the corresponding linear relation interval, so that the calculation and response efficiency of the whole system is improved. If the linear relation is exceeded, calculation is performed according to a common formula, which is the meaning of the linear relation interval provided by the embodiment of the invention. The "common formula" specifically refers to a formula before non-taylor expansion, and the calculation formula in the embodiment of the present invention is a formula for performing post-taylor expansion optimization.

Assuming constant strain, the grating is only affected by temperature, which is affected by thermo-optic and thermal expansion effects, respectivelyEffective refractive index and grating period, temperature induced change Δ λ in the center wavelength of a fiber Bragg grating_BAnd the temperature change amount delta T satisfy the following relation:

modified from the above equation (8):

Δλ_B＝λ_B(α+ξ)ΔT＝α_TΔT (9)

wherein α is a thermal expansion coefficient of the fiber grating, and

xi is the thermo-optic coefficient of the fiber grating, and

α_Tis the temperature coefficient of the grating, and alpha_T＝λ_B(α+ξ)。

As can be seen from the above formula, the temperature variation Δ T and the central wavelength variation Δ λ_BIn a linear relationship and similar to strain, when the technique is actually used for temperature measurement, only the delta lambda needs to be determined through pre-fitting_BRelating to Δ T, i.e. determining the temperature coefficient α of the grating_T。

The above description has been made assuming temperature invariance and analyzing temperature assuming strain invariance, respectively, and temperature and strain can be regarded as independent and linearly superposed. Therefore, combining equation (7) and equation (9), the central wavelength changes Δ λ when analyzing temperature and strain simultaneously_BThe strain epsilon and the temperature change quantity delta T satisfy the following relations:

Δλ_B＝α_εε+α_TΔT (10)

the above formula (10) is a grating formula to be used subsequently.

As shown in fig. 11, the multi-parameter optical fiber sensing method provided in the embodiment of the present invention mainly includes:

and 10, turning on the polarized light source and the Raman light source at the time of T1, turning off the fiber bragg grating light source, so as to perform sensing measurement on the first fiber core a1 in the multi-core fiber by using a Raman optical time domain reflection technology, and perform sensing measurement on the first fiber core a1 and the second fiber core a2 in the multi-core fiber by using a polarized light technology.

By combining the embodiments 1 and 2, the fiber grating technology mainly realizes sensing of temperature and strain, the raman optical time domain reflection technology mainly realizes quantitative sensing analysis of temperature, and the polarized light technology mainly realizes qualitative sensing analysis of strain and vibration. Synchronous sensing of different parameters is achieved through triggering of the synchronous trigger circuit 4, and therefore synchronization of light pulse emission and data acquisition is kept.

The fiber grating technology and the other two detection technologies are time division multiplexing, so that the polarized light source and the Raman light source can be started first, and the fiber grating light source can be closed, so that the Raman optical time domain reflection technology and the polarized light technology can be used for sensing measurement first. Wherein, after the Raman optical time domain reflection technology is used for sensing and measuring the first fiber core a1 in the multi-core optical fiber, the luminous flux psi of Stokes scattered light in the multi-core optical fiber can be obtained_s(T) and anti-Stokes scattered light luminous flux ψ_as(T); after the first fiber core a1 and the second fiber core a2 in the multi-core fiber are subjected to sensing measurement by utilizing a polarized light technology, the change condition of the light intensity in the multi-core fiber can be obtained, and the vibration frequency is extracted. In the process, wavelength division multiplexing is adopted between the Raman optical time domain reflection technology and the polarized light technology, wherein forward light is detected by the polarized light technology, the wavelength of the forward light is consistent with the wavelength of a light source and is 1550nm waveband; the Raman temperature measurement technology detects Stokes light and anti-Stokes light, and the wavelengths are respectively 1660nm waveband and 1450nm waveband.

And step 20, turning on the fiber grating light source at the time of T2, and turning off the polarized light source and the Raman light source so as to perform sensing measurement on the first fiber core a1 in the multi-core optical fiber by using a grating technology.

The time division multiplexing is adopted between the fiber grating technology and the other two detection technologies, the Raman optical time domain reflection technology and the polarized light technology are firstly utilized for sensing measurement, and then the polarized light source and the Raman light are turned offAnd the fiber grating light source is started, so that the sensing of temperature and strain can be realized by continuously utilizing the fiber grating technology. Wherein, after the first fiber core a1 in the multi-core fiber is sensed and measured by the grating technology, the wavelength variation delta lambda of the fiber Bragg grating in the multi-core fiber can be obtained_B. Thereafter, the above steps 10 and 20 are repeatedly executed in a loop with T1+ T2 as one period.

And step 30, comprehensively processing the data acquired by the Raman optical time domain reflection technology, the polarized light technology and the fiber bragg grating technology to determine whether the whole optical fiber link has vibration or strain, and obtaining the current temperature value, strain value and vibration frequency value of the multi-core optical fiber.

The method comprises the following steps of comprehensively processing data collected by a fiber grating technology and a Raman optical time domain reflection technology to obtain a temperature value and a strain value in the current environmental parameters of the multi-core optical fiber; the data collected by the fiber grating technology and the polarized light technology are comprehensively processed, whether the whole optical fiber link has vibration or strain can be determined, and the vibration frequency value in the current environment parameters of the multi-core optical fiber is obtained.

On the first hand, the temperature value and the strain value in the current environmental parameter of the multi-core optical fiber can be obtained by comprehensively processing the data collected by the fiber grating technology and the raman optical time domain reflection technology, and the specific implementation process is as follows:

first, a quantitative analysis of temperature is achieved by Raman time domain reflectometry, i.e. psi detected from Raman optical time domain reflectometry_s(T) and psi_asAnd (T), demodulating the current temperature value T of the multi-core optical fiber by using a Raman formula. The method specifically comprises the following steps: combined with Raman formula

Presetting a reference temperature T₀Corresponding psi_as(T₀) And psi_s(T₀) Are all known, the Raman temperature coefficient μ_TCalibrating in advance; psi at temperature T_as(T) and psi_s(T) has been collected, so the only unknown T can be solved by using the Raman formula.

Then, by RamanThe time domain reflection technology carries out temperature compensation on the fiber grating technology to realize quantitative analysis of strain, namely temperature value T demodulated based on Raman formula and delta lambda detected by the fiber grating technology_BAnd demodulating the current strain value epsilon of the multi-core fiber by using a grating formula. The method specifically comprises the following steps: the temperature variation Δ T can be determined based on the temperature value T obtained above, and then combined with the grating formula Δ λ_B＝α_εε+α_TΔ T, grating strain coefficient α_εAnd temperature coefficient of grating alpha_TAre all calibrated in advance, Δ λ_BThe unique unknown epsilon can be solved by the raster formula after the acquisition.

The process of pre-calibrating the coefficients in the raman formula and the grating formula specifically comprises the following steps:

heating the multi-core fiber to different temperatures for multiple times, and respectively measuring the corresponding psi_sAnd psi_asDetermining the Raman temperature coefficient mu after multiple fitting according to the Raman formula (4)_T；

Heating the multi-core fiber to different temperatures for multiple times (strain needs to be kept unchanged), and respectively measuring the corresponding wavelength variation delta lambda_BDetermining the grating temperature coefficient alpha in the grating formula after fitting for multiple times according to the formula (9)_TAnd the temperature range to which the grating formula is applicable;

applying different strains to the multi-core fiber for multiple times (temperature needs to be kept unchanged), and respectively measuring corresponding wavelength variation delta lambda_BDetermining the grating strain coefficient alpha in the grating formula after multiple fitting according to the formula (7)_εAnd the strain range for which the grating formula is applicable.

In a second aspect, the data collected by the fiber grating technology and the polarized light technology are processed comprehensively to determine whether the whole optical fiber link has vibration or strain, and obtain the current vibration frequency value of the multi-core fiber, specifically as follows:

for the magnitude of the strain or the vibration intensity, the polarized light technology can only realize qualitative analysis, so that the result of the qualitative analysis of the vibration by the polarized light technology is used as a supplement of the point type vibration measurement by the fiber grating technology, and whether the whole optical fiber link has the events such as vibration or strain can be further determined.

In addition, the polarized light technology can also realize the extraction of the vibration frequency, and in short, the vibration frequency of the whole optical fiber can be measured. And when the vibration continuously occurs and the vibration has a periodic relationship, the frequency extraction is not considered, and when the vibration continuously occurs and the vibration has a periodic relationship, the current vibration frequency value of the multi-core optical fiber can be calculated by using the pulse change times in a certain time interval detected by the polarized light technology. When the vibration is a single frequency, the pulse change is measured n times in the time interval t, and the vibration frequency f is equal to n/t. The multi-frequency condition is essentially the superposition of a plurality of single-frequency signals, and the signal frequency can be obtained only through Fourier transform.

In the multi-parameter optical fiber sensing method provided by the invention, the fiber grating technology, the Raman optical time domain reflectometer technology and the polarized light technology are utilized, and a multi-path parallel optical link of a multi-core optical fiber is matched to synchronously measure two fiber cores in the multi-core optical fiber, so that strain, temperature and vibration of the optical fiber can be simultaneously sensed; the optical fiber grating technology and the Raman optical time domain reflectometer technology are combined, so that the temperature and the strain can be synchronously measured and effectively distinguished, quantitative analysis is carried out, the state of the whole optical fiber can be effectively obtained through the combination of the optical fiber grating technology and the polarized light technology, and the vibration frequency is extracted.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims (10)

1. A multi-parameter optical fiber sensing instrument based on a multi-core optical fiber is characterized by comprising a grating demodulator, a Raman temperature measuring instrument, a polarization analyzer and a processor; in three devices, namely a grating demodulator, a Raman thermometer and a polarization analyzer, wavelength division multiplexing is performed between the Raman thermometer and the polarization analyzer, and time division multiplexing is performed between the grating demodulator and the other two devices;

the grating demodulator, the Raman thermometer and the polarization analyzer are externally connected with the front end of a first fiber core (a1) in the multi-core optical fiber through a first optical fiber interface (b1), the polarization analyzer is also externally connected with the front end of a second fiber core (a2) in the multi-core optical fiber through a second optical fiber interface (b2), and the tail end of the first fiber core (a1) is connected with the tail end of the second fiber core (a 2);

the processor is respectively connected with the grating demodulator, the Raman temperature measuring instrument and the polarization analyzer and is used for comprehensively analyzing and processing data acquired by the three devices, judging whether disturbance exists on the whole optical fiber link and obtaining the current temperature value, the strain value and the vibration frequency value of the multi-core optical fiber.

2. The multi-parameter optical fiber sensing instrument based on the multi-core optical fiber as claimed in claim 1, further comprising a synchronous trigger circuit, wherein the synchronous trigger circuit is respectively connected to the grating demodulator, the raman thermometer and the polarization analyzer, and is configured to trigger a device at a specific time to synchronously transmit optical pulses and collect data.

3. A multi-parameter optical fiber sensing instrument based on multi-core optical fibers is characterized by comprising a Raman light source, a polarization light source, an optical fiber grating light source, a polarizer, a coupler, a circulator, a beam splitter, an analyzer, a polarization light detector, a stokes light detector, an anti-stokes light detector, a grating demodulation device, an acquisition card and a processor; among the three light sources, the signals to be detected generated after the emission of the Raman light source and the polarization light source are distributed in different wave bands, the signals are respectively detected after the demultiplexing by the wavelength division demultiplexing technology, and the time division multiplexing is performed between the fiber bragg grating light source and the other two light sources;

the Raman light source, the polarization light source and the fiber grating light source are respectively connected with the coupler, and the coupler, the circulator, the analyzer and the polarization light detector are sequentially connected; the circulator is also connected with the optical splitter, the optical splitter is respectively connected with the grating demodulation device, the stokes photodetector and the anti-stokes photodetector, the grating demodulation device, the stokes photodetector, the anti-stokes photodetector and the polarized photodetector are respectively connected with the acquisition card, and the acquisition card is connected with the processor;

the circulator is externally connected with the front end of a first fiber core (a1) in the multi-core optical fiber through a first optical fiber interface (b1), the analyzer is externally connected with the front end of a second fiber core (a2) in the multi-core optical fiber through a second optical fiber interface (b2), and the tail end of the first fiber core (a1) is connected with the tail end of the second fiber core (a 2);

the processor is used for carrying out comprehensive analysis processing on the data acquired by the acquisition card, judging whether the whole optical fiber link is disturbed or not, and obtaining the current temperature value, strain value and vibration frequency value of the multi-core optical fiber.

4. The multi-parameter optical fiber sensing instrument as claimed in claim 3, wherein the multi-parameter optical fiber sensing instrument further comprises a synchronous trigger circuit connected to the Raman light source, the polarized light source and the acquisition card respectively, for triggering the Raman light source and the polarized light source to emit light pulses and triggering the acquisition card to acquire data, so as to keep the light pulses emitted and the data acquisition synchronized.

5. A multi-parameter optical fiber sensing method based on a multi-core optical fiber is characterized by comprising the following steps:

turning on a polarized light source and a Raman light source at the time of T1, turning off a fiber grating light source so as to perform sensing measurement on a first fiber core (a1) in the multi-core fiber by using a Raman optical time domain reflection technology, and performing sensing measurement on the first fiber core (a1) and a second fiber core (a2) in the multi-core fiber by using a polarized light technology;

turning on a fiber grating light source at time T2, turning off a polarized light source and a Raman light source so as to perform sensing measurement on a first fiber core (a1) in the multi-core optical fiber by using a grating technology;

and comprehensively processing data acquired by a Raman optical time domain reflection technology, a polarized light technology and a fiber grating technology, determining whether the whole optical fiber link has vibration or strain, and obtaining the current temperature value, strain value and vibration frequency value of the multi-core optical fiber.

6. The multi-parameter optical fiber sensing method based on multi-core optical fiber as claimed in claim 5, wherein the wavelength variation Δ λ of the fiber Bragg grating in the multi-core optical fiber is obtained by performing sensing measurement on the first fiber core (a1) in the multi-core optical fiber by using a grating technique_B；

After the first fiber core (a1) in the multi-core optical fiber is subjected to sensing measurement by using a Raman optical time domain reflection technology, the luminous flux psi of Stokes scattering light in the multi-core optical fiber is obtained_s(T) and anti-Stokes scattered light luminous flux ψ_as(T)；

After the first fiber core (a1) and the second fiber core (a2) in the multi-core fiber are subjected to sensing measurement by utilizing a polarized light technology, the change condition of the light intensity in the multi-core fiber is obtained, and the vibration frequency is extracted.

7. The multi-parameter optical fiber sensing method based on the multi-core optical fiber as claimed in claim 6, wherein the step of comprehensively processing the data collected by the raman optical time domain reflection technology, the polarization technology and the fiber grating technology to determine whether the whole optical fiber link has vibration or strain and obtain the current temperature value, strain value and vibration frequency value of the multi-core optical fiber specifically comprises the steps of:

comprehensively processing data acquired by a fiber grating technology and a Raman optical time domain reflection technology to obtain a temperature value and a strain value in the current environment parameter of the multi-core fiber;

and comprehensively processing data acquired by the fiber bragg grating technology and the polarized light technology, determining whether the whole optical fiber link has vibration or strain, and obtaining a vibration frequency value in the current environment parameters of the multi-core optical fiber.

8. The multi-parameter optical fiber sensing method based on the multi-core optical fiber as claimed in claim 7, wherein the data collected by the fiber grating technology and the raman optical time domain reflectometry technology are processed comprehensively to obtain the temperature value and the strain value in the current environmental parameter of the multi-core optical fiber, and specifically comprises:

psi detected from Raman optical time domain reflectometry_s(T) and psi_as(T), demodulating a temperature value T in the current environment parameters of the multi-core optical fiber by using a Raman formula;

temperature value T demodulated based on Raman formula and delta lambda detected by fiber grating technology_BAnd demodulating a strain value epsilon in the current environment parameters of the multi-core optical fiber by using a grating formula.

9. The multi-parameter optical fiber sensing method based on multi-core optical fibers as claimed in claim 8, wherein the raman formula is specifically:

wherein, T₀For reference temperature, #_sFor the luminous flux of Stokes' scattered light in the fibre at the corresponding temperature,. psi_asThe luminous flux of the anti-stokes scattered light in the optical fiber at the corresponding temperature; mu.s_TIs a Raman temperature coefficient and is determined by pre-fitting;

the grating formula is specifically as follows:

Δλ_B＝α_εε+α_TΔT

wherein alpha is_εIs the strain coefficient of the grating, alpha_TThe grating temperature coefficients are determined by pre-fitting.

10. The multi-parameter optical fiber sensing method based on multi-core optical fibers as claimed in claim 7, wherein the data collected by the fiber grating technology and the polarized light technology are processed comprehensively to determine whether the whole optical fiber link has vibration or strain, and obtain the vibration frequency value of the multi-core optical fiber in the current environmental parameters, specifically:

the vibration result of the qualitative analysis of the polarized light technology is used as the supplement of the point type vibration measurement of the fiber grating technology to determine whether the whole optical fiber link has vibration or strain;

when vibration continuously occurs and the vibration has a periodic relation, the current vibration frequency value of the multi-core optical fiber is calculated by using the pulse change times in a certain time interval detected by the polarized light technology.

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