CN109405859B - Multi-path optical fiber current sensor based on wavelength division multiplexing and control method and system thereof - Google Patents
Multi-path optical fiber current sensor based on wavelength division multiplexing and control method and system thereof Download PDFInfo
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- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35383—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using multiple sensor devices using multiplexing techniques
- G01D5/35387—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using multiple sensor devices using multiplexing techniques using wavelength division multiplexing
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Abstract
The invention provides a multiplexing optical fiber current sensor based on wavelength division multiplexing and a control method and a system thereof, wherein a polarized light generating device outputs m paths of linearly polarized light, and each path of linearly polarized light enters a sensing branch; and reflecting the light beam by adopting a reflection type fiber bragg grating in each sensing branch. The reflected light output by each sensing branch may interfere in the polarized light generating device before being transmitted to the optical fiber filter. The optical fiber filters can conduct interference light corresponding to different sensing branches according to a set sequence, the photoelectric detectors convert interference light intensity corresponding to different sensing branches into electric signals, and current values detected in the corresponding sensing branches can be reversely pushed out according to the electric signals detected by the photoelectric detectors. According to the scheme provided by the invention, the same set of optical fiber filter and the photoelectric detector are connected with a plurality of sensing branches based on the wavelength division multiplexing technology, so that currents at different measuring points can be accurately measured, and the economic cost of the optical fiber current sensor is greatly saved.
Description
Technical Field
The invention relates to the technical field of optical fiber current sensing, in particular to a multichannel optical fiber current sensor based on wavelength division multiplexing and a control method and a control system thereof.
Background
The fiber optic current sensor is typically comprised of a collection module and a fiber optic sensing loop, and only one fiber optic sensing loop can be connected to one collection module. The optical fiber current sensor adopting the digital closed loop technology has the characteristics that the eigenfrequency is up to hundreds of kHz, the sampling rate is also in the order of kHz, for partial application occasions, a plurality of current measuring points are often required to be monitored, compared with the signal modulation frequency of the optical fiber current sensor, the current signal to be measured is equivalent to a slow variable or direct current, the requirement on the response speed of measurement is not high, even the requirement on the refresh time of output data is sometimes only in the order of seconds, therefore, the multiplexing optical fiber current sensor structure can be realized by the technical advantage of the optical fiber current sensor, different optical fiber sensing rings are connected by using the same acquisition module, and the scanning measurement on a plurality of current measuring points is realized simultaneously by using the multiplexing technology.
Currently existing multiplexing schemes include space division multiplexing and time division multiplexing. The optical switch is used for connecting a set of acquisition modules with a plurality of optical fiber sensing rings, when the optical switch is switched between different channels, namely the optical fiber sensing rings are connected to different current measuring points, so that multi-path measurement is realized, and because each optical fiber sensing ring has inherent measurement errors, in order to ensure the measurement accuracy of the system, an essential state monitoring element, such as a temperature sensor and the like, is added in the multi-path measuring points in actual use for carrying out online compensation on the measurement errors; the latter is to connect a collection module with a plurality of optical fiber sensing rings through a broadband optical fiber coupler, and add optical fiber delay rings with different lengths into the input optical cable of each optical fiber sensing ring, so the time of the return optical signals of different optical fiber sensing rings is different, the current information returned in each sensing ring can be demodulated by a time division multiplexing method, the scheme increases the cost required for the polarization maintaining optical fiber, the cost of the sensor is increased continuously along with the increase of multiplexing channels, and the scheme cost for carrying out state monitoring on multiple measuring points is also increased.
Disclosure of Invention
The invention aims to provide a multiplexing optical fiber current sensor based on wavelength division multiplexing and a control method and a system thereof, which are used for solving the technical problems of complex structure and high cost when a multiplexing technology is adopted to realize measurement of a plurality of current detection points in the prior art.
In order to solve the problems, the invention provides a multiplexing optical fiber current sensor based on wavelength division multiplexing, which comprises m sensing branches, a polarized light generating device, an optical fiber filter and a photoelectric detector:
the sensing branch comprises an optical fiber ring, an optical fiber wave plate and a reflection type optical fiber grating, wherein the optical fiber wave plate and the reflection type optical fiber grating are arranged at two ends of the optical fiber ring; the inside of the optical fiber ring is penetrated by an electrified conductor; wherein the reflection fiber gratings in different sensing branches are used for reflecting light beams with different wavelengths;
The polarized light generating device outputs m paths of linearly polarized light, and each path of linearly polarized light enters one sensing branch; each path of linearly polarized light comprises two beams of linearly polarized light with mutually perpendicular polarization directions;
In each sensing branch, the linearly polarized light is obtained after being reflected by the reflection type fiber bragg grating after passing through the fiber wave plate and the fiber ring, and the reflected light is output after passing through the fiber ring and the fiber wave plate; the wavelength of the reflected light corresponds to the reflection wavelength of the reflection type fiber grating, the reflected light comprises two linearly polarized light with mutually perpendicular polarization directions and a phase difference, and the phase difference is generated according to the current in the electrified conductor;
The linearly polarized light generating device receives the reflected light output by each sensing branch; two beams of linearly polarized light in each reflected light interfere in the linearly polarized light generating device, and interference light obtained after interference of different reflected light corresponds to different wavelengths;
The optical fiber filter is provided with a plurality of optical channels, and gating wavelengths of different optical channels correspond to interference lights of different sensing branches; the optical fiber filter receives all interference light output by the linearly polarized light generating device, and sequentially conducts all light channels according to a set sequence to output interference light of a corresponding sensing branch;
The photoelectric detector detects the light intensity of the interference light output by the optical fiber filter, and obtains an electric signal corresponding to the light intensity, wherein the electric signal is used for obtaining the current value of the electrified conductor in the corresponding sensing branch.
Optionally, in the above-mentioned multiplexing optical fiber current sensor based on wavelength division multiplexing, the difference Δλ of the reflection wavelengths of the reflection optical fiber gratings in any two sensing branches is greater than Δλ max; wherein Δλ max＝MAX[Δλ1,Δλ2,……Δλm],Δλi is the wavelength drift range of the reflective fiber grating in the ith sensing branch when the temperature changes.
Optionally, in the above wavelength division multiplexing-based multi-path optical fiber current sensor, the polarized light generating device includes a light source, an optical transmission device, a polarizing and coupling device, a polarization-preserving delay optical fiber loop and a beam splitter, wherein:
The first input end of the light transmission device is connected with the output end of the light source, the first output end of the light transmission device is connected with the first input end of the polarization and coupling device, and the light signal emitted by the light source is transmitted to the polarization and coupling device through the light transmission device;
The first output end of the polarization and coupling device is connected with the first input end of the polarization-preserving delay optical fiber ring, and the first output end of the polarization-preserving delay optical fiber ring is connected with the first input end of the beam splitter; the polarization and coupling device converts the optical signal into two linearly polarized light beams with the polarization directions perpendicular to each other and then transmits the two linearly polarized light beams to the beam splitter through the polarization-preserving delay optical fiber ring;
The beam splitter is provided with a second output end, m first output ends and m second input ends, each first output end of the beam splitter is connected with the input end of one sensing branch, and each second input end of the beam splitter is connected with the output end of one sensing branch and the second output end of the beam splitter is connected with the second input end of the polarization-maintaining delay optical fiber ring; the beam splitter divides two linearly polarized lights with mutually perpendicular polarization directions into m paths of linearly polarized lights, and each path of linearly polarized light is output through the polarization-preserving delay optical fiber ring after reflected light obtained by the sensing branch is returned to the beam splitter;
The second input end of the polarization and coupling device is connected with the second output end of the polarization-preserving delay optical fiber ring, receives the reflected light output by the beam splitter, and generates interference in the polarization and coupling device to obtain interference light and then outputs the interference light;
The second input end of the optical transmission device is connected with the second output end of the polarization and coupling device, and the second output end of the optical transmission device is connected with the input end of the optical fiber filter; the optical transmission device receives the interference light output by the polarizing and coupling device and outputs the interference light to the optical fiber filter.
Optionally, in the above multiplexing optical fiber current sensor based on wavelength division multiplexing, the optical transmission device is an optical fiber circulator; or alternatively, the first and second heat exchangers may be,
The optical transmission device comprises an optical fiber isolator and an optical fiber coupler connected with the optical fiber isolator.
Optionally, in the above multiplexing optical fiber current sensor based on wavelength division multiplexing, the beam splitter is a broadband polarization maintaining fiber coupler or a polarization maintaining fiber wavelength division multiplexer.
Optionally, in the above wavelength division multiplexing-based multipath optical fiber current sensor, the polarization and coupling device includes an optical fiber polarizer and a straight waveguide phase modulator; and the tail fiber of the optical fiber polarizer and the tail fiber of the straight waveguide phase modulator are subjected to 45-degree counter shaft fusion.
Optionally, in the above wavelength division multiplexing-based multi-path optical fiber current sensor, the polarization and coupling device includes a Y waveguide phase modulator and a polarization beam combiner; one branch tail fiber of the Y waveguide phase modulator and one branch tail fiber of the polarization beam combiner are subjected to shaft fusion at 90 degrees; and the other branch tail fiber of the Y waveguide phase modulator and the other branch tail fiber of the polarization beam combiner are welded by 0 DEG counter shaft.
The invention also provides a control method of the multiplexing optical fiber current sensor based on wavelength division multiplexing, which comprises the following steps:
acquiring the corresponding relation between the gating wavelength of each optical channel in the optical fiber filter and the sensing branch;
Sequentially conducting each optical channel in the optical fiber filter according to a pre-stored setting sequence, acquiring an electric signal output by a photoelectric detector when each optical channel is conducted, and analyzing each electric signal to obtain a current value;
And determining a sensing branch corresponding to the electric signal output by the photoelectric detector according to the corresponding relation and the setting sequence, and obtaining the corresponding relation between the current value and the sensing branch.
Optionally, the control method of the multiplexing optical fiber current sensor based on wavelength division multiplexing further includes the following steps:
acquiring the working temperature of the reflection type fiber bragg grating in each sensing branch;
Obtaining the drift range of the reflection wavelength of each reflection type fiber bragg grating according to the working temperature of the reflection type fiber bragg grating;
And adjusting the optical fiber filter according to the drift range of the reflection wavelength of each reflection type optical fiber grating to ensure that each optical channel in the optical fiber filter passes the interference light of the corresponding sensing branch.
The present invention also provides a computer-readable storage medium having stored therein program instructions that are read by a computer to perform the control method of any one of the above.
The invention also provides a control system of the multiplexing optical fiber current sensor based on wavelength division multiplexing, which comprises at least one processor and at least one memory, wherein program instructions are stored in the at least one memory, and the at least one processor executes the program instructions to execute the control method of any one of the above.
The invention provides a multiplexing optical fiber current sensor based on wavelength division multiplexing, a control method and a control system thereof, wherein the optical fiber current sensor comprises m sensing branches, a polarized light generating device, an optical fiber filter and a photoelectric detector. The polarized light generating device outputs m paths of linearly polarized light, and each path of linearly polarized light enters one sensing branch; each path of linearly polarized light comprises two beams of linearly polarized light with mutually perpendicular polarization directions. The reflection type fiber bragg grating is adopted in each sensing branch to reflect the light beam, so that the reflected light beam can be ensured to correspond to the reflection wavelength of the corresponding reflection type fiber bragg grating. The reflected light output by each sensing branch may interfere in the polarized light generating device before being transmitted to the optical fiber filter. The optical fiber filters are adopted to gate different optical channels according to a set sequence, and each optical channel corresponds to an optical signal with one wavelength, so that the optical fiber filters can be ensured to conduct interference light corresponding to different sensing branches according to the set sequence. The photoelectric detector converts the interference light intensities corresponding to different sensing branches into electric signals according to the same sequence. Because the sensing branch, the optical channel of the optical fiber filter and the electric signal output by the photoelectric detector have a certain corresponding relation, the current value detected in the corresponding sensing branch can be reversely deduced according to the electric signal detected by the photoelectric detector. According to the scheme provided by the invention, based on the wavelength division multiplexing technology, the same set of optical fiber filter and the photoelectric detector are connected with a plurality of sensing branches, so that currents at different measuring points can be accurately measured, and the economic cost of the optical fiber current sensor is greatly saved.
Drawings
FIG. 1 is a schematic diagram of a wavelength division multiplexing-based multi-path fiber current sensor according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a wavelength division multiplexing-based multi-path fiber current sensor according to another embodiment of the present invention;
FIG. 3 is a schematic diagram showing the relationship between the difference of reflected wavelengths in different sensing branches and the gating filter band of the optical fiber filter according to one embodiment of the present invention;
FIG. 4 is a schematic diagram of multiplexing a fiber optic current sensor based on wavelength scanning of a fiber optic F-P filter according to an embodiment of the invention;
FIG. 5 is a schematic diagram of data acquisition based on an optical fiber F-P filter according to an embodiment of the present invention;
FIG. 6 is a table showing the correspondence between the modulation frequency and the scan voltage of the signal detection system according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of a time-sharing method of modulation and demodulation of the signal detection system according to an embodiment of the present invention;
fig. 8 is a flowchart of a control method of a multiplexing optical fiber current sensor based on wavelength division multiplexing according to an embodiment of the invention.
Detailed Description
Embodiments of the present invention will be further described below with reference to the accompanying drawings. In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between the two components. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
Example 1
The embodiment provides a multiplexing optical fiber current sensor based on wavelength division multiplexing, which comprises m sensing branches 1, a polarized light generating device 2, an optical fiber filter 3 and a photoelectric detector 4 as shown in fig. 1. The sensing branch 1 comprises an optical fiber ring 101, an optical fiber wave plate 102 and a reflection type optical fiber grating 103, wherein the optical fiber wave plate 102 and the reflection type optical fiber grating 103 are arranged at two ends of the optical fiber ring 101; the inside of the optical fiber ring 101 is penetrated by an energizing conductor 104; wherein the reflection fiber gratings 103 in different sensing branches 1 are used for reflecting light beams with different wavelengths; the polarized light generating device 2 outputs m paths of linearly polarized light, and each path of linearly polarized light enters one sensing branch 1; each path of linearly polarized light comprises two beams of linearly polarized light with mutually perpendicular polarization directions; in each sensing branch 1, the linearly polarized light is obtained after being reflected by the reflective fiber grating 103 after passing through the fiber wave plate 101 and the fiber ring 102, and the reflected light is output after passing through the fiber ring 102 and the fiber wave plate 101; the wavelength of the reflected light corresponds to the reflection wavelength of the reflection type fiber grating 103, and the reflected light includes two linearly polarized light beams having polarization directions perpendicular to each other and having a phase difference generated according to the current in the current-carrying conductor 104.
The linearly polarized light generating device 2 receives the reflected light output by each sensing branch 1; two beams of linearly polarized light in each reflected light interfere in the linearly polarized light generating device 2, and interference light obtained after interference of different reflected lights corresponds to different wavelengths; the optical fiber filter 3 is configured with a plurality of optical channels, and the gating wavelength of different optical channels corresponds to the interference light of different sensing branches 1; the optical fiber filter 3 receives all interference lights output by the linearly polarized light generating device 2, and sequentially conducts all light channels according to a set sequence to output the interference lights corresponding to the sensing branches 1; the photodetector 4 detects the light intensity of the interference light output from the optical fiber filter 3, and obtains an electrical signal corresponding to the light intensity, which is used to obtain the current value of the current-carrying conductor 104 in the corresponding sensing branch 1.
In the above scheme, the linearly polarized light with mutually orthogonal polarization directions enters different sensing branches 1 to be transmitted respectively, and is reflected back by the fiber bragg grating 103 at the tail end of the sensing fiber, and the sensing principle of each sensing branch 1 is the same, and the only difference is that the reflection wavelengths on the different sensing branches 1 are different. Taking one sensing branch 1 as an example, two linearly polarized lights with mutually orthogonal polarization directions are respectively changed into left-handed and right-handed circularly polarized lights at the optical fiber wave plate 101, and then are transmitted into the optical fiber ring 102, the current transmitted in the electrified conductor 104 generates a magnetic field, a phase difference, called Faraday magneto-optical phase shift angle, is generated between the two circularly polarized lights in the optical fiber ring 102 based on Faraday magneto-optical effect, after being reflected by the reflective optical fiber grating 103 at the tail end of the sensing optical fiber, the polarization modes of the two circularly polarized lights are interchanged (namely, the left-handed rotation is changed into the right-handed rotation, the right-handed rotation is changed into the left-handed rotation), and the two circularly polarized lights pass through the optical fiber ring 102 again, and undergo the Faraday effect to double the Faraday magneto-optical phase shift angle between the two circularly polarized lights. After the two circularly polarized lights pass through the optical fiber wave plate 101 again, the two circularly polarized lights return to linear polarized light, and the polarization modes are interchanged. The two returned linearly polarized light beams enter the linearly polarized light generation device 2 and interfere, the magnitude of the interference light intensity is modulated by Faraday magneto-optical phase shift angle, so that the interference light signals carry current information in the electrified conductor 104, the interference light signals enter the optical fiber filter 3, the optical fiber filter 3 can carry out gating filtering on the interference light signals in different wavelength intervals, the gated interference light signals reach the photoelectric detector 4 and are converted into electric signals, and the electric signals can be used for demodulating the current information in the electrified conductor 104 after being collected by the signal processing circuit. By controlling the gating wavelength of the optical fiber filter 3, the interference optical signals returned on different sensing branches 1 can be scanned in turn, so that the measurement of the current in the energized conductor 104 in different sensing branches 1 is realized.
In the scheme, based on the wavelength division multiplexing technology, the same set of optical device combination (such as the optical fiber filter 3, the photoelectric detector 4 and the like) can be connected with a plurality of sensing branches 1 so as to accurately measure the currents at different measuring points, and the economic cost of the optical fiber current sensor is greatly saved. Because the scheme adopts the multiplexing structure, the engineering cost of a single current measuring point can be reduced along with the increase of multiplexing branches, and the sensing branches can be increased or decreased at will on the premise of sufficient bandwidth of a light source when the sensor is applied on site, so that the normal work of other sensing branches is not influenced. Moreover, as the sensing light path is designed by adopting a pure optical method, all the adopted optical devices are passive devices and are not influenced by severe environments such as external high voltage, strong magnetic field and the like.
Example 2
As shown in fig. 2, the polarization light generating device 2 provided by the multiplexing-based multiplexing optical fiber current sensor of the present embodiment includes a light source 201, a light transmission device 202, a polarization and coupling device 203, a polarization-preserving delay optical fiber ring 204, and a beam splitter 205, where a first input end of the light transmission device 202 is connected to an output end of the light source 201, a first output end of the light transmission device 202 is connected to a first input end of the polarization and coupling device 203, and an optical signal emitted by the light source 201 is transmitted to the polarization and coupling device 203 through the light transmission device 202; a first output end of the polarization and coupling device 203 is connected to a first input end of the polarization-preserving delay optical fiber ring 204, and a first output end of the polarization-preserving delay optical fiber ring 204 is connected to a first input end of the beam splitter 205; the polarization and coupling device 203 converts the optical signal into two linearly polarized lights with mutually perpendicular polarization directions, and then transmits the two linearly polarized lights to the beam splitter 205 through the polarization-preserving delay optical fiber ring 204; the beam splitter 205 is configured with m first output ends and m second input ends, each of the first output ends is connected with the input end of one sensing branch 1, and each of the second input ends is connected with the output end of one sensing branch 1; the beam splitter 205 divides two linearly polarized lights with mutually perpendicular polarization directions into m paths of linearly polarized lights, each path of linearly polarized light obtains reflected light after passing through the sensing branch 1 and returns to the beam splitter 205, a second output end of the beam splitter 205 is connected with a second input end of the polarization-preserving delay optical fiber ring 204, and the reflected light is output after passing through the polarization-preserving delay optical fiber ring 204; a second input end of the polarization and coupling device 203 is connected with a second output end of the polarization-preserving delay optical fiber ring 204, receives the reflected light output by the beam splitter 205, and outputs the reflected light after interference occurs in the polarization and coupling device 203 to obtain interference light; a second input end of the optical transmission device 202 is connected with a second output end of the polarization and coupling device 203, and a second output end of the optical transmission device 202 is connected with an input end of the optical fiber filter 3; the optical transmission device 202 receives the interference light output from the polarization and coupling device 203 and outputs the interference light to the optical fiber filter 3.
It will be appreciated that in the above-mentioned transmission of the optical signal or beam, in addition to the reflected light output by the sensing branch 1, the optical signal including each wavelength is transmitted in the optical path, and finally, the interference light with different wavelengths can be sequentially selected to enter the photodetector 4 through the gating function of the optical fiber filter 3.
In the above scheme, the optical transmission device 202 is an optical fiber circulator; alternatively, the optical transmission device 202 includes a fiber isolator and a fiber coupler connected to the fiber isolator. The optical transmission device 202 has a main function of optical signal transmission, so that a device generally configured with corresponding optical signal input and output ports, such as an optical fiber circulator, may be used. In addition, in order to prevent the light in different transmission directions from affecting each other, if devices such as an optical fiber coupler are adopted, an optical isolator can be added at the same time, and the adoption of the optical isolator can ensure that reflected light signals cannot interfere with a light source.
In addition, the beam splitter 205 in the above solution has a main function of splitting the optical signal received in the first direction into multiple beams and outputting the multiple beams, and simultaneously combining the multiple beams of optical signals received in the other direction into one beam and outputting the multiple beams of optical signals, where the broad band polarization maintaining fiber coupler or polarization maintaining fiber wavelength division multiplexer can be used, and the broad band polarization maintaining fiber coupler and the polarization maintaining fiber wavelength division multiplexer both support the fast and slow axis operation.
Further, the polarizing and coupling device 203 may be implemented in two ways:
(1) The polarization and coupling device 203 comprises an optical fiber polarizer and a straight waveguide phase modulator; and the tail fiber of the optical fiber polarizer and the tail fiber of the straight waveguide phase modulator are subjected to 45-degree counter shaft fusion.
(2) The polarization and coupling device 203 comprises a Y waveguide phase modulator and a polarization beam combiner; one branch tail fiber of the Y waveguide phase modulator and one branch tail fiber of the polarization beam combiner are subjected to shaft fusion at 90 degrees; and the other branch tail fiber of the Y waveguide phase modulator and the other branch tail fiber of the polarization beam combiner are welded by 0 DEG counter shaft.
The light beams output from the polarization and coupling device 203 become two linearly polarized light beams with mutually orthogonal polarization directions, the linearly polarized light beams are transmitted in the polarization-preserving delay fiber ring, enter the beam splitter 205 with the light beam splitting function, and the linearly polarized light beams with mutually orthogonal polarization directions enter different sensing branches 1 for transmission after passing through the light beam splitter 5.
Preferably, in the above scheme, the optical fiber filter 3 may be an optical fiber F-P filter, and it can be understood that the gating wavelength of the optical fiber F-P filter may be set by adjusting the scanning voltage thereof, so that even if the reflection wavelengths of different reflection-type optical fiber gratings have a certain drift, the scanning voltage of the F-P filter may be adjusted to adapt to the corresponding reflection wavelengths. The typical value of the wavelength scanning range of the optical fiber F-P filter is tens of nanometers, the optical fiber F-P filter can cover the spectrum range of a wide-spectrum light source, the wavelength resolution can reach picometer magnitude, the cost of a measuring instrument is moderate, and the requirements of engineering application can be met. The specific implementation scheme of the multiplexing optical fiber current sensor adopting the F-P optical fiber filter can be divided into two steps of multiplexing data acquisition and modulation and demodulation of multiplexing signals, and is combined with fig. 5, for the F-P optical fiber filter, a time t is allocated to each sensing branch, and the two steps of operations need to be executed within the time t, so that the time t comprises a wavelength scanning interval and a data acquisition interval:
(1) Multipath data acquisition step
The multi-path data acquisition method is specifically divided into two steps, wherein the first step is to scan the central wavelength of the multi-path interference optical signals, and the second step is to acquire the data of the optical power with specific central wavelength.
The specific implementation method of the center wavelength scanning is as follows: since the reflection wavelength of the reflection fiber bragg grating 103 will drift along with the temperature, a certain wavelength difference Δλ should be set between the reflection wavelengths of different sensing branches 1, and the temperature variation range corresponding to the wavelength difference Δλ is ensured to exceed the temperature compensation range of the fiber optic current sensor. That is, the difference delta lambda of the reflection wavelengths of the reflection fiber gratings in any two sensing branches is larger than delta lambda max; wherein Δλ max＝MAX[Δλ1,Δλ2,……Δλm],Δλi is the wavelength drift range of the reflective fiber grating in the ith sensing branch when the temperature changes. When using a fiber F-P filter for gating filtering, the gating bandwidth may be set to be just equal to the wavelength difference, as shown in fig. 3. In the figure, lambda 1 is the reflection wavelength of the reflection type fiber grating 103 in one sensing branch 1, and lambda 2、λ3 is the reflection wavelength of the reflection type fiber grating 103 in the other two sensing branches 1. Because the reflection wavelengths of different reflection-type fiber gratings can be influenced by temperature change to generate drift and influence degrees are possibly different, the difference value of any two reflection wavelengths is larger than the maximum value in the wavelength drift of all reflection-type fiber gratings in the scheme, and the error caused by the temperature change to the fiber current sensor can be avoided.
In the above-mentioned scheme, the optical fiber filter 103 determines the drift amount of the center wavelength of the reflection wavelength of each reflection-type optical fiber grating through wavelength scanning, further calculates the ambient temperature of the reflection-type optical fiber grating according to the relationship between the reflection wavelength of the reflection-type optical fiber grating and the ambient temperature where the reflection-type optical fiber grating is located, and uses the ambient temperature as the temperature source when the optical fiber current sensor performs temperature error compensation in the sensing branch. In addition, when the optical fiber current sensor is switched among different sensing branches, the scanning voltage ranges of the optical fiber F-P filter are different, and the scanning period T with a certain time width can be set according to the number of the sensing branches, so that all the sensing branches can be scanned in each period T. The multiplexing method of different sensing branches on the whole time axis is shown in fig. 4, where T n (n=1, 2,3 … …) is the nth scanning period, and λ m (m=1, 2,3 … …) is the reflection wavelength of the mth sensing branch.
Through the method, the center wavelength of the interference light corresponding to the plurality of sensing branches can be determined, and the optical fiber filter is ensured to only output the interference light with one wavelength at any time and only corresponds to one sensing branch.
(2) Modulation and demodulation of multipath signals
The step is realized by a signal detection system, the signal detection system detects the optical signal output by the photoelectric detector, when the central wavelength of the interference light output by the optical fiber filter in the step (1) and the corresponding sensing branch are determined, the scanning voltage of the optical fiber filter stays at the accurate central wavelength gating position, at the moment, the photoelectric detector performs data acquisition on the light intensity of the interference light output by the optical fiber filter, and the acquired optical power can be used for demodulating the measured current value. The signal processing of different sensing branches can be mutually independent by adopting time-sharing processing. The specific implementation method comprises the following steps:
(1) Setting the correct modulation frequency
The optical path transition time determines the modulation frequency of the signal detection system, and the optical path transition time corresponding to different sensing branches is different, so that the modulation frequency of each sensing branch needs to be correctly debugged during calibration and written into a chip for signal processing, the scanning voltage interval of the optical fiber filter corresponds to the reflection wavelength of the sensing branch one by one, the modulation frequency of each sensing branch is given during calibration and corresponds to the scanning voltage interval of the optical fiber filter, when the scanning voltage of the optical fiber filter changes, the corresponding modulation frequency is obtained through a table look-up method and is applied to the phase modulator, and the corresponding relation between the modulation frequency and the scanning voltage is shown in fig. 6. The sensing branch 1 corresponds to the reflection wavelength lambda 1, the scanning voltage corresponding to the filter is U 0-U1, and the modulation frequency of the signal detection system is f 1. Accordingly, the correspondence of the data is uniformly and correspondingly stored in the signal detection system.
(2) Time-sharing modulation and demodulation
The modulation and demodulation of the optical signal and the data acquisition are performed simultaneously, and because each path of data acquisition is mutually independent, the modulation and demodulation are mutually independent, and the time-sharing method is shown in fig. 7, wherein P nm is the return optical power acquired from the mth sensing branch in the nth cycle period, and I nm is the demodulation current value of the mth sensing branch in the nth cycle period.
As described above, the current value in the energized conductor affects the phase difference of the two polarized lights in the optical fiber ring, the phase difference affects the interference of the two polarized lights, and the interference light intensity corresponds to the electrical signal detected by the photodetector, so that the corresponding current value can be obtained by demodulating the electrical signal of the photodetector.
Example 3
The present embodiment provides a control method of the above-mentioned multiplexing optical fiber current sensor based on wavelength division multiplexing, which can be applied to a signal detection system, as shown in fig. 8, and includes the following steps:
S801: acquiring the corresponding relation between the gating wavelength of each optical channel in the optical fiber filter and the sensing branch; each optical channel in the optical fiber filter is numbered in advance, the optical channels are distinguished by gating wavelengths, and accordingly, the reflected light in each sensing branch corresponds to different wavelengths, and each optical channel in the optical fiber filter can correspond to the reflected wavelength of each sensing branch.
S802: and sequentially conducting each optical channel in the optical fiber filter according to a pre-stored setting sequence, acquiring an electric signal output by the photoelectric detector when each optical channel is conducted, and analyzing each electric signal to obtain a current value. The setting sequence may be preset, for example, gating is performed sequentially from the sensing branch 1 to the sensing branch m. And distributing time for each channel according to the time length required by the corresponding wavelength scanning interval and the data acquisition interval when each sensing branch is gated.
S803: and determining a sensing branch corresponding to the electric signal output by the photoelectric detector according to the corresponding relation and the setting sequence, and obtaining the corresponding relation between the current value and the sensing branch.
Preferably, the method further comprises the steps of:
S804: and determining the drift amount of the reflection wavelength of the reflection type fiber bragg grating in each sensing branch according to the theoretical value of the reflection wavelength of the reflection type fiber bragg grating and the wavelength of interference light actually scanned by the fiber bragg filter.
S805: and obtaining the ambient temperature of the reflective fiber grating according to the corresponding relation between the ambient temperature of the reflective fiber grating in the sensing branch and the reflection wavelength drift amount.
S806: and adjusting the current value of the electrified conductor in the sensing branch according to the ambient temperature of the reflection type fiber bragg grating.
The measurement error of the optical fiber current sensor is doubly influenced by the temperature drift of the sensing optical fiber and the central wavelength drift of the optical signal. The temperature error of the sensing optical fiber mainly comes from the temperature drift of the magneto-optical coefficient of the optical fiber and the measurement error caused by the residual linear birefringence along with the temperature change. The existing common correction schemes are two, namely, a lambda/4 optical fiber wave plate is manufactured to be of a non-standard length (namely, the wave plate length is larger than 1/4 of the wave plate optical fiber beat length), so that circularly polarized light transmitted in a sensing optical fiber is changed into elliptically polarized light, and finally, a nonlinear error is generated in a larger current measurement interval by an optical fiber current sensor; and secondly, the environment temperature of the optical fiber sensing ring is measured in real time by using a high-precision temperature sensor, and the temperature error of the sensing optical fiber is compensated on line in the signal processing unit by utilizing the relation between the measurement error and the temperature. The drift of the center wavelength of the optical signal is mainly caused by the spectrum change caused by the long-term aging of the light source and the optical device, and therefore, the magneto-optical coefficient in the sensing optical fiber is changed, so that the system transformation ratio is changed, and the measurement error is generated.
The reflection type fiber grating is used as a reflecting element and is combined with the fiber filter, and because the reflection type fiber grating has good temperature sensitivity and electromagnetic interference resistance, the central wavelength of reflection is only related to the temperature and stress of the fiber grating, and a protection package is necessarily arranged outside the reflection type fiber grating when the reflection type fiber grating is arranged in a device, and the reflection type fiber grating can be prevented from being influenced by the stress through the protection package, so that the wavelength drift amount of the reflection type fiber grating can be considered to be only related to the temperature, the ambient temperature of the reflection type fiber grating can be determined by using the drift amount of the reflection wavelength of the reflection type fiber grating, and the temperature source is used as a temperature source when the temperature error compensation is performed as a current value calculation result. Meanwhile, the error term generated by the change of magneto-optical coefficient in the optical fiber loop can be reversely deduced according to the drift amount of the reflection wavelength of the reflection type fiber bragg grating, the error of Faraday phase shift in the optical fiber loop can be determined by the two methods, and then the error of interference light intensity and the error of the current value calculation result are obtained, and the current value calculation result can be adjusted according to the error. Thus, a more accurate current value calculation result can be obtained.
Example 4
The present embodiment provides a computer-readable storage medium having stored therein program instructions that are read by a computer to perform the control method according to any one of embodiment 3.
Example 5
The present embodiment provides a control system of a multiplexing optical fiber current sensor based on wavelength division multiplexing, including at least one processor and at least one memory, at least one of the memories storing program instructions, at least one of the processors executing the program instructions to execute the control method according to any one of the aspects of embodiment 3.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.
Claims (11)
1. The multichannel optical fiber current sensor based on wavelength division multiplexing is characterized by comprising m sensing branches, a polarized light generating device, an optical fiber filter and a photoelectric detector:
the sensing branch comprises an optical fiber ring, an optical fiber wave plate and a reflection type optical fiber grating, wherein the optical fiber wave plate and the reflection type optical fiber grating are arranged at two ends of the optical fiber ring; the inside of the optical fiber ring is penetrated by an electrified conductor; wherein the reflection fiber gratings in different sensing branches are used for reflecting light beams with different wavelengths;
The polarized light generating device outputs m paths of linearly polarized light, and each path of linearly polarized light enters one sensing branch; each path of linearly polarized light comprises two beams of linearly polarized light with mutually perpendicular polarization directions;
In each sensing branch, the linearly polarized light is obtained after being reflected by the reflection type fiber bragg grating after passing through the fiber wave plate and the fiber ring, and the reflected light is output after passing through the fiber ring and the fiber wave plate; the wavelength of the reflected light corresponds to the reflection wavelength of the reflection type fiber grating, the reflected light comprises two linearly polarized light with mutually perpendicular polarization directions and a phase difference, and the phase difference is generated according to the current in the electrified conductor;
The linearly polarized light generating device receives the reflected light output by each sensing branch; two beams of linearly polarized light in each reflected light interfere in the linearly polarized light generating device, and interference light obtained after interference of different reflected light corresponds to different wavelengths;
The optical fiber filter is provided with a plurality of optical channels, and gating wavelengths of different optical channels correspond to interference lights of different sensing branches; the optical fiber filter receives all interference light output by the linearly polarized light generating device, and sequentially conducts all light channels according to a set sequence to output interference light of a corresponding sensing branch;
The photoelectric detector detects the light intensity of the interference light output by the optical fiber filter, and obtains an electric signal corresponding to the light intensity, wherein the electric signal is used for obtaining the current value of the electrified conductor in the corresponding sensing branch.
2. The wavelength division multiplexing based multiplexed fiber optic current sensor of claim 1, wherein:
The difference delta lambda of the reflection wavelengths of the reflection fiber gratings in any two sensing branches is larger than delta lambda max; wherein Δλ max＝MAX[Δλ1,Δλ2,……Δλm],Δλi is the wavelength drift range of the reflective fiber grating in the ith sensing branch when the temperature changes.
3. The wavelength division multiplexing based multiplexed fiber optic current sensor of claim 1, wherein the polarized light generating device comprises a light source, a light transmitting device, a polarizing and coupling device, a polarization preserving delay fiber loop, and a beam splitter, wherein:
The first input end of the light transmission device is connected with the output end of the light source, the first output end of the light transmission device is connected with the first input end of the polarization and coupling device, and the light signal emitted by the light source is transmitted to the polarization and coupling device through the light transmission device;
The first output end of the polarization and coupling device is connected with the first input end of the polarization-preserving delay optical fiber ring, and the first output end of the polarization-preserving delay optical fiber ring is connected with the first input end of the beam splitter; the polarization and coupling device converts the optical signal into two linearly polarized light beams with the polarization directions perpendicular to each other and then transmits the two linearly polarized light beams to the beam splitter through the polarization-preserving delay optical fiber ring;
The beam splitter is provided with a second output end, m first output ends and m second input ends, each first output end of the beam splitter is connected with the input end of one sensing branch, and each second input end of the beam splitter is connected with the output end of one sensing branch and the second output end of the beam splitter is connected with the second input end of the polarization-maintaining delay optical fiber ring; the beam splitter divides two linearly polarized lights with mutually perpendicular polarization directions into m paths of linearly polarized lights, and each path of linearly polarized light is output through the polarization-preserving delay optical fiber ring after reflected light obtained by the sensing branch is returned to the beam splitter;
The second input end of the polarization and coupling device is connected with the second output end of the polarization-preserving delay optical fiber ring, receives the reflected light output by the beam splitter, and generates interference in the polarization and coupling device to obtain interference light and then outputs the interference light;
The second input end of the optical transmission device is connected with the second output end of the polarization and coupling device, and the second output end of the optical transmission device is connected with the input end of the optical fiber filter; the optical transmission device receives the interference light output by the polarizing and coupling device and outputs the interference light to the optical fiber filter.
4. A wavelength division multiplexing based multiplexed fiber optic current sensor according to claim 3 wherein:
the optical transmission device is an optical fiber circulator; or alternatively, the first and second heat exchangers may be,
The optical transmission device comprises an optical fiber isolator and an optical fiber coupler connected with the optical fiber isolator.
5. The wavelength division multiplexing based multiplexed fiber optic current sensor of claim 4, wherein:
the beam splitter is a broadband polarization maintaining fiber coupler or a polarization maintaining fiber wavelength division multiplexer.
6. The wavelength division multiplexing based multiplexed fiber optic current sensor of any one of claims 3-5, wherein:
the polarization and coupling device comprises an optical fiber polarizer and a straight waveguide phase modulator; and the tail fiber of the optical fiber polarizer and the tail fiber of the straight waveguide phase modulator are subjected to 45-degree counter shaft fusion.
7. The wavelength division multiplexing based multiplexed fiber optic current sensor of any one of claims 3-5, wherein:
The polarization and coupling device comprises a Y waveguide phase modulator and a polarization beam combiner; one branch tail fiber of the Y waveguide phase modulator and one branch tail fiber of the polarization beam combiner are subjected to shaft fusion at 90 degrees; and the other branch tail fiber of the Y waveguide phase modulator and the other branch tail fiber of the polarization beam combiner are welded by 0 DEG counter shaft.
8. A method of controlling a wavelength division multiplexing based multi-path optical fiber current sensor according to any one of claims 1 to 7, comprising the steps of:
acquiring the corresponding relation between the gating wavelength of each optical channel in the optical fiber filter and the sensing branch;
Sequentially conducting each optical channel in the optical fiber filter according to a pre-stored setting sequence, acquiring an electric signal output by a photoelectric detector when each optical channel is conducted, and analyzing each electric signal to obtain a current value;
And determining a sensing branch corresponding to the electric signal output by the photoelectric detector according to the corresponding relation and the setting sequence, and obtaining the corresponding relation between the current value and the sensing branch.
9. The method for controlling a wavelength division multiplexing based multi-path optical fiber current sensor according to claim 8, further comprising the steps of:
determining the drift amount of the reflection wavelength of the reflection type fiber bragg grating in each sensing branch according to the theoretical value of the reflection wavelength of the reflection type fiber bragg grating and the wavelength of interference light actually scanned by the fiber bragg filter;
Obtaining the ambient temperature of the reflective fiber grating according to the corresponding relation between the ambient temperature of the reflective fiber grating in the sensing branch and the reflection wavelength drift amount;
and adjusting the current value of the electrified conductor in the sensing branch according to the ambient temperature of the reflection type fiber bragg grating.
10. A computer-readable storage medium, characterized in that the storage medium has stored therein program instructions that are read by a computer to perform the control method of claim 8 or 9.
11. A control system for a wavelength division multiplexing based multi-way fibre optic current sensor according to any one of claims 1-7 comprising at least one processor and at least one memory, at least one of said memories having stored therein program instructions, at least one of said processors executing said program instructions to perform the control method of claim 8 or 9.
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