CN211013220U - Vehicle vibration monitoring device based on two-mode optical fiber - Google Patents
Vehicle vibration monitoring device based on two-mode optical fiber Download PDFInfo
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Abstract
The utility model discloses a vehicle vibration monitoring devices based on two mould optic fibre, including laser instrument, pulse light generator, circulator, mode division multiplexer, two mould sensing optical fibre, collection card, digital signal processing unit, 2 polarization controller, 2 photoelectric conversion and signal of telecommunication processing module and 4 optical couplers. The continuous laser emitted by the laser is divided into two parts by the optical coupler, one part is modulated into detection pulses by the pulse generator and sent to the two-mode sensing optical fiber, and the other part is used as local oscillation light; after backward Rayleigh scattering light returned by the two-mode sensing optical fiber is combined with the local oscillator light, the digital signal processing unit carries out data processing and then identifies vehicle vibration. Compared with the prior art, the utility model provides a speed and rate of accuracy of vehicle vibration monitoring discernment.
Description
Technical Field
The utility model relates to an optical fiber sensing technical field, concretely relates to vehicle vibration monitoring devices based on two mode optic fibre.
Background
With the advance of urbanization process and the rapid increase of the number of motor vehicles in China, the traffic volume of highways is continuously increased, and the difficulty of monitoring high-speed vehicles is increasingly high. At present, relatively mature road vehicle monitoring methods mainly comprise vertical monitoring schemes such as annular coils, digital videos and ultrasonic waves, and although the single-point monitoring precision of the technologies is high, the problems of dead angle monitoring, complex networking and the like exist in the vertical monitoring schemes.
The optical fiber sensing technology is a new sensing technology which has emerged along with the optical fiber technology and the optical communication technology in recent decades. The optical fiber sensing sensor uses light waves as sensing signals and optical fibers as signal transmission media to detect external signals, and is different from a traditional electrical sensor in the aspects of sensing modes, signal detection, signal processing and the like. The optical fiber sensor based on the phase-sensitive optical time domain reflectometer is widely applied to the fields of boundary security, petroleum pipeline safety monitoring and the like due to the long-distance, full-distributed, high-sensitivity and other sensing characteristics. The sensing characteristics of the optical fiber are utilized to carry out real-time and whole-course monitoring on the vehicle vibration on the road, and the method has important application value for constructing a road traffic monitoring network with the multi-sensor integration.
The traditional phase-sensitive optical time domain reflectometer uses a single-mode optical fiber as a sensing medium and realizes vibration position positioning by an amplitude difference method. Specifically, the system firstly collects the amplitude data of a backward Rayleigh scattering signal; when the data volume reaches the number set by a user, dividing the collected data into lines according to the length of the optical fiber, wherein the data in each line is a Rayleigh scattering signal generated when the optical pulse completes one-time transmission in the sensing optical fiber; and carrying out difference and absolute value calculation on each row of data and the data of every other k rows, finally accumulating to obtain a frame of data, and determining the position of a vibration peak in the sensing link according to the frame of data.
Although the traditional single-mode optical fiber phase-sensitive optical time domain reflectometer shows better sensing performance in practical application, the following defects still exist: (1) the nonlinear threshold level and the reflected light capture rate of the single-mode fiber are low, so that the injectable pulse light power is limited, and the Rayleigh scattered light signal received by the injection end of the fiber is weak, so that the acquisition and subsequent processing of the scattered signal are not facilitated; (2) the single-mode optical fiber can only transmit optical signals of one mode, is greatly influenced by the non-uniform medium and the non-matched polarization state of the optical fiber, and cannot compensate the sudden change of a vibration peak caused by noise, so that the signal-to-noise ratio is reduced; (3) the difference accumulation algorithm needs to select the number of difference intervals (namely k value) according to the vibration frequency, the difference k value needs to be changed when the vibration frequency is changed, and the selection method of the k value has no clear value selection basis; the algorithm has high requirements on the waveform, and the effect of detecting the irregular vibration source of vehicle vibration is poor.
SUMMERY OF THE UTILITY MODEL
The utility model discloses to the problem that current single mode fiber phase sensitive light time domain reflectometer exists, provide a vehicle vibration monitoring devices based on two mode optic fibre.
In order to solve the above problems, the utility model discloses a realize through following technical scheme:
a vehicle vibration monitoring device based on two-mode optical fibers comprises a laser, a pulse light generator, a circulator, a mode division multiplexer, two-mode sensing optical fibers, a collection card, a digital signal processing unit, 2 polarization controllers, 2 photoelectric conversion and electric signal processing modules and 4 optical couplers, wherein the output end of the laser is connected with the input end of a first optical coupler, one output end of the first optical coupler is connected with the input end of the pulse light generator, the other output end of the first optical coupler is connected with the input end of a second optical coupler, the output end of the pulse light generator is connected with a first port of the optical circulator, and a second port of the optical circulator is connected with L P (wavelength division multiplexing) of the mode division multiplexer01The mode port, the multiplex port of the mode division multiplexer is connected with two mode sensing optical fibers, the two mode sensing optical fibers are laid along the road ground, the third port of the optical circulator is connected with one input end of a third optical coupler, and L P of the mode division multiplexer11The mould port is connected with one input end of the fourth optical coupler; one output end of the second optical coupler is connected with the other input end of the third optical coupler through the first polarization controller(ii) a The other output end of the second optical coupler is connected with the other input end of the fourth optical coupler through a second polarization controller; two output ends of the third optical coupler are simultaneously connected with two input ends of the first photoelectric conversion and electric signal processing module, and two output ends of the first photoelectric conversion and electric signal processing module are simultaneously connected with the acquisition card; two output ends of the fourth optical coupler are simultaneously connected with two input ends of the second photoelectric conversion and electric signal processing module, and two output ends of the second photoelectric conversion and electric signal processing module are simultaneously connected with the acquisition card; the output end of the acquisition card is connected with the input end of the digital signal processing unit.
In the above scheme, the splitting ratio of the first optical coupler is 80:20, wherein 80% of the output end is connected with the input end of the pulse light generator, and 20% of the output end is connected with the input end of the second optical coupler.
In the above scheme, the splitting ratio of the second optical coupler, the third optical coupler and the fourth optical coupler is 50: 50.
In the above scheme, the pulse light generator is an optical fiber coupled acousto-optic modulator, and a pulse period of pulse light generated by the pulse light generator is longer than a round-trip time for light to propagate in the two-mode sensing optical fiber.
In the above scheme, two output ends of the first photoelectric conversion and electric signal processing module output IQ two-path radio frequency signals, which both carry L P01Two output ends of the second photoelectric conversion and electric signal processing module output IQ two-path radio frequency signals which carry L P11And (4) mode backward Rayleigh scattering light information.
Compared with the prior art, the utility model discloses a two mode optic fibre have higher threshold level and reverberation capture rate than single mode optic fibre, can pour into the detection pulse of higher power into two mode optic fibre, produce stronger backward rayleigh scattering signal, be favorable to the collection and the processing of later stage signal simultaneously, allow two kinds of modes (L P) in the two mode optic fibre (L P)01Die sum L P11Mode), two mode signals can be subsequently separated out for noise compensation of an upper computer, misjudgment of the signals of a certain mode caused by noise is weakened, the signal-to-noise ratio of the system and vibration are improvedAnd (4) judging accuracy.
Drawings
Fig. 1 is a schematic structural view of a vehicle vibration monitoring device based on two-mode optical fibers according to the present invention;
fig. 2 is a flowchart of a training phase of a vehicle vibration monitoring method based on two-mode optical fibers according to the present invention;
fig. 3 is the utility model relates to a vehicle vibration monitoring's actual measurement stage's flowchart based on two mould optic fibre.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the following specific examples.
A vehicle vibration monitoring device based on two-mode optical fibers is shown in figure 1 and comprises a high-power narrow-linewidth laser, namely a laser, a pulse light generator, a circulator, a mode division multiplexer, two-mode sensing optical fibers, a collecting card, a digital signal processing unit, 2 polarization controllers, 2 photoelectric conversion and electric signal processing modules and 4 optical couplers, wherein the output end of the high-power narrow-linewidth laser is connected with the input end of a first optical coupler, one output end of the first optical coupler is connected with the input end of the pulse light generator, the other output end of the first optical coupler is connected with the input end of a second optical coupler, the output end of the pulse light generator is connected with a first port of the optical circulator, and a second port of the optical circulator is connected with L P of the mode division multiplexer01The mode port, the multiplex port of the mode division multiplexer are connected with two mode sensing optical fibers, the third port of the optical circulator is connected with one input end of a third optical coupler, and L P of the mode division multiplexer11The die port is connected to an input of a fourth optical coupler. One output end of the second optical coupler is connected with the other input end of the third optical coupler through the first polarization controller. The other output end of the second optical coupler is connected with the other input end of the fourth optical coupler through the second polarization controller. Two output ends of the third optical coupler are simultaneously connected with two input ends of the first photoelectric conversion and electric signal processing module, and two output ends of the first photoelectric conversion and electric signal processing module are simultaneously connected with two input ends of the second photoelectric conversion and electric signal processing moduleAnd connecting an acquisition card. Two output ends of the fourth optical coupler are simultaneously connected with two input ends of the second photoelectric conversion and electric signal processing module, and two output ends of the second photoelectric conversion and electric signal processing module are simultaneously connected with the acquisition card. The output end of the acquisition card is connected with the input end of the digital signal processing unit.
High power narrow linewidth laser generation L P01Continuous laser of mode, the linewidth of the laser is not more than 5kHz in this embodiment, the high power narrow linewidth laser emits continuous laser with wavelength of 1550nm, the linewidth of the laser is 3kHz, the output power is 25mW, and its working mode is L P01And (5) molding.
The first optical coupler divides the output laser of the high-power narrow linewidth laser into two paths with the splitting ratio of 80:20, 80% of the output end of the first optical coupler is connected with the input end of the pulse light generator and used for generating detection light pulse, and 20% of the output end of the first optical coupler is connected with the input end of the second optical coupler to be used as L P01Die sum L P11And (3) coherent detection of the local oscillator light required by the two paths of backward Rayleigh scattering signals.
The pulse light generator is an optical fiber coupling acousto-optic modulator, and the modulation bandwidth is 200 MHz. The pulse light generator modulates continuous laser input by the first optical coupler into pulse light, the pulse width of the pulse light is 100ns, the rising time and the falling time are both 2.5ns, the period of the repeated pulse is determined by the length of the optical fiber, and particularly the period of the repeated pulse is required to be larger than the time of the light transmitting in the optical fiber back and forth. In this example, the length of the optical fiber is 2km, and the time for light to travel back and forth in the optical fiber is about 19.34us, so that the pulse period is set to 20 us. The output frequency of the pulse light is shifted down by 200MHz while the pulse light is modulated.
The circulator converts L P generated by the pulse light generator01The modulus optical pulse passes through a modulus division multiplexer L P01Two-mode sensing fiber injection at the die port L P generated by the two-mode sensing fiber01The model backward Rayleigh scattering signal passes through L P of the model division multiplexer01The mode port returns to the second port of the circulator and is output to one input end of a third optical coupler through the third port of the circulator, L P generated by the two-mode sensing optical fiber11Model backward Rayleigh scattering signalL P with number passing through mode division multiplexer11The mode port is coupled to an input of a fourth optical coupler.
Mode division multiplexer supporting L P in C wave band01Die sum L P11Multiplexing and demultiplexing of mode-optical waves mode-division multiplexers with L P01Mode laser is injected into two-mode sensing optical fiber, and the mode division multiplexer is used for processing L P returned from the two-mode sensing optical fiber01Die sum L P11After the model backward Rayleigh scattering signal is demultiplexed, one path of L P01Model backward Rayleigh scattering signal L P01The mode port is sent to a third optical coupler through a circulator, and one path is L P11Model backward Rayleigh scattering signal L P11The mode port is sent to a fourth optical coupler.
The two-mode sensing optical fiber is laid along a road and used for sensing vehicles. In the two-mode sensing fiber in this embodiment, the normalized frequency V in the C band satisfies: 2.4048<V<3.8327, support L P01Die sum L P11Optical transmission in mode with a length of 2km, L P01When the mode light wave is transmitted in the forward direction in the optical fiber, Rayleigh scattering continuously occurs, and the Rayleigh scattering light exists in L P01And L P11In both modes, L P01Die sum L P11The rayleigh scattered light behind the mode propagates back to the fiber injection end along the sensing fiber.
The second optical coupler divides the laser output by the first optical coupler into a first local oscillator light and a second local oscillator light, the splitting ratio of the first local oscillator light to the second local oscillator light is 50:50, and two output ends of the second local oscillator light are respectively connected with the input ends of the first polarization controller and the second polarization controller.
The first polarization controller PC1 performs polarization control on the first local oscillation light output by the second optical coupler.
The second polarization controller PC2 performs polarization control on the second local oscillation light output by the second optical coupler.
The third optical coupler firstly outputs the first local oscillator light output by the first polarization controller and L P output by the third port of the circulator01And combining the mode backward Rayleigh scattered light, wherein the equation of the light wave electric field after combination is formula (1). Then the beam combination light is split in a ratio of 1:1, the light wave electric field equation after splitting is a formula (2) and a formula (3), and the two paths of split phase differenceAnd pi/2 optical signal.
E＝Esexp(iωst+φS)+ELexp(iωLt+φL) (1)
Wherein E issTo signal light amplitude, ELIs the local oscillator light amplitude.
The fourth optical coupler firstly outputs the second local oscillator light output by the second polarization controller and the mode division multiplexer L P11L P output by mould port11Combining the mode backward Rayleigh scattered light, then splitting the combined light by 1:1, and splitting the split two paths of optical signals with the phase difference of pi/2. The optical wave electric field equation after the fourth optical coupler is combined and split is as described in the third optical coupler.
The first photoelectric conversion and electric signal processing module firstly carries out photoelectric conversion and beat frequency detection on two paths of optical signals with phase difference of pi/2 output by the third optical coupler so as to reduce common mode noise of the system and improve signal-to-noise ratio, detection sensitivity and dynamic range of the signals, then carries out amplification, filtering and IQ demodulation on the electric signals, and sends the demodulated IQ two paths of radio frequency signals to the acquisition card, wherein the radio frequency signals carry L P in two-mode optical fibers01And (4) mode backward Rayleigh scattering light information.
The second photoelectric conversion and electric signal processing module firstly carries out photoelectric conversion and beat frequency detection on two paths of optical signals with the phase difference of pi/2 output by the fourth optical coupler so as to reduce the common mode noise of the system and improve the signal-to-noise ratio, the detection sensitivity and the dynamic range of the signals, then carries out amplification, filtering and IQ demodulation on the electric signals, and sends the demodulated IQ two paths of radio frequency signals to the acquisition card, wherein the radio frequency signals carry L P in two-mode optical fibers11And (4) mode backward Rayleigh scattering light information.
The acquisition card simultaneously carries out A/D conversion on IQ two-path radio-frequency signals sent by the first photoelectric conversion and electric signal processing module and IQ two-path radio-frequency signals sent by the second photoelectric conversion and electric signal processing module, and sends the IQ two-path radio-frequency signals into the digital signal processing module. In addition, the acquisition card sets different sampling rates aiming at the backward Rayleigh scattering signals of the two modes so as to compensate the difference of the propagation speeds of the light of the two modes in the optical fiber. The acquisition card can continuously acquire a part of data and then intensively transmit the data to the digital signal processing module. In this example, the acquisition card provides a maximum real-time sampling rate of 10GS/s on each of four channels, a recording length of 500M points.
The digital signal processing module processes the digital signals sent by the acquisition card, and comprises the steps of extracting time domain signals of sampling points, analyzing characteristics, training a neural network in a training stage, judging vibration positions in an actual measurement stage, analyzing the characteristics of the time domain signals of the vibration positions, processing and identifying the vibration signals by the neural network and the like.
The working process of the vehicle vibration monitoring device with the two-mode optical fiber is as follows:
high power narrow linewidth laser generation L P01In the first branch, the laser (80%) output by the first optical coupler is modulated into detection pulse by a pulse light generator, and the detection pulse sequentially passes through a first port of a circulator, a second port of the circulator and a mode division multiplexer L P01Two-mode sensing fiber with L P in the two-mode sensing fiber01The mode backward Rayleigh scattered light passes through a mode division multiplexer L P in sequence01The mode port, the second port of the circulator and the third port of the circulator are input into one input end of a third optical coupler, L P in the two-mode sensing optical fiber11The mode backward Rayleigh scattered light passes through a mode division multiplexer L P11The mode port is input to one input of a fourth optical coupler. In the second branch, the second optical coupler divides another part of the laser light (20%) divided by the first optical coupler into two local oscillation light paths, which are marked as first local oscillation light and second local oscillation light. The first local oscillator light and the second local oscillator light are respectively input into the third optical coupler and the fourth optical coupler after being subjected to polarization regulation and control by the first polarization controller and the second polarization controller. Third optical couplerL P returned from the third port of the first local oscillator light and the circulator01Combining the light beams by mode back Rayleigh scattering and inputting the light beams into the first photoelectric conversion and electric signal processing module, and combining the second local oscillator light and the mode division multiplexer L P by the fourth optical coupler11L P for mould port return11The light is combined after the mode back Rayleigh scattering and input into a second photoelectric conversion and electric signal processing module. The first photoelectric conversion and electric signal processing module and the second photoelectric conversion and electric signal processing module send the processed optical signals to the acquisition card for acquisition and then input the optical signals to the digital signal processing unit for signal processing.
The vehicle vibration monitoring method based on the two-mode optical fiber comprises the following specific steps of:
step 1, L P01The continuous laser of the mode is divided into two paths, wherein one path generates L P after being modulated01And (4) performing mode light pulse and injecting the mode light pulse into the two-mode sensing optical fiber. And the other path generates local oscillation light after polarization regulation.
(1) Training phase (see fig. 2):
Step 3, L P carrying vibration information01And L P11The Rayleigh scattered light after the mode is transmitted back to the injection end of the two-mode sensing optical fiber and is respectively combined with the local oscillator light to obtain L P01Die sum L P11The beam light signals are combined in a mode.
Step 4, L P01Die sum L P11After the optical signal processing, the photoelectric conversion and the electric signal processing are carried out on the mode beam combination optical signal, L P at the sampling point of the two-mode sensing optical fiber where the sample vehicle is located is obtained through sampling01Die sum L P11The vibrational time domain signal of the mode.
Step 5, L P obtained in step 401Die sum L P11Calculating the variance and range of the vibration time domain signal of the mode to obtain L P01Die sum L P11The variance and range of the modulus time domain signal.
The range calculation formula is as follows:
R＝max(xi)-min(xi) (6)
the variance calculation formula is as follows:
wherein x isiA piece of time-domain data is represented,
is the average value of a time domain number, and n is the data volume of a piece of data.
Step 6, using Empirical Mode Decomposition (EMD) to respectively process L P obtained in step 401Die sum L P11Decomposing the time domain signal of the vibration point of the mode to obtain L P01Die sum L P11Eigenmode component of mode vibration signal, and respectively pair L P01Die sum L P11The eigenmode component of the mode vibration signal is integrated to obtain L P01Die sum L P11And (4) the energy value of the eigenmode component of the mode vibration signal.
Step 7, L P obtained in step 501Die sum L P11Variance and range of the modulus and L P obtained in step 601Die sum L P11And correspondingly inputting the energy value of the eigenmode component of the mode vibration signal into the neural network for training to obtain the trained neural network.
In this embodiment, the characteristic values are trained by using an improved neural network algorithm based on Dropout and ADAM optimizer (not limited to such a neural network), the number of hidden nodes of the network is set to 30, the input layer activation function is Re L U, the output layer activation function is sigmoid function, Dropout is set to 0.4, and the network is optimized by using the ADAM algorithm, the number of iterations is first set to 5000, and the optimal number of iterations is selected by a graph of the number of iterations and the accuracy rate.
And obtaining a trained neural network through the steps, and storing the trained neural network in a data signal processing unit of the vehicle vibration monitoring device based on the two-mode optical fiber.
(2) Actual measurement phase (see fig. 3):
The raw data collected in the training stage is data carrying vehicle vibration signals. The original data collected in this step may or may not carry a vibration signal, and if the original data carries a vibration signal, the original data may or may not be a vibration signal of a vehicle.
Step 9, L P01Die sum L P11After the optical signal of the mode beam combination is processed by optical signal processing, photoelectric conversion and electric signal processing, L P at each sampling point of the two-mode sensing optical fiber is obtained by sampling01Die sum L P11A modulo time domain signal.
Designing different sampling rates aiming at backward Rayleigh scattering signals of different light wave modes, and compensating L P01Die sum L P11The difference in the velocity of the mode in the sensing fiber. The setting of the sampling rate parameters needs to be the same as the sampling rate set during the training phase.
Step 10, L P for each sampling point01Die sum L P11The time domain signals of the module are subjected to coefficient of variation processing by a coefficient of variation method respectively, and two paths of L P obtained by processing the coefficient of variation01Die sum L P11And multiplying the mode signals to obtain a disturbance curve along the optical fiber with high signal-to-noise ratio, and determining the position of the vibration point according to the disturbance curve.
The dispersion degree of the time domain data at the vibration point is far larger than that of the time domain data at the non-vibration point, the dispersion degree of the time domain data is calculated by using a variance coefficient method in statistics, and the position where vibration is likely to occur is judged.
Step 12, L P of vibration point is extracted from the original data obtained in step 901Die sum L P11Time domain data of the modulus, respectively to the L P01Die sum L P11The variance and range of the time domain signal of the module are calculated to obtain L P01Die sum L P11The variance and the range of the modes are very poor.
Step 13, L P of vibration point is extracted from the original data obtained in step 901Die sum L P11Model time domain data, using empirical mode decomposition for L P01Die sum L P11Decomposing the time domain signal of the module to obtain L P01Die sum L P11Eigenmode component of mode vibration signal, and respectively pair L P01Die sum L P11The eigenmode component of the mode vibration signal is integrated to obtain L P01Die sum L P11And (4) the energy value of the eigenmode component of the mode vibration signal.
Step 14, L P obtained in step 1201Die sum L P11Variance and range of the mode and L P obtained in step 1301Die sum L P11The energy value of the eigenmode component of the mode vibration signal is correspondingly sent to a neural network for processing, and the neural network judges and identifies whether the vibration at the position is the vehicle vibration.
It should be noted that, although the above-mentioned embodiments of the present invention are illustrative, the present invention is not limited thereto, and therefore, the present invention is not limited to the above-mentioned embodiments. Other embodiments, which can be made by those skilled in the art in light of the teachings of the present invention, are considered to be within the scope of the present invention without departing from the principles thereof.
Claims (5)
1. A vehicle vibration monitoring device based on two-mode optical fibers is characterized by comprising a laser, a pulse light generator, a circulator, a mode division multiplexer, two-mode sensing optical fibers, a collection card, a digital signal processing unit, 2 polarization controllers, 2 photoelectric conversion and electric signal processing modules and 4 optical couplers;
the output end of the laser is connected with the input end of a first optical coupler, one output end of the first optical coupler is connected with the input end of a pulse light generator, and the other output end of the first optical coupler is connected with the input end of a second optical coupler;
the output end of the pulse light generator is connected with the first port of the optical circulator, and the second port of the optical circulator is connected with L P of the mode division multiplexer01The multiplexing port of the mode division multiplexer is connected with two mode sensing optical fibers; two-mode sensing optical fibers are laid along the road ground;
the third port of the optical circulator is connected with one input end of a third optical coupler and L P of the mode division multiplexer11The mould port is connected with one input end of the fourth optical coupler;
one output end of the second optical coupler is connected with the other input end of the third optical coupler through the first polarization controller; the other output end of the second optical coupler is connected with the other input end of the fourth optical coupler through a second polarization controller;
two output ends of the third optical coupler are simultaneously connected with two input ends of the first photoelectric conversion and electric signal processing module, and two output ends of the first photoelectric conversion and electric signal processing module are simultaneously connected with the acquisition card; two output ends of the fourth optical coupler are simultaneously connected with two input ends of the second photoelectric conversion and electric signal processing module, and two output ends of the second photoelectric conversion and electric signal processing module are simultaneously connected with the acquisition card; the output end of the acquisition card is connected with the input end of the digital signal processing unit.
2. The apparatus of claim 1, wherein the first optical coupler has a splitting ratio of 80:20, wherein 80% of the output is connected to the input of the pulse light generator, and 20% of the output is connected to the input of the second optical coupler.
3. The two-mode optical fiber-based vehicle vibration monitoring device according to claim 1, wherein the second optical coupler, the third optical coupler and the fourth optical coupler have a splitting ratio of 50: 50.
4. The apparatus according to claim 1, wherein the pulse light generator is a fiber coupled acousto-optic modulator that generates pulsed light with a pulse period that is longer than a round-trip time for light to travel through the two-mode sensing fiber.
5. The apparatus as claimed in claim 1, wherein the two outputs of the first optical-to-electrical conversion and signal processing module output IQ two-path rf signals, which carry L P signals01Two output ends of the second photoelectric conversion and electric signal processing module output IQ two-path radio frequency signals which carry L P11And (4) mode backward Rayleigh scattering light information.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113483880A (en) * | 2021-08-17 | 2021-10-08 | 广东电网有限责任公司 | Vibration sensing system based on few-mode optical fiber |
| CN115035667A (en) * | 2022-05-13 | 2022-09-09 | 南京邮电大学 | Photon fence system for optical fiber mode division multiplexing real-time video transmission |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113483880A (en) * | 2021-08-17 | 2021-10-08 | 广东电网有限责任公司 | Vibration sensing system based on few-mode optical fiber |
| CN115035667A (en) * | 2022-05-13 | 2022-09-09 | 南京邮电大学 | Photon fence system for optical fiber mode division multiplexing real-time video transmission |
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