CN106452570A - Optical fiber fault detection system and detection method based on optical fiber phase mediation principle - Google Patents
Optical fiber fault detection system and detection method based on optical fiber phase mediation principle Download PDFInfo
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Abstract
The invention provides an optical fiber fault detection system and detection method based on the optical fiber phase mediation principle. The method comprises the following steps: a laser, a star-shaped coupler, an optical fiber loop, a receiving module and a signal processing module are separately connected; the star-shaped coupler divides a beam of light path emitted by the laser into two beams of coherent light having the same light power; the two beams of coherent light enter the optical fiber loop and are separately transmitted in the optical fiber loop along opposite directions, when the optical fiber loop is interfered by an external signal, an optical signal transmitted by the star-shaped coupler and received by the receiving module contains an external interference signal; the receiving module transmits the optical signal containing the external interference signal to the signal processing module; and the signal processing module demodulates the received optical signal containing the external interference signal in a signal demodulation mode so as to detect the position of the interference signal. By adoption of the optical fiber fault detection system and detection method provided by the invention, the position of an optical fiber fault point can be detected quickly and accurately.
Description
Technical Field
The invention relates to the technical field of communication, in particular to an optical fiber fault detection system and method based on an optical fiber phase adjustment principle.
Background
Optical fiber communication optical fiber is a very important device in the field of communication, and once a fault occurs, the stability of communication is affected, and even the communication is interrupted. Therefore, when the optical fiber fails, the fault point needs to be positioned in time, so that maintenance personnel can maintain or replace the optical fiber in time, and smooth communication is ensured.
At present, an OTDR (Optical Time Domain Reflectometer) based on fresnel reflection is usually adopted to measure the length from a fault point, and the fault point is positioned along an Optical fiber path according to the path direction of the Optical fiber, but the OTDR has the defects of weak reflected signal, poor precision, difficulty in detection and the like, so that the method is difficult to ensure that the fault point is positioned and processed in a short Time, and the Optical fiber fault cannot be timely recovered.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide an optical fiber fault detection system and a detection method based on the optical fiber phase adjustment principle, so as to solve the problems of poor positioning accuracy and difficulty in positioning a fault point of an optical fiber in the conventional fault positioning method.
The invention provides an optical fiber fault detection system based on an optical fiber phase mediation principle, which comprises: the device comprises a laser, a receiving module, a star coupler, an optical fiber loop and a signal processing module; the star coupler is used for dividing a light path emitted by the laser into two beams of coherent light with the same optical power; the star coupler is respectively connected with the optical fiber loop and the receiving module, two beams of coherent light separated by the star coupler enter two ends of the optical fiber loop, are respectively transmitted along opposite directions in the optical fiber loop, and receive optical signals transmitted back by the star coupler through the receiving module; when the optical fiber loop is interfered by an external signal, the optical signal received by the receiving module comprises an external interference signal; the signal processing module is connected with the receiving module and used for receiving the optical signal which is output by the receiving module and contains the external interference signal, and demodulating the received optical signal which contains the external interference signal so as to detect the position of the external interference signal.
In another aspect, the present invention provides a method for detecting an optical fiber fault by using the optical fiber fault detection system based on the optical fiber phase-adjusting principle, including:
respectively connecting a laser, a star coupler, an optical fiber loop, a receiving module and a signal processing module;
the star coupler divides a light path emitted by the laser into two beams of coherent light with the same optical power;
the two beams of coherent light enter the optical fiber loop and are respectively transmitted in the opposite directions in the optical fiber loop, and when the optical fiber loop is interfered by an external signal, the optical signal transmitted back by the star coupler received by the receiving module comprises the external interference signal;
the receiving module transmits the received optical signal containing the external interference signal to the signal processing module;
the signal processing module demodulates the received optical signal containing the external interference signal in a signal demodulation mode to detect the position of the interference signal.
Therefore, the optical fiber fault detection system and the detection method based on the optical fiber phase mediation principle can measure information which is several kilometers or even tens of kilometers along an optical fiber transmission path, are high in sensitivity and large in dynamic range, and when a fault point is detected, a user can quickly and accurately detect the position of the fault point of the optical fiber only by knocking the optical fiber at a test end (namely knocking on an optical fiber loop).
Drawings
Other objects and results of the present invention will become more apparent and more readily appreciated as the same becomes better understood by reference to the following description and appended claims, taken in conjunction with the accompanying drawings. In the drawings:
FIG. 1 is a schematic structural diagram of an optical fiber fault detection system based on an optical fiber phase adjustment principle according to an embodiment of the present invention;
FIG. 2 is a simulation of the superposition of sinusoidal signals of different frequencies;
FIG. 3 is a time domain diagram of phase differences obtained by simulating phase differences;
FIG. 4 is a phase difference spectrum plot obtained by simulating a phase difference time domain signal;
FIG. 5 shows the position R of the interference signal1A relation curve chart between the zero frequency point and the zero frequency point;
fig. 6 is a schematic structural diagram of a test platform constructed by using the optical fiber fault detection system based on the optical fiber phase adjustment principle provided by the invention;
FIG. 7 is a waveform of a tap signal detected after applying the tap signal at point c;
fig. 8 is a phase difference spectrum diagram obtained by applying a tap signal at point c and performing fourier transform on the tap signal.
Detailed Description
Specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
Aiming at the problems that the existing optical fiber fault positioning method has poor positioning precision and is difficult to position an optical fiber fault point, the optical fiber fault positioning method is used for detecting the optical fiber fault based on the optical fiber phase adjustment principle, a sensing system integrating sensing and transmission is formed by a laser, a star coupler, an optical fiber loop, a receiving module and a signal processing module, so that information which is several kilometers or even dozens of kilometers along an optical fiber transmission path can be measured, the sensitivity is high, the dynamic range is large, and when the fault point is detected, a user can quickly and accurately detect the position of the optical fiber fault point only by knocking an optical fiber on a testing end (namely knocking on the optical fiber loop).
In order to illustrate the optical fiber fault detection system based on the optical fiber phase mediation principle provided by the present invention, fig. 1 shows the structure of the optical fiber fault detection system based on the optical fiber phase mediation principle according to the embodiment of the present invention.
As shown in fig. 1, the optical fiber fault detection system based on the optical fiber phase-adjusting principle provided by the present invention includes a laser 10, a receiving module 20, a star coupler 30, an optical fiber loop 40 and a signal processing module 50. The laser is connected with the star coupler and used for dividing a light path emitted by the laser 10 into two beams of coherent light with the same optical power through the star coupler 30; the star coupler 30 is connected to the optical fiber loop 40 and the receiving module 20, respectively, two coherent light beams split by the star coupler 30 enter two ends of the optical fiber loop 40, and are transmitted in the optical fiber loop 40 in opposite directions (i.e., the two coherent light beams are transmitted in opposite directions), respectively, and receive an optical signal transmitted back by the star coupler through the receiving module 20; when the optical fiber loop 40 is interfered by an external signal, the optical signal received by the receiving module 20 includes the external interference signal (i.e., when the optical fiber loop is interfered by the external signal, a phase difference between two coherent light beams may be generated in the optical fiber loop, and the phase difference includes the external interference signal); the signal processing module 50 is connected to the receiving module 20, and is configured to receive the optical signal including the external interference signal output by the receiving module 20, and demodulate the received optical signal including the external interference signal to detect a position of the external interference signal.
Specifically, the signal processing module comprises a preamplifier module, an amplifier module, a demodulation module and a display module; the preamplifier module is connected with the receiving module and is used for pre-amplifying an optical signal which is output by the receiving module and contains an external interference signal; the amplifier module is connected with the preamplifier module and is used for amplifying the optical signal which is pre-amplified by the preamplifier module and contains the external interference signal; the demodulation module is connected with the amplifier module and is used for demodulating the optical signal which is amplified by the amplifier module and contains the external interference signal to obtain a demodulation result; the display module is connected with the demodulation module and used for displaying the demodulation result obtained by the demodulation module. Wherein, the demodulation result displayed by the display module comprises: a time domain waveform of the optical signal including the external interference signal, a frequency spectrum of the optical signal including the external interference signal, and a position value of the external interference signal.
Referring to fig. 1, in one example of the present invention, a laser emits a 1550nm optical path, which is split into 1: 1, respectively. As shown by two opposite arrows in fig. 1, the two coherent light beams enter the optical fiber loop and are transmitted in opposite directions, and according to the theory of light interference, the two coherent light beams conform to the interference conditions of the same frequency, the same vibration direction, and the same phase difference, so that interference is generated inside the optical fiber loop to form interference fringes, when there is no interference signal outside, the interference phenomenon is stable, and when the optical fiber loop is interfered by an external signal (an arrow perpendicular to the optical fiber loop 40 in fig. 1 is an interference signal), the interference fringes change (i.e., the two coherent light beams generate a phase difference). The change (namely, the phase difference generated by the two coherent light beams is acquired) can be detected by the receiving module, and the change of the interference fringes detected by the receiving module is analyzed and processed by the signal processing module, so that the detection of the external interference signal can be realized.
It should be noted that, in practical application, for the laid optical fibers, in order to form the optical fiber loop shown in fig. 1, the corresponding optical fiber spare fibers can be found out in the machine room where the optical fibers to be tested are located according to the fiber core identifier, and the flange plate is used to perform loopback, so as to form the optical fiber loop required by the test.
The star coupler is a device that combines optical powers input by n optical fibers and uniformly distributes the combined optical powers to m optical fibers.
On the other hand, the invention also provides an optical fiber fault detection method based on the optical fiber phase mediation principle, which utilizes the optical fiber fault detection system based on the optical fiber phase mediation principle to detect optical fiber faults, and the method specifically comprises the following steps:
1. respectively connecting a laser, a star coupler, an optical fiber loop, a receiving module and a signal processing module;
2. the star coupler divides a light path emitted by the laser into two beams of coherent light with the same optical power;
3. the two beams of coherent light enter the optical fiber loop and are respectively transmitted in the opposite directions in the optical fiber loop, and when the optical fiber loop is interfered by an external signal, the optical signal transmitted back by the star coupler received by the receiving module comprises an external interference signal;
4. the receiving module transmits the received optical signal containing the external interference signal to the signal processing module;
5. the signal processing module demodulates the received optical signal containing the external interference signal in a signal demodulation mode to detect the position of the external interference signal.
Specifically, the process of detecting the interference signal will be described in detail below with reference to fig. 1. As shown in fig. 1, an optical path propagating clockwise is defined as an optical path 1, and an optical path propagating counterclockwise is defined as an optical path 2. When the external has interference signal (for example, knock optical fiber loop), the external interference signal acts on the optical fiber of the optical fiber loop, which will cause the phase shift change of two beams of light in the optical path 1 and the optical path 2, thereby generating a phase difference, which contains the interference signal, and analyzing the phase difference can realize the detection of the interference signal, wherein, the electric field expressions of the optical path 1 and the optical path 2 are respectively:
in the formula: e1And E2Is the electric field strength; e10And E20The magnitude of the optical electric field of the two paths of light; omegacIs the light wave angular frequency;andthe initial phase of the two paths of light; theta1(t) and θ2(t) is the phase change caused by the external interference signal on optical path 1 and optical path 2. These two phase changes can be expressed as
In the formula:is the amplitude of the phase change signal; omegasIs the angular velocity of the phase change signal; tau is1The time when the light reaches the external interference signal point 1 time after passing through the optical path 1 from the laser; tau is2The time 1 st time after the light passes through the optical path 2 from the laser to the external interference signal point. As shown in FIG. 1, the external interference signal point is at a distance R from the star coupler1And the length of the sensing fiber is L, then tau1And τ2Are respectively represented as
The total optical power detected by the photodetector is
IGeneral assembly＝(E1+E2)·(E1+E2)*＝(E1+E2)·E1 *+(E1+E2)·E2 *
＝E1·E1 *+E2·E2 *+E1·E2 *+E2·E1 *
＝E1·E1 *+E2·E2 *+(E1·E2 *+E2·E1 *)
＝|E1|2+|E2|2+IInterference
(formula 7)
Wherein the interference term is:
therefore, when an external interference signal is applied to the optical fiber in the optical fiber loop, the interference term is detected by the receiving module, and the phase difference can be demodulated from the interference signal by a signal demodulation technology.
From the above, the phase difference generated by the two coherent light beams in the optical fiber loop can be expressed by the following formula:
(formula 9)
Wherein, Delta theta is the phase difference generated by the two coherent light beams in the optical fiber loop, and theta is1(t) interference signals are coherent in one beamOptically induced phase change signal, theta2(t) is a phase change signal caused by the interference signal on the other beam of coherent light,being the amplitude, omega, of the phase-varying signalsIs the angular velocity of the phase-change signal, t is a time variable, τ1The time of the light from the laser to the external interference signal point after 1 st time of the coherent light beam2The time when the light reaches the external interference signal point 1 time after passing another beam of coherent light after being emitted from the laser, Δ τ ═ τ2-τ1Is the delay time difference from the external interference signal point to the end point of the two coherent light beams, whereint＝τ1+τ2。
Fourier transforming equation (9) can facilitate spectral analysis. Namely: fourier transformation is carried out on the phase difference generated by the two beams of coherent light in the optical fiber loop, and a phase difference signal frequency spectrum is obtained; wherein,
acquiring a phase difference signal spectrum by the following formula:
wherein, F (omega) is a signal spectrum; f is a frequency variable; f. ofsIs the interference signal frequency.
Since the external interference signal is a broadband signal, when sinusoidal signals with different frequencies are superimposed, Matlab can be used to simulate the phenomenon of superimposing sinusoidal signals with different frequencies. In which fig. 2 shows a simulation diagram of the superposition of sinusoidal signals of different frequencies.
Fig. 2 shows sinusoidal signals whose frequency ranges from 0 to 10Hz and are superimposed at frequency intervals of 0.01Hz, and it can be seen from fig. 2 that the frequency exists so that the value of the sinusoidal signals is zero. Therefore, in the formula (10), when there is an interference signal, the interference signal is in a wide frequency range of the external interference signalCertain frequencies occur therein so thatThese frequency points are called zero frequency points, and it can also be known that the simulated graph envelope of equation (10) is similar to fig. 2. Therefore, it can be seen that whenfsIs a zero frequency point, and N is a positive integer and generally takes 1.
The equations (9) and (10) are simulated, and the interference frequency f is selectedsIn the range of 700 to 1000HzA sinusoidal signal with a precision of 1 (i.e. with a frequency interval of 1 Hz) is superimposed on the simulated external interference signal and a certain amount of white gaussian noise is superimposed, the frequency variable f is set to 1000, and L is set to 6 × 10 for the convenience of simulation8m，R1Is 2 × 108m, Δ τ is 0.5 s. Fig. 3 and 4 respectively show a phase difference time domain diagram obtained by simulating a phase difference and a phase difference spectrum diagram obtained by simulating a phase difference signal spectrum.
As shown in fig. 4, the phase difference spectrogram is symmetrical about the x-axis frequency equal to 0, and only the right spectrogram having practical significance is taken as a reference, it can be seen that the envelope is similar to that of fig. 2, and due to the existence of noise, the frequency point corresponding to the lowest point of each wave can be regarded as a zero frequency point. Through simulation, it is shown that the detection of the external interference signal can be realized by analyzing the zero frequency point of the external interference signal contained in the phase difference spectrogram.
Position R of external interference signal1And zero frequency point fsThe relationship between them is:
from equation (11), the position R1 of the external interference signal can be derived as
Wherein R is1The position of the external interference signal is detected, L is the length of the optical fiber loop, N is the refractive index of the optical fiber in the optical fiber loop, N is a positive integer which makes the amplitude in the phase difference spectrum signal zero, and usually takes the value of 1, c is the speed of light, so that the interference signal obtained from the receiving module is processed by the signal processing module to obtain the required zero frequency point, that is, the position of the external interference signal can be obtained, thereby realizing the detection of the external interference signal.
Note that, in the case where there is a test blind area in the optical fiber circuit, the simulation analysis of equation (12) is performed, and L is 30km, N is 1, and N is 1.45, since (L-2R)1) Not being zero, taking R1The position R of the external interference signal is obtained and is 0-12 km1The relationship curve with the zero frequency point is shown in fig. 5.
As can be seen from fig. 5, the zero frequency point becomes higher as the interference distance increases. Therefore, the test distance is related to the frequency cut-off point of the interference signal, and the test cannot be carried out when the frequency cut-off point of the interference signal is exceeded, so that a test blind area with the central point of the whole loop as a starting point exists in the test.
The optical fiber fault detection system and the detection method based on the optical fiber phase mediation principle provided by the present invention will be further described below by way of example, wherein fig. 6 shows a structure of a test platform built by using the optical fiber fault detection system based on the optical fiber phase mediation principle provided by the present invention. As shown in fig. 6, the built test platform includes an optical fiber loop 61 and a test platform 62, wherein the test platform 62 includes a laser, a receiving module, a star coupler and a signal processing module. In the experiment, 6 optical fibers looped back by the flange plates for 30km form an optical fiber loop for testing. Each flange plate loops back 5km of optical fiber, three test points (namely interference points) of a, b and c are arranged in the optical fiber loop respectively, and the distances from the interference points to the tail end of the test platform are respectively 0m, 5km and 10 km. Applying a tap at point cThe waveform of the tap signal, detected as a tap signal, is shown in fig. 7. The signal processing module performs fourier transform on the interference signal to obtain a zero frequency point, and the obtained spectrogram is shown in fig. 8. From FIG. 8, the first zero frequency point is 20kHz. The test results of the zero frequency point obtained by performing 10 times of tests on each of the points a, b and c are shown in tables 1, 2 and 3:
| number of tests | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| Zero frequency point value | 6.868 | 6.857 | 6.859 | 6.868 | 6.860 | 6.859 | 6.860 | 6.859 | 6.8575 | 6.858 |
TABLE 1
TABLE 2
| Number of tests | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| Zero frequency point value | 20.3225 | 20.323 | 20.32 | 20.341 | 20.34 | 20.34 | 20.321 | 20.325 | 20.35 | 20.34 |
TABLE 3
Analyzing the test data, and respectively averaging the experimental results:
faverage＝(6.8586kHz，10.2600kHz，20.3344kHz)
Taking the maximum value: f. ofmax＝(6.86kHz，10.264kHz，20.35kHz)
Taking the minimum value: f. ofmin＝(6.857kHz，10.253kHz，20.32kHz)
The absolute error of the distance can be found:
ΔR1 average＝(83.0018m，82.678m，87.3532m)
ΔR1max＝(86.5212m，89.5617m，90.9585m)
ΔR1min＝(79.9236m，78.7486m，83.4534m)
The analysis of the experimental results shows that the maximum test error of the experiment does not exceed 91m, and the detection can be accurately carried out.
In addition, through analysis of results of experiments of multiple different distances, the maximum error of the measured distance of the optical fiber fault detection system and the detection method based on the optical fiber phase mediation principle provided by the invention is not more than 100m, so that the method for detecting the fault by using the optical fiber fault detection system based on the optical fiber phase mediation principle provided by the invention has better stability and accuracy.
The optical fiber fault detection system and detection method based on the optical fiber phase mediation principle according to the present invention are described above by way of example with reference to the accompanying drawings. However, it should be understood by those skilled in the art that various modifications can be made to the optical fiber fault detection system and method based on the optical fiber phase adjustment principle of the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention should be determined by the contents of the appended claims.
Claims (10)
1. An optical fiber fault detection system based on an optical fiber phase modulation principle comprises: the device comprises a laser, a receiving module, a star coupler, an optical fiber loop and a signal processing module; wherein,
the laser is connected with the star coupler and used for dividing a light path emitted by the laser into two beams of coherent light with the same optical power through the star coupler;
the star coupler is respectively connected with the optical fiber loop and the receiving module, two beams of coherent light separated by the star coupler enter two ends of the optical fiber loop, are respectively transmitted along opposite directions in the optical fiber loop, and receive optical signals returned by the star coupler through the receiving module; wherein,
when the optical fiber loop is interfered by an external signal, the optical signal received by the receiving module comprises an external interference signal;
the signal processing module is connected with the receiving module and is used for receiving the optical signal which is output by the receiving module and contains the external interference signal, and demodulating the received optical signal which contains the external interference signal so as to detect the position of the external interference signal.
2. The optical fiber fault detection system based on the optical fiber phase mediation principle as claimed in claim 1,
and according to the fiber core identification of the optical fiber, looping back the optical fiber spare fiber corresponding to the fiber core identification of the optical fiber through the flange plate to form an optical fiber loop.
3. The fiber optic phase-mediation principles-based fiber optic fault detection system of claim 1 wherein the signal processing module comprises a preamplifier module, an amplifier module, a demodulation module, and a display module; wherein,
the preamplifier module is connected with the receiving module and is used for pre-amplifying the optical signal which is output by the receiving module and contains the external interference signal;
the amplifier module is connected with the preamplifier module and is used for amplifying the optical signal which is pre-amplified by the preamplifier module and contains the external interference signal;
the demodulation module is connected with the amplifier module and is used for demodulating the optical signal which is amplified by the amplifier module and contains the external interference signal to obtain a demodulation result;
and the display module is connected with the demodulation module and used for displaying the demodulation result obtained by the demodulation module.
4. The optical fiber fault detection system based on the optical fiber phase mediation principle as claimed in claim 3,
the demodulation result displayed by the display module comprises: a time domain waveform of the optical signal including the external interference signal, a frequency spectrum of the optical signal including the external interference signal, and a position value of the external interference signal.
5. A method for detecting optical fiber faults based on the optical fiber phase-mediation principle, which uses the system for detecting optical fiber faults based on the optical fiber phase-mediation principle as claimed in any one of claims 1 or 4, the method comprising:
respectively connecting a laser, a star coupler, an optical fiber loop, a receiving module and a signal processing module;
the star coupler divides a light path emitted by the laser into two beams of coherent light with the same optical power;
the two beams of coherent light enter the optical fiber loop and are respectively transmitted in the opposite directions in the optical fiber loop, and when the optical fiber loop is interfered by an external signal, an optical signal returned by the star coupler received by the receiving module comprises an external interference signal;
the receiving module transmits the received optical signal containing the external interference signal to the signal processing module;
the signal processing module demodulates the received optical signal containing the external interference signal in a signal demodulation mode to detect the position of the external interference signal.
6. The method for detecting fiber faults based on the principle of fiber phase modulation as claimed in claim 5, wherein the two coherent light beams generate a phase difference in the fiber loop when the fiber loop is interfered by an external signal, wherein,
the phase difference generated by the two coherent light beams in the optical fiber loop is obtained through the following formula:
wherein, Delta theta is the phase difference generated by the two coherent light beams in the optical fiber loop, and theta is1(t) is the phase change signal, θ, caused by the external interference signal on one of the coherent light beams2(t) is a phase change signal caused by an external interference signal on another beam of coherent light,being the amplitude, omega, of the phase-varying signalsIs the angular velocity of the phase-change signal, t is a time variable, τ1The time of the light from the laser to the external interference signal point after 1 st time of the coherent light beam2The time when the light reaches the external interference signal point 1 time after passing another beam of coherent light after being emitted from the laser, Δ τ ═ τ2-τ1Is the delay time difference from the external interference signal point to the end point of the two coherent light beams, whereint＝τ1+τ2。
7. The optical fiber fault detection method based on optical fiber phase mediation principle as claimed in claim 6, wherein the τ is obtained by the following formula1：
The τ is obtained by the following formula2：
Wherein R is1The distance from the external interference signal point to the star coupler is shown, n is the refractive index of the optical fiber in the optical fiber loop, L is the length of the optical fiber loop, and C is the speed of light.
8. The optical fiber fault detection method based on the optical fiber phase mediation principle as claimed in claim 6, wherein a phase difference generated in the optical fiber loop by the two coherent light beams is subjected to fourier transform to obtain a phase difference signal spectrum; wherein,
obtaining the phase difference signal spectrum by the following formula:
wherein, F (omega) is a signal spectrum; f is a frequency variable; f. ofsIs the external interference signal frequency.
9. The optical fiber fault detection method based on the optical fiber phase mediation principle as claimed in claim 8, wherein a phase difference time domain signal is obtained by simulating a phase difference generated in the optical fiber loop by the two coherent light beams; and the number of the first and second groups,
simulating the phase difference time domain signal to obtain a phase difference frequency spectrum signal;
and acquiring an external interference signal zero frequency point contained in the phase difference spectrum signal according to the phase difference spectrum signal, and detecting the position of the external interference signal according to the acquired external interference signal zero frequency point.
10. The optical fiber fault detection method based on the optical fiber phase mediation principle as claimed in claim 9, wherein the position of the external disturbance signal is detected by the following formula:
wherein R is1For the position of the detected external interference signal, L is the length of the optical fiber loop, N is the refractive index of the optical fiber in the optical fiber loop, N is a positive integer that makes the amplitude in the phase difference spectrum signal zero, and usually takes the value of 1, and c is the speed of light.
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