CN110940364A - Distributed two-arm sensing system based on Michelson interferometer - Google Patents
Distributed two-arm sensing system based on Michelson interferometer Download PDFInfo
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- CN110940364A CN110940364A CN201911169094.4A CN201911169094A CN110940364A CN 110940364 A CN110940364 A CN 110940364A CN 201911169094 A CN201911169094 A CN 201911169094A CN 110940364 A CN110940364 A CN 110940364A
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- 239000013307 optical fiber Substances 0.000 claims abstract description 31
- 238000001514 detection method Methods 0.000 claims abstract description 18
- 230000003287 optical effect Effects 0.000 claims abstract description 17
- 230000001427 coherent effect Effects 0.000 claims abstract description 7
- 239000000835 fiber Substances 0.000 claims abstract description 4
- 239000000126 substance Substances 0.000 claims description 7
- 230000000694 effects Effects 0.000 claims description 5
- 230000007613 environmental effect Effects 0.000 claims description 2
- 230000010287 polarization Effects 0.000 claims description 2
- 238000012544 monitoring process Methods 0.000 description 4
- 230000005540 biological transmission Effects 0.000 description 1
- 238000009529 body temperature measurement Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
- G01D5/35306—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 an interferometer arrangement
- G01D5/35325—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 an interferometer arrangement using interferometer with two arms in reflection, e.g. Mickelson interferometer
Abstract
The invention belongs to the technical field of optical fiber sensing, and particularly relates to a distributed two-arm sensing system based on a Michelson interferometer. The system takes two arms of a Michelson interferometer as sensing arms, and the two sensing arms are distinguished through a signal analysis algorithm; the system is formed by connecting a narrow-band laser, an optical isolator, two detectors, a 3 multiplied by 3 optical fiber coupler, two sensing optical cables and two Faraday rotating mirrors through an optical path; the narrow-band laser emits coherent light waves which enter the 3 multiplied by 3 optical fiber coupler and are divided into three beams of light with equal power, wherein one beam of light is coupled out of the fiber core when passing through the knotted optical fiber; the other two beams of light are used as detection light waves and enter the two sensing arms respectively; two beams of detection light waves are reflected by the two Faraday rotation mirrors and then enter the 3 multiplied by 3 coupler again to generate interference; the action of the external environment on the optical cable is recorded in the phases of the two detection light waves; and a computer with an acquisition card is used for acquiring the photoelectric signals and demodulating phase difference information, so that the disturbance intensity and position can be judged.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensing, and particularly relates to a distributed two-arm sensing system based on a Michelson interferometer.
Background
Distributed optical fiber sensors are often applied to the fields of perimeter security, oil pipe leakage monitoring, power cable damage monitoring, bridge safety monitoring and the like. The optical fiber integrates sensing and transmission, can carry out continuous vibration or temperature measurement on the whole length of the optical fiber, and simultaneously obtains the specific position to be measured. The distributed optical fiber sensing system based on the Michelson optical fiber interferometer has the advantages of long monitoring distance, high sensitivity, wide application range, simple structure and the like. However, the current solutions use one of the two michelson arms as the sensing arm and the other arm as the reference arm. And the reference arm needs to be placed in a quiet vibration-free environment. This undoubtedly increases the difficulty of implementing the system and reduces the reliability of the system.
Disclosure of Invention
The invention aims to provide a distributed two-arm sensing system based on a Michelson interferometer so as to improve the stability and working distance of a single set of sensing system.
According to the distributed two-arm sensing system based on the Michelson interferometer, the two arms of the Michelson interferometer are used as sensing arms, and the two sensing arms can be distinguished through a signal analysis algorithm; the system is formed by connecting a narrow-band laser, an optical isolator, a first detector, a second detector, a 3 x 3 optical fiber coupler, a first sensing optical cable, a second sensing optical cable, a first Faraday rotator mirror and a second Faraday rotator mirror through an optical path; the narrow-band laser emits coherent light waves, the coherent light waves enter the 3 x 3 optical fiber coupler and are divided into three beams of light with equal power, and one beam of light is coupled out of the fiber core when passing through the knotted optical fiber; the other two beams of light are used as detection light waves and enter the first sensing arm and the second sensing arm 2 respectively; the first detection light wave and the second detection light wave are reflected back by the first Faraday rotator mirror and the second Faraday rotator mirror and then enter the 3 multiplied by 3 coupler again to generate interference; the effect of the external environment on the optical cable is recorded in the phases of the first detection light wave and the second detection light wave; the phase information is presented through the voltage intensity of the first light detector and the second light detector; and a computer with an acquisition card is used for acquiring the photoelectric signals and demodulating phase difference information, so that the disturbance intensity and position can be judged.
The distributed two-arm sensing system of the Michelson optical fiber interferometer uses the optical isolator to prevent backward scattering light of the sensing arm and reflected signal light from entering the laser and influencing the working state of the laser. And the sensing arms are respectively provided with a Faraday rotating mirror so as to realize that the system keeps a polarization stable state.
According to the distributed two-arm sensing system of the Michelson optical fiber interferometer, both Michelson arms are used as sensing arms and are spread along a path to be monitored.
The distributed two-arm sensing system of the Michelson optical fiber interferometer demodulates a phase difference signal generated by disturbance, analyzes the direction of the initial amplitude of the phase difference, distinguishes the sensing arm where the vibration is located, and calculates the position and the strength of the disturbance.
In the distributed two-arm sensing system of the michelson optical fiber interferometer, the direction of the initial amplitude of the phase difference is analyzed by demodulating the phase difference signal generated by the disturbance, the sensing arm where the vibration is located is distinguished, and the disturbance position and the disturbance intensity are calculated.
In the distributed two-arm sensing system of the michelson optical fiber interferometer, the phase difference expression between the reference arm 1 and the reference arm 2 is as follows:
wherein the content of the first and second substances,φ 1(t) Andφ 1(t) Representing phase information on the first and second sensor arms, respectively. Since the influence of the external temperature and the atmospheric pressure on the optical fiber is slowly changed and weak, it is assumed here that the environmental conditions of the two sensing arms are consistent, i.e. the phase difference between the two sensing arms is zero when there is no disturbance. Assuming that the signal light is disturbed at any point on the sensing arm, the phase change of the signal light caused by the photoelastic effect can be described as a superposition of cosine waves of different frequencies and amplitudes, and the expression is as follows:
wherein the content of the first and second substances,Ψ i ，ω i and phi i Representing the amplitude, angular frequency and phase of the signal, respectively.
When external disturbance is applied to the first sensing arm 1, according to the two-arm phase:
the following results were obtained:
when external disturbance is applied to the second sensing arm 2, according to the two-arm phase:
the following results were obtained:
it can be seen that when external perturbations are applied to different sensing arms, the phase difference obtained is different. According to the interference formula:
wherein the content of the first and second substances,I 0which is indicative of the intensity of the output light,φ 0(t) Representing the random phase of the two sensing arms brought by the external environment,φ 0representing the fixed phase introduced by the 3 x 3 coupler. Adjusted out Δφ(t) Then, the initial direction of the phase difference amplitude is judged, and the sensing arm acted by the disturbance can be distinguished.
Drawings
Fig. 1 is a schematic representation of a distributed two-arm sensing system of a michelson optical fiber interferometer of the present invention.
Fig. 2 shows a distributed two-arm sensing system using the michelson optical fiber interferometer of the present invention to detect an original interference signal of the vibration of the first sensing arm 1.
Fig. 3 shows a distributed two-arm sensing system using the michelson optical fiber interferometer of the present invention, which detects a phase difference signal generated by the vibration of the first sensing arm 1.
Fig. 4 shows a distributed two-arm sensing system using the michelson optical fiber interferometer of the present invention to detect the original interference signal of the vibration of the second sensing arm 2.
Fig. 5 shows a distributed two-arm sensing system using the michelson optical fiber interferometer of the present invention, which detects a phase difference signal generated by the vibration of the second sensing arm 2.
Fig. 6 is a flowchart of an algorithm for distinguishing vibration in the first sensing arm 1 or the second sensing arm 2 of the distributed two-arm sensing system of the michelson optical fiber interferometer of the present invention.
Detailed Description
The following further describes embodiments of the present invention with reference to the drawings.
The distributed two-arm sensing system of the Michelson optical fiber interferometer is shown in figure 1, a narrow-band laser adopts a distributed feedback laser (DFB) to emit coherent light waves, the coherent light waves are divided into three beams of light with equal power by a 3 x 3 optical fiber coupler, and one beam of light is coupled out of a fiber core when passing through a knotted optical fiber. The other two beams of light enter the sensing arm 1 and the sensing arm 2 as detection light waves respectively. The detection light wave 1 and the detection light wave 2 are reflected back by the Faraday rotator and then enter the 3 multiplied by 3 coupler again to generate interference. The effect of the external environment on the optical cable will be recorded in the phase of the detection light wave 1 and the detection light wave 2. The phase information is represented by the voltage intensities of the light detector 1 and the light detector 2. And acquiring photoelectric signals and demodulating phase difference information by using a computer with an acquisition card with a sampling rate of 500kS/s, so that the disturbance intensity and position can be judged. The original interference signal is shown in fig. 2 and 4.
The phase difference expression between the first sensing arm 1 and the second sensing arm 2 can be expressed as follows:
wherein the content of the first and second substances,φ 1(t) Andφ 1(t) Representing the phase information on the sensor arm 1 and the sensor arm 2, respectively. Demodulated phase difference signal Δφ(t) As shown in fig. 3 and 5. Wherein the phase difference of fig. 3 and 5 is reversed from the starting amplitude. Thus, the arm on which the disturbance is located can be identified immediately after automatic recognition by software programming. The flow of the algorithm for discriminating the vibrating arms is shown in fig. 6.
Claims (4)
1. A distributed two-arm sensing system based on a Michelson interferometer is characterized in that the two arms of the Michelson interferometer are used as sensing arms, and the two sensing arms are distinguished through a signal analysis algorithm; the system is formed by connecting a narrow-band laser, an optical isolator, a first detector, a second detector, a 3 x 3 optical fiber coupler, a first sensing optical cable, a second sensing optical cable, a first Faraday rotator mirror and a second Faraday rotator mirror through an optical path; the narrow-band laser emits coherent light waves, the coherent light waves enter the 3 x 3 optical fiber coupler and are divided into three beams of light with equal power, and one beam of light is coupled out of the fiber core when passing through the knotted optical fiber; the other two beams of light are used as detection light waves and enter the first sensing arm and the second sensing arm 2 respectively; the first detection light wave and the second detection light wave are reflected back by the first Faraday rotator mirror and the second Faraday rotator mirror and then enter the 3 multiplied by 3 coupler again to generate interference; the effect of the external environment on the optical cable is recorded in the phases of the first detection light wave and the second detection light wave; the phase information is presented through the voltage intensity of the first light detector and the second light detector; and a computer with an acquisition card is used for acquiring the photoelectric signals and demodulating phase difference information, so that the disturbance intensity and position can be judged.
2. The michelson interferometer-based distributed two-arm sensing system of claim 1, wherein an optical isolator is used to prevent backscattered light from the sensing arm and reflected signal light from entering the laser and affecting its operating state; and the sensing arms are respectively provided with a Faraday rotating mirror so as to realize that the system keeps a polarization stable state.
3. The michelson interferometer-based distributed two-arm sensing system of claim 1, wherein both michelson arms act as sensing arms that are spread along the path to be monitored.
4. The distributed two-arm sensing system based on the michelson interferometer according to claim 1, wherein the sensing arm where the vibration is located is identified by demodulating a phase difference signal generated by the disturbance, analyzing the direction of the initial amplitude of the phase difference, and calculating the position and intensity of the disturbance; the specific algorithm is as follows:
the phase difference expression between the first sensing arm and the second sensing arm is as follows:
wherein the content of the first and second substances,φ 1(t) Andφ 1(t) Representing phase information on the first and second sensing arms, respectively; the environmental conditions of the two sensing arms are assumed to be consistent, namely the phase difference of the two sensing arms is zero when no disturbance exists; when the phase of the signal light is disturbed at any point on the sensing arm, the phase change of the signal light caused by the photoelastic effect is described as the superposition of cosine waves with different frequencies and amplitudes, and the expression is as follows:
wherein the content of the first and second substances,Ψ i ，ω i and phi i Respectively representing the amplitude, angular frequency and phase of the signal;
when external disturbance is applied to the first sensing arm, according to the two-arm phase:
obtaining:
when external disturbance is applied to the second sensing arm, according to the two-arm phase:
obtaining:
therefore, when external disturbance action is applied to different sensing arms, the obtained phase difference is different; according to the interference formula:
wherein the content of the first and second substances,I 0which is indicative of the intensity of the output light,φ 0(t) Representing the random phase of the two sensing arms brought by the external environment,φ 0represents the fixed phase introduced by the 3 x 3 coupler; adjusted out Δφ(t) Then, the initial direction of the phase difference amplitude is judged, and the sensing arm acted by the disturbance can be distinguished.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113267648A (en) * | 2021-03-26 | 2021-08-17 | 浙江大学 | Hybrid integrated optical accelerometer based on Michelson interference |
| CN113607261A (en) * | 2021-07-19 | 2021-11-05 | 复旦大学 | Optical fiber sensing system with phase-sensitive optical time domain reflection and optical fiber interference fusion |
| CN113624323A (en) * | 2021-08-09 | 2021-11-09 | 复旦大学 | Sagnac interference type acoustic wave sensor with delay optical fiber capable of resisting external interference |
| CN113932910A (en) * | 2021-11-15 | 2022-01-14 | 东北石油大学 | Dual-channel vibration measurement method and device based on optical fiber FP interference |
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