CN116481627A - Sagnac interference type optical fiber intrusion sensing system based on diamond optical path difference biasing structure - Google Patents
Sagnac interference type optical fiber intrusion sensing system based on diamond optical path difference biasing structure Download PDFInfo
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- 238000001514 detection method Methods 0.000 description 9
- 238000005259 measurement Methods 0.000 description 9
- 230000008859 change Effects 0.000 description 6
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- 238000001228 spectrum Methods 0.000 description 5
- 238000000034 method Methods 0.000 description 4
- 230000001902 propagating effect Effects 0.000 description 4
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- 230000005540 biological transmission Effects 0.000 description 2
- 238000009530 blood pressure measurement Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 230000009545 invasion Effects 0.000 description 2
- 230000010363 phase shift Effects 0.000 description 2
- 230000008569 process Effects 0.000 description 2
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- 230000003595 spectral effect Effects 0.000 description 2
- 238000003491 array Methods 0.000 description 1
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- 230000036962 time dependent Effects 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
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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
- G01D5/35322—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 one loop with several directions of circulation of the light, e.g. Sagnac interferometer
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
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- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B13/00—Burglar, theft or intruder alarms
- G08B13/02—Mechanical actuation
- G08B13/12—Mechanical actuation by the breaking or disturbance of stretched cords or wires
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Abstract
The invention belongs to the technical field of distributed optical fiber sensing, and discloses a Sagnac interference type optical fiber intrusion sensing system based on a diamond optical path difference biasing structure, which comprises a laser, a diamond optical path difference biasing structure, a sensing optical fiber and a detector; the optical fiber type diamond optical path difference biasing structure comprises 4 optical fiber couplers with 50:50 beam splitting ratio and optical fibers connected with the optical fiber couplers; the four optical fiber couplers are respectively connected into a ring through four optical fibers; wherein the lengths of the four optical fibers are not uniform to introduce an optical path difference bias d. The laser is connected with the first optical fiber coupler through a single mode fiber, and the detector is connected with the third optical fiber coupler through a single mode fiber; and two ends of the sensing optical fiber are respectively connected with the second optical fiber coupler and the fourth optical fiber coupler. The Sagnac interference type optical fiber intrusion sensing system has the outstanding advantages of easy processing and assembly of an all-fiber structure, high algorithm demodulation speed, strong instantaneity, low system cost, simple electrical system and the like.
Description
Technical Field
The invention belongs to the technical field of distributed optical fiber sensing, and relates to a Sagnac interference type optical fiber intrusion sensing system based on a diamond optical path difference biasing structure.
Background
In the 70 s of the 20 th century, with the rapid development of optical fiber communication, the optical fiber sensing technology starts to be a brand-new corner, which is a sensing technology for sensing and transmitting external signals by taking light waves as carriers and optical fibers as media. Compared with the traditional sensor, the optical fiber sensor has the unique advantages of small volume, light weight, electromagnetic interference resistance, corrosion resistance, high sensitivity, large measurement bandwidth, long transmission distance and the like. In particular, the sensitivity of the optical fiber sensor is generally higher than that of the conventional sensor by one or several orders of magnitude, and the optical fiber sensor is widely applied to fields such as object deformation measurement, vibration measurement, pressure measurement, temperature measurement, stress (strain) measurement, magnetic field measurement, refractive index measurement, micro-displacement measurement, sound pressure measurement and the like. The fiber optic Sagnac (Sagnac) interferometer has achieved a certain degree of success in practical applications in both the fiber optic gyroscope and the fiber optic current sensor. In brief, the Sagnac optical fiber interferometer is used as a fully closed ring interferometer, so when the light beam is emitted from the light source, the light beam is decomposed into two light beams, one light beam propagates clockwise, and the other light beam propagates anticlockwise, wherein the clockwise and anticlockwise light beams are modulated by external signals, and the two light beams interfere.
The measured parameter of the interference type optical fiber vibration sensor is vibration, when an external vibration signal acts on the sensing optical fiber, the phase of the light wave in the optical fiber subjected to vibration modulation can be changed, and then the phase change of the light wave is converted into the output light intensity change by utilizing an interference demodulation technology, so that the vibration signal to be measured is restored. In various interferometer structures, the Segreave interferometer has complete reciprocity due to the special structure, the two beams of light are modulated consistently, and the reciprocity can counteract external interference, so that the influence caused by interference of other factors such as environmental temperature is avoided. At present, an intrusion detection sensor based on a Sagnac interferometer principle is used as a commercial sensing device, has been developed in a practical direction, and achieves a certain effect, and the application scene of the intrusion detection sensor is generally in perimeter security protection of hospitals, military areas and the like.
Compared with an interference type Sagnac intrusion detection sensor, the distributed optical fiber sensing technology based on the OFDR technology needs to form a linear sweep frequency light source by a narrow linewidth single longitudinal mode laser and an electro-optic modulator or an acousto-optic modulator, so that the requirement on the light source is high.
The invention has the following innovation points: firstly, the diamond optical path difference structure manufactured by welding four 1*2 optical fiber couplers in pairs can replace the traditional modulation and demodulation scheme, and intrusion positioning measurement can be realized by only one detection module, so that the influence caused by unbalance of a plurality of detectors and light splitting deviation of the couplers is solved, the positioning accuracy is improved, the system stability is improved, and the system complexity is reduced; secondly, the self-developed high-speed broadband wavelength tunable laser control system has the capability of rapid switching of discrete wavelengths, can realize broadband interference spectrum scanning and fixed single-wavelength output, and further optimizes an intrusion positioning system.
Disclosure of Invention
The invention aims to provide a Sagnac interference type optical fiber intrusion sensing system based on a diamond optical path difference biasing structure, which has the outstanding advantages of an all-fiber structure, high algorithm demodulation speed, real-time positioning detection, low system cost and the like.
The technical scheme of the invention is as follows:
a Sagnac interference type optical fiber intrusion sensing system based on a diamond optical path difference biasing structure comprises a laser, a diamond optical path difference biasing structure, a sensing optical fiber and a detector;
the diamond optical path difference biasing structure is formed by 4 optical fiber couplers with 50:50 spectral ratio or adopts a diamond optical path difference biasing structure based on planar optical waveguide (Planar Lightwave Circuit, PLC) technology; the optical fiber type diamond optical path difference biasing structure comprises 4 optical fiber couplers with 50:50 spectral ratio and optical fibers connected with the optical fiber couplers; the first optical fiber coupler and the second optical fiber coupler, the second optical fiber coupler and the third optical fiber coupler, the third optical fiber coupler and the fourth optical fiber coupler are respectively connected into a ring through the first optical fiber, the second optical fiber, the third optical fiber and the fourth optical fiber; wherein lengths of the first optical fiber, the second optical fiber, the third optical fiber and the fourth optical fiber are inconsistent to introduce an optical path difference bias d;
the laser is connected with the first optical fiber coupler through a single mode fiber, and the detector is connected with the third optical fiber coupler through a single mode fiber;
and two ends of the sensing optical fiber are respectively connected with the second optical fiber coupler and the fourth optical fiber coupler.
The laser is a wavelength scanning laser.
The detector is a synchronous detector or a spectrometer.
The sensing optical fiber is a single-mode optical fiber.
The invention has the beneficial effects that: the Sagnac interference type optical fiber intrusion vibration sensing system based on the diamond optical path difference biasing structure has the outstanding advantages of being easy to process and assemble, high in algorithm demodulation speed, strong in instantaneity, low in system cost, simple in electrical system and the like.
Drawings
FIG. 1 is a diagram of a Sagnac interferometric fiber-optic intrusion vibration sensing system;
FIG. 2 is a chart of frequency-intrusion position of zero frequency point of the Sagnac interferometric fiber intrusion vibration sensor;
FIG. 3 is a spectrum contrast diagram in the presence or absence of intrusion;
FIG. 4 is a diagram of a diamond optical path difference bias architecture based on PLC technology;
in the figure: 1 a first optical fiber; 2 a second optical fiber; 3 a third optical fiber; 4 a fourth optical fiber; 5 a first fiber coupler; 6 a second fiber coupler; a third fiber coupler; 8, a fourth optical fiber coupler; 9 a laser; a 10 detector; 11 sensing optical fibers; 12 a first port of a first fiber optic coupler; 13 a second port of the first fiber coupler; 14 a third port of the first fiber coupler; 15 a first port of a second fiber optic coupler; 16 a second port of a second fiber optic coupler; 17 a first port of a third fiber coupler; 18 a second port of a third fiber coupler; 19 a first port of a fourth fiber coupler; 20 a second port of a fourth fiber coupler; a third port of the second fiber coupler 21; 22 a third port of a third coupler; 23 a third port of a fourth fiber coupler; 24 first port; 25 second ports; a third port 26; 27 fourth port; 28 a first waveguide; 29 a second waveguide; a third waveguide 30; 31 fourth waveguide.
Detailed Description
The following describes the embodiments of the present invention in detail with reference to the technical scheme and the accompanying drawings.
The invention provides a Sagnac interference type optical fiber intrusion vibration sensing system based on a diamond optical path difference biasing structure, which is shown in figure 1 and comprises a laser 9, a first optical fiber coupler 5, a second optical fiber coupler 6, a third optical fiber coupler 7, a fourth optical fiber coupler 8, a sensing optical fiber 11 and a detector 10;
the optical output end of the laser 9 is connected with a first port 12 of a first optical fiber coupler through a single-mode optical fiber, a second port 13 of the first optical fiber coupler is connected with a first port 15 of a second optical fiber coupler through a first optical fiber 1, a third port 14 of the first optical fiber coupler is connected with a second port 20 of the fourth optical fiber coupler through a fourth optical fiber 4, a third port 21 of the second optical fiber coupler is connected with a third port 23 of the fourth optical fiber coupler through a sensing optical fiber 11, a second port 18 of the third optical fiber coupler is connected with a first port 19 of the fourth optical fiber coupler through a third optical fiber 3, a first port 17 of the third optical fiber coupler is connected with a second port 16 of the second optical fiber coupler through a second optical fiber 2, and a third port 22 of the third optical fiber coupler is connected with a synchronous detector or spectrometer through a single-mode optical fiber.
In the invention, the optical fiber diamond optical path difference biasing structure is formed by connecting a first optical fiber 1 between a first optical fiber coupler 5 and a second optical fiber coupler 6, connecting a second optical fiber 2 between the second optical fiber coupler 6 and a third optical fiber coupler 7, connecting a third optical fiber 3 between the third optical fiber coupler 7 and a fourth optical fiber coupler 8, and connecting a fourth optical fiber 4 between the fourth optical fiber coupler 8 and the first optical fiber coupler 5.
In the invention, the laser 9 is a wavelength scanning laser or a broad spectrum light source, and the detector 10 is a synchronous detector or a spectrometer.
In this configuration, optical path difference bias of clockwise propagating light and counterclockwise propagating light is achieved with a combination of four 1*2 fiber couplers.
The specific implementation method is as follows:
for clockwise propagating light, starting from the light source, the path traveled is:
the device comprises a laser 9, a first optical fiber coupler 5, a first optical fiber 1, a second optical fiber coupler 6, a sensing optical fiber 11, a fourth optical fiber coupler 8, a third optical fiber 3, a third optical fiber coupler 7 and a detector 10;
for light traveling counter-clockwise, the route traveled from the light source is:
the device comprises a laser 9, a first optical fiber coupler 5, a fourth optical fiber 4, a fourth optical fiber coupler 8, a sensing optical fiber 11, a second optical fiber coupler 6, a second optical fiber 2, a third optical fiber coupler 7 and a detector 10;
wherein the optical path difference bias is caused, and the nonreciprocal optical path parts are respectively:
clockwise: the first optical fiber 1-the second optical fiber coupler 6-the sensing optical fiber 11-the fourth optical fiber coupler 8-the third optical fiber 3;
counterclockwise: the fourth optical fiber 4-fourth optical fiber coupler 8-sensing optical fiber 11-second optical fiber coupler 6-second optical fiber 2;
considering that the second and fourth fiber couplers 6 and 8 and the sensing fiber 11 are common parts of both optical paths, they can be counted in reciprocal optical path parts.
Thus, the optical path part of the clockwise optical path and the anticlockwise optical path which are not reciprocal is as follows:
clockwise: a first optical fiber 1-a third optical fiber 3;
counterclockwise: a fourth optical fiber 4-a second optical fiber 2;
therefore, when the structural light path is designed, the light path difference d in the range of tens of um to several mm can be introduced between the light path combination of the clockwise first optical fiber 1-the third optical fiber 3 and the light path combination of the anticlockwise fourth optical fiber 4-the second optical fiber 2, so that the requirement of offset of the light path difference of two beams of light participating in interference in a white light interference signal demodulation mode is met.
When the sensing optical fiber is subjected to vibration caused by invasion, the length and refractive index of the sensing optical fiber change to generate phase modulation on an interference signal. Let the output light power of the light source be I 0 The interference signals received by the photoelectric detector are as follows:
since the time for the clockwise and counterclockwise propagation light to pass through the intrusion vibration point is different, the time for the propagation light in the two directions to undergo the phase modulation caused by the external vibration is different, and we assume that the phase of the propagation light passing through the clockwise return photodetector is changed to phi CW Phase change to a photodetector via a counter-clockwise path of propagating light CCW Phi can be expressed as:
φ＝φ CW -φ CCW (1.2) the disturbance vibration can be considered to act on a length of optical fibre, resulting in a phase change. We consider that the applied perturbation interval is much smaller than the length of the entire Sagnac fiber optic loop, then the phase shift can be expressed as:
where nd is the known OPD bias introduced; pi is the additional phase difference;is a time dependent phase shift caused by the invasive vibration; τ 1 And τ 2 Respectively represent two light beams along L 1 And L 2 Time of fiber path transmission (l=l 1 +L 2 ). It is possible to take formula (1.3) into formula (1.1):
we assume that the intrusion vibration signal applied to the optical fiber can be expressed by a sine wave form:
φ(t)＝φ 0 sin(ω s t) (1.5) wherein φ 0 Is the amplitude of the phase change caused by the incoming vibration signal, assuming phi 0 Small and ΔΦ=pi/2, then available:
the direct current component in the interference signal received by the PD detector can be filtered by a filter or a signal processing mode, and only the alternating current item part is concerned:
wherein the method comprises the steps of
From equation (1.8), it can be seen that the cosine ac output function has a periodically oscillating amplitude modulation term:
when formula (1.9) satisfies
At this time, there is a frequency defect at some frequency points, and it can be seen that the frequency defect points have a frequency of being
The distance L from the vibration position point to the tail end of the optical fiber can be obtained through a series of zero frequency points in the frequency spectrum 1 :
Wherein: l is the total length of the sensing optical fiber, n is the effective refractive index of the optical fiber, c is the speed of light in vacuum, and all are known quantities; and N is the order of zero frequency point, f s,null The zero frequency point frequency is measured, and the vibration invasion position L can be obtained 1 。
As shown in FIG. 2, which shows a measurement experiment of a vibration intrusion detection sensing system based on a diamond optical path difference biasing structure, it can be seen from the graph that the frequency of a zero frequency point presents a certain functional relationship with the intruded position. Fig. 3 is a spectrum comparison diagram in the intrusion state or not, and it can be seen that a distinct zero frequency point appears in the spectrum diagram in the intrusion state. The experiment shows that the Sagnac distributed intrusion detection sensor based on the diamond optical path difference biasing structure can realize the positioning function.
Alternatively, the diamond-shaped optical path difference biasing structure may be implemented using planar optical waveguide (Planar Lightwave Circuit, PLC) technology. The PLC planar optical waveguide is manufactured by adopting a semiconductor process, the optical waveguide is positioned on the upper surface of the chip, and the optical routing functions such as branching, combining and the like can be integrated in the chip. And respectively coupling the multichannel optical fiber arrays of the input end and the output end at two ends of the chip and packaging. The PLC planar optical waveguide technology is the mainstream mature technology for realizing optical fiber devices such as an optical fiber splitter, an array waveguide grating and the like. The optical path routing functions such as branching, combining and optical path difference offset required by the diamond optical path difference offset structure can be integrated in one PLC planar optical waveguide through the optical waveguide structure design, so that the PLC device with the diamond optical path difference offset structure with compact structure and single chip is realized. As shown in fig. 3, in the waveguide design structure of the PLC device with the diamond-shaped optical path difference bias structure, the lengths of the four sections of the first waveguide 28, the second waveguide 29, the third waveguide 30 and the fourth waveguide 31 are not completely consistent, so as to meet the design requirement of the bias optical path difference d= { first optical fiber 1+third optical fiber 3} - { fourth optical fiber 4+second optical fiber 2}, and d is in the range of tens of um to several mm. The first port 24, the second port 25, the third port 26 and the fourth port 27 are respectively coupled in alignment with corresponding input-output fibers.
After the structure is adopted, the Sagnac distributed intrusion detection sensor based on the diamond optical path difference biasing structure has the advantages of simple structure, simple algorithm, stable work and stable detection in a complex external environment.
While the foregoing disclosure shows exemplary embodiments of the invention, it should be noted that various changes and modifications could be made herein without departing from the scope of the invention as defined by the appended claims. The constituent elements of the claims may be replaced with any functionally equivalent elements according to the structure of the embodiment of the invention described herein. Accordingly, the scope of the invention should be determined from the following claims.
Claims (4)
1. The Sagnac interference type optical fiber intrusion sensing system based on the diamond optical path difference offset structure is characterized by comprising a laser, a diamond optical path difference offset structure, a sensing optical fiber and a detector;
the diamond optical path difference biasing structure is formed by 4 optical fiber couplers with 50:50 light splitting ratio or adopts a diamond optical path difference biasing structure based on a planar optical waveguide technology, and comprises 4 optical fiber couplers with 50:50 light splitting ratio and optical fibers connected with the optical fiber couplers; the first optical fiber coupler and the second optical fiber coupler, the second optical fiber coupler and the third optical fiber coupler, the third optical fiber coupler and the fourth optical fiber coupler are respectively connected into a ring through the first optical fiber, the second optical fiber, the third optical fiber and the fourth optical fiber; wherein lengths of the first optical fiber, the second optical fiber, the third optical fiber and the fourth optical fiber are inconsistent to introduce an optical path difference bias d;
the laser is connected with the first optical fiber coupler through a single mode fiber, and the detector is connected with the third optical fiber coupler through a single mode fiber;
and two ends of the sensing optical fiber are respectively connected with the second optical fiber coupler and the fourth optical fiber coupler.
2. The system of claim 1, wherein the laser is a wavelength scanning laser.
3. The optical fiber intrusion sensing system of claim 1 or 2, wherein the detector is a synchronous detector or a spectrometer.
4. The system of claim 1 or 2, wherein the sensing fiber ring is a single-mode fiber or a polarization maintaining fiber.
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