CN201322810Y - Optical fiber sensing device - Google Patents
Optical fiber sensing device Download PDFInfo
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- CN201322810Y CN201322810Y CNU2008201518997U CN200820151899U CN201322810Y CN 201322810 Y CN201322810 Y CN 201322810Y CN U2008201518997 U CNU2008201518997 U CN U2008201518997U CN 200820151899 U CN200820151899 U CN 200820151899U CN 201322810 Y CN201322810 Y CN 201322810Y
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 94
- 238000001514 detection method Methods 0.000 claims abstract description 42
- 230000003287 optical effect Effects 0.000 claims abstract description 41
- 238000010183 spectrum analysis Methods 0.000 claims abstract description 9
- 239000000835 fiber Substances 0.000 claims description 24
- 239000000523 sample Substances 0.000 claims description 2
- 230000001427 coherent effect Effects 0.000 abstract description 4
- 230000003321 amplification Effects 0.000 abstract 1
- 238000003199 nucleic acid amplification method Methods 0.000 abstract 1
- 238000005516 engineering process Methods 0.000 description 12
- 238000010586 diagram Methods 0.000 description 5
- 238000002168 optical frequency-domain reflectometry Methods 0.000 description 5
- 238000000253 optical time-domain reflectometry Methods 0.000 description 4
- 238000001228 spectrum Methods 0.000 description 4
- 238000000034 method Methods 0.000 description 3
- 239000002184 metal Substances 0.000 description 2
- 238000012544 monitoring process Methods 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 1
- 230000035559 beat frequency Effects 0.000 description 1
- 210000004556 brain Anatomy 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
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Abstract
The utility model relates to an optical fiber sensing device which mainly comprises a laser, a first optical fiber coupler, an optical circulator, a second optical fiber coupler, a photoelectric detection unit and a spectrum analysis unit. The laser light emitted by the laser is divided into detection light and reference light by the first optical fiber coupler, wherein, the detection light enters into a first port of the optical circulator and is emitted out from a second port of the optical circulator to a detection optical fiber, the Rayleigh backscatter light generated in the detection optical fiber enters into the second port of the optical circulator and is emitted out from a third port of the optical circulator, the emitted Rayleigh backscatter light and the reference light enter into the second optical fiber coupler and are detected by the photoelectric detection unit, and the measured signals are input to the spectrum analysis unit. The system fully utilizes the laser source, enables a great part of the Rayleigh backscatter light to enter into the photoelectric detection device, performs amplification to the Rayleigh backscatter light, improves the signal-to-noise ratio of the system and achieves the purpose of higher coherent contrast.
Description
Technical Field
The utility model relates to an optical fiber sensing system, in particular to optical fiber sensing system based on optical frequency domain reflection is one kind and utilizes optic fibre as sensing medium system.
Technical Field
In recent years, optical fiber sensing technology has been greatly developed. The optical fiber has the special advantages of low price, for example, the cost of the common single-mode bare fiber is only less than 100 yuan per kilometer, and the price of the common multimode bare fiber is less than 300 yuan per kilometer; the optical fiber is easy to install and good in concealment, and the detector cannot be used for detecting the existence of the optical fiber because the optical fiber does not contain any metal component; the optical fiber is free from electromagnetic interference, does not contain metal components, and transmits optical signals instead of electric signals, so that the optical fiber is completely immune to electromagnetic interference, can completely and normally operate under severe weather conditions such as thunder and lightning, and can normally work nearby a power node; the optical fiber does not transmit electric signals inside when in normal work, so that potential safety hazards caused by electricity can not be caused in certain sensitive places; the service life of the optical fiber is long, and the optical fiber can normally work for more than 30 years.
In the optical fiber sensing technology, the distributed optical fiber sensing technology has higher performance. In the distributed optical fiber sensing technology, the optical fiber not only serves as a sensing medium to ensure continuous detection, but also serves as a channel for signal transmission, so that the distributed optical fiber sensing technology has great advantages compared with the common point type sensing technology. In the existing distributed optical fiber sensing technology, two principles are mainly used: optical Time-Domain Reflectometry (OTDR) and Optical Frequency-Domain Reflectometry (OFDR). The former is time division multiplexing technology, and is widely applied to communication optical fiber flaw detection and distributed temperature and stress monitoring systems. However, the OTDR technique has its inherent disadvantage that, because the back-scattered signal of the optical fiber is rather weak, it needs to be averaged by a large amount to obtain the required signal-to-noise ratio, and only static or slowly changing parameter monitoring can be performed, and they cannot capture the transient event once; in addition, since the OTDR adopts a pulse modulation technology, the duty ratio of a longer-distance application pulse is extremely low, so that a signal is smaller, and the maximum application distance of the signal is limited; on the order of very high accuracy requirements, such as centimeters and less, the width of the laser pulse is required to be very small, which is difficult to achieve.
Therefore, the OFDR technology is invented to realize the sensing requirement of long distance or extremely high precision. OFDR has been referred to continuous-wave modulation (FMCW) technology in radar technology, which is essentially Frequency division multiplexing. The laser frequency output by the light source is continuously modulated and is incident into the detection optical fiber, and then at the same moment, the light frequency corresponding to each point on the detection optical fiber is different, the frequency of the generated Rayleigh back scattering light is different, and therefore the position of external disturbance can be determined by utilizing the frequency information of the detection return light signal.
Optical frequency domain reflection systems are mentioned in the classic works Optical fiber sensors of Brain Culshaw and Join Dakin, and in the conventional OFDR system shown in fig. 1, a narrow linewidth laser 1 is frequency modulated and then enters a 3dB fiber coupler 2 and enters a single mode fiber 3 of a probe arm, and rayleigh scattering is generated everywhere in the single mode fiber 3, wherein the rayleigh backscattering part returns to the 3dB fiber coupler 2 via the single mode fiber 3. The other end of the 3dB optical fiber coupler 2 is taken as a reference arm, and part of light is reflected. Coherent detection of the rayleigh backscattered light signal of the detection arm and the reflected optical signal of the reference arm results in a beat signal of the two optical signals at the photodetector 4. By analyzing the beat signal with the spectrum analyzer 5, real-time distributed interference information can be obtained.
The intensity of Rayleigh backscattering in standard single mode fiber is very low, about-81 dB of the incident light intensity. After the laser passes through the 3dB coupler, only light less than 1/2 enters the detection fiber, rayleigh backscattered light is generated and returned, 1/2 loss is lost again at the 3dB coupler, and such loss is critical in the case that the original rayleigh backscattered light intensity is weak.
There is therefore a need for a method that can take full advantage of the intensity of the light source and can receive a large portion of the rayleigh backscattered light.
SUMMERY OF THE UTILITY MODEL
An object of the utility model is to solve above-mentioned current not enough of having a problem, provide a light frequency domain reflection sensing system, in this technique, we have utilized the intensity that light circulator comes make full use of laser light source and receive most rayleigh scattering light dorsad, consequently great improvement the intensity of detecting signal light and improved entire system's SNR.
The utility model provides a technical scheme as follows:
an optical fiber sensing device mainly comprises a laser, a first optical fiber coupler, an optical circulator, a second optical fiber coupler, a photoelectric detection unit and a spectrum analysis unit; laser light emitted by the laser is divided into detection light and reference light by the first optical fiber coupler, the detection light enters the first port of the optical circulator and is emitted from the second port to enter the detection optical fiber, Rayleigh back scattering light generated in the detection optical fiber enters the second port of the optical circulator and is emitted from the third port, the emitted Rayleigh back scattering light and the reference light enter the second optical fiber coupler and are detected by the photoelectric detection unit, and the detected signals are input to the spectrum analysis unit.
The splitting ratio of the first optical fiber coupler and the second optical fiber coupler is 10: 90-0.001: 99.999.
The photoelectric detection unit is a PIN photodiode module or an avalanche photodiode module.
An optical amplifier is arranged between the optical circulator and the second optical fiber coupler.
And a variable attenuator is arranged between the first optical fiber coupler and the second optical fiber coupler.
And a refractive index matching device is arranged at the end of the detection optical fiber.
Compared with the prior art, the technical scheme has the following technical effects:
firstly, the first optical fiber coupler is in a non-uniform type, so that most of laser is incident into the detection optical fiber through the optical circulator, and a laser light source is fully utilized;
secondly, the second optical fiber coupler is also non-equipartition, so that most of Rayleigh back scattering light can enter the photoelectric detector;
thirdly, amplifying the Rayleigh back scattering light by using the optical amplifier between the optical circulator and the second optical fiber coupler, thereby not only allowing the use of an optical detector with lower cost, but also greatly improving the signal-to-noise ratio of the system; and a variable attenuator is arranged between the first optical fiber coupler and the second optical fiber coupler, so that the intensity of reference light entering the photoelectric detection unit is changed, and higher coherent contrast is achieved on the premise that the reference light amplifies Rayleigh back scattering light to a certain extent.
Drawings
Fig. 1 is a schematic structural diagram of a conventional optical frequency domain reflection sensing system.
Fig. 2 is a schematic structural diagram of an embodiment 1 of the optical frequency domain reflection sensing system of the present invention.
Fig. 3 is a schematic structural diagram of an embodiment 2 of the optical frequency domain reflection sensing system of the present invention.
Wherein,
1-narrow linewidth laser, 2-3dB optical fiber coupler, 3-single mode optical fiber, 4-photoelectric detector, 5-spectrum analyzer, 6-narrow linewidth optical fiber laser, 7-PZT optical fiber phase modulator, 8-1: 99 optical fiber coupler, 9-optical circulator, 10-refractive index matching device, 11-10: 90 optical fiber coupler, 12-PIN photoelectric detector, 13-radio frequency amplifier, 14-external cavity laser, 15-0.1: 99.9 optical fiber coupler, 16-variable attenuator, 17-optical amplifier and 18-APD optical detector.
Detailed Description
The following detailed description of an optical fiber sensing device according to the present invention is made with reference to the accompanying drawings and specific embodiments, which should not be construed as limiting the scope of the invention.
The optical fiber sensing device mainly comprises a laser, a first optical fiber coupler, an optical circulator, a detection optical fiber, a second optical fiber coupler, a photoelectric detection unit and a spectrum analysis unit; laser light emitted by the laser is divided into detection light and reference light by the first optical fiber coupler, the detection light enters the first port of the optical circulator and is emitted from the second port to enter the detection optical fiber, Rayleigh back scattering light generated in the detection optical fiber enters the second port of the optical circulator and is emitted from the third port, the emitted Rayleigh back scattering light and the reference light enter the second optical fiber coupler and are detected by the photoelectric detection unit, and the detected signals are input to the spectrum analysis unit.
Example 1
Referring to fig. 2, fig. 2 is a schematic structural diagram of an embodiment 1 of an optical frequency domain reflection sensing system according to the present invention. Laser emitted by the narrow-linewidth optical fiber laser 6 passes through the PZT optical fiber phase modulator 7, modulation voltage is added at two ends of the PZT optical fiber phase modulator 7, phase modulation can be carried out on the passing optical signal, so that the purpose of frequency tuning is achieved, the laser is subjected to frequency modulation and then enters the 1: 99 optical fiber coupler 8 serving as a first optical fiber coupler, wherein 1% of the laser is input into the 10: 90 optical fiber coupler 11 serving as a second optical fiber coupler as reference light, and 99% of the light enters the first port 9a of the optical circulator 9, and the optical circulator has the working characteristics that: when light is input from any port, the light can only be transmitted in a single direction in the circulator and is all output from the next port, therefore, laser light is emitted from the second port 9b and enters the single mode fiber 3 for detection, rayleigh back scattering generated at each position in the single mode fiber 3 returns along the single mode fiber 3 and enters the second port 9b of the optical circulator 9, due to the unique property of the optical circulator, the rayleigh back scattering light is emitted from the third port 9c and enters the 10: 90 optical fiber coupler 11, then is subjected to photoelectric conversion by the PIN photoelectric detector 12 and is pre-amplified by the radio frequency amplifier 13, and then, a radio frequency electric signal is subjected to filtering, spectrum calculation and other processing by the spectrum analysis unit 5.
Example 2
Fig. 3 is a schematic structural diagram of an embodiment 2 of the optical frequency domain reflection sensing system of the present invention. In the present embodiment, after laser beams emitted from external cavity lasers 14 and 14 modulated by a triangular wave pass through a 0.1: 99.9 optical fiber coupler 15, 99.9% of the laser beams enter a port 9a of an optical circulator 9, laser beams emitted from a port 9b enter a single mode fiber 3 for detection, backward rayleigh scattered light generated in the single mode fiber 3 returns along the single mode fiber 3 and is emitted from a port 9c to an optical amplifier 17, and an amplified rayleigh backward scattered signal enters a 1: 99 optical fiber coupler 8. The reference light emitted from the other exit end of the optical fiber coupler 15 with the splitting ratio of 0.1: 99.9 passes through the variable attenuator 16 and enters the APD photodetector 18 together with rayleigh backscattered light, wherein the coupling ratio of the rayleigh backscattered light is 99%, and a beat frequency signal measured by the APD photodetector is input to the spectrum analyzer 5 for analysis and processing.
As can be seen from the figure, the difference between this embodiment and embodiment 1 is that, between the light returned by the detection arm and reaching the detector, the light is amplified by the erbium-doped fiber amplifier 17, and then the rayleigh back-scattered light carrying the disturbance information is greatly enhanced; and the variable attenuator 16 changes the intensity of the reference light entering the APD optical detector 18, so that higher coherent contrast is achieved on the premise that the reference light amplifies Rayleigh back scattering light to a certain extent, and the signal-to-noise ratio of the whole system is greatly improved.
The rayleigh backscattering intensity of a standard single mode fiber is about-81 dB, while the fresnel reflection at the fiber end is about-13.6 dB, much larger than the rayleigh backscattering intensity, so we have specially treated the end of the single mode fiber for detection in all the above embodiments, and eliminated the fresnel reflection at the end by the refractive index matching device 10.
The optical fiber sensing device of the present invention has other structural alternatives and combinations, and is not limited to the above-mentioned embodiments. In summary, the protection of the present invention also includes other variants and alternatives that are obvious to a person skilled in the art.
Claims (6)
1. An optical fiber sensing device is characterized in that the main structure of the system comprises a laser, a first optical fiber coupler, an optical circulator, a second optical fiber coupler, a photoelectric detection unit and a spectrum analysis unit;
laser light emitted by the laser is divided into detection light and reference light by the first optical fiber coupler, the detection light enters the first port of the optical circulator and is emitted from the second port to enter the detection optical fiber, Rayleigh back scattering light generated in the detection optical fiber enters the second port of the optical circulator and is emitted from the third port, the emitted Rayleigh back scattering light and the reference light enter the second optical fiber coupler and are detected by the photoelectric detection unit, and the detected signals are input to the spectrum analysis unit.
2. The optical fiber sensing device according to claim 1, wherein the first optical fiber coupler has a splitting ratio of 10: 90 to 0.001: 99.999, and the second optical fiber coupler has a splitting ratio of 10: 90 to 0.001: 99.999.
3. The fiber optic sensing device of claim 1 wherein said photodetecting unit is a PIN photodiode module or an avalanche photodiode module.
4. The optical fiber sensing device of claim 1, wherein an optical amplifier is disposed between said optical circulator and said second optical fiber coupler.
5. The fiber optic sensing device of claim 1, wherein a variable attenuator is disposed between the first fiber coupler and the second fiber coupler.
6. An optical fibre sensing device as claimed in claim 1 wherein the end of the probe optical fibre is provided with index matching means.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNU2008201518997U CN201322810Y (en) | 2008-08-13 | 2008-08-13 | Optical fiber sensing device |
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| Application Number | Priority Date | Filing Date | Title |
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| CNU2008201518997U CN201322810Y (en) | 2008-08-13 | 2008-08-13 | Optical fiber sensing device |
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| CN201322810Y true CN201322810Y (en) | 2009-10-07 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102628698A (en) * | 2012-04-06 | 2012-08-08 | 中国科学院上海光学精密机械研究所 | Distributed optical fiber sensor and information demodulating method |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102628698A (en) * | 2012-04-06 | 2012-08-08 | 中国科学院上海光学精密机械研究所 | Distributed optical fiber sensor and information demodulating method |
| CN102628698B (en) * | 2012-04-06 | 2015-02-18 | 中国科学院上海光学精密机械研究所 | Distributed optical fiber sensor and information demodulating method |
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| CP03 | Change of name, title or address |
Address after: 201203 room 177, No. 203 blue wave road, Zhangjiang hi tech park, Shanghai Patentee after: SHANGHAI BANDWEAVER TECHNOLOGIES CO., LTD. Address before: 201204 Shanghai city Pudong New Area road 289 Lane No. 3 in 5 Patentee before: Shanghai Bohui Communication Technology Co., Ltd. |
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| CF01 | Termination of patent right due to non-payment of annual fee |
Granted publication date: 20091007 Termination date: 20170813 |
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| CF01 | Termination of patent right due to non-payment of annual fee |