CN211317345U - Distributed optical fiber sensing device - Google Patents
Distributed optical fiber sensing device Download PDFInfo
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- CN211317345U CN211317345U CN201922452264.1U CN201922452264U CN211317345U CN 211317345 U CN211317345 U CN 211317345U CN 201922452264 U CN201922452264 U CN 201922452264U CN 211317345 U CN211317345 U CN 211317345U
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Abstract
The utility model provides a distributed optical fiber sensing device, which comprises a loopback optical fiber, an optical fiber circulator and a detector; pulse laser emitted by a first light source enters the loopback optical fiber through the optical fiber circulator, and backscattered light of the pulse laser is received by the detector; continuous laser emitted by a second light source enters the loopback optical fiber, and the continuous laser is received by the detector through the optical fiber circulator; the forward-transmitted pulse laser in the loopback optical fiber is blocked at a blocker, and the backward-transmitted continuous laser in the loopback optical fiber passes through the blocker. The utility model has the advantages of effective detection distance is long, detect weak point consuming time.
Description
Technical Field
The present invention relates to temperature and strain sensing, and more particularly to a device for sensing ambient temperature and/or strain using optical fibers.
Background
The distributed optical fiber sensing technology has the advantages of continuous distributed detection, long detection distance, accurate positioning, rich measurement information, intrinsic safety, low cost and the like, and is widely applied to the fields of electric power, petroleum, bridges, tunnels, slopes and the like.
In various optical fiber sensing technologies, a distributed optical fiber sensing device based on the Brillouin scattering effect is a novel sensing device, and the distributed optical fiber sensing device directly utilizes an optical fiber as a sensing element, integrates sensing and sensing, and can sense the temperature and/or strain along the optical fiber. The distributed optical fiber sensing device comprises a light source, an optical fiber circulator, an optical fiber and a detector, wherein laser emitted by the light source is coupled into the optical fiber through the optical fiber circulator, the laser can generate various scattering effects in the transmission process of the optical fiber, the frequency shift of backward Brillouin scattering is related to the temperature and/or strain along the optical fiber, and the backward scattering light in the optical fiber is detected by the detector after passing through the optical fiber circulator, so that the temperature, strain distribution, position information and the like along the optical fiber can be obtained.
The effective detection distance is one of the core indexes of the distributed optical fiber sensing technology. With the increase of the effective detection distance, the transmission loss of the optical fiber is caused, so that the scattered signal at the tail end of the optical fiber is smaller, and even the detection requirement cannot be met, namely the improvement of the effective detection distance is limited. In order to increase the effective detection distance, the potential solutions are respectively:
1. increasing the power into the optical fiber; increasing the power into the fiber results in non-linear effects that affect the measurement.
To prevent the occurrence of non-linear effects, the power into the fiber cannot be too large; and the longer the distance, the lower the power allowed to enter the fiber, which will further shorten the effective detection distance.
2. The performance of the detector is improved, and a higher signal-to-noise ratio is realized; the performance of the detector is difficult and high in cost, and the scheme is generally not considered.
3. Increasing the pulse width of the pulsed laser; increasing the pulse width of the pulsed laser sacrifices spatial resolution, i.e., the width of the pulsed laser cannot be increased at once.
4. Increasing the accumulated average times; obviously, increasing the number of accumulated averages increases the measurement time, i.e., the number of accumulated averages cannot be increased by the measurement time.
At present, the longest effective detection distance of a distributed optical fiber sensing device based on the Brillouin scattering effect is only 75 kilometers, and the application requirements in the fields of electric power, petroleum and the like cannot be completely met.
SUMMERY OF THE UTILITY MODEL
For solving not enough among the above-mentioned prior art scheme, the utility model provides an effective detection distance is long, detect short distributed optical fiber sensing device consuming time.
The utility model aims at realizing through the following technical scheme:
distributed optical fiber sensing device, including loopback optic fibre, optic fibre circulator and detector, distributed optical fiber sensing device still includes:
the pulse laser emitted by the first light source enters the loopback optical fiber after passing through the optical fiber circulator;
the continuous laser emitted by the second light source enters the loopback optical fiber;
and the forward-transmitted pulse laser in the loopback optical fiber is blocked at the blocker, and the backward-transmitted continuous laser in the loopback optical fiber passes through the blocker and then is received by the detector through the optical fiber circulator.
In this scheme, the pulse laser emitted by the first light source is transmitted forward in the loopback optical fiber and is blocked at the blocker, and at this time, the transmission distance of the pulse laser emitted by the first light source is smaller than the total length of the loopback optical fiber. The smaller the transmission distance of the pulse laser is, the higher the power allowed to enter the loopback optical fiber can be, and the stronger the scattering signal of the loopback optical fiber can be, so that the effective detection distance can be increased; on the other hand, the smaller the transmission distance of the pulse laser is, the larger the repetition frequency of the pulse laser can be, and the more times of accumulating the average in the same measurement time, the effective detection distance is further improved.
Furthermore, the first light source, the second light source, the optical fiber circulator and the detector are all located at the detection end, the loopback optical fiber is located in the sensing area, and the blocker is located on the optical path of the loopback optical fiber.
Preferably, the distributed optical fiber sensing apparatus further includes:
an optical amplifier on the optical path upstream or downstream of the blocker, the power of the continuous laser light backward transmitted in the loopback fiber being increased by the optical amplifier.
The optical amplifier is an erbium-doped fiber amplifier EDFA or a semiconductor optical amplifier SOA.
Preferably, the blocker is built in the optical amplifier, so that the field deployment is convenient.
The blocker is a one-way double-stage optical fiber isolator or an optical fiber circulator.
The optical frequency difference between the first light source and the second light source is 8-14 GHz, the optical frequency of one light source is fixed and unchanged, and the optical frequency of the other light source is periodically changed step by step, so that the Brillouin spectrum of the loopback optical fiber is covered.
Furthermore, this scheme still provides a low-cost multichannel distributed optical fiber sensing device, distributed optical fiber sensing device includes loopback optic fibre, optic fibre circulator, detector, first light source, second light source, blocker and optical amplifier, distributed optical fiber sensing device still includes: the optical switch comprises a first optical switch, a second optical switch, a first optical fiber coupler and a second optical fiber coupler; the first light source enters the plurality of loopback optical fibers after sequentially passing through the optical fiber circulator and the first optical switch; the second light source enters the plurality of loopback optical fibers after passing through the second optical switch; and the plurality of loopback optical fibers enter the blocker and the optical amplifier after being combined by the first optical fiber coupler respectively, and are connected with the plurality of loopback optical fibers after being split by the second optical fiber coupler.
Compared with the prior art, the utility model discloses the beneficial effect who has does:
1. the effective detection distance is long;
the blocking device is added in the middle of the loopback optical fiber to block the pulse laser emitted by the first light source, the blocking device prevents the further transmission of the pulse laser in the loopback optical fiber, namely, the transmission distance of the pulse laser is shortened, which means that the power of the pulse laser can be improved and the repetition frequency of the pulse laser can be improved, the former makes the scattering signal of the loopback optical fiber stronger, and the latter makes the accumulated average times more in the same measurement time, and both can effectively improve the effective detection distance.
Experiments show that the same light source, optical fiber and detector can increase the effective detection distance to more than 120 kilometers through the arrangement of the blocker, so that the effective detection distance is remarkably increased;
2. the measuring time is shorter;
the transmission distance of the pulse laser is shortened, the repetition frequency of the pulse laser is larger, and the required measurement time under the same accumulated average times is shorter.
3. The cost is lower;
the cost of the multichannel distributed optical fiber sensing device is reduced by the beam combination/splitting of the first optical fiber coupler and the second optical fiber coupler, the multiplexing blocker and the optical amplifier.
Drawings
The disclosure of the present invention will become more readily understood with reference to the accompanying drawings. As is readily understood by those skilled in the art: these drawings are only intended to illustrate the technical solution of the present invention and are not intended to limit the scope of the present invention. In the figure:
fig. 1 is a schematic structural diagram of a distributed optical fiber sensing device according to embodiment 1 of the present invention;
fig. 2 is a schematic structural diagram of a distributed optical fiber sensing device according to embodiment 2 of the present invention;
fig. 3 is a schematic structural diagram of a distributed optical fiber sensing device according to embodiment 4 of the present invention.
Detailed Description
Fig. 1-3 and the following description depict alternative embodiments of the invention to teach those skilled in the art how to make and reproduce the invention. For the purpose of teaching the present invention, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations or substitutions from these embodiments that will be within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. Accordingly, the present invention is not limited to the following alternative embodiments, but is only limited by the claims and their equivalents.
Example 1:
fig. 1 schematically shows a simplified structural diagram of a distributed optical fiber sensing apparatus according to an embodiment of the present invention, and as shown in fig. 1, the distributed optical fiber sensing apparatus includes:
a loopback optical fiber 41, such as an optical cable not smaller than the dual-core optical fiber, where the length of the optical cable is 100 kilometers, and the dual-core optical fiber is fused together at the far end of the optical cable to form the loopback optical fiber 41, and the total length of the loopback optical fiber 41 is 200 kilometers at this time;
a fiber optic circulator 21, such as a three-port fiber optic circulator, for example, the incident laser light enters from the first port and reaches the second port, and the backscattered light enters from the second port and reaches the third port;
the detector 31, such as an InGaAs photodetector, is used for detecting the back scattered light of the loopback optical fiber 41 and converting the back scattered light into an electrical signal to realize collection and analysis processing;
the loopback optical fiber, the optical fiber circulator and the detector are all prior art in the field, and the specific structure and the working mode are not described again;
a first light source 11, such as an externally modulated narrow linewidth semiconductor laser, having a center wavelength of 1550.12nm, where pulse laser emitted by the first light source 11 enters the loopback optical fiber 41 after passing through an optical fiber circulator 21;
a second light source 12, such as a narrow linewidth semiconductor laser, having a central wavelength of 1550.04nm, wherein continuous laser light emitted from the second light source 12 enters the loopback fiber 41;
the optical frequency of the first light source 11 is fixed and unchanged, and the optical frequency of the second light source 12 is periodically changed step by periodically changing the driving current, so that the optical frequency difference between the first light source 11 and the second light source 12 is 8-14 GHz, and the Brillouin spectrum of the loopback optical fiber is covered;
the backscattered light of the pulse laser and the continuous laser interact with each other and then are received by the detector after passing through the optical fiber circulator;
the blocker 51, such as a one-way dual-stage optical fiber isolator, has an operating wavelength of 1550 ± 20nm, is transmitted in one direction, has an isolation degree of more than 35dB, and the pulsed laser transmitted in the forward direction in the loopback optical fiber 41 is blocked at the blocker 51, and the continuous laser transmitted in the reverse direction in the loopback optical fiber 41 passes through the blocker 51 almost without loss.
For convenience of installation and maintenance, the first light source 11, the second light source 12 and the detector 31 are all located at the detection end (the proximal end of the optical cable), the loopback optical fiber 41 (the optical cable) is laid in the sensing area, and the blocker 51 is located on the optical path of the loopback optical fiber 41 (the distal end of the optical cable).
In this embodiment, the pulse laser emitted by the first light source is transmitted forward in the loopback optical fiber and is blocked at the blocker, and at this time, the transmission distance of the pulse laser emitted by the first light source is reduced to 100 kilometers, which is less than 200 kilometers of the total length of the loopback optical fiber. To prevent the occurrence of the stimulated effect, the power of the pulse laser incident to the loopback fiber must not exceed the stimulated power threshold. Because the stimulated power threshold value is gradually reduced along with the transmission distance, and the blocker is added in the middle of the loopback optical fiber, the transmission distance of the pulse laser is reduced from the previous 200 kilometers to 100 kilometers, and the power allowed to enter the loopback optical fiber can be increased by about 3dB, so that the scattering signal of the loopback optical fiber is stronger, and correspondingly, the effective detection distance can be increased by about 15 kilometers; on the other hand, the smaller the transmission distance of the pulse laser is, the repetition frequency of the pulse laser can be doubled, and at the moment, under the condition of the same accumulated average times, the measurement time can be shortened by half; or the number of times of accumulating averages in the same measurement time is doubled, so that the effective detection distance is further increased (about 7 km is increased).
Example 2:
according to the utility model discloses distributed optical fiber sensing device, different with embodiment 1 is:
as shown in fig. 2, the distributed optical fiber sensing apparatus further includes an optical amplifier 61, the optical amplifier 61 is located on the optical path upstream or downstream of the blocker 51, and the power of the continuous laser light reversely transmitted in the loopback optical fiber 41 is increased by the optical amplifier 61.
Because the optical amplifier is positioned in the middle of the loopback optical fiber and the gain of the optical amplifier is relatively large, the power of the continuous laser emitted by the second light source and entering the loopback optical fiber can be greatly reduced. When the continuous laser reversely transmitted in the loopback optical fiber reaches the optical amplifier, the continuous laser realizes relay amplification at the optical amplifier, and the transmission loss of the continuous laser in the loopback optical fiber is compensated.
Compared with embodiment 1, due to the addition of the optical amplifier, the power of the continuous laser emitted by the second light source is greatly reduced (far lower than the stimulated power threshold), and only the condition that the power amplified by the optical amplifier does not exceed the stimulated power threshold is satisfied, which means that the power of the continuous laser interacting with the pulse laser is greatly increased, thereby realizing the great increase of the intensity of the backscattered signal.
The optical amplifier can be an erbium-doped fiber amplifier EDFA or a semiconductor optical amplifier SOA, and the gain of the optical amplifier to small signals is not less than 10 dB. In this embodiment, the optical amplifier is a semiconductor optical amplifier SOA, the operating wavelength is 1550 ± 20nm, and the gain for small signals is 20 dB. The power of continuous laser emitted by the second light source is 1mW, after the continuous laser is transmitted by the optical cable with the length of 100 kilometers, the power attenuation of the continuous laser is about 10 muW, the continuous laser is recovered to about 1mW after being relayed and amplified by the semiconductor optical amplifier SOA, the intensity of a back scattering signal is greatly increased at the moment, and the temperature and strain measurement of the optical cable with the length of not less than 100 kilometers in the whole process can be realized.
Example 3:
according to the utility model discloses distributed optical fiber sensing device, different with embodiment 2 is:
the blocker is arranged in the optical amplifier and is positioned behind the output end of the optical amplifier, namely the optical amplifier is a unidirectional optical amplifier, so that the field deployment is convenient.
In this embodiment, the optical amplifier is an erbium-doped fiber amplifier EDFA, the operating wavelength is 1550 ± 20nm, and the gain for small signals is 15 dB. The blocker selects a one-way two-stage optical fiber isolator with working wavelength of 1550 +/-20 nm and one-way transmission, and the isolation degree is more than 35 dB. The unidirectional two-stage optical fiber isolator is directly positioned behind the output end of the erbium-doped optical fiber amplifier EDFA, so that unidirectional small signal amplification is realized, the structure is integrated, the high integration is realized, and the field deployment is convenient.
Example 4:
according to the utility model discloses distributed optical fiber sensing device, different with embodiment 2 is:
as shown in fig. 3, the distributed optical fiber sensing apparatus further includes:
the first light source 11 sequentially passes through the optical fiber circulator 21 and the first optical switch 71 and then enters the plurality of loopback optical fibers 41; the plurality of loopback fibers 41 enter the blocker and the optical amplifier after being combined by the first fiber coupler 81, and are connected with the plurality of loopback fibers after being split by the second fiber coupler 82; the second light source 12 enters the plurality of loopback fibers 41 through the second optical switch 72.
Example 5:
according to the utility model discloses distributed optical fiber sensing device's application example in submarine cable monitoring of embodiment 4.
In the application example, the distance of the submarine cable is 70 kilometers, A, B, C three phases exist, and a single-mode optical cable is arranged in each phase of submarine cable;
the first light source adopts an externally modulated narrow linewidth semiconductor laser, the central wavelength is 1550.12nm, the pulse width is 10ns, and the peak power is 300 mW;
the second light source adopts a narrow-linewidth semiconductor laser, the central wavelength is 1550.04nm, and the continuous power is 4 mW;
the blocker selects a one-way two-stage optical fiber isolator with working wavelength of 1550 +/-20 nm and one-way transmission, and the isolation degree is more than 35 dB;
the optical amplifier selects an erbium-doped fiber amplifier EDFA, and the gain is 26 dB;
the first optical switch and the second optical switch are both 1 × 4 single-mode micro-mechanical optical switches;
the first optical fiber coupler and the second optical fiber coupler are both 1 x 4 fused tapered optical fiber couplers, and the splitting ratio is 25:25:25: 25.
Pulse laser emitted by a first light source sequentially passes through a three-port optical fiber circulator and a first optical switch and then polls a loopback optical fiber (with an optical switch channel as a spare) entering an A, B, C-phase submarine cable; continuous laser emitted by the second light source enters the loopback optical fiber of the A, B, C-phase submarine cable in a polling mode after passing through the second optical switch, and the loopback optical fiber of the A, B, C-phase submarine cable enters the blocker and the optical amplifier after being respectively combined by the first optical fiber coupler and is sequentially connected with the loopback optical fiber of the A, B, C-phase submarine cable after being split by the second optical fiber coupler.
Due to the high cost of the optical amplifier and the blocker, the gain of the optical amplifier for small signals is high. The continuous laser beam is combined by the second optical fiber coupler and enters the input end of the optical amplifier, the amplified continuous laser beam is output by the output end of the optical amplifier, and the amplified continuous laser beam is split by the blocker and the first optical fiber coupler and enters the loopback optical fiber of the A, B, C-phase submarine cable.
The cost of the multichannel distributed optical fiber sensing device is reduced by beam combination/splitting of the first optical fiber coupler and the second optical fiber coupler, multiplexing of the blocker and the optical amplifier;
in this embodiment, after the optical amplifier and the blocker are disposed at the end of the submarine cable, the repetition frequency of the pulsed laser of the first light source is increased from 0.7kHz to 1.4kHz, the power of the continuous laser of the second light source after reaching the end of the submarine cable is increased from 16 μ W to 400 μ W, and finally, on the premise that the effective detection distance is 70 km, the measurement time is reduced from 120 s/channel to 60 s/channel, and the spatial resolution is increased from 5 m to 2 m or less. And through multiplexing blocker and optical amplifier, the cost increase of four-channel distributed optical fiber sensing device is little, and beneficial effect is showing.
Claims (8)
1. The distributed optical fiber sensing device comprises a loopback optical fiber, an optical fiber circulator and a detector; the method is characterized in that: the distributed optical fiber sensing device further comprises:
the pulse laser emitted by the first light source enters the loopback optical fiber after passing through the optical fiber circulator;
the continuous laser emitted by the second light source enters the loopback optical fiber;
and the forward-transmitted pulse laser in the loopback optical fiber is blocked at the blocker, and the backward-transmitted continuous laser in the loopback optical fiber passes through the blocker and then is received by the detector through the optical fiber circulator.
2. A distributed optical fiber sensing apparatus according to claim 1, wherein: the first light source, the second light source, the optical fiber circulator and the detector are all located at detection ends, the loopback optical fiber is located in a sensing area, and the blocker is located on an optical path of the loopback optical fiber.
3. A distributed optical fiber sensing apparatus according to claim 1, wherein: the distributed optical fiber sensing device further comprises: an optical amplifier on the optical path upstream or downstream of the blocker.
4. A distributed optical fiber sensing apparatus according to claim 3, wherein: the optical amplifier is an erbium-doped fiber amplifier EDFA or a semiconductor optical amplifier SOA.
5. A distributed optical fiber sensing apparatus according to claim 3, wherein: the blocker is built into the optical amplifier.
6. A distributed optical fiber sensing apparatus according to claim 1, wherein: the blocker is a one-way double-stage optical fiber isolator or an optical fiber circulator.
7. A distributed optical fiber sensing apparatus according to claim 1, wherein: the optical frequency difference between the first light source and the second light source is 8-14 GHz.
8. A distributed optical fiber sensing apparatus according to claim 3, wherein: the distributed optical fiber sensing device further comprises:
the first light source enters the plurality of loopback optical fibers after sequentially passing through the optical fiber circulator and the first optical switch; the second light source enters the plurality of loopback optical fibers after passing through the second optical switch; and the plurality of loopback optical fibers sequentially enter the blocker and the optical amplifier after being respectively combined by the first optical fiber coupler and are connected with the plurality of loopback optical fibers after being split by the second optical fiber coupler.
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| CN201922452264.1U CN211317345U (en) | 2019-12-30 | 2019-12-30 | Distributed optical fiber sensing device |
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| CN201922452264.1U CN211317345U (en) | 2019-12-30 | 2019-12-30 | Distributed optical fiber sensing device |
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