CN112345060B - DAS system based on far pump amplifier - Google Patents
DAS system based on far pump amplifier Download PDFInfo
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- CN112345060B CN112345060B CN202011003938.0A CN202011003938A CN112345060B CN 112345060 B CN112345060 B CN 112345060B CN 202011003938 A CN202011003938 A CN 202011003938A CN 112345060 B CN112345060 B CN 112345060B
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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
Abstract
The invention discloses a DAS system based on a far pump amplifier, which comprises: a vibration detection unit providing signal light of a first wavelength; a laser source providing pump light of a second wavelength; the head end of the first sensing optical fiber receives the combined beam light of the pump light and the signal light; a first end of the first wavelength division multiplexer is connected with the tail end of the first sensing optical fiber and used for receiving the combined light, a second end of the first wavelength division multiplexer outputs signal light with a second wavelength separated from the combined light, and a third end of the first wavelength division multiplexer outputs signal light with a first wavelength separated from the combined light; an attenuator, one end of which is connected with a second end of the first wavelength division multiplexer; a first circulator. The invention applies the far pump erbium-doped fiber amplifier to the sensing field from the optical communication field, and can prolong the transmission distance of the DAS system from 40km to 80km.
Description
Technical Field
The invention belongs to the field of optical fiber sensing, and particularly relates to a DAS (data acquisition System) based on a far pump amplifier.
Background
A distributed optical fiber acoustic wave sensing system (DAS for short) transmits pulse laser to a sensing optical fiber, and receives coherent light which is spontaneously emitted from the optical fiber and scattered backward in the optical fiber at a light injection end. The external disturbance received by the optical fiber is sensed by detecting the change of the coherent light intensity caused by the external vibration to obtain vibration information. The technical method has the advantages of high sensitivity, high measurement response speed, capability of realizing long-distance fully-distributed sensing, suitability for monitoring the perturbation time, and wide application in the fields of large building structure safety protection, perimeter security protection of important places and the like.
In practical engineering application of the DAS system, signal light needs to be amplified at this time because the actual loss ratio of the optical cable is large or the length of the optical cable exceeds the maximum distance that the DAS can reach.
Disclosure of Invention
In view of the problems in the prior art, the present invention provides a DAS system based on a remote pump amplifier, and some embodiments of the present invention apply the remote pump amplifier to the DAS system. The far pump amplifier can greatly improve the capacity of the existing optical fiber system, increase the detection distance of the sensing system and reduce the cost of the system, so that the far pump amplifier can be widely applied to the fields of long-distance optical fiber communication systems, optical fiber sensing systems, scientific research and the like, and the technology is applied to DAS systems to improve the sensing distance of the systems.
In order to achieve the purpose, the invention adopts the following technical scheme:
a remote pump amplifier based DAS system, the system comprising: a vibration detection unit providing signal light of a first wavelength; a laser source providing pump light of a second wavelength; the head end of the first sensing optical fiber receives the beam combining light of the pump light and the signal light; a first end of the first wavelength division multiplexer is connected with the tail end of the first sensing optical fiber and used for receiving the combined light, a second end of the first wavelength division multiplexer outputs signal light with a second wavelength separated from the combined light, and a third end of the first wavelength division multiplexer outputs signal light with a first wavelength separated from the combined light; one end of the attenuator is connected with the second end of the first wavelength division multiplexer; the second end of the first circulator is connected with the third end of the first wavelength division multiplexer; a first end of the second wavelength division multiplexer is connected with the other end of the attenuator, a second end of the second wavelength division multiplexer is connected with a third end of the first circulator, and incident light of the first end and the second end of the second wavelength division multiplexer is combined and emitted by the third end of the second wavelength division multiplexer; one end of the erbium-doped optical fiber is connected with the third end of the second wavelength division multiplexer; the incident light of the first end of the second circulator exits from the second end of the second circulator, the incident light of the second end of the second circulator exits from the third end of the second circulator, the first end of the second circulator is connected with the other end of the erbium-doped fiber, and the third end of the second circulator is connected with the first end of the first circulator; the head end of the second sensing optical fiber is connected with the second end of the second circulator; the backscattered signal light in the second sensing optical fiber enters the third end of the second circulator from the second end of the second circulator and then enters the second end of the first circulator from the first end of the first circulator; the first sensing optical fiber and the second sensing optical fiber are laid on a circuit to be detected for vibration.
Preferably, a first end of a combined beam of a third wavelength division multiplexer is connected in front of a head end of the first sensing optical fiber, a second end of the split beam of the third wavelength division multiplexer is connected with the vibration detection unit, and a third end of the split beam of the third wavelength division multiplexer is connected with the laser source.
Preferably, a first isolator is connected in series between the third end of the third wavelength division multiplexer and the laser source.
Preferably, a second isolator is connected in series between the second wavelength division multiplexer and the erbium-doped fiber.
Preferably, the length of the first sensing fiber is less than 55km.
Preferably, the length of the second sensing fiber is less than 35km.
Preferably, the length of the first sensing fiber is 50km, and the length of the second sensing fiber is 30km.
Preferably, the first wavelength is 1550nm and the second wavelength is 1480nm.
Compared with the prior art, the invention has the following beneficial effects: the far pump erbium-doped fiber amplifier is applied to the sensing field from the optical communication field, and the transmission distance of the DAS system can be prolonged from 40km to 80km, so that the sensing distance of the system is effectively increased.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a waterfall diagram of a prior art DAS apparatus.
Fig. 2 is a schematic diagram of an application of a far pump amplifier in a DAS system according to an embodiment of the present invention.
Fig. 3 is an 80km raw plot of a DAS system using a remote pump amplifier.
Figure 4 is an 80km waterfall plot of a DAS system after the use of a remote pump amplifier.
Fig. 5 is a schematic diagram of another application of the remote pump amplifier in the embodiment of the present invention.
A vibration detection unit-1; a laser source-2; a first transfer fiber-3; a first wavelength division multiplexer-4; an attenuator-5; a first circulator-6; a second wavelength division multiplexer-7; an erbium-doped fiber-8; a second circulator-9; a second sensing optical fiber-10; a first isolator-11; a second isolator-12; a third wavelength division multiplexer-13.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.
In the description of the present invention, it is to be understood that the terms "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used merely for convenience of description and for simplicity of description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, are not to be construed as limiting the present invention.
The main factors restricting the large-scale application of the high-speed and ultra-long distance communication system are the Optical Signal Noise Ratio, which is abbreviated as: the OSNR and far pump erbium-doped fiber amplifier has unique advantages in the aspect of improving the system OSNR, and the characteristic of low noise coefficient can obviously reduce the degradation speed of the optical signal-to-noise ratio in an optical fiber communication system, thereby having important significance in prolonging the transmission distance, expanding the span distance, reducing the system cost and the like.
A far-pump erbium-doped fiber amplifier is an amplifier placed in a system line, and is distinguished from preamplifiers and power amplifiers used in a receiving end and a transmitting end. By "remote pump" is meant that the pump source of the amplifier is at a relatively long distance from erbium doped fiber 8, which is the gain medium, so that the pump source can be placed at either the transmitting or receiving end. The far-pump erbium-doped fiber amplifier adopts a 1480nm laser as a pump source, has higher efficiency than a 980nnm pump source, and simultaneously, the transmission loss of 1480nm light in a line is much lower than that of 980 nnm. The far pump erbium-doped fiber amplifier can realize continuous output and has the excellent characteristics of high gain, low noise coefficient, extremely wide gain bandwidth and the like.
Sensing measurement is generally performed by using laid optical cables, and the length of some optical cables on an engineering site is longer than the maximum length which can be measured by the DAS. Or even if the cable length is within the maximum length that can be measured by the DAS, the transmission loss of the cable is relatively large for various reasons. Both of these cases can be addressed by using a remote pump amplifier.
Fig. 1 is a waterfall plot of a DAS device of the prior art, and it can be seen that the signal is weak after 40 km. In practical engineering, the total length of the line sometimes exceeds 40km, and in order to meet the requirements of customers, an optical fiber amplifier can be adopted to increase the sensing distance.
Fig. 2 is a schematic diagram of the application of a remote pump amplifier in a DAS system. The length of the detection optical fiber in the system is 80km, and the detection optical fiber consists of a section of 50km optical fiber and a section of 30km optical fiber. The working principle of the system is as follows: a1480 nm laser at one end of the vibration detection unit 1 serves as a far pump source, and light output by the pump source passes through an isolator (the isolator plays a role of preventing reflected light of an optical fiber end face from damaging the laser), enters a third wavelength division multiplexer together with 1550nm signal light output by the vibration detection unit 1, and then enters a 50km detection optical fiber. The passive devices in the dashed box behind the 50km fiber and the erbium doped fiber 8 constitute a far pump amplifier module. The light output by the module passes through a second circulator 9 and then enters a 30km detection optical fiber.
The optical fiber circulator works in 1550nm band and has 3 ports. The working principle of the circulator is as follows: the light input to the 1 port in the circulator is directly output to the 2 port, and the light input to the 2 port in the circulator is directly output to the 3 port.
The operation of the second circulator 9 is as follows: the signal light output by the far pump amplifier enters the 1 port of the second circulator 9 and then directly enters the 2 port, and then enters the 30km optical fiber. Spontaneous backward Rayleigh scattering coherent light generated in the 30km detection optical fiber enters a port 2 of a second circulator 9 and then directly enters a port 3, then enters a far pump amplifier module, a 50km optical fiber and a third wavelength division multiplexer, and finally enters an optical fiber distributed vibration detection unit 1 for signal processing, so that the micro-disturbance of the optical fiber along the path is detected.
The 1480nm far pump source has two functions, that is, the pump source is injected into the long-distance optical fiber to realize distributed amplification of optical signals, and the pump source is transmitted to the far pump amplifier module after 50km of optical fiber to be used as the pump source, thereby effectively increasing the sensing distance of the system.
Fig. 3 and 4 are 80km raw curves and waterfall plots, respectively, of a DAS system employing a remote pump amplifier. It can be seen that the waterfall diagram of each segment of fiber is very clear. After the far pump erbium-doped fiber amplifier is adopted, the transmission distance of the system is prolonged from 40km to 80km, so that the sensing distance of the system is effectively increased.
The key point of the present invention is the injection problem of the pump light in the remote pump amplifier. Unlike optical communication systems, optical sensing systems are susceptible to nonlinear effects such as four-wave mixing and stimulated raman effects as the power of optical pulses increases. The longer the fiber, the less critical optical power for stimulated raman. As before, the 1480nm far pump source plays two roles, the higher the power is when the transmitting end is used as a raman pump source, the higher the signal gain is, but the signal light generated when the 1480nm laser with high power enters the far pump amplifier module after passing through a 50km optical fiber is very large, which easily causes the nonlinear effect. To this end the invention envisages a remote pump amplifier module as shown within the dashed box in figure 2. The most critical place of the module is to separate the pump light and the signal light for transmission by using two wavelength division multiplexers. The working principle is as follows: 1480nm pump light and signal light transmitted in the first 50km optical fiber are separated after entering the first wavelength division multiplexer 4, and an adjustable optical attenuator 5 is added on one side of the pump light to optimize the pump light power entering the erbium-doped optical fiber 8. The 1550nm signal light enters the 2 ports of the first circulator 6 and then directly reaches the 3 ports. The attenuated pump light and the signal light simultaneously enter the second wavelength division multiplexer 7 for beam combination, and then enter the erbium-doped optical fiber 8 for amplifying 1550nm signal light after passing through the isolator. As before, the spontaneous backward rayleigh scattering coherent light generated in the 30km optical fiber enters the 1 port of the first circulator 6 via the 3 port of the second circulator 9 and is directly output to the 2 port. Then enters the first wavelength division multiplexer 4, the 50km optical fiber and the third wavelength division multiplexer, and finally enters the optical fiber distributed vibration detection unit 1 for signal processing so as to detect the micro-disturbance of the optical fiber along the path.
The position of the remote pump amplifier in the DAS system can also be varied and can be placed at the tail end of the sensing fiber as shown in fig. 5.
Although the present invention has been described in detail with respect to the above embodiments, it will be understood by those skilled in the art that modifications or improvements based on the disclosure of the present invention may be made without departing from the spirit and scope of the invention, and these modifications and improvements are within the spirit and scope of the invention.
Claims (8)
1. A remote pump amplifier based DAS system, comprising:
a vibration detection unit providing signal light of a first wavelength;
a laser source providing pump light of a second wavelength;
the head end of the first sensing optical fiber receives the beam combining light of the pump light and the signal light;
a first end of the first wavelength division multiplexer is connected with the tail end of the first sensing optical fiber and used for receiving the combined light, a second end of the first wavelength division multiplexer outputs signal light with a second wavelength separated from the combined light, and a third end of the first wavelength division multiplexer outputs signal light with a first wavelength separated from the combined light;
an attenuator, one end of which is connected with a second end of the first wavelength division multiplexer;
the incident light of the first end of the first circulator is emitted from the second end of the first circulator, the incident light of the second end of the first circulator is emitted from the third end of the first circulator, and the second end of the first circulator is connected with the third end of the first wavelength division multiplexer;
a first end of the second wavelength division multiplexer is connected with the other end of the attenuator, a second end of the second wavelength division multiplexer is connected with a third end of the first circulator, and incident light of the first end and the second end of the second wavelength division multiplexer is combined and emitted by the third end of the second wavelength division multiplexer; one end of the erbium-doped optical fiber is connected with the third end of the second wavelength division multiplexer;
the incident light of the first end of the second circulator is emitted from the second end of the second circulator, the incident light of the second end of the second circulator is emitted from the third end of the second circulator, the first end of the second circulator is connected with the other end of the erbium-doped fiber, and the third end of the second circulator is connected with the first end of the first circulator;
a first sensing optical fiber, wherein the head end of the first sensing optical fiber is connected with the first end of the first circulator;
the backscattered signal light in the second sensing optical fiber enters the third end of the second circulator from the second end of the second circulator and then enters the second end of the first circulator from the first end of the first circulator;
the first sensing optical fiber and the second sensing optical fiber are laid on a circuit to be detected for vibration.
2. The remote pump amplifier based DAS system of claim 1, wherein a first end of a combined beam of a third wavelength division multiplexer is connected in front of a head end of the first sensing fiber, a second end of the combined beam of the third wavelength division multiplexer is connected to the vibration detection unit, and a third end of the combined beam of the third wavelength division multiplexer is connected to the laser source.
3. The remote pump amplifier-based DAS system of claim 2, wherein a first isolator is coupled in series between the third terminal of the third wavelength-division multiplexer and the laser source.
4. The remote pump amplifier-based DAS of claim 3, wherein a second isolator is coupled in series between the second wavelength division multiplexer and the erbium doped fiber.
5. The remote pump amplifier-based DAS system of claim 4, wherein the first sensing fiber has a length less than 55km.
6. The remote pump amplifier-based DAS system of claim 5, wherein the length of the second sensing fiber is less than 35km.
7. The remote pump amplifier-based DAS system of claim 6, wherein the first sensing fiber is 50km in length and the second sensing fiber is 30km in length.
8. The remote pump amplifier based DAS system of claim 7, wherein the first wavelength is 1550nm and the second wavelength is 1480nm.
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