CN102506912A - Optical fiber distributed disturbance sensor - Google Patents
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Abstract
The invention discloses an optical fiber distributed disturbance sensor which comprises an optical fiber laser, a bidirectional distributed Raman amplification unit and a photoelectric detection and signal processing unit, wherein an output end of the optical fiber laser is connected with a first coupler; two output ends of the first coupler are respectively connected with an acoustic optical modulator and a third coupler; the bidirectional distributed Raman amplification unit is connected with the acoustic optical modulator by a first circulator and is connected with the third coupler by the first circulator; the photoelectric detection and signal processing unit is connected with the third coupler and used for receiving an interference-enhanced optical signal in the third coupler, converting the optical signal into an electric signal and carrying out subsequent data processing. In the optical fiber distributed disturbance sensor, the back scattering light intensity and the signal-to-noise ratio of the tail end of the optical fiber can be improved by the bidirectional distributed Raman amplification structure so as to improve the sensing distance of the optical fiber distributed disturbance sensor; and the light power received by a detector can be improved through the interference of a part of continuous light output by a light source and the back scattering light, so as to improve the signal-to-noise ratio of the system. The sensor is a combination of conventional photoelectric devices, has a simple structure and is easy to realize.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to an optical fiber distributed disturbance sensor suitable for long-distance application.
Background
The optical fiber sensor has the excellent characteristics of electromagnetic interference resistance, small volume, light weight, high sensitivity, easy networking, capability of realizing distributed measurement and the like, and has wide application in the industrial, civil and military fields. The optical fiber distributed disturbance sensor has important significance in the fields of perimeter alarm, oil pipeline monitoring and other structure monitoring.
The optical fiber distributed disturbance sensor is an optical fiber distributed sensing system which utilizes an optical fiber as a sensing medium, wherein the optical fiber is used as the sensing medium and also used as an optical transmission medium. The optical fiber distributed disturbance sensor can remotely and real-timely monitor the emergency within a certain accuracy range within the arrangement length of the sensing optical fiber. Therefore, the optical fiber distributed disturbance sensor has great military and civil values and is a development direction of a modern safety protection system. The safety protection device can be applied to safety protection work of important targets such as military bases, missile bases, space bases, weapon and ammunition storehouses, boundary lines, oil and natural gas pipelines, prisons, airports, warehouses, communication lines and the like.
At present, there are various technologies applicable to optical fiber distributed disturbance sensors, which can be mainly divided into four types: (1) optical Time Domain Reflectometry (OTDR) using backscattered light; (2) coupling is generated when the propagation mode of the multimode fiber is disturbed by utilizing forward transmission light; (3) disturbance sensing is realized by monitoring the change of an external parameter by using the movement of the reflection wavelength of a Fiber Bragg Grating (FBG); (4) disturbance sensing positioning is achieved by using interferometer principles such as Sagnac (Sagnac), Michelson (Michelson), Mach-Zehnder (Mach-Zehnder, M-Z) and the like.
At present, the traditional OTDR scheme is mainly applied to optical fiber damage, temperature change and stress strain detection, but is not sensitive to dynamic disturbance and is not suitable for micro-disturbance sensing. The principle of a phase-sensitive optical time domain reflectometer (Φ -OTDR) fiber distributed disturbance sensor is shown in fig. 1, and a fiber laser with narrow line width, high power and low frequency drift is adopted to detect a signal interfered by backward scattering light within a pulse width range. When external disturbance 2 acts on the sensing optical fiber 1, phase information of transmission light changes, so that light intensity of backward scattering light changes, a disturbed curve 3 and an undisturbed curve 4 are formed as shown in the figure, and the sensing optical fiber can be applied to distributed disturbance sensing.
Referring to fig. 1, continuous light output from a light source is converted into pulsed light by a modulator, the pulsed light passes through a directional coupler, the pulsed light passing through the coupler is injected from one end of an optical fiber, backward rayleigh scattered light is detected by a light detector at the other end of the directional coupler, and the detected backward scattered light is subjected to photoelectric conversion and then is subjected to data processing. The output of the sensing system is the result of coherent interference of rayleigh scattered light reflected back within the pulse width region. The phi-OTDR system can derive the location of the disturbance by measuring the time delay between the incoming pulse and the received pulse signal. When a position on the optical fiber circuit is disturbed due to intrusion, the refractive index of the corresponding position of the optical fiber changes, which causes the phase of the light at the position to change, and the change of the phase causes the light intensity of the backward scattered light to change due to interference, so that the time of the light intensity change corresponds to the position of the intrusion.
The relationship between the power of the backward rayleigh scattered light and the power of the incident light in a single mode fiber can be described by equation (1):
wherein S is a Rayleigh scattering capture factor; u. ofgGroup velocity of light pulse propagation in the fiber; w is the optical pulse width; a isRIs the Rayleigh scattering coefficient; a attenuation coefficient in the fiber.
The output of the phi-OTDR system is the result of the coherent interference of Rayleigh scattering light reflected back in a pulse width region, the interference of backward Rayleigh scattering in a pulse range in the optical fiber is approximated to a Fabry-Perot interferometer in the optical fiber, and under the condition, the power of the coherent backward scattering light is
Pbsii＝Pin2R(1+cosf) (2)
P′bsIs the power of the backscattered light after interference, P'inIs the transmitted optical power at that point, R is approximately the backscattering coefficient, and f is the phase difference between the light at the rising edge and the light at the falling edge of the optical pulse.
n is the effective refractive index of the optical fiber, L is the transmission length of the pulse in the optical fiber, and L is the wavelength of the injected light. When external vibration acts on the sensing optical fiber, the optical phase in the pulse range changes, the backward scattering optical power corresponding to the disturbance position is known from the formula (2), and the external vibration can be sensed by the detection optical power change.
Since the variation of the scattered light with time t reflects the distribution of the scattered light in the fiber, the time-corresponding fiber length can be given by equation (4):
t＝2z/ug (4)
it can be seen from the formulas (1) and (4) that when external vibration acts on the sensing fiber, the position information is reflected on the curve of the scattered light power changing with time.
The existing optical fiber distributed disturbance sensor based on the phi-OTDR has the following defects:
(1) under the condition of long-distance sensing, due to transmission loss in the optical fiber, the optical power of pulsed light injected into the optical fiber at the head end and the tail end is obviously different, and the optical power at the tail end of the optical fiber is obviously lower than that at the head end of the optical fiber, so that the backward Rayleigh scattered light power is also obviously different, the signal-to-noise ratio at the tail end of the optical fiber is obviously poor, and the maximum sensing distance of the system is limited;
(2) in order to increase the sensing distance, a method of increasing the optical power of the injected light is generally adopted in the optical fiber distributed disturbance sensor based on the Φ -OTDR. However, when the injected light power is increased to a certain degree, a nonlinear effect will occur in the optical fiber, such as generating unfavorable factors like stimulated brillouin scattering, and the like, so that the detector cannot receive an effective backward rayleigh scattering interference signal.
The mode coupling-based optical fiber distributed disturbance sensor generally needs to use a multimode optical fiber as a sensitive optical fiber, and the multimode optical fiber generally has large loss, so that the length of the sensitive optical fiber is short, the sensor is not suitable for disturbance detection of long-distance facilities, and the sensitivity is low.
Although the detection capability of the optical fiber distributed disturbance sensor based on the FBG is not influenced by light source power fluctuation, optical fiber bending loss and detector aging, the optical fiber distributed disturbance sensor is suitable for long-term safety monitoring, and the FBG has a high-sensitivity sensing function on external parameters such as temperature, stress, pressure, vibration and the like, and has the outstanding advantages of small volume, wide dynamic range, high reliability, large-scale production, strong remote control capability and the like, the FBG can only carry out point-type measurement, a plurality of sensing heads are needed when a plurality of positions are measured, the cost performance is low, and a large number of blind spots exist when long-distance monitoring is carried out; in addition, since the line width of the light source cannot be made infinitely wide, the FBGs that can be multiplexed by one system are limited, which greatly limits the practicability of the scheme.
The interferometer type distributed sensor sensing utilizes interferometers such as Sagnac, Michelson, Mach-Zehnder (M-Z) and the like, when external disturbance acts on a sensing optical fiber, optical phase information transmitted in the optical fiber changes, and the external disturbance information is obtained by demodulating the phase change information. The optical path schematic diagram of the double Mach-Zehnder type optical fiber distributed disturbance sensor is shown in FIG. 2. The interferometer type distributed disturbance sensor is simple in implementation principle and high in sensitivity, but a distance threshold value exists due to scattering problems in long-distance positioning.
Referring to fig. 2, light waves emitted from the light source are split by the coupler a, a part of the light waves are injected into the sensing arm L1 and the reference arm L2 through the coupler B, interfere at the coupler C, are transmitted through the optical fiber L4, and are received by the second photodetector, thereby forming a first interferometer. The other optical wave output by the coupler A is transmitted through an optical fiber L3, is injected into the sensing arm L1 and the reference arm L2 from the coupler C, interferes at the coupler B, and is received by the first photodetector to form a second interferometer. The optical fibers in the above optical paths are all single mode fibers. Wherein,
is phase modulation caused by disturbance, when the disturbance is applied to the sensing arm, the two Mach Zehnder interferometers are subjected to the same phase modulation
However, due to the difference of the lengths of the optical fibers between the two interferometers, the time of the modulated signal arriving at the two detectors is different, namely t1 and t2, and the disturbance position can be obtained by determining the time difference t1-t2, so that the positioning is realized. Assuming that the disturbance occurs at the x position of the sensing arm, the optical path taken by the disturbance signal of the first interferometer 1 to reach the first photodetector is L1-2x+L4The optical path taken by the disturbance signal of the second interferometer to reach the second photodetector is x, and the time difference between the disturbance signals of the two interferometers and the detector is as follows:
Dt＝n(L1-2x+L4) (5)
where n is the effective index of the fiber core and c is the speed of light in vacuum. In order to realize the positioning of the disturbance position, only Δ t needs to be measured, and the disturbance position x can be calculated by the following formula:
x＝(L1+L4-cDt/n)/2 (6)
in the subsequent positioning processing, because the phase modulation signals of the two interferometers are completely correlated in theory, only time delay exists, and the time delay corresponding to the maximum value of the cross-correlation function is determined by calculating the cross-correlation function, so that the time difference can be obtained.
The existing double-M-Z interferometer type optical fiber distributed disturbance sensor has the following defects:
(1) based on a double-M-Z interferometer type optical fiber distributed disturbance sensor positioning algorithm, two paths of detection light are adopted to extract phase change information in a cross-correlation mode, so that the problem that multi-point positioning is difficult to realize is caused;
(2) the fiber distributed disturbance sensor based on the double M-Z interferometer adopts forward transmission light interference, so that backscattering (mainly related to the influence of backward Rayleigh scattering) becomes an inevitable factor for limiting the sensing distance in the case of a long distance.
At present, two technologies, namely a distributed sensor based on an M-Z interferometer and an optical fiber distributed disturbance sensor based on a phase-sensitive OTDR, are mainly used in a long-distance optical fiber disturbance distributed sensing technology. In the distributed sensor based on the M-Z interferometer, when the sensing optical fiber is more than 40km, the backscattering becomes a limiting factor for the increase of the sensing distance. The optical fiber distributed disturbance sensor based on the phi-OTDR adopts the high-power laser, so that when the sensing optical fiber reaches a certain length, high requirements are put forward on the output power and the power stability of the laser, and when the output power of the laser exceeds a certain threshold value, the nonlinear effect in the optical fiber also becomes a negative factor of the increase of the sensing distance.
Disclosure of Invention
Technical problem to be solved
The invention aims to solve the technical problem of how to increase the monitoring distance of an optical fiber distributed disturbance sensor under the condition of inputting proper optical power, avoid the nonlinear effect in an optical fiber and ensure that a system cannot obtain an effective backward Rayleigh scattering curve.
(II) technical scheme
In order to solve the above technical problem, the present invention provides an optical fiber distributed disturbance sensor, including:
the output end of the fiber laser is connected with the first coupler, one output end of the first coupler is connected with the acousto-optic modulator and outputs detection light, and the other output end of the first coupler is connected with the third coupler and outputs reference light;
the bidirectional distributed Raman amplification unit is connected with the acousto-optic modulator through a first circulator and receives pulsed light modulated by the acousto-optic modulator; the first circulator is connected with the third coupler to transmit the pump light subjected to bidirectional Raman amplification to the third coupler;
and the photoelectric detection and signal processing unit is connected with the third coupler, receives the optical signal enhanced by the interference in the third coupler, converts the optical signal into an electric signal and performs subsequent data processing.
Wherein the bidirectional distributed Raman amplification unit comprises: the output end of the Raman fiber laser is connected with the second coupler, one output end of the second coupler is connected with the first wavelength division multiplexer and outputs forward pump light, and the other output end of the second coupler is connected with the second wavelength division multiplexer and outputs reverse pump light; the first wavelength division multiplexer and the second wavelength division multiplexer are connected through a sensing optical fiber; the first wavelength division multiplexer is connected with the first circulator.
And a second circulator is arranged between the first circulator and the third coupler, a filter is connected to the second circulator, and the pump light transmitted by the first circulator enters the third coupler after being filtered by the filter.
And an erbium-doped fiber amplifier is arranged between the acousto-optic modulator and the first circulator.
And a forward second optical isolator is arranged between the Raman fiber laser and the second coupler.
Wherein the second wavelength division multiplexer is connected with a forward first optical isolator.
The photoelectric detection and signal processing unit comprises a photoelectric detector and a signal processing and data acquisition unit which are sequentially connected.
Wherein, the light splitting ratio of the detection light to the reference light is 95: 5.
Wherein, the light splitting ratio of the forward pump light and the backward pump light is 10: 90.
Wherein, the first circulator and the second circulator are both three-port one-way circulators.
(III) advantageous effects
According to the optical fiber distributed disturbance sensor provided by the technical scheme, the backward scattering light intensity and the signal to noise ratio of the tail end of the optical fiber can be improved by adopting the bidirectional distributed Raman amplification structure, so that the sensing distance of the optical fiber distributed disturbance sensor based on the phi-OTDR is increased; the interference of a part of continuous light output by the light source and the backward scattering light is adopted to improve the light power received by the detector, so that the signal-to-noise ratio of the system is further improved; the scheme of the invention adopts the combination of the conventional photoelectric devices, has simple and easily realized technical scheme, and does not have the technical bottleneck and difficulty.
Drawings
FIG. 1 is a schematic diagram of a prior art phi-OTDR based fiber distributed disturbance sensor;
FIG. 2 is a schematic diagram of the optical path of a distributed disturbance sensor based on a double-Mach-Zehnder interferometer in the prior art;
FIG. 3 is a schematic diagram of the optical path of a fiber distributed disturbance sensor according to an embodiment of the present invention.
Wherein, 100: a sensing optical fiber; 200: external disturbance; 300: a disturbance curve exists; and (2) 400 s: no disturbance curve; A. b, C: a coupler; l1: a sensing arm; l2: a reference arm; l3, L4: an optical fiber; 11: a first coupler; 12: a first circulator; 13: a first wavelength division multiplexer; 14: a sensing optical fiber; 15: a second wavelength division multiplexer; 16: a first optical isolator; 17: a second coupler; 18: a second optical isolator; 19: a filter; 20: a second circulator; 21: a third coupler.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
The existing optical fiber distributed disturbance sensor based on the phi-OTDR has the defects that the distance of a sensing optical fiber is long and is about dozens of kilometers, the transmission loss in the optical fiber enables the optical power of pulse light injected into the optical fiber to be obviously different between the head end and the tail end, the optical power of the tail end of the optical fiber is obviously lower than that of the head end of the optical fiber, and therefore the backward Rayleigh scattering optical power also has an obvious difference, the signal-to-noise ratio of the tail end of the optical fiber is obviously poor, and the sensing distance of the sensor is. When the transmission length is increased by increasing the injected light power, the nonlinear effect will occur in the optical fiber after a certain threshold is exceeded, so that the system cannot obtain an effective backward rayleigh scattering curve. In view of this problem, the present embodiment provides a fiber distributed disturbance sensor applied to long-distance monitoring that increases the monitoring distance with a suitable optical power input.
The embodiment is based on the existing optical fiber distributed disturbance sensor based on phi-OTDR, and adds bidirectional distributed Raman amplification to a sensing optical fiber part, and introduces interference enhancement before receiving backscattered light.
The optical path schematic diagram of this embodiment is shown in fig. 3, an output end of the fiber laser is connected to the first coupler 11, one output end of the first coupler 11 is connected to the acousto-optic modulator, the acousto-optic modulator is connected to the driver, and the other output end of the first coupler 11 is connected to the third coupler 21. The output end of the acousto-optic modulator is connected with an erbium-doped fiber amplifier EDFA, the EDFA is connected with a port 1 of a three-port unidirectional first circulator 12, and a port 2 of the first circulator 12 is connected with a bidirectional distributed Raman amplification unit. The bidirectional distributed Raman amplification unit comprises a Raman fiber laser, the output end of the Raman fiber laser is connected with a forward second optical isolator 18, the output end of the second optical isolator 18 is connected with a second coupler 17, one output end of the second coupler 17 is connected with a first wavelength division multiplexer 13 to output forward pump light, and the other output end of the second coupler 17 is connected with a second wavelength division multiplexer 15 to output reverse pump light; the first wavelength division multiplexer 13 is connected with the second wavelength division multiplexer 15 through a sensing optical fiber 14; the first wavelength division multiplexer 13 is connected to the port 2 of the first circulator 12.
The port 3 of the first circulator 12 is connected with the second circulator 20, the second circulator 20 is also a three-port unidirectional circulator, the port 3 of the first circulator 12 is connected with the port 1 of the second circulator 20, the port 2 of the second circulator 20 is connected with a Fiber Bragg Grating (FBG) filter 19, the port 3 of the second circulator 20 is connected with a third coupler 21, the output end of the third coupler 21 is connected with a photoelectric detector, and the photoelectric detector is sequentially connected with a signal processing unit, a data acquisition module and a PC.
Referring to fig. 3, the specific working process of the optical fiber distributed disturbance sensor of this embodiment is as follows: a1550 nm continuous optical fiber laser is adopted to output continuous light, the continuous light is divided into two beams of light by a first coupler 11 connected with the continuous optical fiber laser, the splitting ratio of the first coupler 11 is 95: 5, 95% of light is used as detection light, the light is modulated into pulse light by an acousto-optic modulator connected with the first coupler 11, 5% of continuous light is used as reference light, and the pulse light and returned backward scattering light are subjected to interference enhancement and then are used as optical power received by a photoelectric detector. And the pulse light output by the acousto-optic modulator is sent to the EDFA for power amplification. The amplified pulse light passes through the first circulator 12, and the pulse light output from the port 2 of the first circulator 12 and the pump light split by the 1480nm raman fiber laser through the second coupler 17 are multiplexed into the sensing fiber 14 by the first wavelength division multiplexer 13. At the end of the sensing fiber 14, another part of the pump light branched out by the raman fiber laser through the second coupler 17 is reversely pumped by the second wavelength division multiplexer 15, and the other end of the second wavelength division multiplexer 15 is connected with the forward first optical isolator 16. The splitting ratio of the second coupler 17 is 10: 90, 10% of the light is multiplexed by the first wavelength division multiplexer 13, and 90% of the light is multiplexed by the second wavelength division multiplexer 15. While raman fiber lasers also use a forward second optical isolator 18 to isolate the back light. The port 3 of the first circulator 12 outputs backward scattered light passing through the sensing fiber 14 via the port 2, and the sensing fiber 14 contains a 1480nm raman pump light, which needs to be filtered by a filter to remove the 1480nm pump light, and the second circulator 20 functions as a filter for removing the 1480nm light, specifically, the port 2 of the second circulator 20 is connected to the FBG filter 19 for filtering. The backscattered light is filtered and then subjected to interference enhancement in a third coupler 21 with the continuous light output by the fiber laser. The interfered signals are converted into electric signals by a photoelectric detector, and the electric signals are amplified, filtered, averaged by accumulation or subtracted by accumulation and then collected by a digital acquisition card into a PC for real-time display, post data processing and the like.
The relationship between the power of the backward rayleigh scattered light and the power of the incident light in a single mode fiber can be described by equation (7):
wherein S is a Rayleigh scattering capture factor; u. ofgGroup velocity of light pulse propagation in the fiber; w is the optical pulse width; a isRIs the Rayleigh scattering coefficient; a is the attenuation coefficient in the fiber.
The phase sensitive optical time domain reflection technology receives the interference result of Rayleigh scattering light reflected in a pulse width region, backward Rayleigh scattering in an optical fiber is approximate to a Fabry-Perot interferometer in the optical fiber, and under the condition, the power of coherent backward scattering light is as follows:
Pbsii＝Pin2R(1+cosf) (8)
P′bsis the power of the coherent backscattered light, P'inIs the transmitted optical power at that point, R is approximately the backscattering coefficient, and f is the phase difference between the rising and falling edges of the optical pulse.
n is the effective refractive index of the optical fiber, L is the transmission length of the pulse in the optical fiber, and L is the wavelength of the injected light. When external vibration acts on the sensing optical fiber, the optical phase in the pulse range is changed, the power of the back scattering light at the (8) type disturbance position is changed, and the external vibration can be sensed by detecting the change of the optical power.
To increase the optical power of the received light, coherent light is used to constructively interfere with the returning backscattered light. Since the line width of the light source is very narrow (in the order of kHz), the coherent length of the output continuous light can reach hundreds of kilometers, and therefore the returned backscattered light can still be coherent with the light source.
Since the variation of the scattered light with time t reflects the distribution of the scattered light in the optical fiber, the time-to-fiber length can be given by equation (10):
t＝2z/ug (10)
it can be seen from the equations (7) and (10) that when external vibration acts on the sensing fiber, the position information is reflected on the curve of the scattered light power with time.
The sensing principle and the positioning principle are consistent with those of the existing optical fiber distributed disturbance sensor based on phi-OTDR.
In this embodiment, the bidirectional distributed raman amplification structure is adopted to improve the back scattering light intensity and the signal-to-noise ratio at the end of the optical fiber, thereby improving the sensing distance of the optical fiber distributed disturbance sensor based on the phase sensitive optical time domain reflection technology. Under the action of a strong optical field, a Stokes wave in a medium is rapidly enhanced along with the enhancement of incident optical field energy, so that most of Raman pump light energy is transferred into the Stokes wave, and the nonlinear phenomenon is called Stimulated Raman Scattering (SRS). The weak signal light and the pump light with proper frequency simultaneously pass through the optical fiber, and the signal light can be obviously amplified by a continuous pump source (100mW) with small power. Bidirectional raman amplification is the use of such principles to amplify forward transmitted pulsed light and returned backscattered light.
In addition, in the embodiment, interference constructive is realized by adopting interference of continuous light and backward scattering light to improve the light power received by the detector, so that the signal-to-noise ratio is further improved, and the monitoring distance is effectively increased.
In the embodiment, the third circulator 21 in the optical fiber distributed disturbance sensor based on the phase-sensitive optical time domain reflection technology is replaced by a 50: 50 directional coupler, and the technical effects are completely the same; the acousto-optic modulator can be replaced by an electro-optic modulator or other modulation modes capable of generating pulse light, and comprises a laser and a laser, wherein the laser internally modulates and outputs the pulse light; the splitting ratio of the first coupler 11 and the second coupler 17 is not limited to 95: 5 and 90: 10, and can be changed within a certain range according to the relationship between specific incident light power and sensing optical fiber distance, and the technical effects are completely the same; the purpose of conditioning the output signal of the photoelectric detector through amplification, filtering and the like is to eliminate noise and interference, and the difference of the specific design of the amplification and filtering function design is regarded as the same technical scheme as the invention under the condition of not influencing the realization of the purpose of the invention, no matter the realization mode is a circuit or a virtual instrument and the like; the data acquisition and the post-stage data processing can also be realized by adopting a DSP (digital signal processor) and other circuit modes, and the technical effect is the same as that of the embodiment.
The embodiments of the invention can be seen in that the two-way Raman amplification is adopted, and based on the interference of pulsed light and continuous light and the phase-sensitive optical time domain reflection technology, the over-high requirement of the traditional phase-sensitive optical time domain reflectometer on the output power of a laser can be solved, and the nonlinear effect in an optical fiber can be reasonably avoided; the embodiment adopts a mode of detecting the interference of scattering signals, thereby essentially avoiding the limitation of the scattering on the monitoring distance existing in the optical fiber distributed disturbance sensor of the double Mach-Zehnder interferometer type.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and substitutions can be made without departing from the technical principle of the present invention, and these modifications and substitutions should also be regarded as the protection scope of the present invention.
Claims (10)
1. A fiber optic distributed disturbance sensor, comprising:
the output end of the fiber laser is connected with the first coupler, one output end of the first coupler is connected with the acousto-optic modulator and outputs detection light, and the other output end of the first coupler is connected with the third coupler and outputs reference light;
the bidirectional distributed Raman amplification unit is connected with the acousto-optic modulator through a first circulator and receives pulsed light modulated by the acousto-optic modulator; the first circulator is connected with the third coupler to transmit the pump light subjected to bidirectional Raman amplification to the third coupler;
and the photoelectric detection and signal processing unit is connected with the third coupler, receives the optical signal enhanced by the interference in the third coupler, converts the optical signal into an electric signal and performs subsequent data processing.
2. The fiber optic distributed perturbation sensor of claim 1 wherein the bi-directional distributed raman amplification unit comprises: the output end of the Raman fiber laser is connected with the second coupler, one output end of the second coupler is connected with the first wavelength division multiplexer and outputs forward pump light, and the other output end of the second coupler is connected with the second wavelength division multiplexer and outputs reverse pump light; the first wavelength division multiplexer and the second wavelength division multiplexer are connected through a sensing optical fiber; the first wavelength division multiplexer is connected with the first circulator.
3. The fiber optic distributed disturbance sensor of claim 1, wherein a second circulator is disposed between the first circulator and the third coupler, and a filter is further coupled to the second circulator, and the pump light transmitted by the first circulator enters the third coupler after being filtered by the filter.
4. The fiber optic distributed disturbance sensor of claim 1, wherein an erbium doped fiber amplifier is disposed between the acousto-optic modulator and the first circulator.
5. The fiber optic distributed disturbance sensor of claim 2, wherein a second optical isolator in the forward direction is disposed between the raman fiber laser and the second coupler.
6. The fiber optic distributed disturbance sensor of claim 2, wherein the second wavelength division multiplexer is coupled with a forward first optical isolator.
7. The optical fiber distributed disturbance sensor according to claim 1, wherein the photo-detection and signal processing unit comprises a photo-detector, a signal processing and data acquisition unit connected in sequence.
8. The fiber optic distributed disturbance sensor of claim 1, wherein the split ratio of the detection light to the reference light is 95: 5.
9. The fiber optic distributed disturbance sensor of claim 2, wherein the forward pump light and the backward pump light have a split ratio of 10: 90.
10. The fiber optic distributed disturbance sensor of claim 3, wherein the first and second circulators are each three-port one-way circulators.
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