RU2566603C1 - Distributed sensor of acoustic and vibration impacts - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: sensor comprises a sensitive optical cable, an optical interface, a coherent phase-sensitive optical reflectometer. The reflectometer comprises a source of periodical sequence of optical pulses and a receiver of scattered radiation connected to the interface. The source of periodical sequence of optical pulses and the processing unit are electrically connected to the control and synchronisation unit. The meter is equipped with an optical multiplexer and a source of pump radiation for Raman amplification of the scattered signal. The multiplexer is installed between the optical interface and the sensitive element, the outlet of the optical multiplexer is connected to the sensitive element, the first inlet of the multiplexer is connected to the optical interface, and the second inlet of the multiplexer is connected to the source of pump radiation for Raman amplification of the scattered signal. The source of pump radiation for Raman amplification is made as capable of periodical variation of pump capacity for Raman amplification of the scattered signal in time from P_s(t)=P_min at the moment of time T₀ to P_s(t)=P_max at the moment of time T_max.

EFFECT: increased sensitivity.

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Description

Distributed Acoustic and Vibration Sensor

The invention relates to the field of distributed measurements, namely to distributed sensors of acoustic and vibration effects.

The claimed device can be used to monitor and protect extended objects, such as perimeters and communications, in particular, to monitor the condition of transport pipelines, trunk fiber cables from damage when working near the cable, protect the perimeters of special objects, etc.

A known analyzer of vibroacoustic signals designed to analyze the spectrum of signals and containing optically coupled coherent radiation source, beam splitter, photodetector, amplifier (SU, A.S. No. 1589069, 1990). The known device is not intended for monitoring extended objects.

A known diagnostic system designed to track changes in static strains and measure dynamic strains. The system includes a tunable narrow-band light source, a light guide fiber, reflective sensors, such as Bragg gratings located along the length of the fiber, and a signal processing loop. The system can also be used according to the Fabry-Perot scheme (RF patent No. 2141102). The system provides high sensitivity to deformations, but it is very complex and has a low spatial resolution.

A device is known for monitoring the vibro-acoustic characteristics of an extended object, comprising a narrow-band pulsed optical radiation source in the form of a Q-switched fiber laser, a sensitive element in the form of an optical fiber located longitudinally inside or outside an extended object, an optical radiation input unit into the sensitive element, a photodetector, and a processing unit signal with a processor (RF patent No. 2271446). A disadvantage of the known device is the presence of random variations in the carrier frequency of the testing optical pulses injected into the fiber, associated with the pulsed laser mode and the sensitivity of the fiber laser to technical noise. This limits the range, sensitivity and resolution of the device, and also complicates its use in the field.

As the closest analogue (prototype), a device was selected — a distributed sensor of acoustic and vibration effects — containing a sensing element in the form of an optical fiber placed in a fiber optic cable and optically connected to the fiber through an optical interface with a coherent phase-sensitive optical reflectometer containing optically connected to interface source of a periodic sequence of optical pulses and a scattered radiation receiver that converts the scattered optical and radiation during electrical signal supplied to the processing unit, wherein the source of a periodic sequence of optical pulses and a processing unit electrically connected with the control unit and synchronization (US Patent №5194847).

A disadvantage of the known device is the rapid decrease in sensitivity with increasing distance due to a decrease in the backscatter signal. The decrease in the power of the backscattering signal is associated with two circumstances: firstly, due to attenuation in the fiber, the power of the test signal decreases as it propagates along the fiber; secondly, due to the attenuation of the backscattering signal during propagation back from the test region of the fiber to its beginning. Reducing the power of the backscatter signal reduces the guaranteed sensitivity and range of the device.

The present invention is aimed at solving the problem of improving the reliability of the sensor of acoustic and vibration effects.

The technical result of the invention is to increase the guaranteed sensitivity and range of a distributed sensor of acoustic and vibration effects.

, или источник излучения накачки для рамановского усиления выполнен с возможностью изменения мощности P_p(t) излучения накачки во времени 0≤t≤T_max по корневому закону

или источник излучения накачки для рамановского усиления выполнен с возможностью изменения мощности P_p(t) излучения накачки во времени 0≤t≤T_max по закону P_p(t)=(P_min+S_pt), или источник излучения накачки для рамановского усиления выполнен с возможностью изменения мощности излучения накачки P_p(t) по закону

,The technical result in the implementation of the invention is achieved in that a distributed sensor of acoustic and vibration effects, containing a sensing element in the form of an optical fiber placed in a fiber optic cable, and optically connected to the fiber through an optical interface, a coherent phase-sensitive optical reflectometer containing a source optically connected to the interface periodic sequence of optical pulses and a scattered radiation receiver designed to convert generating scattered optical radiation into an electrical signal for the processing unit, the source of the periodic sequence of optical pulses and the processing unit being electrically connected to the control and synchronization unit, equipped with an optical multiplexer containing at least one output and two inputs and a pump radiation source for combining the spectral channels for Raman amplification of the scattered signal, with an optical multiplexer installed between the optical interface and With the first element, the output of the optical multiplexer is connected to the sensitive element, the first input of the multiplexer is connected to the optical interface, and the second input of the multiplexer is connected to the pump radiation source for Raman amplification of the scattered signal, while the pump radiation source for Raman amplification is configured to periodically change the pump power for Raman amplification of the scattered signal in time from P _p (t) = P _min at time T ₀ to P _p (t) = P _max at time T _max , while the radiation source For pumping Raman amplification, it is possible to change the power P _p (t) of the pump radiation in time 0≤t≤T _max according to the linear law

or the pump radiation source for Raman amplification is configured to change the pump radiation power P _p (t) in time 0≤t≤T _max according to the root law

or the pump radiation source for Raman amplification is configured to change the pump radiation power P _p (t) in time 0≤t≤T _max according to the law P _p (t) = (P _min + S _p t), or the pump radiation source for Raman gain is made with the possibility of changing the pump radiation power P _p (t) according to the law

,

where P _min is the minimum pump radiation power for Raman amplification of the scattered signal, the variation range of which is from 0 to 2α _s / g _R ;

α _s is the attenuation coefficient of the test signal;

g _R is an indicator of Raman fiber gain;

P _max is the maximum radiation power that is either equal to the pump radiation power for Raman amplification, which provides full compensation for the attenuation of the signal scattered from the farthest point of the sensing element, or equal to the threshold power for the occurrence of nonlinear effects, or equal to the maximum technically available pump power;

T ₀ - point in time immediately after the input of the test pulse into the fiber;

T _max = (2Ln) / c is the duration of the trace;

L _n is the length of the sensing element;

c is the speed of light propagation in the optical fiber;

- скорость увеличения мощности излучения накачки для рамановского усиления рассеянного сигнала; $$S_p=\frac{{\alpha }_s{\alpha }_p{\nu }_g}{g_R}$$

- the rate of increase of the pump radiation power for Raman amplification of the scattered signal;

α _p - attenuation coefficient of the pump radiation for Raman amplification of the scattered signal;

ν _g is the group velocity of the pulse in the fiber.

The invention is illustrated by graphic materials, which show:

in FIG. 1 is a block diagram of a distributed sensor of acoustic and vibration effects;

in FIG. 2 - pump pulse shape;

in FIG. 3 - stimulated Raman scattering mechanism: pumping at a wavelength of 1480 nm creates a virtual excited state, under the influence of radiation from a signal at a wavelength of 1550 nm, stimulated inelastic scattering of the pump from the excited state occurs; in FIG. 4 is a trace compensation circuit.

According to the invention, a distributed acoustic and vibration sensor comprises:

source of a periodic sequence of optical pulses 1;

optical amplifier 2;

optical interface 3;

a pump radiation source 4 for Raman amplification of the scattered signal;

optical multiplexer (optical combiner of spectral channels) 5;

a sensing element 6 in the form of an optical fiber placed in a fiber optic cable;

preamplifier 7;

a scattered radiation receiver 8 converting scattered optical radiation into an electrical signal;

a processing, control and synchronization unit 9 (a combined unit including a processing unit 10 electrically connected to the control and synchronization unit 11).

The proposed device differs significantly from the prototype in that the sensor is equipped with an optical multiplexer for combining the spectral channels, containing at least one output and two inputs, and a pump radiation source for Raman amplification of the scattered signal, the optical multiplexer being installed between the optical interface and the sensing element, the output the optical multiplexer is connected to the sensing element, the first input of the multiplexer is connected to the optical interface, and the second stroke multiplexer coupled to the pump light source for Raman amplification of the scattered signal, wherein the source of pump light for the Raman amplification is configured to periodically change the pump power for Raman amplification of the scattered signal in time from _{P p} (t) = P _min at the time T ₀ to P _p (t) = P _max at time T _max . This feature provides a weakening of the degree of decrease in the average power of the backscatter signal with increasing distance z (Fig. 4). In the prototype, the average power of the backscatter signal decreases exponentially with increasing distance z to the scattering region (test region). This leads to a rapid decrease in the power of the useful signal and, consequently, to a decrease in the range of the device. The use of distributed Raman amplification provides compensation for the attenuation of the backscattering signal with increasing distance z. A periodic increase in power from the minimum value immediately after the input of the test pulse into the fiber to the maximum value at time 2Lopt / c provides an increase in the gain of the useful backscattering signal from remote areas. The gain increases for the scattering signal with increasing z coordinate.

. Данный признак обеспечивает упрощение конструкции источника излучения для рамановской накачки.The proposed device differs significantly from the prototype in that the radiation source for Raman amplification is configured to change the pump radiation power P _p (t) in time 0≤t≤T _max according to the linear law

. This feature provides a simplification of the design of the radiation source for Raman pumping.

. Данный признак при незначительном усложнении конструкции источника излучения для рамановской накачки обеспечивает более равномерную компенсацию ослабления сигнала обратного рассеяния.The proposed device differs significantly from the prototype also in that the radiation source for Raman amplification is configured to change the pump radiation power P _p (t) in time 0≤t≤T _max according to the root law

. This feature, with a slight complication of the design of the radiation source for Raman pumping, provides more uniform compensation for the attenuation of the backscattering signal.

(значения получены расчетным путем). Данные признаки обеспечивают уменьшение расхода энергии, увеличение ресурса работы блока рамановской накачки и всего устройства в целом, повышение надежности работы прибора и снижение эксплуатационных затрат за счет уменьшения необходимой для компенсации ослабления сигнала максимальной и средней мощности рамановской накачки.The proposed device differs significantly from the prototype also in that the radiation source for Raman amplification is configured to change the pump radiation power P _p (t) in time 0≤t≤T _max according to the law P _p (t) = (P _min + S _p t ) or

(values obtained by calculation). These signs provide a reduction in energy consumption, an increase in the operating life of the Raman pump unit and the entire device as a whole, an increase in the reliability of the device and lower operating costs by reducing the signal required to compensate for the attenuation of the maximum and average Raman pump power.

The device operates as follows.

A source of a periodic sequence of optical pulses (1) generates periodic sequences of optical pulses, which, after amplification in an optical amplifier (2), are introduced through an optical interface (3) into a sensitive element (6) in the form of an optical fiber placed in an optical fiber cable. At the same time, radiation from the source (4) is introduced into the sensitive element (6) using the optical combiner of the spectral channels (5) to Raman amplification of the scattered signal. In the optical fiber of the sensing element (6), optical pulses are scattered on the inhomogeneities of the fiber without changing the frequency (Rayleigh scattering) and form an optical backscattering signal propagating from the point of scattering in the optical fiber of the sensitive element (6) in the direction of the optical interface (3). During propagation through the fiber, the scattered radiation is attenuated due to non-resonant losses and scattering in the fiber and is amplified due to stimulated Raman (Raman) scattering under the influence of Raman pump radiation. The optical interface directs the optical backscattering signal to the preamplifier (7) and, after amplification, to the scattered radiation receiver (8), which converts the amplified scattered optical radiation into an electrical signal. The electric signal from the scattered radiation receiver (8) enters the combined processing, control and synchronization unit (9).

In the case of pulsed excitation, the time dependence of the average power of the backscattering signal and, accordingly, the photocurrent of the photodetector 6 (reflectogram) in the absence of Raman pumping (prototype) has a form close to the decaying exponent. In this case, the information signal (scattered radiation converted into an electrical signal by the receiver (8), from the remote areas of the sensitive element is significantly smaller than the signal from the areas of the sensitive element located close to the optical interface. This significantly limits the prototype range. To reduce the inequality of information signals from different areas of the sensing element in this invention introduced a radiation source for Raman amplification of scattered radiation. The study of the radiation source for the Raman amplification of the scattered signal periodically changes in time, increasing from 0 immediately after the test pulse is introduced into the fiber to the maximum value at time 2Lopt / s. This temporal dependence of the pump provides the maximum amplification of the signal scattered from the most distant regions of the sensitive element. Thus, the gain of signals from more distant regions is greater, which reduces the difference in the amplitude of the signal generated by the receiver (8 ), made, for example, in the form of a photodetector.

Due to the high coherence of the initial radiation from the periodic sequence of optical pulses (1), the trace (i.e., the amplitude of the signal from the receiver (8)) is randomly cut due to the random phase of the interfering scattered radiation. In the absence of vibroacoustic effects and changes in the carrier frequency of the rectangular test pulse, the reflectograms from different pulses obtained at different points in time coincide. In the presence of a vibro-acoustic effect on the sensitive element, the reflectograms from different impulses in the impact area turn out to be different. The magnitude of the changes determines the intensity of the impact, and the time delay relative to the testing rectangular pulse uniquely determines the coordinate of the impact. The nature and coordinate of the impact are determined by the combined unit (9) of processing, control, and synchronization as a result of the analysis and processing of many reflectograms.

A disadvantage of the known devices is that the average amplitude of the reflectogram decreases exponentially with increasing distance to the test area: A (z) = A (0) exp (-2α _e z).

The use of Raman pumping to amplify the signal from remote areas will eliminate the strong attenuation of the information signal, that is, provide the necessary level of sensitivity along the entire fiber.

To reduce the attenuation of the signal, the functional time dependences of the pump power described above can be used.

The use of the invention allows you to quickly detect violations of the integrity of the perimeter of an extended object or to fix any effects from inside or outside on an extended object. Moreover, the device allows you to determine the coordinates of the location of the defect or point of impact on the object reliably and with a high degree of accuracy.

Based on the foregoing, we can conclude that the task - improving the reliability of the sensor of acoustic and vibration effects - is solved, and the claimed technical result - increasing the range, sensitivity and resolution of the device is achieved.

The analysis of the claimed technical solution for compliance with the conditions of patentability showed that the features indicated in the independent claim are interrelated with each other with the formation of a stable set of necessary features sufficient to obtain the required super-total technical result.

The properties regulated in the claimed technical solution by individual features are well known in the art and require no further explanation.

Thus, the above information indicates the fulfillment of the following set of conditions when using the claimed technical solution:

- an object embodying the claimed technical solution, when implemented, is designed to monitor and protect extended objects, such as perimeters and communications, in particular to monitor the condition of transport pipelines, trunk fiber cables from damage when working near the cable, protect the perimeters of special objects, etc. P.;

- for the claimed distributed sensor of acoustic and vibration effects in the form in which it is described in the independent claim, the possibility of its implementation using the methods and methods described above and known from the prior art on the priority date is confirmed;

- the object embodying the claimed technical solution, when implemented, is able to ensure the achievement of the technical result perceived by the applicant.

Therefore, the claimed object - a distributed sensor of acoustic and vibration effects - meets the requirements of patentability conditions "novelty", "prior art" and "industrial applicability" under the current law.

Claims (5)

1. A distributed acoustic and vibration sensor containing a sensing element in the form of an optical fiber placed in a fiber optic cable and optically connected to the fiber via an optical interface with a coherent phase-sensitive optical reflectometer containing a source of a periodic sequence of optical test pulses and a receiver optically connected to the interface scattered radiation, converting scattered optical radiation into an electrical signal supplied to the unit processing for forming a trace, wherein the source of the periodic sequence of optical pulses and the processing unit are electrically connected to the control and synchronization unit, characterized in that the sensor is equipped with an optical multiplexer for combining the spectral channels containing at least one output and two inputs, and a pump radiation source for Raman amplification of the scattered signal, and an optical multiplexer is installed between the optical interface and the sensitive element ohm, the output of the optical multiplexer is connected to the sensing element, the first input of the multiplexer is connected to the optical interface, and the second input of the multiplexer is connected to the pump radiation source for Raman amplification of the scattered signal, while the pump radiation source for Raman amplification is configured to periodically change the pump power for Raman amplification of the scattered signal in time from P _p (t) = P _min at time T ₀ to P _p (t) = P _max at time T _max , where:
P _min is the minimum pump radiation power for Raman amplification of the scattered signal, the range of which is from 0 to 2α _s / g _R ,
α _s - attenuation coefficient of the test signal,
g _R is an indicator of the Raman gain of the fiber,
P _max - maximum radiation power,
T ₀ - point in time immediately after the input of the test pulse into the fiber,
T _max = (2L _n ) / c is the duration of the trace,
L _n is the length of the sensing element,
c is the speed of light propagation in the optical fiber. 2. The device according to p. 1, characterized in that the radiation source for Raman amplification is configured to change the pump radiation power P _p (t) in time 0≤t≤T _max according to the linear law:

3. The device according to claim 1, characterized in that the radiation source for Raman amplification is configured to change the pump radiation power P _p (t) in time 0≤t≤T _max according to the root law:

4. The device according to claim 1, characterized in that the radiation source for Raman amplification is configured to change the pump radiation power P _p (t) in time 0≤t≤T _max according to the law:

$$S_p=\frac{{\alpha }_s{\alpha }_p{\nu }_g}{g_R}$$

- the rate of increase of the pump radiation power for Raman amplification of the scattered signal,
α _p - attenuation coefficient of the pump radiation for Raman amplification of the scattered signal,
v _g is the group velocity of the pulse in the fiber. 5. The device according to claim 1, characterized in that the pump radiation source for Raman amplification is configured to change the pump radiation power P _p (t) according to the law:

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