CN114577324A - A Distributed Optical Fiber Vibration Monitoring System - Google Patents

Abstract

The invention discloses a distributed optical fiber vibration monitoring system. The optical fiber vibration monitoring system comprises: a laser light source, an optical fiber coupler, a switch-type semiconductor optical amplifier, an optical fiber circulator, a balanced detector, a low-pass filter, and data acquisition and processing. unit and pulse driver; the continuous laser emitted by the laser light source is divided into two paths by the fiber coupler; one of the continuous lasers enters the balanced detector as the local oscillator laser; the other continuous laser enters the switching semiconductor optical amplifier and is pulsed Driven by the driver, it becomes a periodic pulsed laser, which is incident on the sensing fiber through the fiber circulator; the back Rayleigh scattered light returned from the sensing fiber and the local oscillator laser enter the balanced detector, and are converted by photoelectric conversion and filtered out. After the mode signal enters the low-pass filter, it is finally collected and analyzed by the signal acquisition and processing unit to realize the detection of vibration signals along the sensing fiber.

Description

A Distributed Optical Fiber Vibration Monitoring System

technical field

The invention belongs to the technical field of optical fiber sensing, and in particular relates to a distributed optical fiber vibration monitoring system.

Background technique

Distributed optical fiber vibration sensor is a new type of optical fiber sensing technology based on phase-sensitive optical time domain reflectometry (φ-OTDR). Multi-point vibration monitoring, and the positioning accuracy can reach the meter level.

Since the back Rayleigh scattering signal is relatively weak, its demodulation methods mainly include:

The first is the direct intensity demodulation method, which uses a highly sensitive avalanche photodiode or an erbium-doped fiber amplifier + photodiode as a detector to directly detect and collect the back Rayleigh scattered light signal, and perform adjacent sampling on the scattered light interference signal obtained by sampling. Differential detection of vibration signal, this method can only simply determine the position information of the vibration point, and it is difficult to collect the relevant amplitude and frequency information of the vibration;

The second is the coherent demodulation method. The Rayleigh scattered light signal and the local oscillator light signal are entered into the balanced detector, and the local oscillator light is amplified. The acquisition card collects the beat frequency signal, and extracts the amplitude and phase signals from the beat frequency signal. The adjacent difference is used to realize the discrimination of the vibration signal. Compared with the direct intensity demodulation method, the coherent demodulation method is technically difficult to implement, but has higher measurement sensitivity and higher linearity, and can realize longer distance monitoring.

Distributed fiber-optic vibration sensors based on phase-sensitive optical time-domain reflectance require laser pulses with high coherence, so external modulation is required. At present, external modulation is mainly realized by using acousto-optic modulators. The technology of acousto-optic modulators is mature and the extinction ratio is high, but the driving is relatively complicated. The rising edge of the pulse is generally in the order of tens of nanoseconds, which cannot achieve high spatial resolution. When the frequency is shifted to several hundred megabytes, the heterodyne coherent demodulation method needs to be adopted at this time, and the signal demodulation is very difficult.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a distributed optical fiber vibration monitoring system in order to overcome the defects of the prior art. The system of the present invention uses a switch-type semiconductor optical amplifier as an external modulator to realize a pulsed laser without frequency shift, and finally realizes homodyne Coherent detection.

The object of the present invention is achieved through the following technical solutions:

A distributed optical fiber vibration monitoring system, the optical fiber vibration monitoring system includes: a laser light source, an optical fiber coupler, a switch-type semiconductor optical amplifier, an optical fiber circulator, a balanced detector, a low-pass filter, a data acquisition and processing unit, and a pulse driver ; The continuous laser emitted by the laser light source is divided into two channels by the fiber coupler; one of the continuous lasers enters the balanced detector as the local oscillator laser; the other continuous laser enters the switching semiconductor optical amplifier and is driven by the pulse driver. It becomes a periodic pulsed laser, which is incident on the sensing fiber through the fiber circulator; the back Rayleigh scattered light returned from the sensing fiber, and the local oscillator laser enter the balanced detector, and enter after photoelectric conversion and filtering of the common mode signal. The low-pass filter is finally collected and analyzed by the signal acquisition and processing unit to realize the detection of vibration signals along the sensing fiber.

According to a preferred embodiment, the optical fiber vibration monitoring system further includes a first erbium-doped fiber amplifier, the first erbium-doped fiber amplifier is disposed between the switch-type semiconductor optical amplifier and the fiber circulator, and is used for realizing the periodic Amplification of the pulsed laser.

According to a preferred embodiment, the optical fiber vibration monitoring system further includes a second erbium-doped fiber amplifier, the second erbium-doped fiber amplifier is arranged between the fiber circulator and the balance detector, and the back direction returned from the sensing fiber is After the Rayleigh scattered light passes through the fiber circulator, it is amplified by the second erbium-doped fiber amplifier, and the amplified back Rayleigh scattered light is input to the balanced detector.

According to a preferred embodiment, the laser light source is a narrow linewidth semiconductor laser light source. The narrow linewidth semiconductor laser light source is more shock resistant and has a wider operating temperature range.

According to a preferred embodiment, the fiber couplers are not limited to standard couplers, direct-connect couplers, star/tree couplers, and wavelength multiplexers.

According to a preferred embodiment, the low-pass filter is not limited to a Butterworth filter and a Chebyshev filter.

The aforementioned main scheme of the present invention and each of its further options can be freely combined to form multiple schemes, which are all schemes that can be adopted and claimed in the present invention. After understanding the solutions of the present invention, those skilled in the art can understand that there are various combinations according to the prior art and common knowledge, all of which are the technical solutions to be protected by the present invention, and are not exhaustive here.

Beneficial effects of the present invention: The distributed optical fiber vibration monitoring system of the present invention utilizes a switch-type semiconductor optical amplifier as an external modulator to realize pulse laser without frequency shift, and finally realize homodyne coherent detection. Since the switching semiconductor optical amplifier is used as an external modulator, the rising edge of the pulsed laser is very fast (less than 1ns), so a pulsed laser with a pulse width of tens of nanoseconds can be realized, which is beneficial to improve the performance of high spatial resolution; and the switching semiconductor optical amplifier The amplifier itself has a certain signal gain function, which reduces the amplification performance requirements of the first erbium-doped fiber amplifier later.

Description of drawings

FIG. 1 is a schematic structural diagram of a distributed optical fiber vibration monitoring system of the present invention.

Detailed ways

The embodiments of the present invention are described below through specific specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments may be combined with each other under the condition of no conflict.

It should be noted that, in order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention. , not all examples.

In the description of the present invention, it should also be noted that, unless otherwise expressly specified and limited, the terms "arranged", "installed", "connected" and "connected" should be understood in a broad sense, for example, it may be a fixed connection, It can also be a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or the internal communication between the two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in specific situations.

In addition, the present invention should point out that, in the present invention, if the specific structure, connection relationship, positional relationship, power source relationship, etc. are not specifically written, the structure, connection relationship, positional relationship, power source relationship involved in the present invention etc. are all available to those skilled in the art on the basis of the prior art and can be known without creative work.

Referring to FIG. 1, the present invention discloses a distributed optical fiber vibration monitoring system. The optical fiber vibration monitoring system includes: a laser light source, a fiber coupler, a switch-type semiconductor optical amplifier, a first erbium-doped fiber amplifier, and a fiber circulator , a second erbium-doped fiber amplifier, a balanced detector, a low-pass filter, a data acquisition and processing unit and a pulse driver.

Preferably, the laser light source is a narrow linewidth semiconductor laser light source, the center wavelength is 1550nm, the linewidth is less than 5kHz, and it can work stably for a long time in the temperature range of -10°C to +50°C. The fiber optic couplers are not limited to standard couplers, direct-connect couplers, star/tree couplers, and wavelength multiplexers. The low-pass filters are not limited to Butterworth filters and Chebyshev filters.

The continuous laser emitted by the laser light source is divided into two paths by the fiber coupler. Among them, one continuous laser enters the balanced detector as a local oscillator laser. Another continuous laser enters the switching semiconductor optical amplifier and is driven by the pulse driver to become a periodic pulsed laser, which is amplified by the first erbium-doped fiber amplifier and then incident on the sensing fiber through the fiber circulator.

The back Rayleigh scattered light returned from the sensing fiber is amplified by the second erbium-doped fiber amplifier after passing through the fiber circulator. The amplified back Rayleigh scattered light and the local oscillator laser enter the balanced detector, enter the low-pass filter after photoelectric conversion and filter out the common mode signal, and finally be collected and analyzed by the signal acquisition and processing unit to realize the detection of the optical fiber along the sensing fiber. Vibration signal detection.

The distributed optical fiber vibration monitoring system of the present invention utilizes a switch-type semiconductor optical amplifier as an external modulator to realize pulse laser without frequency shift, and finally realizes homodyne coherent detection.

Since the switching semiconductor optical amplifier is used as an external modulator, the rising edge of the pulsed laser is very fast (less than 1ns), so a pulsed laser with a pulse width of tens of nanoseconds can be realized, which is beneficial to improve the performance of high spatial resolution; and the switching semiconductor optical amplifier The amplifier itself has a certain signal gain function, which reduces the amplification performance requirements of the first erbium-doped fiber amplifier later.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (6)

1. a distributed optical fiber vibration monitoring system, is characterized in that, described optical fiber vibration monitoring system comprises: laser light source, optical fiber coupler, switch-type semiconductor optical amplifier, optical fiber circulator, balanced detector, low-pass filter, data Acquisition processing unit and pulse driver; The continuous laser emitted by the laser light source is divided into two paths by the fiber coupler; Among them, a continuous laser enters the balanced detector as a local oscillator laser; Another continuous laser enters the switching semiconductor optical amplifier and is driven by the pulse driver to become a periodic pulse laser, which is incident on the sensing fiber through the fiber circulator; The back-rayleigh scattered light returned from the sensing fiber and the local oscillator laser enter the balanced detector. After photoelectric conversion and filtering of the common mode signal, they enter the low-pass filter. Finally, they are collected and analyzed by the signal acquisition and processing unit to realize sensing. Vibration signal detection along the fiber. 2. The distributed optical fiber vibration monitoring system according to claim 1, wherein the optical fiber vibration monitoring system further comprises a first erbium-doped fiber amplifier, The first erbium-doped fiber amplifier is arranged between the switch-type semiconductor optical amplifier and the fiber circulator, and is used to realize the amplification of the periodic pulsed laser light. 3. The distributed optical fiber vibration monitoring system according to claim 1 or 2, wherein the optical fiber vibration monitoring system further comprises a second erbium-doped fiber amplifier, and the second erbium-doped fiber amplifier is arranged in the fiber circulator between the balance detector, The back-Rayleigh scattered light returned from the sensing fiber is amplified by the second erbium-doped fiber amplifier after passing through the fiber circulator, and the amplified back-Rayleigh scattered light is input to the balanced detector. 4 . The distributed optical fiber vibration monitoring system according to claim 1 , wherein the laser light source is a narrow linewidth semiconductor laser light source. 5 . 5. The distributed optical fiber vibration monitoring system of claim 1, wherein the optical fiber coupler is not limited to a standard coupler, a direct-connected coupler, a star/tree coupler, and a wavelength multiplexer . 6. The distributed optical fiber vibration monitoring system according to claim 1, wherein the low-pass filter is not limited to a Butterworth filter and a Chebyshev filter.

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