CN202182726U - Pulse coding ultra-long-range fully-distributed optical fiber Rayleigh and Raman scattering sensor fused with optical fiber Raman frequency shifter - Google Patents

Abstract

The pulse coding ultra-long-distance fully distributed optical fiber Rayleigh and Raman scattering sensor fused with the optical fiber Raman frequency shifter disclosed by the utility model includes a pulse coding fiber laser drive power supply, a pulse coding fiber pulse laser, and a single-mode fiber and a 1660nm band. Optical fiber Raman frequency shifter, integrated optical fiber wavelength division multiplexer, sensing optical fiber, photoelectric receiving module, encoding, decoding and demodulation digital signal processor and industrial computer composed of optical pass filter. The sensor is based on the principle of optical fiber Raman frequency shifter, pulse encoding principle, optical fiber Rayleigh and Raman fusion scattering sensing principle, and uses the principle of optical time domain reflection to locate the measuring point. The sensor of the utility model has the advantages of low cost, long service life, simple structure, good signal-to-noise ratio, and high reliability, and is suitable for petrochemical pipelines, tunnels, large-scale civil engineering monitoring and disaster forecast monitoring within a range of 80 kilometers from remote or ultra-remote ranges.

Description

A pulse-encoded ultra-long-range fully distributed optical fiber Rayleigh and Raman scattering sensor fused with a fiber-optic Raman frequency shifter

technical field

The utility model relates to the field of optical fiber sensors, in particular to a pulse coded ultra-long-distance fully distributed optical fiber Rayleigh and Raman scattering sensor fused with an optical fiber Raman frequency shifter.

Background technique

For a long time, in the field of engineering at home and abroad, large-scale civil construction, bridges, tunnels, petrochemical pipelines, oil storage tanks and power cables have mainly used electrical strain gauges and thermosensitive electric groups as strain and temperature sensors, and each sensor needs to be connected with wires. , forming a large-scale detection network, the structure is very complicated, this kind of sensor itself is charged, it is inherently unsafe, susceptible to electromagnetic interference, not resistant to corrosion, and cannot be positioned, not suitable for use in harsh environments, let alone applied geology Scenes of disasters and fires.

The optical fiber sensor network developed in recent years can realize the safety and health monitoring and disaster forecasting and monitoring of large-scale civil engineering, electric power engineering, petrochemical industry, traffic bridges, tunnels, subway stations, dams, embankments and mining projects. There are two types of optical fiber sensors: one is a quasi-distributed optical fiber sensor network composed of point sensors such as fiber grating (FBG) and fiber optic method white (F-P) "hanging" (laying) on the optical fiber and using optical time domain technology , the main problem of the quasi-distributed optical fiber sensor network is that the optical fiber between point sensors is only the transmission medium, so there is a detection "blind zone"; another type uses the intrinsic characteristics of optical fiber, optical fiber Rayleigh, Raman and Brillouin Scattering effect, using optical time domain (OTDR) technology to form a fully distributed fiber optic sensor network to measure strain and temperature. The optical fiber in the fully distributed optical fiber sensor network is both the transmission medium and the sensing medium, and there is no detection blind area.

"An ultra-long-distance fully distributed optical fiber Rayleigh and Raman scattering sensor integrated with optical fiber Raman frequency shifter, CN201885733U" proposed by Zhang Zaixuan, which provides a low-cost, simple structure, good signal-to-noise ratio, and good reliability. The distributed optical fiber Rayleigh and Raman scattered photon strain and temperature sensors are suitable for the detection range of medium and long-distance 15-60km fully distributed optical fiber sensor networks. However, it can no longer meet the urgent needs of the safety and health monitoring of oil pipelines and transmission power cables in recent years, and the ultra-long-distance fully distributed optical fiber Rayleigh, Raman and Brillouin scattering strain and temperature sensor networks.

Contents of the invention

The purpose of this utility model is to provide a pulse coding ultra-long-range full-range pulse code fusion optical fiber Raman frequency shifter with low cost, simple structure, good signal-to-noise ratio, good reliability, and suitable for the detection range of 80km fully distributed optical fiber sensor network. Distributed fiber optic Rayleigh and Raman scattering sensors.

The pulse coded ultra-long-distance fully distributed optical fiber Rayleigh and Raman scattering sensor of the fusion fiber Raman frequency shifter of the utility model includes a pulse coded fiber laser drive power supply, a pulse coded fiber pulse laser, and a single-mode fiber and a 1660nm bandpass Optical fiber Raman frequency shifter composed of optical filters, integrated optical fiber wavelength division multiplexer, sensing optical fiber, photoelectric receiving module, codec and demodulation digital signal processor and industrial computer, codec and demodulation digital signal processor One signal output terminal is connected to the pulse code laser drive power supply, and the other signal output terminal is connected to the industrial computer. The time series pulse code signal generated by the codec demodulation digital signal processor controls the pulse code laser drive power supply and drives the pulse code optical fiber. The laser generates time-series coded 1550nm laser pulses as the pump source of the Raman frequency shifter. The input end of the single-mode fiber is connected to the output end of the pulse-coded fiber pulse laser, which consists of a single-mode fiber and a 1660nm bandpass filter. The optical fiber Raman frequency shifter shifts the laser pulse frequency of 1550nm time series code to 1660nm. The integrated fiber optic wavelength division multiplexer has four ports, of which the 1660nm input port is connected with the 1660nm bandpass filter, and the COM output port It is connected with the sensing optical fiber, the 1550nm output port is connected with one input port of the photoelectric receiving module, the 1660nm output port is connected with the other input port of the photoelectric receiving module, and the two output ports of the photoelectric receiving module are respectively connected with the encoding, decoding and demodulation digital signal processor The two input ports are connected.

In the utility model, said pulse-coded fiber pulse laser is composed of F-P semiconductor laser and erbium-doped fiber amplifier, the central wavelength is 1550nm, the spectral width is 3nm, and the unit pulse width of the laser is <6ns.

In the utility model, the central wavelength of said bandpass filter is 1660nm, the spectral bandwidth is 28nm, the transmittance is 98%, and the isolation degree to 1550nm laser is >45dB. Single-mode fiber can use 600m, 900 m or 1200 m single-mode fiber.

In the utility model, said codec demodulation digital signal processor adopts embedded design, is made up of the high-speed collector with ADS62P49 acquisition chip as core and the high-speed digital processor with ADSP-BF561 chip as core.

In the present utility model, said sensing optical fiber is G652 single-mode optical fiber for 80km communication or dispersion-shifted optical fiber or carbon-coated single-mode optical fiber. Carbon-coated single-mode optical fiber is a kind of dense carbon film with a thickness of 35-70nm deposited on the surface of the bare optical fiber during the drawing process, and then coated with a layer of UV-curable organic coating. The dense carbon film can be greatly enhanced in harsh environments. The protection of the bare optical fiber in the environment ensures its durability. The sensing optical fiber is laid on site. The optical fiber is uncharged, anti-electromagnetic interference, radiation-resistant, corrosion-resistant, and has good reliability. The optical fiber is both a transmission medium and a sensing medium.

The pulse-coded fiber pulse laser emits time-series coded laser pulses into the fiber Raman frequency shifter, and the fiber Raman frequency shifter shifts the frequency of the time-series coded laser pulses in the 1550nm band by 13.2THz to the 1660nm band as a fully distributed fiber optic sensor broadband pump source. The broadband optical pulse is injected into the sensing fiber through the integrated optical fiber wavelength division multiplexer, and the back Rayleigh scattering, Stokes and anti-Stokes Raman scattering photon waves generated in the sensing fiber are amplified, After splitting by the integrated optical fiber wavelength division multiplexer, the back Rayleigh scattered light with strain information and the anti-Stokes Raman scattered photon wave with temperature information respectively pass through the photoelectric receiving module to convert the optical signal into The analog electrical signal is amplified, and after the decoding and demodulation of the digital signal processor and industrial computer, the strain information is obtained from the intensity ratio of Rayleigh scattered light, and the strain of each strain detection point on the sensing fiber is given. Strain change speed and direction; from the intensity ratio of anti-Stokes Raman scattered light to Rayleigh scattered light, the influence of strain is deducted to obtain the temperature information of each section of the optical fiber, the temperature of each temperature sensing point, the temperature change speed and direction , There is no cross effect in the detection of strain and temperature, and the optical time domain reflection is used to locate the detection point on the sensing fiber (fiber radar positioning). Through the decoding and demodulation of the digital signal processor and the strain and temperature demodulation software, the strain and temperature changes at each point on the 80km sensing fiber can be obtained within 60 seconds, and the temperature measurement accuracy is ±2oC. It is controlled by the industrial computer communication interface, The communication protocol is used for remote network transmission. When the detection point on the sensing fiber reaches the set strain or temperature alarm set value, an alarm signal is sent to the alarm controller.

The coding and decoding principle of the distributed optical fiber Raman temperature sensor using sequence pulse coding and decoding:

The serial pulse encoding of this sensor is realized by S-matrix transformation, which is a variant of the standard Hadamard transformation, also known as Hadamard transformation. The elements of the S matrix are all composed of "0" and "1". This feature is very suitable for laser sequence pulse coding. In practical applications, "O" can be used to represent the laser off, and "1" can be used to represent the laser on. This encoding method using "0" and "1" can also be called simple encoding. The decoding process is the corresponding inverse S matrix conversion.

It is deduced from the coding principle that the improvement of the signal-to-noise ratio that can be obtained by using N-bit sequence pulse code decoding is:

(1)

It can be seen from (1) that the SNR improvement increases with the increase of the number of encoding bits.

When N is 255:

The spatial positioning resolution of the optical fiber sensor is determined by the narrow pulse width of the unit. Due to the use of multi-pulse emission, the spatial resolution can be improved by narrowing the laser pulse width while increasing the number of emitted photons, and it is not necessary to increase the peak power of a single laser pulse. Therefore, it effectively prevents the deformation of the OTDR curve caused by the nonlinear effect of the optical fiber.

Fiber Raman frequency shifter principle:

When the incident laser ν ₀ interacts nonlinearly with the fiber molecules and scatters, a phonon is released called Stokes Raman scattering photon ν=ν ₀ -Δν, and a phonon is absorbed, called anti-Stokes Raman Scattered photons ν=ν ₀ +Δν, the phonon frequency Δν of fiber molecules is 13.2THz.

ν=ν ₀ ±Δν (2)

It is called fiber optic Raman frequency shifter, which can be made into fiber optic Raman frequency shifter. If the incident laser light exceeds a certain threshold, the Stokes wave ν=ν ₀ -Δν in the fiber increases rapidly in the fiber medium, and most of the power of the pump light can be converted into Stokes light and Raman Amplification, the gain can suppress the transmission loss of the optical fiber, and improve the working distance of the fully distributed optical fiber strain and temperature sensors. This stimulated Raman scattering phenomenon becomes the working principle of the optical fiber Raman frequency shifter.

The principle of distributed optical fiber Rayleigh scattering photon sensor to measure deformation:

The pulse-coded fiber pulse laser emits time-series laser pulses and injects them into the sensing fiber through the integrated fiber wavelength division multiplexer. The interaction between the laser and the fiber molecules produces Rayleigh scattered light with the same frequency as the incident photon. The Rayleigh scattered light is in the There is a loss in the transmission in the optical fiber, which attenuates exponentially with the length of the optical fiber, and the intensity of the scattered light at the back end is expressed by the following formula:

                                      (3)

(3)

为入射到光纤处的光强，L为光纤长度，I为背向瑞利散射光在光纤长度L处的光强，为入射光频率处的光纤传输损耗。 In the above formula

is the light intensity incident on the fiber, L is the length of the fiber, I is the light intensity of the back Rayleigh scattered light at the fiber length L , is the fiber transmission loss at the incident light frequency.

，则总损耗

，局域处的光强有一个跌落，光强由

减少为

，形变造成的附加损耗通过光强的改变进行测量。 Since the optical fiber lays the sensing optical fiber on the detection site, when the site environment is deformed or cracked, the optical fiber laid on the site will be bent, and the optical fiber will generate local loss, forming additional loss of the optical fiber.

, the total loss

, the light intensity at the local area has a drop, and the light intensity is determined by

reduced to

, the additional loss due to deformation is measured by the change in light intensity.

                                       (4)

(4)

The relationship between deformation or crack size and fiber loss is calculated by using a simulation model and measured by a simulation test in a laboratory. the

The principle of temperature measurement by distributed optical fiber Raman scattering photon sensor:

When the incident laser light interacts nonlinearly with the fiber molecules, a phonon is released, called Stokes Raman scattering photons, and a phonon is absorbed, called anti-Stokes Raman scattering photons, the phonon frequency of fiber molecules It is 13.2THz. The thermal distribution of the number of particles on the molecular energy level of the optical fiber obeys Boltzmann's law, and the anti-Stokes back Raman scattering light intensity in the optical fiber is

               （5）

(5)

It is modulated by the fiber temperature, the temperature modulation function R _a

(6)

ν _a is the frequency of anti-Stokes Raman scattering photons, I ₀ is the incident light intensity, α ₀ , α _a are the fiber loss at the incident light frequency and anti-Stokes Raman scattering frequency respectively, L is the optical fiber length, h is Polanck's constant, Δν is the phonon frequency of a fiber molecule, which is 13.2THz, k is Boltzmann's constant, and T is Kelvin's absolute temperature.

In the utility model, the optical fiber Rayleigh channel is used as a reference signal, and the ratio of the intensity of the anti-Stokes Raman scattering light to the Rayleigh scattering light intensity is used to detect the temperature

(7)

The temperature information of each segment of the fiber is obtained from the anti-Stokes Raman scattered light and intensity ratio of the optical fiber Raman optical time domain reflectance (OTDR) curve at the fiber detection point, and the influence of strain is deducted.

The beneficial effects of the utility model are:

The utility model adopts pulse coding to increase the photon number of the emitted signal, so that the back-to-Rayleigh and Raman scattered light intensity is increased, thereby improving the signal-to-noise ratio of the system, effectively increasing the measurement length, and integrating the pulse of the optical fiber Raman frequency shifter Encoded ultra-long-range fully distributed optical fiber Rayleigh and Raman scattering sensor, using optical fiber Raman frequency shifter, the detection laser is moved to the 1660nm band and amplified, which improves the signal-to-noise ratio of the sensor system and increases the measurement length of the sensor , improve the reliability and spatial resolution of the sensor, and can measure the deformation, crack and temperature of the site while measuring the site temperature without intersecting each other. The integrated wavelength division multiplexer is used to reduce the cost; it is superior to the distributed optical fiber Brillouin temperature and strain sensor in terms of cost performance. The sensing optical fiber laid on the disaster prevention site is insulated, uncharged, anti-electromagnetic interference, radiation-resistant, corrosion-resistant, and intrinsically safe. The optical fiber is both a transmission medium and a sensing medium, and it is an intrinsic type of sensor. Sensing optical fiber, and long service life, the utility model is suitable for long-range, ultra-long-distance 80km fully distributed optical fiber strain and temperature sensing network, and can be used for petrochemical pipelines, tunnels, large-scale civil engineering monitoring and disaster forecast monitoring.

Description of drawings

Figure 1 is a schematic diagram of a pulse-coded ultra-long-range fully distributed optical fiber Rayleigh and Raman scattering sensor fused with a fiber-optic Raman frequency shifter.

Detailed ways

Referring to Fig. 1, the pulse coded ultra-long-distance fully distributed optical fiber Rayleigh and Raman scattering sensor fused with a fiber optic Raman frequency shifter includes a pulse coded fiber laser drive power supply 10, a pulse coded fiber pulse laser 11, and a single-mode fiber 12 and Optical fiber Raman frequency shifter composed of 1660nm band-pass filter 13, integrated optical fiber wavelength division multiplexer 14, sensing optical fiber 15, photoelectric receiving module 16, codec and demodulation digital signal processor 17 and industrial computer 18, One signal output end of the encoding, decoding and demodulation digital signal processor 17 is connected with the pulse encoding laser drive power supply 10, and the other signal output end is connected with the industrial computer 18, and the time series pulse generated by the encoding, decoding and demodulation digital signal processor 17 The coded signal controls the pulse coded laser drive power supply 10, drives the pulse coded fiber laser 11 to generate time-sequence coded 1550nm laser pulses, and serves as the pump source of the Raman frequency shifter. The input end of the single-mode fiber 12 is connected to the pulse-coded fiber pulse laser 11, and the optical fiber Raman frequency shifter composed of the single-mode fiber 12 and the 1660nm bandpass filter 13 shifts the laser pulse frequency of the 1550nm time series code to 1660nm , the integrated optical fiber wavelength division multiplexer 14 has four ports, wherein the 1660nm input port is connected with the 1660nm bandpass filter 13, the COM output port is connected with the sensing fiber 15, and the 1550nm output port is connected with an input of the photoelectric receiving module 16 The 1660nm output port is connected to the other input port of the photoelectric receiving module 16, and the two output ports of the photoelectric receiving module 16 are respectively connected to the two input ports of the codec demodulation digital signal processor 17.

The above-mentioned pulse-coded fiber pulse laser is composed of F-P semiconductor laser and erbium-doped fiber amplifier, the center wavelength is 1550nm, the spectral width is 3nm, and the unit pulse width of the laser is <6ns.

For example: fiber Raman frequency shifter consists of 900m single-mode fiber and 1660nm band-pass filter, the band-pass filter has a central wavelength of 1660nm, a spectral bandwidth of 28nm, a transmittance of 98%, and an isolation of 1550nm laser > 45dB . When the 1550nm fiber pulse laser passes through a 900m single-mode fiber, the frequency of the light pulse shifts by 13.2THz, and a laser pulse with a center wavelength of 1660nm and a wide spectrum of 28nm is obtained. When the fiber Raman frequency shifter shifts the frequency of the high-power laser in the 1550nm band 13.2THz to 1660nm band, when used as a broadband pump light source for a fully distributed optical fiber sensor, if the incident laser power exceeds a certain threshold, the Stokes wave ν=ν ₀ -Δν in the fiber increases rapidly in the fiber medium, The power of most of the pump light can be converted into Stokes light, which has a Raman amplification effect. The gain can suppress the transmission loss of the optical fiber and improve the working distance of the fully distributed optical fiber strain and temperature sensors.

The sensing fiber mentioned above is 80km G652 communication single-mode fiber or dispersion-shifted fiber or carbon-coated single-mode fiber.

S矩阵转换规则排列的序列255位编码脉冲驱动。也适用于其它位数的编码，例如：127位等。 The above-mentioned encoding, decoding and demodulation digital signal processor adopts embedded design, and consists of a high-speed collector with ADS62P49 acquisition chip as the core and a high-speed digital processor with ADSP-BF561 chip as the core. Codec and demodulation digital signal processor sends out

The sequence of 255-bit coded pulses arranged regularly by the S matrix is driven. It is also applicable to encodings of other digits, for example: 127 digits, etc.

The coded, decoded and demodulated digital signal processor and industrial computer will decode and process the collected and accumulated coded pulse echo signals, obtain the strain and temperature information on the site where the 80km sensing optical fiber is located, and transmit it to the remote monitoring network.

Claims (6)

1. A pulse-coded ultra-long-range fully distributed optical fiber Rayleigh and Raman scattering sensor fused with a fiber-optic Raman frequency shifter, which is characterized in that it includes a pulse-coded fiber laser drive power supply (10), a pulse-coded fiber pulse laser (11) , an optical fiber Raman frequency shifter composed of a single-mode optical fiber (12) and a 1660nm bandpass filter (13), an integrated optical fiber wavelength division multiplexer (14), a sensing optical fiber (15), and a photoelectric receiving module ( 16), encoding, decoding and demodulation digital signal processor (17) and industrial computer (18), one signal output terminal of encoding, decoding and demodulation digital signal processor (17) is connected with pulse coded laser drive power supply (10), the other The signal output end is connected with the industrial computer (18), and the time-series pulse coded signal generated by the coded, decoded and demodulated digital signal processor (17) controls the pulse coded laser driving power supply (10), and drives the pulse coded fiber laser (11) to generate 1550nm laser pulses coded in time series, as the pump source of the Raman frequency shifter, the input end of the single-mode fiber (12) is connected to the output end of the pulse-coded fiber pulse laser (11), and the single-mode fiber (12) and The optical fiber Raman frequency shifter composed of 1660nm bandpass filter (13) shifts the frequency of laser pulses encoded in 1550nm time series to 1660nm, and the integrated optical fiber wavelength division multiplexer (14) has four ports, of which 1660nm input The port is connected to the 1660nm bandpass filter (13), the COM output port is connected to the sensing fiber (15), the 1550nm output port is connected to an input end of the photoelectric receiving module (16), and the 1660nm output port is connected to the photoelectric receiving module (16 ) is connected to the other input end, and the two output ends of the photoelectric receiving module (16) are respectively connected to the two input ports of the codec-demodulation digital signal processor (17). 2. The pulse coded ultra-long-range fully distributed optical fiber Rayleigh and Raman scattering sensor of the fusion fiber Raman frequency shifter according to claim 1, wherein the pulse coded fiber pulse laser (11) consists of F-P semiconductor laser and erbium doped Composed of fiber amplifiers, the center wavelength is 1550nm, the spectral width is 3nm, and the unit pulse width of the laser is <6ns. 3. The pulse coded ultra-long-range fully distributed optical fiber Rayleigh and Raman scattering sensor fused with a fiber Raman frequency shifter according to claim 1, characterized in that the central wavelength of the 1660nm bandpass filter (13) is 1660nm , the spectral bandwidth is 28nm, the transmittance is 98%, and the isolation to 1550nm laser is >45dB. 4. The pulse code ultra-long-distance fully distributed optical fiber Rayleigh and Raman scattering sensor fused with the optical fiber Raman frequency shifter according to claim 1, characterized in that the single-mode optical fiber (12) is 600m, 900m or 1200m single-mode fiber. 5. The pulse coded ultra-long-range fully distributed optical fiber Rayleigh and Raman scattering sensor fused with the optical fiber Raman frequency shifter according to claim 1, characterized in that the sensing optical fiber (15) is a G652 single-mode optical fiber for 80km communication Or dispersion shifted fiber or carbon coated single mode fiber. 6. the pulse encoding ultra-long-distance fully distributed optical fiber Rayleigh and the Raman scattering sensor of the fusion optical fiber Raman frequency shifter according to claim 1, it is characterized in that the encoding and decoding demodulation digital signal processor (17) is by ADS62P49 It consists of a high-speed collector with an acquisition chip as the core and a high-speed digital processor with the ADSP-BF561 chip as the core.