WO2013020286A1

WO2013020286A1 - Chaotic laser-related fully distributed optical fiber raman and rayleigh photon sensor

Info

Publication number: WO2013020286A1
Application number: PCT/CN2011/078234
Authority: WO
Inventors: 张在宣; 王剑锋; 余向东
Original assignee: 中国计量学院
Priority date: 2011-08-10
Filing date: 2011-08-10
Publication date: 2013-02-14

Abstract

A chaotic laser-related fully distributed optical fiber Raman and Rayleigh photon sensor, which is based on a chaotic laser-related principle and an optical fiber Rayleigh and Raman fusion scattering sensing principle, and uses an optical time domain reflection principle to perform positioning of a measuring point. The sensor employs an optical pulse sequence of a chaotic laser and fluctuating randomly on a time domain, and, by correlation processing a backward probing light of a sensing optical fiber and a local reference light, allows for improved spatial resolution of the sensing system, for effectively increased number of photons of an incident fiber, for improved signal-to-noise ratio of the sensing system, for improved measurement length and measurement precision of the sensing system, and for simultaneous measurement of onsite deformation and cracking while measuring onsite temperature, while not intersecting mutually. The sensor is provided with characteristics of low costs, extended service life, simple structure, special resolution of 15 cm in height, and great signal-to-noise ratio, and is applicable in petrochemical pipelines and tunnels measured within a range of 30 kilometers, in large-scale civil engineering project monitoring, and in disaster prediction monitoring.

Description

Chaotic laser-related fully distributed fiber Raman and Rayleigh photon sensors

Technical field

The invention relates to the field of optical fiber sensors, in particular to a chaotic laser-related high spatial resolution fully distributed optical fiber Rayleigh and Raman scattering strain and temperature sensor.

Background technique

The fiber optic sensor network developed in recent years can realize safety and health monitoring and disaster prediction and monitoring of large civil engineering, electric power engineering, petrochemical industry, traffic bridges, tunnels, subway stations, dams, dykes and mining projects. There are two types of fiber optic sensors: one is a fiber-optic grating (FBG) and a fiber-optic white (FP) point sensor that is "hanged" (layout) on the fiber, using a quasi-distributed fiber optic sensor network composed of optical time domain technology. The main problem of the quasi-distributed fiber optic sensor network is that the fiber between the point sensors is only the transmission medium, so there is a detection "blind area"; the other type uses the intrinsic characteristics of the fiber, the fiber Rayleigh, Raman and Brillouin Scattering effect, using a fully distributed fiber optic sensor network consisting of optical time domain (0TDR) technology to measure strain and temperature. The optical fiber in the fully distributed optical fiber sensor network is both a transmission medium and a sensing medium, and there is no detection dead zone.

Professor Zhang Zaixuan's "Full Distributed Fiber Rayleigh and Raman Scattering Photon Strain, Temperature Sensor" (Chinese invention patent: 200910099463.7, licensed in September 2010) provides a low cost, simple structure, good signal to noise ratio, and reliability. Good distributed fiber Rayleigh and Raman scattering photon strain, temperature sensor. However, it is difficult to improve the spatial resolution of the sensing system. Professor Wang Yuncai's research team proposed the chaotic laser correlation method for 0TDR, and the spatial resolution reached 6cm (Wang Anbang, Wang Yuncai, Chaotic Laser Correlation Optical Time Domain Reflectometry, Chinese Science, Information Science, 2010, Vol. 40, No. 3, pp. 1-7) However, it is not possible to measure the temperature at various points on the sensing fiber.

Summary of the invention

The object of the present invention is to provide a chaotic laser-related fully distributed fiber Raman and Rayleigh photon sensor according to the deficiencies of the prior art. The invention has high spatial resolution, low cost, simple structure, good signal to noise ratio and reliability. High sexual characteristics.

The object of the present invention is achieved by the following technical solutions: a chaotic laser-related fully distributed fiber Rayleigh and Raman scattering sensor, including a semi-conductive LD laser, a first polarization controller, a fiber circulator, and a first fiber Road, dimming attenuator second polarization controller, one-way, EDFA, second fiber splitter, fiber-optic wavelength division multiplexer, sensing fiber, fiber delay line, first optoelectronic reception Module, second optoelectronic receiving module digital signal processor and computer. Semiconductor LD laser The first polarization controller is connected to an input port of the fiber circulator, and an output end of the fiber circulator is connected to the input end of the first fiber splitter, and an output end of the first fiber splitter and the dimmable attenuator The input ends are connected, the output of the tunable optical attenuator is connected to one input end of the optical fiber circulator through the second polarization controller, and is fed back to the semiconductor LD laser via the first polarization controller; the other of the first optical fiber splitter The output end is connected to the EDFA of the erbium-doped fiber amplifier via a one-way device, and the output end of the EDFA of the erbium-doped fiber amplifier is connected to the input end of the second fiber multiplexer, and an output end of the second fiber multiplexer and the fiber-optic wavelength division multiplexer The input end is connected, one output end of the fiber-optic wavelength division multiplexer is connected to the sensing fiber, and the other output end of the second fiber-optic splitter is connected to the first photo-receiving module via the fiber delay line, and the first photo-receiving module outputs The end is connected to the digital signal processor and the computer; the 1550nm output port of the fiber-optic wavelength division multiplexer is connected to the digital signal processor and the computer, and the fiber-optic wavelength division multiplexer 1 The 450nm output port is connected to the digital signal processor and computer.

Further, the chaotic laser-related fully distributed fiber Raman and Rayleigh photon sensor is a semiconductor LD laser connected to an input port of the fiber circulator through a first polarization controller, and one of the fiber circulators The output end is connected to the input end of the first fiber optic splitter, one output end of the first fiber optic splitter is connected to the input end of the dimmable optical attenuator, and the output end of the dimmable optical attenuator is passed through the second polarization controller and the optical fiber The circulator is connected to one input and is fed back to the semiconductor LD laser via the first polarization controller. The semiconductor LD laser is a semiconductor DFB laser with an operating wavelength of 1550 nm and an output power of 10 dBm. The branch ratio of the first fiber splitter is 20:80.

Further, the sensing fiber is a 30km G652 fiber or a DSF dispersion-shifted fiber or a carbon-coated single-mode fiber for communication.

Further, the fiber delay line is composed of a length of single mode fiber for calibrating the zero point of the sensing system. The other output end of the second fiber optic splitter is connected to the first optoelectronic receiving module (22) via a fiber delay line to form a reference optical path. The branch ratio of the second fiber optic splitter is 5:95. When the sensing system is not connected When entering the sensing fiber (corresponding to the zero point of the sensing fiber), measure the correlation curve between the probe light and the reference light, and select the length of the fiber delay line so that the peak value of the correlation curve is at zero.

Further, the first photo receiving module is composed of a broadband low-noise InGaAs photoelectric avalanche diode and a low-noise broadband preamplifier integrated chip and a three-stage main amplifier, and the second optoelectronic receiving amplifying module adopts two-way broadband low-noise InGaAs opto-avalanche diode and low-noise broadband preamplifier integrated chip and three-stage main amplifier.

Further, the digital signal processor is an associated processor that correlates the local reference signal with the 1550 nm Rayleigh signal of the sensing fiber echo and the 1450 nm anti-Stokes Raman signal, and is processed by the computer to display Temperature and strain information.

The chaotic laser emits a time-series laser pulse into the sensing fiber, creating a back-facing direction in the sensing fiber Rayleigh scattering, Stokes and anti-Stokes Raman scattering photon waves, back-reverse Rayleigh scattering, anti-Stokes Raman scattering photonic waves, split by fiber-optic wavelength division multiplexer, with strain The back-scattered Rayleigh scattered light of the information and the anti-Stokes Raman scattering probe light with temperature information are respectively converted into analog electric signals by the photoelectric receiving amplifying module, and amplified, and collected and accumulated by the digital signal processor. After correlating with the local reference light of the chaotic laser, the strain information is obtained from the intensity ratio of Rayleigh scattered light, and the strain, strain change speed and direction of each strain detecting point on the sensing fiber are given; The intensity ratio of Raman scattered light and Rayleigh scattered light, the temperature information of each segment of the fiber is obtained by subtracting the influence of strain, the temperature of each temperature sensing point, the temperature change speed and direction, and the cross-effect of strain and temperature detection are not utilized. Optical time domain reflection is used to locate the detection points on the sensing fiber (Fiber Radar Positioning). In 60 seconds, the strain and temperature changes at each point on the 30km sensing fiber are obtained. The temperature measurement accuracy is ±2° C, the spatial resolution is less than 15cm, and the remote network transmission is performed by the computer communication interface and communication protocol. When the point reaches the set strain or temperature alarm set value, an alarm signal is sent to the alarm controller.

Correlation principle of chaotic laser-related fully distributed fiber Rayleigh and Raman scattering sensors:

The semiconductor laser continuously generates random fluctuations of broadband, low correlation noise chaotic laser, and its correlation curve has a δ function shape. The bandwidth of the nonlinear chaotic oscillation of the semiconductor laser can be greater than 15 GHz, which is independent of the measurement length. High resolution, high precision measurement.

Let the reference light be f ( t ) and the probe light be g ( t ) = Kf ( t- τ );

Cross-correlation function:

When τ = τ. When, the cross-correlation peak is related to the intensity of the probe light. The temperature and strain on the sensing fiber are obtained by collecting, accumulating and correlating the probe light and the reference light by a digital signal processor and a computer. The signal-to-noise ratio of the system determines the measurement length.

The principle of distributed fiber Rayleigh scattering photon sensor for measuring deformation:

The fiber pulsed laser emits laser pulses into the sensing fiber through the integrated fiber-optic wavelength division multiplexer. The interaction between the laser and the fiber molecules produces Rayleigh scattered light at the same frequency as the incident photons. Rayleigh scattered light is transmitted in the fiber. Loss, exponentially attenuated with the length of the fiber, and the back-end scattered light intensity of the fiber is expressed by:

In the above formula /. For the intensity of light incident on the fiber, Ζ is the length of the fiber, and / is the intensity of the light that travels back to Rayleigh at the length of the fiber. The transmission loss of the fiber at the wavelength of the incident light.

Since the optical fiber is used to lay the sensing fiber on the inspection site, when the field environment is deformed or cracked, the optical fiber laid in the field is bent, and the optical fiber generates local loss, which forms an additional loss Δ« of the optical fiber. Then the total loss "= «. +Δ«, there is a drop in the light intensity at the local area, and the light intensity is reduced from /(/) to /'(/), the deformation caused by the deformation

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

The principle of distributed fiber Raman scattering photon sensor for measuring temperature:

When the incident laser produces a nonlinear interaction with the fiber molecule, a phonon is emitted as a Stokes Raman scattered photon, and a phonon is absorbed as an anti-Stokes Raman scattered photon. The phonon frequency of the fiber molecule is 13.2THz. The heat distribution of the number of particles at the molecular level of the fiber obeys Boltzmann's law, and the anti-Stokes back-scattered Raman scattering intensity in the fiber is

Ι _α = / ₀ · ν» ) ε χ ρ [- (α. + c * L) (4) It is modulated by the temperature of the fiber, temperature modulation function ^

R _a (T) = [exp( hA v / kT ) - l]' ¹ (5) h is the Planck constant, Δ v is the phonon frequency of a fiber molecule, which is 13.2 THz, k is the wave The erzmann constant, T is the Kelvin absolute temperature.

In the present invention, the fiber Rayleigh channel is used as a reference signal, and the ratio of the anti-Stokes Raman scattered light to the Rayleigh scattered light intensity is used to detect the temperature.

7^ = (― ) ⁴ · exp[( v/^r) - 1]— ¹ · exp [- (« _fl -«.) ]

Yo (6) The anti-Stokes Raman scattering of the optical fiber Raman optical time domain reflection (0TDR) curve at the fiber detection point and the light intensity ratio of the ray scattering light, the temperature information of each segment of the fiber is obtained by subtracting the influence of the strain. The sensing system can be temperature calibrated using a section of fiber placed in a thermostat.

The invention has the beneficial effects of: the chaotic laser-related fully distributed optical fiber Rayleigh and Raman scattering sensor of the invention adopts the chaotic laser correlation principle to effectively improve the reliability and spatial resolution of the sensor, and increases the access to the sensing fiber. The number of pump photons increases the signal-to-noise ratio of the sensor system, increases the measurement length of the sensor, and measures the deformation, cracks, and temperature of the field while measuring the temperature of the field. The sensing fiber laid on the disaster prevention site is insulated, uncharged, resistant to electromagnetic interference, radiation resistant, and corrosion resistant. It is intrinsically safe. Optical fiber is both a transmission medium and a sensing medium. It is an intrinsic type. Sense optical fiber, there is no blind zone of measurement, and the life is long. The invention is applicable to a 30km fully distributed optical fiber strain and temperature sensing network. It can be used for petrochemical pipelines, tunnels, large civil engineering monitoring and disaster forecast monitoring within 30 km of ultra-long-range. DRAWINGS

Figure 1 is a schematic diagram of a chaotic laser-related fully distributed fiber-optic Rayleigh and Raman scattering sensor.

detailed description

Referring to FIG. 1, a chaotic laser-related fully distributed fiber Raman and Rayleigh photon sensor includes a semiconductor LD laser 10, a first polarization controller 11, a fiber circulator 12, a first fiber splitter 13, and a dimmable attenuator. 14. Second polarization controller 15, one-way device 16, erbium-doped fiber amplifier EDFA17, second fiber-optic splitter 18, fiber-optic wavelength division multiplexer 19, sensing fiber 20, fiber delay line 21, first photo-receiving The module 22, the second photo receiving module 23, the digital signal processor 24, and the computer 25. The semiconductor LD laser 10 is connected to an input port of the fiber circulator 12 via the first polarization controller 11, and the output of the fiber circulator 12 is connected to the input end of the first fiber splitter 13, the first fiber splitter 13 One output is connected to the input of the tunable optical attenuator 14, and the output of the tunable optical attenuator 14 is connected to the other input of the optical circulator 12 via the second polarization controller 15, and then controlled by the first polarization. The device 11 feeds back to the semiconductor LD laser 10; the other output of the first fiber splitter 13 is connected to the erbium-doped fiber amplifier EDFA 17 via the unidirectional device 16, and the output of the erbium-doped fiber amplifier EDFA 17 is split with the second fiber. The input end of the second optical fiber splitter 18 is connected to the input end of the optical fiber wavelength division multiplexer 19, and an output end of the optical fiber wavelength division multiplexer 19 is connected to the sensing optical fiber 20, The other output end of the second optical fiber splitter 18 is connected to the first photo receiving module 22 via the optical fiber delay line 21, and the output end of the first photo receiving module 22 is connected to the digital signal processor 24, and the optical fiber wave Multiplexing is 1550nm and 1450nm output port 19 is connected to the output port of the digital signal processor 24, respectively, coupled to the digital signal processor 24 and a computer 25.

The semiconductor LD laser 10, the first polarization controller 11, the fiber circulator 12, the first fiber splitter 13, the tunable optical attenuator 14, and the second polarization controller 15 constitute a chaotic laser, and the semiconductor LD laser 10 is a semiconductor DFB laser. The working wavelength is 1550nm and the output power is 10dBm. The branch ratio of the first fiber splitter 13 is 20:80.

The sensing fiber 20 is a 30km G652 fiber or DSF dispersion shifted fiber or a carbon coated single mode fiber for communication.

The fiber delay line 21 is composed of a length of single mode fiber used to calibrate the zero point of the sensing system. The other output of the second fiber splitter 18 is coupled to the first optoelectronic receiving module 22 via a fiber delay line 21 to form a reference optical path of the second fiber splitter 18 having a branch ratio of 5:95. When the sensing system is not connected to the sensing fiber (corresponding to the zero point of the sensing fiber), the correlation curve between the probe light and the reference light is measured, and the length of the fiber delay line 21 is adjusted so that the peak value of the correlation curve is at zero.

The first photo receiving module 22 is composed of a broadband low noise InGaAs photoelectric avalanche diode and a low noise broadband preamplifier integrated chip and a three-stage main amplifier, and the second optoelectronic receiving amplifying module 23 is adopted. Two broadband low-noise InGaAs opto-avalanche diodes and a low-noise broadband preamplifier integrated chip and a three-stage main amplifier.

The digital signal processor 24 is an associated processor that correlates the local reference signal with the 1550 nm Rayleigh signal of the sensing fiber echo and the 1450 nm anti-Stokes Raman signal, and is processed by the computer to display temperature and strain information. .

The invention adopts a chaotic laser, and the random pulsed light pulse sequence in the time domain improves the spatial resolution of the sensor system by the correlation processing of the reverse detection light of the sensing fiber and the local reference light; effectively increasing the incident optical fiber. The number of photons improves the signal-to-noise ratio of the sensor system, improves the measurement length and measurement accuracy of the sensor, and can measure the deformation and crack of the field while measuring the temperature of the field, and does not cross the measured temperature. It has the characteristics of low cost, long life, simple structure, high spatial resolution and good signal-to-noise ratio. It is suitable for high spatial resolution 15cm petrochemical pipelines, tunnels, large civil engineering monitoring and disaster forecasting monitoring within 30km.

Claims

A chaotic laser-related fully distributed fiber Raman and Rayleigh photon sensor, characterized in that it comprises a semiconductor LD laser (10), a first polarization controller (11), an optical fiber circulator (12), a first Fiber splitter (13), dimmable attenuator (14), second polarization controller (15), one-way device (16), erbium-doped fiber amplifier EDFA (17), second fiber splitter (18) ), fiber-optic wavelength division multiplexer (19), sensing fiber (20), fiber delay line (21), first photo-receiving module (22), second photo-receiving module (23), digital signal processor (24) And a computer (25); wherein the semiconductor LD laser

(10) connected to an input port of the fiber circulator (12) via the first polarization controller (11), and the output end of the fiber circulator (12) is connected to the input end of the first fiber splitter (13), An output of a fiber optic splitter (13) is coupled to an input of the dimmable attenuator (14), and an output of the dimmable attenuator (14) is coupled to the fiber optic circulator via a second polarization controller (15) The other input of (12) is connected and fed back to the semiconductor LD laser (10) via the first polarization controller (11); the other output of the first fiber splitter (13) is passed through the one-way device (16) Connected to the EDFA (17) with a doped fiber amplifier, the output of the EDFA (17) with the doped fiber amplifier is connected to the input of the second fiber splitter (18), and an output of the second fiber splitter (18) The input ends of the fiber-optic wavelength division multiplexer (19) are connected, one output of the fiber-optic wavelength division multiplexer (19) is connected to the sensing fiber (20), and the other output of the second fiber-optic splitter (18) Connected to the first photo receiving module (22) via the fiber delay line (21), the first photo connection The output module (22) is connected to the digital signal processor (24); the 1550nm output port and the 1450nm output port of the fiber-optic wavelength division multiplexer (19) are connected to the digital signal processor (24), and the digital signal processor ( 24) Connect to the computer (25).

2. The chaotic laser-related fully distributed fiber Raman and Rayleigh photon sensor according to claim 1, wherein the semiconductor LD laser (10), the first polarization controller (11), and the fiber circulator ( 12), the first fiber splitter (13), the tunable optical attenuator (14) and the second polarization controller (15) constitute a chaotic laser; the semiconductor LD laser (10) is a semiconductor DFB laser, and its working wavelength For 1550 nm, the output power is 10 dBm; the branch ratio of the first fiber splitter (13) is 20:80.

3. The chaotic laser-related fully distributed fiber Raman and Rayleigh photon sensor according to claim 1, wherein the sensing fiber (20) is a 30 km G652 fiber for communication, a DSF dispersion shifted fiber or a carbon coating. Single mode fiber.

4. The chaotic laser-related fully distributed fiber Raman and Rayleigh photon sensor according to claim 1, wherein the fiber delay line (21) is composed of a length of single mode fiber for calibrating the sensing system. Zero point; the other output of the second fiber splitter (18) is via the fiber delay line (21) The first photo receiving module (22) is connected to form a reference optical path, and the branch ratio of the second optical fiber splitter (18) is 5:95.

5. The chaotic laser-related fully distributed fiber Raman and Rayleigh photonic sensor according to claim 1, wherein the first photo receiving module (22) is a low-noise low-noise InGaAs photoelectric avalanche diode, low The noise broadband preamplifier integrated chip and the three-stage main amplifier are composed, and the second photoelectric receiving amplifying module (23) is composed of two broadband low-noise InGaAs photoelectric avalanche diodes, a low-noise broadband preamplifier integrated chip and a three-stage main amplifier.