CN216524011U - Long-distance Brillouin optical time domain reflectometer monitoring device - Google Patents
Long-distance Brillouin optical time domain reflectometer monitoring device Download PDFInfo
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- CN216524011U CN216524011U CN202220114400.5U CN202220114400U CN216524011U CN 216524011 U CN216524011 U CN 216524011U CN 202220114400 U CN202220114400 U CN 202220114400U CN 216524011 U CN216524011 U CN 216524011U
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Abstract
The utility model discloses a long-distance Brillouin optical time domain reflectometer monitoring device which comprises a semiconductor narrow-line-width laser, a first optical fiber coupler, a semiconductor optical amplifier, a pulse generator, a first optical fiber erbium-doped optical fiber amplifier, an optical fiber loop device, a wavelength division multiplexer, a Raman laser and a single-mode optical fiber to be tested. The semiconductor optical amplifier is used for replacing an electro-optical modulator to carry out pulse light modulation on laser, so that the extinction ratio is improved, and the stability of long-time measurement of the system is improved; by utilizing the Raman amplification technology, the signal-to-noise ratio of the far end of the detection light in the long-distance sensing is improved, so that the aim of improving the sensing distance while ensuring the detection precision is fulfilled; the semiconductor optical amplifier is combined with the Raman amplification technology, so that the sensing distance of the system is greatly increased while the cost of hardware equipment is saved, the detection precision is ensured, and the method is suitable for the engineering field.
Description
Technical Field
The utility model relates to the technical field of optical sensing, in particular to a long-distance Brillouin optical time domain reflectometer monitoring device.
Background
The returned Brillouin scattering optical signal in the optical fiber is mixed with noise, and along with the gradual change of the optical fiber detection position, the returned Brillouin scattering optical signal is gradually weak due to the optical fiber loss, the noise is increased, the error of the Brillouin scattering optical signal is increased, the detection precision is lowered, the practicability of the long-distance fully-distributed optical fiber sensor based on the Brillouin scattering is restricted, and meanwhile, when the monitoring is carried out for a long time, the stability of a Brillouin optical time domain reflectometer is gradually deteriorated, and the detection precision is further lowered. The problem of too low signal-to-noise ratio in the return signal in the long-distance optical fiber exists all the time, the signal-to-noise ratio of the Brillouin scattering optical signal in the long-distance optical fiber is improved, the influence of noise on detection precision is reduced, and the method is a great challenge in Brillouin optical time domain sensing.
To address this problem, researchers have proposed several solutions: the method comprises the steps of modulating pulse light by using a multi-wavelength light source and a plurality of electro-optical modulators, encoding the pulse light, processing a signal algorithm and the like. However, these methods have problems of high equipment cost, complicated optical path, poor stability of the electro-optical modulator in long-term operation, long detection time, and the like, respectively, and are difficult to be applied in engineering in many cases. When the sensor is used in a long-distance application scene (such as oil and gas pipeline leakage monitoring and submarine optical cable state monitoring) at the present stage, some measurement environments are complex, double-end detection cannot be carried out, and if equipment with a short sensing distance is used for segmented monitoring, the cost is difficult to control.
SUMMERY OF THE UTILITY MODEL
The utility model aims to provide a long-distance Brillouin optical time domain reflectometer monitoring device, which solves the technical problems, utilizes a semiconductor optical amplifier to replace an electro-optical modulator to carry out pulse light modulation on laser, improves the extinction ratio, and also improves the stability of long-time measurement of a system; by utilizing a Raman amplification technology, the signal-to-noise ratio of the detection light at the far end in long-distance sensing is improved, so that the aim of improving the sensing distance while ensuring the detection precision is fulfilled; the semiconductor optical amplifier is combined with the Raman amplification technology, so that the cost of hardware equipment is saved, the sensing distance of a system is greatly increased, the detection precision is ensured, and the Raman amplification system is suitable for the engineering field.
The purpose of the utility model can be realized by the following technical scheme:
a long-distance Brillouin optical time domain reflectometer monitoring device comprises a semiconductor narrow-line-width laser, a first optical fiber coupler, a semiconductor optical amplifier, a pulse generator, a first optical fiber erbium-doped optical fiber amplifier, an optical fiber loop device, a wavelength division multiplexer, a Raman laser and a single-mode optical fiber to be tested.
The semiconductor narrow-linewidth laser is connected with a first optical fiber coupler, one output end of the first optical fiber coupler is connected with the input end of a semiconductor optical amplifier, a pulse generator is connected with the input end of the semiconductor optical amplifier, the semiconductor optical amplifier outputs modulated pulse light which is connected with the input end of a first optical fiber erbium-doped optical fiber amplifier, the output end of the first optical fiber erbium-doped optical fiber amplifier is connected with the input end of an optical fiber circulator, one output end of the optical fiber circulator is connected with one input end of a wavelength division multiplexer, the output end of the Raman laser is connected with the other input end of the wavelength division multiplexer, and the output end of the wavelength division multiplexer is connected with a single-mode optical fiber to be tested.
Furthermore, the monitoring device also comprises a second optical fiber coupler, an optical fiber polarization scrambler, a second optical fiber erbium-doped optical fiber amplifier, a photoelectric detector and a data acquisition and processing module.
Furthermore, the other output end of the first optical fiber coupler is connected with the input end of the second optical fiber erbium-doped optical fiber amplifier through an optical fiber polarization scrambler, the other output end of the optical fiber circulator is connected with one input end of the second optical fiber coupler, the output end of the second optical fiber erbium-doped optical fiber amplifier is connected with the other output end of the second optical fiber coupler, and the output end of the second optical fiber coupler is connected with the input end of the photoelectric detector.
Further, the photoelectric detector performs coherent processing on the brillouin scattering light and the frequency shift reference light input by the second optical fiber coupler, and then inputs the light into the data acquisition and processing module.
Furthermore, the output end of the first optical fiber coupler, of which the output accounts for 90%, is connected with the input end of the semiconductor optical amplifier.
Furthermore, the output end of the first optical fiber coupler accounting for 10% of the output of the first optical fiber coupler is connected with the input end of the second optical fiber erbium-doped optical fiber amplifier through an optical fiber polarization scrambler.
The utility model has the beneficial effects that:
1. the monitoring device uses the semiconductor optical amplifier to replace a traditional electro-optical modulator to perform pulse modulation on laser, compared with the traditional electro-optical modulator, the semiconductor optical amplifier effectively improves the extinction ratio of detection pulses, so that the signal-to-noise ratio of Brillouin scattering light is improved, the sensing distance and the sensing precision are finally improved, meanwhile, the traditional electro-optical modulator has the defects of poor stability and high error of a long-time measuring system, and an instrument can realize long-time accurate measurement after the semiconductor optical amplifier is used, so that the monitoring data are more accurate;
2. the monitoring device uses a forward amplification Raman amplification module (a wavelength division multiplexer and a Raman laser) and utilizes a stimulated Raman scattering effect to transfer the energy of Raman pump light to detection pulse and Brillouin scattering light on line, so that the problem that the far-end signal-to-noise ratio of the detection pulse in long-distance sensing is too low due to optical fiber loss is solved, meanwhile, the Raman amplification process is carried out on the optical fiber to be detected, the optical fiber to be detected is used as a sensing medium and is also used as a Raman amplification medium, and the single-end advantage of the Brillouin optical time domain reflectometer is kept;
3. compared with an engineering test method for performing long-distance measurement by simultaneously using a plurality of Brillouin optical time domain reflectometers or distributed temperature measurement systems, the monitoring device reduces the simultaneous use of a plurality of devices, avoids the problems of large loss, high error and high expense in the process of monitoring a plurality of devices in series, only uses one device, achieves the purposes of accelerating the temperature/stress detection speed, greatly improving the detection precision and saving the construction cost of a construction party;
4. the monitoring device has the advantages of high detection precision and good stability, can be applied to most of engineering fields, and has wide application range.
Drawings
The utility model will be further described with reference to the accompanying drawings.
FIG. 1 is a schematic view of the monitoring device of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
A long-distance Brillouin optical time domain reflectometer monitoring device comprises a semiconductor narrow-linewidth laser 1, two optical fiber couplers (a first optical fiber coupler 2 and a second optical fiber coupler 12), a semiconductor optical amplifier 3, an optical fiber polarization scrambler 4, a pulse generator 5, two optical fiber erbium-doped optical fiber amplifiers (a first optical fiber erbium-doped optical fiber amplifier 6(EDFA) and a second optical fiber erbium-doped optical fiber amplifier (EDFA)11), an optical fiber loop device 7, a wavelength division multiplexer 8, a Raman laser 9, a single-mode optical fiber to be tested 10, a photoelectric detector 13 and a data acquisition processing module 14.
The first optical fiber coupler 2 is an optical fiber coupler with an output ratio of 9: 1; the second fiber coupler 12 is selected to be a 50:50 output ratio fiber coupler.
The semiconductor narrow linewidth laser 1 is connected with the input end of a first optical fiber coupler 2, the laser output by the first optical fiber coupler is divided into two paths, wherein the output end of the output of the first optical fiber coupler accounts for 90 percent and is connected with the input end of a semiconductor optical amplifier 3, the output end of the output of the first optical fiber coupler accounts for 10 percent and is connected with the input end of a second optical fiber erbium-doped optical fiber amplifier 11 through an optical fiber polarization scrambler 4, a pulse generator 5 is connected with the input end of the semiconductor optical amplifier 3, the modulated pulse light output by the semiconductor optical amplifier 3 is connected with the input end of a first optical fiber erbium-doped optical fiber amplifier 6, the output end of the first optical fiber erbium-doped optical fiber amplifier 6 is connected with the input end of an optical fiber circulator 7, one output end of the optical fiber circulator 7 is connected with one input end of a wavelength division multiplexer 8, the output end of a Raman laser 9 is connected with the other input end of the wavelength division multiplexer 8, the output end of the wavelength division multiplexer 8 is connected with a single-mode optical fiber 10 to be tested, the other output end of the optical fiber circulator 7 is connected with one input end of a second optical fiber coupler 12, the output end of a second optical fiber erbium-doped optical fiber amplifier 11 is connected with the other output end of the second optical fiber coupler 12, the output end of the second optical fiber coupler 12 is connected with the input end of a photoelectric detector 13, and the photoelectric detector 13 performs coherent processing on brillouin scattering light and frequency shift reference light input by the second optical fiber coupler 12 and then inputs the light into a data acquisition processing module 14.
The semiconductor narrow linewidth laser 1 is a semiconductor narrow linewidth low-noise laser with the spectral linewidth less than 1KHZ and the wavelength of 1550 nm.
The semiconductor optical amplifier 3 is a high extinction ratio semiconductor optical amplifier with an extinction ratio of 50dB, working wavelength covering 1550nm and maximum peak gain of 30 dB.
The first fiber erbium-doped fiber amplifier 6 and the second fiber erbium-doped fiber amplifier 11 are fiber erbium-doped fiber amplifiers with maximum signal gain of 47dB and saturation output power of 17 dBm.
The Raman laser 9 is a laser with the pulse width less than 10KHZ, the highest output power not less than 1W and the wavelength of 1450 nm.
The photodetector 13 is a photodetector with a 3dB detection bandwidth of more than 22GHz, a wavelength of around 1550nm, and a saturation optical power of 10 mW.
Principle of operation
Laser generated by a semiconductor narrow-linewidth laser 1 is input into a semiconductor optical amplifier 3 and a polarization scrambler 4 by a first optical fiber coupler 2 in proportions of 90% and 10%, respectively;
the pulse generator 5 emits a pulse waveform to be input into the semiconductor optical amplifier 3, laser entering the semiconductor optical amplifier 3 is modulated into pulse light, then the pulse light is input into the first optical fiber erbium-doped optical fiber amplifier 6, the first optical fiber erbium-doped optical fiber amplifier 6 amplifies the pulse light, then the pulse light is input into the wavelength division multiplexer 8 through the optical fiber loop 7, meanwhile, the Raman laser 9 generates Raman pump light to be input into the wavelength division multiplexer 8, the wavelength division multiplexer 8 inputs the modulated pulse light and the Raman pump light into the single-mode optical fiber to be detected 10, backward Brillouin scattered light generated along the single-mode optical fiber to be detected 10 is input into the wavelength division multiplexer 8, and the Brillouin scattered light is input into the second optical fiber coupler 12 through the optical fiber loop 7 after being filtered by the wavelength division multiplexer 8;
the first fiber coupler 2 inputs the laser light into the polarization scrambler 4, the polarization scrambler 4 reduces the noise of the laser light, then the laser light is input into the second fiber erbium-doped fiber amplifier 11, the reference light is amplified by the second fiber erbium-doped fiber amplifier 11 and then input into the second fiber coupler 12.
The second fiber coupler 12 inputs the detection light and the reference light into the photodetector 13 for detection, and then the detection light is input into the acquisition card in the data acquisition processing module 14 through the photodetector 13.
Brillouin scattering light demodulation process
The back brillouin shift in the fiber is:
νB＝2nVa/λ0 (1)
wherein n is the refractive index of the optical fiber, VaIs the speed of sound wave in the optical fiber, lambda0Is the wavelength of the incident light. It can be seen that the brillouin frequency shift is proportional to the effective refractive index of the optical fiber and the acoustic velocity in the optical fiber, and inversely proportional to the wavelength of the incident light.
The acoustic wave velocity in a known optical fiber is represented by the following equation:
wherein k is the Poisson's ratio; e is Young's modulus; ρ is the density of the fiber medium. The refractive index n and these parameters are functions of temperature and stress, denoted as n (ε, T), E (ε, T), k (ε, T), and ρ (ε, T), which are taken to be (1) the Brillouin frequency shift:
brillouin frequency shift and strain relationship
Under the constant temperature condition, when the strain of the optical fiber changes, the interaction potential between atoms in the optical fiber changes, so that the Young modulus and the Poisson ratio of the optical fiber change, the refractive index changes, and the change of the Brillouin frequency shift quantity is influenced.
If the reference temperature is T0Then, formula (3) is:
because the optical fiber mainly comprises the brittle material SiO2So its tensile strain is small. In the case of microstrain, taylor expansion is performed on equation (4) where ∈ 0, and higher order terms of order or more are ignored, so that:
at room temperature, taking typical values for each parameter:
λ 1550nm, Δ n-0.22, Δ k-1.49, Δ E-2.88, and Δ ρ -0.33, the brillouin shift with stress is expressed as:
νB(T0,ε)≈νB(T0,0)(1+4.48Δε) (6)
Brillouin frequency shift versus temperature
When the optical fiber is relaxed, that is, when the strain ∈ is 0, it is obtained from formula (3):
when the temperature of the optical fiber changes, the density and the refractive index of the optical fiber are respectively changed due to the thermal expansion effect and the thermo-optic effect of the optical fiber, and the Young modulus, the Poisson ratio and other physical quantities of the optical fiber are changed along with the temperature due to the change of the free energy of the optical fiber along with the temperature. When the temperature changes in a small range, assuming that the temperature change amount is Δ T, taylor expansion is performed on equation (7), and the high-order series terms above one order are ignored:
under the condition of room temperature (T ═ 20 ℃), when the wavelength of incident light is 1550nm, the corresponding relation of Brillouin frequency shift along with the temperature change is as follows:
νB(T,0)≈νB(T0,0)[1+1.18×10-4ΔT] (9)
as can be seen from formula (9), in the ordinary single-mode optical fiber in a relaxed state, when the wavelength of incident light is 1550nm at room temperature T-20 ℃, the brillouin frequency shift is about 1.2MHz for every 1 ℃.
Combining the above analysis, the Brillouin frequency shift variation amount Delta vBThe amount of change with fiber temperature and strain is approximately linear, and is generally expressed as:
ΔνB＝Cν,TΔT+Cν,εΔε (10)
wherein, Cν,TAnd Cν,εThe temperature coefficient and strain coefficient of the brillouin frequency shift change, respectively. When the wavelength of incident light is 1553.8mm, Cν,T＝1.1MHz/℃,Cν,ε＝0.0483MHz/℃。
In the description herein, references to the description of "one embodiment," "an example," "a specific example" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the utility model. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The foregoing shows and describes the general principles, essential features, and advantages of the utility model. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the utility model as claimed.
Claims (6)
1. A long-distance Brillouin optical time domain reflectometer monitoring device is characterized by comprising a semiconductor narrow-linewidth laser (1), a first optical fiber coupler (2), a semiconductor optical amplifier (3), a pulse generator (5), a first optical fiber erbium-doped optical fiber amplifier (6), an optical fiber loop device (7), a wavelength division multiplexer (8), a Raman laser (9) and a single-mode optical fiber to be tested (10);
the semiconductor narrow-linewidth laser (1) is connected with a first optical fiber coupler (2), one output end of the first optical fiber coupler (2) is connected with the input end of a semiconductor optical amplifier (3), a pulse generator (5) is connected with the input end of the semiconductor optical amplifier (3), the semiconductor optical amplifier (3) outputs modulated pulse light and is connected with the input end of a first optical fiber erbium-doped optical fiber amplifier (6), the output end of the first optical fiber erbium-doped optical fiber amplifier (6) is connected with the input end of an optical fiber circulator (7), one output end of the optical fiber circulator (7) is connected with one input end of a wavelength division multiplexer (8), the output end of a Raman laser (9) is connected with the other input end of the wavelength division multiplexer (8), and the output end of the wavelength division multiplexer (8) is connected with a single-mode optical fiber (10) to be tested.
2. A long-range brillouin optical time domain reflectometry monitoring apparatus in accordance with claim 1, further comprising a second optical fiber coupler (12), a fiber polarization scrambler (4), a second fiber erbium-doped fiber amplifier (11), a photodetector (13) and a data acquisition processing module (14).
3. A long-distance brillouin optical time domain reflectometer monitoring apparatus according to claim 2, wherein the other output end of the first optical fiber coupler (2) is connected to the input end of the second optical fiber erbium-doped optical fiber amplifier (11) through the optical fiber polarization scrambler (4), the other output end of the optical fiber circulator (7) is connected to one input end of the second optical fiber coupler (12), the output end of the second optical fiber erbium-doped optical fiber amplifier (11) is connected to the other output end of the second optical fiber coupler (12), and the output end of the second optical fiber coupler (12) is connected to the input end of the photodetector (13).
4. A long-distance brillouin optical time domain reflectometer monitoring apparatus according to claim 3, wherein the photodetector (13) performs coherent processing on the brillouin scattering light and the shifted frequency reference light input from the second optical fiber coupler (12), and then inputs the processed light into the data acquisition and processing module (14).
5. A long range brillouin optical time domain reflectometry monitoring apparatus according to claim 1, wherein 90% of the output of the first fibre coupler (2) is connected to the input of a semiconductor optical amplifier (3).
6. A long-range brillouin optical time domain reflectometry monitoring apparatus according to claim 3, wherein 10% of the output of the first optical fiber coupler (2) is connected to the input of the second optical fiber erbium-doped fiber amplifier (11) via the optical fiber polarization scrambler (4).
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