CN102116684A - Self-correcting fully-distributed optical fiber Raman scattering sensor - Google Patents
Self-correcting fully-distributed optical fiber Raman scattering sensor Download PDFInfo
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Abstract
The invention discloses a self-correcting fully-distributed optical fiber Raman scattering sensor. In the invention, a duplex fiber cable is utilized as a sensing optical fiber, pump light is divided into a forward beam and a backward beam during the transmission process by welding the tail ends of the duplex fiber cable together so as to obtain two anti-Stokes Raman scattering light beams, and the intensity of the anti-Stokes Raman scattering light beams is measured so as to realize temperature measurement; and the intensity values of the two anti-Stokes Raman scattering light beams can be multiplied so as to achieve the purpose of self-correction of curvature, loss, strain and the like. The sensor disclosed by the invention comprises an optical fiber pulse laser, an optical fiber wavelength division multiplexer (WDM), the duplex fiber cable, a photoelectric receiving module, a digital signal processor (DSP) and a computer. The invention has the advantages that self-correction and temperature measurement can be carried out at the same time only by measuring the intensity of the anti-Stokes Raman scattering spectrums; and the system has a simple structure, and avoids the defects that the traditional measuring system has transmission loss and errors caused by different center wavelength and needs a plurality of photoelectric receivers.
Description
Technical Field
The invention belongs to the field of optical fiber sensing temperature measurement, and relates to a self-correcting fully-distributed optical fiber Raman scattering sensor. The sensor is suitable for occasions requiring simple structure, low cost and wide application, such as real-time continuous monitoring of production process, civil engineering, disaster monitoring and the like.
Technical Field
In recent years, optical fiber sensors, especially distributed optical fiber raman scattering sensors, have gained wide attention and research due to the advantages of simple and safe operation, applicability to severe environments, and the like. The sensor utilizes the intrinsic characteristics of optical fibers, the Rayleigh, Raman and Brillouin scattering effects of the optical fibers and adopts an Optical Time Domain (OTDR) technology to realize temperature monitoring. The optical fibers in the full-distribution optical fiber sensor network are not only transmission media but also sensing media, and a detection blind area does not exist. The sensor can realize the safety and health monitoring and disaster forecasting and monitoring of electric power engineering, petrochemical industry, traffic bridges, tunnels, subway stations, dams, embankments and the like. The traditional distributed optical fiber Raman scattering sensor mainly utilizes the ratio of temperature-sensitive anti-Stokes Raman scattering light intensity to Rayleigh scattering light intensity or Stokes scattering light intensity to obtain temperature information, the method can overcome the measurement error caused by light source fluctuation, but with the increase of the measurement distance, in order to obtain higher measurement accuracy, the transmission loss caused by the difference of anti-Stokes scattering, Stokes scattering and Rayleigh scattering center wavelengths needs to be corrected. Therefore, a method adopting a double light source is provided, the method adopts two main lasers and two auxiliary lasers with different central wavelengths, and eliminates errors caused by different wavelengths by using the anti-stokes Raman scattering wavelength of the main lasers and the central wavelength of the auxiliary lasers to be the same, but the structure needs to be added with one laser, one optical switch and two photoelectric detection modules, and the use cost is increased while the system structure is increased. In 2010, Dusun Hwang et al in Korea proposed a mirror at the end of the sensing fiber to perform self-calibration while monitoring temperature (OPTICS EXPRESS, 2010, Vol.18, No. 10: 9747-.
The invention adopts a method of connecting the tail ends of the double-core optical cables to replace a reflector, provides the self-correcting distributed optical fiber Raman scattering sensor with simpler structure, low cost, good signal-to-noise ratio and high reliability, and the sensor can realize self-correction while monitoring temperature only by one laser and one photoelectric detection module. The key is to replace the traditional single mode fiber with the double-core optical cable to realize sensing measurement, and the tail end of the double-core optical cable is connected to change a pumping light source into two forward and reverse beams, thereby obtaining two anti-Stokes beams for offsetting the loss of the fiber. Meanwhile, self-correction can be realized on bending and transmission loss, the defects of the traditional distributed optical fiber Raman scattering sensor are overcome, and the cost is reduced.
Disclosure of Invention
The invention aims to provide a full-distributed optical fiber Raman scattering sensor which is low in cost, simple in structure, good in signal-to-noise ratio and capable of self-correcting.
The technical solution of the invention is as follows:
the self-correcting full-distributed optical fiber Raman scattering sensor comprises an optical fiber pulse laser, an optical fiber wavelength division multiplexer, a double-core optical cable, a photoelectric receiving module, a digital signal processor and a computer. The optical fiber wavelength division multiplexer has three ports, wherein the 1550nm input end is connected with the optical fiber pulse laser, the COM output port is connected with any end of the double-core optical cable, the 1450nm output port is connected with the input end of the photoelectric receiving module, the output end of the photoelectric receiving module is connected with the digital signal processor, and the signal output end of the digital signal processor is connected with the computer. The center wavelength of the pulse laser is 1550nm, the spectral width is 0.1nm, the laser pulse width is 10ns, the peak power is adjustable at 1-100w, and the repetition frequency is adjustable at 500Hz-20 KHz. The mentioned sensing optical cable is a double-core optical cable, the tail ends of the sensing optical cable are connected, and the optical fiber can adopt G652 communication single-mode optical fiber or carbon-coated single-mode optical fiber.
The optical fiber pulse laser is used as a pumping light source to emit laser pulses which are injected into any end of the double-core optical cable through a 1550nm input port of the optical fiber wavelength division multiplexer, backward Rayleigh scattering, Stokes Raman scattering and anti-Stokes Raman scattering wavelets are generated in the sensing optical cable, the optical cable is the double-core optical cable, and the tail ends of the optical cable are connected, so that the pumping light source is transmitted backwards in any optical fiber of the double-core optical cable when the optical fiber is transmitted forwards to the tail ends, the tail ends of the optical fiber are connected and then transmitted backwards, pumping light in the forward direction and the reverse direction is obtained, two beams of anti-Stokes Raman scattering light are obtained, the backward anti-Stokes Raman scattering wavelets with temperature information are received by the photoelectric receiving module after passing through the optical fiber filter. The temperature information of each section of the optical fiber is obtained by the product of the light intensity of the two anti-Stokes Raman scattering beams, and meanwhile, the bending, the loss, the strain and the like are self-corrected, so that the temperature and the temperature change speed of each temperature sensing detection point and the cross influence of the bending, the strain and the temperature are eliminated. And the digital signal processor is connected with the computer communication interface to transmit the measurement result.
The invention has the beneficial effects that:
the self-correcting full-distributed optical fiber Raman scattering sensor can realize temperature measurement and positioning by monitoring the intensity of anti-Stokes Raman scattering light only by using one pumping light source and one photoelectric detection module, and avoids self-correcting errors such as bending, strain, node loss and the like besides transmission attenuation caused by different central wavelengths of anti-Stokes Raman scattering and Rayleigh scattering or Stokes scattering. Compared with the traditional distributed optical fiber Raman temperature measurement system, the temperature measurement system has the advantages of simple structure and low cost besides the self-correcting capability. The invention is suitable for continuous temperature measurement in occasions requiring self-correction and low cost to prevent various possible disasters such as pipelines, tunnels and the like.
Drawings
Fig. 1 is a schematic structural diagram of a self-correctable distributed fiber raman scattering sensor.
Fig. 2 is a view showing a connection structure of the end of a twin-core optical cable for sensing.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
Referring to fig. 1, the self-correctable distributed fiber raman scattering sensor comprises a fiber pulse laser 11, a fiber wavelength division multiplexer 12, a two-core optical cable 13, a photoelectric receiving module 14, a digital signal processor 15 and a computer 16. The optical fiber wavelength division multiplexer 12 has three ports, wherein a 1550nm input port is connected with an output end of the optical fiber pulse laser 11, a COM output port is connected with any end of the sensing optical cable 13, a 1450nm output port is connected with an input end of the photoelectric receiving module 14, an output end of the photoelectric receiving module 14 is connected with an input port of the digital signal processor 15, and a signal output end of the digital signal processor 15 is connected with the computer 16.
Referring to fig. 2, the dual core optical cable includes an outer package 5 and a dual core optical fiber 6 formed by juxtaposing common single mode optical fibers, wherein the ends of the dual core optical fibers are connected.
The center wavelength of the pulse laser is 1550nm, the spectral width is 0.1nm, the laser pulse width is 10ns, the peak power is adjustable within 1-100w, and the repetition frequency is adjustable within 500Hz-20 KHz.
The sensing optical cable is a double-core optical cable, and the tail ends of the sensing optical cable are connected, so that when pump light is transmitted in an optical fiber, the pumping light can be divided into two opposite direction light beams in a mode of connecting the tail ends of the double-core optical cable to obtain two anti-stokes Raman scattering light beams, self calibration of bending, loss and the like can be realized by calculating the two anti-stokes Raman scattering light beams, and the measurement precision of the fully-distributed optical fiber temperature sensor is improved.
The digital signal processor adopts a general signal processing card and is inserted into a computer.
The invention is based on the following principle:
energy of P0The pump light generates backward anti-Stokes Raman scattering light when transmitting in the forward direction and has an intensity In1When the pump light is transmitted to the tail end of the temperature measuring optical cable for reverse transmission, the energy is P1The generated backward anti-Stokes Raman scattered light has a light intensity of Pn2. According to the temperature measurement principle of the distributed optical fiber Raman scattering photon sensor, the anti-Stokes back Raman scattering light intensity in the optical fiber is as follows:
wherein, P0The intensity of the pump light, g (z, T) is measured in the temperature measuring fiberRaman scattering function at z, alpha, related to temperature Tp(z) and alphaAS(z) total losses such as absorption loss, fusion point loss, connection loss, bending loss, etc., of the pump light and the anti-stokes raman scattered light, respectively, when transmitted in the optical fiber. Z0In order to monitor the length of the temperature region, C is a constant and refers to the background dark current when the photoelectric detection module detects the anti-Stokes backward Raman scattering light intensity.
After the formula (1) is multiplied by the formula (2), the position-dependent integral term can be eliminated, and the temperature-dependent equation is obtained as follows:
wherein,is shown in the whole temperature measuring optical cable Z0The various total losses within the range may be approximated as constants. The temperature function g (z, T) is proportional to the anti-stokes raman scattering intensity, i.e.:
where B is a proportionality coefficient related to the numerical aperture of the sensing fiber, h is the spectral Lanck (Planck) constant, Δ v is the phonon frequency of a fiber molecule, k is the ratio of the wavelength of the sensing fiber to the wavelength of the sensing fiberBIs the boltzmann constant, t (z) is the Kelvin (Kelvin) absolute temperature of the temperature measuring fiber at position z.
Substituting the formula (4) into the formula (3) to obtain the measured length Z0The relationship between the intensity and the temperature of the two anti-stokes raman scattering processes in the range is as follows:
in the present invention, z is measured as the length of the optical fiber0The optical fiber anti-stokes Raman scattering channel is used as a reference signal, the temperature is demodulated only by using the anti-stokes Raman scattering intensity, and a temperature measurement function is obtained according to a formula (5):
the anti-Stokes Raman scattering light intensity of the optical fiber Raman time domain reflection (OTDR) curve at the optical fiber detection point can obtain the temperature signals of each section of the optical fiber, and can automatically correct the influence on the test result caused by bending, strain, various losses and the like.
Claims (3)
1. The self-correcting full-distributed optical fiber Raman scattering sensor is characterized by comprising an optical fiber pulse laser (11), an optical fiber wavelength division multiplexer (12), a double-core optical cable (13), a photoelectric receiving module (14), a digital signal processor (15) and a computer (16); the optical fiber wavelength division multiplexer (12) is provided with three ports, wherein a 1550nm input port is connected with the optical fiber pulse laser (11), a COM output port is connected with any one end of the double-core optical cable (13), a 1450nm output port is connected with the input end of the photoelectric receiving module (14), the output end of the photoelectric receiving module (14) is connected with an input port of the digital signal processor (15), and the signal output end of the digital signal processor (15) is connected with the computer (16).
2. The self-correctable fully distributed fiber raman scattering sensor according to claim 1, wherein the fiber pulse laser (11) has a center wavelength of 1550nm, a spectral width of 0.1nm, a laser pulse width of 10ns, a peak power of 1-100w adjustable, and a repetition frequency of 500Hz-20KHz adjustable.
3. The self-correctable fully distributed fiber raman scattering sensor according to claim 1, wherein the sensing fiber (13) is a two-core fiber cable, the ends of which are connected, wherein the fiber is a G652 communication single mode fiber or a carbon-coated single mode fiber.
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Cited By (7)
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|---|---|---|---|---|
| CN102661817A (en) * | 2012-06-01 | 2012-09-12 | 杭州欧忆光电科技有限公司 | Distributed optical fiber temperature sensing system capable of automatically configuring parameters and configuration method thereof |
| CN102706477A (en) * | 2012-06-08 | 2012-10-03 | 宁波诺驰光电科技发展有限公司 | Distributed optical fiber sensing device and method for simultaneously measuring temperature and strain |
| CN104483040A (en) * | 2014-12-30 | 2015-04-01 | 杭州欧忆光电科技有限公司 | Portable distribution optical fiber temperature sensor |
| CN106404741A (en) * | 2016-10-11 | 2017-02-15 | 北京信息科技大学 | Enhanced Raman spectrum liquid detection method based on double hollow-core fibers |
| CN109004973A (en) * | 2018-07-04 | 2018-12-14 | 广州广电计量检测股份有限公司 | A kind of OTDR capability evaluating device and method |
| CN110441810A (en) * | 2019-07-09 | 2019-11-12 | 哈尔滨工程大学 | A kind of optical fiber radiation probe with bending loss compensation |
| CN115452202A (en) * | 2022-11-10 | 2022-12-09 | 中国空气动力研究与发展中心设备设计与测试技术研究所 | High-temperature thermocouple calibration method based on coherent anti-Stokes Raman scattering spectrum |
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Patent Citations (6)
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| CN101393677A (en) * | 2008-07-25 | 2009-03-25 | 中国计量学院 | Distributed type optical fiber Raman photon temperature sensing fire disaster detector |
| CN101592475A (en) * | 2009-06-08 | 2009-12-02 | 中国计量学院 | Fully distributed fiber Rayleigh and Raman scattering photon strain, temperature sensor |
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| CN102661817A (en) * | 2012-06-01 | 2012-09-12 | 杭州欧忆光电科技有限公司 | Distributed optical fiber temperature sensing system capable of automatically configuring parameters and configuration method thereof |
| CN102706477A (en) * | 2012-06-08 | 2012-10-03 | 宁波诺驰光电科技发展有限公司 | Distributed optical fiber sensing device and method for simultaneously measuring temperature and strain |
| CN102706477B (en) * | 2012-06-08 | 2014-04-23 | 宁波诺驰光电科技发展有限公司 | Distributed optical fiber sensing device and method for simultaneously measuring temperature and strain |
| CN104483040A (en) * | 2014-12-30 | 2015-04-01 | 杭州欧忆光电科技有限公司 | Portable distribution optical fiber temperature sensor |
| CN106404741A (en) * | 2016-10-11 | 2017-02-15 | 北京信息科技大学 | Enhanced Raman spectrum liquid detection method based on double hollow-core fibers |
| CN109004973A (en) * | 2018-07-04 | 2018-12-14 | 广州广电计量检测股份有限公司 | A kind of OTDR capability evaluating device and method |
| CN110441810A (en) * | 2019-07-09 | 2019-11-12 | 哈尔滨工程大学 | A kind of optical fiber radiation probe with bending loss compensation |
| CN110441810B (en) * | 2019-07-09 | 2023-05-12 | 哈尔滨工程大学 | Optical fiber radiation probe with bending loss compensation |
| CN115452202A (en) * | 2022-11-10 | 2022-12-09 | 中国空气动力研究与发展中心设备设计与测试技术研究所 | High-temperature thermocouple calibration method based on coherent anti-Stokes Raman scattering spectrum |
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