WO2018064821A1 - Capteur de gaz à fibre optique distribuée - Google Patents

Capteur de gaz à fibre optique distribuée Download PDF

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Publication number
WO2018064821A1
WO2018064821A1 PCT/CN2016/101521 CN2016101521W WO2018064821A1 WO 2018064821 A1 WO2018064821 A1 WO 2018064821A1 CN 2016101521 W CN2016101521 W CN 2016101521W WO 2018064821 A1 WO2018064821 A1 WO 2018064821A1
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WO
WIPO (PCT)
Prior art keywords
gas
fiber
sensing
laser
absorption
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PCT/CN2016/101521
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English (en)
Inventor
Sune Svanberg
Guangyu Zhao
Bin Zhou
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South China Normal University
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Priority to PCT/CN2016/101521 priority Critical patent/WO2018064821A1/fr
Publication of WO2018064821A1 publication Critical patent/WO2018064821A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/55—Specular reflectivity
    • G01N21/552—Attenuated total reflection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
    • G01N2021/394—DIAL method
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/08—Optical fibres; light guides
    • G01N2201/088—Using a sensor fibre
    • G01N2201/0886—Using a sensor fibre and using OTDR

Definitions

  • the present invention relates to a distributed optical fiber gas sensor based on lidar (light detection and ranging) technology.
  • Optical spectroscopy provides non-intrusive, sensitive and selective gas analysis in real-time (See, e.g. Reference [1-3] ) .
  • Lidar is a remote sensing technology that measures distance by illuminating a target with a laser and analyzing the reflected light. With the help of Mie and Rayleigh scattering, the lidar is also able to record a range-resolved signal from atmospheric particulates and molecules in a free atmospheric volume. (See Reference [4-6] ) .
  • the differential absorption lidar (dial) variety where the transmitted wavelength is alternatively switched between an absorption line of a gas of interest (the on-wavelength) and a neighboring non-absorbed reference wavelength (the off-wavelength) , it is possible to derive a range-resolved gas concentration map for the studied gas (See Reference [7] ) .
  • the lidar system it is difficult for a lidar system to cover arbitrary gas volumes, since an atmospheric lidar system operates on the line-of-sight principle. Also, there might be eye safety considerations. Hence, in some important applications such as monitoring the gas concentration inside buildings, tunnels, factories and mines, the conventional lidar system becomes impractical.
  • a number of solutions have been proposed for multipoint gas monitoring.
  • One of the most important solutions is using wireless technology to connect the gas sensors and create a wireless sensing network.
  • the number of sensors in a sensing network is limited by the network protocol and the cost.
  • To increase the number of the sensors, the distributed sensing technology is required.
  • the present invention discloses the principles of such a distributed gas sensing system, where an optical evanescent field surrounding a light-carrying fiber is used for sensing ambient gas surrounding the fiber. This is in important contrast to evanescent field gas sensing using CW lasers providing no range-resolution as discussed in Reference [8] . Like-wise, range-resolved monitoring of liquids using fiber technology has been described in Reference [9] .
  • the present invention discloses how differential absorption lidar (dial) technology is utilized to probe the gas concentration along a fiber using a pulsed or modulated source, and a time-resolving detection system.
  • a sensing fiber comprising a solid core to guide light, and a porous cladding which can increase the mechanical strength of the fiber and protect the fiber from physical damage.
  • the refractive index of the cladding material is somewhat smaller (usually at the magnitude of 10 -2 ) than that of the core material and small part of the light propagating along the fiber is distributed at the cladding area.
  • the cladding which has a porous structure is permeable to surrounding gas which makes interaction between the gas and the evanescent field from the fiber core being possible.
  • a spectroscopic light source comprising a pulsed or modulated tunable laser. Probing laser light is launched into the fiber.
  • the operation wavelength of the laser should be tuned to match the spectral region of the absorption band of the tested gas and means to quickly change the output between alternating different wavelengths are provided, employing electronics for a flexible operation of the laser, related to laser output characteristics.
  • a signal detecting system comprising an optical detector, e.g. a photomultiplier tube (PMT) which can convert weak back-reflected light from the fiber, generated in Rayleigh/Mie scattering, into an electrical signal.
  • the pulse width of the sensing laser is at the magnitude of tens of nanoseconds to have a high spatial resolution.
  • the response time of the detector should be matched accordingly.
  • a high speed data acquisition card to record the amplitude of the reflected light detected is further provided. The acquiring speed should be fast enough to achieve the spatial resolution required.
  • a differential absorption algorithm comprising step of recording time-resolved backscattered intensities from the sensing fiber which is brought into locations with varying concentrations of surrounding gas to be sensed. Signal intensities are recorded separately for absorbed wavelengths and non-absorbed wavelengths of the laser transmitter. Correspondingly there are two operation modes: “on” and “off” when the laser wavelength is turned to absorbed wavelengths and non-absorbed wavelengths. By dividing signals from an on-wavelength by the signal from an off-wavelength, intensity variations due to e.g. different range intervals are eliminated and only the influence of gas absorption as a function of time and range are obtained. From this data the range-resolved information on gas concentration can be obtained after calibration for the specific gas (es) to be probed.
  • a control system comprising a controller which usually is a computer for signal recording and system synchronizing.
  • the pulse generator and the data acquisition card need to be synchronized in order to determine the range at which the laser light is reflected.
  • the core material of the sensing fiber is silica, in order to lower down the optical losses.
  • the porous cladding material of the sensing fiber could be a polymer material, such as silicone, since firstly the polymer is not fragile and can enhance the mechanical strength effectively; and secondly the polymer material is easy to be made porous and permeable.
  • the pulse width of the pulsed laser is of a magnitude of tens of nanoseconds
  • the response time of the optical detector is less than ten nanoseconds
  • the data acquiring rate of the data acquisition card is more than 100 MHz, as to achieve the required spatial resolution of range.
  • a multi-wavelength differential absorption lidar concept (Reference [10-12] ) can also be implemented for the fiber lidar case. Then the laser source is switched among multiple wavelengths, for which absorption of different gases occur, as well as wavelengths, where there is no gas absorption. Using extended dial evaluation routines, the range-resolved concentration of multiple gases can be evaluated, as illustrated for the case of free atmosphere propagation in Ref. [12] .
  • the gas correlation detection principle earlier demonstrated for the open atmosphere lidar case (Reference [13] ) and the CW non-fiber gas monitoring case employing multi-mode lasers (Reference [14, 15] ) as well as light emitting diodes (Reference [16] ) can be extended to the fiber laser case, as now being disclosed.
  • the output of the light source as filtered through a gas-correlation cell containing an optically thick concentration of the gas of interest, is compared with the light intensity which passed the gas of interest, either in a lidar fashion, or in a long-path absorption implementation, to reveal the presence of the gas in the probed gas volume.
  • the fiber lidar concept now disclosed is fully adaptable to the gas-correlation case.
  • Temporal resolution in spectroscopic measurements can be achieved in the time domain, following pulsed light transmission in a time-of-flight recording mode, as in common in lidar and upper-state lifetime measurement applications, or employing modulated CW light in the frequency domain (Reference [3] ) .
  • the later technique which is usually referred to as the phase-shift method (Reference [17, 18] ) measures the phase-shift and demodulation of light transmitted at different sinusoidally modulated frequencies recorded after propagation through the medium allows time/range resolution as does the time-of-flight technique.
  • the two approaches can be shown to be basically equivalent, although the phase-shift method may offer some practical advantages.
  • the now proposed fiber lidar technique can take full advantage of the phase-shift approach to gain range resolution.
  • the technique is particularly convenient when tunable semiconductor lasers are used, since such sources can be easily modulated and controlled using standard telecom components.
  • the use of the time-resolving capabilities in such contexts was recently demonstrated in light propagation and gas absorption studies in strongly scattering media (Reference [19, 20] ) .
  • Figure 1 is a schematic representation of a distributed optical fiber gas sensing system according to a first embodiment of the invention.
  • Figure 2 shows the cross section structure of the porous cladding optical fiber according to a second embodiment of the invention.
  • Figure 3 shows the light transmission along the porous cladding fiber optical power profile of the fundamental fiber mode over a fiber cross section.
  • Figure 4 shows the OTDR (optical time domain reflectometer) tested loss of a typical sensing fiber.
  • Figure 5 shows the absorption spectrum of the tested gas and the operation wavelength of the tunable pulsed laser at the on-and off-wavelengths of the system.
  • Figure 6 shows the sequence of the controlling signals and received signals, and the differential absorption algorithm.
  • a first embodiment of the invention provides a distributed optical fiber gas sensing system (100) comprising a porous cladding (202) sensing fiber (105) as the sensing unit.
  • a pulsed laser (103) , a 3-dB optical coupler (104) and a photomultiplier tube (PMT) (107) form a typical optical time domain reflectometer (OTDR) sensing system, well-known from prior art.
  • the pulse generator (102) is to control the pulse width, period and duty cycle of the pulsed laser (103) .
  • the data acquisition card (106) is to record the amplitude of the reflected light detected by the PMT (107) .
  • the controller (101) which usually is a computer, is for signal recording and system synchronizing.
  • FIG. 2 shows the cross section structure of the porous cladding optical fiber (200) according to a second embodiment of the invention.
  • the sensing fiber (200) has a solid core (201) to guide light and a porous cladding (202) to protect the fiber from physical damage and to enlarge the interface between guided light and the gas to be probed.
  • the core material of the sensing fiber is silica, in order to lower down the optical transmission loss.
  • the porous cladding material of the sensing fiber could be a polymer, since polymer is not fragile and can enhance the mechanical strength effectively.
  • the length of the sensing fiber is normally more than 1 km.
  • the pulse width of the pulsed laser is typically 10 ns, the response time of the PMT is less than 10 ns and the data acquiring rate of the data acquisition card is 200 MHz, as to achieve the spatial resolution of about 1 meter.
  • Figure 3 shows the light transmission in the porous cladding fiber and the scattering at the cladding.
  • FIG. 4 An experimental curve showing results from a test of a fiber designed to fit the present invention needs is presented in Fig. 4.
  • a standard optical time domain reflectometer (OTDR) is employed, and a useful optical attenuation of 10 dB/km is demonstrated.
  • Figure 5 shows the absorption spectrum of the tested gas and the operational wavelength of the tunable pulsed laser at the on-and off wavelengths.
  • the operation wavelength of the pulsed laser should be tuned exactly at the peak wavelength of the absorption band of the tested gas, and at the off mode, the operation wavelength of the pulsed laser should be tuned off, but not too far away from the absorption band of the tested gas.
  • Figure 6 shows the system with the entire optical and electronics systems located at a single place, and the gas probing fiber extending into the environment, where at a particular location gas to be probed is present.
  • the time-resolved fiber lidar return signals are shown for the affected on-resonance wavelength and the non-affected off-resonance wavelength.
  • the differential absorption lidar (dial) curve is obtained, where the influence of non-spectroscopic signal attenuation is eliminated by forming a dimension-less quantity (See Reference [7] ) .
  • the curve is horizontal, except at locations where gas present as illustrated in the figure.
  • the concentration of the gas surrounding the fiber is calculated (See Reference [7] ) , with higher concentrations larger the slope of the curve is, basically reflecting the Beer-Lambert law (See Reference [3] ) .
  • Calibration is provided by surrounding the fiber with gas of known concentration, whereby all influences of spectroscopic absorption cross sections, as well as of the fraction of the total light which was able to interact with the gas through the evanescent field are included.

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  • Physics & Mathematics (AREA)
  • General Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Optics & Photonics (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

La présente invention concerne un système de détection de gaz à fibre optique distribuée (100) basé sur une détection de champ évanescent, résolu spatialement le long de la fibre (105, 200, 300) et obtenu par l'utilisation de techniques lidar à absorption différentielle. La fibre (105, 200, 300) peut être agencée dans une pluralité de manières et peut comporter une fibre de détection (105, 200, 300) de gaine poreuse (202) en tant qu'unité de détection. La fibre de détection (105, 200, 300) comporte un noyau solide (201) destiné à guider la lumière et une gaine poreuse (202) destinée à protéger la fibre (105, 200, 300) contre des dégâts physiques et à agrandir l'interface du champ évanescent et du gaz de test. Un laser pulsé ou modulé (103), un coupleur optique à 3 dB (104) et un tube photomultiplicateur (PMT pour PhotoMultiplier Tube) (107) forment un système de détection de réflectomètre optique dans le domaine temporel (OTDR pour Optical Time-Domain Reflectometer) typique. Le générateur d'impulsions (102) est destiné à commander la largeur d'impulsion, la période, le cycle de service du laser pulsé (103). La carte d'acquisition de données (106) est destinée à enregistrer l'amplitude de la lumière réfléchie détectée par le tube photomultiplicateur (107). Le dispositif de commande (101) qui est le plus souvent un ordinateur, est destiné à l'enregistrement de signaux et à la synchronisation du système.
PCT/CN2016/101521 2016-10-09 2016-10-09 Capteur de gaz à fibre optique distribuée WO2018064821A1 (fr)

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109406450A (zh) * 2018-10-18 2019-03-01 山东大学 多次吸收式微量气体检测系统
CN110470605A (zh) * 2018-05-11 2019-11-19 西安电子科技大学 一种基于光纤耦合模式的多节点光声气体检测方法
CN110470630A (zh) * 2018-05-11 2019-11-19 西安电子科技大学 一种基于差分模式的分布式光纤气体传感器
CN113484535A (zh) * 2021-07-05 2021-10-08 浙江大学 一种矿井中的风量测量装置和测量方法

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JPH0371043A (ja) * 1989-08-11 1991-03-26 Sumitomo Electric Ind Ltd 光ファイバガスセンサ
CN1648637A (zh) * 2005-01-29 2005-08-03 山西大学 一种光纤气体传感器
CN1670507A (zh) * 2005-04-08 2005-09-21 南开大学 光子晶体光纤流体传感装置
CN202275049U (zh) * 2011-10-12 2012-06-13 山东省科学院海洋仪器仪表研究所 一种用于气体或液体浓度检测的光子晶体光纤传感探头

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JPH0371043A (ja) * 1989-08-11 1991-03-26 Sumitomo Electric Ind Ltd 光ファイバガスセンサ
CN1648637A (zh) * 2005-01-29 2005-08-03 山西大学 一种光纤气体传感器
CN1670507A (zh) * 2005-04-08 2005-09-21 南开大学 光子晶体光纤流体传感装置
CN202275049U (zh) * 2011-10-12 2012-06-13 山东省科学院海洋仪器仪表研究所 一种用于气体或液体浓度检测的光子晶体光纤传感探头

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110470605A (zh) * 2018-05-11 2019-11-19 西安电子科技大学 一种基于光纤耦合模式的多节点光声气体检测方法
CN110470630A (zh) * 2018-05-11 2019-11-19 西安电子科技大学 一种基于差分模式的分布式光纤气体传感器
CN109406450A (zh) * 2018-10-18 2019-03-01 山东大学 多次吸收式微量气体检测系统
CN113484535A (zh) * 2021-07-05 2021-10-08 浙江大学 一种矿井中的风量测量装置和测量方法

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