CN105115939B - A kind of high sensitivity optical fiber methane sensing device based on tapered multimode interference - Google Patents
A kind of high sensitivity optical fiber methane sensing device based on tapered multimode interference Download PDFInfo
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Abstract
A kind of high sensitivity optical fiber methane sensing device based on tapered multimode interference, including the tapered multimode of wideband light source, STMS structures coat the fibre optical sensor of porous sensitive thin film, test air chamber, controlled valve, mass flow controller, spectroanalysis instrument and computer.Wherein, to draw cone to form multimode fibre after single-mode fiber multimode fibre single-mode fiber welding, tapered multimode fiber outer surface is pre-processed STMS structured optical fibers sensor using silane coupler；Sensitive thin film is the porous methane sensitive thin film of α hydrogen ω hydroxyl dimethyl silicone polymers of the A containing cage molecule；When methane gas to be measured and porous methane sensitive thin film act on, sensitive thin film refractive index quickly changes, and makes sensor interferometer spectrum signature wavelength XcMobile, analyte sensors contact front and rear interference spectrum characteristic wavelength amount of movement Δ λ with methane gasc, you can obtain concentration of methane gas to be measured.The present invention has the characteristics that high sensitivity, fast response time, selectivity and stability are good.
Description
Technical field
The invention belongs to technical field of optical fiber sensing, and in particular to a kind of height for the tapered multimode interference for obtaining methane concentration
Sensitivity optical fiber methane method for sensing and device.
Background technology
With the fast development of optical fiber sensing technology, fiber gas sensor research receives significant attention, because it has electricity
Good insulating, anti-strong electromagnetic, it is explosion-proof, can at a distance long-term on-line measurement the features such as and it is inflammable and explosive in suitable adverse circumstances
Gas-monitoring.
Single-mode fiber (SMF)-tapered multimode fiber (TMMF)-single-mode fiber (SMF) structure (STMS) is a kind of based on cone
The optical fiber structure of shape multimode fibre mode-interference mechanism, it is incited somebody to action after being embedded into a segment mark quasi-monomode fiber by one section of multimode fibre
Multimode fibre draws cone to form.This fibre optical sensor based on conical fiber multiple-mode interfence has that simple in construction, cost is cheap, clever
The advantages that sensitivity is higher, can be modulated by wavelength and overcome the influence of light wave strength fluctuation, can be used in humidity, hydrogen, ammonia,
The infomation detections such as oxygen.At present, researcher successively have developed the fibre optical sensor of different STMS structures.Wang Xueping etc. [in
Metering institute of state master thesis, 2014.3.1] propose a kind of tapered fiber humidity sensor of coating polyethylene alcohol (PVA) film
Device, its humidity sensing film are coated in the 5%PVA aqueous solution by multimode fibre conical region and formed, the refractive index of humidity sensing film
It can change with external environment humidity and change, humidity information be obtained according to optical power change, in the range of 35~90%RH of humidity
Sensor peak response is 0.251dB/%RH.Joel Villatoro etc. (Sensors and Actuators B, 2005,
110:23~27；IEEE Sensors Journal,2003,3(4):533~537) palladium is coated to drawing cone multimode fibre surface
Form high sensitivity hydrogen gas sensor, test limit 0.3%, 90 seconds response times.David Monz ó n Hern á ndez etc.
(Sensors and Actuators B,2010,151:219~222) then cone is drawn to be plated to 5-10 μm and with 0.1 angstroms per second optical fiber
Cover palladium, golden film with formed can quick detection hydrogen fibre optical sensor, 2 seconds its response times.(the Advanced such as Fuxing Gu
Optical Materials,2014,2:189~196) monocrystalline palladium nanometer wire is also coated on to the effect of tapered optical fiber sensors
Region, detection limit as little as 0.2% of the palladium nanometer wire to hydrogen.D.Rithesh Raj etc. (Optics Communications,
2015,340:86~92) by nano-Ag particles, polyvinylpyrrolidone and polyvinyl acetate coated on drawing cone plastic optical fiber table
Face, evaluate different nano Silver quality fractions (1.6,3.3 and system 6.6%) to ammonia selectivity.S.A.Ibrahim etc.
(Optics Express,2015,23(3):Polyaniline nano fiber 2837-2845) is then coated to tapered multimode fiber sensing unit
To form ammonia gas sensor, response and recovery time are respectively 2.27,9.73min, reappearance and good reversibility in domain.Renata
(Analytical Letters, 2012,45 (10) such as Jarzebinska:1297~1309) electrostatic self-assembled four-(4- is proposed
Sulfophenyl) porphyrin (TSPP) and PAH (PAH) alternating layer form ammonia gas sensor to conical fiber surface, its
10 μm of beam waist diameter, 100 seconds response times, 240 seconds recovery times.C.Pulido etc. (Sensors and Actuators B,
2013,184:64~69) proposing fluorogen being embedded in draws cone polymer optical fiber to form fiber optic oxygen sensor, is caused using oxygen
Fluorescent quenching signal measure oxygen content, 28 seconds response times.(the Physiological such as Rongsheng Chen
Measurement,2013,34:N71~N81) the Fibre Optical Sensor system of a detectable human body respiration is also established, its principle is
The fluorogen for being mixed with polymer is coated on tapered fiber surface, oxygen has Fluorescence Quenching Characteristics, sensor response time 150
Second, the respiratory rate of 60 times per minute can be monitored.Chen Da such as (ZL201110311888.7) is disclosed based on conical fiber
Bragg grating hydraulic sensing method, sensor-based system includes wideband light source, photo-coupler, spectroanalysis instrument and conical fiber
Bragg grating, when the Bragg grating of conical fiber is placed in hydraulic environment to be measured, by measuring conical fiber Prague light
Grid centre wavelength amount of movement obtains the hydraulic pressure being applied on Bragg grating.
Methane is mine gas main component (accounting for 83~89%), is the emphasis of mining safety monitoring.Cage molecule
Compound (Cryptophanes) is the unique new function molecule to methane with direct photaesthesia response found so far, can
The optical fiber methane sensitive film sensor of high selectivity is combined to form with optical fiber sensing technology, as evanescent wave type, Fluoroscopic type,
The methane transducers such as mode filtered light type, LPFG type, photonic crystal fiber type (Sensors and Actuators
B,2005,107(1):32~39；Analytica Chimica Acta,2009,633(2):238~243；Chinese
Optics Letters,2010,8(5):482~484；Optics Express,2011,19(15):14696~14706).Point
Analysis shows that cage molecule A or E are mainly incorporated into polysiloxanes or styrene-acrylonitrile material by current research work,
And it is coated on PCS plastic-clad silica fibre core, fiber core mismatch type optical fiber or LPFG and forms methane optical fiber sensor.
But the sensitive thin film of these methods coated from cage molecule incorporation polysiloxanes, after SAN and
Into most of cage molecule is wrapped in thin-film material, and it is big methane molecule migration resistance in these thin-film materials easily occur
The problems such as difficult is contacted with cage molecule, makes the response speed of sensor relatively low compared with slow (2~5 minutes), sensitivity.
It can be seen that the technology of the above all has the problem of common, i.e. cage molecule is not directly to be exposed in methane gas,
Thus the ability of cage molecule response methane molecule is influenceed so that transducer sensitivity is relatively low, it is necessary to changes sensitive thin film knot
Structure.
The content of the invention：
In order to solve the problems, such as that above prior art is present, the present invention proposes a kind of high sensitivity, fast response time
Multi-mode interference-type optical fiber methane method for sensing and device, its sensing process are the alpha -hydro-omega -hydroxy-polies two with the A containing cage molecule
Methylsiloxane porous membrane is as methane sensitive material, the tapered multimode fiber sensing unit coated on SMF-TMMF-SMF structures
Domain, you can realize and detected to methane gas high response speed, high sensitivity, high selectivity.
For achieving the above object, the technical solution used in the present invention is as follows：
It is a kind of based on tapered multimode interference high sensitivity optical fiber methane sensing device, including wideband light source, single-mode fiber,
The TMMF of SMF-TMMF-SMF structures coats the methane optical fiber sensor of porous sensitive thin film, test air chamber, controlled valve, quality
Flow controller, spectroanalysis instrument and computer etc. are formed.The multimode fibre MMF both ends respectively with single-mode fiber SMF weldings
And form SMF-TMMF-SMF structures, the both ends single-mode fiber SMF being connected with TMMF after drawing cone is further carried out to multimode fibre
It is connected respectively to wideband light source, spectroanalysis instrument and computer；In test air chamber, test air chamber is passed through fibre optical sensor
The air inlet of methane gas to be measured and gas outlet, air inlet control the mass flow of methane gas to be measured by controlled valve connection
Controller.The tapered multimode fiber outer surface of the SMF-TMMF-SMF structured optical fibers sensor is first water-soluble using silane coupler
Liquid pretreatment re-coating methane sensitive thin film.
The methane sensitive thin film is that the porous methane of alpha -hydro-omega -hydroxy-poly dimethyl siloxane of the A containing cage molecule is quick
Feel film, be first to be placed in optical grade alpha -hydro-omega -hydroxy-poly dimethyl siloxane, cage molecule A, pore-foaming agent ammonium hydrogen carbonate
In dichloromethane and methanol mixed solvent, further ultrasonic mixing is uniform after being stirred 0.5 hour with 2000 revs/min of rotating speeds, then
Automatic lifting is coated on tapered multimode fiber sensitive zones, deviates under the conditions of 90 DEG C of temperature and vacuum 0.08MPa in film
Dichloromethane and methanol mixed solvent and thermal decomposition pore-foaming agent ammonium hydrogen carbonate, make the methane sensitive thin film porous to be formed, hole
Gap rate is 12~15%；Reagent dosage is respectively 600 μm of ol of cage molecule A, optical grade alpha -hydro-omega -hydroxy-poly dimethyl-silicon
Oxygen alkane 1g, pore-foaming agent ammonium hydrogen carbonate 0.1g, volume ratio 5:1 dichloromethane and methanol mixed solvent 12mL.
The sensitive thin film porous that cage molecule and optical resin are mixed to form by the present invention, by thermally decomposing sensitive thin film
Interior pore-foaming agent realizes that dense film changes to perforated membrane, and sensitive thin film has higher porosity, the cage molecule exposed in film
Quantity significantly improves；Meanwhile sensitive thin film is also coated to tapered multimode fiber surface and porous, spread using methane molecule
Quickly change causes sensor transmission interference spectrum signature wavelength to move to refractive index after into porous sensitive thin film, when methane gas to be measured
When body and the porous methane sensitive thin film of tapered multimode fiber outer surface act on, sensitive thin film refractive index quickly changes, and makes sensing
Device interference spectrum characteristic wavelength moves, you can realizes to mesh such as methane gas high sensitivity, high response speed, high selectivity detections
's.
The multimode fibre draws 125 μm of diameter before cone, and beam waist diameter D is 25~35 μm after drawing cone.
Tapered multimode fiber (sensitive zones) length is L, wherein drawing cone length LTFor 0.55~0.85mm；Coat first
Alkane sensitive membrane to conical fiber surface and porous, porosity 12~15%, methane sensitive membrane variations in refractive index can significantly affect
Transmission interference spectrum signature wavelength amount of movement, improve transducer sensitivity.
The tapered multimode fiber outer surface is using KH-550 silane couplers (γ-aminopropyl triethoxysilane)
The aqueous solution is pre-processed, volumetric concentration 0.1%, 10 seconds processing times, to form silane coupler nanometer coat, thickness
Only nanoscale, for improving the adhesive force of methane sensitive membrane and fiber outer surface.
The porous polymer sensitive thin film is the alpha -hydro-omega -hydroxy-poly dimethyl siloxane methane of the A containing cage molecule
Sensitive thin film, the sensitive thin film only have response to methane gas, to oxygen, nitrogen, carbon dioxide, carbon monoxide, hydrogen sulfide etc.
Non-methane class gas is good almost without response, selectivity.
The alpha -hydro-omega -hydroxy-poly dimethyl siloxane methane sensitive thin film of the A containing cage molecule is that low-refraction is quick
Feel material, refractive index 1.41 or so, good toughness.
The wideband light source uses centre wavelength 1550nm DL-CS5014A superradiance wideband light source SLD, bandwidth 40nm.
The spectroanalysis instrument is the Agilent 86140B spectroanalysis instruments of 600~1700nm wave-length coverages.
The sensor transmission interference spectrum signature wavelength amount of movement Δ λcFor after sensor contacts methane gas, the before contact
The difference of m level interference peaks characteristic wavelengths.
The operation principle of the sensing device is as follows：
As basic mode LP01Incident light by single-mode fiber (SMF) through SMF/ tapered multimode fibers (TMMF) welding interface enter
When length is in L TMMF, it will multiple higher order mode LP are excited in TMMF0m, these patterns will be with different propagation constant edges
TMMF travels to a tight waist, further to TMMF and output end SMF weldings interface, is interfered with basic mode and reenters SMF.It is right
In the LP being excited0mFor high-order mode, electric field component is expressed as：
Wherein EmAnd β (r)mFor Electric Field Distribution and the propagation constant of longitudinal m ranks pattern, cmFor SMF LP01Mode excitation arrives
TMMF LP0mRate is imitated, is represented by：
Wherein, Es(r) LP for being SMF01Mode distributions.
LP in TMMF0mPower height and the coefficient of coup η of high-order modemIt is closely related, ηmExpression isηmMore
Show LP greatly0mMould has higher power.It is weak lead approximate condition under, the longitudinal propagation constant difference of the higher order mode in TMMF can
It is expressed as：
Wherein：μm=π (m-1/4) and μn=π (n-1/4) is the root of zero Bessel function；nTIt is TMMF refractive indexes, a is
Multimode fibre is girdled the waist radius, and k=2 π/λ are the wave numbers of incident light, and footnote m and n correspond to the different mode of light, m ranks mould and n ranks
Mould.Phase difference of the light propagation of the two patterns at z is Δ φmn=(βm-βn)z.When sensitive zones length is L, light passes
Phase difference when being multicast to exit end TMMF/SMF interfaces is：
From formula (4), the distance light travels for reaching SMF are L, and the light of these different modes occurs dry because phase is different
Relate to, interference enhancing occur and interference weakens, there is characteristic peak (crest, trough) in interference spectrum, corresponding characteristic wavelength meets
In formula：L is TMMF length；N is positive integer.
When the porous sensitive membrane coated on TMMF outer surfaces contacts with methane gas, its refractive index will occur quickly to change
Become, make the Eigenvalue and eigenmode changes in distribution of light in TMMF, cause interference spectrum characteristic wavelength λcIt is moved.According to characteristic wave
Long amount of movement Δ λcSize, you can calculate concentration of methane gas to be measured.
The present invention has the characteristics that high sensitivity, fast response time, selectivity and stability are good, and specific advantage is as follows：
1. the directly fused multimode fibre of the present invention and single-mode fiber SMF-28, then draw the tapered light of taper by multimode fibre
Fibre, the light of transmission in multimode fibre fibre core can be made more to enter conical fiber/sensitive thin film interface at taper and formed suddenly
Die ripple, drastically increases sensitivity, the detection limit of sensor.
2. the present invention proposes to realize the purpose of exposed cage molecule by methane sensitive thin film porous, sensitive by controlling
Film porosity 12~15% can preferably solve the purpose of transducer sensitivity and response speed raising.Original that its is selected
Material, and most suitable process conditions are used, the methane sensitivity coating solution of use is by cage molecule A, optical grade alpha -hydro-omega -hydroxy-poly
Dimethyl siloxane, pore-foaming agent ammonium hydrogen carbonate, dichloromethane and methanol mixed solvent high-speed stirred and supersound process form, solution
Uniformly, viscosity is easily adjusted；Deviate under the conditions of 90 DEG C of the temperature and vacuum 0.08MPa dichloromethane in film mixed with methanol it is molten
Agent and thermal decomposition pore-foaming agent ammonium hydrogen carbonate, so that methane sensitive thin film porous, improves sensor response speed.
3. the methane sensitive membrane that the present invention uses is by cage molecule A, optical grade alpha -hydro-omega -hydroxy-poly dimethyl siloxane
Composition, makes full use of the hydroxyl (- OH) in alpha -hydro-omega -hydroxy-poly dimethyl siloxane molecular structure can be with cage molecule A
Coordination occurs for oxygen atom in structure, than the formation such as traditional cage molecule A and polysiloxanes, SAN
Methane sensitive membrane (Sensors and Actuators B, 2005,107 (1):32~39；Analytica Chimica
Acta,2009,633(2):238~243；ZL 200710093035.4；ZL 201010593704.6) evenly, stably, film
Layer quality is higher.
4. in order to strengthen the adhesion of methane sensitive membrane and tapered multimode fiber surface, it is proposed that conical fiber surface is carried out
γ-aminopropyl triethoxysilane coupling agent pretreatment, pass through hydroxyl (- OH) and the silane coupler on conical fiber surface
Sent out respectively between the hydroxyl (- OH) of silicon oxygen bond (Si-O-), silicon oxygen bond (Si-O-) and alpha -hydro-omega -hydroxy-poly dimethyl siloxane
Raw interaction, forms nano level coat, realizes the purpose that methane sensitive membrane strengthens in conical fiber surface adhesion force.
Brief description of the drawings
Fig. 1 is optical fiber methane sensing device structural representation of the present invention based on tapered multimode interference.
Fig. 2 is the transmission-type methane optical fiber sensor structural representation based on tapered multimode interference in Fig. 1.
Embodiment
Below in conjunction with accompanying drawing 1 and Fig. 2, the present invention is described in further details：
Referring to Fig. 1, the optical fiber methane sensing device structure based on tapered multimode interference be by α-hydrogen of the A containing cage molecule-
The both ends of the conical fiber methane transducer 2 of ω-hydroxyl-dimethyl silicone polymer sensitive thin film are connected with single-mode fiber SMF-28
Together, and by sensor 2 it is assembled in sensing device test air chamber 3 and seals.Connected using superradiance wideband light source SLD 1
To the input of sensor 2, the output end of sensor 2 connection Agilent86140B spectroanalysis instruments 4, the spectroanalysis instrument 4 passes through
Gpib interface connecting line 5 connects with computer 6.Test air chamber 3 has an air inlet 7 for being passed through pass-out methane gas 11 to be measured respectively
With gas outlet 8, air inlet 7 is by controlled valve 9 with controlling the mass flow controller 10 of methane gas 11 to be measured to be connected.
Referring to Fig. 2, conical fiber methane transducer 2 includes SMF-28 single-mode fibers 21, tapered multimode fiber 22, methane
Sensitive thin film 23.Sensor is made multimode fibre both ends and single-mode fiber welding need to be drawn multimode fibre using cone machine is drawn
As pyramidal structure, tapered multimode fiber (sensitive zones) length is L, wherein drawing cone length LTFor 0.55~0.85mm, girdle the waist
Diameter D is 25~35 μm.Tapered multimode fiber surface coating A containing cage molecule, the alpha -hydro-omega -hydroxy-poly diformazan of ammonium hydrogen carbonate
The method of radical siloxane sensitive thin film is automatic czochralski method；Sensor after film is in 90 DEG C of temperature, vacuum 0.08MPa conditions
Lower abjection dichloromethane and methanol mixed solvent and thermal decomposition pore-foaming agent ammonium hydrogen carbonate, make methane sensitive thin film porous, hole
Gap rate 12~15%.Multimode fibre is that (105 μm of core diameter, covering is straight by Thorlabs AFS105/125Y graded indexs MMF
125 μm of footpath), length 42mm；Single-mode fiber uses healthy and free from worry SMF-28 optical fiber, 9 μm or so of its core diameter, 125 μm of cladding diameter.
The preparation process of methane optical fiber sensor based on tapered multimode interference includes welding and forms SMF-MMF-SMF knots
Structure, taper is drawn into SMF-TMMF-SMF structures, TMMF conical regions coating methane sensitive membrane and methane sensitive membrane porous：
(1) two section single-mould fiber SMF-28 and one section of multimode fibre MMF (cladding diameter is 125 μm) are taken respectively, are used
Optical fiber wire stripper remove the coat of both types optical fiber, with cut after washes of absolute alcohol with optical fiber cutter to be formed it is smooth
End face, through optical fiber splicer automatic mode welding, cutting MMF makes its length be 42mm, forms SMF-MMF-SMF structures.
(2) optical fiber that welding is formed to SMF-MMF-SMF structures is placed on fused conic clinker, CO2Laser is at 10.6 μm
Locate power 30W, heating region is located among MMF by three-dimensional adjustable shelf.Adjust CO2Laser power 15W, passes through zinc selenide
(ZnSe) lens pillar control CO2150 μm of lasing beam diameter, the upper 3 grams of weights of SMF that MMF heating regions are melted and are connected with MMF
Code constant-tension stretching, you can formed and draw cone length LTFor 0.55~0.85mm, beam waist diameter D is 25~35 μm of SMF-
TMMF-SMF structure conical fibers.
(3) conical region of SMF-TMMF-SMF structure conical fibers is immersed into the DBSA of mass ratio 0.1%
Sodium, 5% sodium hydroxide the aqueous solution in, temperature 60 C, 30 minutes time, distilled water cleaning；By the conical region of oil removing degreasing
Immerse room temperature in the hydrofluoric acid aqueous solution of volume ratio 20% to be roughened 5 minutes, thoroughly cleaned with distilled water after taking-up；Immerse volume ratio
10 seconds in the aqueous solution of 0.1%KH-550 silane couplers, you can form the coating of nanoscale silane coupler in fiber outer surface
Layer, can significantly improve methane sensitive membrane and optical fiber surface adhesive force.
(4) coating liquid of sensitive methane is prepared, and takes 600 μm of ol of cage molecule A, optical grade alpha -hydro-omega -hydroxy-poly diformazan
Radical siloxane 1g (molecular weight 4200, density 0.98g/mL, refractive index 1.41), ammonium hydrogen carbonate pore-foaming agent 0.1g, dichloromethane with
Methanol mixed solvent (volume ratio 5:1) 12mL, stirred 30 minutes, 2000 revs/min of mixing speed, further surpassed with high speed agitator
After sound is well mixed, homogeneous transparent solution is formed.
(5) the SMF-TMMF-SMF structure conical fibers of silane coating coupling agent are placed on automatic pulling machine, by TMMF
Immerse in the coating liquid of sensitive methane, (time of repose 3 minutes, 10~30 lis ms/h of pull rate) is adopted in automatic mode
The methane sensitive thin film to form uniform 0.2~0.5 μm of thickness is lifted with automatic pulling machine, finally in 90 DEG C of temperature, vacuum
0.08MPa, deviate from dichloromethane and methanol mixed solvent and thermal decomposition pore-foaming agent bicarbonate in film under the conditions of 1 hour time
Ammonium, make methane sensitive thin film porous, porosity 12~15%.
The methane optical fiber sensor for the SMF-TMMF-SMF structures for coating methane sensitive thin film is assemblied in test air chamber.
When methane gas to be measured through mass flow controller, test air inlet of air chamber enter and it is thin with the porous methane sensitivity on TMMF surfaces
Film is had an effect, and sensitive membrane refractive index quickly changes；And the change of sensitive membrane refractive index, it will directly change sensor transmission interference
Spectrum signature wavelength Xc.Using the situation of movement of spectroanalysis instrument detection interference spectrum characteristic wavelength, analyte sensors and methane gas
Interference spectrum characteristic wavelength amount of movement Δ λ before and after contactc, you can obtain concentration of methane gas to be measured.
Embodiment 1：One section of multimode fibre MMF and two section single-mould fiber SMF-28 weldings are formed into SMF-MMF-SMF structures,
Multimode fibre length 42mm, multimode fibre draw conical region 0.68mm after cone, 30 μm of beam waist diameter；Conical region precoating surfaces
After silane coupler nanometer coating, then along conical fiber surface coating thickness be 350nm the A containing cage molecule α-hydrogen-ω-
Hydroxyl-dimethyl silicone polymer methane sensitive thin film and porous.Standard Gas of Methane using concentration as 0~3.5% (v/v) is
Object, respectively the sensitive thin film with optical fiber surface have an effect, transmission interference spectrum signature wavelength with concentration of methane gas increase and
Moved to shortwave length direction, and trough characteristic wavelength amount of movement Δ λ near transmission interference spectrum 1550nmcBetween methane concentration c
Linear related, its equation of linear regression is：
Δλc=kc+b
C is concentration of methane gas to be measured in formula, Δ λcTrough characteristic wavelength amount of movement is composed for sensor transmission interference, k is
Slope, b are intercept.
Methane mark of the concentration known for 0,0.1,0.5,1.0,1.5,2.0,2.5,3.0,3.5% (v/v) is used in experiment
Quasi- gas is detected respectively.For some methane concentration, the change of trough characteristic wavelength is composed according to transmission interference, can be obtained
Methane gas is taken to be passed through front and rear wavelength amount of movement Δ λc, the transmission interference spectrum trough feature of corresponding various concentrations gas calibrating gas
Wavelength amount of movement Δ λcRespectively 0,0.40,0.80,1.20,1.60,1.90,2.40,2.92,3.30nm, its linear regression side
Cheng Wei：Δλc=0.8825c+0.2307, coefficient R2=0.9903, i.e., in equation of linear regression k, b be respectively 0.8825,
0.2307。
After methane gas to be measured and the sensor contacts, transmission interference spectrum trough characteristic wavelength amount of movement Δ λcFor
1.82nm, concentration of methane gas c=1.80% to be measured can be calculated, 41 seconds its response times, 43 seconds recovery times.
Embodiment 2：Experiment uses conical region 0.55mm, 25 μm of beam waist diameter, sensitive film thickness 380nm conical fiber
Methane transducer, and the methane Standard Gases using concentration known as 0,0.1,0.5,1.0,1.5,2.0,2.5,3.0,3.5% (v/v)
Body is detected, and corresponding transmission interference spectrum trough characteristic wavelength increases with concentration of methane gas and moved to shortwave length direction, its
Interference spectrum trough characteristic wavelength amount of movement Δ λcRespectively 0,0.42,0.82,1.24,1.62,2.02,2.48,3.02,
3.48nm, equation of linear regression are：Δλc=0.9246c+0.2293, coefficient R2=0.9916, i.e., in equation of linear regression
K, b is respectively 0.9242,0.2293.
After methane gas to be measured and the sensor contacts, transmission interference spectrum trough characteristic wavelength amount of movement Δ λcFor
1.54nm, concentration of methane gas c=1.42% to be measured can be calculated, 36 seconds its response times, desorption time 38 seconds.
Embodiment 3：Using conical region 0.76mm, 32 μm of beam waist diameter, sensitive film thickness 330nm conical fiber methane
Sensor, and the Standard Gas of Methane using concentration known as 0,0.1,0.5,1.0,1.5,2.0,2.5,3.0,3.5% (v/v) enters
Row detection, corresponding transmission interference spectrum trough characteristic wavelength increase with concentration of methane gas and moved to shortwave length direction, and it is interfered
Compose trough characteristic wavelength amount of movement Δ λcRespectively 0,0.42,0.88,1.24,1.72,2.16,2.32,3.04,3.46nm, line
Property regression equation is：Δλc=0.9115c+0.2654, coefficient R2=0.9846, i.e., k, b are respectively in equation of linear regression
0.9115、0.2654。
After methane gas to be measured and the sensor contacts, transmission interference spectrum trough characteristic wavelength amount of movement Δ λcFor
3.18nm, concentration of methane gas c=3.20% to be measured can be calculated, 39 seconds its response times, desorption time 43 seconds.
Embodiment 4：Using conical region 0.85mm, 35 μm of beam waist diameter, sensitive film thickness 430nm conical fiber methane
Sensor, and the Standard Gas of Methane using concentration known as 0,0.1,0.5,1.0,1.5,2.0,2.5,3.0,3.5% (v/v) enters
Row detection, corresponding transmission interference spectrum trough characteristic wavelength increase with concentration of methane gas and moved to shortwave length direction, and it is interfered
Compose trough characteristic wavelength amount of movement Δ λcRespectively 0,0.48,0.88,1.26,1.82,2.28,2.32,3.26,3.58nm, line
Property regression equation is：Δλc=0.9496c+0.2767, coefficient R2=0.9783, i.e., k, b are respectively in equation of linear regression
0.9496、0.2767。
After methane gas to be measured and the sensor contacts, transmission interference spectrum trough characteristic wavelength amount of movement Δ λcFor
0.96nm, concentration of methane gas c=0.72% to be measured can be calculated, 32 seconds its response times, desorption time 35 seconds.
Claims (4)
1. a kind of high sensitivity optical fiber methane sensing device based on tapered multimode interference, including wideband light source, optical fiber methane pass
Sensor, test air chamber, controlled valve, mass flow controller, spectroanalysis instrument and computer；The wideband light source connects optical fiber
Methane transducer, the interference signal of methane optical fiber sensor connect spectroanalysis instrument and computer through single-mode fiber；The optical fiber
Methane transducer is in test air chamber, and test air chamber has the air inlet for being passed through methane gas to be measured and gas outlet, and air inlet leads to
Cross the mass flow controller that controlled valve connection controls methane gas to be measured；
It is characterized in that：The methane optical fiber sensor by after multimode fibre both ends welding single-mode fiber further to multimode fibre
Cone is drawn to form；
The multimode fibre length 42, wherein, draw cone length LTFor 0.55~0.85mm, beam waist diameter D is 25~35 μm；Taper
Multimode fibre outer surface uses the pretreatment of the KH-550 silane couplers aqueous solution to form silane coupler nanometer coat, KH-
550 silane coupler aqueous solution volumetric concentrations are 0.1%, and 10 seconds processing times, coat thickness is nanoscale, and re-coating is porous
Methane sensitive thin film, improve methane sensitive membrane and tapered multimode fiber outer surface adhesive force；The porous methane sensitive thin film is
The porous methane sensitive thin film of alpha -hydro-omega -hydroxy-poly dimethyl siloxane of the A containing cage molecule, 200~300nm of its thickness；Institute
It is first by optical grade alpha -hydro-omega -hydroxy-poly dimethyl siloxane, cage molecule A, pore-foaming agent to state porous methane sensitive thin film
Ammonium hydrogen carbonate is placed in dichloromethane and in methanol mixed solvent, further ultrasound is mixed after being stirred 0.5 hour with 2000 revs/min of rotating speeds
Close uniformly, then automatic lifting is coated on tapered multimode fiber sensitive zones, under the conditions of 90 DEG C of temperature and vacuum 0.08MPa
Deviate from dichloromethane and methanol mixed solvent and thermal decomposition pore-foaming agent ammonium hydrogen carbonate in film, make the methane sensitive thin film to be formed
Porous, porosity are 12~15%；Reagent dosage is respectively 600 μm of ol of cage molecule A, optical grade alpha -hydro-omega -hydroxy-poly
Dimethyl siloxane 1g, pore-foaming agent ammonium hydrogen carbonate 0.1g, volume ratio 5:1 dichloromethane and methanol mixed solvent 12mL；
The wideband light source uses centre wavelength 1550nm superradiance wideband light source SLD, bandwidth 40nm.
2. the high sensitivity optical fiber methane sensing device according to claim 1 based on tapered multimode interference, its feature exist
In：The alpha -hydro-omega -hydroxy-poly dimethyl siloxane methane sensitive thin film of the A containing cage molecule is the porous sensitivity of low-refraction
Material, refractive index 1.41, porosity 12~15%.
3. the high sensitivity optical fiber methane sensing device according to claim 1 or 2 based on tapered multimode interference, its feature
It is：The multimode fibre both ends with single-mode fiber SMF-28 weldings.
4. the high sensitivity optical fiber methane sensing device according to claim 1 or 2 based on tapered multimode interference, its feature
It is：The spectroanalysis instrument is the spectroanalysis instrument of 600~1700nm wave-length coverages.
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