CN102359943B - Photonic crystal fibre-optical air chamber active cavity absorption-type gas detection device - Google Patents
Photonic crystal fibre-optical air chamber active cavity absorption-type gas detection device Download PDFInfo
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Abstract
The invention relates to the field of fibre-optical sensing and fibre-optical gas detection. The invention aims to solve a problem that in a trace quantity detection of gas pollutant, a fibre-optical gas detection technology has difficulty in detecting and low detection sensitivity due to small ammonia gas absorption coefficient in ammonia gas detection, and also problems of short absorption distance and low detection sensitivity of a one way air chamber due to restriction by gas pool length and weak stability of a long-distance air chamber due to complex optical configuration of the air chamber. A technical scheme of the invention is as below: the photonic crystal fibre-optical air chamber active cavity absorption-type gas detection device comprises a 980 nm semiconductor laser 1, a 980/1550 nm wavelength division multiplexing 2, an Er-doped fiber 3, a hollow photonic crystal fiber 4, a fibre-optical reflector 5, a tunable fiber grating 6 and a fibre-optical power meter 7. The invention is mainly applied to fibre-optical gas detection.
Description
Technical field
The present invention relates to Fibre Optical Sensor and fiber-optic fiber gas detection field, specifically relate to photonic crystal fibre-optical air chamber active cavity absorption-type gas detection device.
Background technology
In industrial processes, in time, exactly to inflammable, explosive, poisonous, harmful gas carry out monitoring and prediction and automatically control become one of major issue that the industries such as current coal, oil, chemical industry, electric power need to be resolved hurrily.Based on the gaseous spectrum absorption process, utilize the low loss window (1～2 μ m) of silica fibre to carry out gas concentration and detect and obtained to pay close attention to widely.In this wave band, find many pollution gas or toxic gas, for example acetylene (C
2H
2), methane (CH
4) and carbon monoxide (CO), ammonia (NH
3) etc. gas, absorption line is arranged.Wherein, ammonia is one of atmosphere pollution common in industrial production waste gas, and because ammonia is smaller at the near ir absorption peaks absorption cross section, so infrared direct absorption-type optical fiber ammonia detection is more difficult, sensitivity is low.Usually use optoacoustic ammonia optic Fiber Detecting Technology and optics-microwave double resonance ammonia optic Fiber Detecting Technology instead.Since the people such as V.M.Baev in 1992 successfully utilize diode to realize the active inner cavity detection of gas as light source, active inner cavity absorbs gas detection technology to begin receive people's concern and develop rapidly. in recent years, have benefited from the development of Fiber laser technology and optical fiber sensing technology, optical active fiber inner chamber gas detection technology also develops rapidly, and becomes one of study hotspot of gas detection technology.
The active inner cavity gas detection technology refers to sample is placed in detection technique in laserresonator, that is to say and also have the absorption of sample medium in laserresonator except gain medium, the chamber inner light beam is laser concussion spectral line, again the absorption of sample spectral line. the optical active fiber ammonia detects and usually utilizes Er-doped fiber as gain media, main cause be because: first, erbium-doped fiber gain margin wider (Fig. 1), and comprise ammonia in the several important absorption peaks suctions of near infrared (Fig. 2); The second, erbium-doped fiber laser power stable output.
Detecting based on erbium-doped fiber laser instrument active inner cavity gas is to insert the sample chamber in fiber laser cavity. and Fig. 1 is a kind of typically based on erbium-doped fiber laser instrument active inner cavity gas detecting system. and erbium doped fiber laser is by 980nm or 1480nm diode-end-pumped.Realize that by implant air chamber between erbium optical fiber and fiber reflector inner chamber detects.Traditional air chamber generally is divided into one way air chamber and long-range air chamber.The one way air chamber is made of a pair of optical fiber collimator usually, because the optical fiber collimator operating distance generally is no more than 50cm, makes effective absorption distance of gas very short, has therefore greatly limited system testing sensitivity.On the other hand, the one way air chamber causes the air chamber volume large owing to improving absorption distance, uses underaction, is unfavorable for site activity utilization in industry.The long-range air chamber mainly rely on special light path design make light in air chamber repeatedly toward interflection, thereby increased effective light path of gas.Although the long-range air chamber is little than one way air chamber volume, effectively absorption distance is long, and structure is more complicated, debug difficulties, poor stability.In addition, due to light Multi reflection in air chamber, can cause larger loss.Hollow-core photonic crystal fiber is a kind of novel Transmission Fibers, and its leaded light mechanism is all different from common index guide structure type and full-internal reflection type optical fiber.The hollow-core photonic crystal fiber fibre core is the airport structure, the two-dimensional photon crystal structure that covering is comprised of the air of periodic arrangement.The pattern that this structure can be supported certain wavelength in the photon band gap of covering is propagated in airport core district, and can realize that 95% is bound in air-core with glazing.Fig. 3 is two kind of 1.5 micron waveband Hollow-Core Photonic Crystal Fibers sectional view that the commercialization of Denmark NKT company is produced.Wherein 7 thin-walled kapillaries are removed in a central area, 10 microns of its fibre core airport diameters, loss can be that the photon band-gap optical fiber that 19 quartz ampoules are made is taken out in the central area lower than 0.03db/m.b 1.55 microns of centre wavelengths, its center airport diameter is 10 microns, locates to such an extent that loss can be reduced to 0.02dB/m at 1.57 microns.Utilize hollow-core photonic crystal fiber can effectively solve traditional one way air chamber due to the restriction that is subjected to gas cell length as the full optical fiber optical optical road of air chamber, cause absorption distance short, detection sensitivity is low, and the long-range air chamber exists optical texture complexity in air chamber, the shortcomings such as poor stability.
Summary of the invention
For overcoming the deficiencies in the prior art, solve in the gas pollutant trace detection, gas detection with optical fiber on ammonia detects because the ammonia absorption coefficient is little, detection difficult, the difficulty that detection sensitivity is low; Solve in traditional absorption-type optical fiber ammonia gas detection technique, the one way air chamber causes absorption distance short due to the restriction that is subjected to gas cell length, and detection sensitivity is low, and the long-range air chamber is due to optical texture complexity in air chamber, the shortcomings such as poor stability.for achieving the above object, the technical solution used in the present invention is: photonic crystal fibre-optical air chamber active cavity absorption-type gas detection device, comprise: 980 Nano semiconductor laser instruments 1, 980/1550 nanometer wave division multiplexer 2, Er-doped fiber 3, Hollow-Core Photonic Crystal Fibers 4, fiber reflector 5, tunable fiber grating 6, Fiber Dynamometer 7, 980 Nano semiconductor laser instruments 1 adopt coupling fiber to output to 980/1550 nanometer wave division multiplexer 2, 980/1550 nanometer wave division multiplexer 2 other ends and Er-doped fiber 3 weldings, movable access 1m vast sky core photonic crystal fiber between Er-doped fiber 3 other ends and fiber reflector, the tunable fiber grating of fiber reflector 5 and 980/1550 nanometer wave division multiplexer 2 the 3rd end welding consists of resonator cavity, 980 Nano semiconductor laser instrument 1 tunable fiber grating outputs, and utilize Fiber Dynamometer 7 to survey output power and wavelength, be connected between Hollow-Core Photonic Crystal Fibers 4 and Er-doped fiber 3 to adopt and be flexibly connected, reserve the 100um space between two fiber end faces, it is regional that ambient gas this space of process and hollow-core photonic crystal fiber 4 end faces enter hollow-core photonic crystal fiber 4 center pits.
Hollow-core photonic crystal fiber 4 is intertwined into some circles, to increase laser to the absorption light path of gas.
Er-doped fiber 3 and 980 Nano semiconductor laser instruments 1 consist of erbium doped fiber laser, during work, at first erbium doped fiber laser is operated in steady state (SS), then reduce gradually pump power, make erbium doped fiber laser operate at and slightly surpass under the condition of threshold value, obtain higher detection sensitivity to utilize erbium doped fiber laser in the nonlinear effect of Near Threshold.
Its characteristics of the present invention are: the employing hollow-core photonic crystal fiber is air chamber, can realize effective absorption distance of several meters, is conducive to put forward the degree of detection of optical fiber ammonia detection technique; Employing can improve the gas detection sensitivities such as ammonia greatly based on the active inner cavity absorption-type gas detection technology of erbium doped fiber laser.
Description of drawings
Fig. 1 is Er-doped fiber typical absorption spectrum and gain trace.Horizontal ordinate is wavelength, the unit nanometer, and ordinate is absorptivity, the db/m of unit.
Fig. 2 is that ammonia is at the absorption line of 1530nm-1542nm.Horizontal ordinate is wavelength, and unit micron, ordinate are transposition section, the cm of unit
2
Fig. 3 (a) is HC-1550-02 hollow-core photonic crystal fiber end view drawing.
(b) be HC19-1550-01 hollow-core photonic crystal fiber sense end face.
Fig. 4 photonic crystal fiber air chamber active inner cavity ammonia detection system structural drawing.Wherein: 1 is that 980 semiconductor lasers, 980/15502 are that wavelength division multiplexer, 3 is that Er-doped fiber, 4 is that Hollow-Core Photonic Crystal Fibers, 5 is that fiber reflector, 6 is that tunable fiber grating, 7 is Fiber Dynamometer.
Embodiment
A kind of take hollow-core photonic crystal fiber as air chamber, based on the active inner cavity absorption-type ammonia detection technique of erbium doped fiber laser.It comprises: 980 semiconductor lasers (1), 980/1550 wavelength division multiplexer 2, Er-doped fiber 3, Hollow-Core Photonic Crystal Fibers 4, fiber reflector 5, tunable fiber grating 6, Fiber Dynamometer 7, the characteristics of photonic crystal fiber air chamber active inner cavity ammonia detection technique are: full optical fiber optical optical road design, debugging is simple, and is highly sensitive.The sensitivity raising mainly contains following reason: the firstth, and laser Multiple through then out effect, laser cavity is a resonator cavity, laser is vibration repeatedly in the chamber, just looks like light Multiple through then out testing sample.Material is deferred to Beer-Lambert law to monochromatic absorption.The order of reflection of light beam in resonator cavity depends primarily on the reflectivity of outgoing mirror, if the reflectivity of fiber loop mirror is 100%, the transmissivity of output grating is 2%, if so intracavity power density is 50 times of laser output power. intracavity power density does not make corresponding absorption reach capacity, in the chamber, absorbing laser Strength Changes amount has increased 50 times when absorbing outside the chamber, be also to absorb the minimum detectable absorption value in the chamber than dwindling 50 times outside the chamber, in other words, detection sensitivity has improved 50 times. and the secondth, the nonlinear effect of Near Threshold laser gain.According to laser physics, in the situation that pump power is constant, over the threshold value workspace, due to the subtle change of ammonia absorption loss, can cause the acute variation of laser power in the chamber slightly.The 3rd is the mode competition effect.For uniform gain dielectric laser device, a kind of mode competition effect is arranged, although namely the initial gain curve includes a plurality of vertical touching, the mould gain in strength that gains high will consume the intensity of other moulds, makes final oscillation mode only surplus next.In fact, due to reasons such as the doping of spatial hole burning, erbium optical fiber are inhomogeneous, the zlasing mode of erbium doped fiber laser is a lot.Ammonia is that the arrowband absorbs near infrared absorption, when with broad band laser irradiation arrowband absorption ammonia, there is mode competition in ammonia to the absorption of the different spectral lines of laser, and the result of mode competition strengthens the absorption intensity of absorbent core greatly, thereby improves the ammonia detection sensitivity.The 4th, adopt hollow-core photonic crystal fiber to do air chamber, because optical fiber can be wound around, increased effective absorption light path of laser degree ammonia, thereby greatly improved the ammonia detection sensitivity.
Further describe the present invention below in conjunction with drawings and Examples.
Fig. 4 is a photonic crystal fiber air chamber active inner cavity absorption-type ammonia detection system structural representation.Whole system realizes by the hollow photon crystal air chamber being inserted optical fiber erbium doped fiber laser resonator cavity.Erbium doped fiber laser is by 980 diode-end-pumpeds.Pumping 980 semiconductor lasers adopt coupling fiber output, output optical fibre and 980/1550 wavelength division multiplexer welding.The long Er-doped fiber welding of the wavelength division multiplexer other end and 4m.Movable access 1m vast sky core photonic crystal fiber between the Er-doped fiber other end and fiber reflector.Resonator cavity is made of the tunable fiber grating of light reflecting mirror and wavelength division multiplexer the 3rd end welding.Laser tunable fiber grating output again, and utilize fiber optic wavelength power instrumentation output power and wavelength.Be connected between Hollow-Core Photonic Crystal Fibers and Er-doped fiber to adopt and be flexibly connected.Reserve the 100um space between two fiber end faces.Ambient gas enters the center through the Hollow-Core Photonic Crystal Fibers end face, and it is aerial.Hollow-core photonic crystal fiber is intertwined into some circles, to increase laser to the absorption light path of ammonia.Under the pump power certain condition, utilize the fibre-optical tunable wave grating to come the output wavelength of tuning erbium doped fiber laser, and record the corresponding output power of corresponding each wavelength, thereby obtain ammonia at the near infrared absorption spectral line.Last according to the absorbance of certain absorption peak and the concentration of ammonia ammonia in the absorption cross section of this absorption peak is finally inversed by gaseous sample to be measured.
Claims (3)
1. photonic crystal fibre-optical air chamber active cavity absorption-type gas detection device, it is characterized in that, comprise: 980 Nano semiconductor laser instruments (1), 980/1550 nanometer wave division multiplexer (2), Er-doped fiber (3), hollow-core photonic crystal fiber (4), fiber reflector (5), tunable fiber grating (6), Fiber Dynamometer (7), 980 Nano semiconductor laser instruments (1) adopt coupling fiber to output to 980/1550 nanometer wave division multiplexer (2), 980/1550 nanometer wave division multiplexer (2) other end and Er-doped fiber (3) welding, movable access 1m vast sky core photonic crystal fiber between Er-doped fiber (3) other end and fiber reflector, the tunable fiber grating of fiber reflector (5) and 980/1550 nanometer wave division multiplexer (2) the 3rd end welding consists of resonator cavity, 980 Nano semiconductor laser instrument (1) tunable fiber grating outputs, and utilize Fiber Dynamometer (7) to measure tunable fiber grating output power and wavelength, be connected between hollow-core photonic crystal fiber (4) and Er-doped fiber (3) to adopt and be flexibly connected, reserve 100 μ m spaces between two fiber end faces, it is regional that ambient gas this space of process and hollow-core photonic crystal fiber end face enter the hollow-core photonic crystal fiber center pit.
2. device as claimed in claim 1, is characterized in that, hollow-core photonic crystal fiber is intertwined into some circles, to increase laser to the absorption light path of gas.
3. device as claimed in claim 1, it is characterized in that, Er-doped fiber (3) and 980 Nano semiconductor laser instruments (1) consist of erbium doped fiber laser, during work, at first erbium doped fiber laser is operated in steady state (SS), then reduce gradually pump power, make erbium doped fiber laser operate at and slightly surpass under the condition of threshold value, obtain higher detection sensitivity to utilize erbium doped fiber laser in the nonlinear effect of Near Threshold.
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| CN103512860A (en) * | 2012-06-19 | 2014-01-15 | 中南大学 | Method for monitoring dissolved gas in transformer oil based on terahertz wave photonic crystal fibers |
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| CN103335979A (en) * | 2013-07-16 | 2013-10-02 | 山东省科学院激光研究所 | High-sensitivity inner-cavity gas detector based on composite cavity optical fiber laser device |
| CN103913423A (en) * | 2014-03-07 | 2014-07-09 | 天津大学 | Pulse broadband light source high-capacity photonic crystal fiber gas detection method, and system |
| CN103983577B (en) * | 2014-05-16 | 2016-05-04 | 天津大学 | Punching photonic crystal fiber air chamber active inner cavity gas detection method and device |
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