CN105044033A - Intensity-demodulation optical fiber gas sensing device - Google Patents
Intensity-demodulation optical fiber gas sensing device Download PDFInfo
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Abstract
An intensity-demodulation optical fiber gas sensing device includes a broadband light source, an optical fiber coupler, a hollow optical fiber, a long-period fiber Bragg grating, an optical circulator, a chirped fiber grating, a first photoelectric detector, a second photoelectric detector and a single chip microcomputer. An output terminal of the broadband light source is connected to an input terminal of the optical fiber coupler. A first output terminal of the optical fiber coupler is connected to the input terminal of the hollow optical fiber. The output terminal of the hollow optical fiber is connected to the input terminal of the long-period fiber Bragg grating. The output terminal of the long-period fiber Bragg grating is connected to the input terminal of the optical circulator. The first output terminal of the optical circulator is connected to the input terminal of the chirped fiber grating. The input terminal of the first photoelectric detector is connected to a second output terminal of the optical circulator. The input terminal of the second photoelectric detector is connected to the second output terminal of the optical fiber coupler. The output terminals of the first photoelectric detector and the second photoelectric detector are connected to the single chip microcomputer. The device is small in size, is low in cost and is simple in signal processing.
Description
Technical field
The invention belongs to Fibre Optical Sensor field, relate to a kind of intensity demodulation type optical fiber gas sensing device.
Background technology
Along with improving constantly and pay attention to day by day to environmental protection of people's living standard, people more and more pay attention to the development of gas sensor.Because not only monitor the concentration of the poisonous and inflammable gas such as sulfuretted hydrogen, carbon monoxide, chlorine, methane and flammable hydrocarbon in the industrial and mining enterprises such as oil, mining, semi-conductor industry, and detect in the automotive industry in the exhaust gas concentrations such as carbon dioxide, sulphuric dioxide and carbon monoxide, gas sensor all plays an important role.At present, traditional gas sensing is as electrochemical gas sensor, semiconductor gas sensor, vapor-phase chromatography gas sensor.Electrochemical gas sensor can be applicable to portable type measuring, but its complex structure, temperature influence is larger.Semiconductor gas sensor has good sensitivity, but its less stable, affected by environment larger.The selectivity of vapor-phase chromatography gas sensor is good, and the material that character is close is also out separable, but detection speed is its defect slowly.So, traditional gas sensor can not have concurrently be simultaneously easy to carry, simple, highly sensitive, the anti-external environmental interference of structure manufacture, selectivity be good, the functions such as reaction velocity is fast.
Along with the development of optical fiber sensing technology, people start to utilize fiber sensor measuring gas concentration.Fiber gas sensor is highly sensitive, bandwidth, dynamic range is large, loss is little, is suitable for the on-line measurement of long distance, is suitable for measuring flammable explosive gas or working in Flammable atmosphere and strong electromagnetic interference environment, sensing unit structures is simple, cost is low, is easy to form optical fiber sensing network, as spectral absorption type, fluorescent type, evanescent field type fiber gas sensor etc.Spectral absorption type Fibre Optical Sensor overcomes the danger that traditional sensors is easily blasted when measuring inflammable gas, and make measurement sensistivity be improved, but spectral absorption type sensor optical path is complicated, volume is large, be not suitable for carrying, be therefore restricted in practice.Fluorescent type fiber gas sensor is good to the distinctive of measured matter, but detection system is complicated, and cost is higher.Evanescent field type Fibre Optical Sensor volume is little, framework simple, but any material in evanescent field all can cause weakening of its luminous power, easily causes and surveys by mistake.Existing fiber gas sensor patent, complex structure, technological requirement is high, and some is not all optical fibre structure, and its photoelectric processing unit is complicated, adopts spectrometer information of carrying out to export and also makes sensor-based system be not easy to carry, and improve cost.Publication number is the patent of invention " a kind of fiber gas sensor based on Fourier transform spectrometry " of CN101710068A, the structure of air chamber makes light path increase, but bad stability, and interference spectrum will be converted into Fourier's signal by the process of this sensor signal process, the complex process of signal transacting adds the cost of sensor.Publication number is the utility model patent " fiber gas sensor " of CN2581979Y, this structure is not all-fiber sensing arrangement, complicated process of preparation, cost is high, easily error is there is in manufacture process, and the structure of cone prism group is unfavorable for measuring under shake environment, make this sensor be not easy to carry, institute thinks that field condition measurement brings difficulty.
Summary of the invention
The object of the present invention is to provide a kind of intensity demodulation type optical fiber gas sensing device, it is simple that this device has signal transacting, and volume is little, low cost and other advantages.
In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is: a kind of intensity demodulation type optical fiber gas sensing device, comprises wideband light source (1), fiber coupler (2), hollow-core fiber (3), long period fiber grating (4), optical circulator (5), chirped fiber grating (6), the first photodetector (7) and the second photodetector (8), single-chip microcomputer (9), the output terminal of wideband light source (1) is connected with the input end (201) of fiber coupler (2), first output terminal (202) of fiber coupler (2) is connected with the input end of hollow-core fiber (3), the output terminal of hollow-core fiber (3) is connected with the input end of long period fiber grating (4), the output terminal of long period fiber grating (4) is connected with the input end (501) of optical circulator (5), first output terminal (502) of optical circulator (5) is connected with the input end of chirped fiber grating (6), the input end of the first photodetector (7) is connected with second output terminal (503) of optical circulator (5), the input end of the second photodetector (8) is connected with second output terminal (203) of fiber coupler (2), the output terminal of the first photodetector (7) and output terminal access single-chip microcomputer (9) of the second photodetector (8).
The coupling mechanism that described fiber coupler (2) is 1*2, and the first output terminal (202) is 90: 10 with the splitting ratio of the second output terminal (203).
Fibre core (301) diameter of described hollow-core fiber (3) is 50-80 μm, and length is 100-200 μm; Hollow-core fiber (3) is evenly distributed with aperture (302), aperture (302) diameter is 10-20 μm, and spacing is 30 μm; Gas enters the fibre core (301) of hollow-core fiber by aperture (302), interacts with light.
Described fibre core (301), as F-P cavity, produces interference spectrum.
Described long period fiber grating (4) periodicity is 40, and grid region length is 1-2cm, and resonance wavelength is 1554nm, and resonance wave strong point attenuation amplitude is 30dB.
Described chirped fiber grating (6) grid region length is 1-2cm, and centre wavelength is 1556nm, and reflection bandwidth is 4nm.
Described the first photodetector (7) and the minimum resolution of the second photodetector (8) are 0.02 μ W.
A kind of method for sensing of intensity demodulation type optical fiber gas sensing device, the aperture (302) of gas to be measured on hollow-core fiber (3) enters fibre core (301), light multiple reflections between the both sides end face of fibre core (301) forms F-P interferes, export from the output terminal of hollow-core fiber (3), and the movement of different size can be there is according to the concentration of gas in the peak wavelength exporting interference spectrum; The output light of hollow-core fiber (3) is when long period fiber grating (4), the center resonance wavelength 1554nm of long period fiber grating (4) to one section of wavelength coverage 1554-1558nm of right shoulder flat region plays the effect of linear edge filters, wavelength is moved the change being converted into light intensity; The reflected spectral range of chirped fiber grating (6) is limited in wavelength coverage 1554-1558nm, play the effect of bandpass filter, the light reflected through chirped fiber grating (6) is exported by second output terminal (503) of optical circulator (5), enter the first photodetector (7) and obtain light intensity, obtain gas concentration size to be measured by the light intensity-gas concentration linear relationship of demarcating in advance.
Usefulness of the present invention is:
1. adopt the method measure gas concentrations of intensity demodulation, signal transacting is simple, quick, improves the practicality of sensing device.
2. use photodetector replaces the spectrometer in general sensor-based system, reduces instrument cost, reduces the volume of sensing device, be easy to carry.
3. adopt the method for twin-beam reference measure, can the impact of compensatory light fluctuation itself, realization is accurately measured.
4. adopt all-fiber transducing head structure measure gas concentrations, volume is little, highly sensitive.
Accompanying drawing explanation
Below in conjunction with accompanying drawing and concrete embodiment, the invention will be further described.
Fig. 1 is installation drawing of the present invention;
Fig. 2 is the schematic diagram of hollow-core fiber 3 of the present invention;
Fig. 3 is the F-P output spectrum figure under carbon dioxide variable concentrations of the present invention;
Fig. 4 be wavelength of the present invention move be converted into light intensity change schematic diagram.
In accompanying drawing, 1: wideband light source; 2: fiber coupler; 201: the input end of fiber coupler; 202: the first output terminal of fiber coupler; 203: the second output terminal of fiber coupler; 3: hollow-core fiber; 301: fibre core; 302: aperture; 4: long period fiber grating; 5: optical circulator; 501: the input end of optical circulator; 502: the first output terminal of optical circulator; 503: the second output terminal of optical circulator; 6: chirped fiber grating; 7: the first photodetector 8: the second photodetectors; 9: single-chip microcomputer;
Specific implementation method
In Fig. 1, comprise wideband light source 1, fiber coupler 2, hollow-core fiber 3, long period fiber grating 4, optical circulator 5, chirped fiber grating 6, first photodetector 7 and the second photodetector 8, single-chip microcomputer 9, the output terminal of wideband light source 1 is connected with the input end 201 of fiber coupler 2, first output terminal 202 of fiber coupler 2 is connected with the input end of hollow-core fiber 3, the output terminal of hollow-core fiber 3 is connected with the input end of long period fiber grating 4, the output terminal of long period fiber grating 4 is connected with the input end 501 of optical circulator 5, first output terminal 502 of optical circulator 5 is connected with the input end of chirped fiber grating 6, the input end of the first photodetector 7 is connected with the second output terminal 503 of optical circulator 5, the input end of the second photodetector 8 is connected with the second output terminal 203 of fiber coupler 2, the output terminal of the first photodetector 7 and the output terminal access single-chip microcomputer 9 of the second photodetector 8.
In Fig. 2, fiber coupler 2 first output terminal 202 export optical transport to hollow-core fiber 3 time, fibre core 301 as F-P cavity, light between the both sides end face of fibre core 301 multiple reflections and formed F-P interference, produce interference spectrum, export from the output terminal of hollow-core fiber 3.Gas enters the fibre core 301 of hollow-core fiber by aperture 302, interacts with light; When gas concentration change to be measured, the peak wavelength of interference spectrum is caused to be moved.
A kind of method for sensing of intensity demodulation type optical fiber gas sensing device: the aperture 302 of gas to be measured on hollow-core fiber 3 enters fibre core 301, light multiple reflections between the both sides end face of fibre core 301 forms F-P interferes, export from the output terminal of hollow-core fiber 3, and the movement of different size can be there is according to the concentration of gas in the peak wavelength exporting interference spectrum; The output light of hollow-core fiber 3 is when long period fiber grating 4, the center resonance wavelength 1554nm of long period fiber grating 4 to one section of wavelength coverage 1554-1558nm of right shoulder flat region plays the effect of linear edge filters, wavelength is moved the change being converted into light intensity; The reflected spectral range of chirped fiber grating 6 is limited in wavelength coverage 1554-1558nm, play the effect of bandpass filter, the light reflected through chirped fiber grating 6 is exported by the second output terminal 503 of optical circulator 5, obtain light intensity by the first photodetector 7, obtain gas concentration size to be measured by the light intensity-gas concentration linear relationship of demarcating in advance.
Composition graphs 3, Fig. 4, a kind of intensity demodulation type optical fiber gas sensing device course of work is: the light input optical fibre coupling mechanism 2 that wideband light source 1 sends, light is divided into two-way and exports measurement light and reference light by fiber coupler 2, first output terminal 202 of fiber coupler 2 exports measures light to hollow-core fiber 3, the aperture 302 of gas to be measured on hollow-core fiber 3 enters fibre core 301, light multiple reflections between the both sides end face of fibre core 301 forms F-P interferes, export from the output terminal of hollow-core fiber 3, and the movement of different size can be there is according to the concentration of gas in the peak wavelength exporting interference spectrum, F-P output spectrum figure under carbon dioxide variable concentrations of the present invention as shown in Figure 3, when density of carbon dioxide gas increases to 30% from 0%, the peak wavelength of F-P output spectrum moves about 30pm.The output light of hollow-core fiber 3 is when long period fiber grating 4, the center resonance wavelength 1554nm of long period fiber grating 4 to one section of wavelength coverage 1554-1558nm of right shoulder flat region plays the effect of linear edge filters, wavelength is moved the change being converted into light intensity, wavelength of the present invention as shown in Figure 4 moves and is converted into light intensity change schematic diagram, when wavelength move be in wavelength coverage 1554-1558nm time, the output intensity that the light of different wave length is obtained by long period fiber grating 4 varies in size.The output light of long period fiber grating 4 enters the input end 501 of optical circulator 5, chirped fiber grating 6 is inputted from the first output terminal 502 of optical circulator 5, the reflected spectral range of chirped fiber grating 6 is limited in wavelength coverage 1554-1558nm, play the effect of bandpass filter, the light of its commplementary wave length is exported by chirped fiber grating 6 right-hand member, is not received by the system; The light reflected through chirped fiber grating 6 is exported by the second output terminal 503 of optical circulator 5, enters the first photodetector 7 and obtains light intensity, obtain gas concentration size to be measured by the light intensity-gas concentration linear relationship of demarcating in advance; Second output terminal 203 of fiber coupler 2 exports reference light and transfers to the second photodetector 8, and the output intensity of the first photodetector 7 and the second photodetector 8 is done division arithmetic by single-chip microcomputer 9, eliminates the impact of light source fluctuation itself.
Claims (6)
1. an intensity demodulation type optical fiber gas sensing device, comprises wideband light source (1), fiber coupler (2), hollow-core fiber (3), long period fiber grating (4), optical circulator (5), chirped fiber grating (6), the first photodetector (7) and the second photodetector (8), single-chip microcomputer (9); The output terminal of wideband light source (1) is connected with the input end (201) of fiber coupler (2), the input end of the first photodetector (7) is connected with second output terminal (503) of optical circulator (5), the input end of the second photodetector (8) is connected with second output terminal (203) of fiber coupler (2), output terminal access single-chip microcomputer (9) of the first photodetector (7) and the second photodetector (8); It is characterized in that, first output terminal (202) of fiber coupler (2) is connected with the input end of hollow-core fiber (3), the output terminal of hollow-core fiber (3) is connected with the input end of long period fiber grating (4), the output terminal of long period fiber grating (4) is connected with the input end (501) of optical circulator (5), and first output terminal (502) of optical circulator (5) is connected with the input end of chirped fiber grating (6).
2. a kind of intensity demodulation type optical fiber gas sensing device according to claim 1, is characterized in that: the minimum resolution of the first photodetector (7) and the second photodetector (8) is 0.02 μ W.
3. a kind of intensity demodulation type optical fiber gas sensing device according to claim 1, it is characterized in that: fibre core (301) diameter of described hollow-core fiber (3) is 50-80 μm, length is 100-200 μm, hollow-core fiber (3) is evenly distributed with aperture (302), aperture (302) diameter is 10-20 μm, and spacing is 30 μm.
4. a kind of intensity demodulation type optical fiber gas sensing device according to claim 1 or 3, is characterized in that, described fibre core (301), as F-P cavity, produces interference spectrum.
5. a kind of intensity demodulation type optical fiber gas sensing device according to claim 1, it is characterized in that: described long period fiber grating (4) periodicity is 40, grid region length is 1-2cm, and resonance wavelength is 1554nm, and resonance wave strong point attenuation amplitude is 30dB; Described chirped fiber grating (6) grid region length is 1-2cm, and centre wavelength is 1556nm, and reflection bandwidth is 4nm.
6. the method for sensing of a kind of intensity demodulation type optical fiber gas sensing device according to claim 1, it is characterized in that, the aperture (302) of gas to be measured on hollow-core fiber (3) enters fibre core (301), light multiple reflections between the both sides end face of fibre core (301) forms F-P interferes, export from the output terminal of hollow-core fiber (3), and the movement of different size can be there is according to the concentration of gas in the peak wavelength exporting interference spectrum; The output light of hollow-core fiber (3) is when long period fiber grating (4), the center resonance wavelength 1554nm of long period fiber grating (4) to one section of wavelength coverage 1554-1558nm of right shoulder flat region plays the effect of linear edge filters, wavelength is moved the change being converted into light intensity; The reflected spectral range of chirped fiber grating (6) is limited in wavelength coverage 1554-1558nm, play the effect of bandpass filter, the light reflected through chirped fiber grating (6) is exported by second output terminal (503) of optical circulator (5), enter the first photodetector (7) and obtain light intensity, obtain gas concentration size to be measured by the light intensity-gas concentration linear relationship of demarcating in advance.
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| CN110907384A (en) * | 2019-12-10 | 2020-03-24 | 中国海洋大学 | Gas detection system based on Fourier domain optical coherent absorption spectrum technology and working method thereof |
| CN113624267A (en) * | 2021-07-21 | 2021-11-09 | 浙江理工大学 | Fiber grating center wavelength demodulation system and demodulation instrument based on edge filtering |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN110907384A (en) * | 2019-12-10 | 2020-03-24 | 中国海洋大学 | Gas detection system based on Fourier domain optical coherent absorption spectrum technology and working method thereof |
| CN113624267A (en) * | 2021-07-21 | 2021-11-09 | 浙江理工大学 | Fiber grating center wavelength demodulation system and demodulation instrument based on edge filtering |
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