CN102494702A - Long period fiber grating sensor and remote-sensing demodulating system - Google Patents
Long period fiber grating sensor and remote-sensing demodulating system Download PDFInfo
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- CN102494702A CN102494702A CN2011103981388A CN201110398138A CN102494702A CN 102494702 A CN102494702 A CN 102494702A CN 2011103981388 A CN2011103981388 A CN 2011103981388A CN 201110398138 A CN201110398138 A CN 201110398138A CN 102494702 A CN102494702 A CN 102494702A
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Abstract
The invention discloses a long period fiber grating (LPFG) sensor which is structurally characterized by being composed of a common single mode fiber and a hollow core fiber, wherein one end of the common single mode fiber is welded with one end of the hollow core fiber and the length of the common single mode fiber is greater than that of the hollow core fiber; the inner diameter of the hollow core fiber is greater than the diameter of a mode field of the common single mode fiber, and a long-period fiber grating (LPFG) is written into the common single mode fiber. The invention further discloses a remote-sensing demodulating system based on the sensor. The long period fiber grating sensor disclosed by the invention has the beneficial effects that: through the adoption of the long period fiber grating sensor, the LPFG with a transmission type band stop characteristic has a band-pass function; through adoption of the long period fiber grating sensor, the remote-sensing demodulating system has the advantage that a light source and the demodulating system are located at the same end, which is convenient for subsequent process; and the demodulating system can be demodulated by adopting a tunable F-P (Fabry-Perot) demodulating method and a spectrograph is not required to be used in the system, thereby reducing the cost of a remote-sensing system.
Description
Technical field
The present invention relates to a kind of fiber optic remote technology, relate in particular to a kind of long-period fiber grating sensor and telemetry thereof.
Background technology
LPFG (LPFG) can be coupled to cladding mode with the fibre core basic mode, it to external world physical quantity (like refractive index, strain, bending and distortion etc.) have higher sensitivity than Fiber Bragg Grating FBG (FBG).Therefore, LPFG has important use value in biochemistry detection and structural health condition monitoring field.Up to the present, the demodulation means of LPFG sensing are mainly comprised two types, i.e. wave length shift method and edge filter method; There is following problem in these two kinds of demodulation means in practical application:
Adopt the wave length shift method to separate timing, spectrometer is essential instrument, and this not only can make the structure complicated of measurement mechanism, and measuring speed is slow, and has increased the cost of measuring system, simultaneously, has also limited the rig-site utilization of LPFG.
Adopt the edge filter method to separate timing, mainly utilized the linear zone of LPFG transmission stopband, its counter productive be make LPFG to external world the scope of physical quantity be restricted.
In addition; LPFG itself is a kind of device of mode transmission, when utilizing LPFG directly physical quantity to be measured, is used for the instrument of demodulation and the two ends that the input light source lays respectively at total system; Be not easy to subsequent treatment, more serious as far as this problem of long-distance sensing system especially.
Summary of the invention
To the problem in the background technology, the present invention proposes the logical type long-period fiber grating sensor of a kind of low-cost band, its structure is: it is made up of general single mode fiber and hollow-core fiber; One end welding of one end of general single mode fiber and hollow-core fiber, the length of general single mode fiber is greater than hollow-core fiber length; The internal diameter of hollow-core fiber has write LPFG greater than the mode field diameter of general single mode fiber on the general single mode fiber.
Solid section on the exposed end end face of hollow-core fiber is provided with reflectance coating; Temperature environment when reflective film material can be worked according to device is from silver-colored Ag, golden Au or Ti
2O
3In select.
The axial length of hollow-core fiber greater than 0 less than 3mm.
The mode field diameter of general single mode fiber is 10.4 μ m, and the internal diameter of hollow-core fiber is 11 ~ 13 μ m.
On the long-period fiber grating sensor basis of aforementioned structure; The invention allows for a kind of telemetry demodulation system, its structure is: it is made up of long-period fiber grating sensor, pumping source, wavelength division multiplexer, Er-doped fiber, isolator, three-port circulator, coupling mechanism, demodulating system and Polarization Controller;
The output terminal of pumping source all is connected with the input end light path of wavelength division multiplexer with the output terminal of Polarization Controller, and the output terminal of wavelength division multiplexer is connected with the input end light path of isolator through Er-doped fiber; The output terminal of isolator is connected with the input end light path of three-port circulator, and the multiplexing end of the transmitting-receiving of three-port circulator is connected with the general single mode fiber light path of long-period fiber grating sensor; The output terminal of three-port circulator is connected with the input end light path of coupling mechanism, and the output terminal of coupling mechanism is connected with the Polarization Controller light path with demodulating system respectively.
Said demodulating system adopts the most frequently used further demodulation of tunable F-P demodulating system.
Useful technique effect of the present invention is: long-period fiber grating sensor structure of the present invention makes the LPFG that possesses mode transmission band resistance characteristic possess the logical function of band; Have benefited from the long-period fiber grating sensor structure; Telemetry demodulation of the present invention system; Can make light source and demodulating system at same end, be convenient to subsequent treatment, and demodulating system can adopt tunable F-P demodulation method to carry out demodulation process; Avoided in system, using spectrometer, reduced the cost of telemetry system.
Description of drawings
Fig. 1, long-period fiber grating sensor structural representation of the present invention;
Fig. 2, common LPFG transmission spectrum;
Fig. 3, long-period fiber grating sensor transmission spectrum of the present invention;
Fig. 4, telemetry demodulation system architecture synoptic diagram of the present invention;
The output spectral line of Fig. 5, telemetry demodulation of the present invention system.
Embodiment
A kind of long-period fiber grating sensor, its structure is: it is made up of general single mode fiber 1 and hollow-core fiber 2; One end welding of one end of general single mode fiber 1 and hollow-core fiber 2 (hereinafter referred HCF), the length of general single mode fiber 1 is greater than hollow-core fiber 2 length; The internal diameter of hollow-core fiber 2 is greater than the mode field diameter of general single mode fiber 1, and total length has write LPFG (hereinafter referred LPFG) on the general single mode fiber 1.
Common LPFG to the action principle of light is: when the light that transmits in the fibre core in Transmission Fibers through behind the LPFG, LPFG according to phase-matching condition with a certain specific wavelength λ in the wideband light source of input
ResEnergy be coupled in the cladding mode of optical fiber, so in the transmission spectrum of LPFG, can form one with λ
ResStopband (its transmission spectrum is as shown in Figure 2) for centre wavelength;
The principle of work of long-period fiber grating sensor of the present invention is: after touching the general single mode fiber 1 that is provided with LPFG when the light that transmits in the fibre core in Transmission Fibers; That part of light (this part light is designated as the A part) that meets phase-matching condition is coupled in the covering of general single mode fiber 1 and forms cladding mode by LPFG; The A part continues transmission forward with the form of cladding mode; That part of light (this part light is designated as the B part) that does not meet phase-matching condition continues transmission forward in fibre core; When A part and B partly transfer to the intersection of LPFG and HCF; A part just is transferred in the covering of HCF and in the covering of HCF, inspires cladding mode (this cladding mode is designated as the c cladding mode), and B part also transmission is advanced in the hollow of HCF; Get into that part of light in the hollow of HCF, or scattering gets into to inject in the air at last in the covering and loses, or continue in the hollow of HCF transmission forward and finally consume, the B part finally is consumed in a word; The aforesaid c cladding mode that in HCF, is inspired by A part is after being transferred to the end face of HCF; By the end face reflection of HCF return and again transmission advance in the general single mode fiber 1; Again transmission is advanced light in the general single mode fiber 1 owing to meet phase-matching condition, forms passband in the fibre core and exports (I so this part light is coupled back by LPFG again again
Out) (its transmission spectrum is as shown in Figure 3); So long-period fiber grating sensor of the present invention can be described as reflective LPFG (Re-LPFG) again.
When extraneous measurand (such as temperature, strain, bending, refractive index etc.) when changing; The effective refractive index of LPFG cladding mode and grating cycle also change thereupon; Finally cause the drift of LPFG resonance wavelength, the centre wavelength of Re-LPFG passband is drift thereupon also, therefore; The output wavelength of laser instrument also can be drifted about, thereby realizes the purpose of measurement.
For the end face that improves HCF to reflection of light efficient, the present invention has also done following improvement: the solid section on the exposed end end face of hollow-core fiber 2 is provided with reflectance coating 2-1; Reflectance coating 2-1 material can be selected silver-colored Ag, golden Au or Ti according to the temperature environment of work
2O
3
The axial length of hollow-core fiber 2 can be adjusted in greater than 0 scope less than 3mm; The length of hollow-core fiber 2 is short more; The energy loss of device is just more little; But in the practical operation, the accuracy requirement during the shorter cutting of hollow-core fiber 2 is just high more, when the axial length of hollow-core fiber 2 during in the 3mm left and right sides; The energy loss that both can guarantee device can make common cutting equipment just can satisfy processing request again in the reasonable scope; If make the axial length of hollow-core fiber 2 shorter even reach below the 1mm, then must need high-precision cutting equipment, this has just improved the processing cost of device.
A kind of preferred parameter that the inventor proposes is chosen as: the mode field diameter of general single mode fiber 1 is 10.4 μ m, and the internal diameter of hollow-core fiber 2 is 11 ~ 13 μ m.
On the architecture basics of aforesaid long-period fiber grating sensor; The invention allows for a kind of telemetry demodulation system that adopts aforesaid long-period fiber grating sensor, its structure is: it is made up of long-period fiber grating sensor, pumping source 3, wavelength division multiplexer 4, Er-doped fiber 5, isolator 6, three-port circulator 7, coupling mechanism 8, demodulating system 9 and Polarization Controller 10;
The concrete syndeton of above-mentioned a plurality of devices is: the output terminal of the output terminal of pumping source 3 and Polarization Controller 10 all is connected with the input end light path of wavelength division multiplexer 4, and the output terminal of wavelength division multiplexer 4 is connected with the input end light path of isolator 6 through Er-doped fiber 5; The output terminal of isolator 6 is connected with the input end light path of three-port circulator 7; The multiplexing end of the transmitting-receiving of three-port circulator 7 is connected (adopt Transmission Fibers to connect, the length of Transmission Fibers can extend to tens kms) with general single mode fiber 1 light path of long-period fiber grating sensor; The output terminal of three-port circulator 7 is connected with the input end light path of coupling mechanism 8, and the output terminal of coupling mechanism 8 is connected with Polarization Controller 10 light paths with demodulating system 9 respectively.
The principle of work of telemetry demodulation system is: the output of pumping source 3 is coupled into Er-doped fiber 5 through an end (980nm) of 980/1550nm wavelength division multiplexer 4; Form population inversion after 3 pumpings of Er-doped fiber 5 process pumping sources, and amplified spont-aneous emission (ASE) occurs.The wideband light source that ASE is equivalent to import, through 1 mouthful of isolator 6 entering three-port circulators 7, isolator 6 can guarantee light one-way transmission in ring cavity, forms traveling-wave field, thereby has avoided effects of spatial.Then, light gets into 2 mouthfuls from 1 mouthful of three-port circulator 7, obtains bandpass signal through after the filtering of Re-LPFG, and the centre wavelength of passband is the resonance wavelength of LPFG.Bandpass signal through 2 mouthfuls of three-port circulator 7 get into 3 mouthfuls after through the coupling mechanism 8 of a 99:1,99% output terminal of coupling mechanism 8 provides feedback, 1% output terminal provides laser to export demodulating system 9 to.Bandpass signal gets into ring cavity through the other end (1550nm) of wavelength division multiplexer 4 again, accomplishes once circulation.The energy of each cyclic process light wave all obtains amplifying, and the centre wavelength of passband takes the lead in forming laser output.In whole process, can control polarization state of light through regulating Polarization Controller 10, thereby reach the purpose that suppresses the limit mould, optimizes laser activity.When extraneous measurand caused that the effective refractive index of cycle or the cladding mode of LPFG changes, the passband centre wavelength of sensor was drifted about, thereby causes the wavelength of laser instrument to drift about thereupon.
Can find out from the structure of telemetry demodulation system; Light source and demodulating system 9 all are in the same end of long-period fiber grating sensor; And in the prior art, because LPFG has band resistance characteristic, light source and demodulating system 9 must be in the two ends of LPFG; This to the post-processed band sizable inconvenience, and the present invention has just in time solved this problem.
Demodulating system 9 can adopt spectrometer, by its resulting output spectral line referring to Fig. 5, as can be seen from Figure 5; Output spectral line of the present invention is similar to the reflection spectral line of FBG, is therefore separating timing, can utilize the tunable F-P demodulation method that extensively adopts at present fully; Be that demodulating system 9 is when adopting tunable F-P demodulating system; Can avoid the use of spectrometer, obviously reduce the cost of measuring system, improve the dirigibility of system simultaneously.
Claims (6)
1. long-period fiber grating sensor, it is characterized in that: it is made up of general single mode fiber (1) and hollow-core fiber (2); One end welding of one end of general single mode fiber (1) and hollow-core fiber (2), the length of general single mode fiber (1) is greater than hollow-core fiber (2) length; The internal diameter of hollow-core fiber (2) is greater than the mode field diameter of general single mode fiber (1), and general single mode fiber has write LPFG on (1).
2. long-period fiber grating sensor according to claim 1 is characterized in that: the solid section on the exposed end end face of hollow-core fiber (2) is provided with reflectance coating (2-1); The material of reflectance coating (2-1) adopts silver-colored Ag, golden Au or Ti
2O
3
3. long-period fiber grating sensor according to claim 1 is characterized in that: the axial length of hollow-core fiber (2) greater than 0 less than 3mm.
4. long-period fiber grating sensor according to claim 1 is characterized in that: the mode field diameter of general single mode fiber (1) is 10.4 μ m, and the internal diameter of hollow-core fiber (2) is 11 ~ 13 μ m.
5. telemetry demodulation system that adopts long-period fiber grating sensor as claimed in claim 1, it is characterized in that: it is made up of long-period fiber grating sensor, pumping source (3), wavelength division multiplexer (4), Er-doped fiber (5), isolator (6), three-port circulator (7), coupling mechanism (8), demodulating system (9) and Polarization Controller (10);
The output terminal of the output terminal of pumping source (3) and Polarization Controller (10) all is connected with the input end light path of wavelength division multiplexer (4), and the output terminal of wavelength division multiplexer (4) is connected with the input end light path of isolator (6) through Er-doped fiber (5); The output terminal of isolator (6) is connected with the input end light path of three-port circulator (7), and the multiplexing end of transmitting-receiving of three-port circulator (7) is connected with general single mode fiber (1) light path of long-period fiber grating sensor; The output terminal of three-port circulator (7) is connected with the input end light path of coupling mechanism (8), and the output terminal of coupling mechanism (8) is connected with Polarization Controller (10) light path with demodulating system (9) respectively.
6. telemetry demodulation according to claim 5 system is characterized in that: said demodulating system (9) adopts tunable F-P demodulating system.
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| CN103955019A (en) * | 2014-04-25 | 2014-07-30 | 深圳大学 | Expanding type long-period fiber bragg grating based on photonic crystal fiber and manufacturing method of expanding type long-period fiber bragg grating |
| CN108834001A (en) * | 2018-08-01 | 2018-11-16 | 钦州学院 | A kind of electromagnetic remote metering system and method |
| CN108873177A (en) * | 2018-06-20 | 2018-11-23 | 浙江工业大学 | Reflective machinery band-pass filter for long-period fiber gratings |
| JP2022545472A (en) * | 2019-08-21 | 2022-10-27 | オーエフエス ファイテル，エルエルシー | Reduction of coupling loss between optical fibers |
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN103955019A (en) * | 2014-04-25 | 2014-07-30 | 深圳大学 | Expanding type long-period fiber bragg grating based on photonic crystal fiber and manufacturing method of expanding type long-period fiber bragg grating |
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| CN108873177A (en) * | 2018-06-20 | 2018-11-23 | 浙江工业大学 | Reflective machinery band-pass filter for long-period fiber gratings |
| CN108873177B (en) * | 2018-06-20 | 2023-11-28 | 浙江工业大学 | Reflection type mechanical long period fiber grating band-pass filter |
| CN108834001A (en) * | 2018-08-01 | 2018-11-16 | 钦州学院 | A kind of electromagnetic remote metering system and method |
| JP2022545472A (en) * | 2019-08-21 | 2022-10-27 | オーエフエス ファイテル，エルエルシー | Reduction of coupling loss between optical fibers |
| JP7352015B2 (en) | 2019-08-21 | 2023-09-27 | オーエフエス ファイテル，エルエルシー | Coupling loss reduction between optical fibers |
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