CN100350219C - Method and device for multiplexing and demodulating sensor based on optical fiber grating in long cycle - Google Patents
Method and device for multiplexing and demodulating sensor based on optical fiber grating in long cycle Download PDFInfo
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- CN100350219C CN100350219C CNB2005100613834A CN200510061383A CN100350219C CN 100350219 C CN100350219 C CN 100350219C CN B2005100613834 A CNB2005100613834 A CN B2005100613834A CN 200510061383 A CN200510061383 A CN 200510061383A CN 100350219 C CN100350219 C CN 100350219C
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Abstract
The present invention relates to a method and equipment for multiplexing and demodulating sensors on the basis of long-period fiber gratings. At present, a high efficiency low-priced LPGP multiplexing and demodulating method is still not raised by any person. In the present invention, the light intensity of a broadband light source is equally distributed to a plurality of LPGPs with different optical path difference through a fiber coupler, and multiplexing is completed after each path of signal light is converged; the multiplexed signal light enters a 3-dB fiber coupler through a one-way optical isolator, two signal light beams are incident onto reflecting mirrors through a fiber collimator and reflected and coupled back to an optical fiber, and the incoming phase difference of the LPGPs with different optical path difference is compensated by controlling the positional movement of one of the reflecting mirrors; the compensated two paths of optical signals are converged and interfered in the 3-dB coupler, converted into electric signals by a photodiode, and collected by a data acquisition card, and the demodulation is completed finally. The present invention has the advantage of low cost, and is suitable to be integrated and made into instruments.
Description
Technical field
The invention belongs to technical field of optical fiber sensing, particularly a kind of long period fiber grating to the signal multiplexing and the demodulation method of sensor and the equipment of realizing this method.
Background technology
At sensory field of optic fibre, long period fiber grating is to (long-period grating pair, LPGP) because it is very responsive to little curved, temperature, stress, variations in refractive index, and become crucial senser element in the industry, be particularly useful for the high-acruracy survey of liquid refractivity.Utilize first long period fiber grating that the fiber core layer luminous energy is coupled half to fibre cladding, through the propagation of stretch journey again by second grating sandwich layer that is coupled back, converge with second half light through sandwich layer, long period fiber grating is Mach-Zehnder (M-Z) interferometer of two arms in fact having constituted one with fiber core layer and covering.Because the fibre cladding effective refractive index is subjected to the influence of extraneous refractive index, the optical path difference of these M-Z interferometer two arms variations in refractive index to external world is very responsive.Utilize the method for wavelength-modulated, the T.Allsop of UK is used for refractive index sensing with a LPGP, has obtained 1.8 * 10
-6Precision.Awl and lithographic technique are drawn in the utilization of domestic Zhejiang University, and that section optical fiber in the middle of the grating pair is handled, and improve the influence degree of extraneous refractive index to cladding index, and measurement sensitivity has been improved more than five times.
Fiber Bragg Grating FBG since its frequency domain reflectance spectrum very narrow (＜1nm), utilize wave length beam splitting device, asymmetric M-Z interferometer or tunable optical fiber filter can realize its multiplexing and demodulation on frequency domain.But long period fiber grating, its spectrum signature are a plurality of transmission losss peak and deposit, and the relative broad of the frequency domain bandwidth of each loss peak (tens of nm), can't realize multiplexing and demodulation on frequency domain.Although long period fiber grating itself has the sensing characteristics to little curved, temperature, stress, refractive index sensitivity, it seldom is used to distributed measurement.As a same reason, so far, also nobody proposes the multiplexed and demodulation method of a kind of LPGP of efficient cheapness.
Summary of the invention
The present invention is exactly at the deficiencies in the prior art, has proposed a kind of multiplexed and low-coherent light demodulation scheme based on the right sensor of long period fiber grating, and the equipment of realizing this method is provided simultaneously.
Method of the present invention may further comprise the steps:
1, selects the wideband light source at wavelength coverage covering long-period gratings transmission loss peak for use, strip of light wide region 20～60nm; With the LPGP sensor of light intensity mean allocation to the individual different grating centre distances of n (n 〉=2), the light signal in each LPGP sensor is introduced different optical path differences by fiber coupler; The flashlight that carries each road LPGP heat transfer agent converges to a single-mode fiber by fiber coupler, finishes the multiplexed of transducing signal.The optical path difference of the light signal in described each LPGP sensor is to utilize long period fiber grating to be coupled to this characteristic of covering to the luminous energy of fiber core layer, each LPGP sensor is coupled to fibre cladding to half luminous energy by first long period fiber grating, after the propagation through one section light path, by second long period fiber grating sandwich layer that is coupled back, converge with other half luminous energy by sandwich layer, the optical path difference of the light signal in the LPGP sensor is:
OPD＝Δn·L (1)
Wherein Δ n represents that the effective refractive index of fiber core layer and covering is poor, and L represents grating centre distance in the LPGP sensor.
2, the transducing signal after multiplexed enters a 3-dB fiber coupler through a light one-way isolator, and the 3-dB fiber coupler is divided into aplanatic two bundles with light signal; The aplanatic flashlight of two bundles incides on the catoptron by optical fiber collimator respectively and reflects coupled back into optical fibers; Move by the position of controlling one of them catoptron, make between the two paths of signals light and to introduce another and go into optical path difference, and produce scanning, thereby compensate the optical path difference that the LPGP sensor of different grating centre distances is introduced.The effect of one-way isolator mainly is to prevent the destruction of reflected light to light source.
3, the two ways of optical signals after the compensation is converged interference in the 3-dB coupling mechanism, and interference signal is converted into electric signal through an arm of 3-dB coupling mechanism by photodiode, by the data collecting card collection, finishes demodulation.
Can see from (1) formula, the optical path difference difference that the LPGP sensor of different grating centre distances is introduced, scan a certain position so work as an arm of Maxwell interferometer, the optical path difference of certain LPGP sensor is compensated for as zero, and then the low-coherent light interference signal of this LPGP sensor correspondence occurs.By being arranged in parallel the LPGP sensor of a series of different grating centre distances, and a scanning Maxwell interferometer arm wherein, can realize the multiplexing and demodulation of multichannel LPGP sensor.
The resolution of the demodulation scheme of this multiplexed LPGP sensor depends primarily on the coherent length of long-period gratings loss spectra:
Wherein, λ and Δ λ are respectively the centre wavelength and the bandwidth of long-period gratings loss peak.
The equipment of realizing such scheme is: the LPGP sensor input end of the individual different grating centre distances of n (n 〉=2) in parallel is connected with the wideband light source light signal by fiber coupler, and output terminal is connected with another fiber coupler light signal.Light one-way isolator input end is connected with another fiber coupler light signal, and the input end of its output terminal and photodiode is connected with an end light signal of 3-dB fiber coupler, and photodiode output is electrically connected with data collecting card.The other end of 3-dB fiber coupler is connected with two optical fiber collimator light signals respectively, and corresponding two optical fiber collimator positions are provided with two catoptrons, and one of them catoptron moves by its position of step motor control.
The present invention mainly is applicable to the demodulation of multiplexed LPGP sensor signal, spatial resolution is up to tens of microns, the maximum demodulation number of channel reaches hundreds of, can reach very high measuring accuracy by processing to interference signal, compare frequency domain measurement instruments such as those spectrometers simultaneously, have advantage with low cost, be fit to integrated and instrumentation.
Description of drawings
Fig. 1 is an one-piece construction synoptic diagram of the present invention.
Embodiment
As shown in Figure 1, LPGP sensor 3 input ends of a plurality of different grating centre distances in parallel are connected with wideband light source 1 light signal by fiber coupler 2 respectively, and output terminal is connected with another fiber coupler 4 light signals.Light one-way isolator 5 input ends are connected with fiber coupler 4 light signals, its output terminal be connected with an end light signal of 3-dB fiber coupler 6 with the input end of photodiode 10, the output terminal of photodiode 10 is electrically connected with data collecting card 11.The other end of 3-dB fiber coupler 6 is connected with two optical fiber collimator 7 light signals respectively, and corresponding two optical fiber collimator 7 positions are provided with two catoptrons 8, and one of them catoptron moves by stepper motor 9 its positions of control.Above-mentioned a plurality of LPGP sensors 3 are embedded in the monitored buildings as microbend sensor, wideband light source 1 and signal demodulation part are all in monitoring center, broadband light enters a plurality of LPGP sensors 3 by single-mode fiber, passes flashlight back monitoring center by single-mode fiber again and carries out signal demodulation and processing.
Selecting wavelength coverage for use is 60nm (can cover the broadband at long-period gratings transmission loss peak) light source, by fiber coupler the light intensity mean allocation is arrived a plurality of LPGP sensors, the light signal in the LPGP sensor of each different grating centre distance has different optical path differences; The flashlight that carries each road LPGP heat transfer agent converges to a single-mode fiber by fiber coupler, finishes the multiplexed of transducing signal.The optical path difference of the light signal in each LPGP sensor is to utilize long period fiber grating to be coupled to this characteristic of covering to the luminous energy of fiber core layer, each LPGP sensor is coupled to fibre cladding to half luminous energy by first long period fiber grating, after the propagation through one section light path, by second long period fiber grating sandwich layer that is coupled back, converge with other half luminous energy by sandwich layer, the optical path difference of the light signal in each LPGP sensor is:
OPD＝Δn·L (1)
Wherein Δ n represents that the effective refractive index of fiber core layer and covering is poor, and L represents grating centre distance in the LPGP sensor.
Transducing signal after multiplexed enters a 3-dB fiber coupler through a light one-way isolator, and the 3-dB fiber coupler is divided into aplanatic two bundles with light signal; The aplanatic flashlight of two bundles incides on the catoptron by optical fiber collimator respectively and reflects coupled back into optical fibers; Control the position of one of them catoptron and move, make between the two paths of signals light and to introduce another and go into optical path difference, and produce scanning, thereby compensate the optical path difference that the LPGP sensor of different grating centre distances is introduced.
Two ways of optical signals after the compensation is converged interference in the 3-dB coupling mechanism, interference signal is converted into electric signal through an arm of 3-dB coupling mechanism by photodiode, by the data collecting card collection, finishes demodulation.
Can see from (1) formula, the phase differential difference that the LPGP sensor of different grating centre distances is introduced, scan a certain position so work as the Maxwell interferometer, the phase differential of certain LPGP sensor is compensated for as zero, and then the low-coherent light interference signal of this LPGP sensor correspondence occurs.By a LPGP sensor that is arranged in parallel a series of different grating centre distances and a wherein arm that scans the Maxwell interferometer, can realize the multiplexing and demodulation of multichannel LPGP sensor.
The resolution of the demodulation scheme of this multiplexed LPGP sensor depends primarily on the coherent length of long-period gratings loss spectra:
Wherein, λ and Δ λ are respectively centre wavelength and bandwidth such as long-period gratings loss peak, and λ gets 1550nm (optical communication typical case wave band) in the present embodiment, and Δ λ gets 20nm (long-period gratings loss peak normal bandwidth), and according to formula (2), interfering length is 53 μ m.Scanning step motor 1cm, maximum 377 LPGP sensor signals can be by demodulation.Between the LPGP interference signal for adjacent channel aliasing not taking place, according to formula (1) and formula (2), considers that again general single mode fiber sandwich layer cladding index difference Δ n is 10
-2About, adjacent LPGP length difference needs 5.3mm.
Because little curved meeting causes the leakage of cladding mode among the LPGP, thereby weakens the intensity of output terminal interference signal, utilizes the data acquisition and processing (DAP) system that interference signal is extracted envelope, can obtain the little curved signal of LPGP sensor.Scanning Maxwell interferometer has promptly been realized the multiplexing and demodulation of multichannel LPGP.
Utilization can scan optical path difference that the Maxwell interferometer introduces LPGP and compensate and obtain to comprise the low-coherent light interference fringe of transducing signal, thereby has realized the multiplexing and demodulation to the LPGP sensor.The present invention also has the resolution height, measures the advantage that bandwidth is big, demodulation accuracy is high and with low cost.
Claims (3)
1,, it is characterized in that this method may further comprise the steps based on the multiplexing and demodulation method of long period fiber grating to sensor:
(1) select for use wavelength coverage to cover the wideband light source at long period fiber grating transmission loss peak, strip of light wide region 20～60nm; By fiber coupler with the light intensity mean allocation to the long period fiber grating of n different grating centre distances to sensor, n 〉=2 wherein, each long period fiber grating is introduced different optical path differences to the light signal in the sensor; Carry each road long period fiber grating the flashlight of heat transfer agent is convergeed to a single-mode fiber by fiber coupler, finish the multiplexed of transducing signal;
(2) transducing signal after multiplexed enters a 3-dB fiber coupler through a light one-way isolator, and the 3-dB fiber coupler is divided into aplanatic two bundles with light signal; The aplanatic flashlight of two bundles incides on the catoptron by optical fiber collimator respectively and reflects coupled back into optical fibers; Move by the position of controlling one of them catoptron, make and introduce another optical path difference between the two paths of signals light, and produce scanning, thereby compensate the optical path difference of long period fiber grating to introducing in the sensor of different grating centre distances;
(3) two ways of optical signals after the compensation is converged interference in the 3-dB coupling mechanism, and interference signal is converted into electric signal through an arm of 3-dB coupling mechanism by photodiode, by the data collecting card collection, finishes demodulation.
2, as claimed in claim 1 based on the multiplexing and demodulation method of long period fiber grating to sensor, it is characterized in that described each long period fiber grating is to utilize long period fiber grating to be coupled to this characteristic of covering to the luminous energy of fiber core layer to the optical path difference of the light signal in the sensor, each long period fiber grating is coupled to fibre cladding to half luminous energy to sensor by first long period fiber grating, after the propagation through one section light path, by second long period fiber grating sandwich layer that is coupled back, converge with other half luminous energy by sandwich layer, long period fiber grating to the optical path difference of the light signal in the sensor is:
OPD＝Δn·L (1)
Wherein Δ n represents that the effective refractive index of fiber core layer and covering is poor, and L represents that long period fiber grating is to grating centre distance in the sensor.
3, adopt the employed equipment of claim 1 method, the long period fiber grating that it is characterized in that a n in parallel different grating centre distance is connected with wideband light source (1) light signal by fiber coupler (2) sensor (3) input end, n 〉=2 wherein, output terminal is connected with another fiber coupler (4) light signal; Light one-way isolator (5) input end is connected with another fiber coupler (4) light signal, the input end of the output terminal of light one-way isolator (5) and photodiode (10) is connected with an end light signal of 3-dB fiber coupler (6) respectively, and the output terminal of photodiode (10) is electrically connected with data collecting card (11); The other end of 3-dB fiber coupler (6) is connected with two optical fiber collimators (7) light signal respectively, and corresponding two optical fiber collimators (7) position is provided with two catoptrons (8), and one of them catoptron is controlled its position by stepper motor (9) and moved.
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| CN100406938C (en) * | 2006-08-10 | 2008-07-30 | 浙江大学 | Coherent multiplexing method for optical fiber Bragg raster sensor and apparatus thereof |
| CN101968391A (en) * | 2010-09-28 | 2011-02-09 | 中国工程物理研究院流体物理研究所 | Aplanatic fiber Bragg grating pressure sensor |
| CN106525087B (en) * | 2015-09-11 | 2019-03-22 | 中国电力科学研究院 | A kind of highly sensitive fast demodulation system for comb δ function formula minor change |
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| CN106197741B (en) * | 2016-07-14 | 2018-08-28 | 盐城工学院 | Temperature-detecting device based on micro-nano long-period fiber grating sensor and method |
| CN109373933B (en) * | 2018-11-20 | 2020-07-31 | 武汉光迅科技股份有限公司 | Device and method for detecting verticality of diffraction grating |
| CN109374028B (en) * | 2018-12-13 | 2019-10-18 | 金陵科技学院 | A kind of distributed multiplex demodulating system based on cascade-connection long period fiber grating |
| CN110296725B (en) * | 2019-07-09 | 2020-11-03 | 福州大学 | Asymmetric spectrum demodulation method of fiber Bragg grating sensor based on distributed estimation algorithm |
| CN112449295A (en) | 2019-08-30 | 2021-03-05 | 华为技术有限公司 | Microphone chip, microphone and terminal equipment |
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