CN101799331A - Method and system for demodulating DFB (Distribution Feedback) laser wavelength based on adsorption peak of acetylene gas - Google Patents
Method and system for demodulating DFB (Distribution Feedback) laser wavelength based on adsorption peak of acetylene gas Download PDFInfo
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Abstract
The invention relates to a method and a system for demodulating DFB (Distribution Feedback) laser wavelength based on an adsorption peak of acetylene gas, belonging to the technical field of wavelength demodulation. The wavelength of the DFB laser is demodulated by utilizing the adsorption peak of the acetylene gas. The system comprises an optical path, a circuit and an oscillograph and is characterized in that the optical path comprises DFB lasers and the like, wherein the DFB lasers are located in front of a WDM (Wavelength Division Multiplex) coupler; an acetylene gas chamber is located behind the WDM coupler; the circuit comprises two groups of photoelectric detectors which are respectively connected with the input ends of two preamplification circuits; the output ends of the two preamplification circuits are respectively connected with two filtration circuits which are connected with the input end of a divider; the output end of the divider is connected with the oscillograph; the two photoelectric detectors are respectively arranged behind the WDM coupler and the acetylene gas chamber. The demodulation method and system have the advantages of stable system, simple and convenient technique, accurate and intuitional test and lower cost. The used devices can be easily obtained from the market.
Description
Affiliated technical field
The present invention relates to a kind of Wavelength demodulation technology, specifically relate to a kind of Distributed Feedback Laser Wavelength demodulation method and system based on the acetylene gas absorption peak.
Background technology
At present, the application of laser instrument more and more widely, laser output wavelength has certain live width, and because the influence of external factor, the output wavelength of laser instrument can change.The technology of accurately measuring wave length shift is exactly the Wavelength demodulation technology of laser instrument.The drift of the operation wavelength by accurate Laser Measurement device, we can understand the duty and the influence factor of laser instrument, reduce this wavelength fluctuation thereby regulate corresponding environmental factor.Therefore, Wavelength demodulation technology tool in production application of laser instrument plays a very important role.
The DFB fiber laser is different with traditional laser instrument, it does not have traditional chamber mirror, but the optical grating constitution resonator cavity that directly writes at rare-earth doped optical fibre, active area and feedback district are all one, only realize light feedback and wavelength selection with a grating, thereby have advantages such as line width, noise are little, be an important directions of fiber laser development.Distributed Feedback Laser is applied in the sensory field of optic fibre,, will improves the performance of Fibre Optical Sensor greatly as optical fiber sensor head.Therefore wavelength fluctuation how accurately to measure Distributed Feedback Laser becomes the problem that needs solve.At present, existing wavelength demodulation scheme mainly contains following several:
1, adopts in type instrument such as optical wavelengthmeter or spectrometer directly to read the numerical value of wavelength, thereby can draw wavelength change.This method is extremely simple and directly, but spectrometer is bulky and complex structure, needs calibration repeatedly during use, and the high precision spectrometer costs an arm and a leg, and cost is higher.＜applied optics〉magazine, 25, (2004), and p40-43, the article that Zhou Weilin etc. showed " fiber grating sensor wavelength displacement detection method " promptly belongs to these row.
2, ratio probe method promptly transfers wavelength variations to light intensity by linear filter and changes.This method is fairly simple, cost is low, can directly measure the wavelength absolute value, and deficiency is that Measurement Resolution is not high, is not suitable for the Wavelength demodulation of multiplexing fiber-optic grating.
3, wavelength-division multiplex (WDM) fiber coupler demodulation method.This method adopts full optical fibre device to connect, and has reduced reflection and junction loss, but because the polarization characteristic of WDM fiber coupler, the precision that this kind method is measured wavelength is not high.
4, non-equilibrium Mach-Zehnder interferes demodulation method.Though this method has the demodulation ability of bandwidth, high-res, random phase shift makes this method be confined to measure dynamic strain, is unsuitable for the measurement to absolute strain.Above-mentioned 2,3,4 described demodulation methods come from " fiber grating and sensing technology thereof " book that Zhao Yong shows, and are published by National Defense Industry Press.
5,＜Chinese journal of scientific instrument 〉, 27 (2006), the article of Zhang Jian etc. " is used the research that CWDM realizes the FBG sensing and demodulating " and has been disclosed a kind of demodulation method, it is to adopt the method measurement wavelength of linear hypotenuse filters demodulate to move, when the variation of extraneous measured physical quantity caused that the FBG wavelength changes, hypotenuse wave filter output intensity also can change thereupon.This method is simple in structure, is easy to demodulation, all can influence measuring accuracy but the splitting ratio of system, coupled device changes and wave filter is non-linear.Filtering characteristic according to FBG reflectance spectrum and CWDM sideband comes the demodulation wavelength variations, though the measuring error because of intensity of light source fluctuation and the insecure introducing of the joints of optical fibre has been eliminated by this system, but because the polarization characteristic of WDM fiber coupler, the precision of measuring wavelength is not high.
6,＜piezoelectricity and acousto-optic 〉, 30 (2008), the technology that Li Li etc. " the non-equilibrium M-Z of fiber grating interferes demodulation techniques research " proposed is to adopt non-equilibrium M-Z to interfere demodulation techniques, has good dynamic characteristics, be suitable for the detection of Dynamic Signal in the precision measurement, but random phase shift makes this method be confined to measure dynamic strain, is unsuitable for the measurement to absolute strain.
Summary of the invention
In order to overcome defective and the deficiency that prior art exists, the present invention proposes a kind of Distributed Feedback Laser Wavelength demodulation method and system based on the acetylene gas absorption peak, aim to provide stable, Wavelength demodulation method and system cheaply.
Technical scheme of the present invention realizes in the following manner.
A kind of Distributed Feedback Laser Wavelength demodulation method based on the acetylene gas absorption peak, the output light of Distributed Feedback Laser is divided into two-way by the WDM coupling mechanism in 7: 1 ratio, wherein first via light is that proportion is that 7/8 light is by the acetylene gas air chamber, be input to then on first photodetector as metrical information, the second road light is directly inputted on second photodetector as with reference to information, two detectors become electric signal with light signal, pre-amplification circuit by separately and filtering circuit carry out signal and amplify and noise filtering respectively again, then two paths of signals being imported divider handles, two paths of signals after divider is handled is input to oscillograph, promptly can be observed the modified-image of output signal with wavelength fluctuation.
The employed demodulating system of above-mentioned demodulation method, comprise light path, circuit and oscillograph, it is characterized in that optical routing Distributed Feedback Laser, WDM coupling mechanism, acetylene gas air chamber composition, Distributed Feedback Laser is positioned at before the WDM coupling mechanism, and the acetylene gas air chamber is positioned at after the WDM coupling mechanism; Circuit is made up of two groups of photodetectors, pre-amplification circuit, filtering circuit and dividers, two photodetectors are connected respectively to the input end of two pre-amplification circuits, the output terminal of two pre-amplification circuits is connected respectively to two filtering circuits, two filtering circuits are connected to the input end of divider, and the output terminal of divider is connected with oscillograph; Two photodetectors are placed on respectively after WDM coupling mechanism and the acetylene gas air chamber, the light of Distributed Feedback Laser output can be divided into two-way through the WDM coupling mechanism, and one the tunnel delivers to photodetector, and another photodetector is delivered to through the acetylene gas air chamber in another road.
The principle of work of demodulation method of the present invention is as follows: the output light of Distributed Feedback Laser is divided into two-way by the WDM coupling mechanism in 7: 1 ratio, first via light (proportion is 7/8) is by the acetylene gas air chamber, because the absorption peak edge of acetylene gas (rising edge edge or trailing edge edge) is to the selectivity of wavelength, by formula
I＝I
0exp[-α(λ)L]
α (λ) is an absorption coefficient, and L is an air chamber length, I
σBe the initial light intensity of input light, I is for by the output intensity behind the air chamber, and the drift value of Distributed Feedback Laser wavelength is converted to the intensity variations amount, is input to then on first photodetector as metrical information.The second road light (proportion is 1/8) is directly inputted on second photodetector as with reference to information.Two detectors are converted into electric signal by opto-electronic conversion with light signal, zoom into voltage variety through amplifying circuit afterwards, again through filtering circuit filtering DC component and high fdrequency component, then two paths of signals is imported divider and make signal Processing, eliminate because system's light intensity fluctuation that a variety of causes causes, import oscillograph at last, can observe variation intuitively, the modified-image of the voltage variety Δ V of output along with the drift value Δ λ of Distributed Feedback Laser output wavelength.Selecting acetylene gas for use is at the 1530.371nm annex the last one absorption peak to be arranged according to acetylene gas, the output wavelength of Distributed Feedback Laser is generally also about 1530nm, can satisfy the demand that we utilize the precipitous edge of absorption peak to measure, utilize acetylene gas absorption peak edge that the selectivity of wavelength is converted into the light intensity variable quantity with wavelength shift.Because the gas absorption peak is more stable, generally can not be subjected to extraneous factor to produce drift, so this system has good stability.In addition, edge, gas absorption peak is very precipitous, live width is narrower, and small wavelength variations will produce big light intensity and change, so this system is highly suitable for the Wavelength demodulation of narrow linewidth, and precision is very high.Introduced reference information, and reference information and metrical information can effectively be eliminated the interference that laser instrument itself and change of background are brought from same light source
Fig. 5 is the transmissivity of acetylene gas and the graph of a relation of wavelength, transmissivity=1-absorptivity.By the HITRAN2004 database as can be known, acetylene gas has the last one absorption peak at the 1530.371nm place, and the halfwidth degree (Full Width Half Maximum---FWHM) be about 22pm.The Distributed Feedback Laser live width is generally less than 50KHz (being about 0.0005pm), is far smaller than 22pm.When the Distributed Feedback Laser output wavelength is controlled at a numerical value on Fig. 5 trailing edge edge, its corresponding transmitance value, when wavelength was sent out the dirt fluctuation, because trailing edge is along steeper among the figure, transmitance can be sent out the bigger variation of dirt.We can obtain the variable quantity of voltage through subsequent treatment again.
Demodulation method of the present invention and system have the following advantages: system stability, used device all obtain from market easily, and technology is simple and convenient, and test is accurately directly perceived, and cost is lower.
Description of drawings
Fig. 1. be the structural representation of demodulating system of the present invention.
Wherein: 1, Distributed Feedback Laser, 2, the WDM coupling mechanism, 3, the acetylene gas air chamber, 4, photodetector, 5, pre-amplification circuit, 6, filtering circuit, 7, photodetector, 8, pre-amplification circuit, 9, filtering circuit, 10, divider, 11, oscillograph.
Fig. 2 is photodetector and the pre-amplification circuit synoptic diagram in the demodulating system of the present invention.
Fig. 3 is the filtering circuit synoptic diagram in the demodulating system of the present invention.
Fig. 4 is the divider circuit synoptic diagram in the demodulating system of the present invention.
Fig. 5 is the transmissivity of acetylene gas and the graph of a relation of wavelength, transmissivity=1-absorptivity
Embodiment
The present invention will be further described below in conjunction with drawings and Examples, but be not limited thereto.
Embodiment 1:(method embodiment)
As shown in Figure 1, a kind of Distributed Feedback Laser Wavelength demodulation method based on the acetylene gas absorption peak, the output light of Distributed Feedback Laser 1 is divided into two-way by WDM coupling mechanism 2 in 7: 1 ratio, wherein first via light is that proportion is that 7/8 light is by acetylene gas air chamber 3, be input to then on first photodetector 7 as metrical information, the second road light is directly inputted on second photodetector 4 as with reference to information, two photodetectors 4,7 become electric signal with light signal, pass through pre-amplification circuit 5 separately more respectively, 8 and filtering circuit 6,9 carry out signal amplifies and noise filtering, then two paths of signals being imported divider 10 handles, two paths of signals after divider 10 is handled is input to oscillograph 11, promptly can be observed the modified-image of output signal with wavelength fluctuation.
Embodiment 2:(hardware embodiment)
The embodiment of the invention 2 as shown in Figure 1, the employed demodulating system of a kind of above-mentioned demodulation method, comprise light path, circuit and oscillograph, it is characterized in that optical routing Distributed Feedback Laser 1, WDM coupling mechanism 2, acetylene gas air chamber 3 compositions, Distributed Feedback Laser 1 is positioned at before the WDM coupling mechanism 2, and acetylene gas air chamber 3 is positioned at after the WDM coupling mechanism 2; Circuit is made up of two groups of photodetectors 4,7, pre-amplification circuit 5,8, filtering circuit 6,9 and divider 10, two photodetectors 4,7 are connected respectively to the input end of two pre-amplification circuits 5,8, the output terminal of two pre-amplification circuits 5,8 is connected respectively to two filtering circuits 6,9, two filtering circuits 6,9 are connected to the input end of divider 10, and the output terminal of divider 10 is connected with oscillograph 11; Two photodetectors 4,7 are placed on respectively after WDM coupling mechanism 2 and the acetylene gas air chamber 3, the light of Distributed Feedback Laser 1 output can be divided into two-way through WDM coupling mechanism 2, one the tunnel delivers to photodetector 4, and another photodetector 7 is delivered to through acetylene gas air chamber 3 in another road.
Shown in Figure 2 is photodetector and pre-amplification circuit.Wherein be attempted by the input end of operational amplifier after photodetector and the capacitor C p parallel connection, the series circuit of output terminal connecting resistance R1, inductance L and the resistance R 2 of operational amplifier, resistance R 2 other end ground connection; Capacitor C is attempted by on resistance R 1 and the inductance L, is connected the input negative pole end of operational amplifier after feedback capacity Cf and the feedback resistance Rf parallel connection, and the other end is connected on the contact place of capacitor C and inductance L.R2, R1, inductance L and capacitor C are formed selective frequency amplifier circuit, and used resistance is selected all low noise high-precision metal film resistances preferably of temperature characterisitic and frequency characteristic, and electric capacity is selected low noise electric capacity as far as possible.Operational amplifier has played the effect of core in preceding putting, its performance index such as open-loop gain, input bias current, offset current and offset voltage, frequency response and noiseproof feature all exert an influence to preceding putting.Side circuit uses be OPA128 as amplifier, have effect preferably.
Fig. 3 is the filtering circuit in the demodulating system of the present invention, is the wave filter of quadravalence shown in the figure.The embodiment of the invention 2 is used OPA2604 two-way operational amplifier, add capacitance resistance and form the filtering circuit R1 of second order, C2 and R2, C3 constitutes the passive filter of second order, add that integrated transporting discharging OPA2604 constitutes the RC low-pass filter of second order, latter half and first half are similar, and two parts constitute the low-pass filter circuit of one 4 quadravalence.C1, C4 two termination power supplys (+12V ,-12V) and ground, be the decoupling capacitor of power supply, eliminate the influence that exchanges in the power supply circuit.
Fig. 4 is the divider circuit in the demodulating system of the present invention.Adopt common CMOS version 555 timer TLC555, as the RC oscillator (IC2) of free-running operation.The output signal driving resistor device R1 and the C1 of the 3rd pin of IC2 are simultaneously by resistance R 5 and capacitor C 4 ground connection.Input voltage VB is a denominator, by the discharge pin 7 of the resitstance voltage divider drive IC 2 formed by R3 and R4, the other end of R3 and the normal phase input end of IC1B, negative-phase input 6 be input to the low-pass filter that R8 and C3 form after output terminal 7 is connected.The normal phase input end of integrator IC1A is connected with C3, and negative-phase input connects the parallel circuit of R5, R7 and C2, and output voltage to the C1 drive current, is set up a bias voltage by R2, controls the output pulse width of IC2 conversely, constitutes a backfeed loop.R5 and C4 form a low-pass filter circuit.
Claims (2)
1. Distributed Feedback Laser Wavelength demodulation method based on the acetylene gas absorption peak, with the output light of Distributed Feedback Laser by the WDM coupling mechanism in 7: 1 ratio be divided into two-way wherein first via light be that proportion is that 7/8 light is by the acetylene gas air chamber, be input to then on first photodetector as metrical information, the second road light is directly inputted on second photodetector as with reference to information, two detectors become electric signal with light signal, pre-amplification circuit by separately and filtering circuit carry out signal and amplify and noise filtering respectively again, then two paths of signals being imported divider handles, two paths of signals after divider is handled is input to oscillograph, promptly can be observed the modified-image of output signal with wavelength fluctuation.
2. the employed a kind of Wavelength demodulation system of Wavelength demodulation method according to claim 1, comprise light path, circuit and oscillograph, it is characterized in that optical routing Distributed Feedback Laser, WDM coupling mechanism, acetylene gas air chamber composition, Distributed Feedback Laser is positioned at before the WDM coupling mechanism, and the acetylene gas air chamber is positioned at after the WDM coupling mechanism; Circuit is made up of two groups of photodetectors, pre-amplification circuit, filtering circuit and dividers, two photodetectors are connected respectively to the input end of two pre-amplification circuits, the output terminal of two pre-amplification circuits is connected respectively to two filtering circuits, two filtering circuits are connected to the input end of divider, and the output terminal of divider is connected with oscillograph; Two photodetectors are placed on respectively after WDM coupling mechanism and the acetylene gas air chamber.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102494874A (en) * | 2011-12-08 | 2012-06-13 | 山东省科学院激光研究所 | Tunable laser type fiber Bragg grating wavelength demodulation device |
| CN102853914A (en) * | 2011-06-29 | 2013-01-02 | 霍尼韦尔国际公司 | Simple, low power microsystem for saturation spectroscopy |
| CN103472003A (en) * | 2013-09-27 | 2013-12-25 | 山东大学 | Novel method used for phase lock voltage subtraction of micro water vapor detection |
| CN117387673A (en) * | 2023-12-08 | 2024-01-12 | 山东星冉信息科技有限公司 | Fiber bragg grating demodulation method and device based on reference air chamber |
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Non-Patent Citations (3)
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| 《传感技术学报》 20041231 王玉田等 基于光谱吸收式光纤乙炔气体监测系统的研究 619-622 1-2 , 第4期 2 * |
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102853914A (en) * | 2011-06-29 | 2013-01-02 | 霍尼韦尔国际公司 | Simple, low power microsystem for saturation spectroscopy |
| CN102853914B (en) * | 2011-06-29 | 2016-03-02 | 霍尼韦尔国际公司 | For the spectral device of saturation spectroscopy |
| CN102494874A (en) * | 2011-12-08 | 2012-06-13 | 山东省科学院激光研究所 | Tunable laser type fiber Bragg grating wavelength demodulation device |
| CN102494874B (en) * | 2011-12-08 | 2014-07-16 | 兖矿集团有限公司 | Tunable laser type fiber Bragg grating wavelength demodulation device |
| CN103472003A (en) * | 2013-09-27 | 2013-12-25 | 山东大学 | Novel method used for phase lock voltage subtraction of micro water vapor detection |
| CN117387673A (en) * | 2023-12-08 | 2024-01-12 | 山东星冉信息科技有限公司 | Fiber bragg grating demodulation method and device based on reference air chamber |
| CN117387673B (en) * | 2023-12-08 | 2024-02-23 | 山东星冉信息科技有限公司 | Fiber bragg grating demodulation method and device based on reference air chamber |
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