CN100541140C - The Wavelength demodulation method of Fibre Optical Sensor - Google Patents
The Wavelength demodulation method of Fibre Optical Sensor Download PDFInfo
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- CN100541140C CN100541140C CNB2006101698340A CN200610169834A CN100541140C CN 100541140 C CN100541140 C CN 100541140C CN B2006101698340 A CNB2006101698340 A CN B2006101698340A CN 200610169834 A CN200610169834 A CN 200610169834A CN 100541140 C CN100541140 C CN 100541140C
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Abstract
The Wavelength demodulation method of Fibre Optical Sensor belongs to the Wavelength demodulation technology in the Fibre Optical Sensor.Be to utilize method of counting to carry out Wavelength demodulation, utilize the monotonic nature of the output intensity of short birefringence fiber ring mirror, determine the method for the direction of long birefringence fiber counting with wavelength variations to the fiber loop mirror output signal.Counting can be finished by signal processing circuit and the single-chip microcomputer be made up of amplifier and comparer.The present invention has avoided measuring wavelength change by the changes in amplitude of measuring-signal fully, and it is strong to have an antijamming capability, the advantage that measuring accuracy is high.
Description
Technical field
The present invention is applied at Fibre Optical Sensor, and particularly in Fiber Bragg Grating FBG (FBG) sensing, all utilizations are measured optical wavelength and changed to determine by the Application in Sensing of sensing amount (as temperature, strain etc.) variation.Belong to the Wavelength demodulation technology in the Fibre Optical Sensor.
Background technology
In Fibre Optical Sensor, it is that variation by optical wavelength reflects by the variation of sensing amount that some sensings are arranged, and is typically FBG.When the external world by the sensing amount, when changing as temperature or strain etc., corresponding variation also takes place in the optical wavelength that is reflected by FBG, there is certain functional relation in the two.If measured the variation of reflected light wavelength, also just measured the variation of the physical quantity of tendency to develop sense, this process is called Wavelength demodulation.
Existing comparative maturity, and realize that commercial Wavelength demodulation device is to adopt Fabry-Perot (F-P) interferometer to carry out Wavelength demodulation as wave filter, its course of work is shown in Fig. 1 (a).The light that wideband light source 1 sends is through photo-coupler 2 " pass to FBG 3, and have the very narrow a part of light of wavelength to be reflected, catoptrical wavelength is with being changed by the variation of sensing physical quantity around the FBG 3.Reflected light is through coupling mechanism 2 " and first coupling mechanism 2 arrive the F-P wave filter 6 that is subjected to piezoelectric ceramics 7 controls.The voltage signal drive pressure electroceramics 7 that saw-toothed wave generator 8 produces drives F-P wave filter 6 again, and resonance wavelength is scanned.When resonance wavelength equaled wavelength that FBG 3 reflects, light was reflected back toward first coupling mechanism 2 again, and passed to first PIN photodiode 4 and change electric signal into.At this moment, note the instantaneous voltage amplitude of sawtooth wave, just can be corresponding go out the resonance wavelength of F-P wave filter 6, the reflection wavelength of FBG 3 just, thus realize Wavelength demodulation.
What should point out emphatically is that what this method was measured is voltage amplitude.Generally, the amplitude amount is subject to the interference of extraneous factor, and measuring accuracy is not high.In addition, this installs more complicated, costs an arm and a leg, and has limited the widespread use of corresponding Fibre Optical Sensor.
Also have some Wavelength demodulation methods of having reported, these methods all do not enter commercial stage, all are the changes in amplitude that the change transitions of optical wavelength is become electric signal mostly, and same the existence is subject to disturb the problem that measuring accuracy is not high.
Fig. 1 (b) is a method of directly carrying out Wavelength demodulation with spectroanalysis instrument 9 commonly used in the laboratory.It is very simple that this method appears to, but 90 fens costlinesses of spectroanalysis instrument, and huge, heavy, can not in actual engineering, use.
Summary of the invention
The method that the objective of the invention is to propose a kind of counting is carried out the Wavelength demodulation of Fibre Optical Sensor, and this method has been avoided measuring wavelength change by the changes in amplitude of measuring-signal fully, and it is strong to have an antijamming capability, the advantage that measuring accuracy is high.
The Wavelength demodulation method of the Fibre Optical Sensor that the present invention proposes is a kind of in Fibre Optical Sensor is measured, utilization is carried out Wavelength demodulation to the method for counting of fiber loop mirror output signal, utilize the monotonic nature of the output intensity of short birefringence fiber ring mirror, determine the method for the direction of long birefringence fiber counting with wavelength variations.Its concrete steps that adopt are:
1, the light signal with wavelength variations is divided into the two-beam that intensity equates through photo-coupler, the first bundle light is divided into the two-beam that intensity equates and transmits around the same loop of being made up of ordinary optic fibre, long birefringence fiber and Polarization Controller along clockwise direction with counterclockwise respectively through first photo-coupler, return first photo-coupler then, and change electric signal into after outputing to first PIN photodiode simultaneously.The first transmittance graph a that first PIN photodiode obtains, as shown in Figure 5.The second bundle light is divided into the equal two-beam of intensity through second photo-coupler also to be transmitted around the same loop of being made up of another ordinary optic fibre, short birefringence fiber and Polarization Controller respectively along clockwise direction with counterclockwise, return second photo-coupler then, and change electric signal into after outputing to second PIN photodiode simultaneously.The second transmittance graph b that second PIN photodiode obtains, as shown in Figure 5.Short birefringence fiber wherein for make by fiber lengths the second transmittance graph b in measuring wavelength coverage less than the birefringence fiber of half vibration period.
2, rising edge and the negative edge of the first transmittance graph a are all counted, utilize the increase and decrease of the monotonicity judgement wavelength of the second transmittance graph b, as the second transmittance graph b during with the wavelength monotone increasing, counting to the first transmittance graph a increases, as the second transmittance graph b during, the counting of the first transmittance graph a is reduced with the wavelength monotone decreasing.
3, according to the final count value i to the first transmittance graph a, utilize formula λ=i Δ λ to calculate the size of wavelength, wherein, λ is a wavelength, and Δ λ is twice wavelength difference between counting; Thereby determined wavelength change, finished Wavelength demodulation.
Wherein said long birefringence fiber for make by fiber lengths the first transmittance graph a in measuring wavelength coverage every nano wave length greater than the optical fiber of 5 vibration periods.
Wherein, 1., the electric signal of first PIN photodiode 4, the 4 ' output of second PIN photodiode amplifies through first amplifier 18 and second amplifier 18 ' respectively step 2 and 3 can be finished by signal processing circuit and the single-chip microcomputer be made up of amplifier and comparer, and concrete steps are:.The output signal of first amplifier is given rising edge comparer 19 and negative edge comparer 19 ' simultaneously, and reference voltage 20 is as the comparing voltage value of two comparers.When signal voltage rises or descends when crossing reference voltage, two comparers can be exported count signal respectively, and single-chip microcomputer 5 receives this signal.
2., when single-chip microcomputer 5 is successively received the count signal that two comparers send here, be taken up in order of priority the signal that second amplifier 18 ' is sent here to carry out twice A/D conversion, value with twice conversion compares then, monotonicity by short birefringence fiber ring mirror output intensity, can determine that carrying out add-one operation still subtracts 1 computing, carry out computing then.
3., single-chip microcomputer can be converted to the result of counting corresponding wavelength value, and driving display 21 shows wavelength value.
Fig. 3 has provided and has utilized birefringence fiber ring mirror to carry out the schematic diagram of Wavelength demodulation.The optical signals port one 5 of wavelength variations is input in the photo-coupler, be divided into the two-beam that intensity equates and transmit around the loop of forming by ordinary optic fibre, birefringence fiber and Polarization Controller along clockwise direction with counterclockwise respectively at the other end of photo-coupler, return coupling mechanism then, and change electric signal into after outputing to PIN photodiode simultaneously.The size of electric signal has reflected the variation of light intensity after the two-beam interference, the variation of the light intensity transmissivity of birefringence fiber ring mirror just.The variation of this transmissivity is relevant with the variation of input optical wavelength, and its funtcional relationship as shown in Figure 4.As can be seen, light transmission is cyclical variation with wavelength.Theoretical proof, the cycle of variation and the length of birefringence fiber are approximated to inverse ratio, and just the length of wavelength frequency and birefringence fiber is approximated to direct ratio.If adopt long birefringence fiber, just can obtain the very fast transmittance graph of wavelength frequency change as shown in Figure 5.In Fig. 5, establish that wavelength constantly increases when measuring, at the rising edge of transmissivity, as 16 and negative edge, as 17 points, we count, and the size of wavelength that what of counting are just corresponding so just by counting, can realize Wavelength demodulation.What should particularly point out is, the timing point of rising edge and negative edge (as 16 among Fig. 5 and 17 points) is stable with the corresponding of wavelength, if because extraneous interference changes the amplitude of transmissivity, then the peak value of curve and valley can change among Fig. 5, and the respective value of timing point and wavelength can not change, so the method for counting Wavelength demodulation has very strong antijamming capability and very high measuring accuracy.
Though the method for counting has above-mentioned advantage, also need to solve the decision problem of counting increase and decrease direction.In counting process, there are two kinds of situations.A kind of situation is when wavelength increases continuously or reduce continuously, and transmissivity rising edge and negative edge all replace appearance, and count value should constantly increase or constantly reduce.Another kind of situation is afterwards to subtract or subtract earlier when afterwards increasing when wavelength value increases earlier, and transmissivity rising edge and negative edge also all can alternately occur, and the counting direction of this situation should be to increase earlier afterwards to subtract or subtract afterwards earlier to increase.How replacing the above-mentioned two kinds of situations of correct judgement the phenomenon that occurs from identical rising edge and negative edge, making count value and wavelength value energy correctly corresponding be the key issue of counting demodulation method.The front was spoken of, and the wavelength period of fiber loop mirror transmissivity and the length of birefringence fiber are approximated to inverse ratio.Adopt very short birefringence fiber, make a fiber loop mirror in addition, make its transmittance graph can not finish the vibration period half in measuring wavelength coverage, like this, in measuring wavelength coverage, curve is exactly dull with the increase and decrease of wavelength.Utilize long birefringence fiber ring mirror counting, utilize short birefringence fiber ring mirror to judge counting increase and decrease direction simultaneously.The transmissivity range value of the short birefringence fiber the when method of judging is measurement and more adjacent twice counting, because transmittance graph is dull with wavelength change, thus be easy to judge the increase and decrease direction of wavelength, thus the correct increase and decrease direction of counting of adjusting.Should be noted that, though adopted the method for measuring the transmissivity amplitude here, just judge adjacent twice counting amplitude size constantly at short notice qualitatively, do not write down the absolute value of amplitude, so the instability of amplitude amount can not cause any influence here.
Wavelength demodulation method of the present invention has been avoided measuring wavelength change by the changes in amplitude of measuring-signal fully, and it is strong to have an antijamming capability, the advantage that measuring accuracy is high.
Description of drawings
Fig. 1 (a): adopt Fabry-Perot (F-P) interferometer to carry out the device of Wavelength demodulation as wave filter
Fig. 1 (b): adopt spectroanalysis instrument directly to carry out the device of Wavelength demodulation
Fig. 2: count optical wavelength demodulation structure by the sensor that the dual fiber ring mirror constitutes
Fig. 3: the schematic diagram that utilizes birefringence fiber ring mirror to carry out the optical fiber sensing wavelength demodulation
Fig. 4: the funtcional relationship that birefringence fiber ring mirror transmissivity changes with input optical wavelength
Fig. 5: the funtcional relationship that the output intensity (being directly proportional with transmissivity) of the fiber loop mirror that long birefringence fiber and short birefringence fiber constitute respectively changes with input optical wavelength
Fig. 6: monolithic processor controlled processing of circuit system architecture
Fig. 7: Single Chip Microcomputer (SCM) program process flow diagram
Among the figure, 1-wideband light source, 2-first photo-coupler, 2 '-the second photo-coupler, 2 "-photo-coupler, 3-FBG; 4-first PIN photodiode, 4 '-the second PIN photodiode, 5-single-chip microcomputer; 6-F-P wave filter, 7-piezoelectric ceramics, 8-saw-toothed wave generator; 9-spectroanalysis instrument, the long birefringence fiber of 10-, 10 '-short birefringence fiber; 11-first optical fiber, 11 '-the second optical fiber, 12-first Polarization Controller; 12 '-the second Polarization Controller, the 13-cardboard cylinder, 14-signal processing circuit, 15-light input end mouth, point on the 16-rising edge, point on the 17-negative edge, 18-first amplifier, 18 '-the second amplifier, 19-rising edge comparer, 19 '-negative edge comparer, 20-reference voltage, 21-display.
Embodiment
Specify the preferred embodiments of the present invention below in conjunction with accompanying drawing.
The Wavelength demodulation device of designed according to the proposed method Fibre Optical Sensor is referring to Fig. 2, for carrying out the experimental configuration of FBG sensing wavelength demodulation.Comprise that light signal with wavelength variations is divided into the photo-coupler 2 of the two-beam that light intensity equates ", two similar fiber loop mirrors and connect, PIN photodiode, signal processing circuit 14, single-chip microcomputer 5 and display 21.The ring mirror comprises photo-coupler, ordinary optic fibre, birefringence fiber.The loop that first fiber loop mirror is made up of first photo-coupler 2 and first optical fiber 11, long birefringence fiber 10, first Polarization Controller 12 constitutes.The loop formation that second optic fibre environment is made up of second photo-coupler 2 ' and second optical fiber 11 ', short birefringence fiber 10 ', second Polarization Controller 12 '.Light signal by first, second environment output changes electric signal into through first PIN photodiode 4, second PIN photodiode 4 ' respectively, and two PIN photodiode connect signal processing circuit 14, and signal processing circuit 14 is connected on the single-chip microcomputer 5.
The length of the long birefringence fiber 10 of birefringence fiber ring mirror is 30 meters, with it on a cardboard cylinder 13.The length of the short birefringence fiber 10 ' of short birefringence fiber ring mirror is 0.05 meter.Each ring mirror all has a photo-coupler to be respectively first photo-coupler 2 and second photo-coupler 2 ' and first Polarization Controller 12 and second Polarization Controller 12 ' that is wound with 3 circle ordinary optic fibres.The input end of two ring mirrors also connects, the signal of the wavelength variations that common receiving sensor is sent here.Their output terminal by two PIN photodiode, is converted to electric signal with light signal, and gives single-chip microcomputer 5 by signal processing circuit 14 respectively, is handled and is counted by 5 pairs of signals of single-chip microcomputer.
Utilize the device of Fig. 2, we in the 1570nm wavelength coverage, have carried out Wavelength demodulation to the transducing signal of FBG 3 at 1530nm, and its wavelength resolution can reach 0.067nm.The concrete steps of employing method are as follows: utilize wavelength-swept source to carry out continuous sweep output from 1530nm to 1570nm scope interior focusing wavelength, and send into photo-coupler 2 ".Photo-coupler 2 " light is divided into equicohesive two bundles and arrives PIN photodiode 4 and 4 ' through two fiber loop mirrors respectively, be converted to electric signal then and send into signal processing circuit 14.When the signal voltage of first photodiode 4 output increased and crosses reference voltage 20, rising edge comparer 19 output high level sent count signal for single-chip microcomputer 5.Single-chip microcomputer 5 starts the A/D conversion of the signal that pair amplifier 18 ' sends here immediately.Because PIN photodiode 4 outputs is the signal of cycle increase and decrease, signal voltage can reduce subsequently, and reference voltage 20 is crossed in the whereabouts, this moment, negative edge comparer 19 ' was to the high level signal of single-chip microcomputer 5 output countings, and single-chip microcomputer 5 signal sent here of pair amplifier 18 ' immediately carries out second time A/D and changes.If single-chip microcomputer does not receive count signal, then it understands the situation of continuous query counts signal input.Above process belong to judge in the process flow diagram 7 comparer " 19 and 19 ' sends count information? ", carry out the part of respective handling then.If single-chip microcomputer receives count signal in succession twice, its result of twice A/D conversion relatively then, if back time conversion value greater than conversion value last time, then count value i adds 1, on the contrary, then i subtracts 1.This process belongs in the process flow diagram 7 " comparative result meets add-one operation? " the go forward side by side part of row operation.In the process of demodulation, display result if desired, single-chip microcomputer can utilize count value i to carry out corresponding computing, and driving display 21 shows the sensing result, and single-chip microcomputer also can continue the query counts signal input simultaneously, carries out new counting.If do not need display result, single-chip microcomputer just continues counting.This process belong in the process flow diagram 7 " need display result? and carry out the part of respective handling.
By formula Δ λ=λ
0 2/ (L Δ n) can calculate twice pairing wavelength interval of adjacent counting (as 16,17 pairing wavelength difference among Fig. 5).In the formula, Δ λ is the pairing wavelength difference of adjacent twice counting; λ
0For measuring the centre wavelength of wavelength coverage (1530nm is to 1570nm), λ here
0=1550nm; L=30m is the length of our employed birefringence fiber; Δ n=0.0012 is the refringence of our employed birefringence fiber.With corresponding data substitution formula, can calculate Δ λ=0.067nm, in other words, we have obtained the Wavelength demodulation resolution of 0.067nm.As shown in Figure 5, this result and experiment meet.If will further improve resolution, by formula as can be known, the length that only needs to increase birefringence fiber 10 gets final product.
The front is mentioned, and can utilize formula λ=i Δ λ, according to certain count value i constantly, calculates the measurement wavelength X in this moment, and send display 21 to show.In addition, utilize the measurement wavelength and concerned that by the specific function of sensing physical quantity single-chip microcomputer also can calculate by the value of sensing physical quantity, and shows by display.
Claims (2)
1, the Wavelength demodulation method of Fibre Optical Sensor, it is characterized in that: be to utilize method of counting to carry out Wavelength demodulation the fiber loop mirror output signal, utilize the monotonic nature of the output intensity of short birefringence fiber ring mirror with wavelength variations, determine the method for the direction of long birefringence fiber counting, its concrete steps that adopt are:
1), the light signal with wavelength variations is divided into the two-beam that intensity equates through photo-coupler, the first bundle light is divided into the two-beam that intensity equates and transmits around the same loop of being made up of ordinary optic fibre, long birefringence fiber and Polarization Controller along clockwise direction with counterclockwise respectively through first photo-coupler, return first photo-coupler then, and output to first PIN photodiode (4) simultaneously, change electric signal then into; First transmittance graph (a) is for being input to the transmittance graph of first PIN photodiode (4); The second bundle light is divided into the equal two-beam of intensity through second photo-coupler also to be transmitted around the same loop of being made up of another ordinary optic fibre, short birefringence fiber and Polarization Controller respectively along clockwise direction with counterclockwise, return second photo-coupler then, and output to second PIN photodiode (4 ') simultaneously, change electric signal then into; Second transmittance graph (b) is for being input to the transmittance graph of second PIN photodiode (4 '), short birefringence fiber wherein for make by fiber lengths second transmittance graph (b) in measuring wavelength coverage less than the birefringence fiber of half vibration period, long birefringence fiber for make by fiber lengths first transmittance graph (a) in the measurement wavelength coverage every nano wave length greater than the optical fiber of 5 vibration periods;
2), the rising edge and the negative edge of first transmittance graph (a) are all counted, utilize the increase and decrease of the monotonicity judgement wavelength of second transmittance graph (b), when second transmittance graph (b) during with the wavelength monotone increasing, counting to first transmittance graph (a) increases, when second transmittance graph (b) during, the counting of first transmittance graph (a) is reduced with the wavelength monotone decreasing;
3), according to the final count value i of first transmittance graph (a), utilize formula λ=i Δ λ to calculate the size of wavelength, wherein, λ is a wavelength, Δ λ is twice wavelength difference between counting, thereby determines wavelength change, finishes Wavelength demodulation.
2, the Wavelength demodulation method of Fibre Optical Sensor according to claim 1, it is characterized in that: described step 2) and 3) can finish by signal processing circuit and the single-chip microcomputer formed by amplifier and comparer, 1., the electric signal of first PIN photodiode (4), second PIN photodiode (4 ') output amplifies through first amplifier (18) and second amplifier (18 ') respectively concrete steps are:; The output signal of first amplifier is given rising edge comparer (19) and negative edge comparer (19 ') simultaneously, and reference voltage (20) is as the comparing voltage value of two comparers; When signal voltage rises or descends when crossing reference voltage, two comparers can be exported count signal respectively, and single-chip microcomputer (5) receives this signal;
2., when single-chip microcomputer (5) is successively received the count signal that two comparers send here, be taken up in order of priority the signal that second amplifier (18 ') is sent here to carry out twice A/D conversion, value with twice conversion compares then, monotonicity by short birefringence fiber ring mirror output intensity, determine to carry out add-one operation and still subtract 1 computing, carry out computing then;
3., the single-chip microcomputer result that will count is converted to corresponding wavelength value, and driving display (21) shows wavelength value.
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| CN102183325B (en) * | 2011-03-07 | 2012-11-07 | 北京交通大学 | Irregular optical fiber grating group stress sensor based on wavelength and amplitude dual coding |
| CN102274006B (en) * | 2011-06-24 | 2013-02-20 | 山东省科学院激光研究所 | Fiber grating temperature sensor and probe thereof |
| CN103148794B (en) * | 2013-02-07 | 2015-10-28 | 南京航空航天大学 | A kind of axial strain measuring method based on birefringence fiber environment |
| CN106017522B (en) * | 2016-05-11 | 2018-09-14 | 武汉理工大学 | A kind of quick high accuracy signal demodulating method of fibre-optical F-P sensor |
| CN109506684B (en) * | 2018-12-05 | 2020-11-17 | 山东微感光电子有限公司 | Wavelength correction method and system for fast scanning laser demodulation FBG sensor |
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