CN102128639A - Spontaneous Brillouin scattered light time-domain reflectometer on basis of double laser frequency locking - Google Patents
Spontaneous Brillouin scattered light time-domain reflectometer on basis of double laser frequency locking Download PDFInfo
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- CN102128639A CN102128639A CN 201010604834 CN201010604834A CN102128639A CN 102128639 A CN102128639 A CN 102128639A CN 201010604834 CN201010604834 CN 201010604834 CN 201010604834 A CN201010604834 A CN 201010604834A CN 102128639 A CN102128639 A CN 102128639A
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Abstract
The invention discloses a spontaneous Brillouin scattered light time-domain reflectometer on the basis of double laser frequency locking, which is mainly applied to the technical field of optical fiber sensing nets. The invention aims at providing a spontaneous Brillouin scattered light time-domain reflectometer with small volume, low price and stable wavelength difference between vibration light and incident light on the basis of the double-laser frequency locking. In order to solve the problems, the invention adopts the technical scheme that the spontaneous Brillouin scattered light time-domain reflectometer comprises a laser used as the incident light and a laser used as the vibration light. Light emitted by the laser used as the incident light is output to a detecting light path. After the light emitted from the detecting light path passes through an electro-optical modulator, a light amplifier and a circulator controlled by a pulser, the light enters into a sensing fiber to obtain Brillouin scattered light. The Brillouin scattered light passing the circulator and the light emitted by the laser used as the vibration light are in beat frequency interfere through a coupler. At last, electrical signals are output by a photoelectric detector and are collected and processed by a computer with a data acquisition card.
Description
Technical field
The present invention relates to a kind of spontaneous brillouin scattering optical time domain reflectometer, be mainly used in the optical fiber sensor network technical field based on the twin-laser frequency locking.
Background technology
In current distributing optical fiber sensing field, occupy critical role based on the sensor of optical fiber Brillouin scattering principle, and be divided into based on spontaneous Brillouin with based on the sensor of stimulated Brillouin scattering according to the technology class of concrete application.Basic technique principle involved in the present invention is exactly the spontaneous brillouin scattering that comes from the optical fiber.The part photon of incident light is by the thermoacoustics phon scattering in the optical fiber, and photon wavelength generation minor shifts becomes the Brillouin scattering photon, and its wavelength shift amount is relevant with the temperature and the stress of optical fiber.Here it is, and spontaneous brillouin scattering is used for the ultimate principle of Fibre Optical Sensor.Based on the Fibre Optical Sensor of spontaneous brillouin scattering, its system constitutes and is made of light source, light pulse modulation, sensor fibre, Coherent Detection and data processing section usually.Wherein light source and light pulse modulation is the front end of system, is used for that pulsed light is sent into sensor fibre and excites Brillouin scattering.Coherent Detection and data processing are the processing rear ends of system, are used for the frequency spectrum demodulation of spontaneous brillouin scattering light and the storage and the analysis of data.In the Coherent Detection part, in the research that major part has been reported, all be earlier Brillouin scattering and the relevant beat frequency of incident light so to be converted to electric signal with the photodetector of high bandwidth.Because the frequency of this electric signal still is difficult to existing equipment collection about 10GHz, so also need the microwave signal beat frequency close with another frequency, difference frequency signal just can drop to the magnitude of hundreds of million so again, makes things convenient for the collection analysis of data.Obviously in this traditional scheme, microwave signal source is than indispensable equipment, but it is bulky, and price is also more expensive.Differ about 10-11GHz at Brillouin scattering and incident light frequency in addition, thus the bandwidth of the used photodetector of their relevant beat frequency also will be in same magnitude, and the photodetector relative signal-to-noise ratio of high bandwidth is low, price is also expensive.Based on above consideration, the someone has proposed to replace the scheme of microwave signal source in the Coherent Detection system.
D. Iida (the D. Iida and F. Ito of Japanese NTT company in 2009, " Cost-effective bandwidth-reduced Brillouin optical time domain reflectometry using a reference Brillouin scattering beam "
Appl. Opt.48,4302-4309,2009) zone sensors when having reported a kind of Brillouin light that does not need microwave signal source, its core concept is to utilize Brillouin scattering that an optical fiber different with sensor fibre produces as local oscillator light.The Brillouin shift of two kinds of optical fiber is different but differ less about hundreds of million, like this their just direct collection analysis of signal of difference frequency that is concerned with.But this system exists the local oscillator photo-labile to cause the problem of systematic measurement error and consistance difference.When this root was used to produce the temperature of optical fiber of local oscillator light and environment and changes, the Brillouin shift of optical fiber changed thereupon, this means that the local oscillator light wavelength is changing, so can influence the stable of beat signal, the error of measurement is increased.In addition, usually the live width of Brillouin scattering (about 30,000,000) is wideer several times than the live width (about 1-5 million) of general Distributed Feedback Laser in the optical fiber, and the live width of local oscillator light directly has influence on the precision of measurement, so work as Brillouin scattering as the local oscillator light time, can cause measuring accuracy to descend.
Though this novel Brillouin sensing apparatus has been simplified microwave signal source, there is the unstable and roomy problem of local oscillator light of wavelength difference of Brillouin's local oscillator light and incident light.The Brillouin shift that coherent demodulation obtains is directly related with this wavelength difference, so the unstable consistance that can influence the accuracy and the measurement of fiber optic temperature and stress measurement of wavelength difference can make the decline of measuring accuracy and live width is wide.
Summary of the invention
The technical problem to be solved in the present invention provides that a kind of volume is little, the stable spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking of wavelength difference of low price and local oscillator light and incident light.
For addressing the above problem, the technical solution used in the present invention comprises the laser instrument as incident light, laser instrument as local oscillator light, described laser instrument as incident light penetrates light and outputs to the detection light path through coupling mechanism, survey the electrooptic modulator that the ejaculation light in the light path is controlled through the pulse generator, image intensifer, enter sensor fibre behind the circulator and obtain Brillouin scattering, Brillouin scattering penetrates light by the relevant beat frequency of coupling mechanism through circulator and described laser instrument as local oscillator light, by the photodetector output electric signal, electric signal is by computer acquisition that has data collecting card and processing at last.
Described spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking, it is characterized in that this optical time domain reflectometer also comprises a dynamically frequency locking device of two laser wavelength differences of control, described frequency locking device comprises the PIN detector, microwave counter and feedback circuit, described as incident light laser instrument and penetrate light as the laser instrument of local oscillator light and output in the frequency locking light path through coupling mechanism, ejaculation light in the frequency locking light path is incorporated in beat frequency in the PIN detector, the PIN detector is converted to electric signal with light, and send into the microwave counter, it is poor that the microwave counter records optical frequency, and pass to feedback circuit, feedback circuit by relatively optical frequency difference and predefined difference frequency value tuning as incident light laser instrument and as the wavelength of the laser instrument of local oscillator light.
Described spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking is characterized in that described laser instrument as incident light, is distributed feedback type semiconductor laser as the laser instrument of local oscillator light.
Described spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking is characterized in that this optical time domain reflectometer also comprises a wave filter, and described Brillouin scattering is through wave filter input photodetector.
Described spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking is characterized in that described laser instrument as incident light, compares less than 500 MHz with the spontaneous brillouin scattering frequency shift value in the sensor fibre as its wavelength difference of laser instrument of local oscillator light.
Described spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking is characterized in that described photodetector operation wavelength is 900-1630nm, and responsive bandwidth is less than 1GHz.
Described spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking is characterized in that described optical filter is the reflection type optical fiber grating filter.
Described spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking is characterized in that this optical time domain reflectometer also comprises a scrambler, described laser instrument as local oscillator light penetrate light behind scrambler with the relevant beat frequency of described Brillouin scattering.
The above-mentioned spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking has following beneficial effect:
1, do not adopt heavy expensive microwave signal source, and adopt another light source close to be used for the coherent demodulation of Brillouin's signal as local oscillator light with lambda1-wavelength, only need a frequency reducing just Brillouin's signal can be dropped to hundreds of million, directly by the data collecting card collection, simplified the coherent demodulation mode of Brillouin's signal, and reduced equipment volume and reduced equipment cost.
2, between twin-laser, increased frequency locking device (3), the wavelength difference of the detection incident light that this device does not stop and two light sources of local oscillator light, compare with the preset wavelength difference and the wavelength of two light sources of ACTIVE CONTROL, make their wavelength difference constant all the time, so just eliminated the systematic measurement error that the optical source wavelength drift is caused at preset value.
3, the bandwidth of used photodetector (14) allows to be lower than 1GHz.The signal to noise ratio (S/N ratio) of low bandwidth detector is higher relatively, can improve the sensitivity of sensor-based system.
Description of drawings
The present invention is further detailed explanation below in conjunction with the drawings and specific embodiments.
Fig. 1 is a structural representation of the present invention.
Fig. 2 is the control flow chart of frequency locking device of the present invention.
Embodiment
Shown in Figure 1, spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking of the present invention, comprise two semiconductor lasers, be respectively as the laser instrument 1 of incident light with as the laser instrument 2 of local oscillator light, their wavelength difference is set at spontaneous brillouin scattering frequency displacement near sensor fibre 10, and (representative value is: 10.8 GHz).Most of light of laser instrument 1 is as sensing laser, it penetrates light and outputs to the detection light path through coupling mechanism 4, at first the electrooptic modulator of being controlled by pulse producer 76 is modulated into pulsed light, is then continued to amplify by fiber amplifier 8, enters sensor fibre 10 by optical fiber circulator 9 at last.After the pulsed light of modulation enters optical fiber, constantly in optical fiber, be scattered, obtain Brillouin scattering, Brillouin scattering enters with laser instrument 2 as local oscillator light through optical fiber circulator 9 and penetrates light by coupling mechanism 4 relevant beat frequencies, at last by photodetector 14 output electric signals.Because the wavelength as the laser instrument 2 of local oscillator light is close with sensor fibre 10 spontaneous brillouin scatterings frequency, only need a beat frequency just Brillouin's signal can be dropped to hundreds of million, by bandwidth less than 1GHz, operation wavelength is that the photodetector 14 of 900-1630nm is converted to electric signal, is gathered and is handled by the computing machine 15 that has data collecting card at last.
The present invention also comprises a reflecting light fiber filter 11, scrambler 12, and reflecting light fiber filter 11 its centre wavelengths are the output wavelength as the laser instrument 1 of incident light, and three dB bandwidth is 0.08nm.Before relevant beat frequency, scattered light filters out the Rayleigh scattering light part through optical fiber filter 11, Brillouin scattering in the remainder and laser instrument 2 relevant beat frequencies as local oscillator light.Before relevant beat frequency, as the output light of the laser instrument 2 of local oscillator light earlier through scrambler 12 in order to reduce polarization noise.
As shown in Figure 2, the present invention also is provided with a frequency locking device 3, and it is poor to be mainly used in two laser wavelengths of dynamic control.At first in frequency device 3, preestablish a difference frequency value, spontaneous brillouin scattering frequency shift value in this setting value and the sensor fibre 10 differs less than 500 MHz, frequency locking device 3 comprises PIN detector 3a, microwave counter 3b and feedback circuit 3c, as the laser instrument 1 of incident light with tell fraction light as the ejaculation light of the laser instrument 2 of local oscillator light by fiber coupler 4 and enter in the frequency locking light path by the frequency locking light path, ejaculation light in the frequency locking light path is incorporated in beat frequency among the PIN detector 3a, PIN detector 3a is converted to electric signal with light, and electric signal sent into microwave counter 3b, microwave counter 3b and predefined difference frequency value compare, if be not inconsistent with setting value, send feedback signal to regulating its wavelength by feedback circuit 3c as the laser instrument 1 of incident light with as the laser instrument 2 of local oscillator light, consistent until the difference on the frequency of two-beam with setting value.
Claims (8)
1. spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking, it is characterized in that this optical time domain reflectometer comprises the laser instrument (1) as incident light, laser instrument (2) as local oscillator light, described laser instrument as incident light (1) penetrates light and outputs to the detection light path through coupling mechanism (4), survey the electrooptic modulator (6) that the ejaculation light in the light path is controlled through pulse generator (7), image intensifer (8), enter sensor fibre (10) behind the circulator (9) and obtain Brillouin scattering, Brillouin scattering penetrates light by the relevant beat frequency of coupling mechanism (4) through circulator (9) and described laser instrument as local oscillator light (2), by photodetector (14) output electric signal, electric signal is gathered and is handled by the computing machine that has data collecting card (15) at last.
2. the spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking according to claim 1, it is characterized in that this optical time domain reflectometer also comprises a dynamically frequency locking device (3) of two laser wavelength differences of control, described frequency locking device (3) comprises PIN detector (3a), microwave counter (3b) and feedback circuit (3c), described laser instrument (1) and penetrate light as the laser instrument (2) of local oscillator light and output in the frequency locking light path through coupling mechanism (4) as incident light, ejaculation light in the frequency locking light path is incorporated in beat frequency in the PIN detector (3a), PIN detector (3a) is converted to electric signal with light, and send into microwave counter (3b), it is poor that microwave counter (3b) records optical frequency, and passing to feedback circuit (3c), feedback circuit (3c) is by relatively optical frequency difference and the tuning laser instrument as incident light of predefined difference frequency value (1) with as the wavelength of the laser instrument (2) of local oscillator light.
3. the spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking according to claim 1 is characterized in that described laser instrument as incident light (1), is distributed feedback type semiconductor laser as the laser instrument (2) of local oscillator light.
4. the spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking according to claim 1, it is characterized in that this optical time domain reflectometer also comprises a wave filter (11), described Brillouin scattering is through wave filter (11) input photodetector (14).
5. the spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking according to claim 1 is characterized in that described laser instrument as incident light (1), compares less than 500 MHz with the spontaneous brillouin scattering frequency shift value in the sensor fibre (10) as its wavelength difference of laser instrument (2) of local oscillator light.
6. the spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking according to claim 1 is characterized in that described photodetector (14) operation wavelength is 900-1630nm, and responsive bandwidth is less than 1GHz.
7. the spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking according to claim 4 is characterized in that described optical filter (11) is the reflection type optical fiber grating filter.
8. the spontaneous brillouin scattering optical time domain reflectometer based on the twin-laser frequency locking according to claim 1, it is characterized in that this optical time domain reflectometer also comprises a scrambler (12), described laser instrument (2) as local oscillator light penetrate light through scrambler (12) after with the described Brillouin scattering beat frequency that is concerned with.
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| CN102506904A (en) * | 2011-10-17 | 2012-06-20 | 南京大学 | Spontaneous Brillouin scattering optical time domain reflectometer based on superconductive nanowire single-proton detector |
| CN102809430A (en) * | 2012-08-22 | 2012-12-05 | 哈尔滨工业大学 | Device for Brillouin optical time domain reflectometer based on optical phase-locked ring |
| CN102829812A (en) * | 2012-08-22 | 2012-12-19 | 哈尔滨工业大学 | Brillouin optical time domain analysis meter capable of locking frequencies of two lasers based on optical phase-locked loop |
| CN106441447A (en) * | 2016-11-15 | 2017-02-22 | 太原理工大学 | Chaos Brillouin dynamic grating based distributed optical fiber sensing system |
| CN107218902A (en) * | 2017-07-06 | 2017-09-29 | 中国科学院半导体研究所 | The fiber grating signal demodulating system measured based on double laser light source frequency locking and beat frequency |
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| CN102506904A (en) * | 2011-10-17 | 2012-06-20 | 南京大学 | Spontaneous Brillouin scattering optical time domain reflectometer based on superconductive nanowire single-proton detector |
| CN102809430A (en) * | 2012-08-22 | 2012-12-05 | 哈尔滨工业大学 | Device for Brillouin optical time domain reflectometer based on optical phase-locked ring |
| CN102829812A (en) * | 2012-08-22 | 2012-12-19 | 哈尔滨工业大学 | Brillouin optical time domain analysis meter capable of locking frequencies of two lasers based on optical phase-locked loop |
| CN102809430B (en) * | 2012-08-22 | 2014-09-17 | 哈尔滨工业大学 | Device for Brillouin optical time domain reflectometer based on optical phase-locked ring |
| CN102829812B (en) * | 2012-08-22 | 2015-01-07 | 哈尔滨工业大学 | Brillouin optical time domain analysis meter capable of locking frequencies of two lasers based on optical phase-locked loop |
| CN106441447A (en) * | 2016-11-15 | 2017-02-22 | 太原理工大学 | Chaos Brillouin dynamic grating based distributed optical fiber sensing system |
| CN107218902A (en) * | 2017-07-06 | 2017-09-29 | 中国科学院半导体研究所 | The fiber grating signal demodulating system measured based on double laser light source frequency locking and beat frequency |
| CN107218902B (en) * | 2017-07-06 | 2019-08-09 | 中国科学院半导体研究所 | Fiber grating signal demodulating system based on double laser light source frequency locking and beat frequency measurement |
| CN107515100B (en) * | 2017-08-15 | 2019-08-20 | 昆山金鸣光电科技有限公司 | A kind of pulsed light fiber switch condition detecting system |
| CN107515100A (en) * | 2017-08-15 | 2017-12-26 | 昆山金鸣光电科技有限公司 | A kind of pulsed light fiber switch condition detecting system |
| CN109946267A (en) * | 2019-04-18 | 2019-06-28 | 南昌航空大学 | Gas Rayleigh-Brillouin spectral lines measuring device and method |
| CN109946267B (en) * | 2019-04-18 | 2022-02-25 | 南昌航空大学 | Device and method for measuring gas Rayleigh-Brillouin scattering spectral line |
| CN110307862A (en) * | 2019-06-20 | 2019-10-08 | 江南大学 | A kind of fiber grating beat frequency demodulating system based on the detection of radiofrequency signal bandwidth |
| CN110231085A (en) * | 2019-07-09 | 2019-09-13 | 卫欢 | Phase modulation-type optical time domain reflectometer |
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| CN113124994B (en) * | 2021-05-24 | 2022-09-23 | 中国计量大学 | Distributed vibration sensing demodulation method based on weak signal-to-noise ratio signal |
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