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Research On Multiwavelength Fiber Laser And Distributed Fiber Sensing Based On Brillouin Scattering

Posted on:2012-04-11Degree:DoctorType:Dissertation
Country:ChinaCandidate:J G TangFull Text:PDF
GTID:1228330392455573Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
With the increasing demand for information capacity, the high-speed, large-capacity andlong-distance telecommunication are the trends of development in the next generationall-optical network. In order to make good uses of the limited resource in communicationfrequency, the frequency spacing of20GHz or even10GHz is one of development directionfor the future DWDM. Mutiwavelength Brillouin-erbium fiber laser (MBEFL) has beenregarded as a potential and prosperous solution of communication source owing to severalimportant advantages, e.g. the narrow linewidth, rigid wavelength spacing, widely tunablility,low threshold, low intensity noise, the stable single-longitudinal-mode operation at roomtemperature. Moreover, there are potential applications in the fiber optics sensor network, RFand other areas.The distributed Brillouin fiber sensor possesses a distinguishing feature besides otherfiber-optic sensors, can measure temperature and strain simultaneously, and can be appliedto electric power, petrochemical, nuclear power plants, highways, bridges, tunnels, dams,railways, aerospace and other industries, and has attracted more and more attentions in therecent decade. However, the distributed Brillouin sensor is difficult to extensive use due tocomplicated system, immature technology, high cost and long acquisition time.Sponsored by the Industrial Key Projects Programs of Chancheng District of Foshan city,National Natural Science Foundation and Research and Development Program of China in thedissertation, the MBEFL and the distributed Brillouin sensing system are investigated bypreliminary theory and experiments. Several research achievements and contributions aresummarized as the followings:Firstly, according to Brillouin coupled-intensity equations, an approximate analyticexpression is derived under the steady state Brillouin scattering without neglecting the fiberattenuation and pump depletion, and is compared with the exact numerical solution. Brillouinthresholds under the four different conditions are studied and verified by experiment.Temporal and intensity evolution of the Stokes and pump and the effect of frequency detuningcaused by temperature or strain, are simulated, obtain an effective method, which can detectthe position and size of the frequency detuning. Secondly, using a135-m highly nonlinear fiber (HNLF), exploiting passive feedbackfiber ring to enlarge the free spectral range and a3-m unpumped EDF to help theimplementation of ultra-narrow comb filter and frequency stabilization, Brillouin fiber laser(BFL) with a single-longitudinal-mode operation is obtained with the power fluctuations of0.2dBm, which can be used as a local light in the distributed Brillouin fiber sensor.Thirdly, MBEFL is demonstrated Based on a Sagnac fiber ring with a9.4-km singlemode fiber (SMF). The proposed BFL is able to generate up to25Stokes lasing lines withwavelength spacing of10GHz and a tuning range of50nm. The impact of EDFA pumpcurrent and Brillouin pump (BP) power on the number of wavelength and tunableness areanalyzed.Fourthly, a simple configuration for achieving stable and widely tunable dual-wavelengthBrillouin fiber laser is proposed and experimentally investigated.21.316GHz and10.658GHz microwave signals can be achieved simultaneously by beating the Brillouin fiber laser ata high-speed photodetector. The maximum frequency fluctuation of the microwave signal is0.3MHz and3dB linewidth is4.5MHz.Fifthly, we qualitatively analyzed the phase-mismatch condition for degenerate andnon-degenerate four-wave mixing (FWM) processes. Make good uses of linewidth narrowingof Brillouin fiber laser and transparent wavelength conversion of FWM, the tunablemultiwavelength generation based on Brillouin-erbium comb fiber laser assisted by MFWMprocesses is investigated. Under the condition of160-mW pump power using a2.5-km SMF,multiwavelength Brillouin fiber (MBFL) is experimentally achieved19lasing lines with awavelength spacing of21GHz. MBEFL utilizing Brillouin pump preamplification techniqueand cascaded and multiple SBS and FWM processes, is demonstrated experimentally. TheMBEFL with a135-m HNLF can generate20-nm comb spectrum with0.075-nm wavelengthspacing, which is more than150lasing lines in a single-longitudinal-mode operation.However, a9.4-km SMF instead of a135-m HNLF, the MBEFL with a low threshold, atunable range of50nm and good power flatness is achieved.Finally, we propose a single and cost-effective technique that that can reduce theelectrical bandwidth for Brillouin frequency-shift sensors with heterodyne detection withoutthe need for expensive instruments or a complicated system. With this technique, a BFL isused as a local light for heterodyne detection and the bandwidth of photodetector and electronic devices are reduced to200MHz~1.5GHz. A double-pulse Brillouin pump makes agood use of the phonon relaxation properties in order to increase the spatial resolution,signal-to-noise ratio and acquisition time. Moreover, based on the FPGA techonlogy, wedesign and process a PCB with a frequency of200MHz to drive the electro-optic modulatorin order to produce double-pulse pump light. The heterodyne signal with1.4359GHz andBrillouin temperature coefficient of1.094MHz/℃are experimentally achieved by using theBFL with a135-m HNLF as a local light.
Keywords/Search Tags:Stimulated Brillouin Scattering (SBS), Brillouin Fiber Laser (BFL), Multiwavelength Brillouin-erbium Fiber Laser (MBEFL), Brillouin Optical Time-Domain Reflectometer (BOTDR), Multiple Four-Wave Mixing (MFWM), Highly Nonlinear Fiber (HNLF)
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