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Study On The Tunability And Mode-locked Properties Of The Yb3+-doped Ring Fiber Laser

Posted on:2014-01-01Degree:MasterType:Thesis
Country:ChinaCandidate:J R ZhangFull Text:PDF
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Fiber laser offers a number of advantages, including small size, light weight, highpower, wide wavelength tunable range, good stability, strong application and otherfine features. It will be widely applied in fields of high-speed and large-capacity fibercommunication system, and play an increasingly important role in thehigh-performance optical sensing, precision spectroscopy, laser medical treatment,military and other fields at the same time. Among them, applications in densewavelength division multiplexing communication system of the rare earth-doped (Er3+,Yb3+, etc.) fiber laser has received extensive attention. Yb3+has a very wideabsorption spectra and emission spectra, which can be incorporated into the silicafiber as a laser gain medium, or co-doped with other rare earth element as an energytransfer medium. The passively mode-locked is an all-optical non-linear technique,ultra-short pulse output can be achieved in the case of the cavity without any activedevice such as the modulator and so on. Passively mode-locked fiber lasers can not beseparated from the non-linear effect of the fiber. In this article, make use of thenonlinear polarization rotation (NPR) mode-locked mechanism, light fields ofdifferent intensity experience different nonlinear phase shifts because of self-phasemodulation(SPM) and cross-phase modulation(XPM) effect, then combine with theprinciple of polarization filter, producing the intensity dependent loss of optical signalto achieve the self-amplitude modulation (APM) and realize mode-locked output atlast.This article discusses the tunability of continuous-wave and outputcharacteristics which are affected by the effect of fiber optic strain in the ring cavityfiber laser, then analysis and explain the experiment phenomena. Next, studymode-loced tuning of the laser by detailed experiment. Specifically, the thesiscontains four parts as follows: The first part, describe the origin, developmentbackground of the fiber laser, and the main features of such lasers, summarizing the major technical problems that currently exist and its development prospects. Thesecond part, elaborate the phase modulation effect which is induced by the fiber opticstrain, analysis the nonlinear polarization rotation mode-locking mechanism, andprovide theoretical guidance for understanding experimental phenomena andtheoretical basis for further optimization of the performance of the laser. The thirdpart, first, discuss the single wavelength tuning performance which is affected by theeffects of fiber optic strain.7m1060-XP-type single mode fiber are wrapped aroundthe piezoelectric ceramic tube(PZT), using F-P interferometer source to providevoltage and drive the PZT. It will induce more birefringence effect than before, andincrease the fiber stress in their radial direction, thus we can achieve stable continuoustuning of single wavelength and its jumping step is0.36nm. When50V,100V and150V driving voltage are applied to the PZT, single wavelength tuning range does nothave a greater impact, they are namely51nm,53nm,52nm. Next, discuss theinfluence on the laser slope efficiency after driving the PZT. During the experiment,measure the laser slope efficiencies of1032.14nm,1045.46nm and1038.08nm afterapplying a driving voltage of50V,100V and150V on PZT. Contrast the laser slopeefficiencies of the same wavelength under the different driving voltages, when thePZT is driven in use of100V and150V, finding that the slope efficiencies of1032.14nm,1045.46nm and1038.08nm are higher than no voltage is applied. Therefore,drive the PZT to induce fiber strain play an important role on the improvement of theslope efficiency of the laser. The fourth part, discuss the relationship between thecontinuous tuning of the mode-locked pulses with the pump power and wave platespin angle. First, in the case of wave plate spin angular are fixed, it is found that themode-locked pulse changes with pump power, it can achieve continuous tuning from1035.8nm to1033.3nm, and the tuning width is2.6nm. Next, the pump power isfixed in232mW, adjusting the left1/4wave plate and1/2wave plate, mode-lockedpulse tunes continuously from1036.03nm to1038.98nm, the tuning width is close to3nm. After that, measure the tuning range of center wavelength of mode-locked pulsewhich does not require continuous tuning. Collect all the center wavelengths, find thatthe center wavelength of mode-locked pulse tunes from1035.8nm to1043.6nm, the tuning width is7.8nm. Finally, replace the PZT whose diameter is34mm withcylindrical mold (which is called as solenoid) whose diameter is12mm and80mmrespectively, and observe their mode-locked and single wavelength tuning range.When using the solenoid whose diameter is12mm, the birefringence effect thatinduced by fiber bending and stress has been enhanced, therefore the singlewavelength tuning range of the laser is broaden, it ranges from1019nm to1078nm.However, due to the bending radius of fiber is too large, resulting more additional loss,so the laser has been unable to realize a stable mode-locked pulse output. When usethe solenoid whose diameter is80mm, it is easy to realize stable mode-locked pulses,and stay for a long time. Nevertheless, because of the relatively large bending radius,the fiber birefringence effect has been weaken, single wavelength tuning range arenarrowed from1026nm to1053nm with width of27nm. As a result, theoreticalsimulations about the diameter of solenoids should be conducted when they are usedin the laser system to optimize the properties of mode locked and tuning performance.Through this thesis, a deeper understanding of continuous-wave tuning, outputcharacteristics and wavelength tuning of mode-locked pulse is made. In addition,propose some technical solutions to optimize the tuning and output characteristics offiber laser. Moreover, describe some problems that exist in the system and providingexperimental basis for further study of the related performances of such lasers.
Keywords/Search Tags:Ring fiber laser, Yb3+-doped fiber, wavelength tunability, mode-locked, fiberstrain
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