Abstracts Category : Other

Linear and nonlinear properties of tapered fibers andapplications in femtosecond science and technology

by Fei Lu

Over the past few years, successful fabrication ofphotonic crystal fibers and tapered fibers have extended fibers'applications to much broader fields such as frequency metrology,spectroscopy, optical coherence tomography, microscopy, etc. Theirgreat potential in applications stems from their special andengineerable linear and nonlinear properties. Our research isfocused on studying and manipulating the linear and nonlinearproperties of photonic crystal fibers and tapered fibers, anddemonstrating their applications in femtosecond science andtechnology with their unique properties. </br>Wedesign and construct a CO laser tapering system and successfullyuse it to fabricate various kinds of tapered fibers. Using taperedsingle mode optical fibers, we demonstrate supercontinuumgeneration with larger than one octave spectral span. By applyingthe delayed pulse method to characterize the supercontinuum, weobserve a strong dependence of the spectral coherence on the inputwavelength, and then obtain a highly spectral coherentsupercontinuum from 500nm to 1300nm by properly locating the inputwavelength in the relatively deep anomalous dispersion region. Westudy the high order soliton fission process that produces thesupercontinuum. </br>We show numerically andexperimentally that the soliton fission process is extremelysensitive to the input state of polarization even in an isotropicnonlinear medium, which leads to a significantly different vectorsoliton fission scenario compared to the most commonly used scalarscenario. </br>With the diameter-manipulatingability offered by our CO laser tapering system, we introducesub-mm scale dispersion micro- management (DMM) into holey fibers,and demonstrate generation of coherent and stable femtosecondvisible pulses with scalable bandwidth and center-wavelength in therange from 385 to 625 nm. The longitudinal variation of thephase-matching conditions for Cherenkov radiation and four-wavemixing explains these results well. We compare the broadband noiseof these visible pulses generated through DMM holey fibers, taperedfibers and long holey fibers, and find that DMM holey fibers offerthe lowest noise visible pulse generation. </br>Making use of DMM flexibility we propose a newapproach of generating a feedback signal for carrier-envelope phasestabilization, and experimentally obtain a strong feedback signalwith a 37 dB SNR. We demonstrate another application of taperedfibers by fabricating a tapered Yb-doped fiber and put it intolaser cavity, acting as a dispersion compensation component and again medium. We then generate a stable CW mode-locking pulse trainat 1035 nm using this tapered fiber. </br>We alsogenerate and observe other interesting phenomena related with thelinear and nonlinear properties of our tapered fibers. We arecarrying out further investigations to fully exploit theapplication potential of them.