Ultra-broadly Tunable Light Sources Based On The Nonlinear Effects In Photonic Crystal Fibers

The applications of lasers are extending increasingly into new fields. In a lot ofnew application, ultra-broadly tunable light sources operated at unconventionalwavelength regions are in needed. However, it is a hard work to develop new materialthat can emit at new wide wavelength regimes. Nonlinear optics processes can be usedto convert the fine developed laser energy to unconventional wavelength regimes.Photonic crystal fiber is promising medium for nonlinear optical process due to itsflexible dispersion profile and high nonlinear properties. The thesis focuses on theinvestigations of novel wavelength generations at unconventional wavelength bandsbased on the nonlinear effects in photonic crystal fibers.The dependence of the spectral properties of parametric gain on the dispersion,nonlinear coefficient and pump wavelength are investigated theoretically. Subsequently,a PCF with two zero-dispersion wavelengths is designed precisely for wavelengthconvertion of signal located in communication band to blue and green spectral bands.And the expected wavelength conversion over large span is realized experimentally bypumping the PCF with a Ti: sapphire femtosecond laser. The physical mechanism of thegeneration of dispersive wave in PCFs is also studied theoretically. In experiment, thetunable dispersive waves are generated simultaneously at visible and mid-infraredspectral regimes by tuning the pump power. The wavelength of the visible dispersivewave can approach as short as425nm, and the wavelength of the mid-infrareddispersive wave approaches as long as2279nm. The ultraviolet band from200nm to400nm is generated via the cross phase modulation between the visible anti-Stokesband and the pump Raman soliton.A homemade mode-locked ytterbium doped fiber laser would be used as the pumpsource. A kind of dispersion flattened PCF with the zero dispersion wavelength locatednear1064nm is designed precisely. Tunable optical parametric gain bands can beobtained from927nm to1038nm and from1099nm to1228nm. APCF-based opticalparametric amplifier with broadband high gain can be formed by injecting a weak signalwave and a pump wave with high intensity into the PCF simultaneously. The generated spectral components from parametric gain are fed back into the PCFthrough a ring cavity. Hence, the spectral components are amplified repeatly, and aPCF-based optical parametric oscillator (OPO) is formed. The PCF-based OPO can beoperated in a wide wavelength range over340nm by tuning the pump wavelength. Thetenability is facilitated by using the time-dispersion-tuned technique. The outputwavelength can cover a broad band continuously without tuning the pump wavelength.In order to improve the energy conversion efficiency, two methods are used. Forthe first method, a doubly resonant configuration is used, the signal and thephase-matched idler can oscillate simultaneously, and the conversion efficiency can beimproved by2.2to3.8times compared with the traditional single cavity configuration.In the alternative method, based on an all fiber cavity, the inner conversion efficiencyare greatly enhanced, which is as high as36%. To the best of our knowledge, it is thelargest conversion efficiency for PCF-based OPO.