Nonlinear Optical Processes for Spectral Broadening and Short Pulse Generation

The dramatic progress in optical communication is attributed to the development of wavelength-division multiplexing and time-division multiplexing technologies, which employ broadband light source and ultrashort optical pulses respectively to carry signals in optical fibers. Supercontinuum generation is the spectral broadening of narrow-band incident pulses by the propagation through optical waveguides made of nonlinear materials. In this PhD dissertation, I show the design of a tapered lead-silicate optical fiber for supercontinuum generation. The physical mechanisms of optical pulse evolution are explained, which involve various nonlinear optical effects including self-phase and cross-phase modulation, stimulated Raman scattering, four-wave mixing, modulation instability and optical soliton dynamics. I have also proposed planar waveguides with longitudinally varying structure to manage chromatic dispersion, and numerically simulated the generation of (1) broadband and (2) flat octave-spanning supercontinuum output. The coherence property and noise sensitivity of supercontinuum are also investigated in this dissertation, which depend strongly on pumping conditions. A hybrid mode-locked erbium-doped fiber ring laser, which combines rational harmonic active mode-locking technique and graphene saturable absorber, has been designed and experimentally demonstrated to produce optical pulse train. Compared to active mode-locking configuration, the hybrid scheme narrows the pulse width significantly at a high repetition rate of 20 GHz