Silicon-based optical waveguide modulators and mode-locked titanium:sapphire laser dynamics

Single-mode deeply-etched silicon-germanium/silicon (SiGe/Si) rib waveguides have been fabricated and characterized with low propagation losses and strong guiding. Such a waveguide structure is suitable for bent waveguide devices and provides efficient field overlapping, which is needed for devices requiring strong nonlinear coupling.; Using the deeply-etched waveguide technique, we have fabricated Si/SiGe/Si Mach-Zehnder modulators, which show strong single-mode waveguiding but only small electro-optic modulation has been observed so far. Another Si modulator is a Fabry-Perot interferometer. We have demonstrated all-optical modulation at 1.3 {dollar}mu{dollar}m and 1.5 {dollar}mu{dollar}m in the reflection mode of the asymmetric Si Fabry-Perot interferometer by a control light beam at 0.85 {dollar}mu{dollar}m. Both switching-on and switching-off operations are demonstrated by transversely moving the etalon.; In addition, we have analyzed that silicon carbide (SiC) waveguides exhibit low loss for fundamental modes and high loss for higher-order modes at wavelengths from 0.6 to 1.6 {dollar}mu{dollar}m. Electro-optic modulation is analyzed with a SiC-on-SiO{dollar}sb2{dollar} waveguide structure. Such modulators are potential candidates for high-speed electro-optic modulation for silicon-based optoelectronic devices.; Furthermore, we studied the dynamics of a Kerr-lens self-mode-locked Ti:sapphire laser, generating 40-fs pulses and tunable from 750 nm to 920 nm. A moving mirror was first proposed as a starting mechanism for self-mode locking and the starting dynamics is studied in detail. In addition, periodic pulse-train amplitude modulations have been observed and studied. The observation of the amplitude modulation further confirms the dynamic Kerr-lens self-focusing model of self-mode locking in Ti:sapphire lasers and helps us better understand the laser performance. Furthermore, dual-wavelength mode locking is observed over a broad tuning range, which would be very useful for two-wavelength subpicosecond optical sampling, such as pump-probe experiments that require different wavelengths for pumping and probing.