Titanium dioxide (TiO 2 ) has several attractive properties such as high linear and nonlinear refractive indices and the wide bandgap for applying the nonlinear optical devices. We have been studied channel waveguides with TiO 2 as the submicron size core to verify their feasibility as the nonlinear optical devices. In this study, we analyzed optical propagation in the TiO 2 photonic crystal waveguide and demonstrated the enhanced optical nonlinearity due to slow light effect.

We observed photonic band-gap disappearance on Bragg-grating wavelength filters with Si photonic-wire waveguides, and studied the physical mechanism with theoretical and numerical analyses. This is a unique phenomenon observed in channel waveguides with very high index-contrast between the waveguide core and cladding materials. The photonic band-gap disappearance was observed in structures where two different optical field distributions of standing wave degenerate.