Structure-dependent Optical Characteristics of One-dimensional Photonic Crystal Hydrogenated Amorphous Silicon Waveguides

초록

Slow light representing the low group velocity of light in a high-group index medium has become an important field of research. Recently it has been demonstrated that the photonic crystal waveguides with periodic structures deliver a high-group index and thus provide slow-light enhanced optical nonlinear effects. In addition, several other candidate technologies, such as coupled resonators, one-dimensional (1-D) gratings or holes, or two-dimensional (2-D) photonic crystals (PhCs) formed in optical fibers or waveguides, have been studied for the slow light. The increased interaction of the light beam with the waveguide materials due to its reduced group velocity within the periodic structures allows the nonlinear optic devices short even for low optical pump powers. Typically the 1-D periodic structured optical waveguides provide the wavelength-selective properties with high quality factors in a free spectral range (FSR) and the slow light characteristics due to large group indices near the band-edge region. Most PhC waveguide structures exhibit a wide spectral band-gap region, i.e., a wavelength region where no light can propagate, and wide transmission bands beside it. The band-gap wavelength region depends on the structural characteristics of the 1-D PhCs, such as the lattice constant and hole diameter. The transmission spectral profiles of the transmission bands are similar to the interference pattern of Fabry-Perot (FP) filters. In this paper we report on the experimentally measured optical characteristics in 1-D PhC waveguides made of hydrogenated amorphous silicon with various device structures and compare them with numerically simulated results.