Functional components in SOI photonic crystal slabs

We study various types of two-dimensional photonic crystal (PhC) waveguides (WG) on silicon-on-insulator (SOI) substrates for future photonic integrated circuit (PIC) applications. One of our goals is to realize a low-loss single-mode PhC WG. Off-plane diffractive leakage above the cladding layer light line is a serious problem in SOI-based PhC-WGs. We overcame this problem in width-varied line defect waveguides whose core-widths are changed by sliding PhC domains or deforming holes beside the waveguides. Narrow-core WGs have a wide transmission band below the cladding layer light line, and wide-core WGs can greatly suppress the diffractive leakage even above the cladding layer light line, and both types have a very low propagation loss. Another goal is to achieve a highly efficient coupling between SOI-based PhC WGs and single-mode fibers (SMFs). Normally, the loss of such a coupling system is very large, i.e. over 20 dB, because of the quite different mode profiles of the WGs and SMFs, and this loss is an obstacle to the development of PhC-based devices. Our system achieves a very small mode-profile-conversion loss of about 3-4 dB/connection from 1500 to 1600 nm wavelength.