High-Index Contrast Grating based Broadband Out-Coupler on SOI

Abstract

Coupling structures between an optical fiber and waveguide are fundamental components and have been a standing challenge in integrated optics. In an effort to move this important issue along, this thesis work mainly concentrates on analysis of strong grating couplers. Optical grating has been comprehensively studied over the years due to its diverse applications in holography, spectroscopy, lasers, and many other optoelectronic devices. One of the innovative forms of grating is the High-index contrast grating (HCG). It is possible to control the out-coupled and transmitted light by optimizing the HCG parameters. The recent advances of high-index-contrast (HCG) grating and its applications in optoelectronic devices are reviewed. From application point of view, incoming light can be from another optical chip (inter-chip) or from the same chip (intra-chip). An efficient broadband out-coupler on Silicon-on-Insulator (SOI) with high-index contrast grating (HCG) is proposed. The presence of a silicon-air (high-index contrast) grating on the top silicon layer in SOI allows a strong interaction between the guided mode and the grating. The design of the out-coupler is presented by optimizing the various grating parameters, grating thickness ( ), Si thickness ( ), grating period (Λ), duty cycle (C) to obtain the maximum coupling efficiency (η) over a broad range of wavelength (λ). Design and simulation of such an out-coupler is performed with finite difference method. Coupling efficiency of 54% is observed over an ultra-wide wavelength range from 1500nm to 1650nm.Such gratings can also find applications in High Q-resonators. Polarisation insensitivity has been achieved for a wavelength band of 20nm ranging from 1550nm to 1570nm by optimising the grating parameters.