On-Chip Reflector and Absorber based on High Index Contrast Grating on SOI Chip for Optoelectronic Devices

Abstract

In this dissertation, a novel single-layer subwavelength High-Index-Contrast Grating (HCG) is presented, which provides new and promising platform for integrated optoelectronics having applications in lasers, modulators, detectors. Broadband Reflector in near IR range using High Index Contrast Grating is proposed which provides large reflection (>98.5%) over a wavelength range of 1.31-1.76μm with large fabrication tolerance. HCG not only reduces the size of optical devices but also enhances their performance. Various applications of HCGs in optoelectronic devices, including vertical-cavity surface-emitting lasers (VCSELs), high-Q optical resonators, and hollow-core waveguides are discussed. HCG based narrowband Transmission filter is proposed at slightly off normal incidence angle (5˚) which is closer to surface normal incidence. Also a simple design of a broadband terahertz absorber consisting of a High-index Contrast Grating (HCG) on a Silicon-on-insulator (SOI) chip is proposed. A large absorption (98.4%) over a frequency range of 3.57 - 4.54 THz is obtained with large fabrication tolerance (14μm period tolerance for grating height of 2.6μm). The absorption remains high (~ 98 %) for wide range of angle of incidence from 0˚ (Normal incidence) to 60˚. The bandwidth of high absorption (~ 98 %) is also large over a wide range of angles of incidence. The proposed broadband terahertz absorber also exhibits the design flexibility for the realization of polarization insensitivity with respect to the incident light with arbitrary polarizations. The proposed structure is easy-to-fabricate with a large fabrication tolerance which may provide a desirable broadband absorption for practical applications in terahertz devices. The proposed absorber is designed using Rigorous Coupled Wave Analysis (RCWA) and the results are in good agreement (with maximum difference of 0.6%) with those obtained with Finite difference time domain (FDTD) method. The proposed characteristics of the device arise from the broadband nature and wavelength scalability of the HCG.