Designing Subwavelength Grating Devices for the AlGaAs-on-insulator Platform

Abstract

The first demonstration of subwavelength grating (SWG) waveguides on the silicon-on-insulator (SOI) platform has led to the emergence of several SWG devices in silicon photonics. These devices, which include waveguides, couplers, sensors, and ring resonators to name a few, leverage the refractive index and dispersion engineering inherent to SWG waveguides to enhance their performance. Despite the demonstrated success of SWG waveguides in silicon photonics, these engineering techniques have yet to be widely used in combination with III-V semiconductors which are already extensively used for laser sources and nonlinear applications. Thus, the focus of this study is using aluminum gallium arsenide on insulator (AlGaAs-OI) to design subwavelength grating devices. In this thesis, I present the design and computational simulation of subwavelength grating photonic components utilizing the Al0.18Ga0.82As-OI platform, while also reporting on nonlinear optical experiments conducted with novel Huygens’ meta-waveguide SOI resonators. The effective medium theory, Finite-Difference Eigenmode (FDE), and Finite-Difference Time-Domain (FDTD) methods were used for calculating the photonic band-structure and dispersion characteristics of the SWG unit-cells. Using these methods, low-loss SWG waveguides were optimized for different core heights and cladding materials, achieving Floquet-Bloch mode propagation with minimal to no backscattering. Building upon these waveguides, and by exploiting the refractive index engineering inherent to SWG structures, an ultra-compact 30 μm-long fiber-to-chip AlGaAs-OI SWG edge coupler was designed with a peak coupling efficiency of 90.2% (−0.45 dB loss) at 1550 nm for quasi-TE modes. Furthermore, AlGaAs-OI SWG microring resonators were investigated, demonstrating that a hybrid SWG-bus/solid-core ring geometry can leverage mode delocalization to relax coupling gaps while maintaining sufficient coupling and a high quality factor (Q > 75, 000) at 1550 nm. Finally, I report the first physical observation of stimulated four-wave mixing (FWM) in a prefabricated SOI Huygens’ meta-waveguide microring resonator. This work highlights the potential of AlGaAs-OI subwavelength engineered structures as promising building blocks for monolithically integrated, low-loss, and highly efficient linear and nonlinear photonic integrated circuits.