III-V semiconductor waveguides for application in nonlinear optics.

Sammanfattning

This thesis presents studies on III-V semiconductor waveguides with particular emphasis on second-order optical nonlinearity. The nonlinear processes that were investigated in this thesis are the Second Harmonic Generation (SHG) and the Spontaneous Parametric Down-Conversion (SPDC). The optical waveguides are made of InGaP and the waveguide design includes tapered parts for in- and out-coupling of guided light. Simulation of light propagation and modal solutions were done using Lumerical MODE, FDTD, and COMSOL Multiphysics software. The in- and outcoupling for the design of tapered waveguide that utilize the bulk non-linearity is 65 % when the waveguide is 145 nm thick and 2.60 μm wide having PMMA as top cladding. The SHG conversion efficiency for this configuration when the waveguide length is 2 μm long, is found 31 %/W. Three cases of the utilization of the surface non-linearity are proposed too. Preliminary steps toward the fabrication of the waveguide structures are also reported. The particular mesa-isolated substrates are fabricated having a side wall with a negative angle profile that result to a significant undercut. InGaP waveguides were transferred to the target substrates successfully and the process that was used can enable heterogeneous integration of InGaP and SOI platform.