Modelling and characterization of hybrid integrated lasers in 2 to 3 µm wavelength band

Abstract

Hybrid integrated silicon photonic lasers functioning at mid-IR wavelengths have recently emerged as a solution for developing compact optical sensors targeted at trace gas spectroscopy. This thesis concerns a measurement and simulation combined approach to characterize Silicon Nitride photonic integrated circuits (PICs) equipped to work as such lasers. Seven PICs from the same process are first aligned in an end-fire coupling scheme with the III-V gain chip using a closed-loop piezo stage. The gain chip consists of an AlGaInAsSb/GaSb type-I quantum well reflective semiconductor optical amplifier (RSOA). The PICs contain narrow-band long rectangular spiral and round spiral shaped distributed Bragg reflectors (DBRs) which work as external cavities allowing periodic feedback to the gain element. Intensity vs. current sweeps and measurements of the spectra of the uncooled 2 µm lasers demonstrate narrow full-width half-maximum (FWHM) linewidths and remarkable power outputs in continuous wave operation at room temperature. The measurements also give insight into process variation and design reliability, and have led to a recent submission to Optica for publication. A commercial eigenmode expansion solver is used to verify the experimental results as well as to explore the design space for Bragg reflectors at 2 µm and 2.7 µm with a view to optimizing the packing ratio, linewidth and side-mode suppression ratio of the devices for improved laser performance. The rapid and efficient end-fire based optical testing method presented in this work is expected to set a base-line for optimization of mid-IR tunable hybrid lasers.