PhD. of Eslam Fahmy

Author: Eslam Fahmy Promotor: Dries Van Thourhout English Title: Nano-Ridge Surface Emitting Laser Date: 30/4/2026 ISBN number: 978-94-93513-49-5 Thesis: (48.4MB)

Abstract

This dissertation investigates nano-ridge surface-emitting lasers (NRSELs) based on photonic-crystal ridge arrays grown on GaAs with InGaAs quantum wells. It develops a theoretical framework to identify and classify Bloch modes at band edges, emphasizing how symmetry at the Γ-point can suppress radiation and create bound states in the continuum (BICs) and high-Q quasi-BICs suitable for low-threshold lasing and surface emission. Two-dimensional FDTD and band-structure calculations are used to map dispersion, field parity, Q-factors, and vertical extraction for representative geometries, and to relate mode properties to measurable far-field characteristics.

The work then addresses finite device dimensions, demonstrating that reducing the number of periods increases in-plane leakage and raises the lasing threshold. Heterostructure cavities with lateral oxide sections (of higher refractive index) are proposed, which shift the local bandgap and act as in-plane mirrors. Simulations quantify the resulting Q enhancement and improved vertical coupling, while practical limitations arising from disorder, finite size, and edge scattering are discussed.

Finally, the dissertation outlines advanced concepts for post-growth wavelength tuning and beam shaping. Experimental characterization is presented to validate lasing operation, compare spectra and polarization with simulations, and motivate further optimization of efficiency.