1 Nanophotonic Devices, Department of Photonics Engineering, Technical University of Denmark2 Department of Photonics Engineering, Technical University of Denmark3 Nanophotonics Theory and Signal Processing, Department of Photonics Engineering, Technical University of Denmark
This thesis describes the design, fabrication and characterization of photonic crystal slab lasers. The main focus is on coupled photonic crystal cavity lasers which are examined in great detail. The cavity type which is mainly explored consists of a defect formed by a single missing hole in the quadratic lattice. Processing techniques are developed and optimized in order fabricate photonic crystals membranes in gallium arsenide with quantum dots as gain medium and in indium gallium arsenide phosphide with quantum wells as gain medium. Several key issues in process to ensure good quality are identified such as the size and material for the carrier wafer in the III-V etch and the importance of removing all remains of the e-beam lithography mask after the etch of the hard mask. Detailed simulations are shown for a simple system with two coupled cavities in different coupling directions. The results are in good agreement with standard coupled mode theory. Also a novel type of photonic crystal structure is proposed called lambda shifted cavity which is a twodimensional photonic crystal laser analog of a VCSEL laser. Detailed measurements of the coupled modes in the photonic crystals with quantum dots are carried out. In agreement with a simple gain model the structures do not show stimulated emission. The spectral splitting due to the coupling between single cavities as well as arrays of cavities is studied theoretically and experimentally. Lasing is observed for photonic crystal cavity structures with quantum wells. A detailed Analysis is conducted on single cavities, two coupled cavities and arrays of coupled cavities. The lasing threshold is determined by measuring the photoluminescence intensity depending on the excitation power. Changes in the linewidth and peak position for different powers confirm the results. While large arrays of coupled cavities exhibit lasing at a single frequency, multimode lasing is demonstrated in structures with only a few coupled cavities. Moreover, lasing is also observed in the lambda shifted cavities. Simulations are shown to determine the theoretical Q factors and mode volumes of these novel structures.
Main Research Area:
Frandsen, Lars Hagedorn, Hvam, Jørn Märcher, Yvind, Kresten