1 Department of Photonics Engineering, Technical University of Denmark2 Nanophotonics Theory and Signal Processing, Department of Photonics Engineering, Technical University of Denmark3 Nanophotonics, Department of Photonics Engineering, Technical University of Denmark4 Nanophotonic Devices, Department of Photonics Engineering, Technical University of Denmark
This thesis deals with the fabrication and characterization of active photonic crystal waveguides, realized in III-V semiconductor material with embedded active layers. The platform offering active photonic crystal waveguides has many potential applications. One of these is a compact photonic crystal semiconductor optical amplier. As a step towards such a component, photonic crystal waveguides with a single quantum well, 10 quantum wells and three layers of quantum dots are fabricated and characterized. An experimental study of the amplied spontaneous emission and a implied transmission are presented in this thesis. A variation of photonic crystal design parameters are used leading to a spectral shift of the dispersion, it is veried that the observed effects shift accordingly. An enhancement of the amplified spontaneous emission was observed close to the band edge, where light is slowed down due to photonic crystal dispersion. The observations are explained by the enhancement of net gain by light slow down. Another application based on active photonic crystal waveguides is micro lasers. Measurements on quantum dot micro laser cavities with different mirror configurations and photonic crystal designs are shown. Laser emission is observed at wavelengths corresponding to the slow light regions of the cavity mode, where the enhanced gain lead to lower lasing threshold. Gain dynamics of the quantum dot gain material, used in both amplifier er and laser structures, are investigated. The measurements are based on degenerate pump-probe transmission spectroscopy using 180fs pulses. The characteristic gain recovery times are measured to be 2ps and 0:2ps, with little variation over a wavelength span of 260nm. Sub-assemblies of quantum dots which vary in height by one monolayer are observed. No noticeable changes in carrier dynamics can be associated with dots of different number of monolayers.
Main Research Area:
Yvind, Kresten, Mørk, Jesper, Hansen, Per Lunnemann