Photonic crystal defect waveguides with embedded active layers containing single or multiple quantum wells or quantum
dots have been fabricated. Spontaneous emission spectra are enhanced close to the bandedge, consistently with the
enhancement of gain by slow light effects. These are promising results for future compact devices for terabit/s
communication, such as miniaturised semiconductor optical amplifiers and mode-locked lasers.
In this paper we review our theoretical work on slow and fast light effects in quantum dot semiconductor optical
amplifiers (QD SOAs), in particular we investigate the carrier dynamical contributions to the dynamic gain grating and
cross gain modulation induced by unique ultrafast inter-subband carrier dynamics between discrete QD bound states. Our
calculations predict that by increasing the injection current density, additional ultra-fast coherent gain contributions
around 100GHz arise in contrast to the slow sub-gigahertz carrier density pulsation (CDP) effects. For potential
applications in microwave photonics, especially targeting the millimeter wave range, we propose that quantum dot
devices might be used to realize an optically fed microwave phase shifter in the frequency range of 100GHz.