The objective of this research
was to investigate high speed, wavelength tunable ultra-short pulse generation in high power
external cavity laser diodes using novel light emitting structures as gain components. Firstly an initial survey was
done of the wavelength tunability of "inverse bow-tie"(IBT) superluminescent light emitting diodes when
operated in external cavity arrangements. Secondly, the properties of short
pulses propagating in gain guided laser structures with distributed
saturable absorbers were studied as a first step to understanding modelocked propagation in the
IBT-SLEDs. The IBT-SLED is an LED in which current injection is confined to an "inverse
bow-tie"-shaped region whose narrow ends are located at the
emission facets. This shape is rotated through 5 degrees to prevent feed-back from the cleaved facets
allowing laser oscillation. The emission facets are also anti-reflection coated to further suppress feedback.
This geometrical configuration allows high power SLED emission (175mW at 900 mA drive current) since the
wider stripe at the centre of the device allows efficient amplification without
gain saturation. The adiabatic taper of the waveguide dimension from the device centre to the emission facet gives a high
brightness device emission that can be efficiently coupled to optical fibres. In this work an initial evaluation of an IBT-SLED
emitting around
l=830nm as a potential external cavity
laser diode medium was carried out. Three external cavity arrangements were designed and assembled, namely, (i) Fabry-Perot,
(ii) grating tuned Littrow and (iii) grating tuned grazing incidence.