This thesis is concerned with the design, fabrication and investigation of InAs/InP quantum dot mode-locked lasers operating at ~1.55 μm with multi-gigahertz repetition rates. Devices with dual contact configuration operating at ~35 GHz were fabricated and mode-locking characteristics were investigated as a function of the saturable absorber length. The deposition of HR and AR coatings on the two cleaved facets provided an increase in the quantum efficiency and shifted the optimum mode-locking region to a higher injection current. This simple technological step increased the peak power of the emitted pulses by nearly a factor of 2. Furthermore, the appearance of two distinct lobes in the optical spectrum, which is a typical feature of quantum dot material systems, was also investigated. The sonogram technique confirmed the presence of two pulse trains under moderate values of current injection and stable locking of only one lobe at high injection currents. Finally, techniques for high repetition rate mode locking such as colliding pulse, asymmetric colliding pulse and double interval mode-locking were evaluated. Harmonic mode-locking at repetitions rates of ~71 GHz, ~107 GHz and ~238 GHz was demonstrated by placing the absorbers on cavity locations corresponding to the 2nd, 3rd and 7th harmonic, respectively. A monolithically integrated coupled cavity device was also explored, in which an FIB-milled intra-cavity reflector provided mode-locking at a repetition rate of ~107 GHz.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:586833 |
| Date | January 2013 |
| Creators | Mahmood, Shahid |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/4737/ |
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