Monolithic Colliding Pulse Mode-Locked Quantum Well Lasers

The design, fabrication and characterisation of monolithic passive colliding pulse mode-locked (CPM) quantum well lasers are described. Firstly, a standard configuration of CPM laser is realised and mode-locking is obtained at repetition rates in the range of 73 to 129 GHz. These are the first published results on monolithic CPM quantum well laser at short wavelength, i.e. GaAs/AlGaAs based material. This device presented a previously unseen output laser polarisation dependence with the applied reverse bias to the absorber section of this laser. The generation of TE and TM polarised light from the CPM laser is analysed and discussed. A novel configuration of CPM laser, the multiple colliding-pulse mode-locked (MCPM) laser is realised. This multi-section device can have 1, 2, or 3 monolithically integrated saturable absorber sections in the cavity, inducing the laser to operate at the first up to the fourth harmonic of the repetition rate. This is the first observation of geometry dependent switcheable change of harmonics in mode-locked lasers. The different regimes of operation of the MCPM laser are investigated, comprising single mode, multimode, Q-switched and first to fourth harmonic mode-locking, generating pulses of around 1 to 3 ps width at up to 375 GHz repetition rate. Studies of the range of mode-locking at 240 GHz show that mode-locking occurs at two distinct regions of current and reverse bias. This previously unseen feature may represent an indication of the contribution of excitonic nonlinearities to the ultra-fast operation of the device. A monolithic CPM ring laser with two saturable absorbers in the cavity is described. Frequency domain measurements indicate mode-locking operation at 28 GHz repetition rate. The use of two saturable absorbers in colliding pulse configuration in the ring cavity showed improvements on the device operation. The design and fabrication of a CPM laser based device which is intended to perform clock recovery at high repetition rates, above 100 GHz, is described. This device consists of a standard CPM laser which has an extra waveguide in side-injection configuration. This extra waveguide amplifies and guides the optical signal from which the clock is to be recovered to the absorber section of the laser. To achieve clock recovery this signal should contribute to the saturation of the absorber section of the CPM laser, synchronising its saturation with the injected data signal. Preliminary characterisation and tests showed that the CPM laser part of the device works as a standard CPM laser, as expected