Novel methods of tuning semiconductor injection lasers

This thesis is concerned with assessing novel techniques for tuning semiconductor injection lasers. These are based on either the use of Surface Acoustic Waves (SAWs) to provide feedback via the acousto-optic effect or the properties of piezoelectric strained layer devices. Replacing a Distributed Bragg Reflector with a tunable SAW was the first proposal for an acousto-optic laser. However, this proved not to be feasible because the required frequency of SAW was too high to be easily generated. To avoid this problem the method of reflecting light at a grazing angle to the SAW was considered. While this approach is feasible it produces only a small degree of tuning and requires a complicated fabrication process. Better methods of providing the acousto-optic tuning have been modelled, namely the Phonon Assisted Distributed Bragg Reflector, the coupling of different polarisation modes of a single waveguide and coupling of optical modes of a double waveguide structure. This last technique was chosen as the most promising approach for further investigation. The results of the fabrication attempts of the proposed structure are presented. In the second part of the thesis the use of piezoelectric strained layers for tuning lasers is discussed. Single quantum well PIN diode lasers were considered using a structure previously studied at Sheffield. The transition energies of such a quantum well are shown to vary with number of carriers in the well. This effect is modelled for two section lasers where the applied bias to the separate sections is varied while the lasing condition is simultaneously satisfied. The resulting tuning ranges are presented for three different quantum well widths. If both sections are forward biased the tuning available is very small. However, if one section is reverse biased instead the available tuning increases but is discontinuous. (author)