Electronic tuning of semiconductor lasers with multiple quantum well devices

This thesis has been devoted to theoretical and experimental work on tunable semiconductor lasers, devices which play an important role in optical communication. The use of multiple quantum well (MQW) materials as tuning elements has been studied. In theoretical work the static and dynamic characteristics of single and multi-cavity tunable laser systems have been investigated in considerable detail. The various tuning structures were discussed. The refractive index change in MQW materials has been modelled and comparison between MQW and bulk materials has been made. The design details of integrated MQW-Bragg phase modulators are given. The possibility of integrated tunable semiconductor laser utilizing refractive index change in MQW materials was investigated. In experimental work, the electric field induced refractive index change in a PIN MQW device has been used in an electronically tuned external cavity GaAs/AlGaAs laser system. Discontinuous and continuous tuning experiments have been carried out using this structure. The experimental o results show a discontinuous tuning range of over 600GHz (14Å in wavelength) for a 6 V change in device bias with less than 0.6 dB variation in laser output power and a continuous tuning range of over 2 GHz without significant output power change. The results also confirm the predicted refractive index change from absorption measurement. The optical FM Response was also measured using a high resolution Fabry-Perot interferometer and birefringent fibre filter system. A flat modulation response from very low frequencies up to 200 MHz was observed and no thermal tuning effect was found