An investigation of broad gain spectrum in InGaAs/InAlGaAs quantum well lasers latticed matched to InP
This thesis is concerned with quantum well semiconductor lasers that operated at optical communication wavelengths around 1550nm. It concentrates on lasers that are made from the latticed matched InGaAs/InAlGaAs material which have less temperature dependence of their threshold current in comparison to the established phosphorous quaternary semiconductor material. In particular, multiple width quantum wells (which is also referred to as asymmetric wells) are employed in the active region to broaden the gain spectrum. A conventional identical width quantum well structure is also employed in order to assess the advantages of including multiple width wells in the active region. The comparison between the multiple and identical well structures included carrying out spectral TE and TM gain and internal optical loss measurements. Spectral absorption measurements are also presented for both multiple and identical width quantum well devices. This was carried out in order to study the quantum well band edge shift with increasing reverse biased electric field applied perpendicular to the quantum well layers, a process commonly known as quantum confined Stark effect. First colliding pulse mode-locked operation in lasers made from the multiple width quantum well material is also demonstrated. The electric field auto-correlation experiment has been carried out, using both the multiple and identical width quantum well lasers, in order to investigate the influence of the gain broadened material on the pulse width obtained from the mode-locked operation.