Optimisation of four-and five-layer Alx Ga1-x As/GaAs large optical cavity lasers for high power, low threshold current density operation

A detailed optimisation procedure is described for high power, low threshold current density operation of asymmetric four-and five-layer large optical cavity lasers. The analysis of these multilayer waveguides is simplified by using a computer model based on an admittance transformation technique, commonly used in microwave circuit analysis. Effects of compositional and thickness variations on the waveguiding properties are described. The maximum obtainable output power scales with the width of the waveguide, although this results in an increase in threshold current density due to the decreased coupling between the optical distribution and the active layer. If the structure is designed to guide light in the absence of the active layer then the sensitivity of the optical properties to changes in active layer thickness is reduced, providing the active layer is kept thin. Examples of optimised structures are given to illustrate the effects various structural changes have on the optical properties of the device and on the threshold current density.