ABSTRACT
This chapter examines different material systems used to obtain performance in the visible, near infrared and mid infrared spectral regimes and the unique challenges associated with them. It focuses on vertical cavity surface emitting lasers (VCSELs). The edge emitting laser (EEL) is examined more as a means of characterising and evaluating a possible active region for the VCSEL, rather than as a stand-alone device. The geometric differences between EELs and VCSELs have consequences for their threshold current properties. These can be traced to the gain versus loss balance, which occurs in a different regime for EELs and for VCSELs. This presents problems for coupling into fibres, which are generally round in cross section. This problem is endemic to all waveguide devices, not just EELs and there are measures that can be taken to improve the beam shape, such as mode expanders and external collimation, however they all come at a cost of increased complexity of fabrication and assembly.
