Introduction

Semiconductor diode lasers emitting normal to the substrate plane, known as surface-emitting lasers, are extremely promising for addressing a range of applications from optical interconnects, optical communications and optical recording to remote sensing. The most promising aspect perhaps lies in the prospect of eliminating low yield laser fabrication steps, i.e. laser packaging processing including wafer lapping, cleaving and dicing, facet coatings and diode bonding. The possibility of being able to make any number of lasers anywhere on a wafer is also an increasingly important factor for applications such as optical interconnects. At present two completely different approaches are aimed at realizing surface-emitting lasers. The first represents an extension of the existing technology for semiconductor edge-emitting lasers that uses a 45° slanted mirror or a second-order grating to vertically couple the light out (Figure 9.1(1). (2)). The second, pioneered by K. Iga in 1979, uses highly reflective mirrors to clad the active region, resulting in a vertical cavity that produces an output beam propagating normal to the substrate surface (Figure 9.1(3)).

The vertical cavity design offers important advantages over other surface-emitting laser designs. The unique topology of a vertical cavity facilitates large-scale processing, on-wafer testing and pre-process screening. The small lateral dimensions allow for fabrication of large 2-D arrays with high packing density and integration with other optical and electronic devices.