Low-power high-speed vertical cavity lasers for dense array applications

Vertical-cavity lasers have demonstrated the ability to produce mW level output powers in a low divergence circular beam. This has made them attractive sources for high density applications such as free space interconnects and optical computing. Moving from device demonstration to practical applications, however, poses additional demands. High density arrays require very low power consumption for thermal management while the interconnect lines must not introduce excessive stray capacitance. We have developed vertical cavity lasers with intra-cavity contacts on semi-insulating substrates which provide solutions to these practical problems. The intra-cavity design allows the use of ring contacts on the same surface with either top or bottom emission. The lasers can thus be connected in a raster interconnect pattern or any other contacting configuration without impairing the high speed performance. On chip resistors can be incorporated into the circuit so that simple voltage drives can be used. Using a current constriction to provide electrical and optical confinement has removed the limitations of surface recombination, allowing the development of high external efficiency, sub-milliamp threshold vertical cavity lasers. The 7 micrometers diameter lasers have output powers of 1 mW at a bias current of 3 mA with modulation bandwidths above 8 GHz while consuming only 10 mW of power. The lasers can therefore be driven with full on/off current modulation to transmit data at rates exceeding 1 Gbit/s, simplifying the driver electronics considerably. The structure and fabrication sequence is discussed along with bit error rate measurements including on/off modulation conditions.