Tunable extremely low threshold vertical-cavity laser diodes

Submilliampere-threshold wavelength-tunable three-terminal vertical-cavity laser diodes have been fabricated by proton implantation and wet chemical etching. Laser diodes of 8- mu m active diameter exhibit record low threshold currents of 650 mu A and emit upto 170- mu W output power under CW conditions and 0.4 mW under pulsed excitation. Slightly larger devices of about 12- mu m diameter emit up to 1.85 mW in a single mode under pulsed conditions. The emission wavelength is about 970 nm and matched to the spectral gain of the three active InGaAs quantum wells. Individual elements in a two-dimensional array can be continuously tuned over 2.2 nm by applying separate tuning currents of 70 mu A to the corresponding top mesa electrodes. Tuning and laser currents are controlled independently.>