Vertical-cavity surface-emitting laser diodes for short distance optical fiber networks

We have fabricated wavelength tunable vertical-cavity laser diodes in 2D arrays by molecular beam epitaxy, proton implantation, and wet chemical etching. Record low threshold currents of 650 μA for continuous wave and 600 μA for pulsed operation are obtained for devices with 8 μm active diameter. Output power is up to 170 μW CW and 400 μW pulsed. The emission is single longitudinal and transversal mode at about 970 nm wavelength. Three terminals for each laser diode supply two separate currents for the independent control of output power and emission wavelength of individual elements in a 2D laser array. A record wide continuous wavelength tuning range of 8.2 nm is achieved in a slightly larger device with tuning currents of just 2.5 mA. Highly efficient and alignment tolerant coupling to single-mode optical fibers is demonstrated with quasi-planar vertical-cavity laser diodes which provide a two-sided light output. Direct contact butt coupling to flat cut single-mode optical fibers of 4.5 μm diameter core results in coupling efficiencies over 90%. The lateral alignment tolerances defined by a -3 dB coupling efficiency decrease are as large as 5.6 μm. Maximum power coupled into a 9 μm diameter core fiber is 0.75 mW for a non-heat sinked laser diode