2 June 1994 Tunable vertical-cavity laser diodes with submilliamp threshold currents and efficient fiber coupling
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We have fabricated wavelength tunable vertical-cavity laser diodes on n-GaAs substrates in 2D arrays by molecular beam epitaxy, proton implantation, and wet chemical etching. Record low threshold currents of 650 (mu) A for continuous wave and 600 (mu) A for pulsed operation are obtained for 8 micrometers active diameter devices. Output power is up to 170 (mu) W cw and 400 (mu) W pulsed. The Bragg reflectors consist of AlAs-GaAs stacks. The active region contains three strained In0.2Ga0.8As quantum wells. The emission wavelength is about 960 nm. Three terminals for each laser diode supply two separate currents for independent control of output power and emission wavelength of individual elements in the 2D array. A record wide continuous wavelength tuning range of 5.6 nm is achieved with tuning currents just below 1 mA. Highly efficient and alignment tolerant coupling to single-mode optical fibers is demonstrated with modified vertical-cavity laser diodes. Quasi planar devices providing two-sided light output have been fabricated with an inverted npn-doping profile. Direct contact butt coupling to flat cut single-mode optical fibers of 4.5 micrometers diameter core results in over 90% coupling efficiency. The lateral alignment tolerances defined by a -3 dB coupling efficiency decrease are as large as 5.6 micrometers . Maximum power in 9 micrometers diameter core fibers is 0.75 mW for a non-heat-sinked device with 8 micrometers alignment tolerances. The easy fiber attachment is applicable to 2D laser arrays and mass production. The large alignment tolerances will improve reliability and drastically reduce packaging costs making vertical-cavity lasers very attractive for short distance optical interconnects.
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Torsten Wipiejewski, Konrad Panzlaff, Eberhard Zeeb, Karl Joachim Ebeling, "Tunable vertical-cavity laser diodes with submilliamp threshold currents and efficient fiber coupling", Proc. SPIE 2147, Vertical-Cavity Surface-Emitting Laser Arrays, (2 June 1994); doi: 10.1117/12.177213; https://doi.org/10.1117/12.177213

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