Zeljko Spika

Highly reliable 40-W cw InGaAlAs/GaAs 808-nm laser bars

The fundamental question whether aluminum-free semiconductor lasers in the 808 nm band are significantly more reliable than Al-containing lasers is still open. We have fabricated and tested high-power InGaAlAs/GaAs-lasers which show excellent reliability data at and above 40 W cw. The laser structure consists of an InGaAlAs-double-quantum well (DQW) as active layer embedded in a large optical cavity (LOC) waveguide structure. The layers were grown in a low pressure MOVPE (LP- MOVPE) reactor using high quality precursors. Asymmetrically coated bars with a width of 1 cm containing 25 groups of 200 micrometer wide emitters were mounted junction down on actively cooled heatsinks. At a heatsink temperature of 18 degrees Celsius the slope-efficiency is 1.1 - 1.2 W/A. Due to the low series-resistance of 2.2 m(Omega) and the low internal losses in the range of 1.7 cm-1 the overall efficiency at 40 W cw reaches 50%. Lifetime studies over 33 0000 h accumulated device hours show that the laser bars with a resonator length of 900 micrometer can be operated at 40 W with high reliability. The mean degradation rate is -0.11%/kh. This result emphasizes that Al-containing lasers can also have a very high reliability usually claimed for Al-free lasers. As a consequence of these encouraging results we will start further lifetime tests at 50 to 60 W.

VCSELs for datacom applications

The use of oxide confined VCSELs in datacom applications is demonstrated. The devices exhibit low threshold currents of approximately 3 mA and low electrical series resistance of about 50 (Omega) . The emission wavelength is in the 850 nm range. Life times of the devices are several million hours under normal operating conditions. VCSEL arrays are employed in a high performance parallel optical link called PAROLITM. This optical ink provides 12 parallel channels with a total bandwidth exceeding 12 Gbit/s. The VCSELs optimized for the parallel optical link show excellent threshold current uniformity between channels of < 50 (mu) A. The array life time drops compared to a single device, but is still larger than 1 million hours.