Recent progress in growing reliable (AlGa)As DH lasers by molecular beam epitaxy for optical communication systems

Abstract

The cw electro-optical elevated temperature (55–70deg;C) characteristics of 5 μm shallow proton-bombarded stripe lasers, fabricated from MBE grown DH wafers, that have Al 0.08Ga 0.92As active layers are compared with those obtained from similar lasers fabricated from high quality LPE DH wafers that are suitable for system use. The MBE lasers maintain their excellent cw device characteristics even at elevated temperatures. The temperature-dependence of the cw I th of these MBE lasers is characterized by I th ∝ exp( T/ T 0) with T 0 ≳ 150°C. Furthermore, the cw I th 's of these MBE lasers are at least as low as high quality LPE lasers. The high material uniformity of MBE wafers also results in a significant increase in yield of good lasers per MBE wafer. A statistical study of the self-induced pulsation behavior of MBE cw (AlGa)As DH proton-bombarded stripe lasers, during accelerated aging at elevated (70°C) temperature, is made and compared with that of similar lasers grown by LPE. The 5 μm stripe shallow proton-bombarded MBE lasers, after 100 h accelerated burn-in, have pulsation frequencies F 0sc typically > 1 GHz when measured at the power levels used for optical communications. The median pulsation frequencies F 0scm are 1.6 GHz and 1 GHz for MBE and LPE lasers, respectively. In both cases, no mirror-coatings were applied to the lasers. Long-term aging of MBE lasers at elevated temperature (70°C) under constant power output of 3 mW/mirror has also been carried out for lasers from several wafers. Lasers from two early wafers are still operating after 7000 h at 70°C. When plotted on the usual log-normal graph, a median life-time τ m of about 8500 h at 70°C is expected. The MBE lasers have also been evaluated, tested and aged in transmitters. An averaged modulation current I mod of 24.0 ± 4.3 mA is obtained for 125 MBE laser transmitters measured at 30°C for an extinction ratio of 15 to 1. For the same group of transmitters, the 20 MHz noise at 30°C is -(94.2 ± 2.9) dBm. The MBE laser transmitters are still operating stably after 7,000 h when aged at 45 Mb/s data rate at 30°C. The results obtained thus far show that they meet the objectives for use in 45 Mb/s Bell system FT-3 lightwave transmission systems and at present they are being field tested in these systems. Recent results on high through-put, high yield, and highly reproducible (AlGa)As DH laser wafers grown by MBE at accelerated growth rates as high as 11.5 μm/h and others will also be presented.