Wide Temperature Range Operation of 25-Gb/s 1.3-μm InGaAlAs Directly Modulated Lasers

High-speed 1.3-μm directly modulated lasers (DMLs) have been developed to support sharply rising optical communications traffic. The most crucial requirement for these lasers is the ability to operate over a wide temperature range with no power-consuming electric cooler. Due to poor temperature characteristics resulting from its poor electron confinement in the multiquantum well, DMLs with InGaAsP material systems have been replaced by DMLs with InGaAlAs material systems, which have stronger electron confinement. In this paper, progress in uncooled 25-Gb/s 1.3-μm InGaAlAs DMLs is summarized. A 160-μm-long ridge-waveguide-type laser showed a lower threshold current I_th of 14.9 mA at high temperatures up to 95 °C, and a small signal-frequency-response bandwidth f_3dB of 14 GHz was achieved at a bias current of 60 mA at 95 °C. Using this laser, clear 25-Gb/s operation was obtained at 95 °C. In addition, stable operation was achieved for up to 4000 h at 85 °C, indicating the basic applicability of the device to next-generation 25-Gb/s data communication systems. Furthermore, the developed technology was applied to a novel uncooled 25-Gb/s 1.3-μm surface-emitting laser for optical interconnects, in which a 45° mirror and a lens were integrated monolithically.