Recent progress in self-assembled quantum-dot optical devices for optical telecommunication: temperature-insensitive 10 Gb s⁻¹directly modulated lasers and 40 Gb s⁻¹signal-regenerative amplifiers

This paper presents recent progress in the field of semiconductor lasers and optical amplifiers with InAs-based self-assembled quantum dots in the active region for optical telecommunication. Based on our design in terms of the maximum bandwidth for high-speed modulation and p-type doping in quantum dots for high temperature stability, we realized temperature-insensitive 10 Gb s −1 laser diodes on a GaAs substrate at 1.3 µm. The output waveform at 10 Gb s −1 maintained a clear eye opening, average output power and extinction ratio without current adjustments from 20°C to 70°C. We developed ultrawide-band high-power amplifiers in the 1.5 µm wavelength region on an InP substrate. The amplifier showed ultrafast gain response under gain saturation, and enabled signal regeneration at 40 Gb s −1 by suppressing the '1'-level noise due to the beating between the signal and amplified spontaneous emission. We present our amplifier module with polarization diversity to enable a stable polarization-insensitive performance, and also, discuss prospects for polarization-insensitive quantum dots by the close stacking technique.