Photonic-crystal lasers on silicon for chip-scale optical interconnects

Optical interconnects are expected to reduce the power consumption of ICT instruments. To realize chip-to-chip or chip-scale optical interconnects, it is essential to fabricate semiconductor lasers with a smaller energy cost. In this context, we are developing lambda-scale embedded active-region photonic-crystal (LEAP) lasers as light sources for chip-scale optical interconnects. We demonstrated the first continuous-wave (CW) operation of LEAP lasers in 2012 and reported a record low threshold current and energy cost of 4.8 μA and 4.4 fJ/bit at 10 Gbit/s in 2013. We have also integrated photonic crystal photodetectors on the same InP chip and demonstrated waveform transfer along 500-μm-long waveguides. Although LEAP lasers exhibit excellent performance, they have to be integrated on Si wafers for use as light sources for chip-scale optical interconnects. In this paper, we give a brief overview of our LEAP lasers on InP and report our recent progress in fabricating them on Si. We bonded the InP wafers with quantum-well gain layers directly on thermally oxidized Si wafers and performed all process steps on the Si wafer, including high-temperature regrowth. After this process modification, we again achieved CW operation and obtained a threshold current of 57 μA with a maximum output power of more than 3.5 μW at the output waveguides. An output light was successfully guided through 500 × 250-nm InP waveguides.