We demonstrate monolithic integration of a 50-μm-long-cavity membrane distributed-
reflector laser with a spot-size converter, consisting of a tapered InP wire waveguide and an
SiOx waveguide, on SiO_2/Si substrate. The device exhibits 9.4-GHz/mA^ 0.5 modulation
efficiency with a 2.2-dB fiber coupling loss. We demonstrate 25.8-Gbit/s direct modulation
with a bias current of 2.5 mA, resulting in a low energy cost of 132 fJ/bit.

We develop a 50-μm-long-cavity membrane distributed-reflector laser monolithically
integrated with a spot-size converter, consisting of an InP taper and an SiO x waveguide, on
an SiO 2/Si substrate. We achieve high modulation efficiency of 9.4-GHz/mA 1/2 and fiber
butt coupling without any lenses.