Narrow spectral linewidth wavelength tunable laser with Si photonic-wire waveguide ring resonators

We fabricated wavelength tunable laser diodes with Si-wire waveguide ring resonators as an external optical cavity. Less than 100 kHz narrow spectral linewidth was obtained by optimizing design of the ring resonators. The wavelength tunable laser diodes with narrow spectral linewidth are suitable as light sources for digital coherent optical transmission systems.