Heterogeneous integration of ultra-narrow linewidth lasers on silicon for microwave photonics

Heterogeneous integration provides the capability of integrating III-V gain material with ultra-low-loss silicon photonic circuits on a monolithic silicon substrate. This integration results in the dramatic reduction of optical loss of the laser cavity and thus extends the photon lifetime and narrows the linewidth of semiconductor lasers beyond what is achieved with monolithic III-V integration. Recent progress includes widely-tunable III-V/silicon lasers with ultra-wide tuning range and lasers on silicon nitride with narrow linewidth that is comparable with fiber lasers. These lasers will play a critical role in ultra low noise microwave photonics.