UC Santa Barbara

Low noise lasers, with spectral linewidth of the kHz level and below, are in demand by an increasing number of applications, such as coherent communications, LIDAR, and optical sensing. Such a low noise level is currently available only in solid-state lasers, fiber-based lasers, and external cavity lasers. These lasers are typically bulky, expensive and not scalable for mass production. Semiconductor diode lasers, although attractive for their low form factor, mass producibility and compatibility to integrated circuits, are notorious for their low coherence with typical linewidths over several MHz.

Heterogeneous silicon/III-V photonics integration opens a path to understand and develop low noise semiconductor lasers. By incorporating low loss high-Q silicon waveguide resonators as integral/extended parts of the Si/III-V laser cavity, we have demonstrated that it is possible to reduce the quantum noise in semiconductor lasers.

In this thesis, we discuss our attempt and success in pushing the noise level of the heterogeneously integrated Si/III-V lasers to record low levels using ring resonator coupled cavity lasers. The first generation of our lasers achieved Lorentzian linewidth in the kHz level. The second-generation lasers, with a new waveguide architecture for ultralow loss and novel cavity designs on silicon, have reached down to ultralow spectral linewidth of 100s-Hz level. Some of the fabricated lasers also possess an ultrawide wavelength tuning range of 120 nm across three optical communication bands (S+C+L). This unprecedented performance shows the potential for heterogeneous silicon photonics to reshape the future of semiconductor lasers.