Nonreciprocal Frequency Domain Beam Splitter.

The canonical beam splitter-a fundamental building block of quantum optical systems-is a reciprocal element. It operates on forward- and backward-propagating modes in the same way, regardless of direction. The concept of nonreciprocal quantum photonic operations, by contrast, could be used to transform quantum states in a momentum- and direction-selective fashion.

A low-noise photonic heterodyne synthesizer and its application to millimeter-wave radar.

Microwave photonics offers transformative capabilities for ultra-wideband electronic signal processing and frequency synthesis with record-low phase noise levels. Despite the intrinsic bandwidth of optical systems operating at ~200 THz carrier frequencies, many schemes for high-performance photonics-based microwave generation lack broadband tunability, and experience tradeoffs between noise level, complexity, and frequency. An alternative approach uses direct frequency down-mixing of two tunable semiconductor lasers on a fast photodiode.

High-frequency cavity optomechanics using bulk acoustic phonons.

To date, microscale and nanoscale optomechanical systems have enabled many proof-of-principle quantum operations through access to high-frequency (gigahertz) phonon modes that are readily cooled to their thermal ground state. However, minuscule amounts of absorbed light produce excessive heating that can jeopardize robust ground-state operation within these microstructures. In contrast, we demonstrate an alternative strategy for accessing high-frequency (13 GHz) phonons within macroscopic systems (centimeter scale) using phase-matched Brillouin interactions between two distinct optical cavity modes.

A silicon Brillouin laser.

Brillouin laser oscillators offer powerful and flexible dynamics as the basis for mode-locked lasers, microwave oscillators, and optical gyroscopes in a variety of optical systems. However, Brillouin interactions are markedly weak in conventional silicon photonic waveguides, stifling progress toward silicon-based Brillouin lasers. The recent advent of hybrid photonic-phononic waveguides has revealed Brillouin interactions to be one of the strongest and most tailorable nonlinearities in silicon.

On-chip inter-modal Brillouin scattering.

Brillouin nonlinearities-which result from coupling between photons and acoustic phonons-are exceedingly weak in conventional nanophotonic silicon waveguides. Only recently have Brillouin interactions been transformed into the strongest and most tailorable nonlinear interactions in silicon using a new class of optomechanical waveguides that control both light and sound. In this paper, we use a multi-mode optomechanical waveguide to create stimulated Brillouin scattering between light-fields guided in distinct spatial modes of an integrated waveguide for the first time.