Dispersion tailoring in wedge microcavities for Kerr comb generation.

The shaping of group velocity dispersion in microresonators is an important component in the generation of wideband optical frequency combs. Small resonators-with tight bending radii-offer the large free-spectral range desirable for wide comb formation. However, the tighter bending usually limits comb formation as it enhances normal group velocity dispersion. We experimentally demonstrate that engineering the sidewall angle of a small-radius (∼100µm), 3-µm-thick silica wedge microdisk enables dispersion tuning in both normal and anomalous regimes, without significantly affecting the free spectral range. A microdisk with a wedge angle of 55° (anomalous dispersion) is used to demonstrate a 300 nm bandwidth Kerr optical frequency comb.

Brillouin Optomechanics in Coupled Silicon Microcavities.

The simultaneous control of optical and mechanical waves has enabled a range of fundamental and technological breakthroughs, from the demonstration of ultra-stable frequency reference devices, to the exploration of the quantum-classical boundaries in optomechanical laser-cooling experiments. More recently, such an optomechanical interaction has been observed in integrated nano-waveguides and microcavities in the Brillouin regime, where short-wavelength mechanical modes scatter light at several GHz. Here we engineer coupled optical microcavities to enable a low threshold excitation of mechanical travelling-wave modes through backward stimulated Brillouin scattering. Exploring the backward scattering we propose silicon microcavity designs based on laterally coupled single and double-layer cavities, the proposed structures enable optomechanical coupling with very high frequency modes (11 to 25 GHz) and large optomechanical coupling rates (g0/2π) from 50 kHz to 90 kHz.

Brillouin scattering self-cancellation.

The interaction between light and acoustic phonons is strongly modified in sub-wavelength confinement, and has led to the demonstration and control of Brillouin scattering in photonic structures such as nano-scale optical waveguides and cavities. Besides the small optical mode volume, two physical mechanisms come into play simultaneously: a volume effect caused by the strain-induced refractive index perturbation (known as photo-elasticity), and a surface effect caused by the shift of the optical boundaries due to mechanical vibrations. As a result, proper material and structure engineering allows one to control each contribution individually. Here, we experimentally demonstrate the perfect cancellation of Brillouin scattering arising from Rayleigh acoustic waves by engineering a silica nanowire with exactly opposing photo-elastic and moving-boundary effects. This demonstration provides clear experimental evidence that the interplay between the two mechanisms is a promising tool to precisely control the photon-phonon interaction, enhancing or suppressing it.