Abstract
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.
Highlights
3.8 micrometers. (d) Optical dispersion diagram schematic, the optical resonances are represented by discrete points lying along the bulk dispersion curves
The arrows indicate possible resonant optical transitions from the pump to the Stokes mode due to backward Brillouin scattering (BBS) (e) Photonic density of states (PDOS) at the pump and scattered waves when the optical frequency splitting matches the mechanical mode frequency Ω. (f) Photonic density of states obtained for the coupled cavity modes with a quality factor of 105 and splitting rate J = 25 GHz
While in forward Brillouin scattering the phase-matching condition favors mechanical modes close to their cut-off condition M = 0, in backward Brillouin scattering (BBS) the scattered light frequency shift is proportional to the optical wavevector mismatch and can reach tens of GHz in solids
Summary
3.8 micrometers. (d) Optical dispersion diagram schematic, the optical resonances are represented by discrete (red and blue) points lying along the bulk dispersion curves (solid lines). In the proposed compound cavity system, illustrated, the interaction between the optical modes (through their evanescent fields) leads to a frequency splitting that can match the mechanical mode frequency.
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