Abstract
Finite photon lifetimes for light fields in an opto-mechanical cavity impose a bandwidth limit on displacement sensing at mechanical resonance frequencies beyond the loaded cavity photon decay rate. Opto-mechanical modulation efficiency can be enhanced via multi-GHz transduction techniques such as piezo-opto-mechanics at the cost of on-chip integration. In this paper, we present a novel high bandwidth displacement sense scheme employing Rayleigh scattering in photonic resonators. Using this technique in conjunction with on-chip electrostatic drive in silicon enables efficient modulation at frequencies up to 9.1GHz. Being independent of the drive mechanism, this scheme could readily be extended to piezo-opto-mechanical and all optical transduced systems.
Highlights
Cavity opto-mechanical systems have enabled a wide range of experiments pertaining to ultrahigh optical readout sensitivity, photon-phonon translation and mechanical signal amplification in the same device platform [1, 2, 3, 4]
Piezoelectric actuation on the other hand, has traditionally been used in micro-electro mechanical systems (MEMS) for beyond-GHz actuation [9, 10, 11]. This scheme was adopted to optomechanical systems, and piezo-opto-mechanical systems operating at mechanical resonance frequencies in 3-4GHz range were demonstrated [12, 13]
An integrated piezoelectric resonator necessitates metal electrodes atop the resonator for actuating motion [11]. This would lead to huge optical loss in the metal and implementation of piezo-opto-mechanical systems till date has relied on employing electrodes located far away from the resonator (≈50μm) so that the optical performance is not compromised [12, 13]
Summary
Cavity opto-mechanical systems have enabled a wide range of experiments pertaining to ultrahigh optical readout sensitivity, photon-phonon translation and mechanical signal amplification in the same device platform [1, 2, 3, 4]. The component of the intra-cavity energy at the mechanical resonance frequency is diminished, as compared to transduction of signals in the unresolved sideband regime This leads to incomplete modulation, resulting in a low RF signal amplitude when the modulation is sensed using a photo-detector. To counter this inefficiency, we explore the possibility of exploiting Rayleigh scattering induced optical mode splitting in optical whispering gallery mode (WGM) resonators [14] to transduce signals in the resolved sideband regime more efficiently, by using the optical mode doublet to boost the Stokes sideband. Optical doublet resonances could be engineered via Focused Ion Beam (FIB) engineering [17] and this universal sense scheme could readily be extended to transduce mechanical motion at multi-GHz frequencies in piezo-opto-mechanical [12, 13] and all optical transduced systems [18, 19]
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