Electro-mechanically induced GHz rate optical frequency modulation in silicon

Abstract

We present a monolithic silicon acousto-optic frequency modulator (AOFM) operating at 1.09GHz. Direct spectroscopy of the modulated laser power shows asymmetric sidebands which indicate coincident amplitude modulation and frequency modulation. Employing mechanical levers to enhance displacement of the optical resonator resulted in greater than 67X improvement in the opto-mechanical frequency modulation factor over earlier reported numbers for silicon nanobeams.

Extremely Wide Tuning Range of Mechanical Oscillation of a Silicon Waveguide Driven by Optical Gradient Force

“…This demonstration uses a silicon opto-mechanical resonator coupled to a suspended silicon waveguide. Since the micro-ring resonator is designed for higher frequency modes (radial breathing mode at 175MHz and compound radial mode at 1.1GHz) [11], for this experiment we focus on the waveguide modes, which are at much lower frequencies (fundamental in-plane bending mode at 3.4MHz). The device comprises of a silicon waveguide of length 30µm and width 400nm.…”

“…The waveguideresonator gap is <100nm. The fabrication process flow was described in detail in earlier work on multi-GHz opto-mechanical oscillations of the coupled ring resonator [11].…”

“…To probe the mechanical mode of the waveguide, the transmitted light is passed to a Newfocus 1647 Avalanche Photodiode with gain setting of 6,000V/W. The motion of the waveguide and the opto-mechanical ring resonator leads to phase modulation of the intra-cavity light, which is converted into amplitude modulation via shaping by the optical resonator transfer function [11]. The ring resonator is designed such that it does not have mechanical modes in the vicinity of the resonance frequency of the fundamental in-plane and out-of-plane bending modes of the waveguide.…”

Rayleigh scattering boosted multi-GHz displacement sensitivity in whispering gallery opto-mechanical resonators

“…It is thereby desirable to enhance the transduction efficiency in integrated electro-optomechanical resonators. For a resonator with loaded optical cavity linewidth κ, oscillating at a mechanical resonance frequency Ω m , the motion leads to predominant frequency modulation of the circulating light field [5] when Ω m ≫ κ (resolved sideband regime). For transduction of signals with mechanical frequencies in the resolved sideband regime using a singlet WGM optical resonance, we see in Figure 1, that both the Stokes and anti-Stokes motional sidebands lie outside the optical cavity.…”

“…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]. With a view towards realizing truly on-chip integration, several demonstrations of cavity opto-mechanical systems with on-chip electrodes for transduction of motion using electrostatic capactive actuation have been demonstrated [5,6,7]. However, the advantage of employing action-at-a-distance electrostatic actuation comes with the drawback of the inherently low bandwidth of this transduction scheme.…”