Positive and negative pull-back instabilities in mode splitting optomechanical devices

Abstract

Optical gradient forces play an essential role in optomechanical systems. The systems based on coupled microresonators are of great importance for applications in signal processing, sensors, and actuators. Here, we theoretically and experimentally studied, for the first time, positive and negative pull-back instabilities originating from attractive and repulsive optical gradient forces, respectively, in an optomechanical device based on coupled microrings. The device consists of two coupled free-standing waveguides in two identical microrings, fabricated in the silicon-on-insulator process. The coupling between the two microrings results in the symmetric and antisymmetric resonances showing in the transmission spectrum of the device. By measuring the wavelength difference between the self-referenced symmetric and antisymmetric resonances, the wavelength tuning due to the optomechanical actuation is decoupled from the tuning due to the thermo-optical effect. It is demonstrated theoretically and experimentally that the positive pull-back instability originates from the attractive optical gradient force and the negative pull-back instability originates from the repulsive optical gradient force when the pump wavelength increases. The positive pull-back instability significantly increases the wavelength difference between the symmetric and antisymmetric resonances. On the contrary, the negative pull-back instability significantly decreases the wavelength difference.

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ORCID for Jize Yan: orcid.org/0000-0002-2886-2847

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