Beam-coupled microsphere resonators for high-resolution electric field sensing

Abstract

In this paper we present a beam-coupled micro-optical sensor for electric field detection. The main components of the sensor are a microsphere optical resonator and a dielectric micro-beam. The dielectric beam is coupled with the microsphere using two different approaches. In the first approach the beam compresses the sphere causing a shift in its whispering gallery mode (WGM). In the second approach the fine tipped beam perturbs the evanescent field of the sphere thereby causing a shift its WGM. In this approach, electrostriction force exerted by the electric field on the beam induces a change in the gap between sphere and beam perturbing the evanescent field of the sphere. This in turn induces a shift in the whispering gallery modes of the sphere resonator. The material for both the sphere and the beam in the first approach is polydimethylsiloxane (PDMS). The resonator and the beam are made of silica in the second approach. Different beam and sphere sizes are studied to optimize the proposed sensor’s electric field resolution. The optical modes of the sphere are exited using a tapered single mode optical fiber that is coupled to a distributed feedback laser. The transmission spectrum through the fiber is monitored to detect WGM shifts.