Force detection using whispering gallery mode-based micro-optical resonators

Abstract

This paper investigates the feasibility of using micro-optical resonators to develop a force sensor which can be embedded within a material to create members with inherent damage sensing capabilities. The optical resonator is comprised of a polymeric material and has a circular cross section with a diameter ranging from tens to hundreds of micrometers. When light is brought inside the resonator, it starts to travel along the internal surface through total internal reflection, exciting optical resonances, also known as Whispering Gallery Modes (WGMs). Any change in the morphology of the resonator determines a shift of the WGMs in the transmission spectrum. Being the optical resonances extremely narrow, a high optical quality factor is obtained, which in turn, produces a resonator that is very sensitive to external effects that determine small changes in the morphology of the resonator. By embedding the resonator in a polymeric slab, and applying external loading, the encased nature of the sensor results in the resonator deforming along with the slab. The resulting shifts can then be measured and used to calibrate instruments to determine various forces that act on a given structure. Finite element analysis simulations were conducted using a cantilever polymeric beam with Young s modulus of 1.06 MPa with a concentrated tip load varying from 0.001 N to 0.1 N. Results of these simulations showed a linear relationship between the applied load and the WGM shift resulting in a sensitivity ranging from 0.2044 N-1 to 2.016 N-1.