Whispering Gallery Mode Based Micro-Optical Sensor for Electromagnetic Field Detection

Abstract

In this paper we investigate the electrostriction effect on the whispering gallery modes (WGM) of polymeric microspheres and the feasibility of an WGM-based microsensor for electric field measurements. The electrostriction is the elastic deformation (strain) of a dielectric material under the force exerted by an electrostatic field. The deformation is accompanied by mechanical stress which perturbs the refractive index distribution in the sphere. Both the strain and the stress induce a shift in the WGM of the microsphere. In the present, we develop analytical expressions for the WGM shift due to electrostriction for solid and thin-walled hollow microspheres. Our analysis indicates that measurements of electric fields as small as ~500V/m may be possible using water filled, hollow PDMS micro-spheres. The electric field sensitivities for solid spheres, on the other hand, are significantly smaller. The effect of dielectric constant perturbations in the ambient medium on sphere WGM has also been investigated. A preliminary analysis indicates that changes of the order of ~10 -3 in dielectric constant of the medium surrounding the microsphere can be observed by using a water-filled hollow PDMS sphere.