Micro-optical force sensor concept based on whispering gallery mode resonators

A micro-optical force sensor concept based on the morphology-dependent shifts of optical modes of di-electric microspheres is investigated. The optical resonances, commonly referred to as the whispering gallery modes (WGM), were excited by evanescently coupling light from a tunable diode laser using a tapered single-mode fiber. A compressive force applied to the sphere induces a change in both the shape and the index of refraction of the sphere leading to a shift in WGM. By tracking the shifts, the force magnitude is determined using solid silica as well as solid and hollow Polymethyl-methacrylate (PMMA) microsphere resonators. A measurement sensitivity as high as dλ=dF 7:664nm=N was demonstrated with a 960 μm hollow PMMA sphere. © 2008 Optical Society of America OCIS codes: 280.4788, 350.3950, 230.3990, 230.4555, 140.3948. 1