Electrostrictive optical resonators for non-contact displacement measurement

This paper describes a non-contact transduction mechanism for the measurement of linear displacements that is based on the electrostrictive properties of a polymeric optical resonator. The spherical resonators, with a diameter of ∼1  mm and an average optical quality factor of ∼10⁶, are made using a commercially available polymer (Super Soft Plastic-Manufacturing Company). The spherical resonator is immersed in a homogeneous electric field that is generated by applying a voltage difference between two metallic plates. One of the plates is fixed, whereas the other one is movable. By changing the distance between the plates, the electric field intensity changes, leading to a variation of the mechanical forces (electrostrictive effect) acting on the resonator. This effect, in turn, leads to a change in the morphology of the optical resonator and therefore to a shift of its optical resonances. By tracking the shift of the optical modes, it is possible to determine the displacement of the movable plate. Our results indicate a sensitivity ranging from 0.008 to 0.642  pm/μm with a resolution on the order of a few hundreds of nanometers.