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<sup>-1</sup> to 2.016 N<sup>-1</sup>.
In this paper, we investigate the feasibility of a magnetic field sensor that is based on a magnetorheological micro-optical resonator. The optical resonator has a spherical shape and a diameter of a few hundred micrometers. The resonator is fabricated by using a polymeric matrix made of polyvinyl chloride (PVC) plastisol with embedded magnetically polarizable micro-particles. When the optical resonator is subjected to an external magnetic field, the morphology (radius and refractive index) of the resonator is perturbed by the magnetic forces acting on it, leading to a shift of the optical resonances also known as whispering gallery modes (WGM). In this study, the effect of a static and harmonic magnetic field, as well as the concentration of the magnetic micro-particles on the optical mode shift is investigated. The optical resonances obtained with the PVC plastisol resonator showed a quality factor of ∼106 . The dynamical behavior of the optical resonator is investigated in the range between 0 and 200 Hz. The sensitivity of the optical resonator reaches a maximum value for a ratio between micro-particles and the polymeric matrix of 2:1 in weight. Experimental results indicate a sensitivity of 0.297 pm/mT leading to a resolution of 336 μT.
In this paper we present a room-temperature micro-photonic bolometer that is based on the whispering gallery mode of dielectric resonator (WGM). The sensing element is a hollow micro-spherical optical polymeric resonator. The hollow resonator is filled with a fluid (gas or liquid) that has a large thermal expansion. When an incoming radiation impinges on the resonator is absorbed by the absorbing fluid leading to a thermal expansion of the micro-resonator. The thermal expansion induces changes in the morphology of the resonator (size and index of refraction), that in turn lead to a shift of the optical resonances (WGM). The optical resonances are typically excited using a single mode optical fiber. The preliminary analysis presented in this paper, shows that these sensors can measure energies of the order of 0.1J/m<sup>2</sup>.
In this paper we present a high resolution magnetic field sensor that is based on the perturbation of the optical modes (whispering gallery mode, WGM) of a spherical dielectric resonator. The optical resonator is side coupled to a tapered single mode optical fiber. One side of the optical fiber is coupled to a distribute feedback diode laser, while the other end is connected to a photodiode. The optical modes of the dielectric cavity are perturbed using a metglas sheet that is in contact with the resonator. When the metglas sheet is exposed to an external magnetic field it elongates perturbing the optical modes of the dielectric cavity. This in turn leads to a shift in the optical resonances. By measuring the induced WGM shift the magnetic field can be measured. Preliminary results show sensor resolution of a few nanoteslas.