Whispering gallery mode (WGM) microsphere resonators provide a label-free and flexible platform for analyzing a variety of samples, ranging from biological assays to characterizing materials. Importantly, WGM resonators are able to sense refractive index changes by recirculating light within their spherical cavity. The supported wavelength depends, among other parameters, upon the sample’s refractive index; thus, changes in refractive index are detected by measuring resonant wavelength shifts. To improve performance metrics, resonators with high sensitivity are needed. My research objectives have been to create high quality microspheres from tapered single mode optical fibers. By fabricating spheres from optical fiber, smaller and smoother microspheres are produced, which results in more sensitive and effective resonators for sensing applications. Three different sized microspheres were investigated. Resonators with diameters of 20 µm, 40 µm, and 150 µm resulted in measured surface sensitivities of 0.2506 nm/ RIU, 0.1079 nm/RIU, and 0.1259 nm/RUI, respectively. The overall goal is to investigate these resonators in a hybrid atomic force microscopy (AFM) technique that combines topography imaging with refractive index sensing. Our group recently introduced this technique, termed scanning resonator microscopy (SRM), which utilizes WGM resonators to analyze refractive index of a sample surface. SRM can be used to analyze a variety of substrates, including graphene. Interest in graphene exists due to the unique molecular properties of the single carbon layer, which has numerous applications in electronic, biomedical, and energy fields. Combining the resonators with AFM in order to simultaneously analyze topography and refractive index of thin graphene sheets resulted in the observation of optical features that correlated with topography.

Optimizing microsphere whispering gallery mode resonators for sensing

251st National Meeting (2016)

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