Fabrication, Characterization, and Sensor Applications of Polymer-Based Whispering Gallery Mode Microresonators.

The present article critically reviews the fabrication, characterization, and sensor applications of polymer-based whispering gallery mode resonators (WGMRs). Those resonators utilize continuous internal light reflections along curved surfaces to produce sharp resonance peaks influenced by the resonator's geometry, which appeared effective for high-sensitivity optical sensing. Polymer-based WGMRs leverage unique polymer characteristics to enhance sensor performance through parameters like quality factor (QF), free spectral range (FSR), resonance mode shifts, polarization modes, bulk refractive index (RI), sensitivity per refractive index unit (RIU), and thermo-optic effects. All-polymer WGMRs, i.e., resonators entirely made from polymers, offer design flexibility, biocompatibility, low thermal conductivity, and integration capabilities for high sensitivity, detectability, and selectivity. Polymer-coated optical fiber WGMRs improve light-material interaction, support advanced composites, integrate with microfluidics for on-chip diagnostics, and enable remote, multiplexed sensing. (Polymer shell)-(inorganic core) composite-functionalized WGMRs combine the high QFs of inorganic materials with polymers' flexibility and functionalization, providing synergistic optical properties, enhanced sensitivity, detectability, and stability. These advancements make polymer-based WGMR sensors promising for biomedical diagnostics, environmental pollution monitoring, and industrial process control. Future research will presumably optimize fabrication techniques, explore novel polymers, and integrate advanced signal processing for real-time analysis, connected with the Internet-of-Things (IoT) and cloud databases to revolutionize optical and photonic sensing platforms.