Enhanced sensing performance of microsphere cavities based on coreless fibers in aqueous environments

Abstract

This work demonstrates the superior performance of silica microsphere cavities fabricated from coreless fiber (CLF) for optical sensing applications. The optical resonances within CLF microspheres, excited through total internal reflection-induced whispering gallery modes, enable detectable spectral shifts in response to refractive index variations caused by nanoparticle binding. Compared to conventional microspheres using single-mode fibers (SMFs), CLF microspheres exhibit significantly higher quality factors (Q > 108) and enhanced sensitivity of resonance wavelength shifts for nanoparticle detection in aqueous environments. The experimental results reveal that the exceptional material homogeneity and sub-nanometer surface roughness (Ra < 0.5 nm) of CLF microspheres consistently sustain Q-factors exceeding 108. In underwater nanoparticle adsorption experiments, CLF cavities demonstrate more than 1.25 times higher resonance wavelength shift sensitivity than their SMF counterparts. Finite-difference time-domain simulations confirm that the order-of-magnitude improvement in Q-factor constitutes the fundamental mechanism for sensitivity enhancement. These findings establish a novel platform for high-precision underwater biosensing and environmental monitoring.