Surface plasmon resonance in a bent single-mode fiber with a metallized cladding experimental research

The processes of surface plasmon resonance excitation in a bent single-mode optical fiber with a metallized cladding have been studied experimentally. It is shown that, for a certain combination of the bending radius of an optical fiber and the thickness of a metal film, a strong coupling between the fundamental and plasmon–polariton mode is achieved through a whispering gallery mode supported by the fiber cladding, which leads to the formation of a resonance dip with a depth of $\sim$30 dB or more in the transmission spectrum of an optical fiber loop. The position of the dip depends strongly on the ambient refractive index, which provides the possibility of refractometric measurements with a spectral sensitivity of $\sim$5 $\mu$m/RIU and a resolution of $\sim$4 $\times$ 10$^{-6}$. Limits of measurement of the refractive index are determined by the operating spectral range and the bending radius of the optical fiber and are 1.42–1.44 for the setup used.