Bent optical fiber taper for refractive index detection with a high sensitivity.

Highlights: [•] A bent optical fiber taper is proposed for highly sensitive refractive index detection. [•] The peak wavelength is sensitive to external refractive index. [•] The tapered cladding in the downtaper enhances the sensitivity. [•] Higher sensitivity can be obtained from peak at longer wavelength. [•] A high sensitivity of 4000nm/RIU was experimentally obtained. [Copyright &y& Elsevier]