COVERING A FIBER TAPER WITH A REFRACTIVE INDEX MATCHING GEL RESIDUE: A SIGNIFICANT INCREASE OF EVANESCENT-WAVE SIGNAL COLLECTION EFFICIENCY

Huacai Chen, Jianjun Ma, Jiahua Chen, Wojtek J. Bock, Andrea Cusano

Abstract

A novel optical fiber evanescent-wave (EW) sensing platform combining a taper and a refractive index (RI) gel residue is proposed. It includes two identical large core multimode fibers that are positioned perpendicularly to each other with one for excitation light delivery (i-fiber) and one for EW fluorescent signal collection (r-fiber). One end of the r-fiber is decladded to expose a segment of a cylindrical fiber core terminated with a taper. A small drop of rhodamine 6G (R6G) solution sample is distributed in such a way that it surrounds the side wall of the cylindrical portion of the core and covers the i-fiber end face. The fluorescent signal is recorded under the following conditions: 1. the entire taper is exposed to the air; 2. the entire taper is immersed into a large gel block; 3. the taper is covered with a gel residue. A dramatic rise of the fluorescence signal is observed in the third case, which is over 20 times more than the level achieved from the first two cases. We reveal that the combination of the end-face-TIR and the mode mixing accounts for this phenomenon, which will be discussed in detail.

Keywords

fiber-optic sensor, fiber taper, evanescent wave, multimode fiber, fluorescence, spectroscopy, mode mixing.

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DOI

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IMEKO TC

TC2 - Photonics

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