Refractometer based on tilted fiber Bragg grating incorporating with waist-enlarged fusion bitaper

A novel all-fiber refractometer based on a tilted fiber Bragg grating (TFBG) incorporating with a waist-enlarged fusion bitaper (WEFBT) is proposed and experimentally demonstrated. The WEFBT is upstream spliced with the TFBG thus coupling some of the cladding modes launched by the TFBG into core mode while the cladding modes excited by the WEFBT will be combined backward into the core by the TFBG. Surrounding refractive index (SRI) modulates the signal´s intensity when it propagates as cladding mode and thus can be measured. Measurement range 1.358 to 1.448 has been achieved.