A novel fiber-to-fiber tip-reflection sensing configuration for power-referenced refractometry with the capability to measure surrounding refractive index (SRI) as low as 1.33 is proposed and demonstrated. A short D-shaped fiber stub is parallel adjacent to another unshaped fiber containing a weakly tilted Bragg grating (TFBG). Light from the unshaped fiber can be effectively coupled into the adjacent D-shaped fiber through the TFBG which functions as a "bridge" between the core and cladding. Strong "comb" like cladding modes over a broad wavelength range have been recaptured in D-shaped fiber in reflection. These re-coupled cladding modes show different amounts of power as the SRI changes and the sensitivity is much higher than reported in-fiber sensing schemes, especially for low SRI measurement.

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Keywords D-shaped fiber, Optical fiber sensor, Refractometer, Tilted fiber bragg grating
Persistent URL dx.doi.org/10.1117/12.2194702
Conference 24th International Conference on Optical Fibre Sensors, OFS 2015
Cai, Z. (Zhongyue), Guo, T, Liu, F. (Fu), Guan, B.-O. (Bai-Ou), Peng, G.-D. (Gang-Ding), & Albert, J. (2015). Reflective refractometer based on strong optical coupling between a tilted fiber Bragg grating and a parallel D-shaped fiber. Presented at the 24th International Conference on Optical Fibre Sensors, OFS 2015. doi:10.1117/12.2194702