A novel in-fiber structure for power-referenced refractometry with the capability to measure surrounding refractive index (SRI) as low as 1.33 is proposed and demonstrated. A short optical fiber stub containing a weakly tilted Bragg grating is spliced to another fiber with a large lateral offset. The reflection from this structure occurs in two well-defined wavelength bands, the Bragg reflected core mode and the cladding modes. The cladding modes reflect different amounts of power as the SRI changes, while the core-mode reflection from the same weakly tilted FBG remains unaffected by the SRI. The power reflected in the core mode band can be used as a reliable reference to cancel out any possible power fluctuations. The proposed refractometer with improved sensitivity for low SRI measurement together with the tip-reflection sensing feature, is a good candidate for sensing in chemical and biological applications.

Optics Express
Department of Electronics

Guo, T, Tam, H.-Y. (Hwa-Yaw), Krug, P.A. (Peter A.), & Albert, J. (2009). Reflective tilted fiber bragg grating refractometer based on strong cladding to core recoupling. Optics Express, 17(7), 5736–5742. doi:10.1364/OE.17.005736