Enhanced responsivity with skew ray excitation of reflection- and transmission-type refractometric sensors

The responsivity of optical fibers to refractive index can be enhanced using high-order skew rays compared with using meridional rays. Skew rays can have a much higher number of reflections with increased interaction length along the core–cladding interface, which gives rise to stronger interactions with the external medium. Reflection/transmission-type refractometric sensors based on twin-coupled-core and multimode fibers showed one/two orders of magnitude increase in responsivity with skew ray excitation. The responsivity and sensitivity for the two types are $\sim 2000\%/\mathrm{RIU}$, $\sim 1400\%/\mathrm{RIU}$, and $4.9\times {10}^{-5}\mathrm{RIU}$, $7.0\times {10}^{-5}\mathrm{RIU}$, respectively.