Novel design of refractive index sensors and biosensors based on a   dual-core micro-structured optical fiber
  In the present work a new model of a refractive index (RI) sensor is exhibited. This is based on a dual core micro-structured optical fiber (MOF), where two holes are introduced at the core centers. In this way, the model enhances the interaction of the fiber modes propagated in the core region, providing the possibility of increasing the dimensions of the fiber sensor. Thus, the filling of the fiber holes with the fluid under study is facilitated, and generally the practical use of the system as a refractive index sensor is greatly simplified. The sensitivity of the system for various configurations has also been determined. It is found that it can reach record values of the order of 7000 nm/RIU. Finally, the use of the system as a bio-sensor has been examined, giving very promising results regarding both the sensitivity and the ease of the calibration. 
G. Tsigaridas, V. Karvouniaris, G. Chalkiadakis and P. Persephonis
physics.optics