we have investigated the influence of multimode fiber core (MMFC) diameters and lengths on the sensitivity of an SMS fiber based refractometer. We show that the MMFC diameter has significant influence on the refractive index (RI) sensitivity but the length does not. A refractometer with a lower MMFC diameter has a higher sensitivity. Experimental investigations achieved a maximum sensitivity of 1815 nm/ RIU (refractive index unit) for a refractive index range from 1.342 to 1.437 for a refractometer with a core diameter of 80 µm. The experimental results fit well with the numerical simulation results. fiber Bragg grating and multimode fibers using an intensity-based interrogation method", 2008 Optical Society of America

We propose and experimentally demonstrate an enhanced evanescent field fiber refractometer based on a tapered multimode fiber sandwiched between two single-mode fibers. Experiments show that this fiber sensor offers ultrahigh sensitivity [better than 1900 nm/RIU at a refractive index (RI) of 1.44] for RI measurements within the range of 1.33-1.44, in agreement with the theoretical predictions. This is the highest value reported to date (to our knowledge) in the literature.

This paper provides an overview of the different types of fiber optic sensors (FOS) that can be used with composite materials and also their compatibility with and suitability for embedding inside a composite material. An overview of the different types of FOS used for strain/temperature sensing in composite materials is presented. Recent trends, and future challenges for FOS technology for condition monitoring in smart composite materials are also discussed. This comprehensive review provides essential information for the smart materials industry in selecting of appropriate types of FOS in accordance with end-user requirements.

A comprehensive theoretical model for an SMF28-Small-Core SMF (SCSMF) -SMF28 structure based refractometer is developed based on modal propagation analysis (MPA) method. Simulation result shows that the wavelength shift of this refractometer obeys changes exponentially as the surrounding refractive index (SRI) varies. The core diameter of SCSMF does not have a significant influence on the sensitivity of the refractometer but cladding diameter does have. The simulation results are verified experimentally and it is also experimentally demonstrated that a maximum sensitivity of 1808 nm/RIU (refractive index unit) for an SRI range from 1.324 to 1.431 and that as expected the wavelength shift response is an exponential function of SRI.

A refractive index (RI) sensor based on a novel fiber structure which consists of a singlemode-multimodesinglemode (SMS) fiber structure followed by a fiber Bragg grating (FBG) was demonstrated. The multimode fiber (MMF) in the SMS structure excites cladding modes within output singlemode fiber (SMF) and re-couple the reflected cladding Bragg wavelength to the input SMF core. By measuring the relative Bragg wavelength shift between core and cladding Bragg wavelengths, the RI can be determined. Experimentally we have achieved a maximum sensitivity of 7.33 nm/RIU (RI unit) at RI range from 1.324to 1.439.