Lossy mode resonance sensor assisted by dual long-period fiber gratings with core-mode blocker

Abstract

A novel sensor configuration consisting of TiO2 film and dual long-period fiber gratings (LPFG) with an in-between core-mode blocker (CMB) is proposed and numerically investigated. TiO2 film is on the cladding surface of separation fiber between two identical LPFGs and lossy mode resonance (LMR) is induced by a single cladding mode which is coupled from core mode by the first grating. Afterwards, the cladding mode influenced by LMR is recoupled into core mode by the second grating. As a result, the output spectrum is characterized as a dip in the top of a bandpass spectrum curve. The central wavelength of this dip is sensitive to surrounding refractive index and the numerical analysis reveals that the sensitivity reaches 5075 nm/RIU with excellent linearity. In this configuration, the bandwidth of attenuation dip is reduced in a great manner since LMR is induced by a single cladding mode. Moreover, this sensor configuration synthesizes the advantages of both LMR and LPFG, which offers additional degrees of freedom in the sensor design.