Study on the sensing characteristics of a local micro-structured long period fiber grating

Abstract

A simple and effective method employing a local micro-structured long period fiber grating (LMS-LPFG) for the simultaneous measurement of temperature and refractive index is proposed and investigated experimentally. The LMS-LPFG is formed by using the partial etching technique with hydrofluoric (HF) acid in a standard LPFG, in which there are discontinuities in the effective refractive index of cladding modes. Similar to the phase shift theory, a narrow passband and two stopbands are formed. The temperature and the surrounding refractive index (SRI) characteristics of the two stopbands and passband are studied. The temperature sensitivities of the two stopbands and passband are 0.05 nm/°C approximately. The SRI sensitivity of passband (−61.56 nm/RIU) is bigger than that of the two stopbands (−35.62 nm/RIU). Thus, with the sensitive matrix, we can simultaneously measure the changes of temperature and refractive index.