HCPCF-based in-line fiber Fabry-Perot refractometer and high sensitivity signal processing method

Abstract

An in-line fiber Fabry-Perot interferometer (FPI) based on the hollow-core photonic crystal fiber (HCPCF) for refractive index (RI) measurement is proposed in this paper. The FPI is formed by splicing both ends of a short section of the HCPCF to single mode fibers (SMFs) and cleaving the SMF pigtail to a proper length. The RI response of the sensor is analyzed theoretically and demonstrated experimentally. The results show that the FPI sensor has linear response to external RI and good repeatability. The sensitivity calculated from the maximum fringe contrast is -136 dB/RIU. A new spectrum differential integration (SDI) method for signal processing is also presented in this study. In this method, the RI is obtained from the integrated intensity of the absolute difference between the interference spectrum and its smoothed spectrum. The results show that the sensitivity obtained from the integrated intensity is about -1.34× 10 5 dB/RIU. Compared with the maximum fringe contrast method, the new SDI method can provide the higher sensitivity, better linearity, improved reliability, and accuracy, and it's also convenient for automatic and fast signal processing in real-time monitoring of RI.

A Comprehensive Review of Optical Fiber Refractometers: Toward a Standard Comparative Criterion

“…These FPIs are also called all‐fiber FPIs, because all sections of the sensing head are composed of optical fiber. In Figure , it is possible to appreciate diverse designs that have been reported recently: sandwiching sections of photonic crystal fiber (PCF), suspended‐core fiber (SC), or hollow‐core photonic crystal fiber (HCPCF) between SMF fragments. Another FPI with three fiber sections was presented by Deng et al.…”

An Ultra-High Sensitivity Optical Fiber Refractive Index Sensor Based on Plasmonic Mach-Zehnder Interferometer

“…Interferometer, including Michelson interferometer [13], Mach-Zehnder interferometer (MZI) [14], Sagnac interferometer [15], Fabry-Perot interferometer [16], is one of the most sensitive optical interrogation methods [17] . The principle of MZI is that the optical signal is divided into two parts and enters the reference arm and the measuring arm respectively, and then the interference occurs after the convergence at the other end.…”