Curvature and temperature sensing based on a dual-frequency OEO using cascaded TCFBG-FP and SMFBG-FP cavities

Abstract

A dual-frequency optoelectronic oscillator (OEO) incorporating cascaded fiber-Bragg-grating Fabry–Perot (FBG-FP) cavities designed for both curvature and temperature sensing is proposed and experimentally validated. The OEO is composed of two tunable laser diodes (TLDs), a phase modulator (PM), two FBG-FP cavities, a spool of fiber, a photodiode (PD) and an electrical amplifier (EA). One FBG-FP cavity is curved on a twin-core fiber (TCF) and the other is curved on a single mode fiber (SMF), with one core of the TCF aligned and spliced with the core of the SMF. The oscillating frequencies of the OEO are determined by the wavelength differences of the TLDs and the notches of the FBG-FP cavities. The oscillating frequency related to the twin-core-fiber-Bragg-grating Fabry–Perot cavity is both curvature and temperature sensitive thanks to the off-set core of the TCF, while the oscillating frequency corresponding to the single-mode-fiber-Bragg-grating Fabry–Perot cavity is only temperature sensitive. By monitoring the oscillating frequencies of the OEO, high-sensitivity curvature and temperature sensing are realized. The oscillating frequencies are linearly proportional to the curvature and temperature, with sensitivities as high as −1.19 GHz/m−1 and 1.14 GHz/oC, respectively.