FFPI-FBG hybrid sensor to measure the thermal expansion and thermo-optical coefficient of a silica-based fiber at cryogenic temperatures

Abstract

In this Letter, a sensor consisting of a fiber Bragg grating (FBG) and a fiber Fabry-Perot interferometer (FFPI) sensor is developed to measure the coefficient of thermal expansion (CTE) and the thermo-optical coefficient (TOC) of a silica-based optical fiber at cryogenic temperatures. The FFPI is fabricated by welding together two acid-etched fibers. The temperature performance of the FFPI-FBG hybrid sensor is studied in the temperature range of 30-273 K. The CTE and TOC of the optical fiber at cryogenic temperatures are derived analytically and verified by experiments.