Heterodyne Interferometric Measurement of the Thermo-Optic Coefficient of Single Mode Fiber

Abstract

The thermo-optic coefficient of a single mode fiber is determined by a heterodyne interferometric technique. The heterodyne beat signal, resulting from the beating of the carrier and two side-band frequencies, is related to the phase shift difference between the carrier and the side-band waves in a fiber Fabry-Perot interferometer. This phase shift difference is determined with a phase sensitive detection technique and is found to be temperature dependent. From the temperature dependence, the thermo-optic coefficient of the single mode fiber is determined to be 9.2 x 10^-6 C^-1. The experimental result agrees well with a theoretical simulation using the temperature dependent Sellmeier equation for fused silica.