Characteristics of Few Mode Fiber Under Bending

Abstract

Sensing characteristics of a special few mode fiber (FMF) which supports only the fundamental mode LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> and LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> mode under bending are theoretically and experimentally studied in this paper. The mode field distributions, effective indices, and propagation constant differences of the FMF under bending are calculated. With the specifically designed fiber parameters, the transmission spectrum of such FMF will show a critical wavelength at 1556.220 nm. We observed at the first time in experiment and later verified theoretically that the critical wavelength will shift with the change of fiber curvature. The sensitivity of the critical wavelength to the curvature has been calculated and measured, respectively. Also the curvature induced wavelength shifts of the interferometric peaks appeared on both sides of the critical wavelength are analyzed theoretically and measured experimentally. There is a good agreement between theoretical calculation and experimental measurement. The behaviors of curvature depended critical wavelength and shifts of the peaks close to the critical wavelength can be utilized in the design of curvature or curvature relevant displacement and vibration sensors, etc.