Birefringence of Hybrid PCF and Its Sensitivity to Strain and Temperature

Abstract

The modal and group birefringence of a hybrid photonic crystal fiber (hybrid PCF) and the sensitivities of modal birefringence of hybrid PCF to strain and temperature are investigated. The hybrid PCF composes of air-holes and Ge-doped silica rods surrounding a silica core region and light is confined to the core by hybrid index-guiding and photonic bandgap effects. A theoretical model was established and used to calculate these birefringence properties as functions of Ge concentration and diameter of the Ge-doped region. In experiments, the birefringence properties of a hybrid PCF made by University of Bath were measured by using a Sagnac interferometer. The experimental results show that the sensitivities of fringe minimum of this Sagnac interferometer to strain and temperature, at the wavelength of 1550 nm, were 2.01 nm/m <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\varepsilon$</tex></formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${-}$</tex></formula> 0.334 nm/ <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$^{\circ}$</tex></formula> C, respectively, which agree well with the theoretical predictions. The model may be used to design hybrid PCFs with desired birefringence properties.