Nonlinearity in bent optical fibers

Abstract

An interferometric method to study the induced variations of nonlinear parameters in bent optical fiber such as third-order susceptibility chi((3)) and second-order refractive index n(2) is presented. Due to the expected nonlinear response of the Young's modulus of fiber material, the profiles of asymmetric variations of the two parameters with curvature are observed and calculated, revealing the high spatial and index resolution of the method. The investigation is done in single-mode optical fibers at the standard operating wavelengths of 1300 and 1550 nm and at radii of curvature from 5 to 11 mm. At the minimum radius of curvature R=5 mm, the cladding chi((3))=4.131x10(-15) esu on the tensile side, whereas on the compressed side it is 4.601x10(-15) esu for lambda=1300 nm. On the tensile side n(2)=1.09x10(-13) esu, whereas on the compressed side it is 1.216x10(-13) esu. For lambda=1550 nm, the cladding chi((3)) and n(2) on the tensile side are 3.96x10(-15) esu and 1.055x10(-13) esu, whereas in the compressed cladding side they are 4.435x10(-15) esu and 1.174x10(-13) esu, respectively. At lambda=1300 nm and R=5 mm, the core chi((3)) is given by 4.631x10(-15) esu on the tensile side and 4.649x10(-15) esu on the compressed side. The asymmetry in n(2) is given by 1.223x10(-13) esu on the tensile side and by 1.227x10(-13) esu on the compressed side. With lambda=1550 nm, the core chi((3)) asymmetry is given by 4.46x10(-15) esu on the tensile side and by 4.477x10(-15) esu on the compressed side. For n(2) its asymmetry is provided by 1.181x10(-13) esu on the tensile side and by 1.185x10(-13) esu on the compressed side.