Analysis of birefringence and eigen-axes orientation resulting from the interplay between initial and form birefringence in UV-illuminated fiber

Abstract

Birefringence and eigen-axes orientation are computed in UV-illuminated fibers with a high-order isoparametric vectorial finite element method. Form birefringence is included in the index profile of weakly birefringent fibers and various UV-beam orientations are considered.

UV-induced modification of stress distribution in optical fibers and its contribution to Bragg grating birefringence

“…The study of the origin of photo-induced birefringence and its contributing factors in UVexposed optical fibers is important to determine the polarization behavior of in-fiber Bragg gratings [1][2][3][4][5][6][7][8]. Previous studies have identified three main contributions to photo-induced birefringence of gratings: orientation and state of polarization of the UV writing beam [1], transverse gradient in the UV-induced index change profile [2,3] and modification of glass stress profiles from the asymmetric glass densification in the photosensitive regions of the exposed fiber.…”

“…Previous studies have identified three main contributions to photo-induced birefringence of gratings: orientation and state of polarization of the UV writing beam [1], transverse gradient in the UV-induced index change profile [2,3] and modification of glass stress profiles from the asymmetric glass densification in the photosensitive regions of the exposed fiber. Other factors can also influence photo-induced birefringence such as fiber type [1,6], initial intrinsic fiber birefringence [7], hydrogenation [9] and laser writing beam wavelength and operation regime. Dependence of the induced birefringence on the polarization of the writing beam is attributed to the preferential bleaching of defects having their dipole moments aligned with the polarization of the UV writing beam [11].…”

“…Because of the strong UVlight absorption across the photosensitive core, a strong transverse gradient in the UV dose reaching the defects develops and henceforth in the refractive index change adopts a similar profile [2]. Initially thought to be the dominant process to explain the induced birefringence, early numerical studies concentrated on this phenomenon called form birefringence [4][5][6][7][8].…”

“…In previous work [5][6][7], we used a highly accurate vectorial finite element mode solver [16] considering isotropic refractive index distributions having an asymmetric profile. In this paper, we extend our investigation to quantify the photo-induced stress contribution to the UV-induced birefringence in Bragg gratings using the same numerical method and considering an anisotropic dielectric tensor.…”