Annealing of linear birefringence in single-mode fiber coils: application to optical fiber current sensors

Abstract

Abstract-Annealing procedures that greatly reduce linear birefringence in single-mode fiber coils are described in detail. These procedures have been successfully applied to coils ranging from 5 mm to 10 cm in diameter and up to 200

Devitrification in annealed optical fiber

“…The fiber cladding is SiO 2 and the nominally 8 m core is about 4 mole % doped GeO 2 : SiO 2 glass. The fiber jacket is treated with acetone for a few minutes before the annealing and is burned off [4]. Annealing takes about four days.…”

“…Coils annealed at 850 C will be nearly isotropic, but require a slow cooling rate, approximately 0.2 C/min [4]. The heating rate used is limited to about 5 C/min These rates are slow enough to allow a significant amount of nucleation to occur during the annealing cycle.…”

“…Also, the fiber annealing is done in an atmosphere of ambient air where water, oxygen, carbon dioxide, and nitrogen can react with the glass surface to promote crystal growth [8], [11], [15], [16]. However, at this temperature the crystal growth rate is slow, and annealing times of several hours can be used without significantly affecting the performance of a current sensor [4], [8], [10], [20]- [22].…”

Optical fiber current sensors in high electric field environments

“…An optical fiber coil with and 15 cm diameter was twisted and annealed to reduce the linear retardance to about 471 mrad (27 ) [2], [39]. The value of was confirmed with the measured and predicted magnitude of and by the rotating polarizer method [40].…”

“…The EO Kerr effect is an electric-field-induced linear birefringence that arises when an electric field changes the polarizability of the glass molecules [1]. Linear birefringence, either from stress, bending, waveguide form, or the EO Kerr effect, alters the response of a Faraday effect current sensor (a sensor based on a magnetic-field-induced circular birefringence) [2]. In this paper, we analyze the EO Kerr effect on polarimetric and interferometric Sagnac optical fiber current sensors in high electric fields.…”