Research papers - Proceedings Volume 9852, Fiber Optic Sensors and Applications XIII; 98520H (2016)
Interrogation and mitigation of polarization effects for standard and birefringent FBGs
Selwan K. Ibrahim, Jan Van Roosbroeck, John A. O'Dowd, Bram Van Hoe, Eric Lindner, Johan Vlekken, Martin Farnan, Devrez M. Karabacak, Johannes M. Singer
Short description
Optical sensors based on Fiber Bragg Gratings (FBGs) are used in several applications and industries. Several inscription techniques and type of fibers can be used. However, depending on the writing process, type of fiber used and the packaging of the sensor a Polarization Dependent Frequency Shift (PDFS) can often be observed with polarized tunable laser based optical interrogators. Here we study the PDFS of the FBG peak for the different FBG types. A PDFS of <1pm up to >20pm was observed across the FBGs. To mitigate and reduce this effect we propose a polarization mitigation technique which relies on a synchronous polarization switch to reduce the effect typically by a factor greater than 4. In other scenarios the sensor itself is designed to be birefringent (Bi-FBG) to allow pressure and/or simultaneous temperature and strain measurements. Using the same polarization switch we demonstrate how we can interrogate the Bi-FBGs with high accuracy to enable high performance of such sensors to be achievable.