Reproducible ultra-long FBGs in phase corrected non-uniform fibers

Abstract

Ultra-long fiber Bragg gratings (FBGs), i.e., FBGs of several tens of cm in length, have attracted much attention in the last few decades for their potential applications in advanced devices. Although numerous fabrication methods as well as ultra-long functionalized FBGs have been proposed and demonstrated successfully, such devices are difficult to reproduce. We have recently found that specialty optical fibers of the type required for these applications are highly non-uniform on a short length scale, severely affecting the characteristics of ultra-long FBGs. We propose here a new production technique that can be adapted to any non-uniform fiber for ultra-long FBG fabrication. This technique involves a fiber characterization prior to FBG inscription followed by the writing of a phase corrected ultra-long FBG. This technique has no limitations in terms of correction amplitude or FBG length. The results are quite astonishing, as near-perfect 1-m-length-scale FBGs are possible in fibers in which it was impossible to write uniform period gratings prior to phase correction.