Normal free space coupling to fiber Bragg grating sensors

Abstract

In recent decades, optical fiber has proven useful for many sensor applications. Specifically, fiber Bragg grating (FBG) sensors have shown great utility for integrity management and environmental sensing of composite structures. One major drawback of FBG sensors, however, is the lack of a robust, non-pigtail technique for coupling the embedded FBG sensor to an external optical interrogation device. In this paper, a novel method of free space passive coupling of light into FBG sensors has been investigated. Angled 45-degree mirrors integrated directly into fibers were used as an input coupling technique. The approach was applied to both single mode and multimode glass fibers containing FBG’s. For multimode investigations, mirrors were integrated into graded-index multimode fiber by polishing the end face to a 45-degree angle. In single mode investigations, a novel method of coupling to the sensor via splicing and fusing a multimode fiber to a single mode FBG was explored. Associated transmission spectra are shown for each method.