Long-Period Gratings in Highly Germanium-Doped, Single-Mode Optical Fibers for Sensing Applications

• Published in: Sensors (Basel, Switzerland) Vol. 18; no. 5; p. 1363
• Main Authors: Schlangen, Sebastian, Bremer, Kort, Zheng, Yulong, Böhm, Sebastian, Steinke, Michael, Wellmann, Felix, Neumann, Jörg, Roth, Bernhard, Overmeyer, Ludger
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 27.04.2018; MDPI
• Subjects: amplitude mask; Cladding; excimer laser; Excimer lasers; Excimers; Fused silica; Germanium; germanium-doped fiber; Glass substrates; Gratings (spectra); high NA fiber; Inscriptions; Lasers; Light; Liquefied petroleum gas; long-period fiber grating; Manufacturing; Numerical aperture; Optical fibers; Photosensitivity; Radiation; Sensors; Simulation; single-mode fiber; Tapering; single-mode fiber; long-period fiber grating; amplitude mask; high NA fiber; excimer laser; germanium-doped fiber
• ISSN: 1424-8220; 1424-8220
• DOI: 10.3390/s18051363

Long-period fiber gratings (LPGs) are well known for their sensitivity to external influences, which make them interesting for a large number of sensing applications. For these applications, fibers with a high numerical aperture (i.e., fibers with highly germanium (Ge)-doped fused silica fiber cores) are more attractive since they are intrinsically photosensitive, as well as less sensitive to bend- and microbend-induced light attenuations. In this work, we introduce a novel method to inscribe LPGs into highly Ge-doped, single-mode fibers. By tapering the optical fiber, and thus, tailoring the effective indices of the core and cladding modes, for the first time, an LPG was inscribed into such fibers using the amplitude mask technique and a KrF excimer laser. Based on this novel method, sensitive LPG-based fiber optic sensors only a few millimeters in length can be incorporated in bend-insensitive fibers for use in various monitoring applications. Moreover, by applying the described inscription method, the LPG spectrum can be influenced and tailored according to the specific demands of a particular application.