Micro-structured optical multi-mode fibers for sensing applications

Abstract

Grating-based Fiber Optic Sensors (FOSs), i.e. relying on Bragg Gratings (BGs), Long Period Gratings (LPGs), Tilted Fiber BGs (TFBGs), have seen a popularity in recent years for sensing applications, however, most of these are inscribed on Single-Mode Fibers (SMFs). Multi-Mode Fibers (MMF), on the other hand, offer new and different properties in grating design and performance characteristics compared to SMFs, since the spectral response may be tuned by core size, refractive index profile, numerical aperture, and mode coupling characteristics of the gratings. Also, MMFs can be readily coupled with inexpensive light sources and other optical components due to their large core and, thus, gratings in MMFs are preferred to yield lower cost systems. Moreover, in terms of sensing region, MMFs have a greater mode field surrounding the fiber when compared with SMFs, due to the larger core diameters of MMFs and, thus, even greater mode fields can be accessed with a smaller reduction of the fiber diameter which would have better mechanical robustness, when compared with gratings inscribed in SMFs. In this talk we present our latest research in BG structures inscribed in multi-mode optical polymer and glass fibers.