Tunable fiber Bragg grating using evanescent field coupling

In this work, we present experimental results on tenability of fiber Bragg grating incorporating evanescent field coupling. Evanescent field is the exponentially decaying part of an optical mode formed in a waveguide. A section of fiber with a Bragg grating written in it is side-polished until most of the cladding is removed. The evanescent field is modified by applying different index matching oil and by placing a dielectric material on the polished area of the fiber. A tunability as much as 5 nm was demonstrated as the applied index matching oil varied from n = 1.40 to n = 1.45. Polarization dependent behavior of the device was also measured and it was found out that the polarization component that is perpendicular to the polished surface experiences severe loss. A prototype tunable grating device incorporating a MEMS structure is also discussed.