Tunable single-mode fiber reflective grating filter

A single-mode fiber tunable reflective filter is demonstrated by translating a fan-shaped grating structure through the evanescent field of a side-polished fiber. Filter linewidths of about 1 nm were measured over tuning ranges in excess of 65 nm. Reflectivities as high as 88 percent were observed. Using the fiber filter as a feedback element, a multimode semiconductor laser was observed to oscillate in a single mode which could be discretely turned over a wavelength range of 26 nm.