Modified Talbot interferometer for fabrication of fiber-opticgrating filter over a wide range of Bragg wavelength and bandwidth usinga single phase mask

A technique involving a compact apparatus that combines the phase mask and two-beam interferometric techniques is presented. It involves the use of a phase mask to diffract the ultraviolet (UV) beam and a cylindrical lens combined with a pair of mirrors to produce two symmetric virtual line sources of UV light. Bragg wavelength and bandwidth of the fiber gratings can be controlled with a simple translation of the fiber and/or the phase mask. Using a 40-mw continuous-wave frequency-doubled argon-ion laser at 244 mm and a single phase mask, a series of chirped fiber gratings with the Bragg wavelength in a wide range around 600 nm and 1300 nm are fabricated in hydrogen-loaded ordinary fibers