Nano-positioning of a Bragg grating inscription setup for the concatenation of multiple gratings using the diffraction by the grating experienced by the ultraviolet inscription beam

A novel scheme is demonstrated to realize the concatenation of multiple Bragg gratings with an accurate control of the phase matching between the different gratings. This approach uses the grating-induced diffraction of the ultraviolet inscription beam to complete a nano-positioning of the phase mask used for photo-inscription. The efficiency of the method has been probed by concatening up to 20 gratings written in hydrogen loaded and unloaded fiber by means of 244 nm continuous light. A theoretical description of the results obtained for the reflectivity and full-width-half-maximum (FWHM) of the grating is also proposed.