New method to control chirp and wavelength of fibre Bragg gratings for multichannel chromatic dispersion compensation

We propose here new method for the realisation of long, chirped and apodised gratings for multichannel dispersion compensation. We use a process allowing the control of the grating wavelength with a phase mask of given periodicity, by modifying the UV beam convergence. By writing a succession of small elementary gratings, and, between each grating, changing the beam convergence, it is possible to write step-chirped gratings. It is also possible to choose the grating central wavelength. It has been shown that spectral dispersion response of a uniform index profile grating was not linear, and that apodisation was necessary. This method allows the apodisation by controlling the irradiation time on each elementary grating