Chirped fiber Bragg gratings for optical dispersion compensation: how to improve their fabrication accuracy

Sufficiently accurate, chirped fiber Bragg gratings for dispersion compensation at high bit rates are difficult to fabricate. We propose to determine local grating errors from a measured complex reflection spectrum and to correct them by UV light postprocessing. A chirped, sampled fiber Bragg grating could compensate for the dispersion of 50 km of standard fiber in four 40 Gb/s channels but the required fabrication accuracy is extremely high. We have proposed to determine stitch errors between adjacent phase mask areas, and longitudinal refractive index variations, from the measured complex frequency response of the grating. Local UV light postprocessing then allows to correct the errors. We believe this method will permit production of precise fiber Bragg gratings for dispersion compensation and other purposes.