Abstract

In long distance optical communication systems, fiber chromatic dispersion degrades the system’s transmission capabilities by limiting the achievable bit rates and repeater spacings. One way to solve this problem is to perform dispersion compensation, or equivalently pulse compression, in the communications network. Recently, chromatic dispersion compensation in a 5-Gbit/s transmission system has been achieved with a fiber Fabry-Perot optical equalizer. The amount of dispersion compensated by a single Fabry-Perot equalizer is, however, limited. Linearly chirped waveguide grating filters can also be used for dispersion compensation as reported by Ouel lette.¹ In this paper, we derive the grating parameters needed to obtain nearly optimum dispersion compensation. The resulting aperiodic grating filter has both a flat amplitude and a quadratic phase response over the pulse bandwidth. The response corresponds to the ideal transfer function for the compression linearly chirped pulses. The filter is analytically designed by cascading a Butterworth filter with an all-pass network. The pole placement of the all-pass network is selected to give the desired quadratic phase response. The grating parameters, corresponding to this filter, are obtained by solving the inverse problem for contradirectional waveguide coupling using the Gelfand-Levitan-Marchenko method.²

© 1991 Optical Society of America