DISPERSIVE PROPERTIES OF OPTICAL FILTERS FOR WDM SYSTEMS

Wavelength division multiplexing (WDM) communication systems invariabl y require good optical filters meeting stringent requirements on their amplitude response, the ideal being a perfectly rectangular filter. T o achieve high bandwidth utilization, the phase response of these filt ers is of equal importance, with the ideal filter having perfectly lin ear phase and therefore constant time delay and no dispersion, This as pect of optical filters for WDM systems has not received much attentio n until very recently. It is the objective of this paper to consider t he phase response and resulting dispersion of optical filters in gener al and their impact on WDM system performance. To this end we use gene ral concepts from Linear systems, in particular, minimum and nomninimu m phase response and the applicability of Hilbert transforms (also kno wn as Kramers-Kronig relations). We analyze three different classes of optical filters, which are currently being used in WDM systems and co mpare their performance in terms of their phase response. Finally, we consider possible ways of linearizing the phase response without affec ting the amplitude response, in an attempt to approximate the ideal fi lter and achieve the highest bandwidth utilization.