Abstract: A dispersion-balanced optical cable 90 reduces four-photon mixing in Wave Division Multiplexing (WDM) systems and is effective to reduce cumulative dispersion D substantially to zero. The dispersion-balanced optical cable 90 includes one or more optical fibers 90-1 having positive dispersion D.sub.1, and one or more optical fibers 90-2 having negative dispersion D.sub.2. The fibers are singlemode and are suitable for the transmission of optical signals in the 1550 nm region. At this wavelength, the positive-dispersion fibers have a chromatic dispersion of about +2.3 ps/nm.km, and the negative-dispersion fibers have a chromatic dispersion of about -1.6 ps/nm.km. The dispersion-balance optical cable preferably includes an equal number of positive- and negative-dispersion fibers in the same cable.

Abstract: In an optical fiber communication system that operates at a wavelength .lambda..sub.o and comprises optical fiber having a cut-off wavelength .lambda..sub.c >.lambda..sub.o, a "grating", with parameters chosen such that the grating causes resonant coupling between a predetermined guided mode (e.g., LP.sub.11) and a tunneling-leaky mode, can be advantageously used to remove unwanted guided modes. Such removal can substantially improve the bandwidth of such a system.