WDM protocol-transparent distance extension using R2 remodulation

In computer networks using wavelength-division multiplexing (WDM), it is often necessary to extend the length of a given WDM path beyond that of a single segment whose length is limited by the link budget. While wavelength-flattened optical amplifiers are the most obvious solution, this paper calls attention to a simple (albeit less efficient) alternative that works for any number of wavelength channels, but only a modest number of segments and modest bit rates. This scheme substitutes for each optical amplifier stage a multiwavelength 2R remodulator consisting of a WDM demultiplexor, followed by wavelength-by-wavelength zero-crossing detectors, then remodulation wavelength by wavelength, and finally wavelength-division multiplexing back onto a single fiber. Theory and experimental results confirm the usefulness of this primitive technique, which can also be used for add-and-drop links, for wavelength routing or wavelength conversion in scalable wavelength routing networks, for internetwork gateways, and for other applications.