Baseband Linearity and Equalization in Fiber Optic Digital Communication Systems

If a sequence of digitally on-off modulated optical pulses is injected into a dielectric waveguide, these pulses may begin to overlap after a sufficient distance of propagation because of material dispersion and/or group delay spreading. In general, the pulses will not add linearly in power, which can complicate the problem of equalization of the square-law (power) detected overlapping output pulses at baseband. This paper illustrates important situations in which the guide may be treated as “pseudo-linear” in power, meaning that the detected guide output pulses appear to add linearly.