Abstract: Short electromagnetic pulses, preferably optical pulses each of a different wavelength and/or polarization, are injected into a channel containing a medium with many energy levels in which the level populations are specified and in which the transitions between levels are in resonant relationship (resonant or nearly so) with the carrier frequencies of the pulses. When the initial pulse intensities are above a level related to characteristics of the medium, particularly when the areas of the pulses have certain relationships with each other, coincident pulses co-propagate simultaneously, substantially losslessly, and in some cases at velocities well below normal light speed in the medium, but still well above electron drift speeds in conductors, for example. The pulses may be very short in duration.