Solitons on WDM Beams in a Nonlinear Optical Fiber

This paper sets the ultimate limit on the maximum amount of optical data pulses that can be sent through a single fiber in a given period under the wavelength-division-multiplexed (WDM) format. The discovery in 1973 that optical soliton on a single wavelength beam can exist in fiber is one of the most significant events since the perfection of low-loss optical fiber communication. This means that, in principle, data pulses may be transmitted in a fiber without degradation forever. This soliton discovery sets the ultimate goal for optical fiber communication on a single-wavelength beam. Another most significant event is the development of WDM transmission in a single-mode fiber. This means that multiple beams of different wavelengths, each carrying its own data load, can propagate simultaneously in a single-mode fiber. This WDM technique provides dramatic increase in the bandwidth of a fiber. However, due to the presence of complex nonlinear co-propagating pulses on different wavelength beams, it is no longer certain that WDM soliton can exist. The existence of solitons is a blissful event in nature. It is a marvel that the delicate balance between the dispersion effect and the nonlinear effect can allow a specially shaped optical pulse to propagate in the fiber without degradation. They occur only on single-wavelength beams. When beams with different wavelengths co-propagate in a single-mode fiber, such as in the WDM case, interaction of pulses on different beams via the nonlinear cross-phase-modulation (CPM) effect (the Kerr effect) is usually instrumental in destroying the integrity of solitons on these wavelength multiplexed beams. This paper shows that temporal solitons can exist on WDM beams in a single fiber under appropriate conditions. The existence of these solitons critically depends on the presence of the nonlinear CPM effect of the WDM beams. Just as the earlier single-beam soliton case, this discovery sets the ultimate goal for optical fiber communication on WDM beams.