Abstract

We have examined, through numerical simulations, experiment, and analytic theory, the behavior of the polarization state of a stream of solitons in a long distance, all optical transmission system consisting of spans of dispersion shifted fiber having a small (−0.2ps/km^½) randomly varying birefringence and periodically spaced Erbium doped fiber amplifiers. From the theory and simulations we find that a stream of solitons, all launched into such a system in the same polarization state, will emerge with all the soli-tons approximately in a common, well defined, polarization state. The pulse-to-pulse deviations from this average polarization state are small, as they are determined only by the component of the amplifier ASE noise in the polarization mode orthogonal to the soliton itself. An extinction ratio of 23 dB is predicted at 10,000 km, and we have confirmed this experimentally by using a 2.5 GHz stream of 50 ps solitons in a 75 km recirculating loop (Figure 1). Numerical simulations show that solitons launched in orthogonal polarization states maintain their orthogonality as they traverse the system. This is confirmed by the analytic theory. Based on this fact, we propose a polarizatiodtime multiplexing scheme whereby two orthogonally polarized soliton bit streams are interleaved in time (Figure 2). Further simulations indicate that this technique should be able to double the bit rate of any single frequency soliton channel, with no significant increase in bit emror rate.

© 1992 Optical Society of America