Experimental observation of soliton interaction over long fiber paths: discovery of a long-range interaction.

We have studied the interaction of ~55-psec-duration soliton pulse pairs over thousands of kilometers of optical fiber with loss periodically compensated by Raman gain. We indeed observe the expected short-range, phase-dependent interaction. But we also observe a long-range, phase-independent interaction caused by dispersive-wave radiation from the solitons.