Solitary waves consisting of bright and dark pulses in optical fibers

Abstract

It has been discovered that a bright pulse in the anomalous-dispersion (AD) range and a dark pulse in the normal-dispersion (ND) range can support each other through cross-phase modulation to form a solitary wave when they copropagate at the same speed in an optical fiber. Such a solitary wave can be generated by launchinga bright soliton in the AD range and a long pulse of the same speed in the ND range into the fiber. The bright soliton is slightly modified, and a stationary dark pulse is generated on the long pulse. This dark pulse has a shape and phase profile quite different from that of any dark soliton. When a fundamental bright soliton is used for generating such a solitary wave, the soliton must be sharp (the normalized peak amplitude must be larger than 2.5). When a higher-order bright soliton is used, this bright soliton evolves into a pulse close to a soliton of a lower order. The results of this evolution depend on the energy of the input higher-order solitons. For example, a 3- soliton may evolve into a pulse close to a 2-soliton or a fundamental soliton.