Bistable holes in nonlinear optical fibers

Bistable dark solitary-wave solutions (bistable holes) to the generalized nonlinear Schrödinger equation are shown to exist in the normal dispersion regime for nonlinearities that are Kerr-like at low intensities, rise sufficiently rapidly at intermediate intensities, and become Kerr-like again or approach a constant value at large intensities. The bistable nature and soliton character of the holes are confirmed through numerical switching simulations. The concept of asymptotic pinning (of the x-dependent part) of the phase is used to explain the resultant velocities of the output solitons and the observed asymmetry in the emitted radiation.