Experimental Observation of Temporal Soliton Molecules

A bound state of temporal solitons in optical fibers is predicted numerically and demonstrated experimentally. It is appropriately described as a pair of bright solitons, bound together by a dark soliton. This structure exists only in dispersion-managed fiber and is different from bound solitons in fiber lasers.

Figure 1

The soliton molecule consists of two bright pulses with a point of zero power in between; the phase jumps by $\pi$ at the zero. Alternately, the central notch can be thought of as a dark soliton.

Figure 2

Numerical simulation of long-distance propagation of the soliton molecule. Here $S=7.2$ was assumed; the maximum distance shown corresponds to $77L_D$.

Figure 3

Numerical experiment on perturbation of initial separation of the bright constituents. Whether they are launched with too small (top) or too large (center, bottom) separation, they relax towards their equilibrium distance (dotted lines). Propagation distance was $201\mathrm{km}\widehat{=}31L_D$ at $S=5.4$.

Figure 4

Power dependence of bright pulse separation after a propagation distance of $29L_D$.

Figure 5

Experimental data for separation between the bright pulse peaks: output vs input. For large separations the measured points fall onto the bisector. At smaller separation and low power there is repulsion. At increased power the repulsion is counteracted. Lines are from numerical simulations based on the known pulse and fiber parameters.

Figure 6

Experimental results for the separation between the bright constituents as a function of launch power. The initial separation of 525 fs is identified by an arrow.