Experimental observation of Raman-shifting soliton pairs

Here we demonstrate a first experimental realization of a dedicated preparation of such pairs. We consider interaction forces of the solitons producing movement of the pulses. If the peak powers of both pulses are unequal, both are differently affected by both Raman self-frequency shift and nonlinear phase evolution. We obtain parameter triplets of Raman response time T_R, peak power ratio r, and initial separation (7 that fulfil an ´equal acceleration constraint´ and give a rotating phase pair. Beyond this, a further constraint can be imposed which is related to the relative phase φ of the pair; hence, the ´constant phase constraint´.