Nature Commun. 6, 7370 (2015)

Manipulating the temporal position of light pulses can be attractive for optical information processing, allowing pulses to be temporarily stored and reconfigured on the fly without the need for optoelectronic conversion. Jae Jang and colleagues from the University of Auckland in New Zealand experimentally demonstrate how the temporal separation of picosecond pulses of light can be arbitrarily controlled all-optically. In their work, cavity solitons exist as picosecond pulses of light recirculating in a loop of optical fibre. The dispersive temporal spreading of the pulses is controlled by the material nonlinearity and thus related to the power of a continuous-wave 'holding' beam. A gradient in the cavity holding beam will cause an overlapping cavity soliton to move towards, and be trapped at, a point where the gradient vanishes. The team expose the cavity solitons to temporal control gradients in the form of a gigahertz phase modulation imposed on the cavity holding beam. By dynamically changing the phase pattern — translating to a blue shift or red shift and therefore a change in group velocity — they are able to control the movement of the cavity solitons in time. Temporal shifts much larger than the cavity soliton duration are demonstrated both in continuous and discrete manipulations. The approach enables the realization of a fully reconfigurable all-optical buffer and engineered pulse sequences with arbitrary pulse-to-pulse separations.