Ultra-Tight Light Pulses: Mode-Locked Spatial Solitons
Thorsten Ackemann, Gian-Luca Oppo
Light pulses have the natural tendency to broaden and do not remain confined to small regions of space or time. In space this is due to diffraction and in time this is due to dispersion. It has been a long-term dream of researchers in photonics to create light pulses that remain self-confined in all three dimensions – or transverse space and time - through the nonlinear self-action of light propagating in a medium. This dream is now a reality as recently demonstrated by a powerful collaboration between Strathclyde, Nice, Glasgow, and Sydney in a Physical Review Letters paper (Phys. Rev. Lett. 118, 044102, 2017) which was selected as Editors’ suggestion.
The Strathclyde team led both the experimental realization (Prof. Thorsten Ackemann) and the theoretical confirmation (Prof. Gian-Luca Oppo and Prof. William Firth) of ultra-tight light pulses in the form of mode-locked spatial solitons. By using a vertical-cavity surface-emitting semiconductor laser in front of a volume Bragg reflector (see top of the Figure), Prof. Ackemann and collaborators created sequences of spatially confined light pulses (see the panels at the bottom of the Figure) that propagate back and forth from the laser to the reflector without changing their duration and shape in any of the three dimensions. The existence of mode-locked spatial solitons was then confirmed through a series of accurate numerical simulations. Ultra-tight mode-locked laser pulses pave the way for the observation of three-dimensional solitons in bulk materials (also known as light bullets) and find potential application in ultrafast optical digital logic, enhancement of light-matter interactions and powerful optical information-processing systems.