Extremely short laser pulses, containing just a single cycle of the electric field, have been generated at the wavelength used for telecommunications. The achievement, reported online this week in Nature Photonics, could be beneficial in the fields of frequency metrology and in ultrafast sciences, for example ultrafast optical imaging.

Obtaining short laser pulses is difficult because it requires extremely careful synchronization and manipulation of two sets of pulses that are then coherently combined. Any significant timing jitter ― a time variation in signal ― between the two pulse streams ruins the process.

Alfred Leitenstorfer and colleagues have solved this problem by deriving the two separate pulse trains from a single erbium-doped fibre laser source, which is an existing fibre technology. This approach using a single source dramatically reduces the timing jitter between the two pulse trains, allowing the generation of pulses that are just 4.3 femtoseconds long ― close to the shortest possible value for a data bit of information transmitted in the telecoms wavelength of 1.5 micrometres.