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Pulse shaping in mode-locked fibre lasers

EU-funded scientists have for the first time demonstrated three distinct pulse modes, all obtained from a single laser system without applying any changes to the laser’s resonant cavity.
Pulse shaping in mode-locked fibre lasers
Techniques for generating specialised laser waveforms have contributed to significant advancements in scientific areas such as ultrahigh-speed optical communications and optical signal processing. However, commonly employed methods require manual tuning of physical parameters of the laser cavity.

In the EU-funded project ULTRAFIL (Ultra-short pulse fibre laser technology), researchers introduced a new method to achieve control over the output of the laser system through software. By programming dispersion and bandwidth of an in-cavity filter, soliton, dispersion-managed soliton and dissipative soliton, mode-locking modes could switch each other.

Mode-locking is a technique by which a fibre laser is made to produce pulses of light of extremely short duration – on the order of picoseconds and even femtoseconds. To this end, a fixed-phase relationship is established between the longitudinal modes of the laser's resonant cavity.

In the mode-locked laser, researchers used the effects of gain/loss, dispersion (the dependence of wave velocity on frequency) and nonlinearity to shape the pulses produced. In addition, the light dynamics were carefully manipulated to obtain different regimes of mode locking.

The generation and in-cavity evolution of the different laser pulse regimes were confirmed by numerical analysis. Specifically, the ULTRAFIL team carried out a series of numerical simulations reproducing the different nonlinear pulse evolutions inside the laser’s resonant cavity.

The new technique for spectral pulse shaping in mode-locked fibre lasers holds great potential. It promises a high degree of control over the output of ultrafast fibre lasers, in contrast to traditional methods used to regulate the pulse formation mechanism in dispersion-managed fibre lasers.

ULTRAFIL has opened the way for applications of ultrafast fibre lasers in optical signal processing and high-speed optical communications. Versatile ultrafast laser sources that can selectively emit different types of nonlinear waves have possible applications in further scientific areas.

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Pulse shaping, fibre lasers, resonant cavity, ULTRAFIL, dissipative soliton
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