Pure-quartic solitons from a dispersion managed fibre laser

In optical fibre resonators, the balance between anomalous quadratic dispersion and self-phase modulation (SPM) gives rise to optical solitons [1]. These pulses have made a significant impact in a wide range of photonic applications including telecommunications and lasers. However, these conventional soliton-based lasers can only deliver modest pulse energy due to the appearance of Kelly sidebands arising from periodical perturbations in the cavity [2] and a fixed energy-width scaling. Recently, a new class of soliton, arising from the balance of anomalous quartic dispersion and SPM, called pure-quartic soliton (PQS), were observed in a dispersion engineered photonic crystal waveguide [3]. PQSs have huge potential for generating ultrashort pulses with high energy due to their generalized area theorem (E ∼ 1/Δτ³), however they are yet to be observed in fibre platforms [4]. Here we report on the generation of PQS pulses from a passively mode-locked fibre laser incorporating a programmable spectral pulse-shaper that induces a dominant quartic net cavity dispersion. We find that the spectral profile of the generated pulses are in good agreement with the spectral shape of PQSs [3]. We also observe spectral sidebands in this quartic-dispersion cavity, in analogy to the conventional soliton case [2], and find that their positions are in excellent agreement with analytic predictions. These are strong evidences of a novel type of mode-locked laser, the PQS laser, which has the potential to reach dramatically higher energies at short pulse durations than its conventional soliton counterpart [3,4].