26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Low-order Fractional Dispersion in a Passively Mode-Locked Fibre Laser

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral ANZOS | Photonics and Optics (ANZCOP)

Description

Fractional derivatives, particularly fractional Laplacian operators, have attracted growing interest across physics, mathematics, and engineering [1]. In nonlinear optics, they provide a route to generalize the conventional nonlinear Schrödinger equation by replacing the conventional quadratic dispersion with a fractional, nonlocal dispersion law, described by the operator {(-\nabla^2)}^{\alpha/2}. Although fractional optical systems have enabled new forms of soliton dynamics, experimental demonstrations have so far been limited to a few dispersion orders [2,3].
Here, we report the observation of optical soliton-like pulses formed through the interplay between Kerr nonlinearity and a low-order fractional-dispersion regime with α=0.7. In contrast to the α=1 case, for which the spectrum exhibits a kink [3] for α=0.7 both the dispersion relation and the soliton exhibit a cusp. We generate these solitons using an intracavity programmable pulse shaper, which enables the required fractional spectral phase response to be imposed while compensating the quadratic and third-order dispersion in the laser cavity [4]. The cusp feature is observed in the measured optical spectrum and is in good agreement with numerical solutions of the generalized nonlinear Schrödinger equation.
The retrieved pulses decay algebraically in time unlike the exponential decay of conventional solitons, indicating the strongly nonlocal nature of the low-order fractional-dispersion regime with α=0.7. The measured time-bandwidth product is as small as 0.017, in reasonable agreement with the theoretical value of 0.007. These findings provide compelling evidence that the observed pulses belong to a distinct class of low-order fractional soliton-like states.

1. B. A. Malomed, Chaos: An Interdisciplinary Journal of Nonlinear Science 34, 022102429 (2024).
2. S. Liu, et al, Laser Photonics Rev. 19, 2401714 (2025).
3. T. Hoang, et al, Nature Communications 16, 5469 (2025).
4. A. F. Runge, et al, Nature Photonics 14, 492–497391 (2020)