Caustics and Rogue Waves in an Optical Sea

TL;DR

This paper experimentally demonstrates the formation of linear rogue waves in an optical system, highlighting how linear effects like caustics can produce extreme wave amplitudes similar to those seen in nonlinear contexts.

Contribution

It provides a detailed experimental analysis of linear rogue waves in optics, revealing the role of caustic structures and broad spectra in generating extreme events.

Findings

Rogue wave-like peaks are observed in caustic networks.

Intermediate patterns show near-Gaussian amplitude statistics with rogue wave tails.

Intensity peaks meet statistical criteria for rogue waves in the optical system.

Abstract

There are many examples in physics of systems showing rogue wave behaviour, the generation of high amplitude events at low probability. Although initially studied in oceanography, rogue waves have now been seen in many other domains, with particular recent interest in optics. Although most studies in optics have focussed on how nonlinearity can drive rogue wave emergence, purely linear effects have also been shown to induce extreme wave amplitudes. In this paper, we report a detailed experimental study of linear rogue waves in an optical system, using a spatial light modulator to impose random phase structure on a coherent optical field. After free space propagation, different random intensity patterns are generated, including partially-developed speckle, a broadband caustic network, and an intermediate pattern with characteristics of both speckle and caustic structures. Intensity peaks satisfying statistical criteria for rogue waves are seen especially in the case of the caustic network, and are associated with broader spatial spectra. In addition, the electric field statistics of the intermediate pattern shows properties of an optical sea with near-Gaussian statistics in elevation amplitude, and trough-to-crest statistics that are near-Rayleigh distributed but with an extended tail where a number of rogue wave events are observed.