Photonic snakes give rise to a novel type of 2D frequency combs

By July 14, 2023July 17th, 2023ICFO

An international team of researchers, including investigators from the BIST centre ICFO, provide an innovative framework for the understanding and control of the long known highly destructive snake instabilities. The results are published in Nature Photonics.

Microcylinder driven by an incident CW laser beam

A team of researchers provides an innovative framework for the understanding and control of the long known highly destructive snake instabilities. These instabilities form stationary nonlinear photonic snakes, which introduce a novel type of nonlinear wave and, most importantly, provide a generalisation of the concept of optical frequency combs.

Optical frequency combs are laser-controlled discrete spectra that act as rulers to perform absolute measurements of the colours of light very quickly and accurately, a resource that is very useful for understanding our modern world. Since optical frequency combs may consist of up to thousands of frequencies carried by ultra-short pulse trains, they are excellent measuring tools in frequency and time spaces, and hence their applications are manifold, which include ranging, metrology, timekeeping, quantum memories and computation, communications, and spectroscopy, among others.

The formation of reliable optical frequency combs at the micron scale became a solid reality during the last decade thanks to the use of 1D temporal dissipative solitons. Current applications mostly rely on single or double comb forming devices. However, scientists anticipate that with an in-depth understanding of the dissipative soliton physics in higher dimensions, robust two- and three-dimensional frequency combs could be achieved, converting frequency combs in a fundamental measuring tool with a much greater potential.

A cornerstone for succeeding in this direction is the control of the ever-increasing number of the system’s instabilities that appear in non-linear optical phenomena when increasing the system’s dimensions. Such instabilities, when controlled, provide amazing and novel tools for observing and understanding new effects and ways to manipulate light-forms. This is the case for snake instabilities, discovered nearly 50 years ago, which have shown to be responsible for the reshaping of straight states (of light or otherwise) into zigzag paths (like a snake), mainly caused by spontaneous and local transverse drifts.

The ability to understand this temporary instability in the system and learn how to control it to form optical frequency combs to harness the process that could lead to the formation of stationary, permanent, 2D zigzag states, would signify a major change in the field of non-linear sciences in general and optics in particular. This has recently been accomplished in a study published in Nature Photonics. Al team of researchers, including ICFO Director and member of the BIST Community Lluís Torner and former ICFO postdoctoral researcher Carles Milián, now a Professor at the Institut Universitari de Matemàtica Pura i Aplicada, Universitat Politècnica de València, Salim B. Ivars (former Master student at ICFO), and Yaroslav V. Kartashov, have obtained two important theoretical results in the field of nonlinear optics.

Firstly, they have discovered how to control the snake instabilities in cylindrical micro-resonators. That is, by using theoretical approaches and numerical simulation tools, they engineered the micro-cavity in which they let the snake instability occur and then by “freezing” its effects, they were able to achieve a perfectly stationary spatio-temporal zig-zagged optical wave, robust and permanent in time, which they coined “Photonic Snake”. Secondly, they theoretically showed that these photonic snakes correspond to an unprecedented two-dimensional arrangement of heterogeneous photonic rulers or 2D frequency combs, which are all inherently synchronized and individually accessible, leading to a novel and most sophisticated optical ruler.

These findings represent a novel paradigm for frequency comb formation and pave the way for a new research approach on frequency combs as well as on the in-depth understanding and control of dynamical instabilities in dissipative systems. The discoveries point the way towards a novel class of Broadband and reconfigurable Monolithic Multi-Comb devices, which offer the possibility to deliver different combs on demand and in real time, and have the potential to give rise to novel applications as well as broaden the scope of current existing ones.

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ICFO press release