Investigate the interaction of topology and non-Hermitian physics with nonlinear effects

An international team of researchers has investigated the interaction of topology and non-Hermitian physics with non-linear effects. In his article published in the magazine Science, the group describes the construction of an optical waveguide network using a polarized photorefractive crystal and experiments that introduce non-linear effects. Piotr Roztocki and Roberto Morandotti from INRS-Énergie, Matériaux et Télécommunications have published an article in Perspective in the same issue of the journal that describes the benefits of studying non-linear systems and the team’s work in this new endeavor.

As Roztocki and Morandotti point out, nonlinearity has been studied in great depth; its use in artificial networks and other digital electronic applications, for example, has vastly expanded the range of such applications. But they also point out that there are areas where research is lacking. They point out, for example, that systems that include topological and non-Hermitian elements have not been studied much at all. In this new endeavor, researchers have tried to address these gaps by examining the interplay of topology and non-Hermitian physics when nonlinear effects are introduced.

The team’s work involved the construction of an optical waveguide network (with a Su-Schrieffer-Heeger configuration) using a polarized photorefractive crystal. Such platforms have been used in a wide variety of studies because they allow such easy access to their functions, particularly waveguide reconfiguration.

The experiments consisted of modifying the non-linear response of the waveguide, which allowed focusing and defocusing and subsequently changing the way the light passed through the grating. In doing so, they were able to demonstrate both destruction and restoration of states in non-Hermitian topology, in particular, through nonlinear control.

The researchers also studied the sensitivity of their system in parts that they described as rare spots compared to those near protected states. They found that the stability of the inherited topological protective states was eroded from the protected modes depending on how close they were to the exception points.

Roztocki and Morandotti suggest that the work has opened the door to further investigation of nonlinear effects in overlapping disciplines, perhaps leading to the development of new types of devices.

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