Upon reflection near singularities, modulate phase
- Published on 16 September 2021
The team FLATLIGHT, led by Dr. Patrice Genevet at CRHEA CNRS, proposed a new light modulation scheme to design metasurfaces with unexpected optical properties. The approach consists in controlling the phase of the light reflected by an optical system operating near its topological singularities. They have identified, in the parameter space defining the nanostructure geometry, a point of singularity for which the reflection coefficient vanishes. This point, known as the exceptional point, corresponds to the parameters for which both eigenvalues and eigenstates degenerate. This behavior is further confirmed by the secant double Riemann surface representing the eigenvalues of the reflection matrix. Choosing designs in the parameter space located in the vicinity to encircle the exceptional point, various phases ranging from 0 to 2\pi are accessible. They selected nanostructures having reflection phases which vary in steps of 90 ° to realize new optical components capable of deflecting a beam in arbitrary angles or even to make projections of holograms. They also combined the design the topological phase with the Pancharatnam Berry phase to project different holograms on each of the two circular polarization states. Many other intriguing scattering behaviors leading to a singular response are currently reported in photonics. Indeed, any singularity of the diffusion matrix leads to a topological phase addressing including the zero of the diffusion matrix, behavior without reflection, perfect absorption on certain transmission or reflection channels, coherent perfect absorption, bound state in the DC, anapole, non-reciprocity, superdiffusion, etc ... that is to say that all these exceptional optical scattering effects, presenting topological defects, can be utilized for the realization of a whole new class of scalar and vector metasurfaces with unusual optical properties.
More information :
Q. Song, M. Odeh, J. Zúñiga-Pérez, B. Kanté, P. Genevet, “Plasmonic topological metasurface by encircling an exceptional point,” Science 373, 1133-1137 (2021).