Cascaded Janus Meta-Optics: Generalized Platform for Bidirectional Asymmetric Modulation of Light

Abstract

Janus metasurfaces, which manipulate light in different manners depending on illumination direction, hold potential to extend multifunctionality of meta-optics and decrease the size of integrated optical systems, simultaneously. Here, this work proposes a generalized framework for achieving bidirectional asymmetries through a cascaded meta-optics platform comprising multiple dielectric metasurfaces. Using this systematic approach, polarization-independent (scalar) asymmetric meta-holograms, polarization-dependent (vectorial) asymmetric meta-holograms, and fully generalized vectorial asymmetric modulation of forward and backward Jones matrices are proposed for the first time. In addition to unveiling advantages of separation between the two metasurfaces, it turns out that judicious use of a stochastic gradient descent algorithm enables effective optimization of the arbitrary bidirectional asymmetric meta-holograms. Our proposed method holds significance in overcoming the reciprocity-induced relationship between forward and backward Jones matrices, thereby further expanding the degrees of freedom for polarization-direction multiplexing. It is expected that the proposed work will open up new avenues in various mobile or wearable applications requiring multifunctional integrated optical systems.