Fig. 1: Universal vectorial mode conversion using a multi-layer MS.
From: Complete vectorial optical mode converter using multi-layer metasurface
a Schematic of the vectorial mode converter using an L-layer metasurface (MS). The input vectorial mode set \(\{\left\vert {a}_{m}^{{{\rm{in}}}}\right\rangle \,| \,m=1,2,\ldots,M\}\) is transformed into another mode set \(\{\left\vert {a}_{m}^{{{\rm{out}}}}\right\rangle \,| \,m=1,2,...,M\}\) by repeated free-space propagation \({\hat{F}}^{(l)}\) and lightwave conversion by MSs \({\hat{J}}^{(l)}\). The Jones matrices of MSs are optimized using the forward and adjoint (backward) fields. The bottom inset shows a schematic of the birefringent meta-atom with an orientation angle of γ. Arbitrary phase shifts α and β can be obtained by properly designing meta-atom dimensions, Dα and Dβ. b Schematic of a single-chip mode converter with a folded MS configuration using reflective MSs.
