Dielectric metasurface based polarization and orbital angular momentum demultiplexer

Abstract

The development of high-speed optical communication calls for compatible multiplexing dimensions to enlarge transmission capacity and process optical information. Although vortex beam multiplexing has been previously demonstrated by exploiting the orthogonality of orbital angular momentum (OAM) modes, the multidimensional demultiplexer remains elusive due to the limited phase and polarization manipulation capability. We introduce dielectric propagation phase metasurface based demultiplexers and investigate their application in simultaneously demultiplexing OAM and orthogonal linear polarization (OLP) channels. Utilizing the size-dependent anisotropy of dielectric rectangular nano-pillars, we reveal that the multimode fork grating phase masks with different off-axis phase items can be integrated on the same substrate with polarization selectivity, which allows simultaneously demultiplexing OAM and OLP channels. The demultiplexed position and the number of channels depend on its off-axis phase items, and a 16-channel (8-OAM modes and 2-polarization states) demultiplexer is demonstrated. The vortex beams with different OAM modes and OLP states are successfully demultiplexed with the maximum crosstalk is below −9.2 dB. Changing the number of superimposed complex amplitudes and the off-axis phase items in multimode fork grating phase masks, we further present two 12-channel demultiplexers with different channel distributions. Our results provide an approach that breaks the polarization-insensitive in manipulating OAM modes, introducing demultiplexers that apply to OAM mode and OLP states simultaneously.