On-Chip Photonic Spin Hall Lens

Focusing and Fourier transformation are two key functionalities of optical lenses, which are vital for optical information refining and processing. These unique features persist and are even carried forward on a planar configuration that works on a surface wave, enabling on-chip and ultrafast photonic information processing. Here, we design and demonstrate a type of photonic spin Hall lens (pSHL) that works on surface plasmon polaritons. It could perform spatially separated focusing and photonic Fourier transformation controlled by the handedness of the incident circularly polarized light (CPL). Their splitting distance can easily be adjusted by altering the scaling factor of the phase gradient encoded onto the lens, a manifestation of an optical spin Hall effect. The pSHL is designed to retrieve the phase delay required to compensate for the spatial shift of the lens; this is realized using a plasmonic metasurface that yields the spin-dependent Pancharatnam-Berry phases. Applications with the pSHL for photonic spin routing and OAM-mode demultiplexing are demonstrated. The proposed pSHL is ultrathin, compact, and easy to fabricate. It holds a great promise for the development of ultracompact photonic spin devices.