  Manipulating the polarisation of light is crucial for sensing and imaging
applications. One such aspect in particular is selective transmission of one
circular polarisation (spin) when light is transmitted through a medium or a
device. However, most present methods of achieving this have relatively low
efficiency and selectivity, whilst high selectivity examples rely on lossy and
complex three-dimensional helical or multilayer structures. Here, we propose a
dielectric metamaterial approach for achieving spin-selective transmission of
electromagnetic waves, utilizing spin-controlled constructive or destructive
interference between two Pancharatnam-Berry (PB) phases in conjunction with
propagative dynamic phase. The dielectric metamaterial, consisting of
monolithic silicon herringbone structures, exhibits a broadband operation in
the terahertz regime whilst obtaining a spin-selective efficiency upwards of
60%. Such a device is robust and is not easily degraded by errors in
fabrication.
