High-efficiency polarization switching in phase-change-material films at normal incidence

Phase-change materials (PCMs) enable the modification of the polarization of reflected light over nanometer-scale distances. For an isotropic and homogeneous film deposited on planar substrates, this is only possible at oblique angles of incidence, and the greatest modulation occurs near the pseudo-Brewster angle, but at low reflectance. This tradeoff between polarization modulation and output intensity is a limiting factor for applications. In this paper, we explain why stronger polarization switching also tends to occur at low reflectance. We also show that for properly designed structures, switching between maximally separated, i.e. orthogonal, polarization states can occur with low losses. Finally, we compare the polarization switching capabilities of two different PCM materials on corrugated substrates at normal incidence and show that this simple design can achieve orthogonal polarization switching at high reflectance. For example, in the case of GST on a gold-coated grating at a wavelength λ of 1457 nm, near orthogonal switching is possible with a reflectance of around 50 %.