Directional Bloch surface wave coupling enabled by magnetic spin-momentum locking of light

We study the magnetic spin-locking of optical surface waves. Through an angular spectrum approach and numerical simulations, we predict that a spinning magnetic dipole develops a directional coupling of light to transverse electric (TE) polarized Bloch surface waves (BSWs). A high-index nanoparticle as a magnetic dipole and nano-coupler is placed on top of a one-dimensional photonic crystal to couple light into BSWs. Upon circularly polarized illumination, it mimics the spinning magnetic dipole. We find that the helicity of the light impinging on the nano-coupler controls the directionality of emerging BSWs. Furthermore, identical silicon strip waveguides are configured on the two sides of the nano-coupler to confine and guide the BSWs. We achieve a directional nano-routing of BSWs with circularly polarized illumination. Such a directional coupling phenomenon is proved to be solely mediated by the optical magnetic field. This offers opportunities for directional switching and polarization sorting by controlling optical flows in ultra-compact architectures and enables the investigation of the magnetic polarization properties of light.

Automated summary

We study the directional coupling of light to transverse electric (TE) polarized Bloch surface waves (BSWs) through spinning magnetic dipoles. A high-index nanoparticle as a magnetic dipole and nano-coupler is used to couple light into BSWs, with the helicity of the light controlling the directionality of emerging BSWs. Identical silicon strip waveguides on either side of the nano-coupler are utilized to confine and guide the BSWs, allowing for directional nano-routing with circularly polarized illumination.