Broadband silicon photonic circuits for efficient chiral photons distinguishing and splitting

Abstract

The chirality of photons is very crucial for various photonic applications since it plays a dominating role in chiral light–matter interactions. On the silicon photonic platform, the strongly confined chiral light modes in nanophotonic waveguide exhibit extraordinary spin to orbital angular momentum conversion based on spin–orbit interactions, which offer much potential for on-chip spin-dependent applications. However, the chiral-dependent light–matter interactions have faced the challenges of low chirality-directional coupling efficiency and narrow operating bandwidth. Here, in order to break through these limitations and take advantage of the potential of chiral light in the silicon nanophotonic platform, we propose a purely dielectric chirality-distinguishing beam-splitter to distinguish and split opposite handedness of photons into different channels. This design is validated by the finite-different time-domain method and the chirality-directional coupling efficiency is over 96% at the operating wavelength of 1.55 μm. The circuits, composed of a polarization converter and a polarization beam-splitter, with a compact footprint of 12 μm × 2.4 μm, enable routing chiral photons efficiently in a broad bandwidth (from 1.40 μm to 1.70 μm). The underlying physics is the polarization conversion and polarization selection. Owing to the reciprocity, the device can emit photons with selectable spin angular momentum via feeding the corresponding port. The design, compatible with silicon-on-insulator technology, will positively enrich nanophotonic applications where the chirality of photons is urgently required for manipulating chiral light–matter interactions on the silicon photonic platform.