Angular momentum of optical modes in a silicon channel waveguide

The spin and orbital angular momentum (OAM) of optical fields in a silicon channel waveguide are investigated. A vortex beam carrying OAM can be generated by a superposition of two quasi-TE modes. The longitudinal OAM of the superposed vortex beam is intrinsic and mediated by the superposition coefficient. Due to high transverse confinement of the silicon waveguide, the polarization and OAM are inevitably coupled. Their hybridization degree is well described by joint average transverse wave vectors. Further, the OAM part can be separated using the topological Pancharatnam charge and Stokes parameters. Combining polarization and OAM indices, we find that the whole space of structure parameters of the waveguide can be divided into three regimes. Our result offers insight into the relationship between angular momentum and mode confinement, which is beneficial for potential applications of vector beams in photonic integrated circuits.