Dynamics of angular momentum-torque conversion in silicon waveguides

We present a refined theoretical analysis on the relationship between the optical total angular momenta (TAM) and the optical torque (OT) in a birefringent silicon waveguide. By using the vector angular spectrum method, we demonstrate the dynamic evolutions of the OT, TAM, spin angular momentum (SAM), and orbital angular momentum (OAM). The SAM and OAM coexist and evolve simultaneously in the propagation. The ratio between the OAM and TAM is related to the incident wavelength and the size of waveguide. Moreover, we design a three-layer waveguide structure to convert the light chirality and generate high torque. The performance of such torque-generator is analyzed numerically in detail.