Simultaneous light spin and orbital angular momentum detection using orthogonal nanoslit pairs in semi-ring array

Light angular momentum is used to characterize the dynamical rotation of electromagnetic wave, as spin angular momentum describes its polarization rotation while orbital angular momentum describes its phase rotation. Though various methods have been proposed to detect light spin or orbital angular momentum independently, it is still a challenge to determine both of them simultaneously. Here, based on orthogonal nanoslit pairs located in semi-ring array, we design an on-chip simultaneous light spin and orbital angular momentum detector, which can generate focus at different positions sensitive to light angular momenta, thus both spin and orbital angular momenta of the indecent light can be determined. It is verified that spin angular momenta of +/- 1 and orbital angular momenta in wide detection range can be simultaneously determined in high accuracy; moreover, mixed light with multiple spin and orbital angular momenta can also be distinguished. Therefore, the proposed detector provides a way to determine light angular momenta in nanoscale, and can be future applied in the fields of on-chip photonics and plasmonics.