Fig. 2. Representative OAM emission and self-interference.

a OAM emission profile for ∣l∣ = 4. Experimentally measured mid-field and far-field infrared images of the m = 165 mode on a device with N = 169. These five images correspond to different heights of focal planes of the imaging system at approximately {70, 30, 0, −30, −70} μm with respect to the microring. The square boxes correspond to 80 μm × 100 μm on the x–y plane. The x–y–z arrows also serve as scale bars, whose lengths correspond to {20, 50, 20} μm, respectively. b Experimental and simulation schematics showing that in-plane reflection can lead to the observed 2∣l∣ beating patterns. c The simulated visibility $\left(\mid E{\mid }_{\max }^2-\mid E{\mid }_{\min }^2\right)/\left(\mid E{\mid }_{\max }^2+\mid E{\mid }_{\min }^2\right)$ (blue) agrees with a simple equation modeling the reflection by two CW and CCW dipoles (∣E_CWcos(lϕ) + E_CCWcos(−lϕ)∣²) (red).