Figure 1
From: Spiniform phase-encoded metagratings entangling arbitrary rational-order orbital angular momentum
Mechanism of the analog vortex transmitter. (a) Light obtains a helical wavefront with spatially separated phase singularities (black dots) by passing through four transversely located SPPs. (b) Sketch of the transmitter composed of two inclined (inclination angle of γ) gratings with a period of Λ at both sides and a circular aperture of varying diameter (dq), which geometrically acts as an excircle (red dashed circles) tangent to the x-axis at a reference point O. (c) Phase profile encoded into the vortex transmitter. τ denotes the spatial distance between two neighboring phase singularities. ϕ is the angle coordinate of the circular aperture and increases anticlockwise from ϕ=0 (negative y-axis) to 2π. (d) Phase along the circumference (dashed circle in (d)) of the circular aperture for its corresponding q. The phase at ϕ>π is unwrapped by adding 2π. The curves denote the phase values for q (distinguished by the curve colors). (e) The average OAM (Qћ) of a photon as a function of q. The fitting curve (solid red line) of the simulated results (black square boxes) exhibits a root mean square error of 0.04, while the experimental results are denoted by greenish asterisks. Inset: Zoom-in of the data between q=1 and q=1.5.
