Fig. 1. (a) Linearly polarized light carries no SAM (left) and circularly polarized light carries an SAM of ±ℏ per photon (right). (b) Wavefront, intensity, and corresponding phase distribution of vortex beams with topological charge of l = 0, 1, 2.
Fig. 2. Schematic diagrams of (a) converter, (b) SPP, (c) fork grating hologram, and (d) spiral zone plate with topological charges of l = 1.
Fig. 3. Generation of optical vortex beam with digital devices: (a) SLM, (b) DMD. Schematic diagram of experimental apparatus of (a1) SLM and (b1) DMD. (a2) Phase holograms and corresponding far-field diffraction patterns. (a3) Generated vortex beams and OAM spectra
[26]. (b2) Simulated and experimental results of vortex beams with
l = 20 by the Lee method and superpixel method, respectively. (b3) Fidelity and efficiency of the two methods
[33].
Fig. 4. (a1) Schematic view of the spiral photon sieve. Vortex beams generated by (a2) spiral zone plate and (a3) spiral photon sieve
[37]. (b) Target intensity and phase (top left and right) and experimentally measured intensity and plane wave interference pattern (bottom left and right) of (b1) the LG beam with
l = 5,
p = 4 and (b2) superposition of two LG beams with
l = ±5,
p = 0
[38]. (c) Electron vortex beam generated by rotationally symmetric mask based on Archimedean spirals
[39]. (d) Schematics of simulated mask, intensity profile, and OAM spectrum (left to right) for the generation of photonic gear with
l = ±5
[40].
Fig. 5. Generation of optical vortices through metasurfaces based on (a) dynamic phase
[45], (b) geometry phase
[53], (c) the combination of dynamic and geometry phase
[54], and (d) optical vortex generator with multiple focal planes
[55].
Fig. 6. (a) Left to right: phase distribution of a vortex beam with
l = 1, the spiral phase passing through the double slits, and interference intensity distribution
[79]. Schematic and results of (b) angular double-slits interference method
[83]; (c) improved multipoint interferometer
[87]; (d) Mach–Zehnder interferometer with a rotating Dove prism and cascading interferometers
[89].
Fig. 7. (a) Diffraction patterns of triangular aperture
[92]. (b) The intensity distribution of the vortex beam is measured by a cylindrical lens
[99]. (c) Schematic and results of the gradually changing period grating
[97].
Fig. 8. (a) Phase profiles of the transforming and the phase-correcting optical element (top). Schematic of the optical system (bottom)
[101]. (b) Schematic diagram and results of log-polar transformation and spiral transformation for OAM modes sorting
[103]. (c) Schematic and results of the detection of SAM and OAM by photonic momentum transformation
[104].
Fig. 9. (a) Numerical model of the OAM-based communication system. CCD camera, charge-coupled device camera
[112]. (b) CNN-based OAM transmission system scheme. OAM transmission system block diagram, six-layer CNN architecture
[113]. (c) Quantitative analysis of CNN and the recognized OAM modes with fractional topological charge. Confusion matrix from
l = 1.25 to
l = 1.34. First row: phase pictures uploaded on the SLM. Second row: intensity distributions of vortex modes recorded by the CMOS camera
[115].
Fig. 10. Methods for detecting OAM modes based on surface plasmon polariton. (a) A semi-ring plasmonic nanoslit
[119]. (b) A nanograting with straight stripes
[121]. (c) A plasmonic spin-Hall nanograting
[122].