Fig. 1. Schematic illustration of various types of structured lights and their beam profiles.

Fig. 2. Various basic theories and principles of integrated structured light manipulation.

Fig. 3. Four aspects of integrated structured light manipulation: generation, processing, detection, and application.

Fig. 4. Classification of basic theories and various types of integrated structured light generation.

Fig. 5. Typical examples of in-plane to in-plane OAM generation^{[467,469,470,578]}. (a) Conceptual view of the hybrid photonic integrated device composed of a silica PLC and 3D waveguide structure. (b) Silica PLC image^[467]. (c) An asymmetric direction coupler including a standard single-mode waveguide and a doughnut-shaped OAM waveguide is employed to generate different-order OAM beams based on phase matching. The coupling length and coupling spacing are 4 mm and 15 µm, respectively. (d) The cross-section of the doughnut-shaped OAM waveguide structure consisting of 12 slightly overlapping waveguides^[578]. (e) The OAM beam generator based on a trench silicon waveguide^[469]. (f) The OAM beam generator based on a femtosecond laser direct writing trench silica waveguide^[470].

Fig. 6. Typical examples of out-of-plane to in-plane OAM generation^{[471,481,579]}. (a) Conceptual view and (b) top view of the silicon-nanoantenna-patterned silicon-nitride photonic waveguide. (c) Electric field |Ey| and phase distributions for ideal TE01, TE10, and mixed OAM+1 mode. (d) Calculated output electric field |Ey| distributions when only the TE01 mode antenna or TE10 mode antenna (left two panels) exists and both TE01 and TE10 mode antenna waveguides (right two panels) exist. Right most panel is the phase distribution at waveguide right port^[481]. (e), (f) The on-chip OAM generators with higher-order (e) OAM−2 and (f) OAM−3. Left panels are the top views of the antenna waveguides. Right panels are the output electric field |Ey| distributions for individual antenna arrays, the overall OAM field inside the meta-waveguide, and the output optical fields after exiting waveguide right ports after a propagation length of around 20 µm^[471], respectively. (g) Conceptual view of the grating coupler formation by superimposing the TE10 mode and TE01 mode antennas. (h) Numerically calculated amplitude and phase distributions of the field component |Ex| in the target waveguide for the grating coupler formation when the target OAM states are +1 and −1^[579].

Fig. 7. Typical examples of in-plane to out-of-plane OAM generation^{[472–475" target="_self" style="display: inline;">–475,550–553" target="_self" style="display: inline;">–553,580–583" target="_self" style="display: inline;">–583]}. Four different structures of the in-plane to out-of-plane OAM generation include (a), (b) grating array, (c)–(f) microring, (g)–(j) fork grating, and (k), (l) subwavelength structure. (a) The schematic and optical image of the silicon photonic integrated circuit, which consists of an FPR, tunable-phase arrayed waveguides, and vertical grating couplers^[580]. (b) OAM emitter structure including one bus waveguide, one ring, and eight download units, where each download unit includes a grating and an arc waveguide^[581]. (c) Optical vortex beams extracted in whispering gallery modes microring^[472]. (d) Compact tunable integrated OAM emitters^[473]. (e) OAM mode emitters based on multimode microring^[474]. (f) Multimode vortex beam microring emitter based on vertical modes^[475]. (g) The principle and schematic illustration of the holographic fork grating on Si3N4 waveguide^[550]. (h) Schematic illustration of the silicon waveguide surface holographic fork grating for generating the OAM+1 mode, OAM−1 mode, and their synthetization of two modes^[551]. (i) Concept of the holographic fork grating with uniform width grooves and the scanning electron microscopy (SEM) image with flat apodization^[552]. (j) Concept of multi-waveguide holographic gratings^[553]. (k) Schematic illustration of the principle of the OAM emitter with subwavelength structure and the details of the subwavelength structure design^[582]. (l) Concept of the OAM beam generation using the phase delays^[583].

Fig. 8. The in-plane to out-of-plane OAM generation with the superposed fork grating^[555,556]. (a)–(c) Concept and principle of the silicon-based OAM generation with the superposed fork grating. (d) Simulated purity of four polarization diversity OAM modes versus wavelength. (e) Measured SEM image of the superposed fork grating. (f) Measured results (intensity profile and interferogram) for the generation of the polarization diversity OAM modes in the C-band (1530–1565 nm). (g) Measured 4×4 crosstalk matrix and accumulated crosstalk summing up all the noise^[555]. (h) Schematic structure of the high-efficiency OAM generator with a backside metal mirror. (i) Measured power of different emitting OAM modes with/without a mirror^[556].

Fig. 9. The in-plane to out-of-plane OAM generation with digitized subwavelength structure^[584]. (a)–(c), (g), (i) Integrated OAM emitter for generating the x/y-polarization OAM±1. (d)–(f), (h), (j) Integrated OAM emitter for generating the x/y-polarization OAM±1/±2. (a), (d) Digitized nanostructures. (b), (e) Concept and principle of integrated OAM generators. (c), (f) Simulation results of the intensity profiles, interferograms, and phase distributions. (g), (h) Measured optical microscope and SEM images of the fabricated OAM emitters. (i), (j) Measured 4×4 mode crosstalk matrix. (k), (l) Simulation results of the intensity profiles, interferograms, and phase distributions when the digitized subwavelength structure is designed to generate the third-order and fourth-order OAM modes, respectively^[584].

Fig. 10. The out-of-plane to out-of-plane OAM generation with plasmonic metasurface^{[585–587" target="_self" style="display: inline;">–587]}. The plasmonic metasurface mainly includes (a)–(c) resonance phase metasurface and (d)–(k) geometry phase metasurface. (a) Schematic unit cell of V-shaped phase metasurface. (b) SEM image of a representative antenna array. (c) SEM image of the plasmonic interface that produces an OAM beam. The plasmonic metasurface includes eight regions, each occupied by a unit cell of the eight-element set of (a)^[585]. (d) Schematic of L-shaped metasurface for generating the OAM beam. (e) SEM image of L-shaped phase metasurface. (f) Generated OAM±2 beams at 780 nm^[586]. (g) Superposed phase distributions of axicon, spiral phase plate, and Fourier transform lens. (h) Interferometry patterns of OAM with topological charges (ℓ=1,3, 5, 8) at 633 nm, when the axicon periods are 8 and 4 µm, respectively. (i) Measured results of multiple OAM beams with different topological charges and arbitrary location arrangement^[587].

Fig. 11. The out-of-plane to out-of-plane diverse OAM generation with metasurface^{[588–590" target="_self" style="display: inline;">–590]}. (a) Concept of the metasurface consisting of 84 rectangular holes etched on the gold film. (b) Schematic illustration of OAM-carrying vector beam generation^[588]. (c) Structured light generation with phase helix and intensity helix utilizing the reflection-enhanced plasmonic metasurface at 2 µm^[589]. (d) Concept of metasurface at the end/facet of large-core fiber for twisting ultra-broadband light. The incident Gaussian light is coupled into the fiber from either the meta-facet side (scheme 1) or the planar-facet side (scheme 2). (e) Measured phase purity of the ultra-broadband OAM generation with meta-facet fiber tip structure^[590].

Fig. 12. The out-of-plane to out-of-plane OAM generation with dielectric metasurface^{[591–597" target="_self" style="display: inline;">–597]}. (a) Optical microscope and SEM images of the fabricated spiral phase plate composed of eight sections of silicon cut-wires and the interferogram of the generated optical vortex^[591]. (b) Concept of the microwave resonant dielectric metasurface^[592]. (c) Schematic of silicon subwavelength grating and dielectric metasurface consisting of width-modulated concentric ring grating^[593]. (d) Schematic of the designed metasurface with nanopillar arrays generating PVBs for right-circularly polarized (RCP) light^[594]. (e) Schematic of generation of generalized perfect Poincaré beams (PPBs) via dielectric metasurface^[595]. (f) Schematic of the proposed multifunctional metasurface^[596]. (g) Schematic of generation of the longitudinally varying vortex beams. (h) Simulated intensities and phase profiles of transmitted orthogonally polarized fields with LCP/RCP incidence^[597].

Fig. 13. The out-of-plane to out-of-plane OAM generation with spiral phase plate and holographic grating^{[464–466" target="_self" style="display: inline;">–466,598–600" target="_self" style="display: inline;">–600]}. (a) Schematic of wavefront conversion with a spiral phase plate^[598]. (b) Schematic illustration and SEM images of the generator producing multiple axially controllable OAM beams^[599]. (c) Schematic illustration and optical microscope image of the spiral phase plate fabricated on the end face of the single-mode fiber^[464]. (d) Schematic of OAM beam generation using the spiral phase plate on the end face of the ring-core fiber^[465]. (e) Schematic of OAM generation based on the holographic grating fabricated on the fiber facet^[466]. (f) Schematic illustration and SEM images of holographic fork plates with blazed grating^[600].

Fig. 14. The out-of-plane to out-of-plane OAM generation with twisted moiré photonic crystal^[601]. (a) Schematic of the twisted bilayer photonic crystal for OAM-carrying optical vortex emission. (b) Mode intensity spectrum of the twisted bilayer photonic crystal. (c) Light field distributions of the optical vortex emission at peaks “i” and “ii” in (b). (d), (e) Light field distributions of the optical vortex emission under different (d) twist angles from 1.0° to 2.5° and (e) interlayer spacings from 200 to 350 nm^[601].

Fig. 15. The integrated spiral phase plate OAM laser^[602,603]. (a) Schematic of integrated OAM laser combining the VCSEL and the 8×8 spiral phase plate array. (b) Spiral phase plate structures, phase distributions, and intensity profiles of OAM+2, OAM+3, and OAM+4 modes^[602]. (c) Top view SEM images of spiral phase plates, intensity profiles of the generated OAM modes, and simulated intensity and phase profiles of OAM modes. (d) Simulated and experimental results of OAM beams with superposition states^[603].

Fig. 16. The integrated non-Hermitian-controlled OAM laser^{[604–608" target="_self" style="display: inline;">–608]}. (a) Schematic of OAM microlaser with tunable topological charge. (b) Schematic of chiral non-Hermitian control and experimental characterization^[604]. (c) Schematic of the fast switch of the fractional OAM^[605]. (d) Schematic of a hyperdimensional spin-orbit microlaser^[606]. (e) Schematic of OAM microlaser with a microring resonator and alternate Ge and Cr/Ge structures^[607]. (f) Schematic of OAM microlaser with a microring and an S-shaped waveguide^[608].

Fig. 17. The integrated micro-etching OAM laser^{[609–612" target="_self" style="display: inline;">–612]}. (a) Focused-ion beam and SEM images of the Ge micro-gears on silicon pillars. (b) Measured spectra by exciting the micro-gear from the top with laser beams of different powers^[609]. (c) Schematic and SEM image of a benzene-like OAM laser with the cavity etched to form hexagonal rings of coupled micropillars. (d), (e) Phase distributions of the emission showing 4π counterclockwise and clockwise phase vortex under (d) σ+ and (e) σ− circularly polarized pumps^[610]. (f) Schematic of a microring OAM laser based on the guided wave-driven metasurface. (g) Schematic of meta-atom with a metal/dielectric/metal structure. (h) Phase shift of the meta-atom with different parameters. (i) Simulated and measured results for the far-field intensity distributions and the self-interference patterns of OAM mode^[611]. (j) Schematic of the OAM laser with a microring and a distributed feedback laser. (k) Measured mode purities of OAM beams^[612].

Fig. 18. The integrated topological OAM laser^[615,616]. (a) Schematic of the topological OAM laser. (b) SEM and (c) zoom-in SEM images of the topological OAM laser. (d) Calculated bulk bands of the topological photonic crystal (gray curves), and calculated discrete edge modes of the topological OAM laser (red and green dots). (e) Dispersion curves of the conventional whispering gallery modes and topological edge modes. (f) Lasing spectra of the two edge states of opposite momenta with opposite spins. (g) Off-center self-interference of the generated OAM−2 mode. (h) SMSR versus the pump intensity^[615]. (i) Schematic of vortex and anti-vortex disclination nanolasers. (j), (k) SEM images of fabricated (j) vortex and (j) anti-vortex nanolasers. (l)–(n) Measured polarization-resolved lasing images from the cavities of the (l) vortex and (m), (n) anti-vortex nanolasers^[616].

Fig. 19. Higher-dimensional supersymmetric microlaser arrays^[617]. (a) Conceptual view and (b) measured SEM images of higher-dimensional supersymmetric microlaser arrays. (c) Light-light curve showing the lowering of the threshold and the enhancement of lasing output in the supersymmetric microlaser array compared with a single microring laser. (d) Far-field diffraction pattern of vortex emission, corresponding to the superposition of two vortex beams. (e), (f) 1D diffraction patterns of the two distinct vortex beams of (e) ℓ = +1 and (f) ℓ = −1^[617].

Fig. 20. Integrated chiral light generation and LP mode generation^[622,623]. (a) Schematic of resonant chiral metasurface. (b) Top view, side view, and vector field of unit-different cell. (c) Emission spectra of LCP (solid lines) and RCP (dashed lines) in the normal direction. The pumping densities are 16.5mJ/cm2 (bottom) and 58.9mJ/cm2 (top), respectively. (d) Output intensity of LCP (dot-shaped) and RCP (square-shaped) versus the pumping density. (e) Fitted DOP (cross-shaped), absolute DOP (dot-shaped), and FWHM (square-shaped) of LCP light versus the pumping density. (f) Far-field angular intensity distribution of the generated chiral light^[622]. (g) Schematic of three-layer volume. (h) SEM image of the volume element. (i), (j) Experimental results of output intensity for (i) +3° incidence angle to yield LP21 mode and (j) −3° incidence angle to yield LP02 mode^[623].

Fig. 21. Integrated Laguerre-Gaussian (LG) beam generation and Hermite-Gaussian (HG) beam generation^[624,625]. (a) Schematic of the unit cell and SEM image of the metal metasurface. (b) Simulated phase and intensity distribution of the LG2,2 mode. (c) Measured intensity distributions of different LG and HG beams (p=3 and p=10) at an operation wavelength of 1000 nm^[624]. (d) Schematic of the unit cell and metasurface for generating multiple LG modes. (e) Overall SEM and zoom-in SEM images of metasurface for generating multiple LG modes. (f) Simulated and measured diffraction patterns of the combined mode of LG42:LG11=1:1 with different wavelengths. (g) Simulated and measured diffraction patterns of the combined mode of LG11:LG22:LG23=3:4:5 at 1030 nm^[625].

Fig. 22. Integrated Bessel beam generation and Mathieu beam generation^{[385,386,496,627–630" target="_self" style="display: inline;">–630]}. (a) Metasurface for generating individual Bessel beam over the whole visible spectrum^[627]. (b) Metasurface for generating 5×5 polarization-independent Bessel beam arrays^[628]. (c) Optical phased arrays for generating Bessel beam^[496]. (d) Polymer-based phase plate for generating high-quality Bessel beam^[385]. (e) 3D structure consisting of a parabolic lens, a mechanical holder frame, and a helical axicon for generating a Bessel beam^[629]. (f) 870-μm-diameter ring structure with concentrically distributed grating arrays for generating a 10.24-m propagation invariance of broadband Bessel beam^[630]. (g) Helical phase plate for generating a Mathieu beam. (h) Intensity distribution of the even Mathieu beam with m=2 and q=12 at different distances^[386].

Fig. 23. Integrated Airy beam generation^{[631–636" target="_self" style="display: inline;">–636]}. (a) Silver surface for generating Airy beams^[631]. (b) Reflective and transmissive metasurfaces for generating ultra-wideband Airy beams^[632]. (c) All-dielectric metasurface for generating individual and multiple Airy beams^[633]. (d) Dielectric metasurface for generating achromatic terahertz Airy beams^[634]. (e) Synthetic-phase meta-optics with an ultra-compact footprint of 3μm×16μm for generating 1D Airy beams^[635]. (f) Shallow-etched silicon holography grating for generating Airy beams^[636].

Fig. 24. Integrated needle beam and pin beam generation^[74,637]. (a) DOE phase pattern composed of multiple different phases of focal points. (b) Schematic of DOE for generating a needle beam. (c) Experimentally measured results of the needle beam, including y–z and x–y profiles at different z=−100, 0, and 100 µm^[637]. (d) Pin beam generation mechanism by eliminating the transverse wave vector components and the directed truncation of components similar to Airy beams. (e) Side view of the pin beam propagating over 8 km. (f) Intensity profiles captured at z=0, 4, and 8 km^[74].

Fig. 25. Integrated vector beam generation^{[638–641" target="_self" style="display: inline;">–641]}. (a) Ring structure with concentrically distributed 64 grating arrays^[638]. (b) Schematic of silicon nitride microring resonator with shallow-etched gratings on the top of microring waveguide^[639]. (c) Schematic, far-field intensity, and polarization map of conventional and width variation microring^[640]. (d) Schematic of metasurface for generating mid-infrared radially polarized (azimuthally polarized) beam by horizontal (vertical) linear polarization^[641].

Fig. 26. Integrated CVB laser^[642,643]. (a) Schematic 3D structure, (b) top view, and (c) SEM image of the CVB laser. (d) Far-field intensity distribution of measured RPBs without and with a rotating linear polarizer^[642]. (e) Schematic of the cross section of the CVB laser. (f), (g) Schematic of the CVB laser for generating (f) RPB and (g) APB^[643].

Fig. 27. Integrated array beam generation^{[644–646" target="_self" style="display: inline;">–646]}. (a) Schematic and (b) SEM image of nano-slit metasurface for generating array OAM beams. (c) Measured and simulated intensity distributions of the 6×6 array beam with topological charges of ℓ=0 and ℓ=1^[644]. (d) Schematic of metasurface laser for generating array OAM beams. (e) Experimental near-field and far-field distributions of array beam with a topological charge of ℓ=5^[645]. (f) Schematic of phased array system with 64×64 gratings. (g) Experimental near-field distributions with uniform emission of all 64×64 gratings^[646].

Fig. 28. Integrated optical vortex lattice generation^[647]. (a), (b) Schematic of on-chip optical vortex lattice emitter and the tilt grating. (c)–(e) Simulated results of optical vortex lattice based on the three-plane-wave interference, including intensity, phase, and interferogram distributions. (f)–(h) Simulated and (i)–(k) experimentally measured results of the designed and fabricated optical vortex lattice emitter, including near-field intensity distribution of y-polarization electrical field, intensity, and interference of far-field distribution^[647].

Fig. 29. Integrated spatiotemporal beam generation^[648,649]. (a) Schematic of a spatial light modulator based on the photonic crystal. (b) Near-field reflection spectra of inverse-designed cavities. Inset: resonant imaging. (c) Maximum phase shift and half-maximum switching interval versus CMOS trigger duration. (d) Complex reflectivity modulation with fJ-order pulse energies. (e) Frequency-domain power transfer response function^[648]. (f), (h) Transverse mode profiles and (g), (i) interference patterns of the vortex beam with topological charges of ℓ=1 and ℓ=2. (j) Real and imaginary parts of the indium tin oxide (ITO) film permittivity. (k) Measured and fitted transmittance of the epsilon-near-zero (ENZ)-metasurface versus pump fluence. (l) Intensity of output pulses with a 39-mW pump power. (m) Averaged spectrum of the output pulses^[649].

Fig. 30. Integrated spatiotemporal optical vortex (STOV) generation^[650,651]. (a) Schematic of OAM comb for generating spatiotemporal optical pulses with varying OAMs. Each frequency (left) corresponds to the different OAM mode (right). (b) SEM images of the fabricated AlGaAsOI device. (c) Measured spectra of the microcombs in soliton states with a wavelength spacing of 500 GHz. (d) Simulated and (e) measured results of AlGaAsOI OAM comb including the space-time intensity profile of the targeted self-torque pulses and the intensity and phase distribution of transverse cross sections^[650]. (f) Schematic of Si3N4 OAM comb. (g) SEM images of a waveguide-coupled microresonator with angular gratings. (h) Measured optical spectra of the single-soliton Si3N4 OAM microcomb. (i) Simulated and (j) measured reconstructed evolution of the beam profile^[651].

Fig. 31. Integrated knotted and linked beam generation^[255,256]. (a) Schematic of metasurface hologram for generating the optical knots. (b) Experimentally obtained Trefoil knots and Hopf links at the wavelengths of 700, 800, and 900 nm^[255]. (c) Schematic of all-dielectric metasurface hologram for generating switchable optical knots. (d) Simulated results for generating the Hopf links and Trefoil knots, including amplitude and phase distributions at the beam waist plane, phase-only holograms, propagation phase pattern, and orientation angle pattern. (e) Experimentally obtained Trefoil knots and Hopf links. The insets are the top view of the topological structures^[256].

Fig. 32. Integrated in-plane waveguide mode generation^{[497,652–656" target="_self" style="display: inline;">–656]}. (a) Asymmetric directional couplers based on the phase matching for generating in-plane waveguide mode^[497]. (b) Metamaterial-based structure for generating high-order in-plane waveguide mode^[652]. (c) Beam shaping structure composed of a two-port Y branch and π phase difference^[653]. (d) Beam shaping structure composed of a multiport Y branch and parallel π phase difference^[654]. (e) Compact tapered waveguide^[655] and (f) photonic crystal waveguide^[656] based on the coherent scattering method.

Fig. 33. Integrated reconfigurable structured light generation by phase change materials^[657,658]. (a) Schematic of resonator metasurface for generating reconfigurable OAM mode. (b) Measured results of resonator metasurface, including the normalized intensity distribution and phase profiles, when the GST material works on the states of amorphous, crystalline, and reamorphization^[657]. (c) Schematic and (d) SEM image of SiN waveguide with phase-gradient metasurface for generating reconfigurable in-plane waveguide mode. (e) Simulation results of SiN waveguide with phase-gradient metasurface when the GST material works on the states of crystalline and amorphous^[658].

Fig. 34. Integrated reconfigurable structured light generation with ultrafast control^[659]. (a) Schematic of microlaser for reconfigurable generation between the LP mode and OAM mode. (b) SEM image of perovskite metasurface. (c)–(e) Schematics of the experiments and measured far-field intensity profiles when changing the pumping laser beam of the perovskite metasurface. (c) Pumped with a circular laser beam. (d) The pumping region is transferred from a circle to an ellipse. (e) Pumped with two overlapped circular laser beams. (f) Transition process from OAM mode to LP mode. (g) Transition process from LP mode to OAM mode. (g) Transition process from OAM mode to LP mode, then from OAM mode to LP mode^[659].

Fig. 35. Classification of basic theories and various functionalities of integrated structured light processing.

Fig. 36. Out-of-plane OAM multiplexing based on multiplane light conversion and in-plane OAM multiplexing based on trench waveguide structure^[470,501]. (a) Schematic of multiplane light conversion for implementing the conversion from the near-perfect Gaussian beam array to co-axial multiplexed OAM modes. (b) Measured results of OAM mode crosstalk matrix^[501]. (c) Schematic of the trench waveguide-based OAM mode (de)multiplexer. (d) Simulation results and (e) experimental results of OAM mode multiplexer and exchanger based on the trench waveguide^[470].

Fig. 37. Out-of-plane OAM demultiplexing based on spiral transformation and metasurfaces^[502,503]. (a) Schematic of OAM mode sorter (demultiplexer) based on the optical coordinate transformation (spiral transformation). (b) 3×4 array of OAM mode sorters fabricated on the quartz plate composed of (c) an unwrapper, (d) a phase corrector, and (e) a positive lens^[502]. (f) Transmittance and phase shift versus diameter of the TiO2 nanopillar. (g) Schematic of the OAM mode sorter based on TiO2 metasurfaces. (h) Microscope image and tilt-view SEM image of TiO2 metasurfaces. (i) Measured results of the OAM mode sorter (intensity distribution of different OAM modes and mode crosstalk matrix)^[503].

Fig. 38. The in-plane waveguide mode multiplexing^{[498–500" target="_self" style="display: inline;">–500,670]}. (a) Simulated effective index of the in-plane waveguide mode and the schematic of multiple cascaded microrings with multimode bus waveguide for WDM-compatible MDM^[498]. (b) Schematic of 10-channel PDM-compatible MDM^[499]. (c) Schematic of silicon-based 11-channel single-polarization in-plane waveguide mode (de)multiplexer with subwavelength grating (SWG) structures^[500]. (d) Schematic of four-channel TM-polarization mode (de)multiplexer based on different orders of photonic BIC^[670].

Fig. 39. Integer OAM multiplication and division^[504]. (a), (b) OAM mode multipliers for (a) two-fold and (b) three-fold multiplication. (c), (d) OAM mode dividers for (c) two-fold and (d) three-fold division. Each subpicture includes the schematic, two-phase patterns, and numerical simulations of the propagation process^[504].

Fig. 40. Fraction OAM multiplication and division^[671]. (a) Schematic of OAM mode multiplication and division via an arbitrary rational factor. (b) Simulated and (c) measured mode purity through an OAM multiplication with a rational factor of 1.5. (d) Simulated and measured intensity and phase distributions of the input and output OAM beams through an OAM multiplication with a rational factor of 1.5^[671].

Fig. 41. Nonlinear OAM conversion with lithium niobate^[505,506]. (a) Schematic of the spirally poled nonlinear LiNbO3 photonic device for generating OAM states of the SH wave. (b) Measured OAM of the SH wave, including intensity pattern and off-axis interference distribution^[505]. (c) Schematic of the periodically poled lithium niobite photonic waveguide. (d) Simulated intensity and phase distributions of input light and output light^[506].

Fig. 42. Nonlinear OAM conversion/interaction with 2D materials^[507,508]. (a) Schematic of the experimental setup for measuring the SHG and THG nonlinear conversion of OAM from a tungsten disulfide (WS2) monolayer. (b) Microscope image of the WS2 monolayer crystal and dark-field image of the LP fundamental OAM+1 beam. (c) Nonlinear response spectrum under fundamental OAM excitation of WS2 monolayer and measured SHG and THG power from WS2 monolayer versus the pump power. (d) Electron multiplying charge-coupled device (EMCCD) images of the fundamental vortex beam, SHG, and THG focused on the WS2 monolayer sample and cylindrical lens images of the fundamental vortex beam, SHG, and THG^[507]. (e) Intensity profiles, wavefronts, and phase distributions corresponding to OAM+1, OAM+2, OAM+3, and OAM+4. (f) Optical microscope of the MoS2 sample. (g) PL curves recorded at 4 K temperature under the excitation of OAM+0, OAM+1, OAM+2, OAM+3, and OAM+4 beams^[508].

Fig. 43. Nonlinear OAM conversion with micro-nano structures^[674,675]. (a) Schematic of nonlinear photonic metasurface for generating the spin-control OAM in SHG. (b) Real space phase distributions of SHG and SEM images of gold plasmonic metasurface with q=1/3, 2/3, and 1. (c) Measured and (d) simulated intensity distributions of SHG from nonlinear metasurfaces with q=1/3, 2/3, and 1^[674]. (e) SEM image of gold-fork microstructure. (f), (g) Front-pumping scheme. (f) SHG light from the device with the polarization direction of the analyzer set at x direction. (g) THG light of OAM+2 mode at the first diffraction order from the device with the polarization direction of the analyzer set at y direction. (h)–(j) Back-pumping scheme. (h) SHG light of OAM+2 mode from the device with the polarization direction of the analyzer set at x direction. (i) THG light of OAM+2 mode at the first diffraction order from the device with the polarization direction of the analyzer set at y direction. (j) SHG and THG lights of OAM+2 mode produced simultaneously after removing the analyzer in the optical path^[675].

Fig. 44. LP mode switching and array beam transformation^{[509,511,677]}. (a) Schematic of fiber-chip-fiber system using the (b), (d) femtosecond laser inscribed mode (de)multiplexer and (c) silicon switch array^[511]. (e) Schematic of 3D photonic chip for converting the single-mode array beams. (f) Linear and concentric circular distribution of array beams with 19 channels. (g) Measured intensity distribution of concentric circular array beam^[509]. (h) Schematic of 3D photonic chip for converting the few-mode array beams with seven channels. (i) Measured intensity distribution of concentric circular array beams with unit Gaussian beam (left) or unit two-lobe few mode (right)^[677].

Fig. 45. The in-plane waveguide mode processing (mode exchange, mode switch, and mode add/drop)^{[514,678–681" target="_self" style="display: inline;">–681]}. (a) Simulation results of the inverse-design mode exchange device^[514]. (b) Schematic of ultra-compact and ultra-broadband mode exchange device^[678]. (c) Mode switch device consisting of symmetric Y-junctions, crossing, and thermo-optic phase shifter^[679]. (d) Mode switch device introducing bi-level adiabatic tapered waveguide^[680]. (e) Schematic of the direct-access mode add/drop multiplexers^[681].

Fig. 46. The in-plane waveguide mode processing (chiral mode switching)^{[669,682,683]}. (a) Schematic of encircling a moving exceptional point. (b) Simulated Ex field distributions of encircling a moving exceptional point^[682]. (c) Schematic of encircling the exceptional point based on the Hamiltonian hopping^[683]. (d) Schematic of encircling a moving exceptional point with fast parametric evolution along the parameter space boundary of the system Hamiltonian^[669].

Fig. 47. Transformation of different types of structured light^{[510,684–686" target="_self" style="display: inline;">–686]}. (a) Schematic of optical neural network mode mapper with four diffractive layer structures for mapping of OAM mode and LP mode. (b) SEM and (c) zoom-in SEM images of the 3D photonic device fabricated by femtosecond laser direct writing technique. (d) Measured intensity distributions of the input OAM and output LP light fields^[510]. (e) Schematic of mode converter between LP-like mode and in-plane waveguide mode^[684]. (f) Schematic of mode converter including tapered fiber and multistage silicon tapered waveguide^[685]. (g) Schematic of mode converter using a slot waveguide^[686].

Fig. 48. Classification of basic theories and various schemes of integrated structured light detection.

Fig. 49. Integrated structured light detection based on metal micro-nano structures^{[518,708–711" target="_self" style="display: inline;">–711]}. (a) Conceptual view of the on-chip discrimination of OAM with plasmonic semi-ring nanoslit. (b) The SEM image of the semi-ring structure etched on the metal surface. (c) Mechanism and FDTD simulation of the OAM detector under radially polarized OAM beam illumination^[518]. (d) Schematic of the OAM detection process using the nanograting. (e) The vector analysis of the conversion from OAM beam to surface plasmon polariton. The blue curves are the calculated relation of separation D and topological charge l. The red error bars are the experimental data of spot distances extracted from the microscopy images^[708]. (f) Schematic of the OAM and SAM detection. (g) Propagation direction of the generated surface plasmon polariton with an incident OAM beam with different polarizations and topological signs^[709]. (h) The schematic and coordinate system of the on-chip photon angular momentum detector. (i) Details of the arrangement of orthogonal nano slit pairs in semi-annular array^[710]. (j) The schematic of the OAM detector based on the catenary grating structure. (k) Arrangements of the catenary gratings for detecting positive and negative topological charges^[711].

Fig. 50. Integrated structured light detection based on plasmonic metasurface^[712,713]. (a) Schematic view of OAM detector using self-interference. (b) Sketch map of the designed metasurface based on the V-shaped nano-antenna^[712]. (c) Schematic view of OAM detector based on semi-ring plasmonic metasurface. (d) The binary phase distribution of the metal metasurface and the simulated results^[713].

Fig. 51. Integrated structured light detection based on dielectric micro-nano structures (dielectric metasurface, Dammann grating, waveguide grating)^{[519,520,714,715]}. (a) Schematic view of dielectric metasurface based on TiO2 for vortex light detection. (b) The schematic of the single rectangular nanopillar unit. (c) The SEM image of the dielectric metasurface^[519]. (d) Principle of the PMT that translates different OAM modes into rotating focusing patterns, which is leveraged for single-metasurface-based single-shot OAM detection. (e) Simulated polarization conversion ratio (PCR) of the unit cell. Inset: schematic of the unit cell, which is composed of TiO2 nanopillars on a SiO2 substrate in a hexagonal lattice. (f) Top-view and perspective-view SEM images of the fabricated dielectric metasurfaces^[520]. (g) Schematic of OAM-based free-space optical communications using DOVG for MUX/DEMUX^[510]. (h) Left: measured intensity profiles of the OAM beams with different topological charges (ℓ=−3, −9, 15, −21, 27); Middle: measured coaxial vortex beams with 10 OAM states (ℓ=±3, ±9, ±15, ±21, ±27); Right: measured intensity profiles of the Gaussian-like beams after detection of OAM beams (ℓ=−3, −9, 15, −21, 27). (i) Simulation results corresponding to (h)^[714]. (j) Schematic of the arc-shaped waveguide grating coupler (AWGC). (k) Schematic of AWGC-based OAM detector^[715].

Fig. 52. Integrated structured light detection based on orbital photogalvanic effect^[523]. (a) Schematic of the OAM photocurrent detector. (b) Optical image of a photodetector device with U-shaped electrodes on WTe2. (c) Measured photocurrent amplitudes from OAM+1 (red curve) and OAM−1 (blue curve) beams, as a function of the quarter-wave plate angle. The insets are charge-coupled device (CCD) recorded images of OAM+1 and OAM−1 beams. (d) Normalized photocurrent change when switching polarization states of OAM beams with different OAM orders (−4 to 4). Error bars represent the standard deviations of the fitting^[523].

Fig. 53. Integrated structured light detection based on MIR photocurrent detector^[717]. (a) Optical image of a photodetector device with U-shaped electrodes. (b) Schematic of the orbital photogalvanic effect response from light carrying opposite OAM orders. (c) Orbital photogalvanic effect current measurement of TaIrTe4 device with U-shaped electrodes. (d) Schematic diagram of a photodetector device with U-shaped electrodes. The light spot of the LG beam is focused on the center of the arcs defined by the U-shaped electrodes. (e) Measured photocurrent amplitudes under the excitation of LG beams with different OAM orders^[717].

Fig. 54. Integrated structured light detection based on thermoelectric detector with spin-Hall coupler^[524]. (a) Schematic of the on-chip photodetection of angular momentum of vortex structured light. (b) SEM image of the fabricated ring-shaped spin-Hall coupler. (c) Optical image of the on-chip photodetector. The PdSe2 is employed as the active photothermoelectric material, and four bottom-contact electrodes are used as four output ports (P1, P2, P3, P4) for reading the thermoelectric response intensity. (d) Experimentally measured photovoltage responses for LCP and RCP vortex beams with topological charges ranging from −4 to 4^[524].

Fig. 55. Integrated structured light detection based on DMD and diffuser^[718]. (a) Schematic of the OAM mode detector consisting of a complex amplitude wavefront shaper and a diffuser. (b) The amplitude and phase distribution of the target field. (c) The expanded DMD mask is translated from the lookup table. (d) Experimental results for the detection of multiplexed two and three OAM modes^[718].

Fig. 56. Integrated structured light detection based on hybrid optoelectronic neural network^[525]. (a) Schematic of hybrid optoelectronic neural network for OAM spectrum measurement. The diffractive optical neural network manipulates the incident structured light with a certain OAM distribution and transforms the OAM information into a high-dimensional sparse feature in the photoelectric detector plane. (b) Experimental configuration for generating various structured lights (experimental test sets) for OAM spectrum detection. CW, continuous wave; BE, beam expander; HWP, half-wave plate; BS, beam splitter; SLM, spatial light modulator; P, polarizer; L1, L2, lenses. For each test set, the complex optical fields are generated using the four-step phase shift method as shown in the insets (I₁, I₂, I₃, I₄). (c) Intensity and phase distributions of the generated single OAM modes and multiplexed OAM modes (equal/random weights). From left to right: single OAM mode (ℓ=5), multiplexed OAM modes (ℓ=−4 and −1 with equal weights), multiplexed OAM modes (ℓ=−4, −3, 2, 5 with equal weights), multiplexed OAM modes (ℓ=−10–10 with random weights). (d) Structured light detection results of single OAM mode with ℓ from −10 to 10. Different OAM modes are indicated along the horizontal axis while the observed OAM spectrum is represented along the longitudinal axis. (e) Selective results of simultaneous detection of multiple OAM modes. #1: multiple OAM modes with equal weights. #2: multiple OAM modes with random weights. The obtained results of (d) and (e) are averaged from 30 repeated experiments. The error bar represents the standard deviation^[525].

Fig. 57. Integrated structured light detection based on silicon MZI network^[526]. (a) Schematic of a 9×2 diagonal photonic processor comprising two rows of tunable MZIs and implementing structured light detection. The 2D optical antenna array is used to couple free-space light beams into the silicon waveguides, while the output ports WG1 and WG2 are used to couple the light out to a pair of optical fibers for detection. (b) Top-view micrograph of the fabricated silicon chip for structured light detection. (c) The zoom-in detail of the 2D optical antenna array with 3×3 grating couplers in a square configuration. (d) Measured far-field intensity distribution emitted from the 2D optical antenna array when all the grating couplers are excited with the same amplitude and phase. Multiple diffraction orders (grating lobes) are observed within the 5°×9° angular beam width of the emitted pattern of the elementary grating coupler. (e) The zoom-in detail of a thermally tunable beam coupler with a transparent monitor detector integrated at output ports. (f) Photograph of the photonic chip assembled on a PCB, which integrates the CMOS electronic ASIC for the read-out of on-chip detectors^[526].

Fig. 58. Integrated structured light detection based on inverse design subwavelength structure^[527]. (a) Schematic of the inverse design of a planar on-chip mode sorter. (b) Experimental setup with the detector manufactured on a silver layer. Different HG plasmonic beams are excited by a grating coupler, and the detector routes them into separate output ports. (c) Simulated and experimental results of the surface plasmon polariton intensity distribution along the propagation direction of the detector device for detecting the HG0 beam (left output) and HG1 beam (right output). (d) Simulated and experimental results of intensity profiles at the end of the device, corresponding to the red cross-section dashed lines in (c). (e) Measured intensity by the NSOM integrated along the transverse direction when propagating inside the detector device^[527].

Fig. 59. Structured light detection based on silicon nanorod optomechanics^[720]. (a) Schematic of the generation of structured transverse orbital angular momentum (TOAM). An array of optical vortices carrying angular momentum transverse to the propagation direction is produced by separating two focused counter-propagating linearly polarized Gaussian beams along the polarization axis. A silicon nanorod is suspended within the structured light field, which generates a torque and drive rotation in the y–z plane. (b) Experimental setup of the levitated optomechanical sensor for structured light probing and detection. Light after amplification is split into two equal arms, coupled into free space, and then focused by lenses inside a vacuum system to create an optical trap. A separation between the light beams is introduced. The inset depicts the coordinate axis for a silicon nanorod trapped by linearly polarized light. The silicon nanorod undergoes harmonic motion in three linear axes x, y, z and two librational axes α, β. (c) The SEM image of silicon nanorods. (d) Measured torque applied to the silicon nanorod versus the offset δy (blue squares: mean value). (e) The effect of a transverse offset δx on the torque applied to the silicon nanorod by TOAM (red squares: mean value)^[720].

Fig. 60. Classification of basic theories and various scenarios of integrated structured light applications.

Fig. 61. Structured light application in analog signal transmission using OAM modes^[724]. (a) Experimental setup of an analog signal transmission system with photonic integrated vortex emitter and 3.6-km FMF link. RF, radio frequency; PC, polarization controller; EDFA, erbium-doped fiber amplifier; QWP, quarter-wave plate; Pol., polarizer; FMF, few-mode fiber; PC-FMF, polarization controller on few-mode fiber; HWP, half-wave plate; SLM, spatial light modulator; Col., collimator; VOA, variable optical attenuator; PD, photodetector; ESA, electric spectrum analyzer. (b), (c) Measured output power of RF carrier and distortions versus RF input power of (b) OAM+2 at a wavelength of 1531.91 nm and (c) OAM−2 at a wavelength of 1556.56 nm^[724].

Fig. 62. Structured light application in data-carrying digital signal transmission using OAM modes^[725]. (a) Measured SEM image of the fabricated device (etched microring resonator) and schematic of the 3D structure of the photonic integrated vortex emitter with an angular grating patterned along the inner wall of a microring resonator and an Al mirror layer. (b) Illustration of OAM modes emission from the device for transmission in FMF. (c) From left to right: measured intensity profiles of OAM+2 mode at a wavelength of 1529.02 nm after 3.6-km FMF, demodulation of OAM+2 mode, OAM−2 mode at a wavelength of 1552.32 nm after 3.6-km FMF, demodulation of OAM−2 mode. (d) Measured BER performance versus received OSNR of 2-km two-mode FMF link and three-mode FMF link based on the high-emission-efficiency silicon photonic integrated vortex emitter^[725].

Fig. 63. Structured light application in silicon-chip-assisted high-speed spatial light modulation communication^[726]. (a) Concept and principle of high-speed amplitude-to-OAM modulation mapping for OAM encoding assisted by an integrated OAM mode multiplexer. (b), (c) Measured temporal waveforms of two channels (CH1, CH2) and their subtraction (CH1–CH2) of (b) back-to-back (B2B) and (c) after amplitude-to-OAM modulation mapping. (d) Measured BER performance versus received OSNR for high-speed amplitude-to-OAM modulation mapping assisted by an integrated OAM mode multiplexer^[726].

Fig. 64. Structured light application in chip-chip optical interconnects with OAM multiplexing^[470]. (a) Packaged on-chip OAM mode (de)multiplexer with SMFs. (b) Experimental setup for chip-chip optical interconnects with OAM multiplexing (OAM+1, OAM−1). PC, polarization controller; EDFA, erbium-doped fiber amplifier; AWG, arbitrary waveform generator; OC, optical coupler; SMF, single-mode fiber; VOA, variable optical attenuator. (c) Measured crosstalk matrix. (d) Measured BER performance and constellations^[470].

Fig. 65. Structured light application in chip-fiber-chip optical interconnects with OAM multiplexing^[470]. (a) Packaged on-chip OAM mode (de)multiplexer with SMFs and OAM fiber. (b) Experimental setup for chip-fiber-chip optical interconnects with OAM multiplexing (OAM+1, OAM−1). (c) Measured intensity profiles of the generated OAM−1 mode, OAM+1 mode, and their multiplexing transmission after the 2-km OAM fiber. (d) Measured crosstalk matrix. (e) Measured BER performance and constellations^[470].

Fig. 66. Structured light application in direct fiber vector eigenmode multiplexing transmission seeded by integrated optical vortex emitters^[296]. (a) Conceptual illustration of data-carrying fiber vector eigenmode multiplexing transmission seeded by integrated optical vortex emitters. Two data-carrying fiber vector eigenmodes, i.e., radially polarized mode (TM01) and azimuthally polarized mode (TE01) generated using silicon microring resonators with the inner sidewall etched as angular gratings, are multiplexed and transmitted through a large-core fiber (LCF). (b) Intensity distributions of TM01 mode, TE01 mode, and their multiplexing after fiber transmission. A rotating polarizer is also used with varying axis directions of 0°, 45°, 90°, and 135°. Insets: spatially variant polarization distribution. (c), (d) Measured BER versus received OSNR for (c) QPSK and (d) 16-QAM carrying fiber vector eigenmode multiplexing transmission^[296].

Fig. 67. Structured light application in on-chip MDM transmission using in-plane waveguide modes^[652,727]. (a) Schematic and (b) SEM image of the GIM-based coupler designed for mode (de)multiplexing. (c) Experimental setup for the system transmission experiment of the 16-channel MDM chip. (d) BERs of 40-GBaud 16-QAM signals for 16 modes. (e) Recovered 16-QAM constellations for all 16 modes^[727]. (f) Experimental setup for on-chip data transmission of 28-GBaud 16-QAM signals. (g) Microscope image of the fabricated eight-channel MDM chip. (h) SEM image of the TE6-mode multiplexer. (i) Measured summed mode crosstalk. (j) Measured BERs for eight channels. (k) Corresponding recovered 16-QAM constellation diagrams for eight modes^[652].

Fig. 68. Structured light application in multi-dimensional data transmission and processing using 3D/2D integrated photonic chips^{[511–513" target="_self" style="display: inline;">–513]}. (a) Experimental setup of FMF-chip-FMF communication incorporating mode and polarization switching. (b) Measured BER performance of mode/polarization switching^[511]. (c) Experimental setup of hybrid multi-dimensional fiber-chip system. (d) Measured BER performance of hybrid multi-dimensional fiber-chip system^[512]. (e) Concept of multi-dimensional (mode, polarization, wavelength) FMF-chip-FMF data transmission and processing system using ROADM silicon chip and mode (de)multiplexing silica chip. (f) Measured BER performance of add/drop in the multi-dimensional FMF-chip-FMF system^[513]. (g) The zoom-in and (h) the whole optical microscope images of the silica mode (de)multiplexer. (i) Optical microscope images of the silicon 6×6 optical switches. (j) Optical microscope image of microring-resonator-based silicon integrated multi-dimensional (de)multiplexing and processing chip. (k) Optical microscope images of silicon ROADM chip consisting of AWGs and MZIs.

Fig. 69. Structured light application in free-space multimode communications with silicon photonic processor^[526]. (a) Schematic of photonic processor based on the MZI neural network for free-space multimode communications. Two free-space modes (Mode 1: HG00, Mode 2: HG10-like), with the same wavelength and polarization, are coupled into the MZI neural network and separated at the two output ports WG1 and WG2. (b) Normalized received power of the Mode 1 and Mode 2 at the output ports WG1 and WG2. (c) Backward far-field intensity pattern radiated by the 2D optical antenna array when configuring the photonic processor to couple Mode 1 to WG1, Mode 2 to WG2, Mode 2 to WG1, and Mode 1 to WG2. Circles mark the position of the zeroth-order diffraction. (d) Measured eye diagrams of intensity modulated 10-Gbit/s OOK signals corresponding to the configuration in (c). (e) Measured BER curves of free-space multimode communications (Mode 1 and Mode 2) with the modes separated by the photonic processor. (f) Schematic of two free-space modes (Mode 3: HG10-like, Mode 4: HG11-like) coupled into the MZI neural network. (g) Backward far-field intensity pattern radiated by the 2D optical antenna array and measured eye diagrams with the corresponding configuration. (h) Measured BER curves of free-space multimode communications (Mode 3 and Mode 4) with the modes separated by the photonic processor. (i) Schematic of two free-space beams (Beam A and Beam B) coupled into the MZI neural network with mode mixing. (j) Identified Beam A and Beam B by backward far-field intensity pattern radiated by the 2D optical antenna array. (k) Measured BER curves of free-space multimode communications (Beam A and Beam B with mode mixing) with the beams unscrambled and separated by the photonic processor^[526].

Fig. 70. Structured light application in fiber-optic multimode communications with the silicon photonic processor^[729]. (a) Schematic configuration of fiber-optic multimode communication system with the reconfigurable integrated photonic processor. (b) Mode field profiles of the eigenmodes and LP modes in FMF. (c) Silicon multimode grating coupler. (d) Experimental setup for multimode communications. (e) Photograph of the photonic chip under test at the receiver side. (f) Measured eye diagrams for multimode communications with the photonic process inactive or active. (g) Measured BER curves with one mode on, two modes on, and three modes on^[729].

Fig. 71. Structured light application in arbitrary multimode communication with two silicon photonic processors^[730]. (a) Schematic configuration of an arbitrary optical system with M input and N output optical apertures in transmitters and receivers. (b) Photograph of the silicon photonic chip consisting of optical apertures and MZI mesh. (c) Simulated and (d) measured far-field shapes of multiple modes. (e) Performance characterization of a two-processor communication system by transmitting two intensity-modulated 5-Gbit/s OOK signals^[730].

Fig. 72. Structured light application in OAM-multiplexing holography for high-security encryption^[361]. (a) Design of a 10-bit OAM-multiplexing hologram. (b) OAM ciphertext generated by the 10-bit OAM multiplexed hologram. (c) OAM code chart consisting of 10 high-order OAM modes that could be used to reconstruct the 10 OAM-dependent digits based on the OAM ciphertext. (d) Holographic encryption and decryption. Two plaintext messages, “PSERX” and “TUXYL”, are decrypted as “please, receive” and “thank you, wife”, respectively, through the holographic reconstruction of the OAM ciphertext based on two sets of OAM keys, ℓ=(40,−20,40,−50,50,−10,40,−40,30,10) and ℓ=(30,50,30,40,30,10,30,−10,40,30), respectively^[361].

Fig. 73. Structured light application in holography encryption using metasurfaces^[554]. (a) Schematic of an OAM-multiplexing meta-hologram capable of reconstructing multiple distinctive OAM-dependent holographic images. (b) Schematic illustration of the angular momentum holography for optical nested encryption. The angular momentum holography depends on arbitrary superimposition of the SAM and OAM eigenstates in the output field. For the spin-orbital locked holography (SOLH), the reconstruction of the four holographic images “L, R, X, Y” depends on the incident light carrying certain SAM and OAM values (indicated as |σ,ℓ⟩). (c), (d) Top and side views of SEM images of the fabricated meta-hologram, with the scale bar of 1 µm. (e) Numerical and experimental reconstruction of the eight distinctive SOL holographic images through incident circularly polarized OAM beams with specific |σ,ℓ⟩^[554].

Fig. 74. Structured light application in 3D imaging using multi-wavelength dots array^[731]. (a) Schematic of the principle of projecting a multi-wavelength SL dot array by metasurface. (b) Side view and top view of a unit cell. (c) Simulation of the multi-wavelength diffraction patterns calculated using Rayleigh-Sommerfeld diffraction integral. (d) SEM image of the fabricated metasurface obtained using scanning electron microscopy. (e) Image of three areas on the measured sample. (f) Surface obtained by interpolating the point clouds of the wavelengths 405, 532, 633 nm, and multi-wavelength case. The white dashed lines represent the grooves^[731].

Fig. 75. Structured light application in medical imaging using needle beam and multifocal beam^[637,732]. (a) y–z profile of a Gaussian beam and needle beam (NB) with a focal spot size of 1.2 μm at 266 nm (left) and x–y profiles (right) at different z positions. Scale bar: 10 μm. (b) Experimental setup of the NB-PAM system. BS, beam sampler; PH, pinhole; CL, correction lens; UT, ultrasonic transducer; DAQ, data acquisition. (c) Simulated y–z projection images of uniformly distributed microspheres with a diameter of 7 μm show the difference between GB-PAM with a 0.16 numerical aperture (NA) and NB-PAM with a 0.16 NA and the 1000μm×2.3μm DOEs^[637]. (d) Multifocal metasurface composed of multiple phases of M foci via random spatial multiplexing. (e) Multifocal metasurfaces combine with a lens (L) to create hybrid lenses capable of generating multifocal beams. Simulation and experimental results of the multifocal beams are shown. (f) Volumetric imaging of normal human nasal skin by Gaussian with 42 Z-stacks, two-foci (2Foci-2) with 21 Z-stacks, and three-foci (3Foci) beams with 16 Z-stacks. The sample volume is 250μm×250μm×250μm (X×Y×Z)^[732].

Fig. 76. Structured light application in photo-induced force microscopy using tightly focused azimuthally polarized beam^[733]. (a) Schematic of the photo-induced force microscopy instrument. (b) Zoom-in region of the Si truncated cone working as photo-induced magnetic nanoprobe and its image in the glass slip (or substrate). The rotating arrows represent the excited electric field under the magnetic resonance condition, and the bold blue arrows show the directions of the probe and image magnetic dipoles mtip and mimg, respectively. (c) Two photo-induced magnetic polarized nanoparticles exerting a magnetic force on each other. (d)–(g) Focused ion beam images of the ‘‘on-state’’ Si truncated cone probe, ‘‘off-state’’ Si truncated cone probe, blunt Si probe, and sharp Si probe, respectively. (h)–(k) Corresponding measured force maps upon APB illumination from the bottom of the glass slip using the on-state Si truncated cone probe, off-state Si truncated cone probe, blunt Si probe, and sharp Si probe, respectively. The on-state probe (d) measures the solid-center circular spot (h) of the typical APB magnetic field^[733].

Fig. 77. Structured light application in three-dimensional topography using vortex beam^[734]. (a) Schematic of self-referenced spiral interference. (b) Spiral and (c) plane-wave interference patterns of the sample’s elevations. (d) Sampling points on the spiral interference fringe of the glass substrate’s elevations. (e) 2D and (f) 3D graphs of the recovered thickness of the glass substrate’s elevations. (g) Spiral and (h) plane-wave interference patterns of the sample’s depression. (i) Sampling points on the spiral interference fringe of the glass substrate’s depression. (j) 2D and (k) 3D graphs of the recovered thickness of the glass substrate’s depression^[734].

Fig. 78. Structured light application in 3D optical manipulation using the 2D Airy beam^[735]. (a) Schematic of generating a vertically accelerated 2D Airy beam by an all-dielectric cubic-phase metasurface. (b) Numerically calculated beam trajectory of a vertically accelerated 2D Airy beam along the u–z plane and the cross-section of intensity distribution at different propagation planes. (c) The deflection of the main lobe of a vertically accelerated 2D Airy beam is along the diagonal direction of the x–y plane, denoted as the u-direction. (d) Measured intensity distribution of the vertically accelerated 2D Airy beam in water along the propagation direction at different depths. Optical trapping dynamics of microspheres are observed using the vertically accelerated 2D Airy beam generated by the cubic-phase metasurface^[735].

Fig. 79. Structured light application in optical trapping using waveguide modes and optical phased array^{[736–738" target="_self" style="display: inline;">–738]}. (a) Schematic of an SWG waveguide. (b) Electric field distributions of TE polarization when light propagates along the SWG waveguide^[736]. (c) Intensity profiles and effective indices of three guided modes supported by a 510nm×248nm silicon waveguide at the telecom wavelength (1530 nm), which is calculated by the finite-element method. For each mode, the white arrow indicates the direction of the main component of the electric field. (d) Schematic of light coupling. (e) Horizontal and vertical cross-sections of the effective intensity distribution resulting from the co-propagation of TE0−TM0, TE0−TE1, and TM0−TE1 modes along a 10 µm-long portion of waveguide^[737]. (f) Conceptual diagram of the chip-based optical trapping system. A photonic chip emits a focused beam and traps a microsphere. (g) Simplified schematic of the integrated OPA architecture. (h) Measured cross-sectional intensity (in dB) above the photonic chip with top-down intensity shown in the plane of the chip (bottom) and at the focal plane (top). (i) Microscope image of the microspheres in the sample stage with superimposed tracks showing their motion over time (red lines). The motion of the microsphere located at the focal spot of the OPA (circled in white) is greatly reduced compared to its neighbors, indicating successful trapping^[738].

Fig. 80. Structured light application in chiral trapping using silicon-based slot waveguide^[739]. (a) Schematic of chiral trapping by the strongly confined standing evanescent fields in the gap of a slot waveguide. (b) The electric field intensity and (c) the imaginary part of the electromagnetic product (chirality) of the pseudo-transverse-magnetic (PTM) modes. (d)–(f) The resulting trapping force potentials and chiral-dependent trapping shifts in the gap of slot waveguides for (d) R enantiomers, (e) achiral particles, and (f) S enantiomers^[739].

Fig. 81. Structured light application in optical tweezer array^[740]. (a) Schematic representation of a typical holographic optical tweezer array. A collimated laser beam incident from the left is shaped by the DOE, transferred to the back aperture (B) of an objective lens by lenses L1 and L2, and focused into a trapping array. OP* denotes the plane conjugate to the trapping plane. The point B* is conjugated to B. The phase pattern on the lower left (black regions shift the phase by π) produces the traps shown in the lower right filled with 1-mm-diam silica spheres suspended in water. (b) Tiling a hologram encoding a 3×3 array of tweezers scales the spacing between tweezers without sacrificing resolution. Marginal numbers indicate the number of copies tiled into each side^[740].

Fig. 82. Structured light application in nanowires trapping and rotation^[741]. (a) Cross-section SEM image of silicon nanowires obtained after the wet etching of the silicon substrate. The image displays a dense and uniform distribution of nanowires, having approximately 6 µm length. The right image shows the transmission electron microscopy (TEM) characterization image of the top region of a silicon nanowire, showing a good uniformity and a diameter of D=78nm±16nm. (b) The nanowire is aligned parallel to the beam propagation axis. A clear orbital motion around the optical vortex is observed. (c) The nanowire is aligned perpendicularly to the beam propagation axis, and orbiting combined with a reorientation of the silicon nanowire resulting from the transfer of both SAM and OAM of light can be observed. (d) The simultaneous spinning and orbiting of a shorter nanowire are observed. Right parts of (b)–(d): cross-sections of the beam are shown with sketches of the trapped nanowire^[741].

Fig. 83. Structured light application in Doppler cloak by spinning OAM metasurface^[742]. (a) Experiment of Doppler cloak by a spinning OAM metasurface. A Doppler radar is moving with a linear speed and an OAM metasurface is spinning with an angular velocity, and these two motions are generating a linear Doppler shift and an opposite rotational Doppler shift, respectively. Consequently, a zero-frequency shift is obtained to demonstrate the Doppler cloak concept. (b) Measured spectrograms of an ℓ=−1 OAM metasurface in three types of motions: moving, spinning, and both moving and spinning^[742].

Fig. 84. Structured light application in quantum entanglement and logic gate^[743,744]. (a) Entanglement between spin and OAM on a single photon. (b) SEM image of the Si-based geometric phase metasurface. (c) Schematic of the experimental setup^[743]. (d) The transverse modes in a multimode photonic waveguide. Min and max in the scale bar represent the relative energy density. (e) Simulated light propagation in the designed transverse mode-dependent directional coupler. (f) Simulated light propagation in the designed multimode attenuator. (g) Schematic of the entire silicon photonic integrated circuit^[744].

Fig. 85. Structured light application in single-photon sources^[745]. (a) Schematic of the OAM single-photon source. Left: a SiO2-coated Ag substrate, supporting radial surface plasmon polaritons excited by a quantum emitter z-oriented dipole. Middle: a hydrogen silsesquioxane (HSQ) spiral grating, outcoupling surface plasmon polaritons into a well-collimated photon stream. Right: decomposed far-field RCP and LCP intensity profiles. (b) Analytical cross-sectional profiles of the far-field RCP and LCP components produced with radial surface plasmon polariton being outcoupled by a bullseye grating (left) and one-arm counterclockwise spiral grating (middle), and simulated Stokes parameter S3 of RCP and LCP components in the total field (right). (c) Schematic of the spiral gratings and their corresponding analytical phase distributions with different arm numbers of m, and decomposed far-field LCP and RCP intensity profiles normalized to the one-arm spiral grating. (d) Simulated phase windings in the far field for corresponding configurations. (e) SEM images of the fabricated OAM photon sources with arm numbers of m=−1, −3, and −5. Scale bars: 2 µm^[745].

Fig. 86. A summary of integrated structured light manipulation. Several aspects are summarized in terms of multiple materials, multiple working bands, multiple structured light types, multiple processing functions, multiple detection structures, and diverse application scenarios.

Fig. 87. Opportunities, challenges, and possible solutions for integrated structured light manipulation.

Fig. 88. A vision of integrated structured light manipulation.