Fig. 1. Schematic of electromagnetic spectrum

Fig. 2. Wireless communication system model

Fig. 3. Phase front, transverse phase distribution, and intensity profile of OAM modes with different topological charges

Fig. 4. Multiplexing many channels (with OAM channel) on the same frequency through radio vorticity^[67]. (a) Experimental site; (b) experimental schematic diagram

Fig. 5. High-capacity millimeter-wave communications with OAM multiplexing^[33]. (a) Concept diagram; (b) received constellations of 1 Gbaud QPSK signals; (c) measured BER curves for millimeter-wave OAM modes

Fig. 6. High-capacity access network architecture using integrated W-band wireless and free-space optical links with OAM multiplexing^[72]. (a) Architecture diagram; (b) experimental setup; (c) BER performance

Fig. 7. Utilizing multiplexing of structured THz beams carrying OAM for high-capacity communications^[69]. (a) Schematic diagram; (b) measured normalized crosstalk; (c) measured BERs for all 8-multiplexed channels under different SNRs

Fig. 8. Mid-infrared OAM mode encoding and decoding for image transmission^[76]. (a) Experimental setup for the generation and detection of LG modes; (b) beam patterns of produced LG modes and their decomposition results; (c) information transmission using spatial modes of light

Fig. 9. Free-space optical communication systems based on mid-infrared WDM and OAM-based MDM^[77]. (a) Concept diagram; (b) intensity distribution, interference pattern, and normalized crosstalk matrix; (c) experimental setup; (d) measured BER vs OSNR for different spatial modes under single and multiple wavelengths

Fig. 10. Mid-infrared OAM free-space optical communications^[78]. (a) Concept diagram; (b) atmospheric transmission characteristics of different wavelengths (2 transmission windows in the mid-infrared region); (c) modulation and detection methods for two types of mid-infrared beams

Fig. 11. Terabit free-space data transmission employing OAM multiplexing^[94]. (a) Concept and principle; (b) block diagram of experimental setup

Fig. 12. Experimental results for terabit free-space data transmission employing OAM multiplexing^[94]. (a) Transmission of 16-QAM signals over polarization multiplexed OAM beams; (b) data exchange between 100 Gbit/s DQPSK-carrying OAM beams

Fig. 13. N-dimensional multiplexing link with 1.036 Pbit/s transmission capacity and 112.6 (bit/s)/Hz spectral efficiency using OFDM-8QAM signals over 368 WDM polarization multiplexed 26 OAM modes^[95]. (a)‒(g) Measured intensity profiles and phase patterns loaded onto SLMs

Fig. 14. Experimental results for N-dimensional multiplexing link with 1.036 Pbit/s transmission capacity and 112.6 (bit/s)/Hz spectral efficiency^[95]. (a) Measured power distribution; (b) BER performance for single wavelength; (c) BER and Q values for various OAM modes and polarization states over all 368 WDM channels

Fig. 15. N-dimensional multiplexing and modulation link with ultra-high spectral efficiency ^[96]. (a) Conceptual diagram; (b) conversion from Gaussian beams to OAM beams and back-conversion to Gaussian-like beams; (c) experimental setup

Fig. 16. Experimental results for N-dimensional multiplexing and modulation link with ultra-high spectral efficiency ^[96]. (a) BER performance and constellations; (b) measured BER of all 104 channels

Fig. 17. Secure optical interconnects using OAM beams multiplexing and multicasting^[108]. (a) Concept and principle; (b) experimental setup

Fig. 18. Experimental results for secure optical interconnects using OAM beams multiplexing and multicasting^[108]. (a) BER performance for multiplexing communications; (b) BER performance for multicasting communications

Fig. 19. Vortex light communications through turbulent air^[109]. (a) Experimental setup; (b) transmission of greyscale images

Fig. 20. Experimental demonstration of an underwater wireless optical communication link employing OAM modes and fast auto-alignment system^[110]. (a) Measured intensity profiles; (b) influence of fast auto-alignment system on beam position stability and system BER performance

Fig. 21. Multi-dimensional LDPC-coded OAM modulation scheme^[119]. (a) Spatial intensity distributions for OAM modes with p=0; (b) N-dimensional OAM transmitter architecture; (c) N-dimensional OAM receiver architecture

Fig. 22. OAM-based hybrid FSO-THz multi-dimensional encoding modulation and physical-layer security^[122]. (a) Hybrid FSO-THz physical-layer security scheme; (b) example of hybrid networks; (c) BER performance

Fig. 23. Detecting OAM of light in satellite-to-ground quantum communications^[123]. (a) System settings; (b) detection probabilities; (c) crosstalk matrix with adaptive optics

Fig. 24. Analysis of OAM communication in complex satellite-to-earth environment^[121]. (a) Satellite-to-earth OAM-QKD system model; (b) modeling of the atmospheric channel from satellite to earth; (c) schematic diagram of the satellite-to-earth OAM-QKD system

Fig. 25. Ultra-high capacity optical satellite communication system using OAM beams^[120]. (a) General architecture of an optical satellite communication link; (b) system configuration of the optical satellite communication system

Fig. 26. Free-space high-dimensional structured light coding/decoding communications free of obstructions^[124]. (a) Concept and principle; (b) measured transverse intensity profiles; (c) measured BER

Fig. 27. High-base vector beam encoding/decoding communications^[125]. (a) Concept and principle; (b) intensity profiles; (c) experimental results for gray image transmission

Fig. 28. Demonstration of high-speed Bessel beam encoding/decoding link with adaptive turbulence compensation^[126]. (a) Concept and principle; (b) experimental setup; (c) fork phase patterns and measured intensity profiles of Bessel beams

Fig. 29. Experimental results for high-speed Bessel beam encoding/decoding link^[126]. (a) BER performance; (b) eye diagram of back-to-back Ch I; (c) eye diagram of Ch I before compensation; (d) eye diagram of Ch I after compensation; (c) temporal waveforms of Ch I and Ch II

Fig. 30. Challenges and prospects of vortex electromagnetic wave wireless communications