Fig. 1. Schematic illustration of physical dimension resources of photons (wavelength/frequency, time, complex amplitude, polarization, space domain) and manipulating the space domain of lightwaves for structured light field (spatial amplitude, spatial phase, spatial polarization) and space array (spatial position)

Fig. 2. A summary of structured light generation methods

Fig. 3. Schematic illustration of structured light coding/decoding communications. (a) OAM mode coding/decoding communications; (b) vector mode coding/decoding communications

Fig. 4. Classification of structured light coding/decoding communications

Fig. 5. Experimental setup for free-space OAM coding/decoding communications[109]

Fig. 6. Experimental results for free-space OAM coding/decoding communications[109]

Fig. 7. Concept and principle diagram of free-space m-ary coding/decoding communications using Bessel beams[113]

Fig. 8. Measured results for free-space m-ary coding/decoding communications using Bessel beams without obstruction[113]. (a) Coding for hexadecimal numbers with 16 Bessel beams (Δ?=2); (b) intensity profiles of decoded Bessel beams of ?=-7 (hexadecimal number 4), ?=-1 (hexadecimal number 7), and ?=15 (hexadecimal number 15)

Fig. 9. Measured results for free-space m-ary coding/decoding communications using Bessel beams under different conditions[113]. (a) With obstruction; (b) with deviated obstruction

Fig. 10. Experimental bit-error rate for hexadecimal and 32-ary coding/decoding communications using Bessel beams without obstruction, with deviated obstruction, and with obstruction, respectively[113]

Fig. 11. Concept and principle diagrams of (a) high-speed mode coding/decoding communications and (b) mode hopping communications based on OAM modes[114]

Fig. 12. Experimental setup for high-speed OAM mode coding/decoding communications and OAM mode hopping communications[114]. (a) Schematic of setup; (b) intensity profiles and interferograms of OAM modes; (c) offline digital signal processing for data recovery

Fig. 13. Experimental results for high-speed OAM mode coding/decoding communications (20 Gbit·s-1)[114]. (a) Normalized waveforms at the output of the optical switch; (b) eye diagrams at the output of the optical switch; (c) received normalized waveforms when using the OAM mode set {-3, -1, +1, +3}; (d) received normalized waveforms when using the OAM mode set {0, 1, 2, 3}

Fig. 14. Experimental results for OAM mode hopping communications[114]

Fig. 15. Concept and principle diagram of high-speed coding/decoding communications using Bessel beams assisted by atmospheric turbulence compensation[119]

Fig. 16. Experimental results for high-speed coding/decoding communications using Bessel beams assisted by atmospheric turbulence compensation[119]. (a) Phase masks for generating Bessel beams; (b) intensity distributions of input Bessel beams without turbulence; (c) intensity distributions for various Bessel beams before compensation with turbulence; (d) intensity distributions for various Bessel beams after compensation with turbulence; (e) phase masks for emulating moderate atmospheric turbulence; (f)

Fig. 17. Experimental setup for high-speed OAM mode coding/decoding communications in conventional multi-mode fiber

Fig. 18. Concept and principle diagram of high-speed OAM mode coding/decoding communications using photonic integrated circuits

Fig. 19. (a) Concept and (b) principle diagram of hybrid mode coding/decoding communications using LP mode and OAM mode in few-mode fiber[123]

Fig. 20. Experimental results for image transfer using four hybrid spatial modes (LP01, LP11a, LP11b and OAM-1) coding/decoding communications in 1.1 km few-mode fiber[123]

Fig. 21. Transmitted and received grayscale images using four hybrid spatial modes (LP01, LP11a, LP11b and OAM-1) coding/decoding communications in 1.1 km few-mode fiber[123]

Fig. 22. Experimental results for coding/decoding communications using two OAM modes (OAM+1 and OAM-1) in 1.1-km few-mode fiber[123]

Fig. 23. Transmitted and received grayscale images using two OAM modes (OAM+1 and OAM-1) coding/decoding communications in 1.1-km few-mode fiber[123]

Fig. 24. Concept and principle diagram of high-base (e.g. quaternary) vector beam coding/decoding communications[134]

Fig. 25. (a) Experimental setup for visible light high-base vector beam coding/decoding communications; (b) phase pattern loaded onto the SLM to generate a vector beam (P=3, ?0=0); (c) intensity distribution of the detected vector beam captured by a camera (P=3, ?0=0) after demodulation[134]

Fig. 26. 64 pixel×64 pixel Lena gray image transfer achieved by visible light high-base vector beam coding/decoding communications[134]

Fig. 27. Experimental setup for 3 km free-space coding/decoding communications using superposed OAM modes[135]

Fig. 28. Experimental results for free-space 3 km coding/decoding communications using superposed OAM modes[135]. (a) Measured cross talk matrix for 16 superposed OAM modes; (b) transmitted and received two grayscale images by superposed OAM modes coding/decoding communications

Fig. 29. Experimental setup and scene for free-space 143 km superposed OAM modes coding/decoding communications[136]. (a) Schematic diagram of the setup; (b) photo of the sender taken during extremely turbulence conditions; (c) long-time exposure photo showing an OAM superposition of ?=±1 being transmitted over the two islands

Fig. 30. Measured results for free-space 143-km superposed OAM modes coding/decoding communications[136]. (a)-(d) Received different superposed OAM modes; (e)-(h) received different pure OAM modes

Fig. 31. Concept and principle diagram of OAM mode array coding/decoding communications[137]

Fig. 32. Received OAM mode array intensity distribution before demodulation, the loaded complex phase mask, and the intensity distribution of the spatial array after demodulation[137]

Fig. 33. Measured results for image transfer using OAM mode array coding/decoding communications[137]. (a) Original image with 150×150 pixels (256 different grayscale values for each pixel); (b) recovered image after transmission when the correlation length r0 of the turbulence phase mask is 3 mm; (c) recovered image after transmission when the correlation length r0 of the turbulence phase mask is 1 mm

Fig. 34. Concept and principle diagram of ultra-high density polarization array coding/decoding communications

Fig. 35. Future trend and perspective of structured light coding/decoding communications