Fig. 1. Summary of the review, which includes modulation bandwidth improvement, white light emitting diodes (WLED)-based visible light communication (VLC), micro light emitting diode (μLED) detector and applications of VLC towards 6G.Figure reproduced from: ref.^{96, 125, 154, 165}, American Chemical Society; ref.^{139, 153}, Chinese Laser Press; ref.^{161, 166}, OSA Open Access Publishing Agreement; ref.^{175, 184}, Optical Society of America.

Fig. 2. (a) Schematic of the samples’ structure. (b) J–V characteristics of samples. (c) Current densities of peak EQE, and the efficiency drop of samples. (d) Optical micrograph. (e) Power density and (f) junction temperature of the samples at different current densities. Figure reproduced with permission from: (a–c) ref.⁶¹, AIP Publishing; (d–f) ref.⁶⁴, AIP Publishing.

Fig. 3. (a) Transmission electron microscopy (TEM) image. (b) Three-dimensional schematic and (c) scanning electron microscopy (SEM) image of a µLED. (d) −3 dB bandwidth for different current densities. Schematics of fabrication for the growth of μLEDs on a high-electron-mobility transistor (HEMT) template. (e) Deposition of SiO₂. (f) Fabrication of SiO₂ microhole arrays. (g) Growth of μLEDs. (h) SiO₂ mask removal. (i) Modulation bandwidth and (j) electroluminescence (EL) spectra of device. Figure reproduced with permission from: (a–d) ref.⁹⁰, IEEE; (e–j) ref.¹⁰⁰, under a Creative Commons Attribution (CC-BY) License.

Fig. 4. (a) Bandwidth for devices with different crystal orientations. (b) Schematic and (c) frequency response of the nonpolar μLED. (d) Schematic diagram of semipolar (20–21) green μLED structures. (e) Time-resolved photoluminescence (TRPL) curves of semipolar μLED and c-plane μLED. (f) Frequency response of the semipolar μLED. (g) PR and (h) frequency responses of μLED array. (i) BER and signal-to-noise ratio at 4.5 Gbit/s transmission rate with different sampling rates. Figure reproduced with permission from: (a) ref.⁶⁵, AIP Publishing; (b, c) ref.¹⁰³, IEEE; (d–f) ref.⁹⁶, American Chemical Society; (g–i) ref.¹⁰⁹, Optica Publishing Group.

Fig. 5. (a) Schematic. (b) HRTEM image of the QWs. (c) Bandwidth of single chip WLED vs. injection current density. (d) Eye diagram at transmission rate of 50 and 127 Mbps. (e) TEM images of InGaN QDs. (f) –3 dB bandwidth and (g) BER at different current densities. Figure reproduced with permission from: (a–d) ref.¹¹⁸, Optica Publishing Group; (e–g) ref.⁹¹, ACS Publishing.

Fig. 6. SEM images of the nanowires after (a) QW and (b) p-GaN growth and (c) the fully fabricated nanowire μLED device. (d) −3 dB bandwidth of device. (e) TRPL of PLED and control LED. Figure reproduced with permission from: (a–d) ref.¹²⁵, American Chemical Society; (e) ref.¹²⁹, American Chemical Society.

Fig. 7. (a) Schematic diagram of WLED device based on semipolar μLED array. (b) Photographs of the μLED array without current. (c) Spectrum of the WLED. (d) Measured normalized frequency response of μLED array. (e) BER curve of the white-light VLC system. Figure reproduced with permission from: (a–e) ref.⁸⁷, under the Optica Open Access Publishing Agreement.

Fig. 8. (a) White-light VLC system consisting of perovskite quantum dot (PQD) and blue μLED. (b) The longevity of the PL properties of the PNCs. (c) Frequency response of the PNC-μLED. (d) TRPL measurement for semipolar μLED, PQD and CdSe QD papers. (e) Frequency response of PQD paper and PQD film. (f) TEM images of RQDs. (g) TRPL measurement for YQDs and RQDs. (h) Frequency response of red and yellow PNC-PMMA. Figure reproduced with permission from: (a) ref.¹⁵², American Chemical Society; (b, c) ref.¹³⁹, American Chemical Society; (d, e) ref.¹⁵³, Optica Publishing Group; (f–h) ref.¹⁵⁴, American Chemical Society.

Fig. 9. (a) Composition of WLED active region. (b) The distribution analysis of In components in QWs. (c) Modulation bandwidths of different sizes µLEDs. (d) Power spectra of OFDM-modulated waveforms measured at data rates of 4.42 Gbps, 3.72 Gbps, and 336 Mbps. (e) Constellations under corresponding order QAM modulation. Figure reproduced with permission from: (a–c) ref.¹⁶¹, under the OSA Open Access Publishing Agreement; (d, e) ref.¹⁶², under a Creative Commons Attribution (CC-BY) License.

Fig. 10. (a) Cross-section of the μLED and schematic setup for VLC system using the μLED based photodetectors. (b) Current–voltage (I–V) curves of the μLED-based PD with diameters of 60 μm under darkness and illumination. (c) Responsivities of the μLED-based PD measured for various laser wavelengths. (d) Frequency response for μLED-based PD. (e) Eye diagrams at a transmission rate of 160 Mbps. (f) Cross-section of semipolar green μLEDs. (g) Frequency responses of μLED PD. (h) BERs with μLEDs as PD at a transmission rate of 540 Mbps. Figure reproduced with permission from: (a–e) ref.¹⁶⁵, American Chemical Society; (f–h) ref.¹⁶⁶, under the OSA Open Access Publishing Agreement.

Fig. 11. (a) Schematic of setup and (b) photograph and (c) frequency responses of the μLED-based UOWC system. (d) Light output power (LOP) and forward current characteristics of the μLED-on-HEMT arrays. Figure reproduced with permission from: (a–c) ref.¹⁷⁵, under a Creative Commons Attribution license; (d) ref.¹⁷⁶, under a Creative Commons Attribution License.

Fig. 12. (a) Schematic of the VLC system based on μLED and ANN equalizers. (b) Schematic of the arrangement of pilots. (c) BER in simulation with different pilot lengths. BER performance for (d) 50- and (e) 75-µm blue μLEDs. Figure reproduced with permission from ref.¹⁸⁴, Optical Society of America.