Fig. 1. Recent advances in nitride-based LED and LD-based VLC^[23,24]. Modified from the work presented in Refs. [20,22].

Fig. 2. Recent research progress in UWOC^{[27,28,31–40" target="_self" style="display: inline;">–40]}.

Fig. 3. Typical spectral response of Si-based photodetector.

Fig. 4. Recent advances in III-nitride-based LDs and SLD for enabling high data rate VLC systems^{[11,12,15,42–51" target="_self" style="display: inline;">–51]}.

Fig. 5. (a) Electroluminescence emission spectrum of the semipolar violet-emitting LD at an injection current of 400 mA. (b) Schematic of the small-signal modulation response measurement setup. (c) Small-signal modulation response of the violet-emitting LD at an injection current of 400 mA. The LD shows a −3dB modulation bandwidth of ∼3.1GHz. (d) Comparison of modulation bandwidth in commercial LEDs and LDs^[11].

Fig. 6. Comparison of photocurrent versus wavelength spectra in (a) semipolar (202¯1¯) and (b) c-plane (0001) InGaN/GaN QW modulators^[47].

Fig. 7. (a) Three-dimensional (3D) illustration of the 405 nm emitting dual-section SOA-LD on a semipolar GaN substrate. The device involves four pairs of In0.1Ga0.9N/GaN MQWs as the active region and a pair of InGaN separate confinement heterostructure (SCH) waveguide layers. The lengths of the SOA and LD are 300 and 1190 µm, respectively. (b) Effective gain versus laser current relationship of the dual-section SOA-LD at different SOA bias values (VSOA)^[88].

Fig. 8. Comparison of output power versus current in the LD and photocurrent from the WPD at zero bias versus current in the LD^[91].

Fig. 9. (a) 405 nm SLD grown on semipolar (202¯1¯) GaN substrates with tilted facet configuration. (b) Electroluminescence spectra of SLD in comparison with the LD and LED at constant current injection. (c) BER versus data rate for OOK-modulated SLD-based VLC. Inset shows the corresponding eye diagrams at different data rates^[47].

Fig. 10. Emission spectrum of Ce-doped yttrium aluminum garnet (YAG:Ce3+) phosphor for different chemical compositions^[42].

Fig. 11. (a) Measured frequency response of the perovskite-based VLC system. (b) BER of the perovskite-based VLC system at different data rates and the eye diagram of 2 Gbps data rate showing a clear open eye^[12].

Fig. 12. Signal waveforms of different modulation techniques: (a) NRZ-OOK and (b) RZ-OOK.

Fig. 13. Constellation diagrams of (a) 4-PSK, (b) 8-PSK, (c) 4-QAM, and (d) 16-QAM.

Fig. 14. OFDM transmission and reception block diagram^[118,124].