Fig. 1. Schematic of Si-substrate LED vertical structure of the three samples with SL period numbers of 8, 15, and 32.

Fig. 2. (a) Schematic of the V-pits and carrier transportation situation for Samples A–C. SEM images of the MQW layer for three LED samples with SL period numbers of (b) 8, (c) 15, and (d) 32.

Fig. 3. Optoelectronic characteristics of LED Samples A, B, and C. (a) Light output power–current–voltage (L-I-V) characteristics under a CW injection current. (b) EQE under different currents. (c) Luminous efficacy under different currents.

Fig. 4. Electroluminescence (EL) spectra of Samples A, B, and C under various currents.

Fig. 5. Schematic of (a) the bracket and internal circuit structure and (b) layout for the WDM-LED array chip. (c) Graph of the packaged 4×4 WDM-LED array chip. (d) Magnified micrograph of every LED pixel.

Fig. 6. (a) CIE diagram of 16 LED pixels under the current of 100 mA. (b) L-I-V characteristics and relative optical power for 16 LED pixels in the WDM-LED array chip.

Fig. 7. (a) Upper: flow block diagram of the digital signal processing (DSP) in our VLC system. Lower: experimental setup of the VLC system. (b) Block diagram of the principle of the MLC algorithm. (AWG, arbitrary waveform generator; OSC, oscilloscope; DMT Mod., DMT modulation; DMT Demod., DMT demodulation; ZF Equ., zero-forcing equalization.)

Fig. 8. VLC performance of LED Samples A, B, and C. (a) −10-dB bandwidth after hardware pre-equalization. (b) Estimated SNR of the three samples versus frequency. (c) Data rate and BER versus bandwidth for LED Samples A–C.

Fig. 9. Schematic of intensity modulation of LEDs with different resistance (R) and EQE (E) to explain the data rate gain from LED’s relatively more SL periodicity. (V0, the bias voltage; Lc, the bias optical power; I, current; V, voltage; L, light output power.)

Fig. 10. SNR, allocated bit number, and power ratio versus subcarrier for eight LED channels when BPL-DMT modulation is utilized.

Fig. 11. (a) Data rates versus bandwidth; (b) maximum data rates and BER for eight LED channels. (λ1: 456  nm, λ2: 480  nm, λ3: 500  nm, λ4: 526  nm, λ5: 556  nm, λ6: 583  nm, λ7: 631  nm, λ8: 660  nm.)

Fig. 12. Data rates versus bandwidths in a 20-m VLC link. Inset: the received QAM signal diagrams at the data rate of 2.02 Gbps.

Table 1. Recent Achievements Applying WDM-LEDs