## 5 Micro-LED Array-Based VLC
\begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Research Team** & **LED type** & **Drive Current** & **Bandwidth** & **Data Rate** \\ \hline [PERSON] et al. [57] & (11-22) InGaN/GaN blue LED & 4 mA & 1030 MHz & 2.4 Gbps \\  & (20-21) InGaN/GaN green LED & & & \\ [PERSON] et al. [60] & (11-22) InGaN/GaN green & 40 mA & 756 MHz & 1.5 Gbps \\ [PERSON] et al. [59] & LED & & & \\  & (11-22) InGaN/GaN blue & 92 A/cm\({}^{2}\) & 540 MHz & — \\ [PERSON] et al. [62] & LED & & & \\  & (20-2-1) InGaN/GaN super & 20 mA & 150 MHz & 300 Mbps \\ [PERSON] et al. [63] & luminescent diode & & & \\ [PERSON] et al. [64] & (11-22) green LED on GaN template & 600 mA & 560 MHz & — \\  & (20-21) white InGaN LED on & & & \\ [PERSON] et al. [65] & GaN/Sapphire template & 30 mA & 100 MHz & — \\  & & 2 kA/cm\({}^{2}\) & 660 MHz & — \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the reported device performance of the semipolar LED-based Visible Light Communication (VLC) system. WDM2, and the details of which can be found in [77]. In the first set-up, i.e., WDM1, two different streams of input signals are sent using \(\upmu\)-LED channels where one of them is received and demodulated by the optical receiver, and the other simply acts as an interference signal. In the second scheme called WDM2, light from the \(\upmu\)-LED arrays is focused to two dichroic mirrors at an angle of 45 degrees, and the mirrors split the input beam into two separate parts by transmitting one portion of it and by reflecting the other portion. The WDM2 scheme makes it possible to receive signals from both the channels at the same time, though dichroic mirrors cause some power loss to the input signal as a tradeoff. Some characteristic parameters of a communication system like BER, signal-to-noise ratio (SNR), and data rate are calculated for this set-up. The BERs for the blue and green \(\upmu\)-LEDs system as well as blue and violet \(\upmu\)-LEDs system in both WDM set-ups are plotted as a function of the data transmission rate, as shown in Figure 7b,c. In the WDM1 configuration, below the forward error correction (FEC) threshold, the blue and green \(\upmu\)-LEDs will achieve a maximum data rate of 1261 and 667 Mbps, respectively. The maximum data rates for blue and green \(\upmu\)-LEDs below the FEC threshold decreased to 1245 and 410 Mbps, respectively, in the WDM2 configuration. Similarly, for the blue and violet \(\upmu\)-LEDs, the maximum data rate in the WDM1 set-up can reach up to 1130 and 2472 Mbps, respectively, below FEC threshold, while their maximum data rates below FEC threshold in the WDM2 set-up decrease to 842 and 1309 Mbps, respectively. Figure 8 display the SNR for blue-green \(\upmu\)-LED array as well as blue-violet \(\upmu\)-LED array in both WDM set-ups at the highest rate. It can be seen from Figure 8a,b that the blue \(\upmu\)-LED channel shows a higher SNR as compared to the green \(\upmu\)-LED channel due to its higher optical power. Moreover, the SNR curves for the blue channel in both WDM set-ups shows a similar nature, however, the SNR curve for the green channel in WDM2 drops severely when the frequency exceeds 150 MHz as compared  
Figure 7: (**a**) -6 dB modulation bandwidth for violet, green and blue \(\upmu\)-LEDs as a function of current density; (**b**) bit error rate (BER) versus data rate for blue and green \(\upmu\)-LEDs in both wavelength division multiplexing (WDM) schemes; (**c**) BER versus data rate for blue and violet \(\upmu\)-LEDs in both WDM schemes. [77] Figures reproduced with permission from Optical Society of America. to that of the WDM1 set-up, which is attributed to optical power loss of about 25 % resulting from the dichroic mirror used in the WDM2 set-up. However, when it comes to the blue and violet \(\upmu\)-LED channels, as shown in Figure 8c,d, the SNRs curves for both channels are quite similar because of comparable optical power. Like blue-green transmitters, SNR values for blue-violet \(\upmu\)-LED arrays are observed to be well above the FEC threshold.