## 5 Micro-LED Array-Based VLC  
As discussed in the earlier sections, \(\mu\)-LEDs exhibit potential for numerous applications, including VLC which is yet to be fully explored [66; 67]. The usefulness of GaN-based \(\mu\)-LEDs is due to their exceptional performance in terms of high brightness, high contrast, rapid response time, extended operational lifetime, and reduced power utilization [68]. Assemblies of \(\mu\)-LEDs, containing a large number of \(\mu\)-LED components, are usually referred as \(\mu\)-LED arrays. Optical power given out by a single \(\mu\)-LED is quite low due to its ultra-small emitting area. Output optical power can be enhanced by making use of many \(\mu\)-LED components assembled as an array. \(\mu\)-LED arrays can be prepared with both single- and multi-color emission [68; 69]. Multi-color \(\mu\)-LED arrays are quite common in research circles due to the fact that they have widespread scope of application in display technology [70; 71]. In the previous sections, we have discussed applications of only single LED or \(\mu\)-LED elements in VLC technology. In this section, we review works reporting the application of \(\mu\)-LED arrays in the field of VLC. Many applications, including visible light communication (VLC), demand for integration of multi-color emitters on a single chip, which can be realized by combining blue \(\mu\)-LEDs with a color-converting substance (called phosphor), thus facilitating down-conversion of the shorter emission wavelengths to longer ones. Color down-converters are not feasible for many applications owing to their lower efficiency, shorter operational lifetime and slower response time [72]. A solution to this issue is to grow blue, green and red emitters on materials, which suit them and consequently transfer them on a single, shared substrate. Traditional robotic system-based transfer techniques cannot be used to assemble \(\mu\)-LEDs as these techniques are not capable of handling micro-sized dices [73]. An alternative solution is the use of transfer printing along with the techniques to suspend releasable thin \(\mu\)-LED components [74]. VLC transmitters based on single wavelength GaN \(\mu\)-LEDs have been reported in the literature with multi-Gbps transmitting capacity [75; 76]. However, single chip \(\mu\)-LED arrays with multi-color emission have not been explored as VLC transmitters extensively. As a part of \(\mu\)-LEDs array for VLC applications, [PERSON] et al. [77] reported transfer printing-enabled on-chip GaN-based blue-green and blue-violet micro-LED arrays. In the work put forward by [PERSON] et al. [77], there is fabrication of dual-color \(\mu\)-LED arrays by combining blue \(\mu\)-LED platelets with violet and green \(\mu\)-LEDs through transfer printing. The optical characteristics of the \(\mu\)-LEDs for VLC application have been analyzed in the following section. The -6 dB electrical modulation bandwidths of violet, green and blue \(\mu\)-LEDs are measured and found to be 427 MHz, 144 MHz and 134 MHz, respectively, as shown in Figure 7a. Low bandwidth of green \(\mu\)-LED is a consequence of higher ratio of indium content in the active area, which gives rise to a stronger quantum confined Stark effect [78]. The lower bandwidth of blue \(\mu\)-LED is attributed to its larger pixel size and, which consequently results in low current density action. Both sets of \(\mu\)-LED arrays (i.e., blue-violet and blue-green arrays) have the capacity to operate as visible light communication (VLC) transmitters in two different set-ups named wavelength division multiplexing (WDM)1 and