Fig. 1. (a) Schematic of GaN-based series connection micro-LED array. (b) Plan-view SEM image of the 20-μm blue GaN-based series connection micro-LED array. (c) Plan-view optical micrograph images of the series connection micro-LED arrays.

Fig. 2. Current versus voltage curves for (a) 20-μm violet, (b) 20-μm blue, (c) 20-μm green, and (d) 40-μm yellow micro-LED arrays with 1, 4, 6, and 9 pixels in series, respectively.

Fig. 3. Light output power versus current density curves for (a) 20-μm violet, (b) 20-μm blue, (c) 20-μm green, and (d) 40-μm yellow micro-LED arrays with 1, 4, 6, and 9 pixels in series, respectively.

Fig. 4. Emission spectra of the (a) 20-μm 3×3 violet micro-LED array, (b) 20-μm 3×3 blue micro-LED array, (c) 20-μm 3×3 green micro-LED array, and (d) 40-μm 2×2 yellow micro-LED array versus current density. Insets are the microscope images of the yellow micro-LED array at different current densities. (e) The spectra of the four micro-LED arrays used for high-speed long-distance WDM communication.

Fig. 5. (a) The modulation bandwidths versus pixel numbers of the GBYV micro-LEDs under the same injection current density. (b) The frequency responses of the series-biased GBYV micro-LED arrays under the specific current density for VLC measurement. (c) The microwave reflectance (S11) parameters of blue micro-LED arrays with different numbers of pixels in series under the current density of 4  kA/cm2 plotted on the Smith chart from 10 MHz to 1 GHz. (d) The impedance magnitude versus frequency of 20-μm blue micro-LED arrays with different numbers of pixels in series under the current density of 4  kA/cm2.

Fig. 6. Schematic of the experimental setup for the multicolor series connection micro-LED arrays-based long-distance VLC system.

Fig. 7. (a) Light output powers of the 20-μm 3×3 violet micro-LED array at the current density of 6  kA/cm2 and the 20-μm 3×3 blue micro-LED array at the current density of 4  kA/cm2 as a function of operating time. (b) The received average SNR as a function of VPP for the four micro-LED arrays.

Fig. 8. SNR distributions, bit allocations, and power ratios versus frequency for (a) 400-nm, (b) 451-nm, (c) 50-nm, and (d) 556-nm channels.

Fig. 9. Power spectra for (a) 400-nm, (b) 451-nm, (c) 509-nm, and (d) 556-nm channels.

Fig. 10. (a) Constellation plots for the 400-nm channel including the 4, 8, 16, 32, 64, and 128 QAMs. (b) SNR distributions of the 20-μm violet single-pixel and series connection devices under the current density of 6  kA/cm2 before preequalization.

Table 1. Summary of LED-Based WDM-OWC Systems with the Aggregate Data Rate over 10 Gbps in Recent Years

Table 2. Performances of Blue Micro-LED Arrays with Different Pixel Sizes and Different Operating Current Densities