Tingwei Lu, Xiangshu Lin, Wenan Guo, Chang-Ching Tu, Shibiao Liu, Chun-Jung Lin, Zhong Chen, Hao-Chung Kuo*, and Tingzhu Wu**
Fig. 1. Summary of the review, which includes modulation bandwidth improvement, white light emitting diodes (WLED)-based visible light communication (VLC), micro light emitting diode (μLED) detector and applications of VLC towards 6G.Figure reproduced from: ref.
96, 125, 154, 165, American Chemical Society; ref.
139, 153, Chinese Laser Press; ref.
161, 166, OSA Open Access Publishing Agreement; ref.
175, 184, Optical Society of America.
Fig. 2. (
a) Schematic of the samples’ structure. (
b) J–V characteristics of samples. (
c) Current densities of peak EQE, and the efficiency drop of samples. (
d) Optical micrograph. (
e) Power density and (
f) junction temperature of the samples at different current densities. Figure reproduced with permission from: (a–c) ref.
61, AIP Publishing; (d–f) ref.
64, AIP Publishing.
Fig. 3. (
a) Transmission electron microscopy (TEM) image. (
b) Three-dimensional schematic and (
c) scanning electron microscopy (SEM) image of a µLED. (
d) −3 dB bandwidth for different current densities. Schematics of fabrication for the growth of μLEDs on a high-electron-mobility transistor (HEMT) template. (
e) Deposition of SiO
2. (
f) Fabrication of SiO
2 microhole arrays. (
g) Growth of μLEDs. (
h) SiO
2 mask removal. (
i) Modulation bandwidth and (
j) electroluminescence (EL) spectra of device. Figure reproduced with permission from: (a–d) ref.
90, IEEE; (e–j) ref.
100, under a Creative Commons Attribution (CC-BY) License.
Fig. 4. (
a) Bandwidth for devices with different crystal orientations. (
b) Schematic and (
c) frequency response of the nonpolar μLED. (
d) Schematic diagram of semipolar (20–21) green μLED structures. (
e) Time-resolved photoluminescence (TRPL) curves of semipolar μLED and c-plane μLED. (
f) Frequency response of the semipolar μLED. (
g) PR and (
h) frequency responses of μLED array. (
i) BER and signal-to-noise ratio at 4.5 Gbit/s transmission rate with different sampling rates. Figure reproduced with permission from: (a) ref.
65, AIP Publishing; (b, c) ref.
103, IEEE; (d–f) ref.
96, American Chemical Society; (g–i) ref.
109, Optica Publishing Group.
Fig. 5. (
a) Schematic. (
b) HRTEM image of the QWs. (
c) Bandwidth of single chip WLED vs. injection current density. (
d) Eye diagram at transmission rate of 50 and 127 Mbps. (
e) TEM images of InGaN QDs. (
f) –3 dB bandwidth and (
g) BER at different current densities. Figure reproduced with permission from: (a–d) ref.
118, Optica Publishing Group; (e–g) ref.
91, ACS Publishing.
Fig. 6. SEM images of the nanowires after (
a) QW and (
b) p-GaN growth and (
c) the fully fabricated nanowire μLED device. (
d) −3 dB bandwidth of device. (
e) TRPL of PLED and control LED. Figure reproduced with permission from: (a–d) ref.
125, American Chemical Society; (e) ref.
129, American Chemical Society.
Fig. 7. (
a) Schematic diagram of WLED device based on semipolar μLED array. (
b) Photographs of the μLED array without current. (
c) Spectrum of the WLED. (
d) Measured normalized frequency response of μLED array. (
e) BER curve of the white-light VLC system. Figure reproduced with permission from: (a–e) ref.
87, under the Optica Open Access Publishing Agreement.
Fig. 8. (
a) White-light VLC system consisting of perovskite quantum dot (PQD) and blue μLED. (
b) The longevity of the PL properties of the PNCs. (
c) Frequency response of the PNC-μLED. (
d) TRPL measurement for semipolar μLED, PQD and CdSe QD papers. (
e) Frequency response of PQD paper and PQD film. (
f) TEM images of RQDs. (
g) TRPL measurement for YQDs and RQDs. (
h) Frequency response of red and yellow PNC-PMMA. Figure reproduced with permission from: (a) ref.
152, American Chemical Society; (b, c) ref.
139, American Chemical Society; (d, e) ref.
153, Optica Publishing Group; (f–h) ref.
154, American Chemical Society.
Fig. 9. (
a) Composition of WLED active region. (
b) The distribution analysis of In components in QWs. (
c) Modulation bandwidths of different sizes µLEDs. (
d) Power spectra of OFDM-modulated waveforms measured at data rates of 4.42 Gbps, 3.72 Gbps, and 336 Mbps. (
e) Constellations under corresponding order QAM modulation. Figure reproduced with permission from: (a–c) ref.
161, under the OSA Open Access Publishing Agreement; (d, e) ref.
162, under a Creative Commons Attribution (CC-BY) License.
Fig. 10. (
a) Cross-section of the μLED and schematic setup for VLC system using the μLED based photodetectors. (
b) Current–voltage (I–V
) curves of the μLED-based PD with diameters of 60 μm under darkness and illumination. (
c) Responsivities of the μLED-based PD measured for various laser wavelengths. (
d) Frequency response for μLED-based PD. (
e) Eye diagrams at a transmission rate of 160 Mbps. (
f) Cross-section of semipolar green μLEDs. (
g) Frequency responses of μLED PD. (
h) BERs with μLEDs as PD at a transmission rate of 540 Mbps. Figure reproduced with permission from: (a–e) ref.
165, American Chemical Society; (f–h) ref.
166, under the OSA Open Access Publishing Agreement.
Fig. 11. (
a) Schematic of setup and (
b) photograph and (
c) frequency responses of the μLED-based UOWC system. (
d) Light output power (LOP) and forward current characteristics of the μLED-on-HEMT arrays. Figure reproduced with permission from: (a–c) ref.
175, under a Creative Commons Attribution license; (d) ref.
176, under a Creative Commons Attribution License.
Fig. 12. (
a) Schematic of the VLC system based on μLED and ANN equalizers. (
b) Schematic of the arrangement of pilots. (
c) BER in simulation with different pilot lengths. BER performance for (
d) 50- and (
e) 75-µm blue μLEDs. Figure reproduced with permission from ref.
184, Optical Society of America.
Year | Light source | Modulation bandwidth | Transmission rate | Ref. | 2022 | c-plane green μLED (525 nm) | 1.31 GHz | 6 Gbps | ref.86 | 2022 | Semipolar blue μLED (447 nm), yellow phosphor | 849 MHz | 2.8 Gbps | ref.87 | 2022 | c-plane blue μLED (450 nm) | 880 MHz | 1.1 Gbps | ref.88 | 2022 | c-plane red μLED (652 nm) | 271 MHz | 350 Mbps | ref.31 | 2022 | Nonpolar blue μLED (463 nm) | 991 MHz | 2 Gbps | ref.89 | 2022 | c-plane blue μLED (475 nm) | 1.53 GHz | 5.27 Gbps | ref.90 | 2022 | Green quantum dot (QD) LED (495 nm) | 1.22 GHz | 2.1 Gbps | ref.91 | 2021 | Semipolar green μLED (550 nm) | 1.1 GHz | 4.3 Gbps | ref.92 | 2021 | Green QD-LED (550 nm) | 1.3 GHz | none | ref.93 | 2021 | c-plane blue μLED (450 nm) | 251 MHz | 660 Mbps | ref.94 | 2021 | c-plane blue μLED (467 nm) | 1.3 GHz | 2 Gbps | ref.95 | 2020 | Semipolar green μLED (525 nm) | 775 MHz | 1.5 Gbps | ref.96 |
|
Table 1. Summary of research progress in the VLC system based on μLED