Author Affiliations
1Beijing National Research Center for Information Science and Technology (BNRist), Department of Electronic Engineering, Tsinghua University, Beijing 100084, China2Tsinghua-Berkeley Shenzhen Institute (TBSI), Tsinghua University, Shenzhen 518055, China3Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China4Institute of Electronics Engineering, Taiwan Tsing Hua University, Hsinchu 30013, Taiwan, China5e-mail: wanglai@tsinghua.edu.cn6e-mail: hyfu@sz.tsinghua.edu.cn7e-mail: mcwu@ee.nthu.edu.twshow less
Fig. 1. E-O bandwidths versus current densities for the non-polar LED, semi-polar LED, and polar LED comparison between different reports.
Fig. 2. (a) Schematic of the epitaxial structure of the wetting layer LED. (b) A 10 μm × 10 μm AFM image of the bare wetting layer sample. (c) A 1.5 μm × 1.5 μm AFM image of the nano-structured wetting layer. (d) A high-angle annular dark field scanning transmission electron microscope (HAADF STEM) image of the LED sample. (e) A magnified bright-field (BF) STEM image of the wetting layer region.
Fig. 3. (a) 3D view of the designed cross-sectional structure for the micro-LED. (b) The image of the top view of the mesa/anode (75 μm/100 μm in diameter) for the micro-LED observed by scanning electron microscopy (SEM, JSM-7000F).
Fig. 4. (a) Light-current density-voltage (L–J–V) characteristics for the micro-LED and the EQE measurement of the samples. (b) The external quantum efficiency versus applied current densities. (c) The emissive spectra of the micro-LED. (d) The value of peak wavelength shifts with different current densities.
Fig. 5. Schematic of the micro-LED-based VLC system in a typical indoor environment over 3-m link.
Fig. 6. (a) Photograph of the micro-LED-based VLC system in a typical indoor environment. (b) Wetting layer micro-LED-based transmitter and (c) APD module-based receiver.
Fig. 7. (a) TDPL spectra of the sample. The inset is a photograph of the sample excited by the laser. (b) The temperature dependence of peak wavelength and FWHM. (c) TRPL measurement. (d) Calculated τfast and τslow of the decay curves at different temperatures using a bi-exponential decay model.
Fig. 8. (a) E-O bandwidth of the wetting layer micro-LED on wafer measurement for different current densities. (b) Original normalized frequency response. Inset: the device under RF GS micro-probe was observed by optical microscope.
Fig. 9. (a) Normalized frequency responses of the VLC system with various current densities. (b) The extracted 3-dB modulation bandwidth and received optical power.
Fig. 10. Comparison of optical power between the emitter side and the receiver side and the I–V properties of the micro-LED.
Fig. 11. (a) Data rates versus BER for the experimentally obtained results and the eye diagrams of (b) 1.0 Gbps, (c) 1.2 Gbps, (d) 1.4 Gbps, (e) 1.6 Gbps, (f) 1.8 Gbps, and (g) 2.0 Gbps data rates at the driving current density of 528.54 A/cm2.
Fig. 12. SNR versus data rate of the micro-LED-based VLC system using NRZ-OOK format at different current densities.
Fig. 13. (a) Data rate and related BER of QPSK-OFDM at different current densities and the constellation diagrams with the data rate change of (b) 1 Gbps, (c) 2 Gbps, (d) 3 Gbps, and (e) 4 Gbps at the current density of 528.54 A/cm2.
Fig. 14. Corresponding frequency spectrograms with the data rate change from 1 to 4 Gbps at the current density of 178.82 A/cm2.
Current Density () | Highest Data Rate of NRZ-OOK (Gbps) | BER of NRZ-OOK | Highest Data Rate of QPSK-OFDM (Gbps) | BER of QPSK-OFDM |
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94.84 | 1.4 | | 1.0 | | 178.82 | 1.6 | | 4.0 | | 282.72 | 1.8 | | 3.0 | | 409.93 | 2.0 | | 3.0 | | 528.54 | 2.0 | | 3.0 | |
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Table 1. Experimental Performance of Wetting Layer Micro-LED-Based VLC System with Various Modulation Formats at Distance of 3 m
Year | Group | μLEDa Type | Optical Power (mW) | Bandwidth (MHz) | Modulation Format | Highest Data Rate (Gbps) | BER | Distance (m) |
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2014 | [10] D. Tsonev et al. | Blue μLED | 4.5 | 60 | mQAM-OFDMb | 3 | | 0.05 | 2015 | [11] J. McKendry et al. | UVc μLED | 2.5 | 130 | mQAM-OFDM | 3.32 | | – | 2016 | [12] R. Ferreira et al. | Blue μLED | 2.7 | 800 | NRZ-OOKd | 1.7 | | 0.5 | 5.7 | PAM4e | 3.5 | 0.75 | mQAM-OFDM | 5 | 0.75 | 2017 | [13] M. Islim et al. | Violet μLED | | 655 | mQAM-OFDM | 7.91 | | | 2017 | [35] X. Liu et al. | μLED | 0.8 | | NRZ-OOK | 1.3 | | 3 | 1 | | 10 | 0.87 | | 16 | 2018 | [16] S. Mei et al. | μLED + YQDsf | | 85 | NRZ-OOK | 0.3 | | | 2018 | [36] X. Liu et al. | μLED-based detector | – | – | NRZ-OOK | 0.185 | | | 2019 | [17] E. Xie et al. | μLED arrays | | 285 | NRZ-OOK | 2.1 | | 0.3 | PAM4 | 2.55 | 0.3 | mQAM-OFDM | 5.18 | 0.3 | 2019 | [15] X. He et al. | UV μLEDs | 0.196 | 438 | NRZ-OOK | 0.8 | | 0.3 | mQAM-OFDM | 1.1 | 2019 | [37] J. Carreira et al. | Dual-color μLED arrays | 0.85/1.04 | 427/134 | mQAM-OFDM | 3.35 | – | 0.3 | 2020 | Our work | Blue wetting layer μLED | 0.82g | 1000 | NRZ-OOK | 2 | | 3 | QPSK-OFDMh | 4 | 3 |
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Table 2. Performance of VLC Systems Based on Single-Pixeled Micro-LED (Summary of Part of Existing Works)