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Xu ZY, Niu WQ, Liu Y, Lin XH, Cai JF et al. 31.38 Gb/s GaN-based LED array visible light communication system enhanced with V-pit and sidewall quantum well structure. Opto-Electron Sci 2, 230005 (2023). doi: 10.29026/oes.2023.230005
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31.38 Gb/s GaN-based LED array visible light communication system enhanced with V-pit and sidewall quantum well structure
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Abstract
Although the 5G wireless network has made significant advances, it is not enough to accommodate the rapidly rising requirement for broader bandwidth in post-5G and 6G eras. As a result, emerging technologies in higher frequencies including visible light communication (VLC), are becoming a hot topic. In particular, LED-based VLC is foreseen as a key enabler for achieving data rates at the Tb/s level in indoor scenarios using multi-color LED arrays with wavelength division multiplexing (WDM) technology. This paper proposes an optimized multi-color LED array chip for high-speed VLC systems. Its long-wavelength GaN-based LED units are remarkably enhanced by V-pit structure in their efficiency, especially in the “yellow gap” region, and it achieves significant improvement in data rate compared with earlier research. This work investigates the V-pit structure and tries to provide insight by introducing a new equivalent circuit model, which provides an explanation of the simulation and experiment results. In the final test using a laboratory communication system, the data rates of eight channels from short to long wavelength are 3.91 Gb/s, 3.77 Gb/s, 3.67 Gb/s, 4.40 Gb/s, 3.78 Gb/s, 3.18 Gb/s, 4.31 Gb/s, and 4.35 Gb/s (31.38 Gb/s in total), with advanced digital signal processing (DSP) techniques including digital equalization technique and bit-power loading discrete multitone (DMT) modulation format.-
Keywords:
- GaN-based LED /
- LED array /
- VLC /
- V-pit /
- sidewall quantum well /
- high-frequency response
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References
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Supplementary Information
Supplementary information for 31.38 Gb/s GaN-based LED array visible light communication system enhanced with V-pit and sidewall quantum well structure
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Xu ZY, Niu WQ, Liu Y, Lin XH, Cai JF et al. 31.38 Gb/s GaN-based LED array visible light communication system enhanced with V-pit and sidewall quantum well structure. Opto-Electron Sci 2, 230005 (2023). doi: 10.29026/oes.2023.230005
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Figure 1.
(a) The proposed 8-wavelength 4x4 LED array chip image, the colors of each dash line box represent the color of the LED unit. (b) The scanning electron microscope (SEM) image of the V-pit structure. (c) The vertical profile of the V-pit structure. (d) Layers of the red LED units (660 nm and 620 nm). (e) Layers of the GaN-based LED units (wavelengths from 570 nm to 450 nm).
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Figure 2.
The current density distribution in simulation (a) and its detailed view (b). The h+ carriers are attracted by the V-pit structure and enter the sidewall quantum well area. Next, they are horizontally transported into the wells in the flat quantum wells and increases the injection into these wells.
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Figure 3.
Comparison of the maximum recombination rate (SRH, Radiative, and Auger) between the sample with and without V-pits in each quantum well in 30 mA (a) and 350 mA (b) cases. (c) The hole current density simulation for samples with or without V-pits. Notice that the sample with V-pit presents a significant gain in current density in each quantum well.
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Figure 4.
(a) The proposed equivalent circuit for fitting both LEDs with and without V-pits (with tiny V-pits). The branch in the dash yellow box is dedicated to representing the extra current introduced by the V-pit area. And the other branch in the intrinsic LED part represents the flat quantum well region. The fitting result using the proposed equivalent circuit for (b) the sample without V-pits and (c) the sample with V-pits.
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Figure 5.
(a) The comparison between the I-V curves of the LED sample with or without the V-pit structure. (b) The LI (left y-axis) and illumination efficacy (right y-axis) versus the current density of the LED sample with or without the V-pit structure.
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Figure 6.
(a, b) The electroluminescence (EL) spectrum of the LED samples with and without V-pits. (c) The full-width-half-maximum (FWHM) of EL spectrum shown in (a) and (b).
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Figure 7.
(a, b) The pulse response of the LED samples with and without V-pits in 300 mV Vpp. (c, d) The pulse response of LED samples with and without V-pits in 1 V Vpp.
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Figure 8.
The setup diagram and the DSP process in the TX and RX sides. The red blocks represent the bit-power loading process which modifies the modulation order and power of each DMT sub-carrier and helps the system achieve higher spectrum efficiency and communication capacity.
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Figure 9.
The contour diagrams of each LED unit in searching for the best working point of each channel.
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Figure 10.
The spectra of the original, received and NN equalized signals in the channel estimation stage of the communication experiment for each channel.
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Figure 11.
The bit-power loading result in the final communication test. The first row of each subplot shows the modulation order and SNR on each subcarrier, and the second row is the allocated power ratio, demonstrating the modification to the power of subcarriers.
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Figure 12.
Summary of the communication rate. (a) The spectrum efficiency (SE) and modulation bandwidth of the proposed 8-wavelength WDM system. (b) The BER of each channel, all the BERs are lower than the 7% HD-FEC threshold. (c) Comparison in data rate with the original design. The total data rate of the proposed size-improved design device is 31.38 Gb/s.
