Browsing by Author "Nakamura, Shuji"

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Blue Laser Diode Based Free-space Optical Data Transmission elevated to 18 Gbps over 16 m
(2017-09-05)
Huang, Yu-Fang
;
Chi, Yu-Chieh
;
Kao, Hsuan-Yun
;
Tsai, Chen-Ting
;
Wang, Huai-Yung
Up to 18-Gbps direct encoding of blue laser diode (BLD) is demonstrated for free-space data transmission. By reshaping the orthogonal frequency multiplexed (16-QAM OFDM) stream with sidelobe filtering, the raw data rate expedites from 17.2 to 18.4 Gbps. Employing an ultrafast p-i-n photodiode with smaller active area diameter and lower noise equivalent power significantly enlarges the data rate by 1.6 Gbps or upgrades the signal-to-noise ratio (SNR) by 0.2 dB. Replacing the 80-mW BLD with the 120-mW one essentially increases the received SNR by 0.4 dB under enhanced modulation throughput. Reinforcing the beam collimation and collection by increasing the numerical aperture with a plano-convex hyper-hemispherical lens further improves the SNR by 0.6 dB. After optimization, the 16-QAM OFDM data with and without sidelobe filtering are respectively delivered at raw data rates of 16.4 and 18 Gbps with spectral-density usage efficiency as high as 4 bit/s/Hz over 16 m in free space, wherein the BLD carried QAM-OFDM data stream remains its capacity after reformation with sidelobe filtering as the superior inter-carrier-interference immunity reinforces.
Phosphorous Diffuser Diverged Blue Laser Diode for Indoor Lighting and Communication
(2015-12-21)
Chi, Yu-Chieh
;
Hsieh, Dan-Hua
;
Lin, Chung-Yu
;
Chen, Hsiang-Yu
;
Huang, Chia-Yen
An advanced light-fidelity (Li-Fi) system based on the blue Gallium nitride (GaN) laser diode (LD) with a compact white-light phosphorous diffuser is demonstrated for fusing the indoor whitelighting and visible light communication (VLC). The phosphorous diffuser adhered blue GaN LD broadens luminescent spectrum and diverges beam spot to provide ample functionality including the completeness of Li-Fi feature and the quality of white-lighting. The phosphorous diffuser diverged white-light spot covers a radiant angle up to 120 degrees with CIE coordinates of (0.34, 0.37). On the other hand, the degradation on throughput frequency response of the blue LD is mainly attributed to the selffeedback caused by the reflection from the phosphor-air interface. It represents the current state-ofthe- art performance on carrying 5.2-Gbit/s orthogonal frequency-division multiplexed 16-quadratureamplitude modulation (16-QAM OFDM) data with a bit error rate (BER) of 3.1 x 10(-3) over a 60-cm freespace link. This work aims to explore the plausibility of the phosphorous diffuser diverged blue GaN LD for future hybrid white-lighting and VLC systems.