Graduate Institute of Photonics and Optoelectronics, and the Department of Electrical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 10617, R.O.C., Taiwan.
Deaprtment of Photonics, National Chiao Tung University, 1001 Ta Hsueh Rd., Hsinchu, 30050, R.O.C., Taiwan.
Sci Rep. 2017 Sep 5;7(1):10478. doi: 10.1038/s41598-017-10289-y.
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.
高达 18-Gbps 的直接编码蓝激光二极管 (BLD) 被证明可用于自由空间数据传输。通过使用旁瓣滤波对正交频分复用 (16-QAM OFDM) 流进行整形，原始数据速率从 17.2 加快到 18.4 Gbps。采用具有较小有源区直径和较低噪声等效功率的超快速 p-i-n 光电二极管，可将数据速率提高 1.6 Gbps 或提高信号噪声比 (SNR) 0.2 dB。通过用 120mW 的 BLD 替换 80mW 的 BLD，在增强调制吞吐量的情况下，接收 SNR 可提高 0.4 dB。通过使用平面凸超半球透镜增加数值孔径来增强光束准直和收集，可进一步提高 SNR 0.6 dB。经过优化，16-QAM OFDM 数据在有和没有旁瓣滤波的情况下，分别以原始数据速率 16.4 和 18 Gbps 传输，在 16 m 自由空间内的频谱密度使用效率高达 4 bit/s/Hz，其中 BLD 承载的 QAM-OFDM 数据流在经过旁瓣滤波的重构后保持其容量，因为优越的载波间干扰免疫能力增强了。
