Abstract
Violet laser diode (VLD) based ultrahigh-speed free-space optical (FSO) system is demonstrated for point-to-point data transmission. By directly encoding the VLD with 64-quadrature amplitude modulation discrete multi-tone (64-QAM DMT) data stream for optical wireless communication through 0.5–10 m in free space, the point-to-point VLD-based FSO link allows delivering the 64-QAM DMT data at an ultrahigh bit rate of up to 26.4 Gbps. After receiving with a high-speed p-i-n photodiode, such a VLD-FSO link can provide clear constellation plot with error vector magnitude (EVM) of 8.57%, signal-to-noise ratio (SNR) of 21.34 dB and bit error ratio (BER) of 3.17 × 10−3 under forward-error-correction criterion. The EVM increases from 8.8% to 9.4% and the SNR decreases from 21.1 to 20.6 dB to slightly degrade the reachable data rate from 25.8 to 24 Gbit/s with transmission distance lengthening from 3 to 10 m.
Highlights
Nowadays, the demanded data transmission capacity for indoor or harsh free-space environment has rapidly grown up due to the tremendously increased amount of multimedia streaming and data exchange among devices and networks
The Violet laser diode (VLD) is biased at 60 mA with corresponding differential resistances of 16.3 Ω, which is smaller than 50 Ω typically set for commercially available microwave instruments
Matching the impedance of the VLD with adjusting its bias dependent differential resistance, the DC bias current of the VLD is optimized to 60 mA for approaching the forward error correction (FEC) qualified bit error ratio (BER) of the 64-QAM DMT data covering a bandwidth as wide as 4.4 GHz
Summary
The demanded data transmission capacity for indoor or harsh free-space environment has rapidly grown up due to the tremendously increased amount of multimedia streaming and data exchange among devices and networks. To improve the allowable modulation bandwidth of the OWC or FSO link, laser diodes (LDs) with shorter photon lifetime (~ps), narrower spectral linewidth, longer coherent distance and larger transmission capacity were lately recognized as promising candidate for promoting the VLC data rate. The GaN blue LD based point-to-point VLLC has shown its superiority for underwater wireless optical communication (UWOC), including small divergent angle, long propagation distance and low absorption in seawater environment. Aside from the blue LD based VLLC scheme, Janjua et al further utilized the fiber-based red/green/blue (RGB) LD module to set up a wavelength division multiplexing white-lighting OWC with achieving the bit rate of up to 4 Gbit/s for a single LD22. Chi et al preliminarily revealed the capability of 405-nm VLD based point-to-point VLLC for carrying 16-QAM OFDM data at 12 Gbit/s26
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