500 Gb/s PAM4 FSO-UWOC Convergent System With a R/G/B Five-Wavelength Polarization-Multiplexing Scheme

Abstract

A 500-Gb/s four-level pulse amplitude modulation (PAM4) free-space optical (FSO)underwater wireless laser transmission (UWOC) convergent system over 100 m free-space transmission with either 10 m piped underwater link or 5 m turbid underwater link is established, employing a red/green/blue (R/G/B) five-wavelength polarization-multiplexing scheme as a demonstration for the first time. Integrating PAM4 modulation with five-wavelength polarization-multiplexing scheme, the channel capacity of FSO-UWOC convergent systems is significantly increased with an aggregate data rate of 500 Gb/s [50 Gb/s PAM4/wavelength × 5 wavelengths × 2 polarizations (p-and s-polarizations)]. Results reveal that five R/G/B laser diode (LD) transmitters with two-stage light injection and optoelectronic feedback techniques are capably adopted for 500 Gb/s PAM4 signal transmission. Compared with prior FSO-UWOC convergence and visible light communication using polarization-multiplexing R/G/B LDs, it shows a prominent one with the benefits of high aggregate transmission rate and long-range optical wireless link. Excellent bit error rate performance and accepted PAM4 eye diagrams are attained over a 110-m/105-m FSO-UWOC link. This demonstrated five-wavelength polarization-multiplexing FSO-UWOC convergent system is promising because it not only integrates free-space backbone with underwater optical wireless feeder, but it also substantially multiplies total channel capacity.

A contemporary survey on free space optical communication: Potentials, technical challenges, recent advances and research direction

“…Being inspired from the aforementioned concerns, multi-level modulation schemes could be employed in FSO systems to attain better SE in comparison with binary modulations. For example, the optical pulse is modulated on M levels in M ary-PAM [273], M ary-PSK [274], and M ary-QAM [275], which requires a laser source with different emission intensity. All of these M-level modulation methods provide higher SE and EE with respect to binary level modulation schemes.…”

“…The study of ergodic capacity of FSO channels is carried out in [234]- [236], [280]- [285] for the cases of Gamma-Gamma, Rayleigh, Nakagami-m, Malaga, Rician and log-normal fading taken into consideration of AWGN model for the receiver noise. On the other hand, the outage probability [123], [234]- [236], [238], [239], [256], [257], [274]- [276], [280]- [294], bit error rate analysis [104], [105], [234], [236], [239], [256], [257], [274]- [276], [281]- [285], [288], [289], [291], [292], [294]- [300], and throughput performance [104], [105], [235], [236], [273], [275], [286], [287], [293], [295]- [298], [301]- [303] are studied considering the mentioned fading models with AWGN.…”

A Comprehensive Comparison and Analysis of Several Intensity Modulations Based on the Underwater Photon-Counting Communication System

“…This makes high-speed signal modulation and demodulation techniques and high-sensitivity reception techniques an important research topic in the field of UWOC. Currently, the main modulation methods include intensity modulation (IM) [10], nonlinear frequency conversion [11], subcarrier modulation [12], higherorder modulation, signal multiplexing [13], and so on. The nonlinear frequency conversion technique can generate highspeed blue-green light signals with the help of mature 1,064nm high-power devices, but the coherence of the optical signal is demanded in the frequency doubling process that high-energy consumption is needed because of the low electro-optical conversion efficiency.…”

A 400-Gb/s WDM-PAM4 OWC system through the free-space transmission with a water–air–water link

“…Given the characteristics of FSO communication and UWLT system, they can provide high transmission rate over a free-space transmission with an underwater link. With the rapid progress of FSO communication and UWLT system, constructing a high-speed FSO-UWLT convergence is vitally important 12 , 13 . In an actual scenario, no UWLT system passes through the air–water–air interface as the laser beam should flee or enter from the top of the water 14 , 15 .…”