100-m/3-Gbps underwater wireless optical transmission using a wideband photomultiplier tube (PMT)

Abstract

In this paper, a wideband photomultiplier tube (PMT)-based underwater wireless optical communication (UWOC) system is proposed and a comprehensive experimental study of the proposed PMT-based UWOC system is conducted, in which the transmission distance, data rate, and attenuation length (AL) is pushed to 100.6 meters, 3 Gbps, and 6.62, respectively. The receiver sensitivity at 100.6-meter underwater transmission is as low as -40 dBm for the 1.5-Gbps on-off keying (OOK) modulation signal. To the best of our knowledge, this is the first Gbps-class UWOC experimental demonstration in >100-meter transmission that has ever been reported. To further minimize the complexity of channel equalization, a sparsity-aware equalizer with orthogonal matching pursuit is adopted to reduce the number of the filter coefficients by more than 50% while keeping slight performance penalty. Furthermore, the performance of the proposed PMT-based UWOC system in different turbidity waters is investigated, which shows the robustness of the proposed scheme. Thanks to the great sensitivity (approaching the quantum limit) and a relatively larger effective area, benefits of misalignment tolerance contributed by the PMT is verified through a proof-of-concept UWOC experiment.

Current Trend in Optical Internet of Underwater Things

“…Apart from the link configuration optimization to mitigate the PAT issues in the underwater optical channel, creative solutions in the evolution of optical receivers can boost the performance of the optical IoUT systems. Ultra-sensitive detectors are widely applied in UWOC systems for long-distance sensing, such as APD [3], [4], MPPCs [111], and PMTs [5]. High-sensitivity APD can amplify the received photons, but its noise floor limits the SNR.…”

50 m/187.5 Mbit/s real-time underwater wireless optical communication based on optical superimposition

“…Underwater wireless optical communication (UWOC) has the advantages of high data rate and low latency, but with the shortcomings of strict link alignment and limited transmission distance [1][2][3][4] . The blue laser diode (LD), with high power, is gradually becoming the mainstream as the light source in the long-distance UWOC system [5][6][7][8][9][10] . Besides, many researchers employed high-sensitivity optical detectors such as a multi-pixel photon counter (MPPC), single-photon avalanche diode (SPAD), and photomultiplier tube (PMT) as receivers to detect weak optical signals [6][7][8][9][10][11] .…”

“…The blue laser diode (LD), with high power, is gradually becoming the mainstream as the light source in the long-distance UWOC system [5][6][7][8][9][10] . Besides, many researchers employed high-sensitivity optical detectors such as a multi-pixel photon counter (MPPC), single-photon avalanche diode (SPAD), and photomultiplier tube (PMT) as receivers to detect weak optical signals [6][7][8][9][10][11] .…”

“…Besides, the sparse Volterra equalizer, which can effectively reduce the computational complexity, was developed for the UWOC system to realize a data rate of 500 Mbit/s in a 200 m underwater transmission [9] . Recently, a wideband PMT-based UWOC system was proposed, in which the transmission distance and data rate were pushed to 100.6 m and 3 Gbit/s, respectively [10] . The aforementioned UWOC systems have achieved high data rates and long transmission distance, whereas the digital processing algorithms may cause relatively high latency and increase the cost of implementation, which may hinder the practical application of UWOC systems.…”

Pointing Error Control of Underwater Wireless Optical Communication on Mobile Platform

“…In 2018, a light-emitting diode (LED) based system developed by Lu et al achieved a data rate of 205 Mbps in the sea environment [2]. In 2021, Fei et al experimentally demonstrated a laser diode (LD) based 3 Gbps UWOC over 100 meters in a water tank [3]. Although the effective transmission distance of optical signals is relatively short, this is acceptable for mobile platforms, such as autonomous underwater vehicles (AUVs), remotely operated vehicles (ROVs), and underwater gliders.…”