Underwater wireless optical communication (UWOC) is a promising technology that can be a candidate to improve the communication capacity and speed in aquatic media. The aim of this study is to examine the performance of a silicon photomultiplier (SiPM) array-based multiple-input multiple-output (MIMO) UWOC system. A SiPM is a modern solid-state photodetector with extremely high sensitivity up to the single-photon level or a photon-counting ability, which helps in detecting extremely weak light signals after long-distance underwater channel attenuation. We clarify the basic characteristics and photon-counting detection mode of a SiPM. In particular, the photocount of a SiPM is approximated by a Gaussian distribution, and theoretical analysis shows that only 13.3 photons need to be detected during “1” symbol period to achieve a bit error rate of 10⁻³ in an ambient light environment. Moreover, a SiPM also has a better analog mode detection ability than an avalanche photodiode (APD) and realizes 2 Mbps analog communication owing to its unique array structure and high photon detection efficiency. Furthermore, MIMO, i.e., spatial diversity, is applied as an effective method to relax the link alignment, improve the system performance, and alleviate the effect of optical turbulence. In our experiment, with a photon-counting 6×3 MIMO scheme, an energy per bit of 7.38×10⁻⁹ J/bit is achieved at a scintillation index of 4.66×10⁻³ in a 10 m water tank with 1 Mbps on-off-keying (OOK) modulation. To the best of our knowledge, this is the first study on a MIMO-UWOC system based on the photon-counting mode of a SiPM array. This UWOC system combines the advantages of SiPMs and the MIMO scheme and has the potential to realize long-distance UWOC under optical turbulence.

中文翻译：

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由阵列 LED 和 SiPM 实现的用于 MIMO 水下无线光通信的单光子检测

水下无线光通信（UWOC）是一种很有前途的技术，可以成为提高水介质通信容量和速度的候选技术。本研究的目的是检查基于硅光电倍增管 (SiPM) 阵列的多输入多输出 (MIMO) UWOC 系统的性能。SiPM是一种现代固态光电探测器，具有高达单光子级的极高灵敏度或光子计数能力，有助于探测长距离水下通道衰减后的极微弱光信号。我们阐明了 SiPM 的基本特性和光子计数检测模式。特别是SiPM的光子数近似为高斯分布，理论分析表明在“1”符号周期内只需要检测13.3个光子即可实现10的误码率^-3在环境光环境中。此外，SiPM还具有比雪崩光电二极管（APD）更好的模拟模式检测能力，由于其独特的阵列结构和高光子检测效率，实现了2Mbps模拟通信。此外，MIMO，即空间分集，作为一种有效的方法来放松链路对齐，提高系统性能，减轻光湍流的影响。在我们的实验中，使用光子计数 6×3 MIMO 方案，在闪烁指数为 4.66×10 ^{-3 的}情况下实现了 7.38×10 ^-9 J/bit 的每比特能量在具有 1 Mbps 开关键控 (OOK) 调制的 10 m 水箱中。据我们所知，这是基于 SiPM 阵列光子计数模式的 MIMO-UWOC 系统的首次研究。该UWOC系统结合了SiPMs和MIMO方案的优点，具有在光湍流下实现远距离UWOC的潜力。