Oceans cover 71% Oceans cover 71% surface of the earth and are rich in oil and gas resources, marine living resources, renewable energy, mineral resources. The depths of the oceans are often thought of as a silent world, but that was never the case, and oceans have become noisier as human technologies have advanced. Humans have not only added noise to the ocean; they have also eliminated natural sounds. One of the primary noise sources is sonar. Sonar technology is widely used in fish detection, ocean floor mapping, and vehicle navigation. The noise in the ocean dramatically affects the animal’s survival and breaks marine ecological balance. Herein, underwater wireless optical communication (UWOC) and fiber communication and sensing (FC&S) technologies are proposed to minimize the acoustic noise in the ocean. Compared to noisy, powerful acoustic communication technology, UWOC has the merit of silence and takes advantage of high bandwidth, high transmission speed, and power efficiency. Multi-functions FC&S system turns the submarine telecommunication cable network into sensor network. UWOC and underwater FC&S technology can boost the development of Underwater Internet of things (UIoT) by establish large-scale underwater sensor networks. This dissertation aims to investigate and address noisy ocean issues and build large-scale underwater sensor networks by optical communication and sensing technology. The dissertation proposes using UWOC and FC&S technology to replace the conventional acoustic communication technology and reduce the noise in the ocean. UWOC helps achieve high-speed wireless communications between sensors, vehicles, and even humans for UIoT. The significant challenges of developing UWOC systems are the complex underwater environment's attenuation, scattering, and turbulence effects. This dissertation studied the turbulence effects on the UWOC system’s performance and addressed the pointing-acquisition-and-tracking issues. The diffuse-line-of-sight configuration and scintillating-fiber-based detector help the mobile UWOC systems relieve the strict requirements on PAT. FC&S technology is proposed to build underwater communication and sensor networks. Studies pave the way for UIoT and keep ocean silent. Such modality is much sought-after for implementing robust UWOC links in a complex oceanic environment, building large-scale sensor networks across the oceans, and minimizing noise pollution in the ocean.