## 1 Introduction
Popular ROI-based OCC schemes include under-sampled frequency shift on-off keying (UFSOOK) modulation [31; 32] and under-sampled phase shift on-off keying (UPSOOK) modulation [33; 34]. The ROI-based OCC systems can support much longer transmission distances than in the RS-based OCC systems; however, they may need a heavy computational burden to trace and detect multiple light sources. Additionally, the data rate is usually much less than that in RS-based OCC systems. On the other hand, the RS-based OCC systems usually use a typical commercially available CMOS image sensor or camera, with a frame rate of about 30 or 60 frames per second (fps), and a resolution of 1920 \(\times\) 1080 pixels. In the RS operation, the pixel rows in the CMOS camera are activated row by row. At the optical transmitter (Tx) side, when it is modulated faster than the frame rate of the camera, dark and bright fringes standing for the OCC signal \"logic 0\" and \"logic 1\" can be visualized in the image sensor RS pattern. Moreover, in order to enhance the applicability of OCC systems, both the Tx and Rx sides should have a wide field of view (FOV). Recently, wide FOV optical Txs based on light-diffusing fiber (LDF) or side glow optical fiber (SGOF) were proposed [35; 36; 37; 38]. They can provide 360\({}^{\circ}\) uniform light emission around the LDF circumference. This means that the LDF can act as an \"omni-directional optical antenna\". Moreover, it is lightweight and flexibly bendable. Previously, the LDF or SGOF could be installed in an unmanned aerial vehicle (UAV) to provide VLC [35]. Furthermore, the LDF or SGOF can also support sliding and multiple Rxs to obtain a VLC signal along the fiber [38]. Most importantly, SGOF is water resistant; hence, it can be installed in an underwater environment to provide \"omni-directional\" optical signals. Efficient RS thresholding methods are also required to decode the RS pattern correctly. Recently, effective algorithms have been utilized to enhance the performance of OCC, including the convolutional neural network (CNN),the pixel-per-bit labeling neural network (PPB-NN), the long short-term memory neural network (LSTM-NN), transition-based data decoding, etc. [39; 40; 41; 42; 43; 44; 45]. In this work, we present and demonstrate an RS-based underwater optical camera communication (UWOCC) system utilizing the LSTM-NN with SGOF. The optical Tx is a commercially available poly-methyl methacrylate (PMMA) SGOF. As discussed before, SGOF is lightweight and flexibly bendable. Most importantly, SGOF is water resistant; hence, it could be suitable for underwater communication. SGOF is a kind of polymer optical fiber (POF), which is popular for short-distance data communication, decoration, and sensing applications. Instead of sending an optical signal from one end of the fiber to the other end via total internal reflection (TIR), SGOF allows light to leak via the fiber cladding. The main challenge for SGOF is how to emit homogeneous light over the length of the fiber in all directions around its circumference. The SGOF used in the experiment is made of PMMA and is commercially available. Its radial side-emitting mechanism is based on bulk scattering [46]. Radial light emission (or light leakage) is achieved by doping the POF with scattering sites realized using different particles. By carefully controlling the size and concentration of the introduced particles, homogeneous radial light emission can be achieved. Different light-scattering particles, such as zinc oxide (ZnO) and titanium dioxide (TiO\({}_{2}\)) [47], can be utilized. The size of these particles can vary from 50 to 2000 nm. In order to produce Rayleigh scattering, the scattering particle diameter should be smaller than the wavelength of the incident light [48]. In addition, in order to produce Mie scattering, the scattering particle diameter is equal to or larger than the wavelength of the incident light [48].