## 1 Introduction
In this scheme, a large-area and wide FOV Rx was achieved to establish a reliable communication link in a turbulent underwater environment. In 2020, [PERSON] et al. fabricated a wide FOV and high-gain fluorescent optical antenna [39]. The structure consisted of a fluorescent material sandwiched between two glass layers. By using different dyes dispersed in transparent epoxy, wavelength division multiplexing (WDM) operations can be realized. In 2020, [PERSON] et al. demonstrated a 240\({}^{\circ}\) wide FOV VLC Rx for smart phones using a fluorescent fiber [40]. The fluorescent fiber used had a 3-dB response at 80 MHz. By using decision feedback equalization (DFE) with 40 feed-forward and 20 feed-backward taps, the intersymbol interference (ISI) of the on-off-keying (OOK) signal was mitigated, achieving 1.1 Gbit/s operation. In 2022, [PERSON] et al. proposed and illustrated a 360\({}^{\circ}\) wide FOV optical camera communication (OCC) system using a phosphor-coated light diffusing fiber [41]. When a blue laser diode (LD) was coupled at one end of the light-diffusing fiber, blue light was scattered and emitted at the fiber circumference. The yellow phosphor converted the blue light to yellow light; hence, white light was produced by combining the blue and yellow lights. In this system, a rolling shutter camera was used, and the data rate was 3.3 kbit/s. In addition to these special fibers, compound parabolic concentrators (CPCs) [42; 43; 44; 45] can be installed in front of the Rx to increase the Rx FOV. Table 1 summarizes the performance comparison of recent VLC systems using advanced optical antennas to enhance the FOV. From Table 1, we can observe that in order to provide hundreds Megabit/s, wide FOV, and a large VLC detection area, light diffusing fiber can be a promising candidate by allowing 360\({}^{\circ}\) wide FOV VLC detection around the fiber circumference. In this work, we put forward and demonstrate a bi-direction free-space VLC system supporting multiple moveable Rxs using a light-diffusing optical fiber (LDOF). The downlink (DL) signal is red at a wavelength of 633 nm and is launched from a head-end or central office (CO) far away to the LDOF at the client side via a free-space transmission. When the DL signal is launched to the LDOF, which acts as an optical antenna to re-transmit the DL signal to different moveable Rxs. The uplink (UL) signal is green at a wavelength of 520 nm. It is sent via the LDOF towards the CO. In the proof-of-concept demonstration reported here, the LDOF is 100 cm long, and the free space VLC transmission between the CO and the LDOF is 100 cm. The 210 Mbit/s DL and 850 Mbit/s UL transmissions meet the pre-forward-error-correction bit error rate (pre-FEC BER = 3.8 \(\times\) 10\({}^{-3}\)) threshold. When compared with ref. [36; 37; 38], our work proposed here includes both DL and UL transmission, as well as a 1-m FSO transmission to increase the flexibility of the proposed system. When compared with ref. [39], which uses a fluorescent layer sandwiched by 2 glass layers. The FOV is limited to 60\({}^{\circ}\), while our proposed system uses LDOF, which has FOVs of 360\({}^{\circ}\) around the fiber circumference and 120\({}^{\circ}\) along the fiber. The LDOF used here is the same as that in ref. [41]; however, ref. [41] is based on rolling shutter-based OCC. Hence, the data rate is only 3.3 kbit/s, which is limited by the rolling shutter effect of the camera. This paper is organized as follows: In Section 2, the design and structure of the LDOF acting as the omni-directional optical antenna are discussed. The system architecture, experiment, results, and discussion are presented in Sections 3 and 4, respectively. Finally, the conclusion is given in Section 5.