## 1 Introduction
In recent years, some experiments have been also carried out based on multihop VLC. For example, the demonstration of a relay-assisted VLC system based on Multiband carrierless amplitude and phase modulation (M-CAP) was carried out with a data rate of 10 Mbps [10]. A bidirectional multihop VLC was used to monitor large-area indoor fine particles. The distance between two nodes can reach 13.5 m but the data rate is only 115.2 Kbps with on-off keying (OOK) format, which is unsuitable in high-speed scenarios [16]. [PERSON] et al. proposed a relay-assisted vehicle-mounted VLC network based on experimental measurements and presented the eye diagrams from 250 Kbps to 500 Kbps [17]. In addition, the performance of a multihop VLC system can be also tested in a real outdoor environment; however, the work only gave the relationship between the bit-error rate (BER) and average transmission power, which inadequately represents real-time communication [18]. Nonetheless, relatively high-speed multihop experiments are rarely reported. For example, a channel-aware adaptive physical-layer network-coding scheme based on adaptive-loading orthogonal frequency-division multiplexing (OFDM) was proposed, which can double the throughput of a relay-assisted VLC network [19]. A VLC system integrated with vertical-cavity surface-emitting laser (VCSEL) and LED was demonstrated indoors using a DF relay scheme with a data rate of 650 Mbps over a 4 m link [20]. Overall, most reported works on multihop free-space VLC systems are usually based on numerical simulations or only for low-speed scenarios. The data rate of the multihop system was limited significantly by the electrical-to-optical (E-O) bandwidth of the transmitter. Using micro-light-emitting diodes (micro-LEDs) as a transmitter has great potential for high-speed multihop VLC implementation due to their high E-O bandwidth characteristics [21; 22]. In Ref. [23], a high-bandwidth micro-LED with a self-assembled nanostructure InGaN wetting layer was designed and fabricated, which shows great po tential in point-to-point VLC applications. In addition, the maximum achievable data rate of 4 Gbps has been experimentally demonstrated by using OFDM. In order to overcome the limited communication distance and increase the data rate in the real-time NLOS VLC systems, a multihop structure combined with high-bandwidth micro-LED was adopted in this work. Incidentally, micro-LEDs also have great potential in the field of ultraviolet communication (UVC). Both NLOS and relatively low-speed problems can also be solved in ultraviolet (UV) micro-LED-based UVC systems. Recently, an AlGaN-based deep UV micro-LED emitting at 275 nm was proposed with the 3-dB E-O bandwidth of 380 MHz [24]. In addition, high-speed UVC based on a 276.8 nm UV micro-LED with a 3-dB E-O bandwidth of 452.53 MHz was experimentally achieved. A UVC link over 3 m with a data rate of 0.82 Gbps was presented [25]. However, ultraviolet radiation is not suitable for indoor scenarios resulting from its characteristics, which can be harmful and cause different degrees of damage to the human body. Moreover, our proposed dual-hop VLC system based on a blue micro-LED showed a higher communication-data rate compared with UVC. Therefore, UVC is not suitable for solving NLOS problems for indoor applications, and our dual-hop VLC system is a promising solution to tackle high-speed NLOS problems indoors. In this work, in order to explore the potential of the multihop structure, a dual-hop AF relay-based VLC system with a wider coverage range and a higher data rate is proposed. We focus on the application of VLC in an indoor environment, by fully routing data between VLC-based nodes and providing a Gbps communication rate. Two 488 nm blue micro-LEDs with 880 MHz E-O bandwidth were designed and then used as the transmitter in two nodes. The modulation characteristics of the micro-LED are the key reason to enable the high-speed system than other works.