Sustainable photonic communication systems can resolve the global digital divide. Free-space optical (FSO) systems offer the ability to distribute high speed digital links into remote and rural communities where terrain, installation cost or infrastructure security pose critical hurdles to deployment . We will discuss the development of a low-cost FSO system prototype that could allow for out of the box self aligning optical systems that requires no specialist engineer for installation. Our prototype system is based on commercial telescope mount, which is controlled by Raspberry Pi 3 (RPi) compact computer and incorporates 4 spatially multiplexed channels, each with an integrated 1-Gbps small form factor pluggable (SFP) transceiver. Using the global positioning system (GPS), the location of the transceiver is determined and communicated to near by transceivers through low-speed radio link operating at 446-Mhz. The low-speed radio link supports the communication of automated alignment instructions between the remote transceivers. To perform the alignment, we adopt a spiral path alignment method widely for used for inter-satellite and ground-to-space optical communication systems [2, 3]. To facilitate this alignment method both the Transmitter and Receiver systems are equipped with a laser beacon, which is detected by CCD camera located on the external casing of each transceiver. The system automatically completes three stages of alignment to fully align a duplex spatially multiplexed FSO link. In our experimental test of the system over both 15m and 200m, we measured the total link loss to be 10dB and 15dB respectively and demonstrate error free-transmission at 1 Gbps per channel.
1. Lavery et al., “Tackling Africa’s digital divide,” Nature Photonics 12, 249–252 (2018).
2. G. Baister et al., “Pointing, acquisition and tracking for optical space communications," Electronics & Communication Engineering Journal, vol. 6, pp. 271-280 (1994).
3. T. Nguyen at al., "Development of a pointing, acquisition, and tracking system for a CubeSat optical communication module," Proc. SPIE 9354, Free-Space Laser Communication and Atmospheric Propagation XXVII, 93540O (2015).