Low-complexity 24-h 29-km inter-island real-time FSO communication under strong turbulences

Free space optical communication (FSOC) technology can be used for data transmission between ocean islands as backup wireless communication networks to cope with traffic surges and emergencies. In this paper, we experimentally demonstrate the results of a 24-h real-time single-wavelength 2.5-Gbps FSOC between two islands 29 km apart at a low altitude with low complexity. On-off keying signals generated by field-programmable gate array (FPGA) board and commercial low-cost SFP + optical modules are employed as transceiver signals. At the receiving end, a 250-mm large-aperture Cassegrain telescope and 105-µm multi-mode fibers (MMFs) are utilized to reduce the scintillation index from 1.5 to 0.48 and from 0.55 to 0.25 under strong and weak fluctuations, respectively. The averaged receiving optical power, scintillation index, and average bit rate error (BER) are experimentally observed over a 24-hour period with an averaged transmitting power of 36 dBm. The experimental results show that the proportions reach 93.73% and 99.9% for BER below 1 × 10^-6 and 1 × 10^-3, respectively.