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.

A fiber-optic sensor for simultaneously measurement of temperature and salinity of seawater is proposed and demonstrated in this paper. The sensor is fabricated by self-growing a size-controllable UV-photopolymer micro-cone on the fiber facet. The optimal processing process and micro-cone size are obtained through theoretical analysis. This sensor is featured for simple fabrication, low cost and high efficiency, which provides a new lab-on-fiber scheme. And it was experimentally verified that the sensor shows fast responses to both of temperature and salinity of seawater with a high temperature sensitivity of −0.177 nm/°C between 25 °C and 100 °C and a high salinity sensitivity of −0.848 nm/‰ for the salinity range of 3‰ to 12‰. By using the transmission matrix method, simultaneous measurement of temperature and salinity can be realized and the accuracy of sensor detection is verified as well, which enables real-time long-term monitoring of ocean temperature and salinity.