Heavy rain effects on the propagation of free space optical links in Singapore

The range of free space optical (FSO) links operating in temperate regions is limited by fog, but in tropical regions, rain is expected to be the limiting factor. This is one of the reasons why the Infocomm Development Authority of Singapore (IDA) conducted a three months trial for free space optical (FSO) links in Singapore. Three parallel FSO links (from three different vendors) operating in the 780/840 nm wavelengths were set up on top of three Housing Development Board (HDB) buildings in Sengkang estate, northern Singapore. The received signal strengths of the 1000 metre 780 nm links were monitored to investigate the performance of the link especially during heavy rain. The rainfall rates, temperature, humidity and wind speed and directions were data-logged at one end of the 1000 m link (Block 317B) and also at another building (Block 262A) approximate 740 m away, and about 230 meters away from the other terminal.