Free-space Optical Communication - Disadvantages

Disadvantages

For terrestrial applications, the principal limiting factors are:

• Beam dispersion
• Atmospheric absorption
• Rain
• Fog (10..~100 dB/km attenuation)
• Snow
• Scintillation
• Interference from background light sources (including the Sun)
• Shadowing
• Pointing stability in wind
• Pollution / smog

These factors cause an attenuated receiver signal and lead to higher bit error ratio (BER). To overcome these issues, vendors found some solutions, like multi-beam or multi-path architectures, which use more than one sender and more than one receiver. Some state-of-the-art devices also have larger fade margin (extra power, reserved for rain, smog, fog). To keep an eye-safe environment, good FSO systems have a limited laser power density and support laser classes 1 or 1M. Atmospheric and fog attenuation, which are exponential in nature, limit practical range of FSO devices to several kilometres.