Anything that can be done in fiber can be done with FSO 1 Network traffic converted into pulses of invisible light representing 1’s and 0’s 2 Transmitter projects the carefully aimed light pulses into the air 5
Reverse direction data transported the same way.
3 A receiver at the other end of the link collects the light using lenses and/or mirrors 4 Received signal converted back into fiber or copper and connected to the network
1 ° ≈ 17 mrad -> 1 mrad ≈ 0.0573° 1 mrad 1 km 1 m Small angle approximation: Angle (in milliradians) * Range (km)= Spot Size (m) Divergence Range Spot Diameter 0.5 mrad 1.0 km ~0.5 m (~20 in) 2.0 mrad 1.0 km ~2.0 m (~6.5 ft) 4.0 mrad (~ ¼ deg) 1.0 km ~4.0 m (~13.0 ft)
Gain/Loss Multiplier +30 db +20 db +10 db 0 db -10 db -20 db -30 db 1000 100 10 1 .1 .01 .001
Sunlight Building Motion Alignment Window Attenuation Fog Each of these factors can “attenuate” (reduce) the signal. However, there are ways to mitigate each environmental factor. Scintillation Range Obstructions Low Clouds
Uncoated glass attenuates 4% per surface due to reflection
Tinted or insulated windows can have much greater attenuation
Possible to trade high altitude rooftop weather losses vs. window attenuation
Challenges Window Attenuation WAM
Type Cause(s) Magnitude Frequency Tip/tilt Thermal expansion High Once per day Sway Wind Medium Once every several seconds Vibration Equipment (e.g., HVAC), door slamming, etc. Low Many times per second
To those unfamiliar with FSO technology, safety can be a concern because the technology uses lasers for transmission. The two major concerns involve eye exposure to light beams and high voltages within the light systems and their power supplies. Strict international standards have been set for safety and performance.
The FSO industry shows some strength, and the FSO market is growing, though with much less speed.
In spite of this, the commercial future of free-space optical communications remains uncertain.Perhaps the best overall prospects are in space, where progress is being made in improving acquisition and tracking. Once these are perfected, the bandwidth advantages of optical free-space communications should open up a substantial market.
The FSO industry consists of mostly established vendors that manufacture equipment for various distances and speeds of transmission. The highest speed of 2.5 Gb/s promises to be increased to 10 Gb/s in future.