Free Space Optics

BY TAMAL GHOSH ;Electronics & Communication ;AOT

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Only about 5% of commercial buildings are lit with fiber ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Light Source Glass Fiber Strands Detector Network Device ,[object Object],[object Object],[object Object],[object Object],[object Object],Light Source Detector Network Device

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 ,[object Object],[object Object],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

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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)

[object Object],[object Object],[object Object],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

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[object Object],[object Object],[object Object],Challenges: Scintillation >>

[object Object],[object Object],[object Object],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

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],RONJA , a free implemantation of FSO utilizing High intensity LEDs

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[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Two solar-powered satellites communicating optically in space via lasers.

Free Space Optics

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Free Space Optics