Free Space Optics (FSO)

• Uses lasers or infrared transmitting devices.
• Requires line of sight between buildings.
• Typically used for short distances, such as across a street.
• Auto-tracking systems are used to keep lasers aligned despite building movement caused by wind and traffic.

Performance and Limitations

• Current Speeds:

  • Range from T-3 (45 Mbps) to OC-48 (2.5 Gbps).
  • Faster systems are in development.

• Weaknesses:

  • Transmission through fog: Fog significantly impacts signal quality and range.
  • Link Margin: A typical FSO system has a link margin of about 20 dB.
  • Power Reduction: Under ideal conditions, air reduces a system’s power by approximately 1 dB/km.
  • Scintillation: Signal distortion due to atmospheric conditions, especially in hot weather.