Free Space Optics

Research focusing on:

  • Statistical channel modelling
  • Optical equalization
  • Performance analysis

Outdoor optical wireless (OW) systems have recently gained attention as a broadband alternative in niche applications including semi-permanent office interconnections and MAN implementations. Despite the inherent advantages of outdoor OW systems, the transmission of light through the atmosphere can be challenging. Apart from weather-dependent static transmission losses that may limit the system availability, atmospheric turbulence induces time-varying changes in the refractive index, which in turn affect the amplitude, phase and propagation direction of the optical signal. These changes result in time-varying power fluctuations of the received signal and when the turbulence is intense enough, the received signal decreases below the receiver sensitivity and the link is lost. This corresponds to a fade event, which affects the OW system both in terms of capacity, as well as latency. Several million bits may be lost during a msec-long fade at 10 Gb/s, while the link will be in outage for an amount of time approximately equal to the fade duration. In this area, our research includes:

  • Optical wireless channel modelling to accurately analyze to performance of OW systems.
  • Novel fade mitigation techniques as fading channel countermeasures.
  • OW relaying networks.

The proposed optical wireless fade mitigation setup and principle of operation.

Fade probability at the output of a semiconductor optical amplifier versus the normalized threshold with small signal gain 20 dB.

Key Publications: