Testbed for Free-Space Optics

Laser communications for the atmospheric channel

Optical links over the free-space channel require terminals that are robust, cost-effective and superior to microwave systems in terms of data rate. High data rates (> 1 Gb/s) can be achieved using commercial off-the-shelf components from the fiber telecommunication industry. This implies to effectively couple the received free-space beam into a single-mode fiber.

To improve the terminal robustness in an atmospheric environment, we evaluate innovative techniques. One of them is the deployment of multiple apertures with beam coherent combining.

Featured Measurement Types

Quality of fiber coupling

  • Loss during coupling of a large-diameter beam (e.g. 100 mm) into a single-mode fiber
  • Comparison of SMF-coupling techniques: aspheric collimator, GRIN collimator, large-core SMF
  • Beam cross section measured on high-speed InGaAs sensor array
  • Simulation of atmospheric environment

Quality of beam coherent combining

  • Loss due to cascade of various fiber elements
  • Evaluation of various phase shifters: fiber stretcher, phase modulator, piston mirror
  • Impact of scintillation on the coherent combining

Building Blocks

  • Tilt tracking and SMF coupling
  • Coherent beam combining