Optical Frequency Hopped Spread Spectrum: Thoughts and Experiments

Free space optical (lasercomm) links are highly directional making them inherently resistant to jamming. A jammer located off-axis from the transmitter experiences significant attenuation. However, as the power available to the lasercomm jammers increases, the links become vulnerable. This emerging vulnerability motivates the application of frequency hopped spread spectrum (FHSS) to the optical domain. This paper presents the results from a testbed implementing a small (four-channel) OFHSS system. It covers everything from selecting an appropriate error correction scheme, waveform definition, optical implementation to jammer injection. The paper covers options for scaling the system, which is essential since the spreading gain is proportional to the number of channels.