Data transfer in non-axial optical slip-rings

The situations and problems of data transfer via free space optical links represent a challenging area in contemporary communications where a number of factors must be traded off to produce a workable solution. An experimental link was constructed and extensive testing carried out. It was found that laser focussing was critical. Tighter focussing than the levels used for the second power budget estimate reduced the mean power requirement to as low as 60 μW for a 1O MHz link with ~ -30 dB SNR but at a cost of sharply reduced interaction cross-section. A relative rotation rate of 5 Hz was used to demonstrate 10 MHz signal transfer. Pulses used were square wave rather than actual data but receiver signal to noise of 40 dB was obtained for a laser mean power of 0.8 mW. At a higher data rate of 35 MHz the mean power required rose to 2 mW but this was in part due to the laser drive amplifiers reducing in performance. Work to demonstrate 52 Mbits/sec and a route to extend this further to higher data rates is discussed