Performance improvement of terrestrial free-space optical communications by mitigating the focal-spot wandering

Focal-spot wandering is the main cause for the major power loss in free-space optical communications. Thus,mitigating it is a primary requirement for the successful performance improvement. In order to prove this prerequisite, an experimental set-up using 155-Mbps data transmission is built for the link range of 0.5 km at an altitude of 15.25 m. In the experiment, the receiver is equiped with a control system to stabilize the received optical propagation at the detector plane which is called as focal-spot wandering mitigation control so as to couple the power in bucket perfectly to the photodetector. The performance improvements due to mitigating focal-spot wandering are regressively investigated in terms of various quality assessment key parameters. Maximum radial distance of 0.25 mm, maximum effective scintillation index of 0.17, optical signal-to-noise ratio of 9 dB, minimum eye-opening of ±0.37 V, minimum eye-height of ±0.51 V, controlled bit-error-rate of 6.45 × 10−9 to 7.09 × 10−8 and the link margin of 1.83 dB are attained even during strong turbulence level while mitigating focal-spot wandering.