Tip-tilt Pre-Compensation Improvement by Adding a Gaussian Apodization Filter in the Rx Tracking Path
Rudolf Saathof (TU Delft - Aerospace Engineering)
More Info
expand_more
Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons.
Abstract
Tip-tilt pre-compensation adds a significant performance improvement for uplink optical communications channels, such as optical feeder-links. Besides the large contribution of tip-tilt to the wavefront disturbances, tip-tilt aberrations are less sensitive for the point ahead angle than higher order aberrations. Nevertheless, reciprocity between downlink and uplink is not perfect, resulting in residual pointing errors. One effect is the difference in beam shape: the downlink can be considered as a plane wave, whereas the uplink typically is a Gaussian beam. To improve reciprocity between up and donwlink, I propose to use a Gaussian apodization filter inn the part of the downlink beam that is used for measuring tip-tilt. This idea is tested using a numerical wave propagation simulation. In this simulation the reduction of beam wander is 13% and 20% is observed in the direction of the point ahead angle, and its transversal direction respectively. Also, it reduced the scintillation index by 8%. This yielded an improvement of the optical link by 1.5 dB at a probability of 10-3,.