Proof of concept for adaptive sequential optimization of free-space communication receivers

Abstract

In a down-link scenario, performance of laser satellite communications is limited due to atmospheric turbulence, which causes fluctuations in the intensity and the phase of the received signal leading to an increase in bit error probability. In principle, a single-aperture phase-compensated receiver, based on adaptive optics, can overcome atmospheric limitations by adaptive tracking and correction of atmospherically induced aberrations. However, under strong-turbulence situations, the effectiveness of traditional adaptive optics systems is severely compromised. We have developed an alternative intensity-based technique that corrects the wave-front by iteratively updating the phases of individual focal-plane speckles, maximizing the power coupled into a single-mode fiber. Here, we present the proof of concept for this method. We show how this technique improves the quality of the received signal by 4 dB gain with less than 60 power measurements under strong turbulence conditions.

Design and optimization of a self-referencing interferometer for effective wavefront sensing in adaptive optics systems

“…Here, we characterize the pinhole aperture with a transmission coefficient p(xf,yf) and a multiplicative constant 1/(f2) 2 , to give a normalized point-spread function.…”

“…Here, ⊗ denotes the convolution operation and P(xo/(0f2),yo/(0f2))/(0f2) 2 is the normalized point-spread function.…”

“…Notable accomplishments by this technology are seen in astronomical imaging systems 1 and free-space optical communication links. 2,3 These links utilize wavefront sensors and deformable mirrors to measure the wavefront distortion in a received laser beam across its transverse profile 4,5 and compensate for the optical distortion 6 , respectively. In free-space optical communication links, the received laser wavefronts must have accurate representations over a wide range of elevation angles at all times.…”