Intensity-based adaptive optics with sequential optimization for laser communications.

Carlos E Carrizo,Ramon Mata Calvo,Aniceto Belmonte

doi:10.1364/oe.26.016044

Abstract

Wavefront distortions of optical waves propagating through the turbulent atmosphere are responsible for phase and amplitude fluctuations, causing random fading in the signal coupled into single-mode optical fibers. Wavefront aberrations can be confronted, in principle, with adaptive optics technology that compensates the incoming optical signal by the phase conjugation principle and mitigates the likeliness of fading. However, real-time adaptive optics requires phase wavefront measurements, which are generally difficult under typical propagation conditions for communication scenarios. As an alternative to the conventional adaptive optics approach, here, we discuss a novel phase-retrieval technique that indirectly determines the unknown phase wavefront from focal-plane intensity measurements. The adaptation approach is based on sequential optimization of the speckle pattern in the focal plane and works by iteratively updating the phases of individual speckles to maximize the received power. We found in our analysis that this technique can compensate the distorted phasefront and increase the signal coupled with a significant reduction in the required number of iterations, resulting in a loop bandwidth utilization well within the capacity of commercially available deformable mirrors.

Highlights

Free-space optical communication (FSOC) is rapidly becoming a key enabling technology for terrestrial, aerial, and space communication networks
The adaptation approach is based on sequential optimization of the speckle pattern in the focal plane and works by iteratively updating the phases of individual speckles to maximize the received power
We found in our analysis that this technique can compensate the distorted phasefront and increase the signal coupled with a significant reduction in the required number of iterations, resulting in a loop bandwidth utilization well within the capacity of commercially available deformable mirrors

Summary

Introduction

Free-space optical communication (FSOC) is rapidly becoming a key enabling technology for terrestrial, aerial, and space communication networks. The most common AO approach is based on the well-known Shack-Hartmann wavefront sensor Using this technique, successful optical downlinks achieving Gigabits data rates under weak to moderate turbulence have been recently demonstrated [3,4,5,6,7,8]. Indirect wavefront sensing techniques have gained more scientific attention in the field of FSOC [13,14,15], mainly due to improvements associated with fast DMs, parallel processing, and efficient blind search algorithms [15] These sensor-less techniques iteratively optimize the received power, updating the AO phase compensation system based on the analysis of a performance metric, which is generally power in the bucket.

Turbulence compensation system

Method

Findings

Conclusions