Mitigation of low-order atmospheric turbulent effects using sensorless adaptive optics in terrestrial free space optical communication

Abstract

Tip-Tilt and wavefront distortion in the Free Space Optical Communication (FSOC) can be mitigated with Conventional Adaptive Optics (AO) which is widely used in many optical systems to improve the quality of an optical system by manipulating the optical wavefronts using suitable techniques thereby improving BER. This paper describes Sensorless Adaptive optics (SLAO) technique which replaces the high cost wavefront sensor and corrects aberrated optical wavefront by comparing a test wavefront to a perfect, reference wavefront, and then modifying the test wavefront in order to reach the reference wavefront. Artificial Neural Networks (ANN) based reconstruction technique is proposed. The neural network is designed to use the information of tilt in the wave-front acquired by the science camera by extracting the parameters as inputs and estimate the turbulence in terms of Zernike coefficients. Multi-Layer feed forward Neural Network is used to train the inputs and to find actuator control voltages which are applied to DM. In this paper we present a practical implementation of Adaptive Optics system at 850 nm based on a wave-front sensorless architecture. Proposed experimental set-up reduces the complexity and the cost of the conventional adaptive optics system. SLAO provides fast and effective wave-front correction. When compared with the conventional AO systems, the sensorless technique offers the advantage of not requiring the high cost wavefront sensor.