**1. Introduction**

## **1.1. Conventional adaptive optics**

Adaptive optics (AO) was originally developed for astronomical applications and aims to compensate the degrading effect of atmospheric turbulence on optical imaging systems per‐ formance [1]. It was later adapted to other applications such as free-space laser communica‐ tion, surveillance, remote sensing, target tracking and laser weapons [2]. It also found applications in the medical field with retinal imaging [3] and potentially laser surgery. While in the later case degradations are induced by the Earth atmosphere, ocular aberra‐ tions are the limiting factor in the latter case.

Regardless of the application of interest, conventional AO systems typically perform two tasks: (1) they sense the wavefront aberrations resulting from wave propagation through the random media (e.g. the atmosphere), and (2) they compensate these aber‐ rations using a phase conjugation approach. The components required to perform these tasks typically consist of a wavefront sensor (WFS) such as the widely-used Shack-Hartmann WFS, a wavefront corrector (WFC) – typically a deformable or seg‐ mented mirror – and a control device that computes the actuator commands sent to the WFC from the WFS data. This compensation process must be performed at speeds that match or exceed the rate of evolution of the random media – so-called real-time compensation. As a result of this requirement conventional adaptive optics systems are usually complex and often costly.

Although the conventional AO approach successfully mitigates turbulence-induced wave‐ front phase aberrations it presents fundamental and technological limitations.

© 2013 Aubailly and Vorontsov; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Aubailly and Vorontsov; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
