Studying On The Wavefront-sensorless Adaptive Optics Applied In FSO

In the late20thcentury, the rapid improvement of science and technology, especiallythe appearance of laser, promoted the development of free space optical communication(FSO). For its significant advantages such as high-data-rate of transferring, strongcapability of anti-interference, and no regulatory restrictions for frequencies andbandwidths, major communications vendors in the world has lay more and more attentionon it. But because of propagating in the atmosphere, the laser beam suffers from the impactof the atmospheric turbulence inevitably, which causes turbulence of the wave andconstrains the performance of FSO system.In recent years, the principle and technology of adaptive optics (AO) have been appliedinto FSO system to eliminate the influences of turbulent atmosphere. Based onwavefront-sensorless adaptive optical system, this paper analyses some methods of phasereconstruction applied in this region. On the first place, we focus on some characters of thelaser beam propagating in random media and introduce Zernike polynomials, a simple andwidely used mathematical expression. Then some classic theory on optical wave inconstant refractive-index media is reviewed later. Next, our attention will be attracted bythe principle of adaptive optics (AO) and some algorithm using in wavefront-sensorless AOfor phase reconstruction, especially the process of solving the transport of intensityequation (TIE) which establishes direct relationship between the intensity and phase, thenthe solving methods of this equation based on Zernike polynomials with uniform ornonuniform intensity distribution are discussed in detail separately. For the key point ofsolving TIE, the measurement of the intensity gradient, we analyses the classic two-planemethod and a simple optical system to realize it with only one plane array detector. In theend, a novel multi-plane method for gradient derivation is proposed which takes the impactof both detecting noise and higher order derivatives into account and has been proved to own strong capability of noise suppression and accuracy increase by the simulation results.