Optical beam tracking and distortion compensation based on a nonlinear lens mechanism

Optical free-space communications involving moving parties require precise beam pointing and mutual tracking of communicating transceivers. The existing variety of tracking techniques is still the major limiting factor in free-space laser communications. Here we propose a technique for optical beam tracking that utilizes nonlinear optical properties of materials. In our proof-of-concept experiment, a thin layer of a nematic liquid crystal (NLC) with high thermal nonlinearity was used to produce a thermal lens induced by the incoming optical beam. That beam modulated the NLC refractive index. As the transmitted optical beam passed through the same layer, the beam intensity was modulated in the far field. A sharp intensity maximum was formed at the distant communicating party position. This tracking capability has been demonstrated for angular disturbances at a subkilohertz frequency. This tracking mechanism also offers adaptive capability of compensation of strong aberrations. Such compensation has been demonstrated experimentally; numerical modeling performed with the Fresnel integral technique showed very good agreement with the experiment. (C) 2008 Goverment of Canada.