Beam Steering and Divergence Control Using Variable Focus Liquid Lenses for WDM FSO Communications

Optical beam steering and divergence control is a critical function in free-space optical (FSO) communications. Variable focus liquid lenses (VFLLs) can be used for simultaneous realization of beam steering and adaptive beam divergence control. Two off-axis VFLLs are employed to steer the optical beam in 2 dimensional directions, while one on-axis VFLL adjusts the beam divergence adaptively to channel conditions. This VFLL-based system has been studied only for single-wavelength FSO communications. In this letter, we explore the possibility of using the VFLL-based system for wavelength-division-multiplexed (WDM) FSO communications. For this purpose, we investigate the wavelength dependence of VFLL-based optical beam steering and divergence control through experiment and theory. We also demonstrate the transmission of
$4\times 10$
-Gb/s WDM signals over a 104-m FSO link.