In this paper we consider numerical model of an adaptive coherent fiber array system that is utilized for remote transmission of laser power to an active photovoltaic cell (PVC)-based receiver array. The PVC array performs optical-to-electrical power conversion, and provides a feedback signal that is sent to the laser transmitter via optical and/or RF link. The feedback signal is utilized for real-time adaptive shaping of laser power density distribution at the PVC array for achieving the following objectives:
(a) Minimization of laser power losses caused by mismatch between size and shape of the transmitter beam footprint and the PVC array. For optimal performance, the projected laser beam footprint should be adaptively changed to fit the PVC area under continuously changing turbulence strength, distance to the target, system field of view, platform jitter, etc. and
(b) Reduction of laser beam power fluctuations inside the PVC caused by errors in target/load tracking, and laser beam aimpointing and aimpoint stabilization.
In the numerical simulations the optical power with adaptive beam shaping was performed over 3 km and 7 km distances in turbulent atmosphere. The results demonstrate ability of the adaptive fiber array systems with 21 sub-apertures considered, for efficient adaptive beam shaping resulting in significant power beaming efficiency improvement.
In this paper, we focus on the performance improvement of the free space optical communication system and carry out the research on wavefront-sensorless adaptive optics. We use a phase only liquid crystal spatial light modulator (SLM) as the wavefront corrector. The optical intensity distribution of the distorted wavefront is detected by a CCD. We develop a wavefront controller based on ARM and a software based on the Linux operating system. The wavefront controller can control the CCD camera and the wavefront corrector. There being two SLMs in the experimental system, one simulates atmospheric turbulence and the other is used to compensate the wavefront distortion. The experimental results show that the performance quality metric (the total gray value of 25 pixels) increases from 3037 to 4863 after 200 iterations. Besides, it is demonstrated that our wavefront-sensorless adaptive optics system based on SPGD algorithm has a good performance in compensating wavefront distortion.
Adaptive optics (AO) technology is an effective way to alleviate the effect of turbulence on free space optical communication (FSO). A new adaptive compensation method can be used without a wave-front sensor. Artificial bee colony algorithm (ABC) is a population-based heuristic evolutionary algorithm inspired by the intelligent foraging behaviour of the honeybee swarm with the advantage of simple, good convergence rate, robust and less parameter setting. In this paper, we simulate the application of the improved ABC to correct the distorted wavefront and proved its effectiveness. Then we simulate the application of ABC algorithm, differential evolution (DE) algorithm and stochastic parallel gradient descent (SPGD) algorithm to the FSO system and analyze the wavefront correction capabilities by comparison of the coupling efficiency, the error rate and the intensity fluctuation in different turbulence before and after the correction. The results show that the ABC algorithm has much faster correction speed than DE algorithm and better correct ability for strong turbulence than SPGD algorithm. Intensity fluctuation can be effectively reduced in strong turbulence, but not so effective in week turbulence.