Co-Aperture Transceiving of Two Combined Beams Based on Adaptive Fiber Coupling Control

Abstract

We demonstrate the reception and transmission of fiber laser beams using two-element adaptive fiber-optics collimator (AFOC) array under simulated turbulences. Coupling efficiency of laser beam from free space into polarization maintaining fibers is optimized with tip/tilt aberration correction. According to the principle of optical reciprocity, tip/tilt errors of the phase-conjugated collimating laser beams are compensated simultaneously. The average of normalized coupling efficiency of one AFOC increases from 0.61 without control to 0.85 under control and 0.57 to 0.85 for another. The average of diffraction-pattern centroid’s deviation of two outgoing combined beams in the far-field drops from $17.5~\mu $ rad to $2.35~\mu $ rad, and mean-square-error value drops from 6.59 to $1.35~\mu $ rad. Control bandwidth of 30 Hz for tip/tilt correction is achieved with computer-based stochastic parallel gradient descent controller with update rate of 1.15 kHz. Results indicate the potential value of the AFOC array in fiber coupling, laser communication and beam projection applications.