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

Abstract

 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 μrad to 2.35 μrad, and mean-square-error value drops from 6.59 μrad to 1.35 μrad. 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.

Experimental Demonstration of Adaptive Optics Correction of the External Aberrations for Distributed Fiber Laser Array

“…Tip/tilt control here coexists in the wavefront reconstruction procedure. When the power of the coupled laser beacon in each of the AFOC is maximized, subaperture tip/tilt errors have been also corrected for both the laser beams' receiving and transmitting functions of the AFOC array [23], [24]. Sub-aperture wavefront slope vector measured results could reveal the tip/tilt correction performance to some extent.…”

“…The voltages are amplified and drive the AFOCs to maximize the coupled metrics. As discussed in paper [23], the distorted wavefront could be recovered through the voltage values. The distorted phase we want to correct is brought by the glass plate with rough surface.…”

“…Laser beacon carrying with the information of turbulence aberrations is divided by the subapertures and coupled into the single-mode-fibers (SMFs) of the AFOC correspondingly. Through optimizing the coupled power, sub-aperture tip/tilt is corrected and detected [23], [24]. The continuous wavefront is sensed and the sub-aperture averaged pistons are recovered [25], [26].…”

Adaptive SMF Coupling Based on Precise-Delayed SPGD Algorithm and Its Application in Free Space Optical Communication

“…Experimental results tell that the AFC system can further improve the coupling efficiency in both cases of the AO system off and on; however, the calibration of AFC system cannot be fully realized where the presence of higher-order aberrations make it difficult to detect the performance metrics. In addition, technical research of AFC array combined with the mentioned new algorithm is an ongoing effort in our group [14], [15], which is expected to solve the above problems in the future.…”

Experimental Research on Automatic Alignment and Control Algorithm of Spatial Light-Fiber Coupling

“…With the application of fiber-coupled array technology, researchers have found that the existing spatial light-fiber coupling scheme has disadvantages, such as poor reliability and inconvenient array expansion [11]. Moreover, the single-mode fiber (SMF) core diameter is very small (8-10 μm), and it is difficult to realize the coupling and alignment artificially [12].…”