# Complex Wavefront Shaping through a Multi-Core Fiber
## 5 Discussion  
The core-GS algorithm provides a robust way for complex wavefront shaping through a 10,000 core MCF with high fidelity. Combining with the on-the-fly closed-loop control of the light field intensity facilitates a homogeneous dynamic rotating dual-spot profile, which can lead to more precise optical manipulation of biological cells [13]. Recent progresses in MCF amplifiers [41; 42; 43] open new perspectives for wavefront shaping through MCFs. Our approach could become a phase-only way for generating structured light and manipulating the intensity of the light field for an MCF amplifier with a large number of cores.  
It may be a concern that many computational efforts can be taken for iterative generation of a large amount of light field, for instance, phase retrieval of the dual-spot at various orientations. A benefit from the similarity of the light field at neighboring orientations, instead of using a random phase as the input, is that the target phase from the last orientation is used as the input for iteration. This can reduce the iteration time from 20 to 5, resulting in 80% less computational time. The current computation is run on a conventional  
Figure 8: Analysis of the experimental rotation of the fiber output dual-spot profile from 0\({}^{\circ}\) to 90\({}^{\circ}\) in 1\({}^{\circ}\)-steps. (**a**) Comparison of the desired and the experimental rotation angle of the dual-spot. (blue-experimental rotation angle; red-desired rotation angle). (**b**) The deviation between the desired and experimental rotation angle, while the mean deviation is 1.9\({}^{\circ}\) and the maximum deviation is 5.1\({}^{\circ}\). (**c**) Comparison of normalized mean intensity at various rotation angles employing Core-GS algorithm with and without on-the-fly manipulation. The standard deviation of the mean intensity decreased from 5.5% to 3.2% and the maximum deviation from 14.5% to 7.9% with the on-the-fly manipulation. (**d**) Normalized difference between the mean intensity of the two spots (background noise removed). The mean intensity difference strongly dropped from 14.9% to 1.4% and the maximum difference from 24.6% to 4.1% with the on-the-fly manipulation. (**e**) Full width half maximum (FWHM) of each spot with and without on-the-fly manipulation at different orientations. The standard deviation of the FWHM of the right spot optimized from 0.37 μm to 0.24 μm, and for the left spot from 0.32 μm to 0.2 μm.  
CPU (i5-6500); it takes about 13 s to generate each phase modulation frame on average. The computational speed can be boosted with GPU acceleration. The bandwidth of the on-the-fly control can be further increased by using SLM with higher speed.  
The quality of the wavefront shaping through the MCF is strongly influenced by the phase distortion compensation. In this work, the phase distortion is measured at the distal fiber facet, which demands optical access to both fiber tips. In situ calibration of the MCF could employ our previously reported procedure [44] to compensate for the bending and temporal phase distortions without distal access. An alternative way could be employing the recently reported specially twisted MCF which is invariant in conformation and its performance is independent of fiber bending [15]. The quality of the wavefront shaping can be further improved by using MCFs with more cores; however, that will also increase the complexity of the modulation hologram and require more iteration times.