Complete polarization control in multimode fibers with polarization and mode coupling

Multimode optical fibers have seen increasing applications in communication, imaging, high-power lasers, and amplifiers. However, inherent imperfections and environmental perturbations cause random polarization and mode mixing, causing the output polarization states to be different from the input polarization states. This difference poses a serious issue for employing polarization-sensitive techniques to control light–matter interactions or nonlinear optical processes at the distal end of a fiber probe. Here, we demonstrate complete control of polarization states for all output channels by only manipulating the spatial wavefront of a laser beam into the fiber. Arbitrary polarization states for individual output channels are generated by wavefront shaping without constraining the input polarization. The strong coupling between the spatial and polarization degrees of freedom in a multimode fiber enables full polarization control with the spatial degrees of freedom alone; thus, wavefront shaping can transform a multimode fiber into a highly efficient reconfigurable matrix of waveplates for imaging and communication applications.Optics: Controlling polarization key to better performing optical fibersBy controlling the spatial wavefront of light beams, scientists have developed an innovative approach for eliminating polarization distortions in signals transmitted through optical fibers, leading to more efficiency devices for use in communication and imaging technologies. Owing to its high capacity and reliability, multimode fibers (MMFs) have seen increasing use in a range of devices used in communication, imaging, high-power lasers, and amplifiers. However, imperfections and perturbations that occur during signal transmission cause polarization scrambling and random mode mixing of the light, making the output polarization states very different from the input. Led by Hui Cao and colleagues from Yale University in the United States, researchers have developed a method for controlling polarization by utilizing strong mode and polarization coupling in the multimode fibers, which could be used for applications in optical imaging, communications and remote sensing.