Abstract
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.
Highlights
The vectorial nature of electromagnetic waves plays an indispensable role in light–matter interaction, optical transmission, and imaging
Mode coupling To illustrate the critical role played by spatial mode coupling in polarization control, let us first consider an multimode fiber (MMF) with only polarization mixing but no mode mixing
Polarized (LP) modes are the eigenmodes of a perfect fiber under the weak guiding approximation[34]
Summary
The vectorial nature of electromagnetic waves plays an indispensable role in light–matter interaction, optical transmission, and imaging. Control over the polarization state of light has been widely exploited in single-molecule detection, nanoplasmonics, optical tweezers, nonlinear microscopy, and optical coherence tomography. A well-prepared state of polarization can be scrambled by multiple scatterings of light in threedimensional disordered media. Arbitrary polarization states have been attained in a single or a few spatial channels[1,2,3,4,5], transforming the random medium into a dynamic waveplate. For imaging and sensing applications, full polarization control of all output channels can avoid spatial point scanning and acquire information in parallel. It is extremely difficult to control the polarization state of the total transmitted light, and the relatively low transmission through a scattering medium limits the efficiency
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