Polarization-Resolved Transmission Matrices of Specialty Optical Fibers

Abstract: Transmission matrix measurements of multimode fibers are now routinely performed in numerous labs, enabling control of the electric field at the distal end of the fiber and paving the way for the potential application to ultrathin medical endoscopes with high resolution. However, the process of building an experimental setup and developing the supporting code to measure the fiber's transmission matrix remains challenging with full details on experimental design, data collection, and supporting algorithms spread over multiple papers or lacking in detail. Here, we outline a complete and self-contained description of the experiment we use to measure fully polarization-resolved transmission matrices. Our specific implementation of the full polarization experiment is new and is easy to align while providing flexibility to switch between full-polarization and scalar measurements if desired. We introduce a new method to measure and account for the phase and amplitude drift during the measurement using a Levenberg-Marquardt nonlinear fitting algorithm. Finally, we describe creating distal images through the multimode fiber using phase-to-amplitude shaping techniques to construct the correct input electric field and show that results are insensitive to this choice as quantified by measuring the contrast of a razor blade at the distal end of the fiber. Throughout the paper, we discuss applications of our setup and measurement process to a variety of specialty fibers, including fibers with harsh environment coatings, coreless fibers, rectangular core fibers, pedestal fibers, and a pump-signal combiner based on a tapered fiber bundle.