Shaping single photons through multimode optical fibers using mechanical perturbations

Abstract

Multimode optical fibers support low-loss transmission of multiple spatial modes, allowing for the transport of high-dimensional, spatially encoded information. In particular, encoding quantum information in the transverse shape of photons may boost the capacity of quantum channels while using existing infrastructure. However, when photons propagate through a multimode fiber, their transverse shape gets scrambled because of mode mixing and modal interference. This is usually corrected using free-space spatial light modulators, inhibiting a robust all-fiber operation. In this work, we demonstrate an all-fiber approach for controlling the shape of single photons and the spatial correlations between entangled photon pairs, using carefully controlled mechanical perturbations of the fiber. We optimize these perturbations to localize the spatial distribution of a single photon or the spatial correlations of photon pairs in a single spot, enhancing the signal in the optimized spot by over an order of magnitude. Using the same approach, we show a similar enhancement for coupling light from a multimode fiber into a single-mode fiber.