Mode multiplexed single-photon and classical channels in a few-mode fiber.

We classically measure the entire propagation matrix of a few-mode fiber and use a spatial light modulator to undo modal mixing and recover single-photons launched onto each of the eigenmodes of the fiber at one end, but arriving as mixed modal superpositions at the other. We exploit the orthogonality of these modal channels to improve the isolation between a quantum and classical channel launched onto different spatial and polarization modes at different wavelengths. The spatial diversity of the channels provides an additional 35dB of isolation in addition to that provided by polarization and wavelength.

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