Low-dimensional materials allow us to concentrate light down to atomic dimensions while offering improved strategies for controlling the flow of optical energy at such a scale, opening a fascinating range of applications. However, injection and extraction of externally propagating light into nanosystems remain a challenge because of the large size mismatch of ultraconfined polaritons with respect to the optical wavelength. This in/out-coupling problem in nanophotonics has been addressed following several strategies with mixed degrees of success, including free- and tunneling-electron injection, as well as the mediation of optimized couplers, which we discuss here along with recent results and appealing prospects.
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