Polarization Control of Linear Dipole Radiation Using an Optical Nanofiber

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We experimentally demonstrate that a linear dipole is not restricted to emit linearly polarized light, provided that it is embedded in the appropriate nanophotonic environment. We observe emission of various elliptical polarizations by a linear dipole, including circularly polarized light, without the need for birefringent components. We further show that the emitted state of polarization can theoretically span the entire Poincaré sphere. The experimental demonstration is based on elongated gold nanoparticles (nanorods) deposited on an optical nanofiber and excited by a free-space laser beam. The light directly collected in the guided mode of the nanofiber is analyzed in regard to the azimuthal position and orientation of the nanorods, observed by means of scanning electron microscopy. We demonstrate a mapping between purely geometrical degrees of freedom of a light source and all polarization states that could open the way to alternative methods for polarization control of light sources at the nanoscale.