Abstract
Light polarization control is a key factor in modern photonics. Recent advances in surface plasmon manipulation have introduced the prospect of more compact and more efficient devices for this purpose. However, the current plasmonic-based polarization optics remain much larger than the wavelength of light, which limits the design degrees of freedom. Here, we present a plasmonic traveling-wave nanoantenna using a gold-coated helical carbon nanowire end-fired with a dipolar aperture nanoantenna. Our nonresonant helical nanoantenna enables tunable polarization control by swirling surface plasmons on the subwavelength scale and taking advantage of the optical spin–orbit interaction. Four closely packed helical traveling-wave nanoantennas (HTNs) are demonstrated to locally convert an incoming light beam into four beams of tunable polarizations and intensities, with the ability to impart different polarization states to the output beams in a controllable way. Moreover, by near-field coupling four HTNs of opposite handedness, we demonstrate a subwavelength waveplate-like structure providing a degree of freedom in polarization control that is unachievable with ordinary polarization optics and current metamaterials.
Highlights
A wide variety of optical applications and techniques demand light polarization control
By coupling helical traveling-wave nanoantennas (HTNs) of opposite handedness, we demonstrate a subwavelength waveplate-like structure providing a degree of freedom in polarization control that is unachievable when utilizing birefringence and dichroism in materials or artificially reproducing these properties with metamaterials
Relying on the spin–orbit interaction of light, HTNs lead to ultracompact, versatile and robust polarization optics, enabling new degrees of freedom in light polarization control
Summary
A wide variety of optical applications and techniques demand light polarization control. The manipulation of light polarization is realized with bulky optical elements, which utilize birefringent or dichroic materials. This field has recently experienced extraordinary advances with the emergence of plasmonics, which has offered new prospects regarding the light–matter interaction. The nonresonant manipulation of surface plasmons has demonstrated the ability to control light polarization[19,20] Both of these resonant and nonresonant structures rely on collective optical effects on arrays of nanostructures. They are restricted to areas much larger than the wavelength of light, which limits design strategies and functions in polarization control. The individual scatterers developed so far radiate highly diverging optical waves, which may represent limitations in the implementation of subwavelength polarization optics
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