Abstract
Elongated plasmonic nanoparticles have been extensively explored over the past two decades. However, in comparison with the dipolar plasmon mode that has attracted the most interest, much less attention has been paid to multipolar plasmon modes because they are usually thought to be “dark modes”, which are unable to interact with far-field light efficiently. Herein, we report on an intriguing far-field scattering phenomenon, colour routing, based on longitudinal multipolar plasmon modes supported by high-aspect-ratio single Ag nanorods. Taking advantage of the distinct far-field behaviours of the odd and even multipolar plasmon modes, we demonstrate two types of colour routing, where the incident white light can be scattered into several beams with different colours as well as different propagation directions. Because of the narrow linewidths of the longitudinal multipolar plasmon modes, there is little spectral overlap between the adjacent peaks, giving rise to outstanding colour selectivity. Our experimental results and theoretical model provide a simple yet effective picture for understanding the far-field behaviour of the longitudinal multipolar plasmon modes and the resultant colour routing phenomenon. Moreover, the outstanding colour routing capability of the high-aspect-ratio Ag nanorods enables nanoscale optical components with simple geometries for controlling the propagation of light below the diffraction limit of light.
Highlights
The control of light propagation is essential for constructing optical circuits that use light or photons as the medium for carrying information and processing signals
The colour routing effects came to our attention through single-particle dark-field scattering measurements (Fig. 1a) on individual plasmonic nanoparticles of different shapes
For the arrays of N = 3 in both cases, the radiated power is highly concentrated along the waist directions perpendicular to the electric dipole arrays
Summary
The control of light propagation is essential for constructing optical circuits that use light or photons as the medium for carrying information and processing signals. Bulky optical elements such as mirrors, prisms and diffraction gratings are frequently used for modulating the wavefront of a propagating light wave, which is realized over a distance much larger than the wavelength of light. Nanoscale optical components with similar functions are in strong demand for constructing optical nanocircuits, yet this is still very challenging due to the diffraction limit of light[4,5]. Colour routing allows for nanoscale light manipulation with multiple frequency channels, which is highly desired for all-optical communication devices and wavelength-encoded quantum information processing
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