posted on 2016-06-17, 00:00authored byAlejandro Manjavacas
Photonic systems
containing active and passive elements with balanced gain and loss
are attracting increased attention due to their extraordinary properties.
These structures, usually known as PT-symmetric
systems, display strongly asymmetric behaviors. Here we study the
optical response of finite nanostructures composed of pairs of active
and passive nanospheres operating close to the PT-symmetry
condition. We find that, despite their highly regular geometry, these
systems scatter light predominantly toward the gain side of the structure
when illuminated perpendicularly to their axis. Furthermore, the backscattering
intensity for illumination parallel to the axis depends strongly on
the side of incidence, being several times larger for light coming
along the gain side. Interestingly, under the same conditions, the
forward scattering and, consequently, the extinction cross-section
remain independent of the side of incidence. This leads to an asymmetric
absorption cross-section that can be made arbitrarily small for light
impinging on the gain side of the structure. These results contribute
to the basic understanding of the optical properties of active–passive
finite nanostructures with potential applications for the design of
novel nanostructures displaying asymmetric and tunable responses.