The field of plasmonics—in which surface plasmon resonances of
metals are used to manipulate light at the sub-wavelength scale—
is transforming our understanding of nanophotonics and integrated
optics. Now, researchers are harnessing the power of plasmonics,
paving the way to wavefront engineering of laser beams.
I
n nanophotonics, light is controlled using metallic and dielectric nanostructures with fea-
ture sizes much smaller than a wavelength. The first modern application of nanophotonics
was probably the near-field scanning optical microscope. But there is also historical evi-
dence that ancient Greek and medieval artisans unwittingly used nanophotonics to impart
bright colors on glass objects; the glass had been doped with metallic nanoparticles that caused
it to absorb and scatter light at certain wavelengths.
Absorption in metallic nanoparticles is caused by confined collective oscillations of electrons interacting with an electromagnetic field, known as surface plasmon resonances. Surface
plasmons can also propagate along the interface between a metal and a dielectric as electron
density waves coupled to the electromagnetic field. Researchers have known about plasmons for
decades, but it wasn’t until recently that they began integrating plasmonic structures onto common optical components, such as semiconductor lasers and optical fibers, in order to engineer
their near- and far-fields and create new functionalities.
The manipulation of light using surface plasmons—known as plasmonics—has a wide range
of applications in imaging, sensing, communications and optical manipulation. Unlike conventional optical components, plasmonic structures manipulate light at the sub-wavelength level in
real space or over a wide range of k vectors in wave-vector space.
Our work explores the use of plasmonics for laser beam shaping based on monolithic
integration. Currently, laser beams are manipulated externally using optical components such
as lenses, beam-splitting polarizers and wave plates. These components are often bulky and
expensive and don’t provide the degree of flexibility and the range of new functionalities made
possible by integrated optics.
Plasmonics could provide a compact and universal solution to beam shaping for semiconductor
lasers and optical-fiber-based light sources. By fabricating in situ on their facet sub-wavelength
metallic-dielectric structures, researchers can design the near-field and far-field almost at will to
achieve major performance improvements or to add new functionalities.
