Gordon McKay Labs:
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Research | Plasmonics / Metamaterials

Flat lenses based on metasurfaces
F. Aieta, N. Yu, M. Kats, P. Genevet
Flat lenses based on metasurfaces

Using the concept of optical phase discontinuities we design and demonstrate a planar lens that can correct optical aberrations. The surface of a dielectric substrate is coated with concentric rings of metallic nano-antennas that introduce an abrupt phase shift on the scattered wavefront. At a 60 nanometers thick, the flat lens is essentially two-dimensional, yet its focusing power approaches the physical diffraction limit. The planar lens eliminates spherical aberrations while an alternative design on a curved substrate creates the so called aplanatic metasurface, a single interface that focuses light without coma and spherical aberrations reproducing the effect of multiple cascaded elements.

Ultra-thin thin film coatings
M. Kats, R. Blanchard, S. Zhang, P. Genevet, S. Byrnes
Ultra-thin thin film optical coatings

Though they are much thinner than conventional optical thin films and interference coatings, nanometer-thick films made of optically absorbing materials can nonetheless display strong interference effects. We have designed and demonstrated highly-absorbing ultra-thin films for coloring and labeling, tunable infrared absorbers, and anomalous infrared emitters, and are now exploring applications for energy harvesting and photodetection.

Radial beam holograms
P. Genevet, M. Kats, J. Lin
Nanostructured holograms

Nanostructured holographic interfaces can manipulate phase, amplitude, and polarization of light over a broad wavelength range. This is achieved by replacing the large openings of conventional holograms by arrays of subwavelength apertures, oriented to locally select a particular state of polarization. The ability of a single holographic interface to simultaneously shape the amplitude, phase, and polarization of light can find widespread applications in photonics.

Coupling to Flatland
J.P.B. Mueller
Coupling to flatland

What happens when three-dimensional matter interacts with two-dimensional light? The answers are not quite intuitive – and offer some fascinating new perspectives for the development of optical technology.

Holographic plasmonic detector for the angular momentum of light
P. Genevet, M. Kats, J. Lin
Holographic plasmonic detector for the angular momentum of light

Metallic components such as plasmonic gratings and plasmonic lenses are routinely used to convert free-space beams into propagating surface plasmon polaritons and vice versa. This generation of couplers handles relatively simple light beams, such as plane waves or Gaussian beams. Using the concept of holography, we propose a generalization of this strategy to light with more complex wavefronts. Integrating these holographic plasmonic interfaces into commercial silicon photodiodes,we demonstrated selective detection of the orbital angular momentum of light. This holographic approach is very general and can be used to design new types of couplers like planar axicons and new surface waves such as plasmonic bottle beams.

Dynamically Tunable Plasmonic Antennas with Graphene
Y. Yao
Dynamically tunable plasmonic antennas with graphene

In situ control of plasmonic resonances is highly desirable in many applications including multispectral detectors, biochemical sensors, spatial light modulators and ultra-compact optoelectronic devices. Graphene is emerging as a broadband optical and plasmonic material which can be dynamically tuned by electrostatic doping. However, direct application of graphene in optical and optoelectronic devices is limited due to its small thickness and the resultant weak interaction with light. By combining metal and graphene in a hybrid plasmonic structure, it is possible to enhance graphene-light interaction and thus achieve in situ control of the optical response.

Templated Self Assembly on elastomer substrates
L. Sun
Templated self assembly on elastomer substrates

Through template self assembly, we are able to make well defined arrays of clusters of metallic nanoparticles and/or quantum dots for plasmonic and quantum optical applications. When creating templates with elastomer substrates, we are able to reshape the structures by mechanical manipulation such as stretching, compressing, bending, which gives us a new degree of freedom in creating novel optical devices.

N. Yu, M. Kats, P. Genevet, F. Aieta, Z. Gaburro
Modified laws of reflection and refraction

Reflection and refraction are two of the most common phenomena in classical optics and are governed by well-established and simple laws. A key feature of these laws is that the incident, reflected and transmitted beams lie in the same plane, i.e. the plane of incidence. The concept of subwavelength phase discontinuities at an interface between two media opened up a new scenario where some of the classical physical laws must be reviewed. A powerful 3D extension of the laws of refraction and reflection shows that a phase discontinuity interface imparts a tangential wavevector to the incident light leading to anomalous beams, which in general are non-coplanar with the incident beam.

P. Genevet, N. Yu, M. Kats, F. Aieta and Z. Gaburro
Optical phased array: A sudden twist of light

V-shaped plasmonic antenna arrays spatially modulate light beams over a distance much smaller than the wavelength, creating mid-IR optical vortices that are shown to develop after a sub-wavelength propagation distance from the array. The concept of phase discontinuity employed here opens the door to the development of ultra thin and integrated photonics devices.

R. Blanchard, P. Genevet, M. Kats, N. Yu, in collaboration with S. Boriskina and L. Dal Negro (Boston University).
Multi-wavelength near-field focusing

Novel photonic-plasmonic antennas are capable of confining electromagnetic radiation at several mid-infrared wavelengths to a single sub-wavelength spot. The structure relies on the coupling between the localized surface plasmon resonance of a bow-tie nanoantenna with the photonic modes of surrounding multi-periodic particle arrays. We observed the presence of Fano-like interference effects resulting from the interaction of the bow-tie antenna with the surrounding nanoparticle arrays. We imaged the near-field of the multi-wavelength antenna using an aperture-less near-field scanning optical microscope. This antenna could be used for the development of near-field probes for nanoimaging, spectroscopy and biosensing.

N. Yu, M. Kats.
Beam shaping with metasurfaces

Surface plasmons can be used to shape the beams of edge-emitting semiconductor lasers and greatly reduce their large intrinsic beam divergence. Using quantum cascade lasers as a model system, we show that by defining subwavelength apertures and metallic gratings on their facet, a beam divergence angle as small as a few degrees can be obtained in directions both perpendicular and parallel to the laser waveguide layers, representing a reduction in beam spread by more than one order of magnitude compared with the original lasers used. Despite having a patterned facet, our collimated lasers do not suffer significant reductions in output power. Plasmonic collimation provides a means of efficiently coupling the output of a variety of lasers into optical fibres and waveguides, or to collimate them for applications such as free-space communications, ranging, and remote sensing.

P. Genevet, J.P. Tetienne
Plasmonic nanocavity grating

A plasmonic nanocavity grating can dramatically enhance surface optical processes. It consists of resonant cavities that are periodically arranged to combine local and grating resonances, exhibiting very high electric fields in the grooves when the grating launches surface waves corresponding to an incident wavelength which is also resonant with the intrinsic cavity mode. These nanocavities can be filled with molecules or materials of interest, enabling potential applications to nanophotonic devices, nonlinear optics, and spectroscopy.

J. Fan, L. Sun
Plasmonic nanostructures fabricated with templated self assembly

Metal nanoclusters have demonstrated great capability in concentrating light into adjacent nanogaps, opening up their potential for high sensitivity diagnostics. With the assistance of Templated Self Assembly, we can fabricate such clusters in an orderly fashion in large scale. Furthermore, by using soft materials such as PDMS as a substrate, we can deform the cluster patterns into a 3D device which permits 360 degree in situ detection. This project aims to develop a range of techniques to fabricate high quality 2D, 3D Nanoclusters on soft substrates, to study the physics of such clusters, and to eventually leverage these new physical properties to design high-sensitivity diagnostic techniques.

F. Degirmenci with I. Bulu, P. Deotare, M. Khan (Loncar Group)
On-Chip SERS Spectroscopy

Conventional plasmonic sensors rely on the change in refractive index of the medium which requires labeling of sensors in order to make them selective for specific analytes. In order to make a label-free sensor that can detect key molecular fingerprints, it is essential to use spectroscopic tools such as SERS. However, conventional SERS spectroscopy uses free-space coupling and bulky optics. In order to achieve a portable sensor which can do efficient SERS spectroscopy, we propose a waveguide integrated plasmonic platform on-chip.

F. Degirmenci
Carbon Nanotubes as Near Field Probes

Carbon nanotubes (CNTs) are practically one dimensional molecules with diameters around a nanometer and lengths that can reach up to a hundred microns or more. By employing the one dimensional character and spectroscopic properties unique to CNTs such as the “Raman antenna effect”, it is possible to utilize CNTs as polarization sensitive near-field probes with ultra high resolution.