A broadband, background-free quarter-wave plate based on plasmonic metasurfaces.

We demonstrate optically thin quarter-wave plates built with metasurfaces that generate high-quality circularly polarized light over a broad wavelength range for arbitrary orientation of the incident linear polarization. The metasurface consists of an array of plasmonic antennas with spatially varying phase and polarization responses. Experimentally demonstrated quarter-wave plates generate light with a high degree of circular polarization (>0.

Aberration-free ultrathin flat lenses and axicons at telecom wavelengths based on plasmonic metasurfaces.

The concept of optical phase discontinuities is applied to the design and demonstration of aberration-free planar lenses and axicons, comprising a phased array of ultrathin subwavelength-spaced optical antennas. The lenses and axicons consist of V-shaped nanoantennas that introduce a radial distribution of phase discontinuities, thereby generating respectively spherical wavefronts and nondiffracting Bessel beams at telecom wavelengths. Simulations are also presented to show that our aberration-free designs are applicable to high-numerical aperture lenses such as flat microscope objectives.

Out-of-plane reflection and refraction of light by anisotropic optical antenna metasurfaces with phase discontinuities.

Experiments on ultrathin anisotropic arrays of subwavelength optical antennas display out-of-plane refraction. A powerful three-dimensional (3D) extension of the recently demonstrated generalized laws of refraction and reflection shows that the interface imparts a tangential wavevector to the incident light leading to anomalous beams, which in general are noncoplanar with the incident beam. The refracted beam direction can be controlled by varying the angle between the plane of incidence and the antenna array.

Effect of radiation damping on the spectral response of plasmonic components.

We explore the relationship between the near-field enhancement, absorption, and scattering spectra of localized plasmonic elements. A simple oscillator model including both internal and radiative damping is developed, and is shown to accurately capture the near- and far-field spectral features of linear optical antennas, including their phase response. At wavelengths away from the interband transitions of the metal, we expect the absorption of a plasmonic element to be red-shifted relative to the scattering, and the near-field to be red-shifted relative to both.

Light propagation with phase discontinuities: generalized laws of reflection and refraction.

Conventional optical components rely on gradual phase shifts accumulated during light propagation to shape light beams. New degrees of freedom are attained by introducing abrupt phase changes over the scale of the wavelength. A two-dimensional array of optical resonators with spatially varying phase response and subwavelength separation can imprint such phase discontinuities on propagating light as it traverses the interface between two media.

A design for a photonic syringe with multimode coupled slot waveguides.

A design is proposed that allows non-stationary field distribution with Bragg gratings in multiple slot waveguides. Selective coupling between modes is achieved or suppressed, according to controllable selection rules, based on mode symmetry. By applying such rules, backward pulling radiation pressure - i.

Photon energy lifter.

We propose a time-dependent, spatially periodic photonic structure which is able to shift the carrier frequency of an optical pulse which propagates through it. Taking advantage of the slow group velocity of light in periodic photonic structures, the wavelength conversion process can be performed with an efficiency close to 1 and without affecting the shape and the coherence of the pulse. Quantitative Finite Difference Time Domain simulations are performed for realistic systems with optical parameters of conventional silicon technology.

Porous silicon-based rugate filters.

We report an experimental study of porous silicon-based rugate filters. We performed filter apodization, following a half-apodization approach, which successfully attenuated the sidelobes at both sides of the photonic stop band. We achieved successful reduction of interference ripples through the insertion of index-matching layers on the first and last interfaces.

Zener tunneling of light waves in an optical superlattice.

We report on the observation of Zener tunneling of light waves in spectral and time-resolved transmission measurements, performed on an optical superlattice made of porous silicon. The structure was designed to have two photonic minibands, spaced by a narrow frequency gap. A gradient in the refractive index was introduced to create two optical Wannier-Stark ladders and, at a critical value of the optical gradient, tunneling between energy bands was observed in the form of an enhanced transmission peak and a characteristic time dependence of the transmission.

Polarized optical gain and polarization-narrowing of heavily oxidized porous silicon.

We report on a polarization-sensitive optical gain in a blue-emitting Si/SiO(2) nanocrystalline system having a high degree of emission polarization memory. This system can show a positive optical gain or optical loss depending on the polarization state of the pump and emitted light. Under optical gain conditions, the degree of polarization of the amplified spontaneous emission increases with the pumping fluence.

Light transport through the band-edge states of Fibonacci quasicrystals.

The propagation of light in nonperiodic quasicrystals is studied by ultrashort pulse interferometry. Samples consist of multilayer dielectric structures of the Fibonacci type and are realized from porous silicon. We observe mode beating and strong pulse stretching in the light transport through these systems, and a strongly suppressed group velocity for frequencies close to a Fibonacci band gap.