Andreas C. Liapis

Surface-plasmon polaritons on metal-dielectric nanocomposite films.

We demonstrate both theoretically and experimentally that the surface plasmon polaritons supported by a metal-dielectric nanocomposite film have properties that fall into one of three distinct categories depending on the metal fill fraction.

Measurement of the complex nonlinear optical response of a surface plasmon-polariton

We observe experimentally the self-phase modulation of a surface plasmon-polariton (SPP) propagating along a gold film bounded by air in a Kretschmann-Raether configuration. Through analyzing the power dependence of the reflectance curve as a function of the incidence angle, we characterize the complex-valued nonlinear propagation coefficient of the SPP. Moreover, we present a procedure that can further extract the complex value of the third-order nonlinear susceptibility of gold from our experimental data. Our work provides direct insights into nonlinear control of SPPs utilizing the nonlinearity of metals, and serves as a practical method to measure the complex-valued third-order nonlinear susceptibility of metallic materials.

On-chip spectroscopy with thermally tuned high-Q photonic crystal cavities

Spectroscopic methods are a sensitive way to determine the chemical composition of potentially hazardous materials. Here, we demonstrate that thermally tuned high-Q photonic crystal cavities can be used as a compact high-resolution on-chip spectrometer. We have used such a chip-scale spectrometer to measure the absorption spectra of both acetylene and hydrogen cyanide in the 1550 nm spectral band and show that we can discriminate between the two chemical species even though the two materials have spectral features in the same spectral region. Our results pave the way for the development of chip-size chemical sensors that can detect toxic substances.

Optimizing photonic crystal waveguides for on-chip spectroscopic applications.

We investigate the applicability of photonic crystal waveguides to high-resolution on-chip spectrometers. We argue that the figure of merit by which their performance should be gauged is not the group index bandwidth product, which photonic crystal waveguides are usually optimized for, but the working finesse, which relates to the maximum number of spectral lines resolvable by a slow-light spectrometer. Through numerical simulation, we show that a properly-optimized photonic crystal waveguide could form the basis of a spectrometer with a spectral resolution of 0.04 nm over a 12.5 nm bandwidth near 1550 nm and with a footprint six times smaller than a conventional spectrometer.

Simulating Quantum-Mechanical Barrier Tunneling Phenomena with a Nematic-Liquid-Crystal-Filled Double-Prism Structure

We present an electrically-controlled nematic-liquid-crystal-filled double-prism structure that can be used to simulate quantum-mechanical tunneling through a barrier of variable height. Measurements of time delay in reflection from this structure, taken with femtosecond resolution using entangled photon pairs in a Hong-Ou-Mandel interferometer, are compared to theoretical predictions. We show that the Goos-Hänchen contribution to the tunneling delay is unmeasurable in this geometry. Our research contributes to the understanding of quantum-mechanical barrier tunneling times, and can lead to the fabrication of optical analogues to the tunnel junction and other photonic devices.

Plasmonic transparent conductors

Many of today’s technological applications, such as solar cells, light-emitting diodes, displays, and touch screens, require materials that are simultaneously optically transparent and electrically conducting. Here we explore transparent conductors based on the excitation of surface plasmons in nanostructured metal films. We measure both the optical and electrical properties of films perforated with nanometer-scale features and optimize the design parameters in order to maximize optical transmission without sacrificing electrical conductivity. We demonstrate that plasmonic transparent conductors can out-perform indium tin oxide in terms of both their transparency and their conductivity.

Nanocrystal fluorescence in photonic bandgap microcavities and plasmonic nanoantennas

Results are presented here towards robust room-temperature single-photon sources based on fluorescence in nanocrystals: colloidal quantum dots, color-center diamonds and doped with trivalent rare-earth ions (TR3+). We used cholesteric chiral photonic bandgap and Bragg-reflector microcavities for single emitter fluorescence enhancement. We also developed plasmonic bowtie nanoantennas and 2D-Si-photonic bandgap microcavities.

Development of a slow-light spectrometer on a chip

We discuss the design and development of a slow-light spectrometer on a chip with the particular example of an arrayed waveguide grating based spectrometer. We investigate designs for slow-light elements based on photonic crystal waveguides and grating structures. The designs will be fabricated using electron-beam lithography and UV photolithography on a silicon-on-insulator platform. We optimize the geometry of these structures by numerical simulations to achieve a uniform and large group index over the largest possible wavelength range.

Chirped circular dielectric gratings for near-unity collection efficiency from quantum emitters in bulk diamond

Efficient collection of fluorescence from nitrogen vacancy (NV) centers in diamond underlies the spin-dependent optical read-out that is necessary for quantum information processing and enhanced sensing applications. The optical collection efficiency from NVs within diamond substrates is limited primarily due to the high refractive index of diamond and the non-directional dipole emission. Here we introduce a light collection strategy based on chirped, circular dielectric gratings that can be fabricated on a bulk diamond substrate to modify an emitter’s far-field radiation pattern. Using a genetic optimization algorithm, these grating designs achieve 98.9% collection efficiency for the NV zero-phonon emission line, collected from the back surface of the diamond with an objective of aperture 0.9. Across the broadband emission spectrum of the NV (600–800 nm), the chirped grating achieves 82.2% collection efficiency into a numerical aperture of 1.42, corresponding to an oil immersion objective again on the back side of the diamond. Our proposed bulk-dielectric grating structures are applicable to other optically active solid state quantum emitters in high index host materials.

Plasmonic nanoantennas with liquid crystals for nanocrystal fluorescence enhancement and polarization selectivity of classical and quantum light sources

ABSTRACT We discuss plasmonic nanoantennas for emitter fluorescence enhancement and wavelength tunability of plasmonic resonance using liquid crystals. The results of numerical modeling of a plane wave scattered by bowtie nanoantennas in isotropic liquid crystal media with different refractive indexes are presented for two plasmonic materials. Experimental results are reported on fabricated gold bowtie nanoantenna arrays by high-precision electron-beam lithography. Photon antibunching from nanocrystal quantum dot within a bowtie nanoantenna gap was obtained, proving nonclassical behavior of light from such a source. In addition, the first results towards gap/patch nanoantennas with single emitters in liquid crystal hosts as well as photon antibunching are reported for nanodiamonds with NV-color-centers dispersed in nematic liquid crystal hosts. Depending on nanocrystal concentration our results can find applications in displays, organic light-emitting diodes, microlasers, and single photon sources for secure quantum communication.