Exceptional point based lattice gyroscopes

Ring laser gyroscopes (RLGs) based on non-Hermitian exceptional points (EPs) have garnered much recent interest due to their exceptional sensitivity. Such gyroscopes typically consist of two-ring laser resonators, one with loss and one with an equal amount of optical gain. The coupling strength between these ring resonators is a key parameter determining the sensitivity of EP-based RLGs. Here we explore how the exceptional sensitivity demonstrated in this coupled dimer may be further enhanced by adding more dimers in an array. Specifically, we propose two types of ring laser gyroscope lattice arrays, each composed of N coupled dimers arrayed serially or concentrically with periodic boundary conditions, that guide counter-propagating photons in a rotating frame. Using coupled mode theory, we show that these lattice gyroscopes exhibit an enhanced effective coupling rate between the gain and loss resonators at the EP, thereby producing greater sensitivity to the angular rotation rate than their constituent dimers. This work paves the way toward EP-based RLGs with the necessary sensitivity for GPS-free navigation

Ultra-compact modulators based on novel CMOS-compatible plasmonic materials

We propose several planar layouts of ultra-compact plasmonic waveguide modulators that utilize alternative CMOS-compatible materials. The modulation is efficiently achieved by tuning the carrier concentration in a transparent conducting oxide layer, thereby tuning the waveguide either in plasmonic resonance or off-resonance. Resonance significantly increases the absorption coefficient of the plasmonic waveguide, which enables larger modulation depth. We show that an extinction ratio of 86 dB/um can be achieved, allowing for a 3-dB modulation depth in less than one micron at the telecommunication wavelength. Our multilayer structures can potentially be integrated with existing plasmonic and photonic waveguides as well as novel semiconductor-based hybrid photonic/electronic circuits

Alternative Plasmonic Materials: Alternative Plasmonic Materials: Beyond Gold and Silver (Adv. Mater. 24/2013):Inside Front Cover

Materials research plays a vital role in transforming breakthrough scientific ideas into next‐generation technology. Similar to the way silicon revolutionized the microelectronics industry, the proper materials can greatly impact the field of plasmonics and metamaterials. Currently, research in plasmonics and metamaterials lacks good material building blocks in order to realize useful devices. Such devices suffer from many drawbacks arising from the undesirable properties of their material building blocks, especially metals. There are many materials, other than conventional metallic components such as gold and silver, that exhibit metallic properties and provide advantages in device performance, design flexibility, fabrication, integration, and tunability. This review explores different material classes for plasmonic and metamaterial applications, such as conventional semiconductors, transparent conducting oxides, perovskite oxides, metal nitrides, silicides, germanides, and 2D materials such as graphene. This review provides a summary of the recent developments in the search for better plasmonic materials and an outlook of further research directions

Ultrabroadband terahertz conductivity of highly doped ZnO and ITO

The broadband complex conductivities of transparent conducting oxides (TCO), namely aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO) and tin-doped indium oxide (ITO), were investigated by terahertz time domain spectroscopy (THz-TDS) in the frequency range from 0.5 to 18 THz using air plasma techniques, supplemented by the photoconductive antenna (PCA) method. The complex conductivities were accurately calculated using a thin film extraction algorithm and analyzed in terms of the Drude conductivity model. All the measured TCOs have a scattering time below 15 fs. We find that a phonon response must be included in the description of the broadband properties of AZO and GZO for an accurate extraction of the scattering time in these materials, which is strongly influenced by the zinc oxide phonon resonance tail even in the low frequency part of the spectrum. The conductivity of AZO is found to be more thickness dependent than GZO and ITO, indicating high importance of the surface states for electron dynamics in AZO. Finally, we measure the transmittance of the TCO films from 10 to 200 THz with Fourier transform infrared spectroscopy (FTIR) measurements, thus closing the gap between THz-TDS measurements (0.5-18 THz) and ellipsometry measurements (200-1000 THz). (C)2015 Optical Society of Americ

A comparative study of semiconductor-based plasmonic metamaterials

Recent metamaterial (MM) research faces several problems when using metal-based plasmonic components as building blocks for MMs. The use of conventional metals for MMs is limited by several factors: metals such as gold and silver have high losses in the visible and near-infrared (NIR) ranges and very large negative real permittivity values, and in addition, their optical properties cannot be tuned. These issues that put severe constraints on the device applications of MMs could be overcome if semiconductors are used as plasmonic materials instead of metals. Heavily doped, wide bandgap oxide semiconductors could exhibit both a small negative real permittivity and relatively small losses in the NIR. Heavily doped oxides of zinc and indium were already reported to be good, low loss alternatives to metals in the NIR range. Here, we consider these transparent conducting oxides (TCOs) as alternative plasmonic materials for many specific applications ranging from surface-plasmon-polariton waveguides to MMs with hyperbolic dispersion and epsilon-near-zero (ENZ) materials. We show that TCOs outperform conventional metals for ENZ and other MM-applications in the NIR.Comment: 16 pages, 7 figure

Temperature-dependent optical properties of titanium nitride

The refractory metal titanium nitride is promising for high-temperature nanophotonic and plasmonic applications, but its optical properties have not been studied at temperatures exceeding 400 °C. Here, we perform in-situ high-temperature ellipsometry to quantify the permittivity of TiN films from room temperature to 1258 °C. We find that the material becomes more absorptive at higher temperatures but maintains its metallic character throughout visible and near infrared frequencies. X-ray diffraction, atomic force microscopy, and mass spectrometry confirm that TiN retains its bulk crystal quality and that thermal cycling increases the surface roughness, reduces the lattice constant, and reduces the carbon and oxygen contaminant concentrations. The changes in the optical properties of the material are highly reproducible upon repeated heating and cooling, and the room-temperature properties are fully recoverable after cooling. Using the measured high-temperature permittivity, we compute the emissivity, surface plasmon polariton propagation length, and two localized surface plasmon resonance figures of merit as functions of temperature. Our results indicate that titanium nitride is a viable plasmonic material throughout the full temperature range explored