We demonstrate a compact optical transducer (~50μm) based on a gold film perforated with a square array of square holes. The lattice constant (separation between nearest holes) is chosen to be a ~1μm to detect refractive index change around (n~1.4) with resonant wavelength (λ~1.5μm). Both reflectance measurement and finite difference time domain (FDTD) simulations are performed to evaluate the performance of the sensors. The responsivity of the resonant wavelength is measured to be Δλ/Δn ~835nm RIU-1 (RIU= refractive index unit). The linewidth and contrast of resonance are compared with different size of holes from experimental measurement and FDTD simulations. Coupled mode theory analysis is also used to understand the change reflectance spectrum as a function of hole width.
While much work has focused on simulation and measurement of plasmon resonances in noble metal nanostructures, usually the simulation tool is used as a confirmation of experimental results. In this work we use a finite difference time domain (FDTD) technique to calculate the plasmon resonance and electric field enhancement of Ag nanoparticles in regular arrays on quartz substrates. Such structures have also been prepared by e-beam lithography, and the plasmon resonance and surface-enhanced Raman scattering strength of arrays with different nanoparticle size and spacing have been investigated. Arrays of cylindrical nanoparticles were fabricated with varying particle size and interparticle spacing. The observed extinction peaks agree very well with the extinction peaks as calculated by FDTD; typically within a few percent. Experimental plasmon peak widths are considerably larger than their ideal values due to inhomogeneous broadening. As expected, the particle array with highest SERS enhancement has its plasmon resonance nearest the laser and Stokes-shifted wavelengths. We believe the FDTD modeling tool is accurate enough to use as a predictive tool for engineering plasmonic nanostructures.
Electrical operation of III-Nitride light emitting diodes (LEDs) with photonic crystal structures is demonstrated. Employing photonic crystal structures in III-Nitride LEDs is a method to increase light extraction efficiency and directionality. The photonic crystal is a triangular lattice formed by dry etching into the III-Nitride LED. A range of lattice constants is considered (a ~ 270 - 340nm). The III-Nitride LED layers include a tunnel junction providing good lateral current spreading without a semi-absorbing metal current spreader as is typically done in conventional III-Nitride LEDs. These photonic crystal III-Nitride LED structures are unique because they allow for carrier recombination and light generation proximal to the photonic crystal (light extraction area) yet displaced from the absorbing metal contact. The photonic crystal Bragg scatters what would have otherwise been guided modes out of the LED, increasing the extraction efficiency. The far-field light radiation patterns are heavily modified compared to the typical III-Nitride LED’s Lambertian output. The photonic crystal affects the light propagation out of the LED surface, and the radiation pattern changes with lattice size. LEDs with photonic crystals are compared to similar III-Nitride LEDs without the photonic crystal in terms of extraction, directionality, and emission spectra.
The transmission spectra of photonic crystal add-drop filters created in the microwave region are measured. The photonic crystal is a two dimensional square lattice of dielectric rods. The add-drop filters consist of two waveguides formed by removing rods along a line and a cavity lying between the two waveguides. The cavity is formed by removing rods or by replacing them with smaller diameter rods. Depending on the cavity geometry, certain wavelengths can be dropped from one waveguide and added to the other waveguide via resonant coupling through the cavity. A systematic study of the add-drop characteristics is performed as the cavity region is modified. Theoretical results, obtained from finite difference time domain calculations, are in good agreement with measurements.
In this paper, the experimental realization and promises of three-dimensional (3D) photonic crystals in the infrared and optical wavelengths will be described. Emphasis will be placed on the development of new 3D photonic crystals, the micro- and nano-fabrication techniques, the construction of high-Q micro- cavities and the creation of 3D wave-guides.
Shawn-Yu Lin, Joel Wendt, G. Allen Vawter, James Fleming, Dale Hetherington, Bradley Smith, W. Zubrzycki, Edmond Chow, Steven Kurtz, B. Hammons, Pierre Villeneuve, John Joannopoulos, Rana Biswas, Kai Ho, Mihail Sigalas
In this paper, I describe realistic applications of photonic band gap (PBG) materials in optoelectronics at the mm-wave, IR and optical wavelength regimes. Examples are highly dispersive PBG-prisms and PBG-lasers. I will also describe our recent breakthrough at Sandia in the successful fabrication of 3D silicon photonic crystal operating at IR wavelengths.
The transfer matrix method has been used for the calculation of transmission and reflection properties of periodic and/or disordered dispersive photonic band gap (PBG) materials. We have studied the transmission properties of: (1) PBG materials constructed of low resistive Si wafers forming the newly proposed layer-by-layer structure and exhibiting PBG at around 100 GHz; (2) a two-dimensional square lattice consisting of metallic wires; (3) materials having structural gaps close to a polariton gap.
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