Search

It is shown that isospectral Hamiltonians and partner potentials can be found for self-consistent solutions of the Schrödinger and Poisson equations in the presence of identical non-interacting electrons. Perturbation of these systems by an external electric field can be used to break symmetry and spectrally distinguish between states. For a given pair of partner potentials, symmetry may also be broken by a change of electron density or temperature. [ABSTRACT FROM AUTHOR]

The electromagnetic scattering properties of identical parallel dielectric cylinders configured to closely match a desired response are investigated. Spatial arrangements obtained using a computationally efficient gradient-based optimizer and finite difference forward solver are aperiodic and nonintuitive. We find good agreement between calculations and experiments performed at 37.5 GHz and suggest that finite-sized aperiodic configurations may provide access to functionality inaccessible by conventional periodic, photonic crystal inspired, designs. [ABSTRACT FROM AUTHOR]

Synthesis of semiconductor device design requires access to realistic physical models and adaptive algorithms. To demonstrate that such synthesis is feasible we design elements of a quantum-confined Stark-effect modulator. Optimization with respect to a target function is achieved using a genetic algorithm. It is then shown how automated searches of configuration space may be performed without the need to input a specific target function. [ABSTRACT FROM AUTHOR]

The photon scattering properties of aperiodic nanoscale dielectric structures can be tailored to closely match a desired response by using adaptive algorithms for device design. We show that broken symmetry of aperiodic designs provides access to device functions not available to conventional periodic photonic crystal structures. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Using adaptive algorithms, the design of nanoscale dielectric structures for photonic applications is explored. Widths of dielectric layers in a linear array are adjusted to match target responses of optical transmission as a function of energy. Two complementary approaches are discussed. The first approach uses adaptive local random updates and progressively adjusts individual dielectric layer widths. The second approach is based on global updating functions in which large subgroups of layers are adjusted simultaneously. Both schemes are applied to obtain specific target responses of the transmission function within selected energy windows, such as discontinuous cutoff or power-law decay filters close to a photonic band edge. These adaptive algorithms are found to be effective tools in the custom design of nanoscale photonic dielectric structures. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a model for quantitative analysis of microdisk laser emission spectra. Resonances of an ideal optically transparent dielectric disk; Model for the effects of semiconductor optical gain and loss; Summary and findings.

Studies the nonlinear spectroscopy near half-gap in bulk and quantum well gallium and aluminum compounds waveguides. Required properties of all-optical switching and quantum optics applications; Experimental apparatus and semiconductor samples; Nonlinear index from self-phase modulation.

Presents a study that examined the growth of gallium arsenide (GaAs)/aluminum-GaAs quantum-well lasers using trimethylamine alane. Methodology; Determination of the epitaxial structure of the quantum well laser; Analysis of the properties of the quantum well laser.

We show that the I-V characteristics of graphene-silicon junctions can be actively tuned from rectifying to Ohmic behavior by electrostatically doping the graphene with a polymer electrolyte gate. Under zero applied gate voltage, we observe rectifying I-V characteristics, demonstrating the formation of a Schottky junction at the graphene-silicon interface. Through appropriate gating, the Fermi energy of the graphene can be varied to match the conduction or valence band of silicon, thus forming Ohmic contacts with both n- and p-type silicon. Over the applied gate voltage range, the low bias conductance can be varied by more than three orders of magnitude. By varying the top gate voltage from -4 to +4 V, the Fermi energy of the graphene is shifted between -3.78 and -5.47 eV; a shift of ±0.85 eV from the charge neutrality point. Since the conduction and valence bands of the underlying silicon substrate lie within this range, at -4.01 and -5.13 eV, the Schottky barrier height and depletion width can be decreased to zero for both n- and p-type silicon under the appropriate top gating conditions. I-V characteristics taken under illumination show that the photo-induced current can be increased or decreased based on the graphene-silicon work function difference. [ABSTRACT FROM AUTHOR]

The authors experimentally demonstrate feedback-controlled electro-optic bistability in the whispering gallery travelling-wave optical resonance of a LiNbO3 microdisk. Simulations confirm the physical origin of the behaviour. [ABSTRACT FROM AUTHOR]

The dielectric properties of metallic nanoclusters in the presence of an applied electromagnetic field are investigated using the non-local linear response theory. In the quantum limit we find a nontrivial dependence of the induced field and charge distributions on the spatial separation between the clusters and on the frequency of the driving field. Using a genetic algorithm, these quantum functionalities are exploited to custom-design sub-wavelength lenses with a frequency-controlled switching capability. [ABSTRACT FROM AUTHOR]

We present a self-homodyne photonic microwave receiver architecture that uses linear optical modulation and optical filtering for data down-conversion from a microwave carrier. Preliminary results demonstrate the feasibility of this technique for demodulating up to 100 Mb/s digital data from carrier frequencies above 10 GHz. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 345–350, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23065 [ABSTRACT FROM AUTHOR]

Control of material composition at the nanometer and atomic scale dramatically increases electronic device design space due, in part, to quantum effects. New engineering tools are needed to explore this space and ensure that the best, technologically significant device designs are discovered in a most efficient manner. Using a few prototype examples, this paper describes how a methodology for synthesis might be implemented to advance quantum engineering for electronics. [ABSTRACT FROM AUTHOR]

Nonlinear optical modulation combined with simultaneous photonic and RF resonance in an LiNbO3 microdisk modulator is used to create a self-homodyne photonic RF receiver. Carrier and sidebands are mixed in the optical domain, and the modulated optical signal is detected using a photodetector. The photodetector has a bandwidth matched to the baseband signal. It filters out the high-frequency components and generates the baseband photocurrent. Receiver operation is demonstrated by demodulating up to 100-Mb/s digital data from a 14.6-GHz carrier frequency without any high-speed electronic components. A bit error rate of 10-9 is measured for 10-Mb/s downconverted digital data at -15-dBm received RF power. Preliminary results of employing this photonic RF receiver in a short-distance Ku-band wireless link demonstrate the potential of using high-quality optical microresonators in RF receiver applications. [ABSTRACT FROM AUTHOR]