Dennis G. Hall

Island size effects in nanoparticle-enhanced photodetectors

We report the effect of metal-island size variation in nanoparticle-enhanced photodetectors. Nanoparticle size was controlled by varying the deposition and annealing conditions used to produce the metal-island films. Increasing the size of silver-island particles fabricated onto 165 nm thick silicon-on-insulator (SOI) photodetectors resulted in a dramatic increase in the observed photocurrent. A nearly factor-of-20 photocurrent enhancement was observed for light of wavelength 800 nm, a significant improvement over previously reported results. The improvement is linked to two physical effects: the increased scattering efficiency of the larger nanoparticles and a qualitative change in the resonance characteristics of the metal-island film due to radiative coupling to the SOI waveguide modes.

Absorption enhancement in silicon‐on‐insulator waveguides using metal island films

We report the degree to which the resonances associated with metal island films can be used to enhance the sensitivity of very thin semiconductor photodetectors. The island films can couple incident light into the waveguide modes of the detector, resulting in increased absorption. To characterize the coupling, silver‐, gold‐, and copper‐island layers were formed on the surface of a thin‐film photodetector fabricated in the 0.16 μm thick silicon layer of a silicon‐on‐insulator (SOI) wafer. The copper islands gave the best result, producing more than an order of magnitude enhancement in the photocurrent for light of wavelength 800 nm. The enhancements appear to be due primarily to coupling between the metal island resonances and the waveguide modes supported by the SOI structure.

Vector-beam solutions of Maxwell’s wave equation

The Hermite-Gauss and Laguerre-Gauss modes are well-known beam solutions of the scalar Helmholtz equation in the paraxial limit. As such, they describe linearly polarized fields or single Cartesian components of vector fields. The vector wave equation admits, in the paraxial limit, of a family of localized Bessel-Gauss beam solutions that can describe the entire transverse electric field. Two recently reported solutions are members of this family of vector Bessel-Gauss beam modes.

Circularly symmetric operation of a concentric‐circle‐grating, surface‐ emitting, AlGaAs/GaAs quantum‐well semiconductor laser

A surface‐emitting semiconductor laser that utilizes a concentric‐circle grating defined by electron‐beam lithography is observed to oscillate in a circularly symmetric fashion. The laser emits a circularly symmetric beam with a total beam divergence of less than 1°. Despite its broad‐area geometry, the laser shows no evidence of filamentation. The laser maintains a relatively narrow wavelength spectrum approximately 1 A in width.

Free-space azimuthal paraxial wave equation: the azimuthal Bessel-Gauss beam solution.

We develop a paraxial wave equation for an azimuthally polarized field propagating in free space. The equations beamlike solution is composed of a plane-wave propagation factor multiplied by a Bessel function of the first kind, of order one, and a Gaussian factor, which describe the transverse characteristics of the beam. We compare the propagation characteristics of the azimuthal Bessel-Gauss beam solution with a solution of the more familiar scalar paraxial wave equation, the linearly polarized Bessel-Gauss beam.

Emission through one of two metal electrodes of an organic light-emitting diode via surface-plasmon cross coupling

We report strong surface emission from an organic light-emitting diode in which the luminescent material resides between two nearly opaque metal electrodes. Experimental and theoretical analyses indicate that cross coupling between surface plasmons on opposite sides of the metal cathode layer enables the transmission of electroluminescence through the practically opaque metal. The application of this physical process has the potential to expand the range of device structures possible for organic light-emitting diodes and other electroluminescent devices.

Sinusoidal-Gaussian Beams in Complex Optical Systems

Sinusoidal-Gaussian beam solutions are derived for the propagation of electromagnetic waves in free space and in media having at most quadratic transverse variations of the index of refraction and the gain or loss. The resulting expressions are also valid for propagation through other real and complex lens elements and systems that can be represented in terms of complex beam matrices. The solutions are in the form of sinusoidal functions of complex argument times a conventional Gaussian beam factor. In the limit of large Gaussian beam size, the sine and cosine factors of the beams are dominant and reduce to the conventional modes of a rectangular waveguide. In the opposite limit the beams reduce to the familiar fundamental Gaussian form. Alternate hyperbolic-sinusoidal-Gaussian beam solutions are also found.

Nonlinear optics of long range surface plasmons

We analyze codirectional and counterpropagating second harmonic generation, degenerate four‐wave mixing, and intensity‐dependent refractive index phenomena based on surface plasmon polaritons guided by thin metal films. Promising cross sections are predicted for three out of the four cases.

Optical waveguides in oxygen-implanted buried-oxide silicon-on-insulator structures.

We analyze the waveguiding properties of the oxygen-implanted, buried-oxide, silicon-on-insulator structures currently being developed for use in microelectronics. We find that in spite of the fact that the buried-oxide layer is only a few tenths of a micrometer thick, the single-crystal overlayer can support TE0 guided-wave propagation, at subbandgap wavelengths, with losses due to substrate radiation leakage at or below the benchmark level of 1 dB/cm.

Circularly symmetric distributed feedback laser: coupled mode treatment of TE vector fields

The vector orientation of transverse electric (TE) fields in deriving coupled mode equations for radially outward- and inward-going modes in a circular waveguide diffraction grating is treated. The equations are derived for cylindrical waves in a system that is translationally invariant along the cylinder axis; the derivation is then extended to the waveguide geometry. The coupled mode equations are used to describe the operation of the circularly symmetric distributed feedback (DFB) laser. While predicting a similar dependence of the laser threshold gain on an azimuthal mode order to that found by a simpler, scalar-field treatment, the vector-field treatment predicts a fundamental difference in the location of the cavity resonances. The circular DFB laser is expected to lase in multiple azimuthal modes but maintain a relatively narrow overall spectral width. >