James J. Burke

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.

Linear propagation characteristics of periodically segmented waveguides

Periodically segmented planar waveguides are modeled by using the rigorous modal method of diffraction gratings. The radiation loss, effective index, and electric-field strength distribution are analyzed for different segment duty cycles. It is shown that except for the low radiation loss and possible presence of stop bands, a segmented waveguide behaves much like a uniform waveguide. The theoretical calculation confirms the low radiation loss observed experimentally.

Surface-polaritonlike waves guided by thin, lossy metal films

Surface-plasmon polaritons guided by thin, lossy metallic films bounded by dissimilar dielectric media are investigated. New solutions to the dispersion relation are found, representing waves that are leaky (radiative) in one of the dielectrics. The new waves are interpreted in terms of the coupling of a damped surface plasmon at one interface with continuum modes at the other. Their excitation by end-fire coupling techniques is suggested.

Comparison of bending losses in integrated optical circuits

We present measured losses in waveguide sections that are caused by connecting two parallel noncollinear straight waveguides and compare the results with theory. Two different offset transitions are considered, one composed of a straight section with sharp corner bends and the other exhibiting a smooth S-shaped transition. These two types of transitions are compared with each other to determine when each has the lowest loss. In general, sharp corner bends are preferred for small offsets, whereas larger offsets exhibit lower loss with the S-bend design. The experimental results were measured for 3-microm-wide Ti-diffused LiNbO 3 single-mode waveguides.

Gaussian beams from variable groove depth grating couplers in planar waveguides

Analysis, fabrication, and characterization of variable groove depth planar waveguide grating couplers are presented. A formula is derived to describe the grating groove depth variation necessary to produce an outcoupled beam of arbitrary profile. A variable depth grating for producing a Gaussian beam profile is fabricated on a waveguide by ion-beam etching through a scanning slit apparatus. A photoresist grating placed on the waveguide provides a mask to define the grating etched onto the waveguide. The near-field irradiance of the outcoupled beam is measured and shown to approach a Gaussian profile.

Scattering of guided waves by surface periodic gratings for arbitrary angles of incidence: perturbation field theory and implications to normal-mode analysis

A first-order perturbation theory describing the deflection of guided optical waves by sinusoidal surface corrugations on a slab waveguide is presented. The wave equation is satisfied everywhere in space, and the tangential fields are continuous across all interfaces to order δ0k, where k is the optical wave vector and δ0 is the maximum surface displacement. Analytical expressions are derived for synchronously generated normal modes for the geometries TEm → TEm′, TEm → TMm′, TMm → TMm′, and TMm → TEm′. Comparison with normal-mode analyses for the backscattering problem show agreement for TEm → TEm for both the local- and ideal-mode approximations. However, for TMm → TMm the results differ when ideal modes are used to describe the incident fields.

Long‐range surface plasmons in electrode structures

We show that surface plasmon polaritons guided by thin metal electrodes can achieve millimeter plus propagation distances in the near infrared.

Propagation Constants of Resonant Waves on Homogeneous, Isotropic Slab Waveguides

A general graphical study of the complex valued propagation constants, defining the various types of TE waves that are resonant on optical thin-film (slab) waveguides, is presented. The dielectric constants of both the slab and its surroundings are allowed to take on all possible complex values. The corresponding waves are classified into two general types: surface waves, with conductive losses only; and leaky waves, with both conductive and radiative losses.

Restoring with Maximum Entropy, II: Superresolution of Photographs of Diffraction-Blurred Impulses*

Can photographic images, e.g., corresponding to star clusters, be superresolved? Or alternatively, can already good (diffraction-limited) images be improved by restoring methods? To test this hypothesis, objects have been prepared that can be resolved only if the bandwidth in the restoration exceeds that of the image data. The objects are double and triple slits with separations equal to fractions (0.33, 0.50, or 0.65) of Rayleigh’s resolution distance. These are incoherently imaged in quasimonochromatic light by a slit-aperture optical system, and developed as photographs. The amount of diffraction blur is made comparable with the grain-limited resolution distance, since this is the usual situation for an efficient optics–film design. The photos are scanned across the slit directions, digitized, and computer restored by the method of maximum entropy. Results indicate that two object slits can be well resolved when separated by one-half of Rayleigh’s resolution distance, and that three object slits are resolvable subject to a definite hierarchy of confidence: Most accurately restored is the number of object impulses, next are their positions, and least accurate is information on their amplitudes.

Design and fabrication of a single leakage-channel grating coupler

We describe the modeling and fabrication of waveguide grating couplers with theoretical outcoupling efficiencies into a single diffracted order nearing 100%. Termed single leakage-channel grating couplers (or SLCGCs), these devices utilize a high-reflectivity dielectric stack to reflect the outcoupled beam diffracted toward the substrate and back up into the air region, where it constructively adds with the beam diffracted into the air region. Computer modeling shows that the branching ratio and the leakage rate can be independently controlled, and that the branching ratio is independent of grating depth and grating period. A SLCGC with a branching ratio of 97.1% is fabricated by the use of a combination of vacuum-evaporation and wet-chemical techniques.