A. Sharon

Resonant grating–waveguide structures for visible and near-infrared radiation

A new ray picture model based on the multiple interference of light waves in dielectric resonant grating–waveguide structures is presented. The model clearly elucidates the phase relationship between the incident plane wave and the waves diffracted from the resonant grating structure that is responsible for the interference of these waves. As a result of this interference process the incident wave can be totally reflected at a certain wavelength and orientation angle. The model is used to describe and analyze this resonance behavior of the grating–waveguide structures as a function of wavelength and incidence angle. The analysis is verified experimentally with semiconductor (InGaAsP/InP) structures at wavelengths of 1.55 μm and also with dielectric (silicon nitride/SiO2) structures at wavelengths of 0.6 μm. All of the structures were formed by electron beam lithography and chemical vapor deposition. The measured results reveal that subnanometer resonance bandwidths and finesses as large as 6000 can be achieved at contrast ratios of 50 with relatively compact structures.

Light modulation with resonant grating–waveguide structures

Resonant grating-waveguide structures formed with InP/InGaAsP semiconductor materials were tested to show light modulation at a wavelength of 1.55 microm. Narrow, subnanometer resonant spectral bandwidths and a ratio of ref lected intensities between resonance and away from resonance of greater than 50 were measured. For a resonant structure with an area of 3 mm x 3 mm, the modulation frequency reached 5 MHz.

Narrow spectral bandwidths with grating waveguide structures

Under certain conditions grating/waveguide structures have a resonant behavior with narrow spectral bandwidths. Several such structures were designed, fabricated, and evaluated, demonstrating resonances with narrow spectral bandwidths ranging to as low as 0.035 nm at full width at half maximum. These can be exploited as compact spectral filters having high finesse.

Metal-based resonant grating waveguide structures

A new analytic model, based on the interference of waves, and numerical calculations are exploited for analyzing the spectral behavior of the transmitted and reflected intensities from metal-based grating–waveguide structures. The results reveal that strong intensity changes can occur near resonance with resonance bandwidths in the subnanometer range. These intensity changes are found to be strongly dependent on specific parameters of the structures, particularly the height of the grating and the absorption in the metallic layer. Several structures were fabricated and evaluated experimentally to demonstrate that spectral bandwidths of 0.1 nm and intensity changes as large as 60% can be achieved.

LONG-RANGE SURFACE PLASMON RESONANCES IN GRATING-WAVEGUIDE STRUCTURES

Resonant grating-waveguide structures were used for the excitation of long-range surface plasmons. Resonance spectral bandwidths of 1.9 nm were experimentally measured in both the reflected and transmitted intensities from these structures. Numerical calculations indicate that interference rather than the usual surface plasmon absorption mechanism plays the dominant role in the resonance response when the thickness of the guiding metal layer in the structures is reduced below 10 nm.

Spectral shifts and line-shapes asymmetries in the resonant response of grating waveguide structures

Abstract The resonant spectral response that grating-waveguide structures display in the transmitted and reflected intensities, is analyzed with the aid of a newly developed wave interference model. The resonant response is shown to be generally accompanied by wavelength shifts for the transmitted and reflected intensities, resulting in asymmetric resonance line-shapes. A simple rule that relates the ratio of these resonant shifts to the reflected intensity from the structure away from resonance is obtained. The predicted results from the model were confirmed experimentally with both dielectric as well as metal based grating-waveguide structures.

Active semiconductor-based grating waveguide structures

Under certain conditions, a high-finesse resonance phenomenon can occur in a grating waveguide structure (GWS). By varying these conditions, a shift in the resonance wavelength can be achieved. Specifically, utilizing the high finesse property of the GWS, small changes in the refractive index can result in a tuning range larger than the resonance bandwidth. Here, we consider different electric-field and charge carrier mechanisms that can affect the refractive index in semiconductor materials, and exploit them in order to control the refractive index change and, therefore, the resonance wavelength in the GWS. The predicted results are verified experimentally with an active GWS formed with semiconductor materials and operated in a reverse voltage configuration.

Resonant Structures for Optical Processing and Communication

When a grating-waveguide structure is illuminated with an incident light beam at a specific wavelength and angular orientation, a resonant phenomenon occurs. The resonance spectral bandwidth can be very narrow, so the structure can serve either as a spectral filter or an optical modulator. The basic principles, analytic and numerical models, design and fabrication procedures, and calculated and experimental results are presented. The results reveal that passive resonant structures can have spectral bandwidths as low as 0.085 nm, and active structures can be modulated at 10 MHz.

Resonance phenomena in grating/waveguide structures

An optical resonance phenomena, based on an interference effect that occurs when a plane wave is incident on a dielectric grating/waveguide structure, is presented. The incident wave excites a guided mode in the waveguide which in turn is partially diffracted by the grating in the direction of the transmitted zero order beam, interfering destructively. As a result most of the light energy is contained in the reflected zero order beam. This resonance phenomena is explained with a ray picture of the multiple interference and analyzed by solving Maxwells equations for the exact eigenfunctions in a grating/waveguide structure. Some basic structures have been fabricated and experimentally tested. The results reveal that the resonance beamwidth and bandwidth depend strongly on the parameters of the grating/waveguide structure. Measurements indicate that the bandwidth of the resonances can be as narrow as 1 nm, with a corresponding angular beamwidth on the order of minutes of arc.