The chief properties and possible applications of periodic waveguides and their leaky modes are presented in this paper. After summarizing the basic physics of the guided-mode resonance, computed leaky-mode field patterns are provided to illustrate their structure and the high local focal field enhancement obtainable. An example fabricated bandstop filter is found to exhibit 90% efficiency, 1 nm linewidth, and low sidebands. Computed spectra for a single-layer bandpass filter operating at 1.55 μm wavelength yield low sidebands, extending 100 nm, and an angular aperture of ~1.7°. Resonant vertical-cavity surface-emitting lasers (VCSEL) are presented in which multilayer Bragg-stack mirrors are replaced with leaky-mode resonance layers. The use of guided-mode resonance mirrors provides optical power flow across and laterally along the laser active region. The round-trip gain is thereby increased resulting in high laser efficiency and relaxed mirror reflectivity constraints. As the GMR mirror achieves high reflectivity at resonance, the laser wavelength is locked at the resonance wavelength principally defined by the period. Example resonant VCSEL embodiments are shown along with their computed characteristics. Resonant biosensors are addressed last. The high parametric sensitivity of the guided-mode resonance effect, a potential limitation in filter applications, can be exploited for sensors as illustrated by several examples.
Photoexcited intrinsic silicon 'pixels' are applied as coupling elements between microstrip lines. Under proper illumination, the free-carrier concentration of the silicon increases sufficiently to pass a microwave signal across the pixels. Illumination is accomplished through the use of multimode fiber coupling between high-power laser diodes and multimode prismatic-waveguide output couplers. The prismatic couplers are fabricated on the endfaces of thick glass slab waveguides to direct the light onto the silicon pixel. This configuration delivers up to approximately 75% of the total laser diode light to the prism-waveguide couplers and these couplers, in turn, deliver up to approximately 70% of the input light to the silicon pixels. The prismatic waveguide couplers provide illumination uniformity within approximately ± 15% over the length of a 1mm X 5mm pixel. As a simple in-line coupler between microstrip lines, the fully illuminated pixel allowed an increase in transmitted signal of > 5dB over most of the range from 0.5GHz to 15GHz with > 10dB obtained over intermediate ranges. A silicon pixel tunable transmission line termination exhibits impedance matching at increasing wavelengths by successive illumination of multiple pixels, effectively increasing the length of the termination. This is illustrated by shifts in the resonant frequencies of the device reflection characteristics.
Optics is a key technology in a broad range of engineering and science applications of high national priority. Engineers and scientists with a sound background in this field are needed to preserve technical leadership and to establish new directions of research and development. To meet this educational need, a joint Electrical Engineering/Physics optics course sequence was created as PHYS 3445 Fundamentals of Optics and EE 4444 Optical Systems Design, both with a laboratory component. The objectives are to educate EE and Physics undergraduate students in the fundamentals of optics; in interdisciplinary problem solving; in design and analysis; in handling optical components; and in skills such as communications and team cooperation. Written technical reports in professional format are required, formal presentations are given, and participation in paper design contests is encouraged.
High-efficiency resonance coupling effects in zero-order diffractive multilayer structures have applications in fields such as optical filtering and laser technology. These resonance effects arise on phase matching of an incident laser beam to a leaky waveguide mode. Then, in theory, complete energy exchange between the input wave and a reflected wave can take place within narrow ranges in wavelength, angle of incidence, index of refraction, or layer thickness. This paper addresses theoretical modeling, experimental realization, and applications of this so-called guided-mode resonance (GMR) effect. In particular, the achievable GMR-filter efficiencies, spectral linewidths, sideband levels, and polarization characteristics are treated with a plane-wave model and a Gaussian-beam model. Resonance bandpass filters operating in reflection and transmission are shown to exhibit high efficiencies and extended low sidebands. Genetic algorithms are applied to solve inverse resonance-filter design problems. Applications including GMR laser mirrors, electro-optic modulators, and resonant Brewster filters are presented. Experimental results are shown to agree well with theoretical calculations.
The principles and chief properties of optical reflection and transmission filters based on guided-mode resonance (GMR) effects in multilayer structures comprising gratings and homogeneous thin films are presented. Detailed fiber characteristics (center wavelength, lineshape, and linewidth) are calculated using rigorous coupled-wave analysis for TE and TM polarized incident waves. These filters exhibit desirable characteristics such as high resonance efficiency with narrow or wide linewidths. Near- zero reflectance sidebands over extended wavelength ranges are obtainable using multilayer waveguide-grating structures. To illustrate the potential of this technology, calculated GMR reflection and transmission example characteristics are presented for filters made with common thin-film materials operating in the visible spectral region. Excellent reflection-filter features are found when antireflection conditions prevail away from the resonance wavelength. The transmission filter is optimized when the structure is highly reflective off resonance. It is found that long-range, low sidebands are obtainable for a single- layer GMR filter with a TM-polarized plane wave incident at the Brewster angle. GMR filter fabrication tolerances are briefly discussed. A calculated example illustrates the sensitivity of the filter center wavelength to variations in layer thickness. The effects of absorptive loss are treated. It is shown that, in general, GMR filters suffer loss- dependent wavelength shifts such that the reflection peak occurs at a different wavelength than the corresponding transmission notch. However, under antireflection conditions, the resonance location becomes insensitive to loss. Finally, reflective GMR thin-film structures that support multiple waveguide modes are studied. These devices exhibit characteristic angular and spectral signatures with unique appearance.