Profiled absorber design illuminated uniformly by parabolic reflectors.

In this paper, a general method is proposed in order to develop a special absorber profile that receives sunlight from parabolic reflectors uniformly. Different parameters were taken into consideration while performing the simulation including reflector focal length, collector length, and concentration ratio. The total power reflected to the absorber was calculated by accounting for the Fresnel angular dependency and the shadowing effect by the absorber. Furthermore, a verification method based on the ray tracing technique was also developed in order to verify that uniform illumination was achieved. The uniformity of the sunlight flux onto the absorber is expected to improve solar system efficiency and extend its life service. Therefore, the validated absorber profile design in this theoretical work can be useful for applications which employ parabolic concentrators with the concern of reaching higher performance by achieving a uniform concentration ratio on the absorber.

Uniform sunlight concentration reflectors for photovoltaic cells.

Sunlight concentration is essential to reach high temperatures of a working fluid in solar-thermal applications and to reduce the cost of photovoltaic (PV) electricity generation systems. Commonly, sunlight concentration is realized by parabolic or cylindrical reflectors, which do not provide uniform concentration on the receiver finite surface. Uniform concentration of sunlight is favored especially for the PV conversion applications since it not only enhances the conversion efficiency of sunlight but also reduces the thermal variations along the receiving PV cell, which can be a performance and life-span limiting factor. In this paper a reflector profile that uniformly infiltrates the concentrated sunlight into the receiving unit is attempted. The new design accounts for all factors that contribute to the nonuniform concentration, like the reflector curvature, which spatially reflects the sunlight nonuniformly, and the angular dependency of both the reflector reflectivity and the sunlight transmission through the PV cell.

Broadened phase-matching bandwidth in waveguide-frequency-doubling devices.

Second harmonic generation in optical planar waveguides is the most promising mechanism for frequency doubling of laser emission since light can be highly confined to the nonlinear waveguide medium. However, this advantage is achievable only by precise phase matching between the fundamental wave and the doubled frequency wave, which is hard to control at the fabrication stage. Two tasks are addressed: a basic design for the layer thicknesses of a two-layer waveguide to achieve phase matching, and second, a multi-layer-waveguide design to achieve broadened phase matching bandwidth.

Titania, silicon dioxide, and tantalum pentoxide waveguides and optical resonant filters prepared with radio-frequency magnetron sputtering and annealing.

Mixing dielectric materials in solid-thin-film deposition allows the engineering of thin films' optical constants to meet specific thin-film-device requirements, which can be significantly useful for optoelectronics devices and photonics technologies in general. In principle, by use of radio-frequency (rf) magnetron sputtering, it would be possible to mix any two, or more, materials at different molar ratios as long as the mixed materials are not chemically reactive in the mixture. This freedom in material mixing by use of magnetron sputtering has an advantage by providing a wide range of the material optical constants, which eventually enables the photonic-device designer to have the flexibility to achieve optimal device performance. We deposited three combinations from three different oxides by using rf magnetron sputtering and later investigated them for their optical constants. Each two-oxide mixture was done at different molar ratio levels. Moreover, postdeposition annealing was investigated and was shown to reduce the optical losses and to stabilize the film composition against environmental effects such as aging and humidity exposure. These investigations were supported by the fabricated planar waveguides and optical resonant filters.

Experimental characterization of simultaneous spatial and spectral filtering by an optical resonant filter.

Simultaneous spatial and spectral filtering by an optical resonant filter has been characterized experimentally to furnish additional insight into the operation and applications of optical resonant filters. Our experimental study can be useful for applications that depend on spatial filtering, spectral filtering, spatial-spectral filtering, and polarization selectivity. One significant application is the integration of an optical resonant filter with semiconductor lasers to control the spatial-spectral radiation for optimum performance.

Fabrication methods of optical resonant filters with a close-to-rectangle filtering profile.

The potential applications of optical resonant filters for optical communication systems can be significant. Three approaches to achieve a close-to-rectangle filtering profile for optical resonant filter were investigated and proven experimentally. The combination of the filtering sharpness, which comes from the resonance nature, and a flattened filtering window realized the close-to-rectangle filtering profile that can enhance the bandwidth efficiency.

High-resolution photometric optical monitoring for thin-film deposition.

Real-time monitoring of thin-film deposition with high resolution is important for precise fabrication of thin-film devices in a technological environment with ever-increasing demands for smaller size and better performance. Using photometry, we were able to achieve a real-time optical monitoring resolution of film thickness that is comparable with a single atomic layer scale (i.e., subnanometer). Filtering noise efficiently and compensating for sources of error by use of an appropriate model produced this high resolution. The procedure proved reliable and can be useful in the thin-film-deposition industry.

Heat treatment for reduction of surface roughness on holographic gratings.

Controlled postdevelopment heat treatment of the photoresist polymer used in the preparation of holographic gratings has been shown to enhance the diffraction efficiency of gratings and reduce the scattering losses. We prove this effect by analyzing the resonant reflection spectra of a waveguide grating and observing the reduction in the arc-shaped light scattering associated with the excitation of waveguide modes.

Reliable fabrication technologies for optical resonant filters.

A reliable technology for optical resonant filters can be useful for optoelectronics technologies, optical communications systems, and biomedical applications. Positioning the resonance at a specific target wavelength is challenging because of the sensitivity of placing a narrow spectral filtering window tothe error factors that are associated with the fabrication and characterization processes. We describe and prove experimentally two fabrication approaches to overcome this challenge.