Large bandwidth, highly efficient optical gratings through high index materials

We analyze the diffraction characteristics of dielectric gratings that feature a high index grating layer, and devise, through rigorous numerical calculations, large bandwidth, highly efficient, high dispersion dielectric gratings in reflection, transmission, and immersed transmission geometry. A dielectric TIR grating is suggested, whose -1dB spectral bandwidth is doubled as compared to its all-glass equivalent. The short wavelength diffraction efficiency is additionally improved by allowing for slanted lamella. The grating surpasses a blazed gold grating over the full octave. An immersed transmission grating is devised, whose -1dB bandwidth is tripled as compared to its all-glass equivalent, and that surpasses an equivalent classical transmission grating over nearly the full octave. A transmission grating in the classical scattering geometry is suggested, that features a buried high index layer. This grating provides effectively 100% diffraction efficiency at its design wavelegth, and surpasses an equivalent fused silica grating over the full octave.Comment: 15 pages, 7 figure

Light trapping properties of cylindrical well diffraction gratings in solar cells: Computational calculations

Light trapping using diffraction gratings is a promising approach to increasing absorption in solar cells. In this paper, the computationally calculated absorption enhancement expected from a diffraction grating consisting of a triangular array of cylindrical wells is presented. Angle-extended polychromatic illumination is considered, and special attention is paid to absorption of sub-bandgap photons in an intermediate band solar cell. Results are compared to the absorption enhancement expected from an ideal Lambertian (randomizing) scatterer, which is considered as a baseline. It is found that for cells which absorb very weakly, the diffraction grating provides absorption enhancement above that of the ideal Lambertian scatterer over a wide wavelength range. For cells which absorb more strongly, the grating underperforms the ideal Lambertian scatterer over almost all wavelengths. Finally, the grating period, well height and well radius are optimised. Keywords: Light Trapping, Diffraction Grating, Intermediate Band Solar Cel

Transmissive Suppressed-Order Diffraction Grating (SODG)

We present a novel type of Suppressed-Order Diffraction Grating(SODG). An SODG is a diffraction grating whose diffraction orders have all been suppressed except one that is selected to provide electromagnetic deflection. The proposed SODG is a transmissive grating that exhibits high-efficiency refraction-like deflection for all angles, including large angles that are generally challenging to achieve, while featuring a deeply subwavelength thickness, as required in the microwave regime. We first present the design rationale and guidelines, and next demonstrate such a 10.5 GHz SODG that reaches an efficiency of 90% at 70 degrees

Electromagnetic diffraction efficiencies for plane reflection diffraction gratings

Results are presented of research activities on holographic grating research. A large portion of this work was performed using rigorous vector diffraction theory, therefore, the necessary theory has been included in this report. The diffraction efficiency studies were continued using programs based on a rigorous theory. The simultaneous occurrence of high diffraction efficiencies and the phenomenon of double Wood's anomalies is demonstrated along with a graphic method for determining the necessary grating parameters. Also, an analytical solution for a grating profile that is perfectly blazed is obtained. The performance of the perfectly blazed grating profile is shown to be significantly better than grating profiles previously studied. Finally, a proposed method is described for the analysis of coarse echelle gratings using rigorous vector diffraction that is currently being developed

Design and fabrication of a two dimentional grating light valve using temperature dependence of the refractive index of liquids

Design and fabrication of a two dimensional tuneable grating has been proposed. A transmissive 2D square well grating is fabricated. The holes of the grating then is filled with a liquid which it’s refractive index is depend on the temperature. By changing the temperature the efficiency of the diffraction patterns is changed