Hybrid two-dimensional subwavelength surface-relief grating-mesh structures.

The homogeneous behavior of periodic two-dimensional subwavelength surface-relief structures that contain both gratings and meshes (inverse gratings) are investigated. It is shown that when effective indices are synthesized near the higher index (substrate region), mesh structures yield larger feature sizes compared with their grating counterparts, whereas grating structures yield larger feature sizes when effective indices are synthesized near the lower index (incident region). For each type of structure investigated, a relation between the parameters of the structure and an effective refractive index is determined. It is shown that an equal area occupied by the high- or low-index media within the grating cell does not, in general, result in equal effective indices. The effective index of the grating is shown to be characterized by both the shape (local distribution) and the area of the high- or low-index medium within the unit grating cell. Finally, the advantages of subwavelength gratings and meshes are combined to produce hybrid grating-mesh structures that are less demanding on the fabrication process.

Effects of process errors on the diffraction characteristics of binary dielectric gratings.

The effects of fabrication errors on the predicted performance of surface-relief phase gratings are analyzed with a rigorous vector diffraction technique. For binary elements, errors in the dimensions of the profile [depth, linewidth (fill factor), and grating period], as well as errors in the shape of the profile, are investigated. It is shown that the dimension errors do not have a significant effect on grating performance when the grating is designed for either maximum or minimum diffraction efficiency. A trapezoid is used to model the shape error of the profile. For the first time, design rules that significantly reduce the effects of any shape error are presented.

Xanthopsia treated with thiamine.

A patient with a history of extensive alcohol abuse developed xanthopsia, ataxia, and mental changes. Thiamine was given in the dosage of 200 mg daily, and the xanthopsia disappeared rapidly followed by normalization of the other symptoms. Xanthopsia might be due to a thiamine deficiency.