HYBRID 2-DIMENSIONAL SUBWAVELENGTH SURFACE-RELIEF GRATING-MESH STRUCTURES

The homogeneous behavior of periodic two-dimensional subwavelength sur face-relief structures that contain both gratings and meshes (inverse gratings) are investigated. It is shown that when effective indices ar e synthesized near the higher index (substrate region), mesh structure s 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 ea ch type of structure investigated, a relation between the parameters o f the structure and an effective refractive index is determined. It is shown that an equal area occupied by the high- or low-index media wit hin the grating cell does not, in general, result in equal effective i ndices. The effective index of the grating is shown to be characterize d 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 g rating-mesh structures that are less demanding on the fabrication proc ess. (C) 1996 Optical Society of America