Fabrication and application of subwavelength gratings

Binary gratings with periods below the wavelength of visible light may be fabricated by e-beam direct writing in a resist layer and then transferred into other materials by ion beam etching. We used a well-adapted e-beam writer ''LION LV1'' (Leica Lithografie Systeme Jena) which allows feature sizes of 100nm and below and arbitrary directions of the grating lines as well as radial, circular or elliptical grating lines. By transfering such gratings into metallic layers polarization effects may be obtained which depend both on the parameters of the gratings and of the metal layer. The dependence of the polarization on grating period and duty cycle was measured far chromium layers with 35nm thickness. By writing concentric circular grating lines, interesting polarization analyzers may be fabricated. In addition to metal stripe gratings, dielectric subwavelength gratings show interesting properties, too. They may be used for coupling free space light into a planar or rib waveguide with incoupling efficiencies higher than 50%. Both for metallic and dielectric gratings, the optical properties strongly depend on an accurate and reproducible fabrication process which, therefore, has to be subject of further research.