SMALL-FEATURE-SIZE FAN-OUT KINOFORM ETCHED IN GAAS

A binary fan-out kinoform for focusing and splitting an incident beam into a 4 X 4 spot array, with a largest deflection angle of 28 degrees , was designed, fabricated in GaAs, and evaluated. The kinoform was de fined in resist with electron-beam lithography and etched into GaAs wi th chemically assisted ion-beam etching. Light at wavelength 0.98 mu m from a single-mode fiber was used to illuminate the kinoform. The eff iciency was measured to be 34%, and the uniformity error for the 4 x 4 spots was 29%. Although the typical feature size of the kinoform is o nly roughly two wavelengths, we found that the scalar theory of diffra ction can be used. A first kinoform was designed with the customary Fr esnel-diffraction theory, which was found to be too coarse, resulting in a fan-out exhibiting some distortion. A second kinoform was designe d with the more rigorous Fresnel-Kirchhoff expression, and its fan-out shows no distortion. (C) 1996 Optical Society of America