AR-coated arrays of binary lenses for interconnection networks at 1.5 mu m

Arrays of two different sizes, each consisting of 16 by 16 blazed Fresnel zone lenses were fabricated in quartz glass by means of microstructuring techniques. The lenses were designed for free space optical interconnection networks operating in the IR. In order to achieve high diffraction efficiencies the kinoform profile of the microlenses was approximated by a staircase-like profile. The fabrication of the lenses involved multiple steps of repeated pattern transfer by photolithography and successive reactive ion etching. We fabricated Fresnel zone lenses with 16 levels per zone and with different focal lengths. The individual elements of the two arrays have circular and square apertures with a diameter of 2 mm and 200 mu m respectively and were designed to operate at a wavelength of 1.52 mu m. In order to reduce reflection losses, optical crosstalk as well as optical feedback effects, the Fresnel zone lens arrays were antireflection coated. The measured spot-sizes of our F/11-Fresnel zone lenses were close to the diffraction limited values and the diffraction efficiencies of the 2 mm-lenses were higher than 90%.