SEGMENTED FRESNEL ZONE LENS ELEMENTS WITH SEVERAL PRIMARY FOCI

The use of holographic elements containing segmented Fresnel zone lens es to generate more than one primary focus is investigated. Elements a re designed to provide tolerance to misalignment in free space optical interconnection architectures where this is a key consideration. The kinoform profile is approximated in multi-level form in quartz glass u sing micro-structuring technologies. Elements are of 2 mm diameter, f/ 5 performance and intended for use at 1.52 mu m wavelength. To optimis e their efficiency they are provided with anti-reflection coatings by ion beam sputter deposition. Diffraction efficiencies are 70% for 8-le vel structures divided between two focal spots, and 36% for 2-level st ructures generating four foci. The measured spot diameter is 21 mu m b etween first minima. Tolerance to misalignment is demonstrated.