Binary phase Fresnel lenses for generation of two-dimensional beam arrays

Two-dimensional arrays of mutually coherent optical beams are needed in holographic interconnections for both recording and reading gratings. We analyze the use and limitations of binary phase Fresnel lenses to generate beams for these applications. Two known techniques of ion beam milling and thin film deposition are compared to fabricate such lens arrays in SiO2 and Si3N4. Each lens in the 8 × 8 arrays has a 1.2-mm square aperture with a focal length of 20 mm. Diffraction of a single argon-ion beam into an 8 × 8 array of highly uniform coherent focused beams (with 12-μm spot size) was achieved by the lenses with an efficiency of ~30% (41% theoretical limit).