<title>Multimple-imaging and multiple-focusing Fresnel lenses with high numerical aperture</title>

Abstract

We report the successful design and fabrication of integrated devices that combine optical beam splitting and lensing into a single element. These elements are made by etching a 4-phase level pattern into quartz glass using electron beam lithography and reactive ion etching. They are designed using an algorithm based on simulated annealing to optimize the Fresnel-Kirchhoff integral that transforms the lens pixel pattern, containing up to 4 million pixels, to fit the desired output pattern. The devices can be optimized for any conjugate ratio; we have made examples of both imaging and focusing elements. At a working wavelength of 1.52 micrometers , measured efficiencies have been obtained of 67% for 4-phase level, F/2 single lenses and around 62% for 4-level F/2 and F/5 multiple imaging lenses that produce 16 output spots from a single input. In all cases for both the single and multiple lenses the output spots were diffraction limited.