<title>Imaging optical system using a pair of replicated binary micro-Fresnel-lens arrays</title>

Abstract

An imaging optical system with a short conjugate length (6.6 mm) was designed and fabricated using a pair of replicated binary micro Fresnel lens arrays. Two aperture arrays were placed between the lens arrays to prevent crosstalk images from adjacent lenses in the array. Our imaging optical system also has an off-axis configuration to eliminate the adverse effects of the zero-diffraction order light that is inevitable with diffractive optical elements. First, binary lens arrays were fabricated on a 0.5 mm thick quartz substrate by sub-micron photolithographic and reactive ion etching techniques, and the imaging optical system was constructed from these quartz binary lens arrays. In reading experiments, that quartz lens imaging optical system exhibited an excellent modulation transfer function value of 73% for an 8 line/mm test pattern. Then, replicated binary lens arrays were fabricated on a 0.5 mm thick polycarbonate substrate by employing a photopolymerization (2P method) replication process from a Ni stamper. This Ni stamper was fabricated by electroplating a quartz lens substrate, which was the original master. Then the replicated lens imaging optical system was constructed and also exhibited a good MTF value in reading experiments.