High efficiency Fresnel lens design and fabrication in a two-stage photopolymer

Diffractive optical elements (DOEs) assimilate optical functionality within thin (≤100 µm), lightweight films. With the recent advent of high dynamic range two-stage photopolymers, gradient-index volume DOEs can now achieve diffraction efficiencies competitive with conventional surface-relief DOEs, while also offering the advantages of contact-free, self-processing optical recording into a flat film that can be laminated between protective sheets. Here we design and fabricate Fresnel lenses with what we believe to be the highest reported diffraction efficiencies achieved to date using this gradient-index DOE approach. Our analysis shows that these high diffraction efficiencies are crucially enabled by the high index modulation of the photopolymer (n₁ > 0.01) and the high pixel count of the single-shot recording exposure (6400 × 6400 pixel chrome mask). The recorded lenses are 50 µm in thickness and up to 16 mm in diameter, with f-numbers ranging from 16 – 24 and diffraction efficiencies up to 85%. This high performance represents an important step toward practical applications, ranging through solar energy concentrators, customized vision optics, integrated photonics, heads-up displays, and hybrid lenses.