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

We show the design and fabrication of high diffraction efficiency, optically recorded gradient-index Fresnel lenses in a two-stage photopolymer. A design analysis reveals that lens f/# is limited by the material refractive index contrast, motivating use of recent high-contrast polymers. The number of pixels required for the optical exposure is typically well beyond available spatial light-modulator resolutions, motivating the use of a photolithographic mask. We use a dithered binary chrome mask with 9000×9000 pixels of 2.5 μm diameter to write lenses up to 23 mm in diameter. Lenses down to f/44 with 76% diffraction efficiency and f/79 with 83% diffraction efficiency are demonstrated.