Fabrication and optical characterization of large aperture diffractive lenses using greyscale lithography

Diffractive lenses can replicate the optical functions of their refractive counterparts using an equivalent surface relief phase profile, enabling more compact optical assemblies and microsystem integration. Greyscale lithography enables the direct definition of tridimensional photoresist lenses atop glass substrates, providing a simple nanofabrication process for complex micro-optics, compatible with nanoimprint replication. In this work, we report the greyscale fabrication and optical characterization of 10 × 10 mm2, NA ≈ 0.25, photoresist diffractive lenses for near-infrared LIDAR applications and evaluate their optical performance in the visible range for imaging. We demonstrate a two-lens varifocal system integrating diffractive lenses for λ = 1550 nm operation with a 55–215 mm focal length tuning range and an average spot size of ø188 ± 82 μm. In addition, we characterize the strong longitudinal chromatic aberration, typical of diffractive lenses, and evaluate their optical performance for imaging in the visible range.