Two-wavelength achromatic diffractive microlens designed by height optimization method fabricated by two-photon...

Three-dimensional two-photon nanolithography (3D TPN) enables the mask-free fabrication of arbitrary 3D microstructures, which makes it a powerful tool for creating complex micrometer-scale diffractive optical elements (DOEs) in micro-optics and nanophotonics. Among these, the development of multiwavelength achromatic diffractive microlenses has emerged as a critical challenge, as conventional methods often rely on computationally intensive full-wave Maxwell simulations (e.g., finite-difference time-domain, FDTD) or complex meta-atom fabrication processes. Here, we propose an optimization framework that integrates the optical path difference equation into the Rayleigh-Sommerfeld diffraction equation, enabling direct optimization of height distribution for multiwavelength diffractive microlenses with significantly reduced computational demands compared to FDTD-based approaches. As a demonstration, we designed and fabricated a dual-wavelength (green and near-infrared) height-optimized achromatic microlens using 3D TPN, achieving excellent agreement between experimental characterization and theoretical calculations. Our approach offers a computationally efficient strategy for advancing multiwavelength DOE design, with potential applications in integrated photonics and bioimaging.