Broadband Achromatic Metalens With Enhanced Field of View for Thermal Image

Despite the increasing interest in metalenses for imaging applications, there is a scarcity of research on metalenses designed to deliver broadband achromatic performance while preserving a wide field of view (FOV). In this work, we present a single-layer broadband achromatic metalens (BAM) designed for a specified FOV within a longwave infrared (LWIR) regime. Utilizing an advanced genetic algorithm coupled with diffraction theory, we optimize the BAM to minimize the coefficient of variation (CV) of focal lengths. The proposed BAM operates across wavelengths from 8 to 12 mu m, facilitating an FOV of 40 degrees. Our methodology is validated through the initial design of a BAM with a 200 mu m aperture. Simulation outcomes reveal a low CV of 2.56% and an average focusing efficiency of over 40%. Furthermore, a 5 mm-diameter metalens prototype was fabricated and characterized by our custom measurement setup, which is both precise and less prone to subjective error than traditional testing methodologies. The prototype demonstrates an average focal length of 5.478 mm with minimal distortion at 2.18%. The Modulation Transfer Function (MTF) analysis confirms alignment with design specifications. Last, the imaging characterization of the metalens is carried out through experiments, demonstrating that the metalens can clearly resolve the measured object.