Transmission optimized LWIR metalens

Inverse Design of Aberration-Corrected Hybrid Metalenses for Large Field of View Thermal Imaging Across the Entire Longwave Infrared Atmospheric Window

Long wave infrared (LWIR) cameras play a pivotal role across diverse applications due to their distinctive features. The growing demand for high-performance thermal imaging optics, characterized by a broad working bandwidth, large field of view (FOV), aberration-free design, lightweight construction, compactness, and cost-effectiveness, poses significant challenges for LWIR lens design. Here, we propose an inverse design method for LWIR hybrid metalenses, specifically aiming to achieve aberration-corrected thermal imaging with both a large FOV and a broad working bandwidth. Our approach involves optimizing phase profiles of metalens' unit cells guided by a loss function that compares the hybrid lens design to diffraction-limited results for various incident angles and wavelengths. As a result, we demonstrate an aberration-corrected thermal camera with a 30° FOV and an achromatic working bandwidth spanning the entire LWIR atmospheric window (8 to 14 μm). Significantly, the total optical path length, the entrance pupil to the sensor plane of the charge-coupled device (CCD), is a mere 13.6 mm. Our work merits advantages in the FOV, working bandwidth, and compactness, which surpass state-of-the-art LWIR hybrid metalens designs and find numerous imaging and sensing applications.

Aberration-corrected hybrid metalens for longwave infrared thermal imaging

Wide-angle metalenses in the longwave infrared have shown great advantages over the traditional refractive doublets or triplets, due to light weight, CMOS compatibility, and low cost. However, previous endeavors have been plagued by challenges including a narrow waveband, large F-number, distortion, and spherical aberration. To address these problems, this study introduces two dispersive metasurfaces, placed near the front focal plane and upon the rear plane of a plano-convex lens, to correct optical aberrations. Utilizing this methodology, we propose and experimentally demonstrate an aberration-corrected hybrid metalens for thermal imaging in the 8-12 μm waveband, featuring an FOV of 24°, F-number of 1.2, and diameter of 12.2 mm. The developed hybrid metalens rigorously evaluated, exhibits Modulation Transfer Function (MTF) values exceeding 0.2 at 20 Lp/mm across the full FOV, and features an average transmission of 48.7 %, a relative focusing efficiencies of up to 42.1 %, polarization insensitivity and broadband imaging capacity. These results emphasize the potential applications of our system in diverse fields, such as camera lenses, autonomous driving, healthcare, and environmental monitoring.

Broadband thermal imaging using meta-optics

Subwavelength diffractive optics known as meta-optics have demonstrated the potential to significantly miniaturize imaging systems. However, despite impressive demonstrations, most meta-optical imaging systems suffer from strong chromatic aberrations, limiting their utilities. Here, we employ inverse-design to create broadband meta-optics operating in the long-wave infrared (LWIR) regime (8-12 μm). Via a deep-learning assisted multi-scale differentiable framework that links meta-atoms to the phase, we maximize the wavelength-averaged volume under the modulation transfer function (MTF) surface of the meta-optics. Our design framework merges local phase-engineering via meta-atoms and global engineering of the scatterer within a single pipeline. We corroborate our design by fabricating and experimentally characterizing all-silicon LWIR meta-optics. Our engineered meta-optic is complemented by a simple computational backend that dramatically improves the quality of the captured image. We experimentally demonstrate a six-fold improvement of the wavelength-averaged Strehl ratio over the traditional hyperboloid metalens for broadband imaging.

Large field-of-view thermal imaging via all-silicon meta-optics

A broad range of imaging and sensing technologies in the infrared require large field-of-view (FoV) operation. To achieve this, traditional refractive systems often employ multiple elements to compensate for aberrations, which leads to excess size, weight, and cost. For many applications, including night vision eye-wear, air-borne surveillance, and autonomous navigation for unmanned aerial vehicles, size and weight are highly constrained. Sub-wavelength diffractive optics, also known as meta-optics, can dramatically reduce the size, weight, and cost of these imaging systems, as meta-optics are significantly thinner and lighter than traditional refractive lenses. Here, we demonstrate 80° FoV thermal imaging in the long-wavelength infrared regime (8-12 µm) using an all-silicon meta-optic with an entrance aperture and lens focal length of 1 cm.