Equal-group-delay-metasurface-enabled hybrid lens for wide-field-of-view thermal imaging

Long-wave infrared thermal imaging has become indispensable for critical applications ranging from industrial facility maintenance to advanced security surveillance. While refractive-diffractive hybrid lenses offer potential for compact infrared optics, existing implementations face fundamental limitations in achieving performance parity with conventional thermal lenses—particularly regarding spatial resolution, restricted field of view (FOV), and inherent challenges in phase control under group delay constraints. Considering these issues, herein, a refractive-metasurface-based hybrid lens, enabled by equal-group-delay metasurfaces (EGDMs), was studied. The design combines optimized optical geometry to minimize oblique light incidence on the metasurface with the unique capabilities of EGDMs in providing large-aperture continuous phase modulation. The resulting system achieves diffraction-limited performance across the full 8–12 μm spectral band without requiring aspheric components, featuring an F-number of 1.08 while maintaining a wide 60° FOV. Notably, the lens demonstrates exceptional optical performance with a modulation transfer function of 0.44 at 29.4 lp/mm. Its compact size makes it compatible with handheld thermal imagers for versatile deployment scenarios. This work demonstrates the viability of EGDM-enabled hybrid designs for next-generation thermal imaging systems that combine commercial-grade performance with unprecedented compactness.