Production-ready double-side fabrication of dual-band infrared meta-optics using deep-UV lithography

Meta-optics, the application of metasurfaces into optical systems, is seeing an accelerating development owing to advantages in size, weight and cost and the ability to program optical functions beyond traditional refractive optics. The transition of meta-optics from the laboratory into applications is enabled by scalable production methods based on highly reproducible semiconductor process technology. Here, we introduce a novel method for fabrication of double-sided metasurfaces through deep-UV lithography as a production-ready method for achieving high-quality meta-optics. We achieve patterning of a silicon wafer on both sides with mutual alignment of around 25 $\mu$m based on tool accuracy, without requiring through-wafer alignment markers other than the wafer notch. A first novel application highlighting the benefits of double-sided design is demonstrated in the form of a dual-band metalens with independent control over focal lengths in mid- and long-wave infrared bands. Using multi-reticle stitching we demonstrate a 40 mm diameter, large-area metalens with excellent broadband imaging performance, showing partial cancelling of chromatic dispersion when used in a hybrid configuration with a BaF$_2$ refractive lens. Our work opens new avenues for infrared meta-optics designs and double-side meta-optics fabrication through a production-ready technique which can be directly translated into scalable technology for real-world applications.