Solid-Immersion Metalenses for Infrared Focal Plane Arrays

Novel optical components based on metasurfaces (metalenses) offer a new methodology for microlens arrays. In particular, metalens arrays have the potential of being monolithically integrated with infrared focal plane arrays (IR FPAs) to increase the operating temperature and sensitivity of the latter. In this work, we demonstrate a new type of transmissive metalens that focuses the incident light ({\lambda} = 3-5 {\mu}m) on the detector plane after propagating through the substrate, i.e. solid-immersion type of focusing. The metalens is fabricated by etching the backside of the detector substrate material (GaSb here) making this approach compatible with the architecture of back-illuminated FPAs. In addition, our designs work for all incident polarizations. We fabricate a 10x10 metalens array that proves the scalability of this approach for FPAs. In the future, these solid-immersion metalenses arrays will be monolithically integrated with IR FPAs.