Hybrid refractive-metalens design for imaging applications

Metalenses can be used as standalone single elements or incorporated as one component of a subassembly that also includes other non-metalens optical elements. Because of the sub-wavelength length scale of the meta-atoms, ray-based methods for analysis and optimization may not be considered appropriate. However, by treating the imparted phase appropriately, ray-based methods can be used to design and analyze optical systems that incorporate one or more metalenses. These methods can be applied to imaging systems or illumination systems composed solely of metalenses, or systems that incorporate a mix of metalenses and conventional refractive, reflective, or diffractive optical elements. There are two pieces of information that are required by the ray trace: i) the ray directions following the metalens, and ii) the amount of energy that the ray carries. The distribution of the meta-atoms in the metalens can be used to determine ray directions and Fourier analysis allows for estimation of the energy carried by the rays. The method relies on having access to the imparted phase (from an EM solver, say) that can be accessed during the ray trace. This approach allows for workflows that are familiar to lens designers—even those without experience designing metalenses—while offering results that are in excellent agreement with more rigorous wave-based analyses. This approach is applicable to both polarization-insensitive and polarization-sensitive designs. In this paper, we discuss the design approach and offer design examples.