In conventional imaging, the information transfer from the object to the image plane is accomplished either with the help of a traditional lens that performs a one-to-one mapping or an unconventional lens that performs a one-to-many mapping. In the first case, the image is formed directly, whereas in the second case, the image is formed after a computation. The conventional lens approach is preferred in most cases due to the high signal-to-noise ratio achievable at each image pixel. By appealing to the fact that for most of the imaging applications, it is only the intensity, which is measured by the detector, the phase of the field in the image or focal plane is a free parameter, something that comes from the inverse diffraction transform. Therefore, it is easy to visualize that this phase of the plane wave after it transmits the lens can have multiple forms. Hence, the final choice can be made based upon specific application tailored requirements like achromaticity, depth-of-focus, wide-angle imaging, etc. This concept was exploited to design an achromatic MDL via inverse design across almost the entire electromagnetic spectrum (λ = 450 nm to 15 μm). Furthermore, a MDL with a Field Of View (FOV) up to 50° for wide-angle imaging as well as a MDL to enable an extreme Depth of Focus (EDOF) imaging of up to 6 m in the NIR were also designed.
In this presentation, we will describe the design, fabrication and characterization of flat lenses that operate in any desired spectral regime. Specifically, we will describe flat lenses in the visible band, in the visible and near-IR band, and also in the LWIR band. We have shown that multi-level diffractive optics, when designed properly can enable high efficiency broadband imaging . Here, we will extend the performance to the IR and show experimental results. We further compare our optics with metalenses, and emphasize that metalenses offer no additional advantage . In fact, metalenses are far more challenging to fabricate. Please refer to papers below for details.
 M. Meem, A. Majumder and R. Menon, “Full-color video and still imaging using two flat lenses,” Opt. Exp. 26(21) 26866-26871 (2018).
 S. Banerji, M. Meem, B. Sensale-Rodriguez and R. Menon, “Imaging with flat optics: metalenses or diffractive lenses?,” arXiv:1901.05042 [physics.optics]