Free-form broadband flat lenses for visible imaging

The resolution of a conventional lens is governed by its numerical aperture (NA) while light-concentration ability f-number (f/#), both which are dependent on the diameter and focal length lens. Hence, these properties for inherently coupled. Here, we show that utilizing principle free-form broadband diffractive optical elements (BDOEs), can create ultra-flat able to concentrate incoming light over fixed different sized spots engineered in shape square. decouple NA f/# being independently control size input devices. Specifically, designed, fabricated, characterized three BDOE lenses operating visible band (450nm–750nm), each having 11.25, but with NAs 0.00075, 0.0067, 0.054, respectively. We further use simulations emphasize such decoupling possible even at much higher NAs. Experiments confirm achromatic focusing imaging. One exhibited depth-of-focus almost 2 orders magnitude larger than diffraction limit. Such eliminate need anti-aliasing filters could also be very useful focal-plane arrays large pixel sizes, where collection efficiency needs maintained. Furthermore, abandoning rotational symmetry, one achieve geometries spot, as square more closely match geometry sensor pixel.