Performance Comparison of Ultra-Miniature Diffraction Gratings with Lenses and Zone Plates

A new class of ultra-miniature diffraction gratings has been recently proposed [1]. These gratings impose phase antisymmetry on the incoming wavefront effectively producing optical nulls which enable them to exhibit relatively constant response across wavelengths as well as insensitivity to manufactured grating thickness [2]. Hardware verification of these tiny gratings (on the scale of μm) has also been performed [3]. Admittedly, the purpose of such designs is not high-resolution imaging but their size and low cost could open new frontiers for their use in endoscopy, medical sensing or machine inspection and surveillance. Additionally, their design could be optimized for specialized non-imaging applications (e.g., QR-code reading, face detection) [3]. Unlike traditional optical elements, which aim at producing a small Point Spread Function (PSF) in order to focus the incoming radiation, these diffraction gratings purposely diffract the incoming light producing a wide PSF. However, the measured PSF has been demonstrated to retain high frequency information while remaining relatively unchanged for a wide range of incident angles of radiation [2, 3], effectively enabling computational calculation of the captured scene using a reconstruction algorithm. In this work, we analyze the imaging capabilities of sensors employing such gratings as compared to traditional optical elements (e.g., Fresnel zone plates and refractive lenses).