A novel binary and multilevel phase masks for enhanced depth-of-focus infrared imaging

This paper introduces novel binary and multilevel phase masks (BPMs) for improved depth of focus (DoF) in infrared imaging. The procedure developed for design of BPMs combines two ideas: cubic wavefront coding (WFC) of continuous absolute phase and original discretization of this phase profile. Both these ingredients of the design make the optical system robust with respect to defocus and uncontrolled variations in the optical system. The method allows us to design a flat and very thin BPM using piecewise invariant diffractive optical element (DOE) of simple geometry. The BPMs are used for wavefront modulation in two optical setups: a lensless system and a lens/BPM optical hybrid. Computational inverse imaging (deblurring) is applied in order to reconstruct a sharp image from respective blurred observations. The optical system is optimized end-to-end, including both the BPMs and the deblurring algorithm. Simulation experiments demonstrated for midwave infrared (MWIR) imaging, show high quality imaging even for very large amounts of defocus. Imaging systems incorporating this method show advantages over conventional optical systems with a refractive lens.