  This paper introduces a two-and multi-level phase mask design for improved
depth of focus. A novel technique is proposed incorporating cubic and
generalized cubic wavefront coding (WFC). The obtained system is
optical-electronic requiring computational deblurring post-processing, in order
to obtain a sharp image from the observed blurred data. A midwave infrared
(MWIR) system is simulated showing that this design will produce high quality
images even for large amounts of defocus. It is furthermore shown that this
technique can be used to design a flat, single optical element, systems where
the phase mask performs both the function of focusing and phase modulation. It
is demonstrated that in this lensless design the WFC coding components can be
omitted and WFC effects are achieved as a result of the proposed algorithm for
phase mask design which uses the quadratic phase of the thin refractive lens as
the input signal.
