Extended depth-of-field imaging through radially symmetrical conjugate phase masks

We proposed a radially symmetrical conjugate phase mask (PM) pair to yield an invariant imaging property for extending depth-of-field imaging. This conjugate PM pair is a two-radially symmetrical phase function with opposite orientation of the phase modulation. Compared with a single-radially symmetrical PM, the proposed conjugate PM pair shows a symmetrically imaging property on both sides of the focal plane and high magnitude of modulation transfer function (MTF). The quartic phase mask (QPM) with optimized phase parameters is employed to demonstrate our concept. Several evaluation approaches, including point-spread function, MTF, and image simulation, are used to realize the performance comparison among a traditional imaging system, an original QPM system, and a conjugate QPM. The results are proof that the proposed conjugate PM has a superior performance in extending depth of field imaging.