A recent publication [Opt. Express 16, 20540–20561 (2008)] presented a way for extending the depth of field (DOF) of imaging systems using a binary phase mask made of annular rings delivering a -phase shift. Usually, such masks are designed with respect to some central wavelength; they will thus deliver a different phase shift for other wavelengths. This issue is reexamined in this paper, where it is shown that polychromatic masks that deliver the same phase shift over a wide range of wavelengths provide improved imaging over an extended DOF. The simulation results demonstrate the improved performance of imaging systems using such masks.
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