Phase(x,y) = mod( 20pi( x3 + y3 ) , 2pi ), |x|<1, |y|<1
The ridges of this element correspond to 2pi, or one wavelength, phase steps.
When used in a principal plane of an incoherent optical system, this mask alters the system in such a way as to become focus-invariant. The resulting point spread function (PSF), and optical transfer function (OTF) are nearly invariant with misfocus. With conceptually simple digital filtering of the resulting images, both diffraction-limited and focus-invariant imagery result.
Click here for the world's first set of focus-invariant imagery. This first-generation cubic-phase mask was fabricated through collaboration with Joseph van der Gracht of ARL, and Rochester Photonics.