ZEMAX Development Corporation thanks Mr. Robert E. Fischer of Optics 1 for the permission to use the graphics from his book Optical System Design, and also for providing us the original graphic files.

Many surfaces in ZEMAX can have diffractive power in addition to refractive power. Diffractive power is independent of the index and the surface sag and changes the phase of the rays.  For more information on how diffractive surfaces are modeled in ZEMAX, please refer to the article "How Diffractive Surfaces are Modeled in ZEMAX."

The diffractive power in a Binary 2 surface introduces continuous phase change across the surface according to the following formula:


 where the coefficients A_i are in units of radians.

Since the phase change is continuous across the surface, a Binary 2 surface represents an ideal binary diffractive optical element, in which the size of the binary (discrete) steps are infinitesimally small or at least very small compared to the wavelength.

Generally, the physical DOE modeled by the Binary 2 surface will have diffractive zones with varying period as a function of radial distance from the vertex, as shown in the following diagram. ZEMAX can calculate the radial coordinates of each diffraction zone, where the phase differs exactly by 2p from adjacent zones.

Figure 13.5 from Optical System Design


The amount of phase in waves added by a Binary 2 surface at a particular radial coordinate is independent of wavelength. The wavelength-dependent optical path length (OPL) is given by

OPL = (Phase*wavelength)/ (2p)

The following layout shows the chromatic effect due to a Binary 2 surface.