Abstract: Using the coherent superposition，diffractions are deduced when a plane wave incidents on

a phase grating. Results show that the ±1 order diffraction of the phase grating can get the

maximum intensity and realize the splitting function，overcoming the problems in amplitude grating

where the 0 order diffraction has the maximum in- tensity but with no splitting function. The

diffraction efficiency of ±1 order diffraction with respect to the duty ratio and phase introduced

by the phase material are discussed. The method we provided here has implicit physical mean- ings

and is easy to adapt to other diffraction structure.

Key words: phase grating, diffraction, diffraction efficiency, splitting function