A diffraction-grating based demultiplexer is made to have low polarization dependence and high diffraction efficiency properties. The device is made is made of a Si grism working in reflection and having optimised grove profile easily manufactured by standard crystallographic etch of Si surface.
We look at the behavior of three different plane gratings in spectral regions where they exhibit anomalous efficiency behavior. Circumstances are presented where anomalies are either shifted, reduced, or enhanced. The gratings chosen are 1200 grooves per mm blazed at 26.75 degree(s), 1200 grooves per mm holographic sinusoidal with 18% modulation, and an 1800 groove per mm holographic `self blazed' at 13 degree(s).