Analysis of the vectorial diffraction characteristics of grating light modulators for MOEMS spectrometer

Grating light modulators are the key wavelength scanning devices for a MOEMS spectrometer. In this paper, we build a vectorial diffraction model of grating light modulators theoretically based on Finite Beam Rigorous Coupled Wave Analysis theory. Then we calculate the diffraction efficiency of grating light modulators at the spectral range from 900nm to 1700nm. The numerical spectra indicate that the grating light modulators can realize wavelength scanning by changing the distance between the upper and the bottom layers. The grating light modulator can act as a programmable pixilated optical switch with high contrast. The diffraction efficiency is stable when the theta changes from -10 degrees to 10 degrees and the Phi changes from -30 degrees to 30 degrees. The effects of the bandwidth on the diffraction efficiency of the grating light modulators can be ignored. The average on state diffraction efficiency is 0.83 and the average off state diffraction efficiency is 0.05 when the grating light modulators chip has 256 pixels. The experimental results show that the vectorial diffraction model is more efficient than the scalar diffraction model.