Diffraction-efficiency Correction of Polarization-independent Multilayer Dielectric Gratings

We fabricate a polarization-independent dielectric multilayer thin-film diffraction grating for a spectral-beam-combining (SBC) system with a simple grating structure and low aspect ratio. Due to the refractive index and thickness error of the manufactured thin films, the diffraction efficiency of the fabricated diffraction grating was lower than that of the design. The causes of the errors were analyzed, and it was confirmed through simulation that diffraction efficiency could be compensated through an additional coating on the manufactured diffraction grating. As a result of sputtering an additional Ta2O5 layer on a fabricated diffraction grating, the diffraction efficiency was corrected and a maximum 91.7% of polarization-independent diffraction efficiency was obtained.