Demonstration of polarization-independent broadband multilayer gratings

Multilayer dielectric gratings (MDGs) have been widely used in spectral beam combining, chirped pulse amplification, and external cavity diode lasers systems. However, the one-dimensional MDGs suffer from the polarization-sensitive properties due to the modulation in only one direction. Two-dimensional (2D) MDGs have more flexible control ability to realize polarization-independent properties but are rarely reported. Here, we demonstrate the realization of polarization-independent broadband MDGs via 2D grating array. The 2D Si:H MDG exhibits more than 97% non-polarized diffraction efficiency over 90 nm. Further, the influence of the refractive index on high-efficiency bandwidth of the MDGs was investigated via a comparative study using Si:H and TiO2, materials with a large difference in refractive indexes. The high-efficiency bandwidth of Si:H MDGs is near 1.4 times the breadth of TiO2 MDGs. Our results provide a new platform and deeper understanding to realize polarization-independent broadband MDGs.