Polarizing beam splitter of two-layer dielectric rectangular transmission gratings in Littrow mounting

We theoretically investigated the design of polarizing beam splitters (PBS) of two-layer dielectric rectangular transmission gratings in Littrow mounting. The PBS grating is aimed to separate TE and TM polarized waves into two different transmitted orders, i.e. the 0th and −1st orders. The polarization-dependent diffraction process is analyzed by using a simplified modal method. The mode reflection and transmission at the interface of the two layers are illustrated. Design equations are given based on the average mode indices of the even and odd modes inside the grating region, which are verified by using rigorous coupled wave analysis. Moreover, with simulated annealing algorithm, two kinds of two-layer PBS gratings are optimized for operation over the C-band (1520–1570nm). Compared with the single-layer transmission PBS gratings, such two-layer scheme exhibits a great flexibility of design. The PBSs of two-layer dielectric transmission gratings should be useful for practical applications.