Deep-etched high-spatial-frequency metal-based sandwiched grating for reflective dual-function beam splitter

We describe a novel reflective dual-function beam splitter by a deep-etched high-spatial-frequency metal-based sandwiched grating. For TE polarization, the presented grating can show high efficiency in the reflective −1st order. And for TM polarization, two-port output can be obtained with good uniformity in the reflective 0th and the −1st orders. Physical analysis of modal method and numerical calculation of rigorous coupled-wave analysis (RCWA) are utilized to optimize such a dual-function beam splitter grating. Grating duty cycle is chosen properly for the grating period by the effective indices difference of excited modes in the grating region based on modal method. And grating depth and covering layer thickness are optimized using simulation of RCWA. The presented dual-function beam splitter grating can have advantages of the special incident angle of 45°, high efficiency and uniformity, and wide incident angular bandwidth, which should be a useful element for various optical systems.

► A reflective dual-function element is presented by a metal-based sandwiched grating.
► The grating has merits of special incident angle of 45° and wide angular bandwidth.
► Reflective high efficiency and uniformity can be shown for different polarizations.