We describe a sandwiched two-layer grating as a three-port beam splitter, which can achieve high-efficiency diffraction with polarization independence in the 0th and the +/- 1st orders. Diffractive efficiencies of 32.4/32.9 can be diffracted into the 1st and the 0th orders for TE polarization, and 33.1/32.8 can be diffracted for TM polarization. In addition, good splitting ratio uniformity can be exhibited within the broad duty cycle for both TE and TM polarizations. Moreover, the positioning tolerance of the gratings that constitute the sandwich is analyzed. (C) 2017 Optical Society of America
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