Polarization-insensitive 3 × 3 splitter by two-dimensional SiO2/(C2H4)n square-pillars

Abstract This paper presents a high-efficiency polarization-insensitive 3 × 3 beam splitter utilizing a two-dimensional square-pillar dielectric grating structure. Operating at a wavelength of 118.83 μm under normal incidence, the device achieves uniform diffraction of incident light into nine distinct orders ((0,0), (±1,0), (0,±1), and (±1,±1)). The polarization insensitivity is realized through the inherent symmetry of the square-pillar geometry, which eliminates polarization-dependent phase modulation. The rigorous coupled-wave analysis (RCWA) and the simulated annealing (SA) algorithm were employed to optimize the grating parameters. Numerical results indicate that the efficiency of each diffraction order exceeds 10.002%, with an average efficiency of 10.972% and an average polarization-dependent loss (PDL) of 0.130 dB. As a fundamental optical component, the 3 × 3 beam splitter holds potential application value in terahertz imaging, multi-beam interferometry, and structured light projection.