An encapsulated metal-dielectric reflective grating is presented for broadband polarization-independent two-port beam splitting under normal incidence at the central wavelength of 800 nm. Different from traditional two-port grating splitters in the resonant region, this grating splitter is capable of separating light energy into ±1st orders with high efficiency in a broad waveband for both TE and TM polarizations. A unified method is proposed here for designing this grating splitter, which enables one to choose a grating structure quickly to realize an ultrabroad working waveband. The simulation results indicate that a bandwidth of 46.4 nm could be achieved for diffraction efficiency (defined as the ratio of the light energy diffracted only at the first order to the incident light energy) over 46% at the central wavelength of 800 nm. Moreover, the parameters of the grating structure can be flexibly adjusted with wavelengths using the unified method for various other applications, such as augmented reality, optical interconnections for computing, coherent beam combination, and complex vector beam shaping.
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