Anisotropic polarization beam splitter based on metal slit array

Abstract

Polarizing beam splitter (PBS) can separate the propagating directions of two incident orthogonally polarized light beams. However, conventional PBS and multi-layered metamaterial structures are complicated and neither of them can meet the requirements for broadband characteristics due to their resonant characters. In this paper, an anisotropic beam splitter based on metal slit array of the metal-dielectric structure is proposed in order to simplify the structure and improve the beam splitting efficiency. Because of the transverse momentum generated by the inhomogeneous interface, the transverse magnetic (TM) wave is negatively reflected from the surface of the gold film after it has entered into the slit with the waveguide mode of the plasma. When the free electrons on the metal surface oscillate, the transverse electric (TE) wave parallel to the grating direction can cause electrons to oscillate along the grating direction, so that the TE light cannot enter into the slit, resulting in specular reflection. The finite element method is used to study the effects of TM and TE polarized light such as negative reflection (NR) and specular reflection (SR). The results show that when the incident angle of the polarized light is set to be in a range from 20 to 70, the incident TM light has a strong NR of about 0.9, but the TE light is weakly reflected and decreases sharply with the increase of the wavelength. The ideal NR points of the beam splitter and the perfect symmetrical response of the reflection surface are calculated, and the ideal NR point satisfies P=/(2sin 0). When the incident light angle changes, the variations of the wavelength of the negative and zero order reflection peak are different from those of TM and TE wave, which is more conducive to the tuning of the interaction between light and grating structure. The NR and SR spectral reflectance of different polarized light beams are calculated by rigorous coupled-wave analysis, and the extinction ratios in the two cases are both 106. In addition, those designs of plasmonic splitters will pave the way for the practical applications of plasmonic devices in data storages and optical holography.