Metagrating-Based Terahertz Polarization Beam Splitter Designed by Simplified Modal Method

Abstract

Terahertz waves are finding important applications in diverse fields, and meanwhile the manipulation of terahertz waves calls for the development of various functional devices. Here, we have designed and fabricated a metagrating-based polarization beam splitter for terahertz waves using the simplified modal method. By only considering two propagation modes and treating the grating as a Mach-Zehnder interferometer, the method can greatly simplify the reverse grating design process. The parameters of the grating are first obtained under the guidance of the simplified modal method and then improved upon by the finite element method. The fabricated device is finally experimentally demonstrated with a terahertz time-domain spectroscopy system. The diffraction efficiencies of the polarization beam splitter at 0.9 THz are measured to be 69 and 63% for TE and TM waves relative to that of a silicon plate, respectively. The corresponding extinction ratios are 12 and 17 dB for TE and TM waves, respectively. The experiment results agree well with the simulations.

Terahertz wideband quarter wave plate based on freestanding grating structures

“…The dispersion equation of the Bloch waveguide modes is governed by Refs. 22 and 23: cos(βηΛ)cos(γ(1−η)Λ)−(βaγ+aγβ)sin(βηΛ)sin(γ(1−η)Λ)=1,where k0 is the vacuum wave vector, β=k0n2−neff2 and γ=k01−neff2 are the lateral wave vector inside the grating and in the gap, neff is the effective refractive index. a is n2 for TM polarization and 1 for TE polarization.…”