Tunable TE/TM mode converter with an orthogonal graphene-based grating structure

A novel TM/TE polarization converter constructed with orthogonal double-layer graphene gratings is proposed. The high-performance TM/TE polarization conversion was explored by optimizing the Fermi energy and geometric parameters of the two-layer graphene gratings. As the Fermi level of graphene is dynamically adjustable, tunable polarization modulation can be achieved by the same design. Here we utilize the finite element method and improved coupled-mode theory to simulate and verify the conversion and modulation characteristics of TM and TE polarization. Proof-of-concept experiments demonstrated that this TM/TE converter provided excellent optical efficiency in polarization conversion and strong modulation stability against incident wave angle (up to 30°) and polarization status. This simple and easy-to-implement grating structure paves the way for the development of future micro-nano devices such as unimodal filters, and its functions can be further translated to study absorption and reflection spectra in nanophotonic applications.