Birefringent and Complex Optical Properties of Monolayer Graphene Investigated by Ellipsometry and Waveguide Integration

Though much effort has been dedicated to the development of graphene-based optoelectronic devices, its birefringent properties need further investigation. Here, a monolayer graphene is thoroughly studied as a uniaxial crystal with birefringent and complex dielectric functions via spectroscopic ellipsometry. The obtained dielectric model is verified at three incident angles. The graphene–polymer hybrid waveguide is subsequently designed and fabricated to further validate the correctness of the birefringent dielectric model. The polarization-dependent transmissions for transverse electric and transverse magnetic modes are compared experimentally, and the results are in good agreement with the theoretical predictions. Contrary to the previous reports, for the vertically polarized light, a considerable absorption is observed in the hybrid waveguide, as a direct result from the nontrivial imaginary part of the dielectric function for graphene at that polarization. These results are essential for the development of optoelectronic devices where graphene is adopted as an integral part of the waveguide.