Abstract
Optical polarizing devices exploiting graphene embedded in waveguides have been demonstrated in the literature recently and both the TE- and TM-pass behaviors were reported. The determination of the passing polarization is usually attributed to graphene’s Fermi level (and, therefore, doping level), with, however, no direct confirmation of this assumption provided. Here we show, through numerical simulation, that rather than graphene’s Fermi level, the passing polarization is determined by waveguide parameters, such as the superstrate refractive index and the waveguide’s height. The results provide a consistent explanation for experimental results reported in the literature. In addition, we show that with an accurate graphene modeling, a waveguide cannot be switched between TE pass and TM pass via Fermi level tuning. Therefore, the usually overlooked contribution of the waveguide design is shown to be essential for the development of optimized TE- or TM-pass polarizers, which we show to be due to the control it provides on the fraction of the electric field that is tangential to graphene.
Highlights
Graphene is a one-atom thick carbon allotrope arranged in a crystalline hexagonal structure that presents remarkable properties such as a high electronic mobility and linear electronic dispersion in which the valence and conduction bands touch at a single momentum-space point[1]
The waveguide was designed for operation at ~1550 nm wavelength, which is used in the majority of the reported experiments and is of major interest for telecommunication systems
A simulation was performed for the exact waveguide presented by Kou et al and the calculated attenuation for the TE and TM modes were 0.075 dB/μ m and 0.025 dB/μ m respectively, consistent with the mean experimental values reported of 0.09 dB/μ m and 0.05 dB/μ m13
Summary
Graphene is a one-atom thick carbon allotrope arranged in a crystalline hexagonal structure that presents remarkable properties such as a high electronic mobility and linear electronic dispersion in which the valence and conduction bands touch at a single momentum-space point[1] The latter characteristic leads to a constant 2.3% absorption when light, over a broad optical band, traverses a single graphene layer at normal incidence[1,2]. Even with the optical absorption per unit length being remarkably high in graphene, the net absorption it provides is low due to its atomic thickness For this reason, optical devices that incorporate graphene usually enhance the light-graphene interaction by embedding it longitudinally, close to the core of waveguides[2]. The graphene length was ~7 mm and the measurements were performed at 1310 nm wavelength
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