  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.
