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The performance of an electro-optic modulator based on quantum confined Stark effect in a SiGe filled metal
stub, coupled to an underlying Si-waveguide, is investigated using finite element simulations. The transmission
of the system is controlled by changing the absorption coefficient of the material filling the stub, which modifies
both the power transmitted by the stub itself and the field profile, and hence the coupling of this field into
the single-mode output waveguide. An extinction ratio of ~8.5 dB with an insertion loss of ~8.5 dB can be
achieved via electro-absorption derived from the quantum confined Stark effect (QCSE), assuming that the stub
is filled with Ge/SiGe multiple quantum wells (MQWs) or Ge quantum dots (QDs) in a silicon matrix. With
the sub-wavelength dimensions of the device offering low power operation and high switching speeds, the effect
is of potential interest for application in silicon platform integrated photonics. Comparison is then made with an
alternative class of plasmonic modulators based on metal-gap-dielectric structures, relying on the sensitivity of
the gap plasmon mode losses near the mode cutoff to the precise refractive index profile, which can be changed
via free carrier accumulation. These devices offer reduced insertion losses and, in contrast to the stub structures,
their insertion loss and modulation depth scale with device length.
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