  Electro-optic modulation is a key function for data communication. Given the
vast amount of data handled, understanding the intricate physics and trade-offs
of modulators on-chip allows revealing performance regimes not explored yet.
Here we show a holistic performance analysis for waveguide-based
electro-absorption modulators. Our approach centers around material properties
revealing obtainable optical absorption leading to effective modal
cross-section, and material broadening effects. Taken together both describe
the modulator physical behavior entirely. We consider a plurality of material
modulation classes to include two-level absorbers such as quantum dots, free
carrier accumulation or depletion such as ITO or Silicon, two-dimensional
electron gas in semiconductors such as quantum wells, Pauli blocking in
Graphene, and excitons in two-dimensional atomic layered materials such as
found in transition metal dichalcogendies. Our results show that reducing the
modal area generally improves modulator performance defined by the amount of
induced electrical charge, and hence the energy-per-bit function, required
switching the signal. We find that broadening increases the amount of switching
charge needed. While some material classes allow for reduced broadening such as
quantum dots and 2-dimensional materials due to their reduced Coulomb screening
leading to increased oscillator strengths, the sharpness of broadening is
overshadowed by thermal effects independent of the material class. Further we
find that plasmonics allows the switching charge and energy-per-bit function to
be reduced by about one order of magnitude compared to bulk photonics. This
analysis is aimed as a guide for the community to predict anticipated modulator
performance based on both existing and emerging materials.
