Under no biasing voltage, ITO acts almost as a dielectric. However, by carefully tuning the biasing voltage, the free carrier concentration beneath the ITO surface is changed. This allows a dramatic alteration in the complex permittivity of the ITO reaching an epsilon-near-zero (ENZ) value at some point. At this region, the ITO acts as a metal and a plasmonic mode is present at an ITO-dielectric interface. A heavily doped silicon slab can be used as a contact for the gating voltage to be applied on in order to accumulate free carriers on the ITO surface.
In this work, an all-silicon indium tin oxide-integrated electro-optical modulator is designed. The modulator exhibits superior parameters (e.g. insertion loss and extinction ratio) that outperform the current modulators based on the same technology.