  The epsilon-near-zero (ENZ) tunneling phenomenon allows full transmission of
waves through a narrow channel even in the presence of a strong geometric
mismatch. Here we experimentally demonstrate nonlinear control of the ENZ
tunneling by an external field, as well as self-modulation of the transmission
resonance due to the incident wave. Using a waveguide section near cut-off
frequency as the ENZ system, we introduce a diode with tunable and nonlinear
capacitance to demonstrate both of these effects. Our results confirm earlier
theoretical ideas on using an ENZ channel for dielectric sensing, and their
potential applications for tunable slow-light structures.
