  Energy squeezing attracts many attentions for its potential applications in
electromagnetic (EM) energy harvesting and optical communication. However, due
to the Fabry-Perot resonance, only the EM waves with discrete frequencies can
be squeezed and, as far as we know, in the previous energy-squeezing devices,
stringent requirements of the materials or the geometrical shape are needed. We
note that the structures filled with epsilon-near-zero (ENZ) mediums as
reported in some works can squeeze and tunnel EM waves at frequencies (e.g.
plasma frequency). However, the group velocity is usually near zero which means
few EM information travel through the structures. In this paper, low-loss
energy squeezing and tunneling (EST) based on unidirectional modes were
demonstrated in YIG-based one-way waveguides at microwave frequencies.
According to our theoretical analysis and the simulations using finite element
method, broadband EST was achieved and the EM EST was observed even for
extremely bended structures. Besides, similar EM EST was achieved in a
realistic three-dimensional remanence-based one-way waveguide as well. The
unidirectional modes-based EST paving the way to ultra-subwavelength EM
focusing, enhanced nonlinear optics, and designing numerous functional devices
in integrated optical circuits such as phase modulator.
