  In this study, we investigate plasmon-induced transparency (PIT) in a
resonator structure consisting of two orthogonally-arranged
metal-insulator-metal (MIM) nanocavities with the aim of spectral modulation of
a specific resonant order of the resonator. Our FDTD simulations demonstrate
that when both cavities in this structure resonate at the same frequency, the
PIT effect can be used to induce spectral modulation. This spectral modulation
depends on the resonance order of the cavity coupled directly to the external
field, occurring when first-order resonance is exhibited, but not with
second-order resonance. We confirmed that this behavior is caused by the
discrepancies between odd-order and even-order resonances using classical
mechanical models analogous to the nanocavities. By tuning the resonance
frequency and resonance order of the cavities, one can modulate the spectrum of
the resonator structure in an order-selective manner.
