  We experimentally realize indirect coupling between two cavity modes via
strong coupling with the ferromagnetic resonance in Yttrium Iron Garnet (YIG).
We find that some indirectly coupled modes of our system can have a higher
microwave transmission than the individual uncoupled modes. Using a coupled
harmonic oscillator model, the influence of the oscillation phase difference
between the two cavity modes on the nature of the indirect coupling is
revealed. These indirectly coupled microwave modes can be controlled using an
external magnetic field or by tuning the cavity height. This work has potential
for use in controllable optical devices and information processing
technologies.
