  Microfocused Brillouin light scattering (BLS) and microwave absorption (MA)
are used to study magnon-photon coupling in a system consisting of a split-ring
microwave resonator and a yttrium iron garnet (YIG) film. The split-ring
resonantor is defined by optical lithography and loaded with a 1 $\mu$m-thick
YIG film grown by liquid phase epitaxy. BLS and MA spectra of the hybrid system
are simultaneously recorded as a function of the applied magnetic field
magnitude and microwave excitation frequency. Strong coupling of the magnon and
photon modes is found with a coupling strength of $g_\text{eff}/2 \pi = 63$
MHz. The combined BLS and MA data allows to study the continuous transition of
the hybridized modes from a purely magnonic to a purely photonic mode by
varying the applied magnetic field and microwave frequency. Furthermore, the
BLS data represent an up-conversion of the microwave frequency coupling to
optical frequencies.
