  As one of the fundamental magnonic devices, a magnonic splitter device has
been proposed and spin wave propagation in this device has been studied
numerically and experimentally. In the present work, we fabricated a T-shaped
magnonic splitter with 6 $\mu$m-wide three arms using a 100 nm-thick yttrium
iron garnet film and, using time-resolved magneto-optic Kerr microscopy,
observed that spin waves split into both, the vertical and the horizontal
direction at the junction. Analyzing the results, we found that spin wave modes
are converted into another during the splitting process and the splitting
efficiency is dominantly dependent on the 1st order of incoming spin waves.
