  We demonstrate direct focused ion beam (FIB) writing as an enabling
technology for realizing spin-wave-optics devices. It is shown that ion-beam
irradiation changes the characteristics of YIG films on a submicron scale in a
highly controlled way, allowing to engineer the magnonic index of refraction
adapted to desired applications. This technique does not physically remove
material, and allows rapid fabrication of high-quality architectures of
modified magnetization in magnonic media with minimal edge damage (compared to
more common techniques such as etching or milling). By experimentally showing
magnonic versions of a number of optical devices (lenses, gratings,
Fourier-domain processors) we envision this technology as the gateway to
building magnonic computing devices that rival their optical counterparts in
their complexity and computational power.
