Abstract: In a high-frequency light polarization modulating device including a source of polarized light (SL), a generator (BOBI) of a periodic magnetic field (H.sub.p) having a pulsation (.omega.) and a magnetooptical garnet (GRI) receiving the beam (F.sub.i) emitted by the source and the field (H.sub.p), in order to produce a beam (F.sub.mi) of modulated polarized light, the invention provides that the generator (BOBI) comprises a microcoil disposed on the garnet in such a manner as to produce a magnetic field perpendicular to it. The garnet (GRI) is monocrystalline, in thin layers, and anisotropic, and its direction of easy magnetization is perpendicular to its plane. The invention is applicable to magnetooptical memories.