Characterization of garnet films for magnetostatic wave modulation of light

Abstract

The goal of the present work at the laboratory is the construction of a magnetostatic wave optical modulator. To accomplish said goal, material must be found that permits guided optical modes to propagate with low attenuation, possesses high Faraday rotation (to produce high diffraction efficiencies), and has a narrow ferrimagnetic linewidth to allow the magnetostatic waves to operate at high frequencies with little attenuation. Presently the material of choice is yttrium iron garnet (YIG) but Bi-substituted YIG offers improved Faraday rotation with little or no increase in optical absorption, as indicated by the magnetooptic figure of merit (Faraday rotation divided by the optical absorption). The Faraday rotation of Bi-containing film and an unsubstituted YIG film was measured at a wavelength of 1.3 μm. The technique employs the extinction method utilizing a rotatable analyzer and uses a curve fitting scheme to calculate the total rotation of the saturated samples. The optical absorption coefficient of both Bi substituted and unsubstituted YIG films was measured using a guided wave technique. This technique scans the surface of the waveguide, collecting scattered light using a fiber-optic bundle. Additionally ferrimagnetic resonance linewidth measurements were carried out on thin films of Bi-substituted YIG using a modified cavity technique.