MAGNETOOPTICAL WAVE-GUIDES OF ALUMINUM GARNET

Planar waveguides of high refractive index aluminum garnets containing magnetic rare-earth cations have been epitaxially grown on [111]-orie nted crystal wafers of yttrium aluminum garnet (Y3Al5O12, YAG). Epitax y was by the liquid phase solution growth technique from supercooled m ixtures of lead oxide and boron oxide, as is common for the epitaxy of the magneto-optical iron garnets. The liquid phase epitaxy technique is well established for aluminum garnets, so that mixed garnet composi tions, such as (R(a)R(b))3Al5O12, can be prepared easily as crystal la yers on YAG. The typical lattice constant mismatch which is tolerated for defect-free epitaxy is about 0.1%. Reduction of stress-induced bir efringence demands a still closer matching of the epitaxial layer to t he substrate, of the order of 0.01%. Such matching to a YAG substrate can be achieved in mixed garnet compositions, such as (R(a),R(b))3Al5O 12, in which R(a) and R(b) are large and small cations which average t o the cationic size of yttrium. One composition which is particularly suited for magneto-optical waveguides is Tb1.65Lu1.35Al5O12, which has a refractive index at 632.8 nm of about 1.8545, as compared with 1.82 80 for YAG, and has no absorption bands in the visible and near-IR spe ctra. The room temperature Verdet constant of this composition has bee n measured over the wavelength range of 500-675 nm, and it is comparab le to that of Tb3Al5O12. Magnetic field modulation of light intensity of 4.4 ppm/cm/Oe at 632.8 nm has been measured in a planar waveguide o f the Tb1.65Lu1.35Al5O12 composition. Since aluminum garnets have melt ing points greater than 1900-degrees-C, such waveguides should find ap plication in high temperature magneto-optical sensors and isolators.