Magnetooptical garnets combine high Faraday rotation with low optical losses in the near infrared region where optical communication via glass fiber is established. In this spectral range garnets are the only materials discussed to realize nonreciprocal devices as optical isolators and circulators. Although such devices are available as microoptical components, practical versions of their integrated counterparts are still lacking. Numerous concepts have been developed theoretically many of which are tested experimentally. This paper presents an overview of the state of the art of the applications of garnet films in integrated optics. Also the technique of combining garnets with semiconductor materials is shortly discussed.
Garnet films of composition Lu3−xBixFe5−yGayO12 are grown by liquid-phase epitaxy on [111]-oriented substrates of gadolinium gallium garnet. Faraday rotation and saturation magnetization are measured as a function of substitution levels, which range up to x=1.4 and y=1.8, respectively. Nonreciprocal propagation of the TM0 is studied at a wavelength of 1.3 μm. It is shown that the difference between forward and backward propagation constants can be optimized using double layers with opposite sign of the Faraday rotation. Agreement between experiments and calculations is excellent.
Channel waveguide lasers in crystals of neodymium-doped gadolinium-gallium-garnet are realized. They are based on single-mode rib waveguides prepared by liquid phase epitaxy. By this growth technique the incorporation of certain impurities, which may cause severe quenching, is inevitable. The dominant quenching process could be identified and eliminated. Channel waveguides with extremely low losses, down to 0.25 dB/cm for both TE and TM modes, are fabricated by ion-beam etching. As a result, low thresholds of 5 mW and high slope efficiencies of 48% at the laser wavelength of 1.062 μm could be achieved when pumping at a wavelength of 807 nm.
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