The nonreciprocal effect is the difference Deltabeta = beta(forward)-beta(backward) between forward and backward-propagation constants of optical modes. This effect is analyzed for the fundamental TM00 mode of channel waveguides in epitaxially grown magnetic garnet films. To increase |Deltabeta|, double layers with opposite signs of Faraday rotation are used to prepare the waveguides. It is shown that the temperature dependence of Deltabeta can be reduced considerably if the layer with positive Faraday rotation, which is at room temperature close to the Curie point, is replaced by a paramagnetic layer with negligible Faraday rotation. Concurrently, however, |Deltabeta| is decreased by approximately 35% at 295 K.

Garnet films of composition (Lu, Bi) 3 (Fe, Ga, Al) 5 O 12 and (Tm, Bi) 3 (Fe, Ga) 5 O 12 are grown by liquid-phase epitaxy on [111]-oriented substrates of gadolinium gallium garnet. Ferrimagnetic films with positive or negative Faraday-rotation as well as paramagnetic films with negligible Faraday-rotation are produced by variations of the rare earth ion substitutions. The temperature dependence of Faraday-rotation is fitted with a molecular field model. Optical rib waveguides in single and double layer garnet films with different Faraday-rotations are realized. The nonreciprocal phase shift of the TM 0 -Mode is studied both theoretically and experimentally at a wavelength of 1.3 μm. Results show that the maximum nonreciprocal effect at room temperature of double layer films with opposite Faraday-rotation is 1.6 times as large as that of comparable single layer waveguides. But, because of the large temperature dependence of the Faraday-rotation of the positive rotating films, these waveguides show a large temperature dependence of the nonreciprocal phase shift. This problem can be avoided if the positive rotating layer is replaced by a paramagnetic layer. Agreement between calculations and measurements is excellent.