Isolator in integrated optics using the Faraday and Cotton-mouton effects

The general principle for calculating the mode conversion obtained by the association of a gyromagnetic guide with an anisotropic guide is given. The results for a unidirectional mode converter (UMC) and a gyrator are presented together with the principle of an optical isolator and of an optical circulator. An isolator for integrated optics has been implemented by associating a unidirectional mode converter and a polarizer. The UMC is composed of two mode converters (TEo → TMo), one through the Faraday effect and the other through the Cotton-Mouton effect. Light at 1.15 μm wavelength is propagating in a gadolinium-gallium substituted YIG film grown by epitaxy on a <111> - oriented GGG substrate. The thickness of the film is 5 μm. The stress due to the lattice mismatch induces birefringence producing degeneracy of the TEo - TMo modes. In the Faraday mode converter, the length of which is 3 mm, the magnetic field of 15 Oe is applied parallel to the propagation direction. The Cotton-Mouton converter has a length of 12 mm and the magnetic field (≃ 250 Oe) is applied approximately at 22.5 deg of the plane of the film and is perpendicular to the propagation direction. The polarizer is a metal deposited thin-film of Aluminium giving a strong absorption for the TMo mode. Experimental results are given showing the fundamental properties of the isolator.