Waveguide-type optical isolator with in-plane magnetization structure

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Abstract
A novel unidirectional mode converter, which has the advantage of a simple magnetization structure, is proposed for an application to a waveguide-type optical isolator. The proposed mode converter is constructed with in-plane magnetization in the whole device, where the magnetization component along a light propagation direction produces a mode conversion between TE0 and TM0 modes, while the magnetization perpendicular to the propagation direction provides a nonreciprocal phase shift to the TM0 mode. The unidirectional mode converter, in which, in the backward direction, 100% TE-TM mode conversion is produced but, in the forward direction, an input TE mode emerges as a TE mode, is realizable by virtue of the nonreciprocal phase shift of the TM0 mode. Design examples are shown by using the (LuBi)3Fe5O12 guiding layer / (YBi)3Fe5O12 cladding layer / Gd3Ga5O12 substrate structure. A typical length of the mode converter is 15.5 mm at the wavelength of 1.152 .tm for the guiding layer thickness of O.575jim and with the magnetization direction tilted by 87 degree from the light propagation direction in the film plane. A relatively large device length is reduced by using a magnetooptic material having a large first-order magnetooptic coefficient.

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