An Analysis of Isolation Properties of Mono-Sectional Optical Isolators Using Bi:YIG Thin-Films

Yasumitsu MIYAZAKI  Kazunari TAKI  

IEICE TRANSACTIONS (1976-1990)   Vol.E72   No.6   pp.742-750
Publication Date: 1989/06/25
Online ISSN: 
Print ISSN: 0000-0000
Type of Manuscript: PAPER
Category: Electro-Optics

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A mono-sectional optical isolator consists of two mode selectors and one mode converter whose magnetization is uniform and tilts in the plane transverse to the light propagation direction by an elevation angle θ from the film plane. Nonreciprocal mode conversion properties of the converter which is the gyrotropic waveguide magnetized in an arbitrary direction have been theoretically investigated by using hybrid modes, and isolation properties of the mono-sectional optical isolator have been derived. The unidirectional mode conversion can be achieved in one mode converter because the mode conversions through the first and second order magnetooptic factors, and f44M2, add up and cancel each other in the backward and forward directions, respectively, when the film thickness is near the cut-off. The propagation length for the unidirectional mode conversion becomes small with the increase of and θ depends on f44M2/. When the refractive index and the optical birefringence are 2.18 and 1.28103, 4.185103, f44M20.2 for the Bi:YIG guide layer and the refractive index of the substrate is n22.165, the isolation ratio of 30dB can be achieved at θ82 for the length of 5.0mm and the guide layer thickness of 1.64µm. Under this condition, the single mode operation which is essential to the optical isolator can be guaranteed.