12 September 2005 Single domain magneto-optical circulators in photonic crystals
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Abstract
During the past decade, defect engineering in photonic crystals has successfully miniaturized many optical devices, such as optical filters and lasers, to a sub-wavelength scale. In the field of magneto-optics, previous researches on one-dimensional photonic crystals have demonstrated that magnetic cavities can be used to create Friday rotation in sub-wavelength optical paths, important for integrated optical isolators. In this paper, we study an optical circulator formed of a bismuth-iron-garnet defect infiltrated in a two dimensional silicon photonic crystal. The additional dimension of the field confinement allows further miniaturization and paves the way for monolithic in-plane integration with current integrated optical devices. The magneto-optical defect is constructed to support two doubly-degenerate TE modes and side-coupled to three photonic-crystal waveguides to form a three-port Y-junction circulator. When maximized with geometrically-optimized bismuth-iron-garnet domain, the gyrotropic effects cross couple the two modes and split them into a pair of counter-spinning states. We use the coupled-mode theory to derive the general criterion between the magneto-coupling and resonance decay constant for complete transmission and isolation. Numerical experiments with finite-difference time-domain methods confirmed the coupled mode theory and demonstrate a Y-junction circulator with an isolation ratio greater than 40dB. The design principle for this two dimensional photonic crystal defect can be readily transferred to magneto-optical defects in three dimensional slab photonic crystals. The silicon/air based system has a small footprint of one wavelength squared and good compatibility for integration with other planar optical devices.
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Zheng Wang, Shanhui Fan, "Single domain magneto-optical circulators in photonic crystals", Proc. SPIE 5926, Tuning the Optical Response of Photonic Bandgap Structures II, 59260M (12 September 2005); doi: 10.1117/12.614007; https://doi.org/10.1117/12.614007
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