It is found that, in contrast to the usual situation of a uniform bias magnetic field perpendicular to the YIG-film plane, a tilted bias magnetic field results in modification to the phase matching condition, and may possibly facilitate enhanced MO Bragg diffraction efficiency. On the other hand, recent experiments also show that the Bragg diffraction efficiency could be significantly enhanced by utilizing a bias magnetic field which is nonuniform but still perpendicular to the waveguide film plane. A diffraction efficiency as high as approximate 70% has been measured in comparison to a 12% diffraction efficiency for a typical modulator utilizing a uniform magnetic field. In this paper, a summary of theoretical treatment for Bragg diffraction under tilted bias magnetic field and some of the most recent experimental results for Bragg diffraction under nonuniform bias magnetic preliminary result presented.
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