Photonic Crystal Ridge Waveguides on Magnetic Garnet Films
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J1.7.1
Photonic Crystal Ridge Waveguides on Magnetic Garnet Films R. Li1, X. Huang2, M. Levy2, and H. C. Yang1 1 Materials Science Department, Michigan Technological University, Houghton, MI USA 49931; 2 Physics Department, Michigan Technological University, Houghton, MI USA 49931
ABSTRACT
This paper discusses the fabrication and testing of on-chip photonic crystals in ferrite waveguides. Photonic bandgap engineering can produce Faraday rotators with highly enhanced polarization rotation for ultra-small integrated optical isolators. The main challenges to such devices are the elimination of linear birefringence and the fabrication of planar photonic bandgap nanostructures. These challenges are addressed in the present article. In particular, we demonstrate the presence of stopbands and resonant polarization response in single-defect magneto-optic photonic crystal ridge waveguides. Keywords: Magnetic photonic crystals, magneto-optic photonic crystals, photonic bandgap structures, optical isolators
INTRODUCTION One-dimensional magnetic photonic crystals have been shown to produce an enhanced Faraday response in stacked multi-layered structures.[1-4] The optical beam is transmitted across the film, normal to the surface. Two kinds of structures have been reported: (1) a single iron garnet layer sandwiched between non-magnetic dielectric stacks [1-3] and, (2) all-garnet multi-layers consisting of yttrium iron garnet (YIG) and bismuth iron garnet (BIG), [4] with a single quarter-wave phase shift. An alternative to stacked systems consists of planar one-dimensional magnetic photonic crystals, where refractive index contrast is achieved by patterning a periodic relief on the surface of optical waveguide films.[5-8] Here the confinement of the beam immediately presents serious complications. Optical waveguides generally possess a built-in birefringence between TE and TM modes, even in the absence of stress. This degrades the Faraday response by inhibiting TE to TM mode conversion. Stacked structures do not present this problem since the propagation is normal to the plane of the film. However, an appealing feature of the waveguide approach is that it avoids multi-layer fabrication beyond the cladding and core, particularly in view of the fact that a strong Faraday response and the simultaneous optimization of optical transmittance and polarization rotation require a large multiplicity of layers in the stacked configuration.[5-8] In addition, it appears that the introduction of multiple quarter-wave phase-shift steps and the fabrication of single-domain rotators without bias magnets can be more readily accomplished in the planar geometry.[1-3,8] Below we address birefringence control, the patterning of planar photonic crystal structures and their optical response.
J1.7.2
THE FABRICATION OF PLANAR MAGNETIC PHOTONIC CRYSTAL WAVEGUIDES AND THE ELIMINATION OF BIREFRINGENCE Two key questions must be addressed for the fabrication of waveguide photonic crystals in magneto-optic films. One is the elimination of birefringence;
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