Numerical Analysis of Square Graded-index Optical Waveguides

초록

Square graded-index optical waveguides (SGOW) are emerging as promising structures for optical communication, nonlinear optics, and quantum mechanics, as they bridge the gap between traditional GRIN fibers and integrated photonics. This study explores the optical characteristics of three SGOW configurations: Linearly distributed, radially distributed, and squeezed structures. Numerical simulations using the finite element method (FEM) were performed to analyze effective refractive index distributions, mode characteristics, and degeneracy-breaking behavior. Linearly distributed SGOWs exhibited mode splitting due to broken cylindrical symmetry, enabling enhanced mode-division multiplexing and mode separation. Radially distributed SGOWs, analogous to GRIN fibers, achieved equal mode spacing with a second-order refractive index profile, demonstrating their suitability for applications requiring uniform mode behavior. Squeezed SGOWs, derived from mechanically deformed cylindrical waveguides, showed dual behavior: Lower-order modes resembled radial distributions, while higher-order modes transitioned to linear behavior. Notably, a second-order index profile ensured a uniform effective index distribution in squeezed SGOWs, aligning their performance with radially distributed structures. These findings provide valuable insights into SGOW design, fabrication, and application, and support their development for compact, high-performance photonic systems. This study contributes to advancing SGOW technology for next-generation optical and quantum devices.

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