Abstract
Single-mode waveguiding devices are desired for photonic integrated circuits. Previous studies on the single-mode conditions (SMCs) of a silicon-on-insulator (SOI) rib waveguide lack a comprehensive discussion to include a large to small range of cross-section cases, thus revealing the discrepancies of various determination methods. Here, we reanalyze the SMCs for large and small SOI rib waveguides by utilizing a finite-element method mode solver. The results are compared with both classical SMCs of Soref's expression and Pogossian's effective-index method, indicating that the constant value ${\alpha }$ shown in the Soref's analytical expression depends on the rib heights and polarizations. For transverse-electric polarized light and the waveguide height exceeding 5 µm, ${\alpha }$ is approaching that of Soref's equation; if the height is ≤5 µm, then ${\alpha = \boldsymbol{ } $ 0.35, 0.4, 0.45, 0.7, and 1.0 are determined for the cases of 5, 3, 2, 0.8, and 0.4 µm heights, respectively. However, for transverse-magnetic polarized light, if the height ≥ 2 µm, ${\alpha }$ is constant (0.25) and independent on the rib heights, and $\boldsymbol{ \alpha = $ 0.18 and 0.12 are attained for the cases of 0.8 and 0.4 heights, respectively. This detailed analysis indicates that a wider rib width can be used while preserving a SMC leading to devices with improved coupling efficiencies and reduced insertion losses for on-chip photonic circuits.
Published Version
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