Development and design of a dielectric optical waveguide with reduced bend loss

研究成果の概要 (和文) : 屈折率差の大きい強導波路が屈曲した場合の損失を明らかにするために、円筒座標系フルベクトル虚軸ビーム伝搬法に強調した増幅係数を導入する手法を開発した。これを用いて、埋め込み型シリコン細線導波路のコア位置が伝搬特性に及ぼす効果を明らかにした。特にコアの縦横比が屈曲損に及ぼす効果を検討した。結果として、界分布のピーク値から５％に当たる位置に空気界面からの埋め込み量を選ぶと、効果的に屈曲損を低減できることを明らかにした。また、コア側壁のラフネスがどの程度屈曲損を増加させるかを明示した。加えて、直交座標系で屈曲導波路を解析する際に多用されている変換屈折率法に関して、より適切な変換法を明らかにした。研究成果の概要 (英文) : The imaginary-distance procedure with an enhanced amplification factor is applied to the Yee-mesh-based implicit beam-propagation method in the cylindrical co-ordinate system. The developed technique is adopted to study the effect of core location in a buried Si-wire waveguide with various aspect ratios. Reduced bend loss is achieved when the air-cladding interface is placed at the position where the field amplitude decays to 5% of its peak. In comparison with the results obtained from the transformed index method in the rectangular co-ordinate system, we find the transformed technique based on an exponential function is superior to that obtained from a linear function.We finally investigate the effect of the sidewall roughness on the propagation behavior. It is found that the bend loss becomes largest when the correlation length is around 100 nm, and that the polarization crosstalk remains rather small, compared with the crosstalk generated with a tilted sidewall