采用渐变圆弓形散射元实现光子晶体结构慢光效应

Realization of Slow Light Effect for Photonic Crystal Waveguide Using Graded Eye-Shaped Scatterers

采用渐变圆弓形散射元构建线性缺陷波导，并将其应用于光子晶体的慢光效应。在工作波长λ=1550nm时，通过圆弓形散射元单列纵向渐变，获得群折射率在31．4～95．0，低色散（△ng〈10％）带宽在3．7-11．8nm，无量纲标量积ng×（△λ）以在0．2268-0．2390，超低色散带宽（△ng〈1％）在2．2～4．8nm之间的慢光；通过三列圆弓形散射元纵向周期性渐变，获得群折射率在31．6～108．2，低色散（△ng〈10％）带宽在4．0～13．0nm，无量纲标量积ng×（△λ）／1在0．2650-0．2792，超低色散带宽（△ng〈1％）在2．6-6．8nm之间的慢光；通过圆弓形散射元横向渐变，获得群折射率在32．189．3，低色散带宽在2．9～9．3nm，无量纲标量积ng×（△λ）／λ在0．1670～0．1926，超低色散带宽在1．6～3．5nm之间的慢光。可见，采用散射元纵向渐变和横向渐变，特别是纵向渐变，可以实现慢光效应，从而为慢光结构设计和应用提供了新的方向。

With operating wavelength λ= 1550 nm, two-dimensional graded eye-shaped scatterers are applied into photonic crystal waveguide （PCW） for slow light effect in three ways： 1） getting slow light with the group index ng from 31.4 to 95.0, the low-dispersion bandwidth （△ng〈10%） from 3.7 nm to 11.8 nm, the scalar product ng × （AA）/A from 0.2268 to 0. 2390, and the ultralow-dispersion bandwidth （△ng〈1%） from 2. 2 nm to 4. 8 nm by grading the single-row eye-shaped scatterers along the longitudinal direction; 2） getting slow light with the group index ng from 31.6 to 108.2, the low-dispersion bandwidth （△ng〈10%） from 4. 0 nm to 13. 0 nm, the scalar product ng×（△λ）/A from 0. 2650 to 0. 2792, and the ultralow-dispersion bandwidth （△ng〈1% ） from 2. 6 nm to 6.8 nm by grading the triple-row eye-shaped scatterers periodically along the longitudinal direction; 3） getting slow light with the group index ng from 32.1 to 89.3, the low-dispersion bandwidth from 2.9 nm to 9.3 nm, the scalar product ng× （△λ）/λ from 0. 1670 to 0. 1926, and the ultralow-dispersion bandwidth from 1.6 nm to 3.5 nm by grading the eye-shaped scatterers along the transverse direction. It means that graded structures, especially the graded eye-shaped scatterers along the longitudinal direction, can achieve slow light effect well and may provide a new way to design and apply slow light.