Finlayson C E, Cattaneo F, Perney N M B, Baumberg J J, Netti M C, Zoorob M E, Charlton M D B, Parker G J
School of Physics & Astronomy, University of Southampton, Southampton SO17 1BJ, UK.
Phys Rev E Stat Nonlin Soft Matter Phys. 2006 Jan;73(1 Pt 2):016619. doi: 10.1103/PhysRevE.73.016619. Epub 2006 Jan 30.
We report time-of-flight experiments on photonic-crystal waveguide structures using optical Kerr gating of a femtosecond white-light supercontinuum. These photonic-crystal structures, based on engineered silicon-nitride slab waveguides, possess broadband low-loss guiding properties, allowing the group velocity dispersion of optical pulses to be directly tracked as a function of wavelength. This dispersion is shown to be radically disrupted by the spectral band gaps associated with the photonic-crystal periodicity. Increased time-of-flight effects, or "slowed light," are clearly observed at the edges of band gaps in agreement with two-dimensional plane-wave theoretical models of group velocity dispersion. A universal model for slow light in such photonic crystals is proposed, which shows that slow light is controlled predominantly by the detuning from, and the size of, the photonic band gaps. Slowed light observed up to time delays of approximately 1 ps, corresponds to anomalous dispersion of approximately 3.5 ps/nm per mm of the photonic crystal structure. From the decreasing intensity of time-gated slow light as a function of time delay, we estimate the characteristic losses of modes which are guided in the spectral proximity of the photonic band gaps.
我们报告了使用飞秒白光超连续谱的光学克尔门控对光子晶体波导结构进行的飞行时间实验。这些基于工程氮化硅平板波导的光子晶体结构具有宽带低损耗导光特性，能够直接跟踪光脉冲的群速度色散随波长的变化。结果表明，与光子晶体周期性相关的光谱带隙会彻底扰乱这种色散。在带隙边缘清楚地观察到飞行时间效应增强，即“慢光”，这与群速度色散的二维平面波理论模型一致。本文提出了此类光子晶体中慢光的通用模型，该模型表明慢光主要由与光子带隙的失谐以及带隙大小控制。观察到的慢光延迟时间长达约1皮秒，对应于光子晶体结构每毫米约3.5皮秒/纳米的反常色散。根据时间选通慢光强度随时间延迟的降低，我们估算了在光子带隙光谱附近被引导的模式的特征损耗。
