Ashrafi Reza, Li Ming, LaRochelle Sophie, Azaña José
Institut National de la Recherche Scientifique—Énergie, Matériaux et Télécommunications, Montréal, QC H5A1K6,
Opt Express. 2013 Mar 11;21(5):6249-56. doi: 10.1364/OE.21.006249.
A superluminal space-to-time mapping process is reported and numerically validated in grating-assisted (GA) co-directional couplers, e.g. fiber/waveguide long-period gratings (LPGs). We demonstrate that under weak-coupling conditions, the amplitude and phase of the grating complex apodization profile of a GA co-directional coupling device can be directly mapped into the device's temporal impulse response. In contrast to GA counter-directional couplers, this mapping occurs with a space-to-time scaling factor that is much higher than the propagation speed of light in vacuum. This phenomenon opens up a promising new avenue to overcome the fundamental time-resolution limitations of present in-fiber and on-chip optical waveform generation (shaping) and processing devices, which are intrinsically limited by the achievable spatial resolution of fabrication technologies. We numerically demonstrate the straightforward application of the phenomenon for synthesizing customized femtosecond-regime complex optical waveforms using readily feasible fiber LPG designs, e.g. with sub-centimeter resolutions.
据报道，在光栅辅助（GA）同向耦合器中，例如光纤/波导长周期光栅（LPG），存在一种超光速的时空映射过程，并通过数值验证。我们证明，在弱耦合条件下，GA同向耦合器件的光栅复变迹分布的幅度和相位可以直接映射到器件的时间脉冲响应中。与GA反向耦合器不同，这种映射的时空缩放因子远高于真空中的光速传播速度。这一现象为克服当前光纤和片上光学波形产生（整形）及处理器件的基本时间分辨率限制开辟了一条有前景的新途径，这些器件本质上受制造技术可实现的空间分辨率限制。我们通过数值证明了该现象在使用易于实现的光纤LPG设计（例如具有亚厘米分辨率）来合成定制的飞秒级复杂光学波形方面的直接应用。
