Experimental demonstration of light propagation with ultralow group velocity, i.e., slow light, allows for revolutionary solutions for time-domain processing and buffering of optical signals. It can spatially compress optical energy, which lessens the device footprint and enhances linear and nonlinear optical effects. Photonic crystal waveguides (PCWs) are appealing for producing slow light since they can be on-chip integrated and operated under room temperature. However, most PCW slow-light devices are restricted to the narrow spectral range of material resonance, leading to a small delay-bandwidth product, which restricts the maximum data rate, operation frequency, and storage capacity. Furthermore, the lack of broadly tunable slow light hinders practical applications in tunable photonic devices. We propose a reconfigurable slow-light device using a PCW based on a prototypical chalcogenide glass, Ge2Sb2Te5 (GST225) to solve the problems. We find that the operating wavelength of the slow light within the structure can be reversibly switched between 3575 and 4905 nm by changing the structural state of GST225 between amorphous and crystalline ones. The corresponding average group indices are 40.8 and 54.4, respectively. We experimentally illustrate that the reversible phase transition of GST225 between amorphous and crystalline ones can be realized in nanoseconds. Our proof of concept may provide a platform for actively engineering slow light that might otherwise be difficult to obtain in photonic systems. We expect it to improve the device performance in the fields of nonlinearity and sensing.

中文翻译：

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相变光子晶体波导中的可重构慢光

超低群速光传播的实验演示，即慢光，为时域处理和光信号缓冲提供了革命性的解决方案。它可以在空间上压缩光能，从而减少器件占用空间并增强线性和非线性光学效应。光子晶体波导 (PCW) 对产生慢光很有吸引力，因为它们可以在芯片上集成并在室温下运行。然而，大多数PCW慢光器件受限于材料谐振的窄光谱范围，导致延迟带宽积很小，从而限制了最大数据速率、工作频率和存储容量。此外，缺乏广泛可调的慢光阻碍了可调光子器件的实际应用。我们提出了一种可重构慢光设备，使用基于原型硫属化物玻璃 Ge2Sb2Te5 (GST225) 的 PCW 来解决这些问题。我们发现通过在非晶态和晶态之间改变 GST225 的结构状态，可以在 3575 和 4905 nm 之间可逆地切换结构内慢光的工作波长。相应的平均组指数分别为 40.8 和 54.4。我们通过实验说明 GST225 在非晶态和晶态之间的可逆相变可以在纳秒内实现。我们的概念验证可以为主动设计慢光提供一个平台，否则在光子系统中可能难以获得。我们期望它能够提高非线性和传感领域的设备性能。