Su Xinzhou, Zou Kaiheng, Wang Yingning, Yessenov Murat, Zhou Huibin, Song Hao, Ko Wing, Zeng Ruoyu, Alhaddad Abdulrahman, Ramakrishnan Murale, Duan Yuxiang, Abouraddy Ayman F, Tur Moshe, Christodoulides Demetrios N, Willner Alan E
Department of Electrical and Computer Engineering, Univ. of Southern California, Los Angeles, CA, USA.
CREOL, The College of Optics & Photonics, University of Central Florida, Orlando, FL, USA.
Nat Commun. 2025 Feb 27;16(1):2027. doi: 10.1038/s41467-025-56982-9.
Space-time wave packets (STWPs) with correlated spatial and frequency degrees of freedom exhibit time-dependent spatial interference, thereby giving rise to interesting dynamic evolution behaviors. While versatile spatiotemporal phenomena have been demonstrated in freely propagating fields, coupling spatiotemporal light into multimode fibers remains a fundamental experimental challenge. Whereas synthesizing freely propagating STWPs typically relies on a continuum of plane-wave modes, their multimode-fiber counterparts must be constructed from the discrete set of fiber modes whose propagation constants depend on fiber structures. Here, we demonstrate STWPs with axially controllable motion of the transverse profile and reconfigurable group velocity in graded-index multimode fibers. This is accomplished by introducing a linear association between frequency comb lines and corresponding fiber modes. The synthesized STWPs present dynamic rotation and translation with a 4.8-ps period. Simultaneously, the group velocity can be tuned from positive subluminal and superluminal to negative values (e.g., 0.870, 1.35, 10, and -3.3 × 10 m/s, respectively).
具有相关空间和频率自由度的时空波包（STWP）表现出随时间变化的空间干涉，从而产生有趣的动态演化行为。虽然在自由传播的场中已经展示了多种时空现象，但将时空光耦合到多模光纤中仍然是一个基本的实验挑战。合成自由传播的STWP通常依赖于连续的平面波模式，而它们在多模光纤中的对应物必须由离散的光纤模式集构建，其传播常数取决于光纤结构。在此，我们展示了在渐变折射率多模光纤中横向分布具有轴向可控运动且群速度可重构的STWP。这是通过在频率梳线和相应的光纤模式之间引入线性关联来实现的。合成的STWP呈现出周期为4.8皮秒的动态旋转和平移。同时，群速度可以从正的亚光速和超光速调谐到负值（例如，分别为0.870、1.35、10和 -3.3×10米/秒）。
