Conservation of orbital angular momentum in air-core optical fibers
Conservation of orbital angular momentum in air-core optical fibers
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DOI：
10.1364/optica.2.000267
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发表时间：
2015-03-20
期刊：
影响因子：
10.4
通讯作者：
Ramachandran, S.
中科院分区：
文献类型：
--
作者：
Gregg, P.;Kristensen, P.;Ramachandran, S.
光的轨道角动量（OAM）是圆柱对称介质中的守恒量。然而，它很容易被自由空间湍流或光纤弯曲破坏，因为各向异性扰动会产生角动量。我们观察到，即使在存在强弯曲扰动的情况下，OAM的守恒性，具有适当地塑造模态态密度的空气芯的纤维。类似于旋转陀螺随着角速度的增加而增强的稳定性，这些状态的寿命随着OAM幅度的增加而增加。因此，与系统的基态是最稳定的传统智慧相反，空芯光纤中的OAM寿命随着模阶数而增加。借助于这个基本量的守恒，我们证明了12个不同的高阶OAM模式的光纤传播，其中8个在更长的传播后保持低损耗并且从近简并耦合中获得> 98%的纯度。第一次实现长寿的高阶OAM状态，迄今为止假设只存在于真空中，是实现在实际距离上实现高维经典和量子通信的必要条件。(C)2015美国光学学会
Light's orbital angular momentum (OAM) is a conserved quantity in cylindrically symmetric media. However, it is easily destroyed by free-space turbulence or fiber bends, because anisotropic perturbations impart angular momentum. We observe the conservation of OAM even in the presence of strong bend perturbations, with fibers featuring air cores that appropriately sculpt the modal density of states. Analogous to the enhanced stability of spinning tops with increasing angular velocity, these states' lifetimes increase with OAM magnitude. Consequently, contrary to conventional wisdom that ground states of systems are the most stable, OAM longevity in air-core fiber increases with mode order. Aided by conservation of this fundamental quantity, we demonstrate fiber propagation of 12 distinct higher order OAM modes, of which eight remain low loss and > 98% pure from near-degenerate coupling after kilometer-length propagation. The first realization of long-lived higher order OAM states, thus far posited to exist only in vacuum, is a necessary condition for achieving the promise of higher dimensional classical and quantum communications over practical distances. (C) 2015 Optical Society of America