Roth Paul, Frosz Michael H, Weise Linda, Russell Philip St J, Wong Gordon K L
Opt Lett. 2021 Jan 15;46(2):174-177. doi: 10.1364/OL.413557.
We report the first, to the best of our knowledge, observation of cross-phase modulational instability (XPMI) of circularly polarized helical Bloch modes carrying optical vortices in a twisted photonic crystal fiber with a three-fold symmetric core, formed by spinning the fiber preform during the draw. When the fiber is pumped by a superposition of left-circular polarization (LCP) and right-circular polarization (RCP) modes, a pair of orthogonal circularly polarized sidebands of opposite topological charge is generated. When, on the other hand, a pure LCP (or RCP) mode is launched, the XPMI gain is zero, and no sidebands are seen. This observation has not been seen before in any system and is unique to chiral structures with -fold rotational symmetry. The polarization state and topological charge of the generated sidebands are measured. By decomposing the helical Bloch modes into their azimuthal harmonics, we are able to deduce the selection rules for the appearance of modulational instability sidebands. We showed that the four waves in the nonlinear mixing process must exhibit the same set of azimuthal harmonic orders.
据我们所知，我们首次报道了在具有三重对称纤芯的扭曲光子晶体光纤中，对携带光学涡旋的圆偏振螺旋布洛赫模式的交叉相位调制不稳定性（XPMI）的观测，该光纤是通过在拉丝过程中旋转光纤预制棒形成的。当光纤由左旋圆偏振（LCP）和右旋圆偏振（RCP）模式的叠加泵浦时，会产生一对具有相反拓扑电荷的正交圆偏振边带。另一方面，当注入纯LCP（或RCP）模式时，XPMI增益为零，且看不到边带。这种观测在任何系统中都未曾见过，是具有三重旋转对称性的手性结构所特有的。测量了所产生边带的偏振态和拓扑电荷。通过将螺旋布洛赫模式分解为其方位角谐波，我们能够推导出调制不稳定性边带出现的选择规则。我们表明，非线性混合过程中的四个波必须呈现相同的方位角谐波阶数集。
