Entangled photons leaving parametric down-conversion sources exhibit a pronounced polarization correlation. The data violate Bell's inequality thus proving that local realistic theories cannot explain the correlation results. Therefore, many physicists are convinced that the correlation can only be brought about by non-local interactions. Some of them even assume that instantaneous influences at a distance are at work. Actually, assuming a strict phase correlation of the photons at the source the observed polarization correlation can be deduced from wave optical considerations. The correlation has its origin in the phase coupling of circularly polarized wave packets leaving the fluorescence photon source simultaneously. The enlargement of the distances between photon source and observers does not alter the correlation if the polarization status of the wave packets accompanying the photons is not changed on their way from the source to the observers. At least with respect to the polarization correlation of entangled photons the principle of locality remains valid.

离开参数下转换源的纠缠光子表现出明显的偏振相关性。数据违反了贝尔的不等式，因此证明了局部现实理论无法解释相关结果。因此，许多物理学家相信，这种关联只能通过非局部相互作用来实现。他们中的一些人甚至认为远距离的瞬时影响正在起作用。实际上，假设光源处的光子具有严格的相位相关性，则可以从波动光学考虑因素推导出观察到的偏振相关性。该相关性起源于同时离开荧光光子源的圆偏振波包的相位耦合。如果伴随光子的波包的偏振状态在从光源到观察者的途中没有发生变化，则光子源与观察者之间距离的扩大不会改变相关性。至少对于纠缠光子的偏振相关性，局部性原理仍然有效。