Opt Lett. 2019 Jan 15;44(2):219-222. doi: 10.1364/OL.44.000219.
Vector beams (VBs) are widely investigated for their special intensities and polarization distributions, which are useful in optical micromanipulation, optical microfabrication, optical communication, and single molecule imaging. To date, nonlinear frequency conversion (NFC) and manipulation of VBs remain challenging because of the polarization sensitivity of most nonlinear processes. Here we report an experimental realization of NFC and manipulation of VBs that can be used to expand the available frequency band. The main idea of our scheme is the introduction of a Sagnac loop to solve the polarization dependence problem of NFC in nonlinear crystals. Additionally, we find that a linearly polarized VB should be transformed into a hybrid-polarized VB in exponential form before performing NFC. The experimental results agree well with those of our theoretical model. The proposed method is also applicable to other wavebands and second-order nonlinear processes, and may be generalized to the quantum regime for single photons.
矢量光束（VBs）因其特殊的强度和偏振分布而被广泛研究，它们在光学微操纵、光学微加工、光通信和单分子成像等方面都有重要应用。迄今为止，由于大多数非线性过程对偏振的敏感性，非线性频率转换（NFC）和 VB 的操控仍然具有挑战性。在这里，我们报告了一种实验实现的 NFC 和 VB 的操控，这可以用来扩展可用的频带。我们方案的主要思想是引入萨格纳克环来解决非线性晶体中 NFC 的偏振依赖性问题。此外，我们发现，在进行 NFC 之前，线性偏振的 VB 应该先被转换为指数形式的混合偏振 VB。实验结果与我们的理论模型吻合较好。该方法也适用于其他波段和二阶非线性过程，并可推广到单光子的量子领域。
