State Key Laboratory of Advanced Optical Communication Systems and Networks, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant No. 11574211)
Received Date:08 September 2020
Accepted Date:06 October 2020
Available Online:25 February 2021
Published Online:05 March 2021
Abstract:In this paper the optical vortices with topological charge q = –1, 1, 2, 4 are recorded in azo polymer films by using holographic technology. The forked holographic gratings formed by the Gaussian beam and optical vortex beam are recorded in the sample films, the original forked holographic grating and the recording rate are analyzed. The vortex beam is reconstructed by illuminating the sample film with a reference beam, and the recording quality is analyzed. Also the erasability and durability of the sample are tested. The experimental results show that the recording rates of vortex beams with different topological charges are relatively uniform, which means that the optical vortices with different topological charges can be recorded at the same speed. The forked holographic grating of the high-order optical vortex splits in the recording process due to the disturbances, such as anisotropic nonlinear light, atmospheric turbulence, and background light field. However, the split vortex beam still maintains a stable ring structure. The reconstructed optical vortex and the original optical vortex are highly consistent in morphology, and the interference fringes of the reconstructed optical vortices are highly consistent with the original vortex holographic gratings, indicating that the topological charge information in the optical vortices can be effectively recorded and read out. The recorded information can be erased by heating the sample to about 97 ℃, and new information can be re-recorded after cooling. There appears no fatigue in the sample after the information has been erased 100 times and good durability is still retained. Optical vortices theoretically have infinite states of topological charges, based on which great success is achieved in optical communication and information encoding. Therefore, storing and reading information of topological charges in optical vortices may have potential applications in optical information storage. Keywords:holography/ azo polymer/ optical vortex/ topological charge
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2.1.样 品
实验采用的记录材料为偶氮苯染料和聚离子液体(PIL, Sigma-Aldrich)通过离子自组装[28]形成的超分子薄膜材料. 其制备过程如下:选择带电聚合物聚(1 butyl-vinylpyridinium bromide) PIL作为主链段, 甲基橙染料(MO, Sigma-Aldrich)作为构建单元. 将2.5 mg/mL PIL水溶液以1∶1摩尔电荷比滴加到 MO水溶液中, 将沉淀的聚合物用双蒸馏水反复清洗几次, 并在60 ℃的真空环境中干燥10 h, 干燥后的粉末加热至200 ℃左右熔化, 在冷却阶段出现了高取向顺序的聚合物. 用Dektak轮廓仪测得合成的薄膜的厚度约为6 μm. 聚合物薄膜的吸收光谱、样品的原子力显微镜(atomic force microscope, AFM)图像、样品的结构和化合物的化学结构如图1所示. 样品的吸收峰在350—550 nm之间, 实验选取波长为532 nm的激光作为记录光源, 样品薄膜的表面起伏在10 nm范围内, 具有较高的平整度, 能有效减少表面不平整对光场的影响, 利于光学信息的记录. 图 1 偶氮苯聚合物薄膜的吸收光谱, 插图为样品AFM图像, 封装后的样品结构和化合物的化学结构 Figure1. Absorption spectra of the azo-benzene polymer film. Inset: AFM image and structure of the sample, and chemical structure of the compound.