中国光学期刊网

提出一种基于光学亮环晶格进行空间光信息编码通信的方法。基于面向目标的计算全息术,生成4种简单模式的光学亮环晶格对应的计算全息图,并将其加载在反射式空间光调制器(SLM)上,SLM调制入射光,直接重建4种简单模式的光学亮环晶格。4种光学亮环晶格模式对应4个不同的四进制数,易于识别,通过光学亮环晶格模式的组合完成一幅32 pixel×56 pixel的256阶灰度图的编码与空间传输。距离发射端2 m处的电荷耦合器件(CCD)接收光学亮环晶格图像并通过计算机对数据进行解码,可以在部分干扰情况下,无差错地恢复原始图像信息。在此基础上,实验拓展单个光学亮环晶格至2×2和4×4阵列,传输效率和系统容量提升了4倍和16倍。本研究成果为光学亮环晶格的编码通信研究提供了理论和实验依据。

轨道角动量(OAM)是具有螺旋相位的光束的自然属性,且不同拓扑荷的OAM光束之间相互正交。利用OAM光束的这种特性,可以把OAM光束作为一种新的信息载体应用到复用技术之中。OAM复用技术在不需要额外带宽的情况下可以极大提升信道容量和频谱效率。光纤作为一种优良的传输介质,是现代通信网络中的首选,基于光纤传输的OAM复用技术引起了研究者的广泛关注。介绍了轨道角动量的基本原理,讨论了适于携带OAM光束传输的光纤、OAM光束的生成与检测方法、OAM复用技术相关器件及其复用系统实验等方面的研究进展,最后探讨了现有技术存在的问题和发展趋势。

An all fiber femtosecond vortex laser based on common fiber components is constructed. It can produce femtosecond orbital angular momentum modes whose pulse width of time is 398fs. The topological charge of output OAM modes from this setup can be adjusted among 0, +1, -1 easily while it is also easy to convert between continuous OAM modes and pulse OAM modes.

In this work, an all-fiber-based mode converter for generating orbital angular momentum (OAM) beams is proposed and numerically investigated. Its structure is constructed by cascading a mode selective coupler (MSC) and an inner elliptical cladding fiber (IECF). OAM modes refer to a combination of two orthogonal LP_lm modes with a phase difference of ±π/2. By adjusting the parameters and controlling the splicing angle of MSC and IECF appropriately, higher-order OAM modes with topological charges of l = ±1, ±2, ±3 can be obtained with the injection of the fundamental mode LP₀₁, resulting in a mode-conversion efficiency of almost 100%. This achievement may pave the way towards the realization of a compact, all-fiber, and high-efficiency device for increasing the transmission capacity and spectral efficiency in optical communication systems with OAM mode multiplexing.