基于手征光纤的全光纤圆偏振器件的研究与制备

There are some advantages of circularly polarized light over linearly polarized light such as no need to aim the optical axis when connecting different fibers, the polarization states of the reflected light and incident light are orthogonal, easy to detect the Faraday Effect and so on. So it had attracted extensive attention from domestic and foreign experts. But there is no mature product of all fiber circular polarizer. In general terms a circularly polarized light can be only transformed from linearly polarized light that is generated by a linear polarizer. How should we develop the fiber circular polarization technology by leaps and bounds and expand its application prospects? The nodus and key is how to design and product all fiber circular polarized devices by a simple and effective method. To deal with this challenging and attractive problem, a new method of designing and producting the devices based on chiral fiber grating (CFG) which was generated through twisting the linear polarization fiber is proposed. First，to study the mode coupling mechanism of the new CFG and build a modus or software of design of the new CFG devices; then to manufacture a equipment of the new CFG; finally using the CFG to fabricate all fiber circularly polarized devices such as optical fiber circular polarizer, circularly polarized filter, single circular polarization fiber and other fiber optic devices. These devices not only can be used in the fiber-optic current sensors but also have potentially applications in the situations of using linearly polarized light such as high-precision fiber-optic laser gyro. It will contribute to the development of the circular polarization technique in the fiber-optic sensing and coherent optical communication.

圆偏振光具有不必对光轴、反射光与入射光偏振态正交、易于检测法拉第效应等良好性能，已引起国内外专家的广泛关注。但尚无成熟光纤圆偏振产品，而且圆偏振光在光纤中的起偏一般用从线偏振光转换成圆偏振光的间接起偏方法。为使光纤圆偏振技术得到长足的发展，扩大其应用前景，如何简便有效地设计和制作全光纤圆偏振器件是其中的难点和关键。为解决这个问题，本项目提出在熔融状态下扭转线保偏光纤形成手征光纤光栅（CFG）进行设计和制作全光纤圆偏振器件的方法。首先研究新型CFG中模式的耦合机理，建立一套设计新型CFG元件的方法或软件；然后制作一台新型CFG制作设备；最后利用CFG制作光纤圆偏振起偏器、圆偏振滤波器、单圆偏振光纤等全光纤器件。不仅可用于光纤电流传感等测试系统，而且凡是线偏振光应用的场合如高精度光纤激光陀螺都有圆偏振光潜在用武之地。此将为圆偏振技术在光纤传感和相干光通信中得到发展而做出贡献。

手征光纤光栅是一种新型的光波导结构，它是通过熔融条件下高速扭转截面非圆对称光纤制作而成。它具有偏振选择和波长选择的双重特性，在圆起偏、滤波、传感（尤其是高温和恶劣环境下的传感）、相干光通信等方面均有重要应用。我们针对如何利用手征光纤光栅简单有效地设计和制作全光纤圆偏振器件这一问题进行了深入研究。课题实施过程中主要研究进展包括三个方面：一是采用耦合模理论，建立了手征光纤光栅的统一理论模型，给出了模式耦合的相位匹配条件；二是研究了不同结构的手征光纤光栅的传输谱和偏振选择特性，给出了宽带圆偏振起偏器的设计方案（带宽大于50nm，圆偏振消光比大于20dB）；三是建立了新型光纤光栅制作系统，并且制备了基于双螺旋手征光纤光栅的圆偏振起偏器，谐振峰中心波长处的消光比在0.5到2dB之间，接近圆偏振状态。课题整体研究思路和研究进展较好地达到了课题计划书预期任务和目标，相关研究成果具有一定的实际应用价值。课题执行3年期间输出论文9篇。