STTR Phase I: Chiral Long Period Grating Fiber Sensors

这个小型企业创新研究(STTR)第一阶段项目将展示创新的光学手性光纤传感器(CFS)技术的可行性。一种节距大大超过波长的双螺旋结构将由非圆形芯子的玻璃纤维扭曲，当它们通过一个具有增强的温度和运动控制的“扭曲塔”中的微型烤箱时。手性长周期光栅(CLPG)将芯模和包层模耦合在一起，在芯模的传输过程中产生一系列的凹陷。这些凹陷的中心波长和深度是对光纤的应变、压力、扭矩和温度以及光纤周围材料的折射率的敏感测量。CPLG的设计将以分析计算的创新组合为指导，辅助二维混合横向有限元电磁模拟和波传播的全三维有限向量元模拟。这些模拟将得到芯模和包层模之间的耦合强度。随着温度、伸长率和周围折射率的变化，透射率测量的结果将被用于完善计算的假设。改进后的模型将用于制造CLPG和设计用于CFS的换能器。创新的CLPG具有广泛的玻璃材料选择的明显优势，可用于在高温和/或辐射水平下耐恶劣环境的选择，如油井、核反应堆或外层空间中的环境。相比之下，在紫外线敏感的玻璃纤维中产生的传统光纤光栅在这种恶劣的环境中会显著退化。多功能制造方法允许通过改变计算机控制的扭转和拉伸速率，通过单一工具灵活地生产在宽频率范围内工作的全套传感器。这种制造工艺将使制造高灵敏度的均匀CLPG成为可能，同时与传统的光纤光栅相比，大大降低了生产成本，传统的光纤光栅需要精确的紫外线辐射图案化。改进的制造工艺还将用于生产其他基于手性光纤的器件，用于滤光片、激光、传感器和偏振器应用。所建立的计算模型将加深对手性光纤光学相互作用的理解，从而促进新型手性光纤器件的发展。

This Small Business Innovative Research (STTR) Phase I project will demonstrate the feasibility of an innovative optical chiral fiber sensor (CFS) technology. A double helix structure with pitch greatly exceeding the wavelength will be imposed by twisting glass fibers with noncircular cores as they pass through a miniature oven in a "twisting tower" with enhanced temperature and motion control. The chiral long period grating (CLPG) will couple core and cladding modes to produce a series of dips in transmission of the core mode. The central wavelengths and depths of these dips are sensitive measures of the strain, pressure, torque, and temperature of the fiber and of the refraction index of the material surrounding the fiber. The CPLG design will be guided by an innovative combination of analytical calculations assisted by 2-D hybrid transverse finite elements electromagnetic simulations and fully three-dimensional finite vector elements simulations of wave propagation. These simulations will yield the coupling strength between the core and cladding modes. The results of transmission measurements with varying temperature, elongation and surrounding refractive index will be used to refine the assumptions of the calculations. The improved model will be used to fabricate the CLPG and to design a transducer for a CFS. The innovative CLPGs present a clear advantage of a broad choice of glass materials, which may be selected for resistance to harsh environments at high temperatures and/or radiation levels such as those in oil wells, nuclear reactors or outer space. In contrast, conventional fiber gratings created in UV sensitive glass fibers are significantly degraded in such harsh environments. The versatile fabrication approach allows for the flexible production of a full suite of sensors functioning over a broad frequency range by a single tool by changing the computer controlled twist and draw rates. This manufacturing process will make it possible to fabricate highly sensitive uniform CLPGs while dramatically lowering the production cost relative to conventional fiber gratings, which require precise patterning of UV radiation. The improved manufacturing process will also be used to produce other devices based on chiral fibers for filter, laser, sensor and polarizer applications. The computational model developed will enhance the understanding of optical interactions with chiral fibers and thereby facilitate the development of new chiral fiber devices.