Effect of Vortex Order on Helical-Phased Donut Mode Launch in Multimode Fiber

In the quest for real-time monitoring of structural health, optical fiber sensors are gaining rapid adoption. Compared to traditional mechanical and electrical sensors, optical fiber sensors have attractive features such as small diameter, light weight, immunity to electromagnetic interference and corrosion [1, 2] which are well-suited for structural health monitoring. Optical fiber sensing technology is effective for monitoring the life cycle of structures comprising construction, operation and strengthening and rehabilitation. Mode division multiplexing (MDM) plays an increasingly vital role in sensing systems for multiparameter measurements. Few mode fibers (FMFs) have recently been designed for structural health monitoring based on MDM. In [3], a FMF was designed for detecting curvature variations using the visibility of interference fringes between LP01 and LP02 modes. In [4], a FMF was designed such that LP01 and LP11 exhibit different sensitivities to temperature and refractive index, thus allowing simultaneous measurements of both parameters. Simultaneous strain and temperature