Department of Electronic and Information Engineering, Photonics Research Institute, The Hong Kong Polytechnic University, Kowloon, Hong Kong.
Department of Electrical Engineering, Photonics Research Institute, The Hong Kong Polytechnic University, Kowloon, Hong Kong.
Sensors (Basel). 2022 Dec 6;22(23):9523. doi: 10.3390/s22239523.
Helical twist provides an additional degree of freedom for controlling light in optical waveguides, expanding their applications in sensing. In this paper, we propose a helical broken-circular-symmetry core microstructured optical fiber for refractive index sensing. The proposed fiber consists of pure silica and its noncircular helical core is formed by a broken air ring. By using finite element modeling combined with transformation optics, the modal characteristics of the fiber are investigated in detail. The results show that for the core located at the fiber center, the confinement loss of fundamental core modes increases with twist rate, whereas for a sufficiently large core offset the modes can be well confined owing to the twist-induced light guidance mechanism, showing decreases with rising twist rate in the loss spectra. Moreover, we have found that for large twist rates and core offsets, resonant peaks occur at different twist rates due to the couplings between the fundamental core modes and the highly leaky modes created by the helical structure. The refractive index sensing performance is also studied and the obtained results show that the proposed fiber has great potential in fiber sensing.
螺旋扭曲为控制光学波导中的光提供了额外的自由度，扩展了它们在传感中的应用。在本文中，我们提出了一种用于折射率传感的螺旋破圆对称芯微结构光纤。所提出的光纤由纯二氧化硅组成，其非圆螺旋芯由破环空气构成。通过使用有限元建模结合变换光学，详细研究了光纤的模式特性。结果表明，对于位于光纤中心的芯，基本芯模的限制损耗随扭曲率的增加而增加，而对于足够大的芯偏移，由于扭曲诱导的光导机制，模式可以很好地限制，在损耗谱中随扭曲率的增加而减小。此外，我们发现对于较大的扭曲率和芯偏移，由于基本芯模和螺旋结构产生的高泄漏模之间的耦合，在不同的扭曲率处会出现共振峰。还研究了折射率传感性能，得到的结果表明，所提出的光纤在光纤传感中有很大的潜力。
