Abstract

Geometrically modified fiber optic sensors (FOS), particularly U-bent FOS, have gained significant attention due to their remarkably high refractive index (RI) and evanescent wave absorbance (EWA) sensitivity, as well as their ergonomic design and ease in handling. In this article, we present a theoretical model for the U-bent FOS probes to predict the sensor behavior by numerically simulating the light propagation in an equivalent 2D semi-circular ring using ray tracing approach. In addition to the effects due to the modification of geometry, this article presents a thorough investigation of the influence of the bend-induced material deformation on the nature of light propagation and refractive losses. We introduce “bend ratio” (ratio of bend radius to fiber core radius) to explain the influence of geometry modification and the bend-induced inhomogeneity in RI (BIRI) of the fiber core on RI sensitivity. The bend ratio of bent plastic optical fiber sensors falls under one of the four bending regimes, namely, gentle, geometric, saturation, and plastic, for which the bend ratios are less than ∼35, ∼25, 17, and 7, respectively. The results also show that for bend ratios less than 7, BIRI inhomogeneity is responsible for the high RI sensitivity observed with U-bent probes as opposed to the simple geometric modification. This article also indicates the existence of an optimum bend ratio (for a given value of RI of the surrounding medium) where RI sensitivity is maximum. These findings were validated with previously reported experimental results.

Investigation of a macrobending micro-plastic optical fiber for refractive index sensing

Ning Jing, Jie Zheng, Xiaowei Zhao, and Chuanxin Teng
Appl. Opt. 53(34) 8145-8150 (2014)

Highly sensitive temperature and refractive index sensor based on no-core fiber cascaded with a balloon-shaped bent single-mode fiber

Xiaojun Zhu, Mengqiang Song, Xing Liu, Wen Liu, Yongquan Pan, Juan Cao, Guoan Zhang, Yongjie Yang, Yuechun Shi, and Wuming Wu
Appl. Opt. 62(35) 9266-9273 (2023)

Refractive index sensor based on a multi-notched plastic optical fiber

Chuanxin Teng, Ning Jing, Fangda Yu, Yue Ding, and Jie Zheng
Appl. Opt. 56(7) 1833-1838 (2017)

Vector magnetic field sensor based on U-bent single-mode fiber and magnetic fluid

Yongxi Li, Shengli Pu, Zijian Hao, Shaokang Yan, Yuxiu Zhang, and Mahieddine Lahoubi
Opt. Express 29(4) 5236-5246 (2021)

Sensitive liquid refractive index sensors using tapered optical fiber tips

Yi-Hsin Tai and Pei-Kuen Wei
Opt. Lett. 35(7) 944-946 (2010)