Theoretical and Experimental Analysis of the Directional RI Sensing Property of Tilted Fiber Grating

In this article, we have theoretically and experimentally investigated the unique vector refractive index (RI) sensing property of tilted fiber grating (TFG). Due to the orthogonal symmetric grating structure, TFGs would mainly achieve the coupling between the fiber core mode and the two orthogonal...

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Bibliographic Details
Published in:Journal of lightwave technology 2021-01, Vol.39 (2), p.674-681
Main Authors: Sun, Yuezhen, Lu, Tean, Moreno, Yarien, Li, Liangye, Wang, Hushan, Zhou, Kaiming, Sun, Qizhen, Liu, Deming, Yan, Zhijun, Zhang, Lin
Format: Article
Language:English
Subjects:
Azimuth
Bragg gratings
Cladding
Coupled mode analysis
Coupling coefficients
Couplings
Directional sensitivity
Fiber gratings
Optical fiber polarization
Optical fiber sensors
optical sensors
Refractivity
Sensitivity
Skewed distributions
Submerging
vector measurement
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Summary:In this article, we have theoretically and experimentally investigated the unique vector refractive index (RI) sensing property of tilted fiber grating (TFG). Due to the orthogonal symmetric grating structure, TFGs would mainly achieve the coupling between the fiber core mode and the two orthogonal polarization LP1m of cladding mode. And the numerical simulation results showed that the coupling coefficient between fundamental core mode to the LP1m cladding mode is higher than the others. In the experiment, we have furthermore observed the cladding mode field distribution of excessively TFG (Ex-TFG) and long period fiber grating (LPFG), which indicated that the evanescent field distribution of cladding mode of TFG shows an asymmetric near field distribution with two lobes oriented along the fast axis of TFG, and the one of LPFG has a circularly symmetric cladding mode field distribution. In addition, by employing side-immersion method, we have measured the azimuth RI sensitivities of Ex-TFG, tilted fiber Bragg grating (TFBG) and LPFG, which exhibited that both Ex-TFG and TFBG have shown a direction-dependency RI sensitivity, and the RI sensitivity with side-immersion along fast axis is almost half of the one along slow axis, and the RI sensitivity of LPFG is azimuth independent. Overall, the experiment results show that the TFGs inherently show unique directional RI sensing property, which could be potentially applied in vector sensing area.
ISSN:0733-8724
1558-2213
DOI:10.1109/JLT.2020.3027947