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

Abstract

In this paper, 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.

Excessively Tilted Fiber Grating Sensors

“…In 2020, Sun et al have revealed the orientational RI responsivity of an Ex-TFG by analyzing the mode field distribution of cladding mode, which was verified in the experiment. This study pointed out that the Ex-TFG mainly excites the LP1m cladding mode, which has a non-circular symmetric evanescent field, thus resulting in orientational RI response [29]. Simulated results have shown that the LP1m cladding modes have orthogonal mode field distributions as depicted in Fig.…”

“…2. Coupling coefficient of different cladding modes with l=1,2,3 in anEx-TFG with 80° tilt angle[29].…”

Polyelectrolyte/Graphene Oxide Nano-Film Integrated Fiber-Optic Sensors for High-Sensitive and Rapid-Response Humidity Measurement

“…As reported, ,, ex-TFG can be regarded as an LPFG with a very short period. It has a low temperature coefficient and higher RI sensitivity than LPFG and tilting FBG (TFBG).…”

Demonstration of a fast-training feed-forward machine learning algorithm for studying key optical properties of FBG and predicting precisely the output spectrum

“…Conventional FBGs with periodic refractive index (RI) are successfully used for dispersion compensation as well as in a large number of sensors covering various physical perturbations such as acoustic, magnetic, temperature, strain, refractive index, rotation etc. [4][5][6]. A π phase-shifted FBG can be achieved by slightly modifying the geometry of the conventional FBG structure.…”