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In this study, a high sensitivity and easy fabricated plastic optical fiber (POF) displacement sensor is proposed. A POF specimen subjected to dual cyclic bending is used to improve the sensitivity of the POF displacement sensor. The effects of interval between rollers, relative displacement and number of rollers on the sensitivity of the displacement sensor are analyzed both experimentally and numerically. A good agreement between the experimental measurements and numerical calculations is obtained. The results show that the interval between rollers affects sensitivity most significantly than the other design parameters. Based on the experimental data, a linear equation is derived to estimate the relationship between the power loss and the relative displacement. The difference between the estimated results and the experimental results is found to be less than 8%. The results also show that the proposed POF displacement sensor based on dual cyclic bending can be used to detect displacement accurately.

Optical fibers are widely used in communication systems because of their low attenuation, light weight, higher data transmission rates and no electromagnetic influence [

In theoretical and practical applications, the prediction of radiation loss in bent optical waveguides is an important topic [

In this study, a highly sensitive plastic optical fiber displacement sensor (POF displacement sensor) based on cyclic bending is analyzed both experimentally and numerically. The POF sensor is pressed by cylindrical models without surface damage. Dual bending model is used to increase the sensitivity of the POF displacement sensor. The effects of number of rollers, the distance between top and bottom plates, and the interval between two rollers on sensitivity of the sensor are discussed.

In this study, a highly sensitive POF displacement sensor based on cyclic bending is proposed.

The geometrical model of the POF displacement sensor is shown in _{N}_{roller}_{0}_{0} −

Both the experimental measurement and the numerical analysis are used to explore the sensitivity of the POF displacement sensor. In this study, the bending shape of pressed POF sensor is obtained from an elastic-plastic three-dimensional finite element simulation. The simulations are performed using a commercial finite element package (ABAQUS). The power losses then can be calculated by substituting the deformed POF geometrical dimensions into the optical numerical software-ZEMAX. In the numerical simulation, a 3-D ray tracing model is used. The light input is assumed to be uniformly distributed over the core cross section because the light source used in experiment is a LED. The ray tracing model includes meridional and skew rays. The maximum ray's angle with respect to the fiber center axle is 20°. The power of the POF sensor before and after deformation are denoted as _{i}_{0}_{i}_{0}_{N}_{roller}_{0}_{i}

_{0}_{i}_{N}_{roller}_{e}_{co}_{roller}_{N}

Thus, the power loss of the proposed POF displacement sensor is mainly attributed to R2 and R3, because the curvature radii R2 and R3 are less than 30 mm as the relative displacement is increased from 1.5 to 4.5 mm, as shown in

_{roller}_{roller}_{roller}

Once again, the results confirm that no power loss is observed when the relative displacement is less than 1.5 mm, even more rollers are used. Meanwhile, it can be seen that when the relative displacement is larger than 1.5 mm, the power loss presents a nearly linear dependence with the relative displacement. The results also show that the power loss increases with an increasing number of rollers. More rollers imply that the POF sensor undergoes more geometric deformations, and thus the radiation loss increases with the number of rollers. For example, as the relative displacement is increased from Δ_{N}_{N}_{0}_{i}

Note that the unit of Δ_{N}_{N}_{N}_{N}^{−2}, 6.36 × 10^{−3}, 6.43 × 10^{−3} and 5.20 × 10^{−3}, respectively, and all the corresponding degrees of freedom are 7. Therefore, it can be concluded that the proposed

Compared with the results shown in

This study has conducted experimental and numerical investigations into the effects of relative displacement, number of rollers, and interval between two rollers on the sensitivity of a cycling bending POF displacement sensor. The experimental measurements and numerical results indicate that the proposed POF sensing model is feasible for measuring the displacement. The results show that the POF displacement sensor based on cycling bending is significantly affected by the number of rollers, relative displacement and the interval. The power ratio reduces significantly as the number of roller is increased and the interval is decreased. The results of a basic ray tracing analysis show that most of the optical power is lost at the first turn and its turning points. Based upon the experimental results, an empirical expression is formulated to relate the power loss and the relative displacement. The maximum deviation between the predicted power loss obtained from the proposed equation and the experimental result is found to be less than 8%. Thus, the suitability of the relative displacement as a means of predicting the power loss in deformed POF sensors is confirmed. Overall, the presented results confirm the viability of POF sensors based on cyclic bending and suggest that the sensitivity of such devices can be enhanced by increasing the number of rollers or decreasing the interval between rollers. The potential applications of the developed cyclic bending-POF sensing element can be found in measuring small displacements at certain areas or alarming landslide for its high sensitivity under deformation.

Experimental setup used to measure power loss in cyclic bending POF sensor.

Three-dimensional finite element model of a cyclic bent POF specimen and load-displacement curve.

Variation of the power ratio with number of rollers.

Variation of the power ratio _{0}_{i}

Deformed POF displacement sensor.

Variation of the curvature radius with the relative displacement for _{N}_{roller}

Variation of the power ratio _{0}/P_{i}

Ray path of ray tracing model in deformed POF sensor.

Light loss in a deformed POF sensor.

Variation of the power ratio _{0}_{i}

Variation of power ratio _{0}_{i}

The mechanical properties of the POF specimen used in finite element model.

| |||
---|---|---|---|

3000 | 215 | 200 | |

σ_{v} |
56 | 11.3 | 9.8 |

σ_{ult} |
68 | 55 | 17.15 |

0.4 | 0.46 | 0.49 |