For the first time, we experimentally study the transversal-stress (T-stress) induced polarization crosstalk behaviors in polarization maintaining fibers (PMFs) including the linearity, sensitivity, response time and recovery time, using a distributed polarization crosstalk analysis (DPXA) system. Using two Panda PMFs with or without polyacrylate buffer coating and one Bow-tie PMF with golden polyimide coating as experimental samples, we find that: I) the polarization crosstalk can be highly linear with the T-stress for PMFs no matter with or without coating; II) the polyacrylate coating can reduce the crosstalk sensitivity of naked PMFs by more than hundreds of times, while replacing the polyacrylate coating with polyimide coating can increase the sensitivity by tens or even hundreds of times; III) the polyacrylate coating can induce a significant recovery time of crosstalk when a T-stress is removed after a long loading time compared with that in naked PMFs or golden PMF with polyimide coating, however the crosstalk response speed is too fast to be measured by the DPXA system. Additionally, we also find that the current polyimide coating technique still needs to be improved further to reduce the crosstalk base level. This work will be very useful for PMF-based distributed sensing applications and sensing PMF manufacturing.
Polarization crosstalk is a phenomenon that the powers of two orthogonal polarization modes propagating in a polarization maintaining (PM) fiber couple into each other. Because there is certain mathematical relationship between the polarization crosstalk signals and external perturbations such as stress and temperature variations, stress and temperature sensing in PM fiber can be simultaneously achieved by measuring the strengths and locations of polarization crosstalk signals. In this paper, we report what we believe the first distributed temperature sensing demonstration using polarization crosstalk analysis in PM fibers. Firstly, by measuring the spacing changes between two crosstalk peaks at different fiber length locations, we obtained the temperature sensing coefficient (TSC) of approximately −0.73 μm/(°C•m), which means that the spacing between two crosstalk peaks induced at two locations changes by 0.73 μm when the temperature changes by 1 °C over a fiber length of 1 meter. Secondly, in order to bring different temperature values at different axial locations along a PM fiber to verify the distributed temperature sensing, four heating-strips are used to heat different fiber sections of the PM fiber under test, and the temperatures measured by the proposed fiber sensing method according to the obtained TSC are almost consistent with those of heating-strips measured by a thermoelectric thermometer. As a new type of distributed fiber temperature sensing technique, we believe that our method will find broad applications in the near future.
We present a method to accurately measure the polarization parameters of high birefringence polarization-maintaining (PM) fibers using a distributed polarization analyzer. By measuring a equidistant periodic cross-talks peaks along the PM fiber induced by the pressure of an thin metal cylinder between the spool and the wound fiber, the group birefringence perturbations along the length of PM fiber can be accurately obtained. By finding the widths of measured cross-talk envelopes at known distances along the PM fiber, the birefringence dispersion variable of fiber can be obtained. By analyzing cross-talk peaks purposely induced at both ends of the PM fiber, the temperature coefficient of group birefringence can be accurately obtained.
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