The strain-temperature cross-sensitivity effect on Brillouin frequency shift (BFS) in plastic optical fibers (POFs) is fully investigated. First, we show that the strain coefficient of the BFS is dependent on temperature. In the strain ranges of 0– 1.2% and 4.0–9.0%, the temperature dependence is linear with coefficients of 1.5 MHz/%/°C and –0.4 MHz/%/°C, respectively. We then find that the temperature coefficient of the BFS is linearly dependent on strain with a coefficient of 1.5 MHz/°C/% in the strain range from 0 to 1.2%. For 4.0–9.0% strains, the BFS basically decreases with increasing temperature. These results indicate that temperature (and strain) compensation for the strain (and temperature) sensitivity of the BFS is required to correctly detect the strain and temperature magnitude in POF-based Brillouin sensing. We also show that temperature sensing with no sensitivity to strain is potentially feasible by using POFs pre-strained for >13%.
We evaluate whether the measurement stability of Brillouin optical correlation-domain reflectometry (BOCDR) using plastic optical fibers (POFs) can be enhanced by polarization scrambling. Two major factors that affect the signal-to-noise ratio in BOCDR, i.e., the spatial resolution and the incident power are varied, and their influences on the distributed measurements with polarization scrambling are experimentally investigated. We thus clarify that in POF-based BOCDR, unlike BOCDR using standard silica glass fibers, polarization scrambling is effective in enhancing the measurement stability only when the spatial resolution is sufficiently low or when the incident power is sufficiently high.
Poly(pentafluorostyrene) (PPFS), which can be easily synthesized and has a low optical loss window at 850 nm, is a promising alternative for a costly perfluorinated polymer as a base material of polymer optical fibers (POFs). To investigate the potential of a PPFS-POF as a Brillouin-based temperature sensing fiber, the Brillouin frequency shift and its temperature dependence of PPFS were estimated using an ultrasonic pulse-echo technique. The temperature coefficient, which determines the sensitivity of the temperature sensing, was approximately –7.1 MHz/K independently of the molecular weight and was nearly identical to that in perfluorinated POFs.
With their high thermal stability compared with other plastic optical fibers (POFs), partially chlorinated graded-index
POFs (PCGI-POFs) are a promising candidate to develop the sensing heads of Brillouin-based distributed strain and
temperature sensors. In this study, the Brillouin frequency shift (BFS) and its temperature dependence in a PCGI-POF
are estimated by using ultrasonic pulse-echo technique. The estimated BFS is ~4.43 GHz with its temperature coefficient of approximately –6.9 MHz/K at 1550 nm. Its absolute value is ~5.8 times as large as that of silica single-mode fibers, and even larger than that of a perflurointated GI-POF. Its fracture strain of ~3.0% (mostly in elastic region) is small compared with other POFs, and so it appears difficult to estimate the BFS dependence on strain in a PCGI-POF with this technique. These experimental results imply that the Brillouin scattering in PCGI-POFs is potentially applicable to highprecision temperature sensing.
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