Cross Effect of Strain and Temperature on Brillouin Frequency Shift in Polymer Optical Fibers

The strain-temperature cross-sensitivity effect on the Brillouin frequency shift (BFS) in polymer optical fibers (POFs) is fully investigated. First, we show that the strain coefficient of the BFS is dependent on the temperature. In the strain ranges of 0-1.2% and 4.0-9.0%, the temperature dependence is linear with coefficients of 1.5 and - 0.3 MHz/(%·°C), respectively. We then find that the temperature coefficient of the BFS is linearly dependent on the strain with a coefficient of 1.5 MHz/(%·°C) in the strain range of 0-1.2%. For strains of 4.0-9.0%, 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 magnitudes of the strain and temperature in POF-based Brillouin sensing. For strains >13%, we show that temperature sensing with no sensitivity to strain is potentially feasible using the BFS in POFs. The height of the Brillouin gain spectrum is also evaluated.