## Abstract

We demonstrate a highly sensitive temperature sensor based on a stress-induced high-birefringence-fiber Sagnac loop that uses a Nd-doped-fiber amplified spontaneous emission source. Relative temperature sensing is done in the spectral domain by shifts of a resonant wavelength ${\lambda}_{r}$ and absolute temperature sensing by changes in separation between resonances $\mathrm{\Delta}\lambda $. The measured relative change of these parameters with temperature in the range 15–110 °C, is $\left(1/{\lambda}_{r}\right)\left(\delta {\lambda}_{r}/\delta T\right)=-\left(1/\mathrm{\Delta}\lambda \right)\left(\delta \mathrm{\Delta}\lambda /\delta T\right)\approx \left(1/\mathrm{\Delta}n\right)\left(\delta \mathrm{\Delta}n/\delta T\right)\left(-0.94\pm 0.02\right)\times {10}^{-3}/\mathrm{K}$, with measured fiber birefringence $\mathrm{\Delta}n=8\times {10}^{-4}$. This gives a wavelength-shift sensitivity of $-1.00\mathrm{nm}/\mathrm{K}$ at $1.065\mathit{\mu}\mathrm{m}$ and a resonance separation sensitivity of $0.006\mathrm{nm}/\mathrm{K}$ for $\mathrm{\Delta}\lambda =6.8\mathrm{nm}$. This telemetric point sensor has a loop length of 80 m, an operational bandwidth of more than 50 nm, and a temperature accuracy of better than 1 °C.

© 1997 Optical Society of America

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