ALL-FIBER ABSOLUTE TEMPERATURE SENSOR USING AN UNBALANCED HIGH-BIREFRINGENCE SAGNAC LOOP

We demonstrate a highly sensitive temperature sensor based on a stress -induced high-birefringence-fiber Sagnac loop that uses a Nd-doped-fib er amplified spontaneous emission source. Relative temperature sensing is done in the spectral domain by shifts of a resonant wavelength lam bda(r) and absolute temperature sensing by changes in separation betwe en resonances Delta lambda. The measured relative change of these para meters with temperature in the range 15-110 degrees C, is (1/lambda(r) )(delta lambda(r)/delta T) = -(1/Delta lambda)(delta Delta lambda/delt a T) approximate to (1/Delta n)(delta Delta n/delta T)(-0.94 +/- 0.02) x 10(-3)/K, with measured fiber birefringence Delta n = 8 x 10(-4). T his gives a wavelength-shift sensitivity of -1.00 nm/K at 1.065 mu m a nd a resonance separation sensitivity of 0.006 nm/K for Delta lambda = 6.8 nm. This telemetric point sensor has a loop length of 80 m, an op erational bandwidth of more than 50 nm, and a temperature accuracy of better than 1 degrees C. (C) 1997 Optical Society of America.