Fiber optic calorimeter

Pepe G. Davis; Stephen Bayliss; Clifford R. Rudy

doi:10.1117/12.372984

9 December 1999 Fiber optic calorimeter

Pepe G. Davis, Stephen Bayliss, Clifford R. Rudy

Proceedings Volume 3860, Fiber Optic Sensor Technology and Applications; (1999) https://doi.org/10.1117/12.372984
Event: Photonics East '99, 1999, Boston, MA, United States

Abstract

A twin-bridge fiber optic calorimeter has been built and is currently being tested at Los Alamos National Laboratory (LANL). The intrinsic optical phase shift in single mode optical fiber induced by changes in temperature is measured in both a measurement chamber and an identical reference chamber. The walls of each canister are surrounded by optical fiber configured in a Michelson interferometer arrangement driven by a 1319 nm diode pumped YAG laser. The interferometers have an optical path mismatch of 1.6 km and a temperature sensitivity of 471,000 radians/C. A digital demodulation scheme is used which produces a 32 bit phase word and tracks up to 3 X 10⁶ radians with a resolution of 10^-3 radians, giving the system a dynamic range greater than 10⁹. This dynamic range was used to match the 1.6 km optical path mismatch of the sample and reference Michelson interferometers to within 1 mm in order to minimize phase errors produced by frequency drifts of the optical source. Both interferometers are demodulated simultaneously at a rate of 83 kHz. The phase difference between the reference and sample interferometers is proportional to the temperature difference between the chambers and therefore measures the power produced by a sample placed in the measurement chamber. The calorimeter sensitivity was initially measured to be 151 radians/mW, however, the calorimeter sensitivity has subsequently been increased to 383 radians/mW by the addition of foam insulation around the thermals. With this sensitivity, the theoretical calorimeter resolution should be less than 20 nW, however, the observed long term optical phase drift of 18 radians limits the calorimeter resolution to 47 (mu) W. Nevertheless, the fiber optic calorimeter performance has been observed to exceed that of a state-of-the-art wire wound calorimeter of similar dimensions by a factor of 2. The optical system performance will be described along with calorimetric measurement results.

Citation Download Citation

Pepe G. Davis, Stephen Bayliss, and Clifford R. Rudy "Fiber optic calorimeter", Proc. SPIE 3860, Fiber Optic Sensor Technology and Applications, (9 December 1999); https://doi.org/10.1117/12.372984

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