Multichannel temperature sensing by differential coherence multiplexing

The method of differential coherence multiplexing is demonstrated for multichannel temperature sensing. The idea of the method is to introduce into the conventional coherence-multiplexed sensor array a chain of stable etalon interferometers connected to the interrogating interferometer in parallel to the sensor chains. Optical delays of sensor interferometers are obtained from the phase shift of the interference maximums of the etalon and sensor coherence peaks. The technique is inherently insensitive to low-frequency phase noise in the interrogating interferometer and does not require any means for measurement of the optical path difference of the interrogating interferometer. Multiplexed temperature sensing is demonstrated in a chain of four extrinsic Fabry-Perot temperature sensors in the range of 400 degrees C with a root-mean-square noise of 0.005 degrees C. Theoretical estimations show a possibility of increasing the dynamic range to the units of 10(5).