Multiplexing fiber-optic sensors by frequency modulation: cross-term considerations.

The cross-term problem in a multiplexed fiber-optic sensor system using a frequency-modulated laser source is described, and two proposed solutions are presented. One is to eliminate cross terms by locating them at different frequencies from the signal frequencies. The other is to separate the sensors by several source coherence lengths so that their outputs do not interfere. The latter technique is demonstrated experimentally, resulting in only two peaks corresponding to the two fiber interferometers at frequencies of 200 Hz and 1 kHz.