Demodulation of fiber Bragg grating sensors based on dynamic tuning of a multimode laser diode

Dither demodulation of fiber Bragg grating sensors illuminated with multimo de light from laser diodes is theoretically and experimentally investigated . Quasi-static temperature and strain sensitivities of 0.09 degrees C/root Hz and 0.6 mu epsilon/root Hz are obtained. We show that it is possible to measure small ac signals that lie outside the feedback loop bandwidth by us ing a synchronous detection referenced to twice the dither frequency. In th is situation, dynamic strain sensitivity of 3.3 n epsilon/root Hz is achiev ed. (C) 1999 Optical Society of America.