Efficient fiber Bragg grating and fiber Fabry-Pe'rot sensor multiplexing scheme using a broadband pulsed mode-locked laser

A pulsed broadband mode-locked laser (MLL) combined with interferometric interrogation is shown to yield an efficient means of multiplexing a large number of fiber Bragg grating (FBG) or fiber Fabry-Perot (FFP) strain sensors with high performance. System configurations utilizing time division multiplexing (TDM) permit high resolution, accuracy, and bandwidth strain measurements along with high sensor densities. Strain resolutions of 23-60 n epsilon/Hz(1/2) at frequencies up to 800 Hz (expandable to 139 kHz) and a differential strain-measurement accuracy of +/- 1 mu epsilon are demonstrated. Interrogation of a low-finesse FFP sensor is also demonstrated, from which a strain resolution of 2 n epsilon/Hz(1/2) and strain-measurement accuracy of +/- 31 n epsilon are achieved. The system has the capability of interrogating well in excess of 50 sensors per fiber depending on crosstalk requirements. A discussion on sensor spacing, bandwidth, dynamic range, and measurement accuracy is also given.