Fiber Bragg grating strain sensor demodulation with quadrature sampling ofa Mach-Zehnder interferometer

A simple and highly sensitive phase-demodulation technique is proposed, and its use for a fiber Bragg grating strain sensor is experimentally demonstr ated. Sampling a phase-modulated Mach-Zehnder output with controlled time d elay produced two quadrature data streams that have relative quadrature pha se difference (90 degrees). The Bragg wavelength-dependent phase informatio n is extracted by application of digital arctangent function and phase unwr apping to the quadrature signals. By use of this technique with a reference grating, strain sensing at as much as a 30-kHz sampling rate was obtained with strain resolution of 3.5 microstrains and 6 nanostrains/root Hz in qua si-static and dynamic strain measurements, respectively. (C) 2000 Optical S ociety of America.