A four-element fiber grating sensor array with phase-sensitivedetection

A four-element, time-division multiplexed, fiber grating sensor array operating between the wavelengths of 1280 and 1310 nm was constructed and tested. The array consists of a 1300-nm edge-emitting LED that illuminates four gratings spaced five meters apart. Each grating in the array reflects a spectrally narrow-band (0.3-0.5 mn) wavelength region. Measurand-induced changes in the grating period change the wavelength of the light reflected by each grating. The wavelength shifts are converted to phase changes by routing the reflected signal through a nearly path balanced fiber Mach Zehnder interferometer. The minimum detectable strain was measured to be as low as 2 nanostrain/√(Hz) for frequencies greater than 10 Hz