INTERFEROMETRIC TEMPERATURE-INSENSITIVE STRAIN-MEASUREMENT WITH DIFFERENT-DIAMETER FIBER BRAGG GRATINGS

An interferometric strain-sensing system that combines an unbalanced M ach-Zehnder wavelength discriminator and spliced different-diameter fi ber Bragg gratings is presented that has the capability to distinguish strain from temperature effects. Because the gratings are written in 135- and 165-mu m-diameter fibers drawn from the same preform, when th ey are spliced they show similar temperature sensitivities but differe nt responses to applied strain. Thus the relative Bragg wavelength dif ference of the two gratings is affected only by strain, and one can me asure it accurately by monitoring the amplitude variation of the inter ference signal rather than the conventional phase variation. (C) 1997 Optical Society of America.