Monitoring fiber Bragg grating pair interferometer sensor with a modulated diode laser

A new technique of monitoring a fiber Bragg grating pair interferometer (FBGPI) sensor with a modulated diode laser is demonstrated. The sensing element includes a pair of fiber Bragg grating (FBG) sections separated with a short fiber cavity, so that the reflectance spectrum is a superposition of a gradually changing reflectance envelope over a sinusoidal modulation. Modulating the drive current of a diode laser produces laser chirping to scan over -2.6 fringes of the FBGPI reflectance spectrum. The spectral position of the sensor is precisely determined from the phase of the scanned interference pattern. It is an absolute measurement because the fringe order numbers of the interference pattern can be determined according to the average reflectance changes. Temperature measurements are performed over the range from 24 to 367 degreesC with a resolution of 0.004 degreesC. (C) 2003 Elsevier Science B.V. All rights reserved.