Interrogation of fiber gratings using spectral interferometry of a low-coherence light source

Summary form only given. Fiber Bragg gratings are important for various applications in optical communication systems and in optical metrology. Several methods for analyzing the performance of complex fiber gratings have been recently demonstrated. However, those methods do not give direct information on the spatial distribution of the grating. By measuring the spatial distribution of the grating one can improve the quality of gratings and increase the spatial resolution of fiber sensors. We present an innovative yet simple method for interrogating fiber Bragg gratings. The method is based on analyzing the interference between a low-coherence beam that is reflected from a grating and a reference beam. Using the Fourier and the Gabor transformations we can find the impulse response of the grating and its response to short pulses with different central frequencies. Because fiber gratings are distributed elements and because the propagation time of photons depends on the location of the region that scattered the photons, the impulse response contains information on the spatial distribution of the grating. We describe two methods for obtaining the spatial distribution and the chirp of the grating from its impulse response.