Spectral profile and multiplexing of Bragg gratings in photosensitive fiber

We describe a technique of optically writing several gratings in a photosensitive germanosilicate fiber. Each grating is written using the same single-frequency argon-ion laser source, but by varying the strain applied to the fiber during writing the resonant frequency of the gratings can be controlled. Frequency differences between gratings of 182 GHz have been demonstrated. The spectra of the gratings formed in the fiber were measured by periodically stretching the fiber while illuminating it with a single-frequency laser. This permits a frequency-resolved real-time analysis of the passband. The grating properties are also shown to be highly dependent on the polarization of the writing beam.