The theory of Fresnel diffraction images is applied to Bragg-grating formation in a germanium-doped silica fiber. Fresnel diffraction images arise from the near-field diffraction at a periodic mask. The diffraction images are calculated as a function of the propagation distance for several mask configurations. The average of the diffraction-image intensities is calculated for a single longitudinal repetitive interval, and it is shown that the period of the resulting average intensity field is twice that of the original mask period. In some cases the periodic mask can be predicted for a desired average intensity field by calculation of the magnitude of its Fourier coefficients.
© 1994 Optical Society of America
J. D. Prohaska, E. Snitzer, and J. Winthrop, "Theoretical description of fiber Bragg reflectors prepared by Fresnel diffraction images," Appl. Opt. 33, 3896-3900 (1994)