Undepleted pump regime of Hill grating formation in optical fibers

Abstract

A bleaching model describing the dynamics of Hill grating formation in optical fibers, [K.O. Hill, Y. Fujii, D. C. Johnson, and B. S. Kawasaki, Appl. Phys. Lett. 32, 647 (1978)], is analytically solved in an undepleted pump approximation. This regime provides quantitative predictions about grating dynamics in the early stages of grating growth. A series of experiments in which heating effects and surface reflections from the input end of the fiber have been eliminated show quantitative agreement with the theory to 2%.

Long-period fiber gratings spontaneously written by a mechanism markedly different from Hill grating formation

“…Unlike HG formation which originates from the simple interference between the two counterpropagating core modes, the spontaneous LPFG formation cannot be attributed to the simple interference between the copropagating core mode and LP 0,23 cladding mode, otherwise the writing wavelength would be coincident with the first-order diffraction of the LPFG corresponding to LP 0,23 . Thus, the proposed mechanisms for HG formation [3][4][5] are invalid for the spontaneous LPFG formation.…”