Index structure of fiber Bragg gratings in Ge–SiO_2 fibers

Abstract

The behavior of the concentration of photoinduced color centers in Ge-SiO(2) optical fibers was compared with that of the index modulation associated with fiber Bragg gratings (FBG's) written in the same fibers. We find that the fluence dependence of the photoinduced Ge E? center, its thermal annealing behavior, and its reaction with H(2) are similar to that of the index modulation generated in both H(2)-loaded and unloaded Ge-SiO(2) fibers. The much higher photosensitivity of H(2)-loaded Ge-SiO(2) fibers is attributed to the much higher formation efficiency of Ge E? centers, with an additional contribution from GeH. A diamagnetic structure, possibly densification, is also found to contribute to the index modulation of FBG's.

Uniform component of index structure induced in Ge-SiO2 fibers by spatially modulated ultraviolet light

“…1 However, the physical structures associated with the index of fiber Bragg gratings ͑FBGs͒ have not been totally identified: The structures associated with the index modulation (⌬n mod ) of FBGs in unloaded Ge-SiO 2 core fibers that have been identified are Ge EЈ centers 2 and densification. [2][3][4] In H 2 -loaded fibers, besides the association of Ge EЈ and densification, GeH was also found 2 to contribute to ⌬n mod of the FBG.…”

“…The spacing ͑⌳͒ dependence of ultraviolet ͑UV͒ light bleaching of the pre-existing Ge EЈ centers illustrates that the electron diffusion length is greater than ⌳ of the spatially modulated UV light used in the fabrication of fiber Bragg gratings ͑FBGs͒ with Bragg wavelengths р1.5 m ͑short period grating͒ for laser powers as low as 25 mJ/cm 2 . The Ge͑1͒ and Ge͑2͒ centers are uniformly induced by the spatially modulated UV light and therefore contribute to the uniform component of the index structure of FBGs.…”

“…2 One thing that remains to be elucidated is the contribution of Ge͑1͒ and Ge͑2͒ centers to the index structure of FBGs via their optical absorptions 5 at 4.4 and 5.8 eV, respectively, through the Kramers-Kronig relationship.…”

Étude des processus photochimiques primaires dans les fibres optiques germanosilicates lors d'une insolation ultraviolette

“…Par conséquent, nous attribuons cette aile de bande d'absorption induite aux centres Ge(1). L'évolution des pertes induites avec la densité d'énergie dans les fibres vierges et hydrogénées est cohérente avec les résultats rapportés par Tsai et al [17]. Ces auteurs ont mesuré, en utilisant la technique de résonance paramagnétiqueélectronique (RPE), la concentration des espèces Ge(1) dans un domaine couvrant les densités d'énergie utilisées ici.…”

Low loss Type II regenerative Bragg gratings made with ultrafast radiation

“…For a 500-1000 °C temperature range, the traditional method of annealing UV laser-induced type I FBGs with temperatures a few hundred degrees higher than the operational temperature is not possible. For temperatures above 600 °C the type I grating structure, which is mainly composed of color center defects [1], is almost completely annealed [2].…”