Characteristics Of Low Valence Bismuth Active Centers In Bi-doped Silica Optical Fiber

With the development of broadband optical communication,demand for network transmission capacity has been increasing in recent years.This situation put higher requirements for high performance devices.Main current Erbium-doped optical fiber amplifier(EDFA)has a narrow bandwidth concentrated in C+L band(1530-1610 nm),while Bismuth-doped fiber has a luminescence broadband,and has potential in broadband fiber amplifiers.However,near infrared region(NIR)luminescence mechanism in Bismuth-doped fiber is still unclear.Bismuth active centers(BAC)which related with NIR luminescence are divided into the following three categories:high valence Bismuth,low valence Bismuth and point defects.This paper mainly study BAC of divalent Bismuth(Bi2+)in Bi-doped optical fiber.The main contents of this paper are as follows:(1)Construction and optimization of Bi-doped optical fiber models.Molecular Dynamic(MD)is used to generate Bi-doped optical fiber models:silica model,Bi2+ models,Bi2+-point defects models.Optimization,geometry structures and stability of all models are studied.(2)Optical properties of Bi2+ models in Bi-doped optical fiber.Considering "Si-O-Si" rings in silica model,we use first-principle calculations to calculate silica model and four Bi2+ models.By analyzing the difference in electronic structures and optical properties between models with and without Bi2+,we reveal that Bi-doped in 3-membered rings(3MRs)are main contributions to the characteristic red emission(600 nm)in Bi-doped optical fiber.(3)NIR luminescence center of Bi2+-point defect models in Bi-doped optical fiber.We calculate the reaction path of Bi2+-ODC(?)?Bi2+-ODC(?)?Bi2+-E' center.By comparing the electronic structures and optical properties of three Bi2+-point defect models,we infer that Bi2+-ODC(?)is the active center for 1520 nm absorption band.We reveal the optical transition process of 1520 nm through transition energy level of Bi2+-ODC(?).