Ultra-Wideband Amplification in Telecom Bands With Bi-Doped Multi-Layered Glass Fibers

In this paper, we propose a novel design of bismuth-doped fibers (BDFs) for wideband amplification within telecom wavelength range based on a multi-layered heterogeneous glass core structure, where different types of bismuth active centers (BACs) can be formed. This concept offers potential benefits on “smart” control of formation and spatial selection of different BACs by variation of chemical composition of the core glass layers. According to the proposed approach, step-index single-mode active fibers with a core consisting of bismuth-doped layers made of P$_{2}$O$_{5}$–SiO$_{2}$ and GeO$_{2}$–SiO$_{2}$ glass have been fabricated by MCVD technique. We have performed a comprehensive study of optical properties of the preforms and developed BDFs, their chemical composition analysis, including the radial distribution of various types of BACs. As a result, it was experimentally found that the developed fiber design can successfully be used to obtain optical amplification in an extra wide wavelength region from 1250 to 1500 nm ($\approx$ 250 nm bandwidth) due to overlapping the gain bands of the BACs associated with P and Si atoms. In addition, we demonstrate lasing in various spectral bands in the studied BDFs under cladding-pumping with commercially available multimode diodes at 793 and 808 nm. The presented results may be useful for further advance in development of key optical devices for wideband communication systems.