Hybrid Active Center in Bismuth-Doped AlPO$_{4}$-Containing Glass Fibers for T+O-Band Lasers and Amplifiers

The development of active media with unique gain characteristics in a wavelength range of 1-2$\mu$m is highly attractive for realizing ultrabroadband amplifiers for the deployment of multi-band wavelength platform to maximize the transmission capacity in existing optical communication and next-generation systems exploiting a spectral region from T- to U-bands. In this regard, fibers with bismuth active centers (BACs), which possess incredible optical properties, are suitable candidates for creating high-gain amplifiers for telecom bands. In this paper, the discovery of a novel BAC, which is formed in Bi-doped fibers with AlPO$_{4}$structural units, is reported. This BAC has a hybrid “nature” as it exhibits features of two types of BACs, specifically BAC associated with Al and P atoms. The discovered BAC offers a gain band peaked at 1240 nm, which bridges the gap between the ones of BAC-Al and BAC-P. The excellent performance characteristics of hybrid BACs are confirmed by the development of the first (to our knowledge) watt-level Bi-doped laser at a wavelength of 1256 nm and a 30-dB Bi-doped fiber amplifier for T+O-band. This study provides a better understanding of the structural features of BACs and offers an effective pathway for developing new fibers with advanced characteristics.