Dual-wavelength NIR lasers based on cladding-pumped bismuth-doped heterogeneous fibers

In this paper, we report on the cladding-pumped lasers for the near IR based on the optical transitions of spatially separated different types of active centers formed in a Bi-doped heterogeneous glass core fiber serving as an active medium with a peak gain per meter of 0.12 dB/m. The design of the Bi-doped fiber offers confined distributions of bismuth active centers associated with P (BACs-P) and Si atoms (BACs-Si) in different parts of the fiber core doped with the appropriate glass modifier. The absorption characteristics of such the fiber were studied that allowed to reveal the kinds of BACs formed and estimate their concentration ratio. In addition, we achieved laser operation in various cavity configurations with forward pumping provided by multimode semiconductor diodes at 793 and 808 nm. We found the required conditions for starting single- and dual-wavelength laser oscillations at a wavelength of ≈ 1.3 and 1.4 μ m. Furthermore, we demonstrate the tuning capabilities of the laser wavelength within the gain bandwidth of a specific BAC. The peculiarities in spectral and power characteristics of such lasers are discussed.