Towards a broadband gain-flattened thulium doped fiber amplifier

Jose, Amala, Guasoni, Massimiliano, Coillet, Aurelien, Dinda, Patrice Tchofo, Grelu, Philippe and Kanagaraj, K. Nithyanandan (2025) Towards a broadband gain-flattened thulium doped fiber amplifier. Optics Communications, 578, [131452]. (doi:10.1016/j.optcom.2024.131452).

Abstract

Tm-doped fiber amplifiers (TDFAs) are capable of generating a broadband emission spanning from 1600 nm to 2100 nm. This wavelength range is significant for important applications, such as eye-safe atmospheric propagation, spectroscopy, sensing, and material processing. Utilizing this broadband emission can enhance the capacity of the optical communication channels. However, for dense wavelength division multiplexing, along with broadband amplification, a flat gain is equally desirable. Achieving a flat spectral gain profile is challenging due to the wavelength-dependent parameters in the TDFA, including the gain and inversion. To address the challenge of achieving flat broadband gain, we propose a scheme referred to as a “gain-guided amplifier”. By integrating and optimizing a passive gain-flattening filter within a dual-stage amplifier configuration, we report an ultra-flat broadband spectral gain from 1690 nm to 1986 nm. Furthermore, the parameters such as pump configuration, fiber length, and attenuation functions have been optimized to produce up to 30 dB gain having ±0.05 dB tilt along with a noise figure less than 5 dB. This is one of the broadest and flatter gains ever predicted for a TDFA, which can pave the way for next-generation optical communication networks.

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