Theoretical simulations of the soliton self-frequency shift of mid-infrared femtosecond pulses in step-index tellurite optical fibers: broadband tunability and high efficiency

Abstract

Broadband tunable ultrafast lasers using mid-infrared (MIR) fibers operating at a 3-5 µm atmospheric transmission window are attractive sources because of their numerous applications. Tellurite fibers possess the merits of large linear and nonlinear refractive indices, sufficient chemical stability, and wide transparency range up to ∼5 µm; also, they are highly suitable for high efficiency MIR ultrafast fiber laser sources based on soliton self-frequency shift (SSFS). We numerically simulate SSFS of MIR femtosecond pulses in step-index tellurite optical fibers. A femtosecond erbium-doped fluoride fiber laser at 3.5 µm is employed as the pump source. Parameters including the peak power of the input pulse and nonlinear fiber length are optimized for high efficiency broadband tunable MIR ultrafast laser performance. Our results show that a high-efficiency 3.5-6 µm wavelength-tunable femtosecond laser can be realized by employing SSFS in a 22-cm-long segment of tellurite step-index fiber pumped by femtosecond pulses with 10-300 kW peak powers at 3.5 µm. Ultra-high energy ratios of the most redshifted solitons to the input pulses of >50% are obtained across the 3.5-5 µm tuning range. The presented numerical study provides valuable guidance for SSFS of MIR femtosecond pulses in step-index tellurite fibers and is valuable for future high efficiency wavelength-tunable MIR ultrafast fiber laser development.