High‐Energy Femtosecond All‐Fiber Laser Systems in 1.7–1.8 μm Using a Normal‐Dispersion Tm‐Doped Fiber

A W‐type normal dispersion thulium‐doped fiber (NDTDF) is utilized to generate high average power, high‐energy femtosecond pulses at 1.7 μm region for bio‐imaging applications. Net normal dispersion cavity fiber lasers are used to generate positively chirped soliton pulses, which are subsequently amplified through the NDTDF. Because of the normal dispersion of the Tm‐doped silica fiber, the amplified pulses are able to be compressed using a conventional telecommunication fiber such as SMF‐28. Hence, an all‐fiber ultrafast laser source is constructed in the 1.7 μm wavelength region for deep tissue imaging applications. This paper reports ≈230 nJ, with its corresponding average power as high as 1.74 W. Further adjustment of dispersion in the all‐fiber configuration allows the main pulse duration to be compressed to ≈200 fs. Core size scalability of the proposed W‐type NDTDF has also been investigated.