Sub-50 fs, 2.8 μm Pulse Generation Enabled by Nonlinear Pulse Stretching and Compression in a Chalcogenide–Fluoride Fiber-Integrated System

We report the generation of sub-50 fs mid-infrared (MIR) pulses using a fiber-integrated system comprising a several-centimeters-long chalcogenide (As2S3) fiber and a fluoride (ZBLAN) fiber. Initially, 127 fs pulses at 2.8 µm are generated via the soliton self-frequency shift in the fluoride fiber. These pulses are then coupled into the As2S3 fiber, which provides substantial normal dispersion at this wavelength, enabling temporal stretching to achieve pulse durations of 1.02 ps (8 cm), 2.06 ps (15 cm), and 4.45 ps (24 cm), corresponding to a maximum stretch factor of approximately 35. Simultaneously, the pulses undergo significant spectral broadening via self-phase modulation during this process. Subsequent nonlinear compression within an optimized ZBLAN fiber yields compressed pulses as short as 46 fs, representing a compression ratio of approximately 63%. This work represents, for the first time, picosecond stretching and sub-50 fs nonlinear compression in a fiber-integrated architecture at 2.8 μm, establishing a critical component for future all-fiber MIR-chirped pulse amplification systems.