165 MHz highly stable femtosecond Er:ZBLAN fiber laser operating at 2.8 µm

Three-micrometer mid-infrared (MIR) femtosecond pulse sources with a high repetition rate (HRR) have potential applications in a number of fields such as biological imaging, optical frequency combs, and gas detection. In this paper, by optimizing the fiber length and the cavity structure, we demonstrated a highly stable, self-starting mode-locked fluoride fiber laser (MLFFL) with a fundamental repetition rate of ∼165 MHz and a signal-to-noise ratio (SNR) of 90 dB. As far as we know, this stands as the highest fundamental repetition rate ever acquired directly from an ultrafast MLFFL in the >2.5 µm MIR region. Stable 352-fs pulses at 2795 nm with an average output power of 392 mW and a low integrated relative intensity noise (RIN) of 0.018% [10 Hz, 10 MHz] were generated. The root mean square (RMS) power fluctuation is 0.17% over 2 h, which indicates excellent oscillator stability. This high-performance laser offers a practicable scheme both for scaling the repetition frequency in MIR MLFFLs and high-precision ultrafast applications at longer wavelengths.