Variable wavelength-multiplexed dual-comb generation and spectroscopic measurement by a free-running all-normal-dispersion Yb-doped fiber laser

Single-cavity Er-doped mode-locked fiber lasers that can generate dual frequency combs with distinct repetition rates hold significant potential for low-complexity dual-comb metrology applications. Recent studies on dual-comb Yb-doped light sources with an all-normal dispersion mechanism have been proposed. In this work, we experimentally and numerically demonstrate a variable and switchable all-normal dispersion dual-wavelength Yb-doped fiber mode-locked laser based on a birefringent filter. In contrast to the previous dual-comb spectroscopy demonstrations directly enabled by the single-wavelength dual-comb all-normal dispersion Yb-doped laser, this work demonstrates broadband spectral coverage expansion in a dual-wavelength dual-comb laser source through an external Yb-doped fiber amplifier and photonic crystal fiber, with little additional intensity and phase noise. To evaluate mutual coherence and verify the feasibility by utilizing broadening combs, we performed proof-of-concept dual-comb spectroscopy of the transmission measurements with a homemade Sagnac filter; the results showed very good agreement with those obtained using an optical spectrum analyzer. It is of great significance to use a periodic filter in the cavity and eventually measure the transmission curve of such a periodic filter. Our work paves the way for the development of broadening all-normal-dispersion Yb-doped fiber lasers, which are well-suited for dual-comb applications.