Towards visible-wavelength passively mode-locked lasers in all-fibre format

Mode-locked fibre lasers (MLFLs) are fundamental building blocks of many photonic systems used in industrial, scientific and biomedical applications. To date, 1-2 μm MLFLs have been well developed; however, passively mode-locked fibre lasers in the visible region (380-760 nm) have never been reported. Here, we address this challenge by demonstrating an all-fibre visible-wavelength passively mode-locked picosecond laser at 635 nm. The 635 nm mode-locked laser with an all-fibre figure-eight cavity uses a Pr/Yb codoped ZBLAN fibre as the visible gain medium and a nonlinear amplifying loop mirror as the mode-locking element. First, we theoretically predict and analyse the formation and evolution of 635 nm mode-locked pulses in the dissipative soliton resonance (DSR) regime by solving the Ginzburg-Landau equation. Then, we experimentally demonstrate the stable generation of 635 nm DSR mode-locked pulses with a pulse duration as short as ~96 ps, a radio-frequency signal-to-noise ratio of 67 dB and a narrow spectral bandwidth of <0.1 nm. The experimental results are in excellent agreement with our numerical simulations. In addition, we also observe 635 nm noise-like pulse operation with a wide (>1 nm) and modulated optical spectrum. This work represents an important step towards miniaturized ultrafast fibre lasers in the visible spectral region.