All-Fiber Mode-Locked Deep-Red Laser by a Phase-Biased NOLM

Deep-red ultrafast fiber lasers show great potential for life sciences, biomedicine, and scientific research. However, directly achieving mode-locked emission in an all-fiber deep-red laser remains challenging. Here, we demonstrate an all-fiber passively mode-locked deep-red laser operating at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 717 nm to tackle this issue. The laser uses a figure-9 all-fiber cavity with a double-clad Pr<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3+}$</tex-math></inline-formula>: ZBLAN fiber as the gain medium and features a phase-biased nonlinear optical loop mirror for mode locking. Stable dissipative soliton resonance pulses with a tunable pulse duration ranging from 57.3 to 135 ps, a narrow 3-dB bandwidth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 0.29 nm at 717.5 nm, and a repetition rate of 14.5854 MHz were achieved. A maximum average power of 41.6 mW was obtained, corresponding to a pulse energy of 2.85 nJ and peak power of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 22 W. Additionally, we conducted a theoretical investigation into the performance of the laser, with the simulation results closely matching the experiment. This work extends the capabilities of all-fiber mode-locked picosecond lasers into deep-red light, demonstrating its potential for bioimaging, biomedicine, and UV laser generation.