Reduced Repetition Rate Yb3+ Mode-Locked Picosecond Fiber Laser With Hollow Core Fiber

Anti-resonant guiding negative curvature hollow core fiber operating at a wavelength of 1064 nm is used in the cavity of an ytterbium (Yb
³⁺
) mode-locked fiber laser to increase cavity length without increasing the nonlinear phase shift. Repetition rates from 37 to 5.4 MHz are demonstrated using lengths of hollow core fiber up to 48 m in length. Each constructed cavity produced coherent 4-ps 1/e2 duration soliton-like pulses, with no degradation of the pulse peak power or pulse shape at lower repetition rates. Both the spectral distributions and the autocorrelations of output pulses are compared along with the mode-locking and multi-pulse power thresholds.