High-frequency vector harmonic mode locking driven by acoustic resonances.

A controllable passive harmonic mode locking (HML) in an erbium-doped fiber laser with a soliton pulse shaping using a single-wall carbon nanotube has been experimentally demonstrated. By increasing the pump power and adjusting the in-cavity polarization controller, we reached the 51st-order harmonic (902 MHz) having the output power of 37 mW. We attribute the observed high-frequency HML to the electrostriction effect caused by periodic pulses and leading to excitation of the radial and torsional-radial acoustic modes in the transverse section of the laser. The exited acoustic modes play the role of the bandpass filter, which stabilizes the high-frequency HML regime.