Harmonically mode-locked fibre laser: stabilisation and precise control of the pulse repetition rate using a cw spectral component

Abstract: This paper examines a soliton fibre laser with harmonic mode locking via nonlinear polarisation rotation. A characteristic feature of its spectrum is the presence of a cw component. We show that, as the wavelength of the cw component approaches that of a Kelly peak, the supermode noise level in the radiofrequency spectrum of the laser can be reduced by 27 – 32 dB at pulse repetition rates from 275 to 1230 MHz. In addition, we demonstrate the feasibility of tuning the pulse repetition rate with the highest possible accuracy, equal to the fundamental cavity frequency, throughout the range of its variation, up to the highest value of 1760 MHz. Such tuning is possible if the wavelength of the cw component lies in a certain resonance region of the soliton spectrum.

Keywords: soliton, fibre laser, mode locking, pulse repetition rate