Picosecond pulse‐width ultra‐low repetition rate passive mode‐locked fibre ring laser

The authors experimentally demonstrate an ultra‐low repetition rate passive mode‐locked fibre ring laser with a semiconductor optical amplifier works like as a gain medium and non‐linear polarisation rotation. A unidirectional erbium‐doped fibre amplifier provides additional gain to increase cavity power. By exploiting non‐linear polarisation rotation combined with dispersion management stable 5.18 ps optical pulses with 67.2 kHz repetition rate and energy of 1.75 nJ were generated with an extinction ratio >35 dB. The central wavelength is 1557.89 nm and the optical 3‐dB bandwidth 1.82 nm very appropriate for optical applications that often require high‐peak‐power, low repetition rate and picosecond pulses.