Wavelength-tunable and pulsewidth-variable actively modelocked short-cavity fibre laser using bismuth-based highly nonlinear erbium-doped fibre

A wavelength and pulsewidth-tunable actively modelocked fibre ring laser employing a 151 cm-long bismuth-oxide-based highly nonlinear erbium-doped fibre (Bi-HNL-EDF) and a bandwidth-variable tunable filter is demonstrated. An 80 nm continuous wavelength tuning from 1535 to 1615 nm can be achieved by utilising the wide gain bandwidth of the Bi-HNL-EDF. The pulsewidth can also be tuned from 7.8 to 23.1 ps by changing the filter bandwidth. High nonlinearity of the Bi-HNL-EDF collaborates with spectral filtering by the filter to suppress the supermode noise quite effectively. The total cavity length is as short as 14 m. Thus, clean pulses with a repetition rate of 10 GHz are successfully obtained over the entire tuning ranges. Back-to-back bit error rate tests also confirm bit error free modelocking operation.