20 nm wavelengty tunable singlemode picosecond pulse generation at 1.3 μm by self-seeded gain-switched semiconductor laser

A back reflection of less than 0.25% of the monochromatised emitted power of a gain switched laser diode is shown to switch the laser from longitudinal multimode to singlemode pulsed operation. The pulse shape (FWHM = 45 ps) is not affected by the feedback. A wavelength detuning of 20 nm with a sidemode suppression ratio better than 13 dB and a peak value of 22 dB were found from a simple experimental setup using a 9:1 fibre coupler and an external grating.