Performance improvements in high-frequency modulation of a laser diode under enhanced optical feedback

Improvement in the high-frequency modulation characteristics of a Fabry-Perot laser diode has been observed when the device is driven in an external cavity that provides an amplified optical feedback. At a driving frequency of 10 GHz, the weak sinusoidal waveform in the original output is turned into a train of narrow pulses with a width of 23 ps. Under an optimized feedback level, an improvement of 15.4 dB in the electrical modulation efficiency and 21.2 dB in the sidemode suppression ratio are observed. The output pulses also exhibit a reduced chirp with a minimized total root-mean square noise.