Fundamental and harmonic mode-locking with pulse repetition rate between 200 MHz and 6.8 GHz in a quantum-dot external-cavity laser

In this paper, we present our latest results achieved with a 1.27-μm QD-ECMLL based on a two-section superluminescent diode chip (total length of 4mm, 15% absorber-to-total-length ratio) and a 53% output coupler as an external cavity front facet with a total optical cavity length of 75 cm (the back facet, on the absorber side, is high-reflection coated). A record-low repetition rate of 200 MHz and record-low-3dB RF linewidth of -240 Hz from a QD-ECMLL are achieved under stable fundamental mode-locking (FML), with the forward current of 300 mA and reverse bias of 8 V at 20°C.