O-band DWDM data transmission with quantum dot mode-locked comb laser and semiconductor optical amplifier

There is a long-standing prospect of using a single comb laser chip emitting multiple low-noise spectral modes for DWDM data transmission in the O-band. This goal is hindered by unacceptably high total power requirements for such a source to overcome losses in a PIC and to provide at least 1 mW per data channel in a fiber. We solve this problem by simultaneously re-amplifying more than 20 lines depleted after the PIC using a low-noise quantum dot (QD)-based SOA. In this way, we demonstrate O-band DWDM data transmission of a PAM4 signal with a total bit rate of up to 2.3 Tb/s in fiber with a single QD comb laser source. The other problem related to the application of semiconductor comb lasers is the insufficiently large interline separation to be compatible with the state-of-the-art DWDM PIC technologies. We present comb laser devices with and without a saturable absorber section, providing up to 23 lines with 100 GHz intermode separation, 10 lines with 138 GHz separation, 4 lines with 163 GHz separation, and 3 lines with 216 GHz separation, suitable for data transmission. We show that in the mode-locking regime, both the relative intensity noise (RIN) of the comb laser and the associated bit error rate (BER) are determined by the optical power of the laser mode.