High-channel-count 20 GHz passively mode-locked quantum dot laser directly grown on Si with 41 Tbit/s transmission capacity

Low-cost, small-footprint, highly efficient, and mass-producible on-chip wavelength-division-multiplexing (WDM) light sources are key components in future silicon electronic and photonic integrated circuits (EPICs), which can fulfill the rapidly increasing bandwidth and lower energy per bit requirements. We present here, for the first time to our knowledge, a low-noise high-channel-count 20 GHz passively mode-locked quantum dot laser grown on a complementary metal-oxide-semiconductor compatible on-axis (001) silicon substrate. The laser demonstrates a wide mode-locking regime in the O band. A record low timing jitter value for passively mode-locked semiconductor lasers of 82.7 fs (4–80 MHz) and a narrow RF 3 dB linewidth of 1.8 kHz are measured. The 3 dB optical bandwidth of the comb is 6.1 nm (containing 58 lines, with 80 lines within the 10 dB bandwidth). The integrated average relative intensity noise values of the whole spectrum and a single wavelength channel are −152  dB/Hz and −133  dB/Hz in the frequency range from 10 MHz to 10 GHz, respectively. Utilizing 64 channels, an aggregate total transmission capacity of 4.1 terabits per second is realized by employing a 32 Gbaud Nyquist four-level pulse amplitude modulation format. The demonstrated performance makes the laser a compelling on-chip WDM source for multi-terabit/s optical interconnects in future large-scale silicon EPICs.