  Quantum Dash (Q-Dash) Passively Mode-Locked Lasers (PMLLs) exhibit
significant low frequency Relative Intensity Noise (RIN), due to the high Mode
Partition Noise (MPN), which prevents the implementation of multilevel
amplitude modulation formats such as PAM4. The authors demonstrate low
frequency RIN mitigation by employing 8B/10B and Manchester encoding with PAM4
modulation format. These encoding techniques reduce the overlap between the
modulation spectral content and the low-frequency RIN of the Q-Dash devices, at
the expense of increased overhead. The RIN of the 33.6 GHz free spectral range
Q-Dash PMLL was characterized, and the results obtained show very high levels
of RIN from DC to 4 GHz, but low levels for higher frequencies. The performance
improvement for 28 GBaud 8B/10B and Manchester encoded PAM4 signal has been
demonstrated compared to the case when no encoding is used. Finally, the effect
of RIN on the system performance was demonstrated by comparing the Bit Error
Rate (BER) performance of the PAM4 signaling obtained with an External Cavity
Laser (ECL) to those obtained with Q-Dash PMLL.
