Mitigation of relative intensity noise of quantum dash mode-locked lasers for PAM4 based optical interconnects using encoding techniques

Abstract

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.

InAs/InP Quantum Dash Semiconductor Coherent Comb Lasers and their Applications in Optical Networks

“…The low frequency RIN does not exceed -118 dB/Hz for our device unlike the measurements shown in Ref. [44] which is up to -90 dB/Hz. The integrated RIN values for all 48 filtered individual channels are approximately -130 dB/Hz in the frequency range from 10 MHz to 10 GHz.…”

Photonically integrated gain‐switched lasers for optical frequency comb generation

“…Furthermore, optical networks employing multi-level intensity modulation schemes, such as PAM4/8, have more stringent requirements on the RIN values. 25 To characterize the RIN of the device, an experimental setup shown in Figure 2(A) is used. The output of the laser is detected by a 50 GHz photodetector.…”

“…In order to use a directly modulated laser as a transmitter in an optical network, the RIN value of the laser typically should not exceed −120 dB/Hz. Furthermore, optical networks employing multi‐level intensity modulation schemes, such as PAM4/8, have more stringent requirements on the RIN values 25 . To characterize the RIN of the device, an experimental setup shown in Figure 2(A) is used.…”

Characterization and Direct Modulation of a Multi-Section PIC Suited for Short Reach Optical Communication Systems

“…RIN is another important parameter of an optical transmitter, quantifying the intensity fluctuations of the laser output power [25]. High RIN values (>−120 dB/Hz) can be a limiting factor for the usage of a laser in DCNs, especially ones employing multi-level intensity modulation schemes such as PAM 4/8 [26]. Moreover, it can also have a negative effect on other modulation schemes such as orthogonal frequency division multiplexing (OFDM) and discrete multi-tone transmission (DMT) [27] that may be used to directly modulate the laser transmitter.…”