Impact of laser flicker noise and linewidth on 64 to 96  Gbaud/DP-nQAM metro coherent optical links

Abstract

We experimentally investigate the impact of laser flicker noise and linewidth on 64 Gbaud/DP-64QAM, 96 Gbaud/DP-32QAM and 64 or 96 Gbaud/DP-16QAM links. To give a more practical viewpoint, the examined flicker noise closely follows that of an industry forum (OIF 400ZR). We have found that higher modulation order (e.g., 64QAM) is sensitive to phase noise from the linewidth and flicker noise, even in the back to back case. Significant optical signal to noise ratio (OSNR) and cycle slip rate penalties can also be observed with a transmission distance > 200 k m for both 64QAM and 32QAM signals, which mainly comes from equalization-enhanced phase noise. Moreover, with the increasing of transmission distances, the effective linewidth of a tunable laser with a higher flicker noise and higher linewidth (210 KHz) increases significantly, while it remains unchanged for an external cavity laser (ECL) with 47-kHz linewidth. The result indicates the importance of more stringent flicker noise and linewidth requirement for future ultrabaud rate transmissions.

A comprehensive review on the development and applications of narrow‐linewidth lasers

“…In many specific applications, the laser is also required to maintain a long-term single-frequency operation without frequency hopping; meanwhile, phase noise should be minimized. 34,35 Therefore, to fulfill the requirements of different applications, it is necessary to understand the properties of different types of narrow-linewidth lasers and their output parameters. This section summarizes several representative approaches to narrow-linewidth lasers.…”

“…In general, an SLM laser is assumed to be a single‐frequency laser if its linewidth is narrower than the resolution of a spectrum analyzer or the nonlinear gain bandwidth of a specific medium. In many specific applications, the laser is also required to maintain a long‐term single‐frequency operation without frequency hopping; meanwhile, phase noise should be minimized 34,35 . Therefore, to fulfill the requirements of different applications, it is necessary to understand the properties of different types of narrow‐linewidth lasers and their output parameters.…”

Digital back-propagation in optical fiber communication systems considering equalization enhanced phase noise

“…Distortions from EEPN will result in a significant degradation of the system performance. Tremendous investigations with EEPN have been carried out for linear optical transmission systems 7,[14][15][16][17][18][19][20][21][22] . It is indicated that the EEPN, a source of severe performance degradation in long-haul transmission systems, increases with the accumulated CD, local oscillator (LO) laser linewidth, the modulation format and the symbol rate of the system 7,15,19 .…”