title: Laser Frequency Noise in Coherent Optical Systems: Spectral Regimes and Impairments.
abstract: Coherent communication networks are based on the ability to use multiple dimensions of the lightwave together with electrical domain compensation of transmission impairments. Electrical-domain dispersion compensation (EDC) provides many advantages such as network flexibility and enhanced fiber nonlinearity tolerance, but makes the system more susceptible to laser frequency noise (FN), e.g. to the local oscillator FN in systems with post-reception EDC. Although this problem has been extensively studied, statistically, for links assuming lasers with white-FN, many questions remain unanswered. Particularly, the influence of a realistic non-white FN-spectrum due to e.g., the presence of 1/f-flicker and carrier induced noise remains elusive and a statistical analysis becomes insufficient. Here we provide an experimentally validated theory for coherent optical links with lasers having general non-white FN-spectrum and EDC. The fundamental reason of the increased susceptibility is shown to be FN-induced symbol displacement that causes timing jitter and/or inter/intra symbol interference. We establish that different regimes of the laser FN-spectrum cause a different set of impairments. The influence of the impairments due to some regimes can be reduced by optimizing the corresponding mitigation algorithms, while other regimes cause irretrievable impairments. Theoretical boundaries of these regimes and corresponding criteria applicable to system/laser design are provided.
authors.affiliation: Optics and Photonics Division, KTH Royal Institute of Technology, Electrum 229, SE-16440, Kista, Sweden. adityak@kth.se.|Networking and Transmission Laboratory (NETLAB), Acreo Swedish ICT, AB, SE-16425, Kista, Sweden. adityak@kth.se.
authors.forename: Aditya
authors.identifier: http://orcid.org/0000-0001-8389-158X
authors.initials: A
authors.lastname: Kakkar
authors.affiliation: Optics and Photonics Division, KTH Royal Institute of Technology, Electrum 229, SE-16440, Kista, Sweden. jaime.rodrigo-navarro@acreo.se.|Networking and Transmission Laboratory (NETLAB), Acreo Swedish ICT, AB, SE-16425, Kista, Sweden. jaime.rodrigo-navarro@acreo.se.
authors.forename: Jaime
authors.initials: J
authors.lastname: Rodrigo Navarro
authors.affiliation: Optics and Photonics Division, KTH Royal Institute of Technology, Electrum 229, SE-16440, Kista, Sweden.
authors.forename: Richard
authors.initials: R
authors.lastname: Schatz
authors.affiliation: Networking and Transmission Laboratory (NETLAB), Acreo Swedish ICT, AB, SE-16425, Kista, Sweden.
authors.forename: Xiaodan
authors.initials: X
authors.lastname: Pang
authors.affiliation: Networking and Transmission Laboratory (NETLAB), Acreo Swedish ICT, AB, SE-16425, Kista, Sweden.
authors.forename: Oskars
authors.identifier: http://orcid.org/0000-0001-9839-7488
authors.initials: O
authors.lastname: Ozolins
authors.affiliation: Networking and Transmission Laboratory (NETLAB), Acreo Swedish ICT, AB, SE-16425, Kista, Sweden.
authors.forename: Aleksejs
authors.initials: A
authors.lastname: Udalcovs
authors.affiliation: VPIphotonics GmbH, DE-10587, Berlin, Germany.
authors.forename: Hadrien
authors.initials: H
authors.lastname: Louchet
authors.affiliation: Optics and Photonics Division, KTH Royal Institute of Technology, Electrum 229, SE-16440, Kista, Sweden.
authors.forename: Sergei
authors.initials: S
authors.lastname: Popov
authors.affiliation: Networking and Transmission Laboratory (NETLAB), Acreo Swedish ICT, AB, SE-16425, Kista, Sweden.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Jacobsen