Cleland, D.A.; Cox, J.D.; Ellis, A.D.; Gu, X.Y.: 'Limitations of WDM transmission over 560 km due to degenerate four wave mixing', Electronics Letters, 1992, 28, (3), p. 307-309, DOI: 10.1049/el:19920190
IET Digital Library, https://digital-library.theiet.org/;jsessionid=2lebt0c0eqcj9.x-iet-live-01content/journals/10.1049/el_19920190