Ultra-long-haul 112 Gb/s PM-QPSK transmission systems using longer spans and Raman amplification Downie, John D. ; Hurley, Jason ; Pikula, Dragan ; Zhu, Xianming Abstract Publication: Optics Express Pub Date: April 2012 DOI: 10.1364/OE.20.010353 Bibcode: 2012OExpr..2010353D