title: Generation and detection of 240-Gb/s PDM-64QAM using optical binary synthesizing approach and phase-folded decision-directed equalization.
abstract: We present new generation and detection methods for high symbol-rate 64-ary quadrature amplitude modulation (64QAM). The 64QAM signal is created by tandem in-phase/quadrature (I/Q) modulators driven by electrical binary signals. The first I/Q modulator, which has four drive arms (i.e. a dual-drive I/Q modulator), yields 16QAM with an offset at the 1st quadrant of the complex plane. Subsequently, the second modulator switches this 16QAM signal over four quadrants via the typical quadrature phase-shift-keying (QPSK) modulation scheme, hence the desired 64QAM is generated. To mitigate the impacts of transmitter imperfections, we also propose a phase-folded decision-directed (PF-DD) linear equalizer at the receiver. Using these new techniques, we experimentally demonstrate the 120- and 240-Gb/s polarization-division-multiplexed (PDM) return-to-zero (RZ) 64QAM systems. The required optical signal-to-noise ratio (OSNR) for a bit-error rate (BER) of 2.4x10(-2) is measured at 20.2 or 23 dB, respectively, which is ~3.5 dB off the theoretical limit.
authors.affiliation: KDDI R&D Laboratories Inc., Ohara, Fujimino, Saitama, Japan. hchoi@kddilabs.jp
authors.forename: Hyeon Yeong
authors.initials: HY
authors.lastname: Choi
authors.forename: Takehiro
authors.initials: T
authors.lastname: Tsuritani
authors.forename: Hidenori
authors.initials: H
authors.lastname: Takahashi
authors.forename: Wei-Ren
authors.initials: WR
authors.lastname: Peng
authors.forename: Itsuro
authors.initials: I
authors.lastname: Morita
mesh_terms: D017076:Computer-Aided Design; D005336:Fiber Optic Technology / Q000295:instrumentation* / Q000379:methods*; D008962:Models, Theoretical; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D013685:Telecommunications / Q000295:instrumentation*