Open AccessGeneration and detection of 240-Gb/s PDM-64QAM using optical binary synthesizing approach and phase-folded decision-directed equalization
Author(s) -
Hyeon Yeong Choi,
Takehiro Tsuritani,
Hidenori Takahashi,
Wen-Chih Peng,
Ramon Casellas
Publication year - 2012
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.20.027933
Subject(s) - quadrature amplitude modulation , amplitude and phase shift keying , phase shift keying , optics , qam , physics , phase modulation , polarization division multiplexing , phase noise , electronic engineering , bit error rate , computer science , telecommunications , wavelength division multiplexing , engineering , decoding methods , wavelength
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.