Abstract
To meet the increasing demand to expand wavelength division multiplexing (WDM) transmission capacity, ultrahigh spectral density coherent optical transmission employing multi-level modulation formats has attracted a lot of attention. In particular, ultrahigh multi-level quadrature amplitude modulation (QAM) has an enormous advantage as regards expanding the spectral efficiency to 10 bit/s/Hz and even approaching the Shannon limit. We describe fundamental technologies for ultrahigh spectral density coherent QAM transmission and present experimental results on polarization-multiplexed 256 QAM coherent optical transmission using heterodyne and homodyne detection with a frequency-stabilized laser and an optical phase-locked loop technique. In this experiment, Raman amplifiers are newly adopted to decrease the signal power, which can reduce the fiber nonlinearity. As a result, the power penalty was reduced from 5.3 to 2.0 dB. A 64Gbit/s data signal is successfully transmitted over 160 km with an optical bandwidth of 5.4 GHz.
Original language | English |
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Pages (from-to) | 417-424 |
Number of pages | 8 |
Journal | IEICE Transactions on Communications |
Volume | E94-B |
Issue number | 2 |
DOIs | |
Publication status | Published - 2011 Feb |
Keywords
- Coherent transmission
- Frequency-stabilized laser
- Optical phase-locked loop
- Quadrature amplitude modulation
- Spectral efficiency
ASJC Scopus subject areas
- Software
- Computer Networks and Communications
- Electrical and Electronic Engineering