Synthesis of 16 Quadrature Amplitude Modulation Using Polarization-Multiplexing QPSK Modulator

Isao MOROHASHI  Takahide SAKAMOTO  Masaaki SUDO  Atsushi KANNO  Akito CHIBA  Junichiro ICHIKAWA  Tetsuya KAWANISHI  

Publication
IEICE TRANSACTIONS on Communications   Vol.E94-B   No.7   pp.1809-1814
Publication Date: 2011/07/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E94.B.1809
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Joint Special Section on Opto-electronics and Communications for Future Optical Network)
Category: 
Keyword: 
modulation format electro-optic vector digital-to-analog converter,  quadrature amplitude modulation,  quad-parallel Mach-Zehnder modulator,  polarization multiplexing,  

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Summary: 
We propose a polarization-multiplexing QPSK modulator for synthesis of a 16 QAM signal. The generation mechanism of 16 QAM is based on an electro-optic vector digital-to-analog converter, which can generate optical multilevel signals from binary electric data sequences. A quad-parallel Mach-Zehnder modulator (QPMZM) used in our previous research requires precise control of electric signals or fabrication of a variable optical attenuator, which significantly raises the degree of difficulty to control electric signals or device fabrication. To overcome this difficulty, we developed the polarization-multiplexing QPSK modulator, which improved the method of superposition of QPSK signals. In the polarization-multiplexing QPSK modulator, two QPSK signals are output with orthogonal polarization and superposed through a polarizer. The amplitude ratio between the two QPSK signals can be precisely controlled by rotating the polarizer to arrange the 16 symbols equally. Generation of 16 QAM with 40 Gb/s and a bit error rate of 5.6910-5 was successfully demonstrated using the polarization-multiplexing QPSK modulator. This modulator has simpler configuration than the previous one, utilized a dual-polarization MZM, alleviating complicated control of electric signals.