Proposal and Verification of Auto Calibration Technique for Bias Control Circuit Connecting to Built-In Optical Power Monitor in Imperfect IQ-Modulator

Shoichiro KUWAHARA
Yoshiaki KISAKA

IEICE TRANSACTIONS on Communications   Vol.E103-B    No.11    pp.1299-1304
Publication Date: 2020/11/01
Publicized: 2020/05/22
Online ISSN: 1745-1345
DOI: 10.1587/transcom.2019OBP0010
Type of Manuscript: Special Section PAPER (Joint Special Section on Opto-electronics and Communications for Future Optical Network)
optical transmitter,  IQ-modulator,  optical QAM,  auto bias control,  calibration,  

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We show that imperfection in an IQ-modulator degrades the accuracy of the auto bias control (ABC) circuit connected to the modulator's complementary port. Theoretical analyses show that the IQ-modulator constructed by a nested Mach-Zehnder modulator with a low extinction ratio can distort a constellation of modulated light observed at the complementary port. We propose an auto calibration technique for the ABC circuit that can effectively suppress this degradation. Experimental results using 32-Gbaud, 16-QAM signals showed the measured Q-factor improved by 0.5dB with our proposed technique.