New metric for IQ imbalance compensation in optical QPSK coherent systems

Abstract : We report on a simple alternative method for the compensation of quadrature imbalance in optical quadrature phase-shift-keying (QPSK) coherent systems. By introducing a new metric, the phase imbalance can be determined and compensated. The proposed method is theoretically and numerically analyzed. In particular, it is shown that the method exhibits a small bias of estimated phase imbalance value. Thanks to its deterministic property, this bias can be simply compensated by incorporating at the receiver a phase rotator (or phase shift) whose value can be determined based on an analytical analysis. Moreover, the algorithm is also experimentally validated through bit-error-rate and error vector magnitude (EVM) measurements. A good agreement on the performance of the proposed method with that of the Gram–Schmidt orthogonalization procedure is shown in a 20-Gbit/s optical QPSK experiment. The robustness of both methods was verified with up to 30° phase imbalance by comparing the signal with and without phase imbalance compensation. A 10% reduction in EVM is achieved with our method for a high phase imbalance of 30°, while the implementation complexity can be reduced owing to the suppression of the use of square-root operators.
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https://hal.inria.fr/hal-01941892
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Submitted on : Wednesday, December 12, 2018 - 11:16:26 AM
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Trung Hien Nguyen, Pascal Scalart, Mathilde Gay, Laurent Bramerie, Christophe Peucheret, et al.. New metric for IQ imbalance compensation in optical QPSK coherent systems. Photonic Network Communications, Springer Verlag, 2018, 36 (3), pp.326-337. ⟨10.1007/s11107-018-0783-7⟩. ⟨hal-01941892⟩

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