Receiver IQ Imbalance and Skew Compensation for High Order Modulation Formats by Frequency Domain 4 × 2 MIMO

• Published in: Journal of lightwave technology Vol. 41; no. 2; pp. 558 - 569
• Main Authors: Liang, Junpeng, Chai, Jia, Chen, Xue, Lu, Guo-Wei, Feng, Zhenhua, Zhang, Liangjun, Wang, Weiming
• Format: Journal Article
• Language: English
• Published: New York IEEE 15-01-2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Adaptive frequency domain equalizer; Algorithms; Compensation; Defects; digital signal processing; Equalizers; Frequency domain analysis; IQ imbalance; IQ skew; MIMO; MIMO communication; Noise tolerance; optical fiber communication; optical fiber dispersion; Optical fibers; Optical polarization; Optical transmitters; Parallel processing; Polarization; Q-factor; Quadrature amplitude modulation; Transceivers
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2022.3219866

A typical coherent front-end may encounter imperfections, such as amplitude imbalance, phase imbalance and skew, between four sampling channels. These receiver (Rx) imperfections, together with traditional chromatic dispersion (CD) compensation, would induce in-phase (I) and quadrature (Q) mixing, which greatly degrades the system performance. In this work, we propose a modulation format independent frequency domain (FD) 4 × 2 multi-inputs and multi-outputs (MIMO) based on decision directed least mean square (DD-LMS) algorithm to solve this problem. Compared with traditional 2 × 2 MIMO, it enables to compensate for all of Rx imperfections. Compared with 4 × 4 MIMO, it can eliminate performance penalty induced by the IQ mixing after optical fiber transmission. Compared with traditional time domain 4 × 2 MIMO, the proposed FD 4 × 2 MIMO has advantages in terms of complexity and parallel processing. We also evaluate the Rx imperfections compensation capability, noise tolerance tolerance, polarization tracking capability, residual CD and transmitter imperfections tolerance of the proposed equalizers. The proposed FD 4 × 2 MIMO algorithms are verified by numerical simulation with different modulation formats and experimentally validated with 40 Gbaud polarization division multiplexed 16-ary quadrature amplitude modulation signal.