Single-pixel optical modulation analyzer: a low-complexity frequency-dependent IQ imbalance monitor based on direct detection with phase retrieval

Tiny mismatches in timing, phase, and/or amplitude between in-phase (I) and quadrature (Q) tributaries in an electro-optic IQ modulator, namely IQ imbalance, can severely affect high baud-rate and/or high modulation-order signals in modern coherent optical communications systems. To maintain such analog impairment within the tight penalty limit over wavelength and temperature during the product lifetime, in-service in-field monitoring and calibration of the IQ imbalance, including its frequency dependence, become increasingly important. In this study, we propose a low-complexity IQ monitoring technique based on direct detection with phase retrieval called a single-pixel optical modulation analyzer (SP-OMA). By reconstructing the optical phase information lost during the detection process computationally via phase retrieval, SP-OMA facilitates the in-service in-field monitoring of the frequency-dependent imbalance profile without sending dedicated pilot tones and regardless of any receiver/monitor-side IQ imbalance. The feasibility of SP-OMA is demonstrated both numerically and experimentally with a 63.25-Gbaud 16QAM signal. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Automated summary

Small mismatches between in-phase and quadrature tributaries in an electro-optic IQ modulator, known as IQ imbalance, can greatly impact high baud-rate and/or high modulation-order signals in coherent optical communications systems. In this study, a low-complexity IQ monitoring technique based on direct detection with phase retrieval, called SP-OMA, is proposed for in-service in-field monitoring of frequency-dependent imbalance profile without requiring dedicated pilot tones or being affected by receiver/monitor-side IQ imbalance. The feasibility of SP-OMA is demonstrated both numerically and experimentally with a 63.25-Gbaud 16QAM signal.