Transceiver impairment robust and joint monitoring of PDL, DGD, and CD using frequency domain pilot tones for digital subcarrier multiplexing systems

Optical performance monitoring is vital for enabling dynamically reconfigurable optical networks. This paper introduces a monitoring scheme that is robust to transceiver impairments for coherent digital subcarrier multiplexing (DSCM) systems that simultaneously monitors polarization-dependent loss (PDL), differential group delay (DGD), and chromatic dispersion (CD). In the proposed scheme, a pair of frequency domain pilot tones (FPTs) are inserted into the ${X}$ and ${Y}$ polarizations of the transmitted dual-polarization signal. Both the signal and the FPTs endure identical channel impairments during fiber transmission. At the receiver side, the transmitted FPTs are extracted to monitor the channel impairments. We begin by establishing a simplified system model using a single frequency tone to analyze the effects of system impairments on the frequency domain pilots. Based on this model, CD, PDL, and DGD are jointly and accurately estimated. In addition, the influences of temporal, amplitude, and phase mismatches between in-phase (I) and quadrature (Q) components of transceivers on channel impairment monitoring are completely eliminated. This achieves a channel impairment monitoring scheme that is robust to transceiver impairments. Experimental verification shows that the proposed scheme can jointly and accurately estimate a wide range of CD, PDL, and DGD. Additionally, the proposed monitoring scheme demonstrates strong robustness against transceiver impairments, rapid polarization fluctuations, and amplified spontaneous emission (ASE) noise.