Ultra-fast SOP rotation tracking and its enabled feedforward adaptive equalization based on superimposed chirp pilot
Optics Express
|August 13, 2025
Summary
We introduce a novel method using chirp pilots and fractional Fourier transform (FrFT) to track state of polarization (SOP) rotation in optical signals. This technique enhances signal-to-noise ratio and enables efficient adaptive equalization.
Area of Science:
- Optical communications
- Signal processing
- Photonics
Background:
- State of polarization (SOP) rotation is a significant challenge in optical fiber communication systems.
- Accurate tracking of SOP rotation is crucial for maintaining signal integrity and performance.
- Existing methods may struggle with high rotation speeds or introduce spectral inefficiency.
Purpose of the Study:
- To propose and verify a novel scheme for tracking state of polarization (SOP) rotation using chirp pilots and fractional Fourier transform (FrFT).
- To improve the optical signal-to-noise ratio (OSNR) penalty caused by signal superimposition.
- To enable feedforward adaptive equalization (FFD-AEQ) for enhanced system performance and reduced complexity.
Main Methods:
- Utilizing chirp pilots processed through fractional Fourier transform (FrFT) superimposed on dual-polarization data signals.
- Employing FrFT with a MIMO structure to distinguish chirp pilots based on their fractional energy peaks.
- Leveraging aggregated peaks in the matched fraction domain to estimate SOP rotation.
- Implementing a fractional domain digital match filter (DMF) to mitigate superimposition impact.
- Developing a feedforward adaptive equalization (FFD-AEQ) scheme incorporating pre-equalization.
Main Results:
- The proposed scheme successfully tracks SOP rotation up to 5 Mrad/s for 480Gb/s DP-16QAM and 600Gb/s DP-32QAM signals over 25 km fiber.
- The fractional domain DMF reduces the OSNR penalty from over 4.0 dB to 0.9 dB.
- FFD-AEQ effectively handles SOP rotation up to 4.1 Mrad/s under HD-FEC.
- FFD-AEQ with pre-equalization achieves a 39.1% reduction in complexity compared to conventional MIMO.
Conclusions:
- The proposed FrFT-based chirp pilot method offers an efficient and spectrum-efficient approach for tracking high-speed SOP rotation.
- The fractional domain DMF significantly improves OSNR performance by reducing superimposition effects.
- FFD-AEQ provides a robust and computationally efficient solution for adaptive equalization in the presence of SOP rotation.
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