PDM-SHD NFDM transmission with envelope-detection feedback polarization tracking and optical injection locking

Area of Science:

• Optical Communications
• Nonlinear Signal Processing
• Photonics

Background:

• Nonlinear frequency division multiplexing (NFDM) and eigenvalue communications offer potential beyond the nonlinear Shannon capacity limit.
• Existing eigenvalue communication systems face limitations in baud rate and mitigation of laser frequency impairments like phase noise and frequency offset (FO) in intradyne detections (IDs).
• Digital signal processing (DSP) struggles with these impairments at higher baud rates.

Purpose of the Study:

• To introduce a novel polarization division multiplexing-self-homodyne detection (PDM-SHD) technique for NFDM systems.
• To overcome limitations of phase noise and FO in eigenvalue communications.
• To enhance the robustness and capacity of optical communication systems.

Main Methods:

• Integration of PDM-SHD into the NFDM link, utilizing a pilot carrier transmitted via orthogonal polarization.
• Development of a carrier to signal power ratio (CSPR) unrestricted adaptive polarization controlling strategy based on optical intensity fluctuation.
• Application of optical injection locking (OIL) to amplify the pilot carrier and mitigate signal-signal beat interference (SSBI).

Main Results:

• The PDM-SHD system demonstrates a 17-fold increase in tolerable frequency offset (FO) range, reaching approximately 3.5 GHz compared to ID systems.
• Identical Q-factor performance for 16-APSK and 64-APSK constellations is achieved across various laser types (DFB, ECL, FL), indicating insensitivity to laser linewidth.
• Significant Q-factor improvement (up to 8.73 dB) is observed for 16-APSK signals after 1500 km transmission under cycle slip, comparing ECL-SHD to ECL-ID systems.

Conclusions:

• The proposed PDM-SHD eigenvalue communication structure effectively mitigates phase noise and frequency offset in NFDM systems.
• The system exhibits remarkable insensitivity to laser linewidth, enabling the use of diverse laser sources.
• PDM-SHD offers a robust solution for long-haul, high-capacity optical communication, overcoming limitations of traditional detection methods.