Zero-guard-interval coherent optical OFDM with overlapped frequency-domain CD and PMD equalization.

Area of Science:

• Optical Communications
• Digital Signal Processing
• Telecommunications Engineering

Background:

• Orthogonal Frequency-Division Multiplexing (OFDM) systems commonly use cyclic prefixes (CP) to mitigate inter-symbol interference.
• Chromatic Dispersion (CD) and Polarization Mode Dispersion (PMD) are significant impairments in high-speed optical fiber transmission.
• Existing reduced-guard-interval (RGI)-CO-OFDM systems still incur some overhead and have limitations in dispersion tolerance.

Purpose of the Study:

• To propose and evaluate a novel Zero-Guard-Interval CO-OFDM (ZGI-CO-OFDM) system.
• To demonstrate the elimination of CP overhead in OFDM transmission.
• To assess the performance of ZGI-CO-OFDM in compensating for CD and PMD.

Main Methods:

• Development of an overlapped frequency-domain equalizer (OFDE) for ZGI-CO-OFDM.
• Compensation of CD and PMD prior to OFDM demodulation.
• Verification of PMD tolerance under various conditions and comparison with RGI-CO-OFDM.
• Analysis of channel estimation accuracy using intra-symbol frequency-averaging (ISFA).
• Computational complexity analysis comparing ZGI-CO-OFDM with conventional and RGI-CO-OFDM.

Main Results:

• ZGI-CO-OFDM successfully eliminates CP overhead.
• Superior PMD tolerance demonstrated compared to RGI-CO-OFDM.
• Improved channel estimation accuracy achieved with larger ISFA lengths under high PMD.
• Enables the use of smaller FFT sizes (<128) without CP overhead.
• ZGI-CO-OFDM shows a modest increase in computation complexity (~13.6%) over RGI-CO-OFDM.

Conclusions:

• ZGI-CO-OFDM is an effective technique for high-speed optical transmission, offering significant advantages in dispersion compensation and overhead reduction.
• The proposed system provides a viable alternative for future high-capacity optical networks.
• Further research can explore optimization of the OFDE and ISFA parameters for even greater performance gains.