No-guard-interval coherent optical OFDM with self-tuning receiver

Area of Science:

• Optical communications
• Signal processing
• Telecommunications engineering

Background:

• Coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems are crucial for high-capacity optical networks.
• Traditional CO-OFDM systems often require complex digital filtering and baseband mixing for subcarrier demultiplexing and equalization.
• Guard intervals are typically used to mitigate inter-symbol interference but reduce spectral efficiency.

Purpose of the Study:

• To propose and demonstrate a novel no-guard-interval (No-GI) CO-OFDM system.
• To reduce computational complexity in optical communication systems.
• To enhance spectral efficiency and transmission performance in optical networks.

Main Methods:

• Utilizing Fractionally-Spaced Time-Domain Equalizers (FS-TDE) for simultaneous subcarrier demultiplexing and equalization.
• Employing Least-Mean-Squares (LMS) algorithms to tune each FS-TDE to its specific subcarrier.
• Transmitting short, unique training sequences on each subcarrier for adaptive blind equalization.

Main Results:

• Demonstrated error-free transmission over 800 km using a three-subcarrier 30 Gb/s system and a five-subcarrier 33.33 Gb/s system.
• Achieved required OSNRs of 8.6 dB and 9.3 dB for a BER of 10⁻³, within 1.5 dB of the theoretical limit.
• Eliminated the need for digital filtering and baseband mixing, leading to significant computational efficiency.

Conclusions:

• The proposed No-GI CO-OFDM system with FS-TDE offers a computationally efficient and high-performance solution for optical communication.
• The system achieves excellent transmission quality, approaching theoretical limits, over long fiber distances.
• This technology has the potential to significantly advance the capacity and efficiency of future optical networks.