OFDM and PAM comparison using a high baudrate low resolution IM/DD interface for 400G Ethernet access

Area of Science:

• Optical Communications
• Digital Signal Processing
• High-Speed Data Transmission

Background:

• 400G Ethernet requires advanced modulation techniques for high-speed data transmission.
• Intensity Modulation/Direct Detection (IM/DD) interfaces are crucial for cost-effective optical links.
• Orthogonal Frequency Division Multiplexing (OFDM) and Pulse Amplitude Modulation (PAM) are leading candidates for next-generation Ethernet.

Purpose of the Study:

• To compare the performance of OFDM and PAM modulation formats for 400G Ethernet.
• To evaluate the impact of a 3-bit high baudrate IM/DD interface on transmission capabilities.
• To investigate the potential for capacity improvement through adaptation and equalization.

Main Methods:

• Experimental comparison of OFDM and PAM over 10km of single-mode fiber (SMF) at 1550nm.
• Utilizing a 3-bit high baudrate IM/DD interface.
• Employing realistic simulations based on experimental data to extrapolate performance under varied conditions.

Main Results:

• Demonstrated 27Gb/s and 32Gb/s transmission for OFDM and PAM, respectively.
• Achieved 42Gb/s and 64Gb/s for OFDM and PAM with adaptation/equalization.
• Identified quantization noise as a key impairment for OFDM on the considered interface.
• Observed superior performance for PAM under the specified interface limitations.

Conclusions:

• Pulse Amplitude Modulation (PAM) offers better performance than Orthogonal Frequency Division Multiplexing (OFDM) for the evaluated 3-bit IM/DD interface in 400G Ethernet.
• OFDM's performance is significantly impacted by quantization noise at lower resolutions.
• When quantization limitations are relaxed, OFDM demonstrates superior potential, highlighting the importance of interface design in modulation format selection.