Single-fiber bidirectional 400G technology support

Single-fiber bidirectional 400G technology enables full-duplex 400 Gbps transmission over a single optical fiber using coherent transceivers and wavelength multiplexing.

Overview

Single-fiber bidirectional (BiDi) 400G technology allows simultaneous transmission and reception on a single fiber strand, effectively halving fiber usage compared to conventional two-fiber systems . This approach is particularly valuable in fiber-constrained environments, such as urban access networks, data centers, and high-capacity backhaul links.

Technical Approaches

1. Coherent Digital Subcarrier Multiplexing (DSCM): Experimental demonstrations, such as the Allegro EU Project, achieved 400 Gb/s bidirectional transmission over a single fiber using DSCM with subcarrier interleaving to mitigate Rayleigh back-scattering, maintaining less than 1 dB power penalty over distances up to 20 km .
2. Dual-Laser Coherent Transceivers: Commercial solutions, like the Cisco 400G Digital Coherent BiDi CFP2, use a dual-laser approach to separate transmit (Tx) and receive (Rx) wavelengths on a single fiber. These transceivers support software-configurable modulation and line rates, enabling flexible deployment for different reach and capacity requirements .
3. DWDM Single-Core BiDi Solutions: Dense Wavelength Division Multiplexing (DWDM) devices can support 4 to 8 wavelengths at 400G over a single fiber, integrating with standard Ethernet, Fibre Channel, and OTU client interfaces. This allows cost-effective use of dark fiber and supports point-to-point, ring, or linear add-drop topologies .

Benefits

• Fiber Savings: Reduces fiber consumption by 50%, lowering operational and leasing costs .
• Full-Duplex 400G: Supports simultaneous bidirectional traffic at 400 Gbps on one fiber strand .
• Flexible Modulation: Software-configurable modulation formats (e.g., QPSK, 16-QAM) optimize the trade-off between reach and capacity .
• Deployment Efficiency: Compatible with existing CFP2 or QSFP-DD form factors, enabling integration with current network hardware .

Applications

• Data Center Interconnects (DCI): High-capacity links between racks or sites with limited fiber availability.
• Metro and Access Networks: Fiber-constrained urban deployments benefit from reduced fiber usage.
• Backhaul Networks: Supports 400G aggregation over single-fiber links, reducing infrastructure costs.

Summary

Single-fiber bidirectional 400G technology combines coherent optics, dual-laser transceivers, and wavelength multiplexing to deliver full-duplex 400 Gbps over a single fiber. It offers significant fiber savings, flexible modulation, and cost-effective deployment, making it suitable for data centers, metro networks, and high-capacity backhaul applications .