Single-fiber bidirectional (BiDi) NRZ systems transmit and receive data simultaneously over a single optical fiber using different wavelengths, effectively doubling fiber utilization while maintaining NRZ modulation.

Overview of Single-Fiber BiDi NRZ

Single-fiber bidirectional (BiDi) systems allow simultaneous upstream and downstream data transmission over a single optical fiber by using wavelength-division multiplexing (WDM). In NRZ (Non-Return-to-Zero) modulation, each bit is represented by a distinct voltage or light level without returning to zero between bits, which simplifies transmitter and receiver design and reduces bandwidth requirements compared to multi-level formats like PAM4 .

How BiDi NRZ Works

• Wavelength Assignment: Two different wavelengths are used for opposite directions. For example, one wavelength (e.g., 1310 nm) transmits from point A to B, while another (e.g., 1490 nm) transmits from B to A .
• Transceivers: BiDi transceivers contain two lasers—one for transmitting and one for receiving—allowing full-duplex communication on a single fiber .
• Mux/Demux Components: Multi-wavelength BiDi systems use optical multiplexers/demultiplexers (Mux/Demux) with thin-film filters or optical zig-zag glass blocks to separate wavelengths and reduce interference .

Advantages

• Fiber Savings: Reduces fiber usage by 50% compared to traditional duplex systems, which require two fibers for bidirectional communication .
• Cost Efficiency: Minimizes infrastructure costs and simplifies network deployment, especially in dense urban or data-center environments .
• Scalability: Multi-wavelength BiDi modules can increase capacity to 100G, 200G, or 400G over a single fiber while maintaining NRZ or higher-order modulation formats .

Performance and Applications

• Transmission Distance: Single-fiber BiDi NRZ systems can achieve distances up to 40 km for 100 Gb/s links using standard single-mode fiber (SMF) without complex dispersion compensation .
• Data Rates: NRZ is suitable for 1G, 10G, 25G, and 50G per wavelength, while multi-wavelength BiDi systems can combine multiple NRZ channels to reach 100 Gb/s or higher .
• Use Cases: Ideal for data-center interconnects (DCIs), 6G mobile backhaul, and metro networks, where fiber resources are limited and high-speed bidirectional communication is required .

Comparison with PAM4

While NRZ uses two levels per bit, PAM4 uses four levels, effectively doubling the data rate per wavelength but increasing system complexity and sensitivity to noise. NRZ remains simpler and more robust for medium-distance single-fiber BiDi links, making it a practical choice for many Mexican network deployments where cost and reliability are priorities .

Summary

Mexican Single-Fiber Bidirectional NRZ systems leverage WDM to transmit and receive data simultaneously over a single fiber, offering fiber savings, cost efficiency, and reliable medium-distance performance. They are widely applicable in data centers, metro networks, and mobile backhaul, and can be scaled with multi-wavelength BiDi modules to meet growing bandwidth demands while maintaining the simplicity of NRZ modulation .