In the rapidly expanding landscape of 5G backhaul and metropolitan data center interconnects (DCI), fiber is a finite and expensive resource. Many service providers and enterprises are facing "fiber exhaustion," where existing underground conduits are at full capacity. The traditional dual-fiber approach—one for transmit (TX) and one for receive (RX)—is increasingly seen as inefficient. This technical guide explores how QSFP28 100G BIDI 80KM and 40KM solutions allow operators to double their bandwidth instantly using a single strand of fiber, providing a high-ROI path for 2026 network upgrades.
Bidirectional (BIDI) technology utilizes Wavelength Division Multiplexing (WDM) to combine TX and RX signals onto one fiber. By using two different wavelengths—typically 1271nm and 1331nm—the module can send and receive data simultaneously without interference.
For municipal rings and campus interconnects, the QSFP28 100G BIDI 40KM offers a seamless replacement for standard QSFP28 100G ER4. While the ER4 requires a fiber pair, the BIDI 40KM achieves the same distance on a single strand. This is particularly effective for connecting edge computing hubs where leasing extra fiber pairs would incur significant monthly recurring costs (MRC).
The QSFP28 100G BIDI 80KM represents the pinnacle of long-reach single-fiber engineering. Utilizing high-sensitivity APD receivers and stabilized EML lasers, it maintains signal integrity over 80km of G.652 single-mode fiber. This module is essential for rural broadband expansion and long-haul ISP backhaul, offering a carrier-grade alternative to the dual-fiber QSFP28 100G ZR4.
As the single-fiber links aggregate at the central office or core data center, the transition to 400G becomes necessary to manage the cumulative traffic. The synergy between 100G BIDI and 400G form factors creates a highly scalable network hierarchy.
In the core, the QSFP112 form factor allows for massive density. A single 400G port can handle the traffic from four 100G BIDI 80KM regional links. Because the QSFP112 uses 112G SerDes technology, it offers lower latency and better power efficiency, making it the ideal companion for high-performance 100G edge deployments.
While BIDI handles the distance, the QSFP56-DD-400G-VSR4 and OSFP112-400G-VSR4 manage the intra-rack connectivity within the DCI hub. The VSR4 modules provide the high-speed interconnects needed for the switches and servers that process the data arriving from the regional 80km spans. Using QSFP56-DD-400G-DR4 for 500m links further ensures that the single-mode fiber consistency is maintained across the entire network architecture.
Sourcing 100G BIDI modules requires a rigorous audit of the physical layer to ensure 24/7 uptime. Key metrics include:
Wavelength Isolation: High-quality internal filters are required in the QSFP28 100G BIDI 80KM to prevent "cross-talk" between the 1271nm and 1331nm channels over long distances.
Optical Budget Management: For spans reaching the 80km limit, auditing the fiber loss (dB per km) and splice quality is critical. If the link is shorter, such as 10km, use an attenuator to protect the sensitive APD receiver.
EEPROM Interoperability: Ensure the modules are coded for your specific switch platform (e.g., Cisco, Arista, Juniper) to maintain full DOM/DDM telemetry.
A: No. BIDI modules work in pairs. You must use a "U" (Upstream) module at one end and a "D" (Downstream) module at the other (e.g., 1271nm-TX/1331nm-RX paired with 1331nm-TX/1271nm-RX).
A: Most 400G breakout ports (like QSFP56-DD-400G-DR4) are designed for dual-fiber or parallel fiber. To connect a BIDI 100G module, you would typically need a 100G native port or a specialized single-fiber patch system.
A: For the QSFP28 100G 100KM or ZR4, the typical power budget is around 27-30dB. For an 80km-100km span, your fiber loss should ideally be 0.25dB/km or lower to ensure a stable link margin.
Whether you are combating fiber scarcity with QSFP28 100G BIDI 80KM or building a high-density 400G core with QSFP112, the integrity of the optical link determines the reliability of your entire service. Univiso provides lab-vetted, carrier-grade optics that help you maximize every strand of fiber in your plant. By choosing the right BIDI and 400G solutions, you protect your OpEx and ensure your network is ready for the bandwidth demands of tomorrow.
Running out of fiber in your metro network? Contact Univiso’s technical team for a free link budget audit and a quote on our high-performance 100G BIDI and 400G optical solutions.
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