Multimode SR-BIDI Technology in 40G QSFP+ and 100G QSFP28
Published by: Research & Development Department, Technologie Optic Inc., June 2025
Multimode SR-BIDI (Short Range Bidirectional) technology is a cost-effective and efficient optical transceiver solution designed to support high-speed data transmission over existing multimode fiber (MMF) infrastructure. It enables data center operators to upgrade from 10G to 40G or 100G without the need to replace legacy cabling, making it a popular choice for scalable network expansion.
In the 40G QSFP+ form factor, SR-BIDI transceivers utilize two wavelengths—typically 850 nm and 900 nm—on a single strand of MMF. These wavelengths are transmitted in opposite directions over the same fiber pair, allowing full-duplex communication. This approach contrasts with traditional 40G SR4 transceivers, which require eight fibers (four transmit and four receive). By reducing the fiber count to just two, SR-BIDI significantly lowers cabling complexity and cost.
The 100G QSFP28 SR-BIDI transceivers build on the same principle but operate with four wavelengths in each direction, typically in the 850–940 nm range. These transceivers use advanced wavelength division multiplexing (WDM) to achieve 100G throughput over a duplex MMF link. This innovation allows data centers to leverage existing OM3 or OM4 cabling infrastructure while upgrading to higher bandwidths, avoiding the need for expensive parallel fiber installations.
One of the key advantages of SR-BIDI technology is its backward compatibility and ease of deployment. Since it uses standard LC connectors and duplex MMF, it integrates seamlessly into existing fiber plant layouts. This makes it especially attractive for brownfield deployments where re-cabling is impractical or cost-prohibitive.
However, SR-BIDI does have limitations. Its reach is typically constrained to 70 meters on OM3 and 100 meters on OM4 fiber, which may not be sufficient for larger data centers. Additionally, the use of proprietary wavelength schemes can lead to vendor lock-in, so interoperability should be carefully evaluated during procurement.
In summary, multimode SR-BIDI technology in 40G QSFP+ and 100G QSFP28 transceivers offers a practical path to higher data rates with minimal disruption. By maximizing the utility of existing cabling, it provides a bridge between legacy infrastructure and modern high-speed networks, making it a strategic choice for many enterprise and cloud data centers.