BiDi Optics: A New Solution for 40GbE Transmission


The number of cloud applications, virtualized workloads, coupled with a host of devices housed in data centers, all these increase at an amazing speed in this technological world. When walking past the data center, you may hear such a call for more capacity and greater performance from your servers. This call doesn’t slack with everyday passing, but it grows vigorously. In order to accommodate these applications that require higher data transport rates, it’s not advised to sit still for some enterprises. If your data center hasn’t shifted from 10Gbps to 40Gbps infrastructure, now it’s your chance by deploying 40GbE with BiDi QSFP+ optics (ie. Cisco QSFP-40G-SR-BD) at lower costs than using 40G QSFP+ optics.

What Is BiDi?

BiDi stands for “bi-directional”. This new BiDi optical technology is available only from Cisco. Cisco BiDi optics is a standard QSFP, MSA-compliant optical connector that can operate with any Cisco switch that supports QSFP modules and connects with any vendor’s standards-compliant equipment. It uses two different wavelengths on the same fiber, with one wavelength headed in one direction and the second wavelength traveling in the other direction.

How Does 40G BiDi Optics Work?

BiDi technology uses specialized, multilayer, thin-film dielectric coating and lensing, which allows components to pass and reflect optical signals at the same time. And it uses Bidirectional Optical Sub-Assembly (BOSA) technology to support two wavelengths (20Gbps total) on each fiber. Each QSFP can deliver 40Gbps over the same duplex multi-mode fiber (MMF) cabling you use right now.

Inside this module, four channels each of 10Gbps signal transmission and reception are converted to two bidirectional channels of 20Gbps signals over two different wavelengths (usually 850nm and 900nm) respectively. BiDi optics represents a new solution to deploy 40GbE that meets all 40GBASE-SR4 performance criteria. The signal is sent to a target device via 850nm on one fiber. Then the signal from the target device is sent via 850nm on the other fiber. This also works for signals on 900nm, as is shown in the following image. To put it simply, BiDi provides 40GbE on two MMFs and duplex LC connectors, just like the existing 10G infrastructure that is deployed today.

BiDi Optics: A New Solution for 40GbE Transmission 1

40G BiDi Optics – Easier 40GbE Deployment

With 40G BiDi, upgrading from 10G to 40G is much easier: to replace the existing 10G optical modules with 40G BiDi optical modules.

For instance, in 10GbE transmission, 10GBASE-SR optics uses two MMFs and duplex LC connectors for transmitting on one of the fibers and receiving on the other fiber. As for current 40GbE, 40GBASE-SR4 (eg. 40G-QSFP-SR4) uses four 10G lanes to support 40G through 12-fiber trunks and patch cords terminated with MPO connectors., with four for receiving, four for transmitting and the rest four fibers unused. This difference requires the change of infrastructure when upgrading 10G network to 40G network. If the 40G BiDi QSFP+ transceiver for short distance also using the duplex transmission mode, things would be much easier. That’s why choose 40G BiDi QSFP transceiver.

BiDi Optics: A New Solution for 40GbE Transmission 2

Besides, with 40G QSFP+ optics only using 8 of the 12 fibers in a 12-fiber trunk, this results in the disappearance of one third of the total bandwidth available to a data center when migrating from 10G to 40GbE. If select 40G BiDi QSFP+ optics, this bandwidth disappearance can be avoided, since only a pair of cables are used.

40G BiDi Optics – Cost- & Time-saving Solution

Just as what has been mentioned above, 40G BiDi transceiver modules give you 40Gbps over your existing 10Gbps cable plant, meaning that you can connect your top-of-rack switches using the same MMF and patch cables you are using right now, to get 40Gbps performance. If you were building a new 40Gbps data center fabric the traditional way, you would need to run 8 MMF strands between your access and aggregation layers. What a costly project. But with BiDi optics, there is no need for expensive 40G migration cassettes, and no need to add additional fiber infrastructure.


In an upgrading project, cost and time are the critical factors which should be considered. 40G BiDi optical modules offer another way to deploy 40G Ethernet: it’s less costly to implement 40G Ethernet using two MMFs (vs. the 8 fibers required by 40GBASE-SR4). With 40G BiDi optics, 40Gbps performance is no longer a luxury. With 40G BiDi optics, there is no need to rewire your data center to get the next level of capacity and performance. With 40G BiDi optics, it’s possible to upgrade capacity without having to upgrade cabling, a huge cost saving. Fiberstore supplies various 40G BiDi QSFP+ transceivers for your smooth 40G migration. You can visit Fiberstore for more information about 40G BiDi transceiver modules.

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