As we know, the most commonly used solution for 40GbE multimode application is based on the interface standard QSFP-40G-SR4, which is running over multimode fiber (MMF) pre-terminated with 8-fiber MPO/MTP connectors. This causes a problem of fiber waste of the existing 10GbE infrastructure. So, how to reuse the exsiting 10GbE LC MMF cabling to achieve 40GbE network? The 40G BiDi QSFP+ transceiver may be an ideal choice for this requirement.
Today’s data centers are architected around 10 GbE, primarily focusing on 10GBASE-SR using duplex MMF with LC connectors. Data center operators want to upgrade from 10G to 40/100G without touching the duplex MMF infrastructure. This is becoming one of the data center interconnect trends. In order to meet this demand, the 40GbE BiDi QSFP+ transceiver has launched to the market. It offers users an option to run 40 GbE over duplex MMF with LC connector.
How can 40G BiDi QSFP+ transceiver do this? Now, turn to its working principle. As we know, 40GBASE-SR4 QSFP+ optics use independent lanes for transmit and receive (4 x Tx and 4 x Rx). The data rate of each lane is 10 Gbps. Thus, 8-fiber strands (8-fiber MPO/MTP) are required for using this optics. But for 40GbE BiDi QSFP+, as shown in the picture below, only two lanes are required, for each of 20Gbps. Each transmitted and received simultaneously on two wavelengths over a single MMF, enabling an aggregated 40Gbps link over a two-strand multimode fiber connection.
40GBASE-SR4 QSFP+ Working Principle
40GbE BiDi QSFP+ Working Principle
Obviously, 40G BiDi QSFP+ transceiver has the absolute superiority on using the duplex MMF. However, some users may care the cost since that the cost of a 40G BiDi QSFP+ transceiver is much expensive than a 40GBASE-SR4 QSFP+ optics. But on the whole cost, you may find that the 40G QSFP+ BiDi transceiver is more cost-effective. Because you can save more on the fiber cost since the cost of fiber optic cables is also a big spending in your whole project.
| Optics | Channel | Data Rate per Channel | Fiber Type | Price |
| 40GBASE-SR4 QSFP+ | 4 | 10 Gbps | 8-fiber MPO/MTP MMF | US$ 65.00 |
| 40GbE BiDi QSFP+ | 2 | 20 Gbps | Duplex LC MMF | US$ 300.00 |
If you are still finding a way that can offer maximum reutilization of existing 10GbE fiber plant on 40/100G, help you achieve the 40GbE migration in a more cost-effective manner, the 40GbE BiDi QSFP+ transceiver may be your preferred choice. And in FS.COM, you can always find the high-performance transceivers in the most competitive price.
