What is the difference between 40G QSFP+ singlemode and QSFP+ multimode?

Singlemode QSFP+ and multimode QSFP+, here, refer to QSFP+ optical modules that work on different types of optical fiber, i.e., singlemode QSFP+ is used with singlemode optical fiber, while multimode QSFP+ is used with multimode optical fiber. So what is the difference between them?

Product Application:

Multimode QSFP+: Used for rack-to-rack, data center, 40G Ethernet, Infiniband QDR, DDR and SDR for multimode applications.

Singlemode QSFP+: Used in singlemode applications for high-speed interconnections between data centers and Internet Exchange Points, between switches, routers, and transport devices for servers, rack-to-rack, panel-to-panel, and Infiniband SDR, DDR, and QDR applications for 40G-LR4 Ethernet links.

What should we pay attention to when using multimode and singlemode QSFP+ optical modules?

◆ Make sure that the QSFP+ optical modules connected at both ends of the fiber patch cable are of the same wavelength. An easy way to do this is that the pull ring color of the module must be the same.

◆ In general, to ensure the accuracy of data, short-wave QSFP+ optical modules are connected to multi-mode fiber (i.e., lake blue OM3 or OM4 fiber optic patch cords), while long-wave QSFP+ optical modules are connected to single-mode fiber (i.e., yellow fiber optic patch cords).

◆ Do not over bend or wrap the fiber optic cable when using it. This will increase the light degradation during transmission.

◆ When the QSFP+ optical module is not in use, the optical hole must be protected with a dust plug.

When we choose the QSFP+ optical module, we must confirm the transmission distance and wavelength to be used, which will help us to choose the right QSFP+ optical module more effectively. In addition, the cost of optical modules is increasing over time, which will put pressure on the budget of many users. To save more resources, we can choose low-cost compatible optical modules without sacrificing any quality or reliability.