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Fiber optic transceiver, as an important optical component, is widely used for transmitting and receiving optical signals to facilitate communication. To meet the increasing demand for higher speed and bandwidth, fiber optic transceiver has continued to evolve, from SFP, 10G SFP+, 40G QSFP+ to 100G CFP and QSFP28. Among them, 100G QSFP28 transceiver is now very popular on the market. We know that fiber optic transceiver can be divided into singlemode transceiver and multimode transceiver, so this article will make a comparison between singlemode QSFP28 and multimode QSFP28.

Singlemode QSFP28

Singlemode QSFP28 is usually used with singlemode fiber. We know that the core of singlemode fiber is smaller and the laser wavelength is narrower. Therefore, singlemode fiber permits the transmission of signals at higher bandwidth thus facilitating the data transmission at a longer distance. Singlemode QSFP28 mainly works at 1310nm wavelength and is commonly used for long distance data transmission. There are different types of singlemode QSFP28 which can achieve different data transmission distance, such as 100GBASE-PSM4 QSFP28 can support 500 meters, 100GBASE-CWDM4 QSFP28 can support 2 kilometers and 100GBASE-LR4 QSFP28 can support 10 kilometers. And there are some other differences among them. The 100GBASE-PSM4 QSFP28 is designed with 12-fiber MTP connector interface, so it is used with MTP cable; while 100GBASE-CWDM4 QSFP28 and 100GBASE-LR4 QSFP28 are structured with duplex LC connector interface, so they are used with duplex LC patch cable.

Multimode QSFP28

Multimode QSFP28 is usually used with multimode fiber. The core of multimode fiber is much bigger and multimode fiber usually uses a wider wavelength of light. In addition, it permits the use of inexpensive LED light sources and alignment of the connectors with a coupling that is less critical than that of singlemode fiber. As a result, fiber optics used over multimode fiber have a higher capability to gather light from the laser and are cheaper. Multimode QSFP28 mostly works at 850nm wavelength and is used for short optical link length, like 70 meters over OM3 and 100 meters over OM4. There is only one type of multimode QSFP28—100GBASE-SR4 QSFP28. It has 12-fiber MTP connector interface, so it has to be used with MTP cable.

Comparison Between Singlemode QSFP28 and Multimode QSFP28

From the above, we can clearly see some differences between singlemode QSFP28 and multimode QSFP28. This part will make a summary from several aspects.

Transmission media: Singlemode QSFP28 works with singlemode fiber while multimode QSFP28 works with multimode fiber. It is noted that 100GBASE-PSM4 QSFP28 is used with singleomde MTP cable and 100GBASE-SR4 QSFP28 is used with multimode MTP cable; while 100GBASE-CWDM4 QSFP28 and 100GBASE-LR4 QSFP28 are used with singlemode duplex LC patch cable.

Transmission distance: Singlemode QSFP28 can reach 500 meters, 2 kilometers and 10 kilometers while multimode QSFP28 is able to support 100 meters optical link.

Power consumption: Multimode QSFP28 consumes less power than singlemode QSFP28, which is an important consideration especially when assessing the cost of powering and cooling a data center.

Cost: Singlemode QSFP28 are nearly two or three times higher in price when compared to multimode QSFP28. Because singlemode fiber requires more expensive laser sources and costs more to make as it is more “fragile”.

Compatibility issue: When it comes to issues dealing with compatibility, the two types of QSFP28 transceivers are not compatible due to the differences in fiber core size and wavelengths.

Conclusion

This article makes a comparison between singlemode QSFP28 and multimode QSFP28. Both of them have their own advantages in data center applications. As for which one to choose, it all depends on your specific requirement of deployment. There are various QSFP28 optics on the market.