Tag Archives: QSFP-40G-CSR4

What Is the Difference Between Singlemode QSFP+ and Multimode QSFP+?


The singlemode and multimode QSFP+ here mean the transceivers which work at different types of optical fibers, ie singlemode type will work with singlemode fiber, while multimode one will work with multimode fiber. So, what’s the different between them? And what should we notice when using them? Which one should I choose? In this article, we will have a discussion around this topic.

Singlemode vs. Multimode QSFP+

  • Singlemode

Singlemode fiber (SMF) has much tighter tolerances for optics used. The core is smaller and the laser wavelength is narrower. This means that SMF has the capability for higher bandwidth and much longer distances in transmission. Singlemode QSFP+ works mainly in 1310nm wavelength and is mostly used in long distances transmission. There are many different types of them, and different type can achieve different transmission distance, such as 500m, 1km, 2km, 10km and 40km. he color of compatible fiber optic patch cord is yellow. SMF QSFP+ usually uses duplex LC connector, but there also are some types use MPO/MTP connector.

Singlemode QSFP+

  • Multimode

Multimode fiber (MMF) uses a much bigger core and usually uses a longer wavelength of light. Because of this, the optics used in MMF have a higher capability to gather light from the laser. In practical terms, this means the optics are cheaper. The common multimode QSFP+ works in 850nm wavelength and is only used for short distance transmission reaching 100m and 500m. Though it’s not able to transport for long distance, it can transport many kind of optical signals. It usually uses MPO/MTP connector, but some SMF&MMF ones can also use duplex LC connector.

Multimode QSFP+

Choose a Singlemode or Multimode QSFP+?
SMF and MMF QSFP+ may have different transmission distance and connectors, which is the most important factors you should consider when to make a decision. In the table below, I display the specifications of some main SMF and MMF 40G modules. Hope to help you to choose the right one for your network.

Type Wavelength Fiber and Distance Connector Original model
40GBASE-SR4  4x850nm 100m(OM3) 150m(OM4) Male MPO Cisco 40G-SR4
40GBASE-CSR4  4x850nm 300m(OM3) 400m(OM4) Male MPO Cisco 40G-CSR4
40GBASE-LX4  1270,1290,1310,1330 nm 100m(OM3) 150m(OM4) 2km(SMF) Duplex LC Juniper JNP-QSFP-40G-LX4
40GBASE Universal  1270,1290,1310,1330 nm 150m(OM3) 150m(OM4) 500m(SMF) Duplex LC Arista QSFP-40G-UNIV
40GBASE-PLRL4  4x1310nm 1km(SMF) Male MPO Arista QSFP-40G-PLRL4
4x10GBASE-LR Lite 4x1310nm 2km(SMF) Male MPO Finisar FTL4P1QL1C
40GBASE-LR4  1270,1290,1310,1330 nm 10km(SMF) Duplex LC Cisco 40G-LR4
40GBASE-LR4-Lite 1270,1290,1310,1330 nm 2km(SMF) Duplex LC Finisar FTL4C1QL1C
40GBASE-LRL4  1270,1290,1310,1330 nm 1km(SMF) Duplex LC Arista 40G-LRL4
40GBASE-PLR4  4x1310nm 10km(SMF) Male MPO Arista 40G-PLR4
40GBASE-ER4  1270,1290,1310,1330 nm 40km(SMF) Duplex LC Cisco 40G-ER4

What Should We Notice When Using Singlemode & Multimode QSFP+

  • Ensure that the transceiver in both ends of the fiber patch cord are of the same wavelength. A simple method is that the color of the modules must be consistent.
  • In general, to ensure the data accuracy, short-wave QSFP+ modules use with multimode fibers (ie. aqua OM3 or OM4 fiber patch cord), while long-wave modules use with single-mode fiber (ie. yellow fiber patch cord).
  • Do not over bend or winding fiber optic cables when using them. This will increase the attenuation of light in transit.
  • If you don’t use this module, you must use the dust plug to protect the optical bore.

When we choosing the QSFP module, we must confirm the transmission distance and wavelength we want to use in. This will help us to choose the right QSFP modules more efficiently. In addition, the costs for transceiver modules which keep adding up over time will be a budget pressure for many users. To save more, we can choose the compatible module without sacrificing any quality or reliability but only with a low cost. Fiberstore, an excellent supplier, supplies 100% compatible fiber optic transceiver modules of many brands, such as Cisco, HP, Juniper, Brocade, Finisar etc. with a incredible discount that may be a good choice for you.

Related Article: QSFP BiDi – 40GbE Over LC Duplex Multimode Fiber

Differences Between 40G QSFP LRL4 and PLRL4 Modules


Data centers regularly undertake their own great migration, to ever-higher-speed networks. Since IEEE 802.3ba Ethernet standard introduced the 40 Gigabit Ethernet in 2010, 40G has been an unstoppable tendency in the future. At present, QSFP, CXP and CFP are three 40G transceiver module options. Among QSFP is the most common one. In terms of 40G QSFP modules, there are many different types available, such as QSFP-40G-CSR4, QSFP-40G-LR4, QSFP-40G-SR4, QSFP-40G-LRL4 and QSFP-40G-PLRL4 etc. We can see that QSFP-40G-LRL4 and QSFP-40G-PLRL4 look like similar. One difference is QSFP-40G-PLRL4 has a word “P”. So, what does this word mean? This passage will explain it and tell you some other differences between them.

In fact, QSFP PLRL4 refers to QSFP parallel LRL4. In general, digital data transmission can occur in two basic modes: serial or parallel. In parallel transmission, multiple bits are sent simultaneously on different channels within the same cable, or radio path, and synchronized to a clock. However, in serial transmission, bits are sent sequentially on the same channel which reduces costs for wire but also slows the speed of transmission. So 40G QSFP PLRL4 module uses parallel transmission which is achieved with MPO/MTP multifiber connectors. 40G QSFP LRL4 module uses serial transmission of which the connector is LC.


For these two modules both operate on 40GBASE-LRL4 standard, they actually both support link lengths of up to 1 kilometers over a standard pair of G.652 single-mode fiber. But besides the optical connectors they used, the wavelength and the interoperability of them are also different.

Wavelength (nm)

  • 40GBASE-LRL4 QSFP (Multiplexing and demultiplexing of the four wavelengths): 1270 nm, 1290 nm, 1310 nm, 1330 nm
  • 40GBASE-PLRL4 QSFP: 4 x 1310nm


  • For 40GBASE-LRL4 QSFP, the 40 Gigabit Ethernet signal is carried over four wavelengths. Multiplexing and demultiplexing of the four wavelengths are managed within the device.
  • For 40GBASE-PLRL4 QSFP, the 4x10G connectivity is achieved using an external 12-fiber parallel to 2-fiber duplex breakout cable, which connects the 40GBASE-LR4 module to four 10GBASE-LR optical interfaces. QSFP-40G-PLRL4 is optimized to guarantee interoperability with any IEEE 40GBase-LR4 and 10GBase-LR (in 4x10G mode).

All the comparisons between 40G QSFP LRL4 and PLRL4 modules above are listed in the following table. From this chart, you may get a more intuitive understanding.

Name Distance Wavelength Connector Interoperability
QSFP-40G-LRL4 1km (G.652) 1270nm, 1290nm, 1310nm, 1330nm LC 4-Channel CWDM Mux/Demux inside with SFP+ CWDM
QSFP-40G-PLRL4 1km (G.652) 4 x 1310nm MPO/MTP 4 x 10G operations on SMF with SFP+ LR

After reading this passage, you may know more about these two kinds of QSFP modules. Each one of them has their own features, which can satisfy different applications. You should choose the most suitable module for your use. fs.com has a large number of QSFP-40G-PLR4 and QSFP-40G-PLRL4 modules in stock with super quality and competitive price. You can visit that website to  choose your optics.

Related Article: 40G Transceiver Module: QSFP+ Module And CFP Module