100G CWDM4 vs LR4 vs PSM4, What Are the Differences? – QSFPTEK

100G CWDM4 vs LR4 vs PSM4, What Are the Differences?

100G optical transceivers have been widely applied in data centers with the development of optical communication and market demand. In 2018, IEEE released the IEEE 802.3cd protocol and formulated the 100G Ethernet standard. Since then, 100g optical modules have quickly moved towards the commercial stage. 100G QSFP28 CWDM4, 100G QSFP28 LR4, and 100G QSFP28 PSM4 optical modules are three major high-speed interconnection options for 100G Ethernet medium-and-long distance interconnection. What are their differences? This blog will tell how they differ in working principle, structure, specification, cost, etc.

What Is 100G QSFP28 CWDM4? 

100G QSFP28 CWDM4 (Coarse Wavelength Division Multiplexing 4-lane) optical module complies with IEEE 802.3cd. It supports a transmission distance of 2km over single-mode fiber. 

How does CWDM4 work? Through the electrical interface, the electrical signals enter the PCB of the module. After being identified and processed by the chip and MCU, the electrical signals convert to four lines of optical signals through the DML laser of the transmitter. The center wavelengths of the four lines of optical signals are 1271nm, 1291nm, 1311nm, and 1331nm. And then, through the MUX component, the four-lane signals are multiplexed as one strand optical signal into the single-mode fiber and transmitted to the receiver side. On the receiver side, through the DEMUX component, the one-strand optical signal is demultiplexed into four-lane optical signals conversely. And then, the optical signals are converted into weak electrical signals by the PD(Photodiode). Finally, through the TIA(Transimpedance Amplifier ), the weak electrical signals are amplified and then transmitted to the optical module circuit board and the receiver chip. The simplified working diagram of 100G QSFP28 CWDM4 is shown below.

100G QSFP28 CWDM4 Working Diagram

What is 100G QSFP28 LR4?

100G QSFP28 LR4 enables a long-haul transmission distance of 10km over single-mode fiber.

How does 100G LR4 work? Similar to CWDM4, LR4 also uses 4-lane signals, but their wavelengths are different. The centra wavelengths of the LR4 module are 1295nm, 1300nm, 1304nm, and 1309nm. The wavelength interval of 100G LR4 is smaller than CWDM4. The four-lane 4x25G signals also need to experience multiplexing/demultiplexing through the MUX/DEMUX component. However, since the LR4 has a long-distance transmission requirement, it generally uses the EML laser. The working diagram of the LR4 is shown below.

100G QSFP28 LR4 Working Diagram

What is 100G QSFP28 PSM4?

100G QSFP28 PSM4 (Parallel Single Mode Quad) supports short and middle-range transmission of 500m over single-mode fiber. The special is 100G PSM4 uses MTP/MPO connector and it works on MPO fiber optic cable. Needn’t multiplexing and demultiplexing, PSM4 uses four integrated silicon photon modulators and a DFB laser to transmit and receive 100G data rates at four single channels. The working diagram of the 100G PSM4 is shown below.

100G QSFP28 PSM4 Working Diagram

CWDM4 vs LR4 vs PSM4, What Are the Differences?

Distance: 100G LR4 enables a long-range transmission of 10km. 100G CWDM4 support a mid-range of 2km, and 100G PSM4 supprt a short and mid-range of 500m.

Connector: Both 100G CWDM4 and LR4 use duplex LC connectors, whereas PSM4 uses MTP/MPO connectors.

Cables: All of the three work on single-mode fiber, but CWDM4 and LR4 use LC optical fiber cables while the PSM4 uses MTP/MPO fiber cables. And since 100G PSM4 transmits 100G data rates through four individual channels and is structured with an MTP/MPO connector, it supports a breakout connectivity mode by using an MTP to 4xLC breakout fiber optic cable, which connects one 100G QSFP28 PSM4 transceivers at one end and connects four 25G SFP28 optical modules at the other end. Therefore, the 100G PSM4 transceiver is considered an ideal solution for 25G to 100G upgrading.

Wavelength: Both CWDM4 and LR4 have four-channel wavelengths. The centra wavelengths of 100G CWDM4 are 1271nm, 1291nm, 1311nm, and 1331nm, whereas 100G LR4 are 1295nm, 1300nm, 1304nm, and 1309nm. The wavelength interval of LR4 is smaller than CWDM4. And the wavelength of 100G PSM4 is 1310nm.

Cost: Since 100G QSFP28 LR4 has the highest transmission distance requirement, it has higher requirements for optical components, such as the optical laser. Naturally, 100G LR4 is more costly than CWDM4 and PSM4. All of 100G CWDM4, LR4, PSM4 are available at reasonable price in QSFPTEK.


100G QSFP28 CWDM4, LR4, and PSM4 have similarities and also many differences. Hope this article will help you distinguish them effectively. With the development of 5G marketing, the demand for 100G QSFP28 transceivers must be continually increasing. It is important to arrange suitable 100G QSFP28 optics for data centers in advance. QSFPTEK provides a comprehensive product line of 100G high-speed interconnection products. Besides optical products, we are also here to give you help with optical communication solutions. Welcome to consult via sales@qsfptek.com.

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