QSFP 40G LR4 Optical Module: QSFP+ CWDM vs PSM

QSFP 40G LR4 optical modules are widely used in 40G networks, and it contains two types of QSFP 40G LR4 CWDM optical modules and QSFP 40G LR4 PSM optical modules. The former is used to connect WDM links and the latter is used to connect parallel single-mode fiber links, but what is the difference between these two types of modules?

What is CWDM and PSM?

Before exploring the difference between QSFP+ 40G LR4 CWDM modules and 40G PSM LR4 modules, let's understand the terms CWDM and PSM: CWDM (Coarse Wavelength Division Multiplexing) refers to coarse wavelength division multiplexing, CWDM is one of the WDM (wavelength division multiplexing) CWDM is a kind of WDM (Wavelength Division Multiplexing), which can send and receive signals in multiple channels on a single fiber, and is usually used in point-to-point structured cabling in communication networks.

PSM (Parallel Single Mode Fiber) refers to parallel single mode fiber technology. Unlike CWDM optical modules that transmit or receive signals on multiple channels on a single fiber, PSM can receive and transmit signals simultaneously on four parallel fibers.

QSFP 40G LR4 CWDM Optical Module Overview

QSFP 40G LR4 CWDM module usually refers to QSFP+ 40G LR4 optical module, which has LC duplex interface, four independent transceiver channels, each channel support can carry 10Gbps rate, and comply with 40GBASE LR4 and IEEE P802.3ba standard. To minimize dispersion, the QSFP 40G LR4 CWDM optical module must be used with single-mode fiber and has a maximum transmission distance of 10 km.

QSFP 40G LR4 CWDM optical module transmitter uses 4-channel distributed feedback laser (DFB) array to convert 4-channel 10Gbps electrical signal into 4-channel CWDM optical signal, and then multiplex the 4-channel CWDM optical signal into single-channel 40Gbps optical signal for transmission on single-mode fiber; the receiver decomposes and multiplexes the 40Gbps optical signal into 4-channel CWDM optical signal and convert it to 10Gbps electrical signal through optical detector.

QSFP 40G LR4 CWDM optical module works

The four CWDM channels of QSFP 40G LR4 CWDM are centered at 1271nm, 1291nm, 1311nm and 1331nm and are compliant with ITU-T G694.2 standard.

QSFP 40G LR4 PSM Optical Module Overview

The QSFP 40G LR4 PSM optical module is also known as QSFP 40G PLR4 by Arista, Flying Speed (FS) and other optical module vendors. LR4 PSM QSFP+ optical module with MTP/MPO interface provides four independent transmit and receive channels, each operating at 10G on single-mode fiber over a transmission distance of up to 10 km. The transmitter module of QSFP 40G LR4 PSM receives CML-compatible electrical input signals, and then the receiver module converts the parallel input signals to output signals via photodetector arrays. Usually, there are guide pins inside the MTP/MPO interface socket, which can be used to align the correct interface when inserting the module. When users insert the fiber patch cable with MTP/MPO connector into the QSFP+ 40G LR4 PSM optical module, it can avoid the problem of fiber damage because the interface is not aligned.

How QSFP 40G LR4 PSM Optical Module Works

Difference between QSFP 40G LR4 CWDM and PSM optical modules

Both QSFP 40G LR4 CWDM and 40G QSFP LR4 PSM optical modules can be used for long-distance transmission, but there are differences in optical transmitters, MUX/DEMUX, and interfaces. The following table shows the detailed parameters of QSFP 40G LR4 CWDM and PSM optical modules.

QSFP 40G LR4 CWDM/PSM Optical Module FAQ

Q: Can QSFP 40G LR4 CWDM/PSM optical modules be used for 4x10G transmission?

A: The QSFP 40G LR4 CWDM optical module cannot be used for 4x10G transmission because its four wavelengths are transmitted on a pair of single-mode fiber patch cords with LC duplex interfaces, and splitting the wavelengths takes a lot of time. However, the QSFP 40G LR4 PSM optical module can be used for 4x10G transmission because it uses parallel fiber patch cords with MTP/MPO interfaces and can be split into four fiber pairs for transmission.

Q: What is the difference between QSFP+ PSM IR4 optical module and QSFP+ PSM LR4 optical module?

A: Both 40G optical modules are MTP/MPO fiber ribbon interfaces - integrated four-channel optical modules, the only difference is their transmission distance. 40G PSM LR4 has a maximum transmission distance of 10 km over a single-mode fiber patch cable, while 40G PSM IR4 has a maximum transmission distance of only 1.4 km.

Q: What is the difference between QSFP+ CWDM LR4 optical module and QSFP+ LX4/ER4 optical module?

A: The biggest difference between them is the transmission distance. QSFP+ CWDM LR4 on single-mode fiber patch cable has a maximum transmission distance of 10 km, LX4 CWDM QSFP+ supports up to 2 km on single-mode fiber patch cable, and only 150 m on multimode fiber patch cable, while QSFP+ 40G ER4 optical module on single-mode fiber patch cable has a maximum transmission distance of 40 km. transmission distance can reach 40 km on a single-mode fiber patch cable.