Do you know the difference between 40G QSFP+ CWDM and PSM?
363 2023-05-11
QSFP 40G LR4 optical module is widely used in 40G network, it includes two types of QSFP 40G LR4 CWDM optical module and QSFP 40G LR4 PSM optical module.
What are CWDM and PSM?
CWDM (Coarse Wavelength Division Multiplexing) refers to coarse wavelength division multiplexing. CWDM is a kind of WDM (wavelength division multiplexing). It can send and receive signals on multiple channels on a single optical fiber. It is usually used in communication networks. point-to-point structured wiring.
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 simultaneously receive and send signals on four parallel fibers.
Overview of QSFP 40G LR4 CWDM Optical Transceiver
QSFP 40G LR4 CWDM module usually refers to QSFP+ 40G LR4 optical module, which has LC duplex interface, four independent transceiver channels, and each channel supports a rate of 10Gbps. In order to minimize dispersion, the QSFP 40G LR4 CWDM optical module must be used with single-mode fiber, and the maximum transmission distance is 10 kilometers.
The transmitter of the QSFP 40G LR4 CWDM optical module uses a 4-channel distributed feedback laser (DFB) array to convert 4-channel 10Gbps electrical signals into 4-channel CWDM optical signals, and then multiplex the 4-channel CWDM optical signals into a single-channel 40Gbps optical signal Transmission is carried out on single-mode optical fiber; the receiving end de-multiplexer the 40Gbps optical signal into 4-channel CWDM optical signal and converts it into a 10Gbps electrical signal through the optical detector.
The central wavelengths of the 4 CWDM channels of QSFP 40G LR4 CWDM are 1271nm, 1291nm, 1311nm and 1331nm, which conform to the ITU-T G694.2 standard.

Overview of QSFP 40G LR4 PSM optical module 
QSFP 40G LR4 PSM optical module has MTP/MPO interface, provides 4 independent transmission and reception channels, each channel can run at 10G rate on single-mode fiber, and the transmission distance is up to 10 kilometers. The transmitter module of the QSFP 40G LR4 PSM receives an electrical input signal compatible with CML, and then the receiver module converts the parallel input signal into an output signal through a photo detector array, and the output signal of the receiver module is also compatible with CML. 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 the user inserts the fiber jumper with the MTP/MPO connector into the QSFP+ 40G LR4 PSM optical module, it can avoid The problem of fiber damage due to misalignment of the interface.
You can choose a suitable optical module according to your needs.