Both 4WDM and CWDM4 belong to 100G QSFP28 series optical transceiver and are certainly related to WDM (wavelength division multiplexing)tech. Maybe there are still people confused about what differences between QSFP28 4WDM and QSFP28 CWDM4 optical transceiver are.
An Introduction to 100G QSFP28 4WDM Optical Transceiver
4WDM(4-Wavelength Wavelength Division Multiplexing) optical module is defined by 4WDM MSA, targeted for longer reaches, lower costs, and lower power consumption, smaller form factor(QSFP28 form factor is usually preferred). 100G QSFP28 4WDM optics have three specifications including 100G QSFP28 4WDM-10, 100G QSFP28 4WDM-20, 100G QSFP28 4WDM-40. QSFP28 4WDM-10 is one type of 100G (4x25G) optical transceivers for the 10 km based on the CWDM4 wavelength grid; QSFP28 4WDM-20 and QSFP28 4WDM-40 are types of 100G (4x25G) optical transceivers respectively for 20kms and 40kms based on the LAN-WDM wavelength grid over duplex single-mode fiber (SMF). With respect to the benefits of 4WDM, its main advantages are lower in cost and power dissipation, and longer in transmission distance.
An Introduction to 100G QSFP28 CWDM4 Optical Transceiver
The QSFP28 100G CWDM4 optical transceiver is a full duplex, photonic-integrated optical transceiver module that provides a high-speed link with a maximum transmission distance of 2km for 100G Ethernet. 100G QSFP CWDM4 is designed for optical communication applications compliant with the QSFP MSA, CWDM4 MSA and portions of IEEE P802.3bm standard. CWDM4 interfaces with LC duplex connectors. It converts 4 input channels of 25Gb/s electrical data to 4 channels of CWDM optical signals and then multiplexes them into a single channel for 100Gb/s optical transmission. Specifically speaking, four lanes with center wavelengths of 1270nm, 1290nm, 1310nm and 1330nm are controlled on the transmitting end. On the receiving end, four lanes of optical data streams are optically de-multiplexed by an integrated optical demultiplexer. With an optical multiplexer and de-multiplexer, one just uses a duplex single-mode fiber to connect two CWDM4 QSFP28 optical transceivers.
A Comparison of QSFP28 4WDM and QSFP28 CWDM4
QSFP28 100G CWDM4 and QSFP28 4WDM are defined with different distances(respectively are 2km/10km/20km/40km) and wavelengths(respectively are CWDM wavelength and LAN WDM wavelength). 2km and 10km use CWDM wavelength. 20km and 40km use LAN WDM wavelength.
With the different size of the CWDM and LAN WDM wavelengths, the wavelength-transmitting TOSA for LAN WDM must be carried with a TEC (Thermo Electric Cooler). As the stable wavelength drifts with temperature, TEC consumes an extra 0.5W of power, so the overall power consumption of optical transceivers with LAN WDM wavelengths will be higher than that of CWDM optical transceivers. More differences between 100G QSFP28 CWDM4 and 100G QSFP28 4WDM are as follows:
By the above comparison of QSFP28 CWDM4 and QSFP28 4WDM optical transceiver, the difference between them is very apparent. For QSFP28 4WDM series optical module, Gigalight has currently pushed out 100G QSFP 4WDM-40 and 100G QSFP 4WDM-20 optical transceiver module, but the QSFP28 4WDM 40km optics is the key one for promotion at present.
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