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What is the difference between 100G QSFP28 PSM4 and CWDM4 optical modules
Knowledge Base + 2024.01.09

With the advent of the 5G era, significant opportunities have emerged in the optical communication industry. The increasing demand for high-speed data transmission from users has also driven the upgrade from 100G to 400G. Among the 100G optical modules, QSFP28 is the most common type.

I. 100G QSFP28 PSM4 Optical Module

The packaging form of the 100G QSFP28 PSM4 optical module is a hot-swappable QSFP28. It operates within a temperature range of 0°C to 70°C and features DDM digital diagnostic monitoring. Its interface type is a 12-core MPO/MTP (with the middle 4 cores of optical fibers not in use). The maximum power consumption is less than 3.5W. It is a four-channel full-duplex integrated module, with each channel supporting a data rate of 25.78Gbps. The highest data rate is up to 103.125Gbps. It complies with the Multi-Source Agreement (MSA) and is a low-power and high-speed product.

II. 100G QSFP28 CWDM4 Optical Module

The 100G QSFP28 CWDM4 optical module is mainly used in 100G CWDM4 Ethernet and InfiniBand 4x EDR links. It employs Coarse Wavelength Division Multiplexing (CWDM) technology, combining optical signals of different wavelengths (1270nm, 1290nm, 1310nm, and 1330nm) on a single optical fiber for transmission. The transmission rate is 103.1Gbps, and the interface is a duplex LC optical interface. Paired with single-mode OS2 jumpers, the maximum transmission distance can reach 2KM.

III. 100G QSFP28 PSM4 vs. 100G QSFP28 CWDM4 Optical Modules

Cost: CWDM4 optical modules are cheaper than PSM4 optical modules. For longer link distances, CWDM4 only requires two single-mode optical fibers, while PSM4 requires 8-core single-mode optical fibers.

Laser: PSM4 uses four integrated silicon photonics modulators and a distributed feedback laser, while CWDM uses four CWDM non-cooled DFB lasers (wavelength spacing 20nm).

Interface: CWDM4 optical modules use a duplex LC interface, while PSM4 optical modules have an interface type of 8/12-core MPO/MTP.

Central Wavelength: The central wavelength of PSM4 optical modules is 1310nm, while the CWDM4 optical modules have central wavelengths of 1271nm, 1291nm, 1311nm, and 1331nm.

Transmission Distance: PSM4 optical modules and CWDM4 optical modules have four transmission distance options: 500M, 2KM, while the farthest transmission distance for CWDM4 optical modules is 2KM.

Operating Principle: CWDM4 optical modules use Coarse Wavelength Division Multiplexing technology by combining optical signals of four wavelengths on a single optical fiber. PSM4 optical modules use parallel transmission technology by transmitting four identical wavelengths through 4 independent single-mode optical fibers.

Fiber Type: CWDM4 optical modules are connected through duplex single-mode LC fiber jumpers, while PSM4 optical modules use ribbon single-mode MPO fiber jumpers (8/12 cores).

In comparison with PSM4 optical modules, CWDM4 optical modules have advantages not only in terms of lower cost but also in transmission distance. Currently, 100G CWDM4 is the preferred choice for most people.

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