What is the difference between 100G CWDM4 and 100G PSM4?

1. QSFP28 100G CWDM4 Optical Module

The QSFP28 100G CWDM4 optical module uses the QSFP28 form factor. It is a 100G transmission mode based on single-mode Coarse Wavelength Division Multiplexing (CWDM) technology. It is hot-swappable and employs a duplex LC interface. It transmits optical signals at four central wavelengths: 1271nm, 1291nm, 1311nm, and 1331nm. Each wavelength transmits 25G. Using CWDM technology, the QSFP28 100G CWDM4 optical module multiplexes these four central wavelengths onto a single-mode fiber for transmission. When used with single-mode fiber, the transmission distance can reach 25G. km, meeting the various long-distance transmission requirements of data center networks.

It is used for fiber optic links with forward error correction (FEC) and is widely used in CATV (cable TV), FTTH (fiber to the home), 1G and 2G Fiber Channel, 100M and Gigabit Ethernet, synchronous optical networks SONET OC-3 (155Mbps), OC-12 (622Mbps), and OC-48 (2.488Gbps), as well as security and protection systems.

2. QSFP28 100G PSM4 Optical Module

The QSFP28 100G PSM4 optical module features four parallel transmission channels, with each channel transmitting up to 26Gbps. This optical module uses a 1310nm wavelength for transmission, with a transmission distance of up to 2km. The optical interface utilizes a single-mode 12-core MTP (MPO) connector. Each 100G module utilizes four independent channels using eight single-mode fibers, each transmitting 25G data. The interface utilizes a 12-core MPO interface, with the four middle fibers of the MPO interface disabled. Each channel supports 25G. The optical transmission model is similar to 100GBase-SR4. The major difference is that PSM4 uses single-mode fiber as the transmission medium and a 1310nm laser light source. The transceiver also utilizes the compact QSFP28 interface, with a single-mode MTP/MPO connector.

3.100G QSFP28 PSM4 Optical Module vs. 100G QSFP28 CWDM4 Optical Module

3.1 Cost

CWDM4 optical modules are less expensive than PSM4 modules. For longer link distances, they only require two single-mode fibers, while PSM4 requires eight.

3.2 Lasers

PSM4 utilizes four integrated silicon photonic modulators and a distributed feedback laser, while CWDM utilizes four CWDM uncooled DFB lasers (with a wavelength spacing of 20 nm).

3.3 Interfaces

CWDM4 optical modules utilize duplex LC interfaces, while PSM4 optical modules utilize 8/12-core MPO/MTP interfaces.

3.4 Center Wavelength

The center wavelength of the PSM4 optical module is 1310 nm, while the center wavelengths of the CWDM4 optical module are 1271 nm, 1291 nm, 1311 nm, and 1331 nm.

3.5 Transmission Distance

PSM4 and CWDM4 optical modules offer four transmission distances: 500M and 2km. The maximum transmission distance of CWDM4 optical modules is 2km.

3.6 Operating Principle

CWDM4 optical modules utilize coarse wavelength division multiplexing (CWDM4) technology, combining four wavelengths of optical signals onto a single optical fiber for transmission. PSM4 optical modules utilize parallel transmission technology, transmitting four identical wavelengths using four independent single-mode optical fibers.

3.7 Fiber Type

CWDM4 optical modules are connected using duplex single-mode LC fiber optic patch cables, while PSM4 optical modules are connected using ribbon single-mode MPO fiber optic patch cables (8/12 cores).