What Are the Differences Between QSFP28 4WDM and QSFP28 CWDM4 Optics?

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 of what differences between QSFP28 4WDM and QSFP28 CWDM4 optical transceiver are. Then in this article, a comparison between them will be made by Gigalight.

An Introduction to 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 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.

QSFP28 4WDM vs. QSFP28 CWDM4: What Are the Differences?

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 above comparison of QSFP28 CWDM4 and QSFP28 4WDM optical transceiver, the difference between them are 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 100GE 4WDM-40 QSFP28 optics is the key one for promotion at present. If you want to know more information about the products, pls visit Gigalight official website(www.gigalight.com).

A Brief Introduction to 4WDM Optical Transceiver

In current optical communication market, optical transceiver products are developed in the trend of high data transmission rate, longer reaches, lower power consumption, etc. To keep pace with the trend better, many new optical module products with high transmission rate and longer reaches emerge, such as the latest one, QSFP28 4WDM(4-wavelength Wavelength Division Multiplexing) optical transceiver. In this article, we will mainly talk about it.

What is 4WDM MSA?

The 4WDM MSA is an industry consortium dedicated to defining optical specifications and promoting adoption of interoperable 100G (4x25G) optical transceivers for 10 km based on the CWDM4 wavelength grid, and for 20 km and 40 km based on the LAN-WDM wavelength grid, over duplex single-mode fiber (SMF). These extended reaches are important for modern datacenter interconnects and mobile backhaul applications. The 4WDM MSA participants are responding to previously unmet industry needs for longer reaches, lower costs, and lower power consumption, as compared to previously available standards, in small form factors.

An Introduction to 4WDM Optical Module

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). 4WDM optics have three specifications including 4WDM-10, 4WDM-20, 4WDM-40. 4WDM-10 is one type of 100G (4x25G) optical transceivers for the 10 km based on the CWDM4 wavelength grid; 4WDM-20 and 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.

Specifications of 4WDM Optical Module: 4WDM-10, 4WDM-20, 4WDM-40

The 100G-4WDM-10 is based on the CWDM4 wavelength grid. To some degree, the 100G-4WDM-10 technical specification leverages the success of the CWDM4 2 km specification that has found broad acceptance in its target datacenter market. Like CWDM4, the 100G-4WDM-10 specification employs 4 lanes of 25Gb/s using Coarse Wavelength Division Multiplexing (CWDM) technology to transport 100G optical traffic across duplex single mode fiber (SMF). Both specifications take advantage of Forward Error Correction (FEC) on the host port, in accordance with IEEE 802.3bj KR4 RS FEC. One key advantage of CWDM is that the lasers do not need to be cooled or temperature controlled, resulting in lower power consumption and simplicity of manufacturing. 100G 4WDM-10 transceivers share these advantages and furthermore are specified to be fully interoperable with CWDM4 products. The 100G-4WDM-10 specification does not restrict the form-factor although high-density QSFP28 modules are expected to be dominant.

4WDM-20 and 4WDM-40 are added on the basis of the 100G 4WDM-10. They employ LAN-WDM wavelength grid on the basis of IEEE 100GBASE-LR4 and ER4, over duplex single-mode fiber (SMF). Simultaneously, they also utilize the IEEE 802.3 KR4 RS FEC used on the host interface to reduce the cost.

This specification defines 4 x 25Gbps Local Area Network Wavelength Division Multiplex (LANWDM)optical interfaces for 100Gbps optical transceivers for Ethernet applications including 100GbE. Forward Error Correction (FEC) is a link requirement in order to ensure reliable system operation. Two transceivers communicate over single mode fibers (SMF) of length from 2 meters to at least 20 or 40 kilometers. The transceiver electrical interface is not specified by this MSA but can have, for example, four lanes in each direction with a nominal signaling rate of 25.78125Gbps per lane.

In addition, the 4WDM-20 specification, which is an extension of the 100G-4WDM-10 10 km specification, enables customers to increase their reach using the same kind of optical components as 100GBASE-LR4 products. Similarly, the 100G-4WDM-40 enables 40 km reach with lower power consumption and in a smaller form factor than existing 100GBASE-ER4 compliant products that utilize a power-hungry SOA (Semiconductor Optical Amplifier).

Summary

It is commented by related expert that the new 20kms and 40kms specifications are an important milestone to enable this market. Thus, the prospect of 4WDM optical transceivers are worth expecting. For most of optical component suppliers, it means another opportunity. Gigalight, as the design innovator in global optical interconnect field, surely seizes the chance and pushes out one new product: QSFP28 4WDM 40KM. (About this product, you can click it or visit Gigalight website to know more).