First generation QSFP28 100G transceivers are, in most cases, four transceivers in one. These include 100GBASE-SR4, 100GBASE-LR4, 100G-CWDM4, and 100G-PSM4. Each of these transceiver types achieve 100G transmission by using 4 laser transmitters and 4 optical receivers each operating at 25G. As the industry moves on to aggregate rates of 400G, 800G and higher, the question of increasing the channel rate from N x 25G to N/4 x 100G was an obvious one, one admirably addressed by the 100G Lambda Multi-Source Agreement (MSA) group. It is roughly estimated that a single optical lane of 100G is about 40% lower cost than four lanes of 25G.
Cost Advantages of Single Lambda 100G vs Multi-lane 100G
Single Lambda 100G solutions reduce the number of transmitters and receivers by 4:1. In addition, for both FR (2km) and LR (10km), single only a single lambda (transmitter) is involved, the CWDM multiplex devices are also eliminated. The following diagrams depict this reduction in parts and complexity for each interface type.
First is the migration from a 100G-PSM4 migration to a link using the new 100GBASE-DR to cover link lengths of up to 500m on single mode fiber. The 100G-PSM4 interface uses four parallel fiber pairs each running at 25G at 1310nm. There is no wavelength division multiplexing involved in this type of transceiver. The 100GBASE-DR interface still retains a 4:1 advantage in the number of transmitters and receivers required to achieve this link.
We will now examine 100G transceivers designed for up to 2km transmission on single mode fiber. The existing QSFP28 100G interface for this distance is the CWDM4. As the name indicates, this interface type uses Coarse Wavelength Division Multiplexing to combine and separate four different wavelengths in each link direction. The new single lambda 100G interface, the 100GBASE-FR, combines all four 25G lanes into a single 100G PAM4 lane. So the FR, like the DR interface, boasts a 4:1 reduction in transmitters and receivers as well as complete elimination of the CWDM mux and demux devices.
To achieve up to 10km transmission, the existing QSFP28 interface is the 100GBASE-LR4. As shown in the diagram, this interface, like the CWDM4, utilizes four CWDM wavelengths. Each wavelength is created by separate transmitter and receiver. Also like the CWDM4, a CWDM mux/demux system is required at each end. Again, the new single lambda 100G solution achieves a substantial reduction and parts and complexity versus the original, QSFP28-based 4X 25G design.
Lower Complexity = Lower Cost
IEEE working groups have carefully analyzed the value of the reducing parts and complexity. Per the diagram below (credited to Lumentum), the savings in Optics (optical transmitters and receivers, integrated circuits and PCB/mechanicals) result in projected savings of more than 40% in the CWDM4 vs Single Lambda 100GBASE-FR.
New Single Lambda 100G interfaces have been defined that should accelerate migration to 400G and beyond. These new interfaces support 100G as the fundamental lane speed versus the previous generation utilizing 25G lanes. To read more, including detailed product data sheets, please visit Fluxlight 100G Transceivers. Fluxlight has these and much more, in stock and ready for you to upgrade your network.