As discussed in our last blog post, QSFP28 100G transceivers are, in most cases, four transceivers in one. The 100G-LR4, for example, achieves 100G transmission by using 4 CWDM laser transmitters and 4 optical receivers each operating at 25G. The 4 wavelengths are combined and separated by integrated passive CWDM multiplex devices, allowing the convenience of using a Single Mode Fiber (SMF) duplex LC optical connector. The single lambda alternative combines the four CAUI-4 NRZ 25G data streams into a single 100Gbps transmission.
Cost Advantages of Single Lambda 100G LR1 vs Multi-lane 100GBASE-LR4
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/demultiplex devices are also eliminated.
The existing QSFP28 100G interface defined for 10km SMF transmission the LR4. This interface type uses Coarse Wavelength Division Multiplexing (CWDM) to combine and separate four different wavelengths in each link direction. The new single lambda 100G interface, the 100GBASE-LR1, combines all four 25G lanes into a single 100G PAM4 lane. So the LR1, versus the LR4, achieves a 4:1 reduction in optical transmitters and receivers as well as complete elimination of the CWDM mux and demux devices.
Another advantage of the single lambda 100G LR1 versus the LR4 is the ease and efficiency of interconnection between existing 100G QSFP28 platforms and new 400G equipment. Without the single lambda 100G option, new 400G equipment would require allocating some of its ports to run at 100G just to allow for connection to earlier 100G switches. As shown in the diagram below, four 100G ports (on one or across several switches) may be interconnected only occupying a single QSFP-DD port in the 400G switch. An MPO-12 to 4x Duplex LC breakout cable is all that is required to accomplish the upgrade.
QSFP28 LR1 Internals
The QSFP28 LR1 single lambda transceiver relies heavily on Digital Signal Processing (DSP) to combine and separate four 25G lanes into a single 100G connection. The DSP also converts between Non-Return to Zero (NRZ) modulation on the 25G side and 56Gbaud PAM4 on the 100G side.
Optical transmission is single mode at 1310nm supporting link lengths of up to 10 kilometers. The optical connector is a standard Duplex LC.
Conclusion
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. The following are links to some example parts used in this post:
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.