Single Lambda 100G CWDM: Scale to 400G on One Fiber Pair
Overview
Bandwidth demand keeps climbing across data center interconnect, metro and enterprise networks, single lambda 100G CWDM answers this directly - it lets a network engineer scale one existing dual fiber pair from 100G up to 400G by adding wavelengths one at a time. EDGE supplies the full passive path for this upgrade, the CWDM-100G-Q28-SL40 (and CWDM-100G-Q28-SL10 for 10km reach) transceivers and the DCMD-4-2733 MUX so growth becomes a transceiver order not a construction project.
Budget calculation
The link budget is why two reach options exist. The SL40 transceiver has a 15.8 dB optical budget. The two DCMD-4-2733 units in the path account for 2.4 dB (1.2 dB each), leaving 13.4 dB for the fiber span itself, enough for the rated 40 km reach on the 1291 nm, 1311 nm, and 1331 nm channels, and 30 km on the 1271 nm channel. The SL10 transceiver works the same way on a smaller 6.3 dB budget: the same 2.4 dB mux/demux loss leaves 3.9 dB of fiber budget, rated for 10 km.
Alternative
For shorter links, the SL10 variant is the better order: same wavelength plan, same DCMD-4-2733 mux/demux, same cabling, only the transceiver changes, at a lower cost than the 40 km optics. And note that the transceivers have FEC integrated in DSP, meaning the FEC on the host platform should be disabled. The solution is passive only, with no amplifier or dispersion compensation anywhere in the path.
Bill of materials
Every product in the diagram above, with the quantity each one appears. Open a row for full specifications, pricing and ordering.
- 8xCWDM-100G-Q28-SL40Double Fiber CWDM 100G-ER Single Lambda PAM4 QSFP28 Module (Tx: 4Ch, 106.25 Gbps, Max. 30km over SMF with FEC, 15.8 dB, Temp. 0-70C, LC/UPC)
- 2xDCMD-44-channel double fiber passive CWDM mux/demux with configurable housing, wavelength band, and monitor port.
- 1xLC/UPC-LC/UPC-OS2-DX-B-LSZH-XLC/UPC to LC/UPC, Type A to B, Duplex, OS2 9/125μm, LSZH Patch cable, Length 0.5-100 meter
Frequently Asked Questions
Can I scale from 100G to 400G on this link without pulling new fiber?
Yes. The upgrade path is passive: a DCMD-4 CWDM mux/demux at each end lets you add single lambda 100G CWDM wavelengths onto the same duplex fiber pair you already have, up to 4 channels (400G total). Growth becomes a transceiver order, not a construction project.
What's the difference between the SL40 and SL10 transceivers in this solution?
Reach and link budget. The CWDM-100G-Q28-SL40 carries a 15.8 dB optical budget, rated for 40 km on the 1291/1311/1331nm channels and 30 km on the 1271nm channel. The CWDM-100G-Q28-SL10 uses the same wavelength plan and mux/demux but a smaller 6.3 dB budget, rated for 10 km. Pick SL10 for the shorter link; it costs less than the 40 km optics.
Do I need to disable FEC on my switch for this to work?
Yes. Both transceivers carry forward error correction integrated in the DSP, so the host platform's own FEC should be disabled to avoid double-correcting the signal.
Does the 40 km reach need optical amplification?
No. The solution is passive only — no amplifier, no dispersion compensation anywhere in the path. The SL40's 15.8 dB budget minus 2.4 dB of mux/demux loss (1.2 dB at each of the two DCMD-4 units) leaves 13.4 dB for the fiber span itself, which is what covers the rated reach.