Single Lambda 100G CWDM: 10km and 40km Over One Wavelength
Single Lambda 100G CWDM puts a full 100 Gbps stream on one CWDM wavelength, reaching 10 km or 40 km over G.652 single-mode fiber depending on the transceiver budget. This guide covers the architecture, the link-budget math for a 10 km and a 40 km build, and the difference between Single Lambda CWDM and 4-wavelength CWDM4 transceivers.
A 100G CWDM Single Lambda transceiver achieves the 100 Gbps line rate on one optical wavelength: 1271, 1291, 1311, or 1331 nm. These correspond to the first four channels of the CWDM grid defined in ITU-T G.694.2 (20 nm spacing, first nominal channel at 1270 nm). Inside the module, four 25.78 Gbps CAUI-4 electrical lanes (per IEEE 802.3bm Annex 83E) are mapped onto a single PAM4 optical signal at 50 Gbaud. The industry currently ships Single Lambda variants reaching 10 km and 40 km.
A typical 100G CWDM Single Lambda deployment combines a passive MUX/DEMUX at each end, a pair of 1271 to 1331 nm CWDM transceivers per channel, and one fiber pair carrying up to four channels (400 Gbps aggregate). The link budget is built by adding the loss contributions across that path:
- •MUX/DEMUX choice: the DCMD-4L adds 1.2 dB of insertion loss per unit. A pair of DCMD-4L units (one at each end) adds 2.4 dB to the link.
- •10 km transceiver: the CWDM-100G-Q28-SL10 ships with a 6.3 dB optical budget. After the MUX pair, 6.3 dB minus 2.4 dB leaves about 3.9 dB for the fiber span and connectors.
- •40 km transceiver: the CWDM-100G-Q28-SL40 ships with a 15.8 dB optical budget. After the MUX pair, 15.8 dB minus 2.4 dB leaves about 13.4 dB for the fiber span and connectors.
- •Fiber loss: on G.652 SMF (per ITU-T G.652.D, at most 0.4 dB/km at the 1310 nm reference point, applied here as a conservative planning figure across the O-band), the SL10 supports roughly 10 km and the SL40 supports roughly 33 km of fiber after MUX losses, with margin reserved for connectors and ageing.
10km Solution
The CWDM-100G-Q28-SL10 ships with a 6.3 dB standard optical budget, with an extended 7.7 dB option available. The 1291 to 1331 nm wavelength variants reach the full 10 km. The 1271 nm variant is the SL10's shortest-reach channel: it sits at the lower edge of the low-band CWDM channel plan, furthest from the G.652.D zero-dispersion wavelength (1300 to 1324 nm), resulting in a higher accumulated chromatic dispersion penalty than the 1291 to 1331 nm channels, so the SL10 product caps it at 10 km in the published reach table. Always confirm the per-wavelength reach against the transceiver datasheet for your specific channel.
40km Solution
The CWDM-100G-Q28-SL40 reaches 40 km on the 1291, 1311, and 1331 nm channels. The 1271 nm channel on the SL40 caps at 30 km in the published reach table for the same chromatic-dispersion reasons that constrain it on the SL10. The per-wavelength reach is fixed in the SL10 and SL40 product datasheets, not a property of the wavelength itself, so confirm both ends of any planned channel against the datasheet for the model you order.
Single Lambda 100G CWDM combined with a passive MUX/DEMUX gives Data Center Interconnect, metro, and enterprise networks a path to 400 Gbps aggregate over one fiber pair without active wavelength conversion. The architecture reuses the existing CWDM passive infrastructure that operators already deploy for 1G and 10G CWDM and is a more compact alternative to 4-wavelength CWDM4 modules for spans beyond 2 km.
EdgeOptic CWDM 100G Single Lambda product set:
| Part Number | Description |
|---|---|
| CWDM-100G-Q28-SL10 | CWDM 100G Single Lambda QSFP28, 1271 to 1331 nm, up to 10 km on G.652 SMF, 6.3 dB optical budget |
| CWDM-100G-Q28-SL40 | CWDM 100G Single Lambda QSFP28, 30 km on 1271 nm and 40 km on 1291 to 1331 nm, 15.8 dB optical budget |
| DCMD-4L | 4-channel double-fiber low-band passive CWDM MUX/DEMUX, 1.2 dB insertion loss per unit |
Single Lambda 100G CWDM FAQs
What is the difference between 100G CWDM Single Lambda and 100G CWDM4?
CWDM4 multiplexes four 25 Gbps NRZ lanes onto four wavelengths inside the module and reaches 2 km, with no external passive MUX needed. Single Lambda CWDM puts a single 100 Gbps PAM4 stream at 50 Gbaud on one CWDM wavelength (1271, 1291, 1311, or 1331 nm) and uses an external passive MUX/DEMUX to combine up to four channels onto one fiber pair, reaching 10 km or 40 km depending on the transceiver budget.
Does 100G CWDM Single Lambda require FEC on the switch?
Yes. Single lambda PAM4 transceivers need RS-FEC (Reed-Solomon FEC) enabled on both switch ports for the link to come up cleanly. Some platforms enable RS-FEC automatically when a 100G PAM4 module is detected; others require manual configuration. Verify the FEC mode on each port against your switch vendor's documentation before commissioning.
Why does 1271nm reach a shorter distance than the other CWDM wavelengths?
1271 nm sits at the lower edge of the low-band CWDM channel plan (ITU-T G.694.2 grid) and carries a higher chromatic dispersion penalty. The zero-dispersion wavelength of G.652.D SMF falls in the 1300 to 1324 nm range, so 1271 nm sits further from zero-dispersion than the 1291 to 1331 nm channels and accumulates more dispersion over the same span. EdgeOptic's CWDM-100G-Q28-SL10 caps the 1271 nm variant at 10 km, and the SL40 caps the 1271 nm variant at 30 km, while the 1291 to 1331 nm SL40 variants reach the full 40 km. Always check the per-wavelength reach in the transceiver's datasheet.
Do I need a passive MUX/DEMUX to use 100G CWDM Single Lambda transceivers?
Only when you want to combine multiple 100G channels onto a single fiber pair. A single point-to-point 100G link runs directly between two Single Lambda transceivers tuned to the same wavelength, with no MUX in the path. The passive MUX/DEMUX (such as the EdgeOptic DCMD-4L) is what aggregates four channels of Single Lambda CWDM into a 400G aggregate over one fiber pair, which is the typical Data Center Interconnect use case for this technology.