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CWDM and DWDM Wavelength and Frequency Grid Reference

Wavelength division multiplexing places many signals on one fiber, each at its own carrier on an ITU-defined grid. This reference lists the 18 CWDM wavelengths and 21 DWDM 100 GHz channels around the 193.1 THz anchor with their frequency and wavelength.

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Grid	Channel	Frequency (THz)	Wavelength in vacuum (nm)
CWDM	1271 nm	235.87	1271.00
CWDM	1291 nm	232.22	1291.00
CWDM	1311 nm	228.67	1311.00
CWDM	1331 nm	225.24	1331.00
CWDM	1351 nm	221.90	1351.00
CWDM	1371 nm	218.67	1371.00
CWDM	1391 nm	215.52	1391.00
CWDM	1411 nm	212.47	1411.00
CWDM	1431 nm	209.50	1431.00
CWDM	1451 nm	206.61	1451.00
CWDM	1471 nm	203.80	1471.00
CWDM	1491 nm	201.07	1491.00
CWDM	1511 nm	198.41	1511.00
CWDM	1531 nm	195.81	1531.00
CWDM	1551 nm	193.29	1551.00
CWDM	1571 nm	190.83	1571.00
CWDM	1591 nm	188.43	1591.00
CWDM	1611 nm	186.09	1611.00
DWDM 100 GHz	193.1 THz + 10 x 100 GHz	194.1	1544.53
DWDM 100 GHz	193.1 THz + 9 x 100 GHz	194.0	1545.32
DWDM 100 GHz	193.1 THz + 8 x 100 GHz	193.9	1546.12
DWDM 100 GHz	193.1 THz + 7 x 100 GHz	193.8	1546.92
DWDM 100 GHz	193.1 THz + 6 x 100 GHz	193.7	1547.72
DWDM 100 GHz	193.1 THz + 5 x 100 GHz	193.6	1548.51
DWDM 100 GHz	193.1 THz + 4 x 100 GHz	193.5	1549.32
DWDM 100 GHz	193.1 THz + 3 x 100 GHz	193.4	1550.12
DWDM 100 GHz	193.1 THz + 2 x 100 GHz	193.3	1550.92
DWDM 100 GHz	193.1 THz + 1 x 100 GHz	193.2	1551.72
DWDM 100 GHz	193.1 THz (anchor)	193.1	1552.52
DWDM 100 GHz	193.1 THz - 1 x 100 GHz	193.0	1553.33
DWDM 100 GHz	193.1 THz - 2 x 100 GHz	192.9	1554.13
DWDM 100 GHz	193.1 THz - 3 x 100 GHz	192.8	1554.94
DWDM 100 GHz	193.1 THz - 4 x 100 GHz	192.7	1555.75
DWDM 100 GHz	193.1 THz - 5 x 100 GHz	192.6	1556.55
DWDM 100 GHz	193.1 THz - 6 x 100 GHz	192.5	1557.36
DWDM 100 GHz	193.1 THz - 7 x 100 GHz	192.4	1558.17
DWDM 100 GHz	193.1 THz - 8 x 100 GHz	192.3	1558.98
DWDM 100 GHz	193.1 THz - 9 x 100 GHz	192.2	1559.79
DWDM 100 GHz	193.1 THz - 10 x 100 GHz	192.1	1560.61

CWDM wavelengths follow the 20 nm grid of ITU-T G.694.2 and DWDM channels the frequency grid of ITU-T G.694.1 anchored at 193.1 THz. Wavelengths are calculated as 299,792.458 divided by the frequency in THz, in vacuum. Vendors often print rounded values and their own channel numbers, so confirm against the optic label.

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How to use the table

Search by wavelength, frequency or channel to find the matching entry, then export the table to Excel or PDF for your channel plan. CWDM channels are spaced 20 nm apart from 1271 to 1611 nm, which lets uncooled lasers and wide filters be used. DWDM channels are on a frequency grid anchored at 193.1 THz, here at 100 GHz spacing, which is about 0.8 nm in the C-band.

Use frequency, not wavelength, when you plan DWDM channels
Check that the mux, ROADM and transceiver all use the same grid
Reserve the OSC wavelength if your system needs an optical supervisory channel

Where the numbers come from

The DWDM grid defined in ITU-T G.694.1 uses frequencies of 193.1 THz plus or minus multiples of the spacing. Wavelength follows from lambda = c / f, with c equal to 299,792.458 km/s, so 193.1 THz is 1552.52 nm. The CWDM grid in ITU-T G.694.2 runs from 1271 nm to 1611 nm in 20 nm steps; the frequency column here is derived from those wavelengths for comparison and is not itself a grid definition.

Practical notes

Most DWDM equipment is sold on a 50 GHz or 100 GHz grid in the C-band, which spans roughly 1530 to 1565 nm, with extended L-band systems around 1565 to 1625 nm. Flex-grid systems from G.694.1 allocate slices in 12.5 GHz units, so a coherent 400G carrier may occupy 75 GHz or more. When a transceiver label shows a wavelength and your plan shows a frequency, convert with the formula and allow for the rounding in the labels.

Common mistakes

Mixing CWDM and DWDM transceivers on the same mux is a frequent cause of dark ports. Others confuse wavelength in vacuum with wavelength in glass, which is shorter by the refractive index, or read channel numbers from different vendors as though they were standard. A single misprinted channel number can place a carrier on a neighbor's wavelength, so always cross-check the frequency.

Frequently Asked Questions

What is the DWDM anchor frequency?

ITU-T G.694.1 uses 193.1 THz as the reference for the frequency grid, which corresponds to about 1552.52 nm in vacuum. Channels are placed at multiples of the spacing from it.

How far apart are CWDM channels?

20 nm, from 1271 nm to 1611 nm for the 18 channels in G.694.2. The wide spacing allows uncooled lasers and low-cost filters but gives fewer channels than DWDM.

Is wavelength in vacuum different from in fiber?

Yes. In glass the wavelength is shorter by the index, about 1.468, but the nominal wavelength used in grids and on labels is the vacuum value.

Why is 100 GHz about 0.8 nm?

Because delta lambda = lambda squared x delta f / c. At 1550 nm and 100 GHz this is about 0.8 nm, and 50 GHz is about 0.4 nm.

Netray can help you keep channel plans and circuit inventory consistent with the equipment and spare records in your ERP.

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