Optical fiber

DWDM / CWDM Grid

Convert between frequency (THz), wavelength (nm) and ITU channel, and list the channels of a band at the chosen spacing. Based on ITU-T G.694.1 and G.694.2.

redzilla.cl — wdm

Frequency —

Wavelength —

Channel n —

CWDM —

Exact frequency

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Wavelength

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Optical band

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Channels of the band

n	Frequency (THz)	λ (nm)

CWDM grid · ITU-T G.694.2 (18 channels)

Channel	λ (nm)	Frequency (THz)	Band

How it works · the ITU grid

1. DWDM (G.694.1): the grid is anchored at 193.1 THz. Each channel is f = 193.1 + n·(spacing/1000), with spacing in GHz and n an integer (positive or negative).

2. The wavelength comes from λ = c / f, with c = 299792.458 nm·THz. So 193.1 THz equals 1552.524 nm.

3. The C band spans ~191.35–196.10 THz (1530–1565 nm): at 100 GHz it fits about 48 channels; at 50 GHz, twice as many.

4. CWDM (G.694.2) uses not frequency but 18 fixed wavelengths from 1271 to 1611 nm, every 20 nm.

Runs locally in your browser · no sign-up · nothing leaves your browser

How it works

The planner converts between the three ways of naming a DWDM optical channel: frequency in THz, wavelength in nm and channel number n of the ITU-T G.694.1 grid. You enter any of the three and it computes the other two for the chosen spacing (100, 50, 25 or 12.5 GHz), reports the optical band (O, E, S, C, L, U), lists every channel in the selected band and shows the CWDM reference table (ITU-T G.694.2).

The DWDM grid is defined in frequency and anchored at 193.1 THz: every channel satisfies f = 193.1 + n × (spacing_GHz / 1000), with n a positive or negative integer. Wavelength is derived with λ = c / f, using c = 299792.458 nm·THz. If your value does not land exactly on the grid, the tool rounds to the nearest channel and flags your input as off-grid. CWDM, by contrast, does not use frequencies: it is 18 fixed wavelengths from 1271 to 1611 nm, spaced 20 nm apart.

Example: which channel does 1550.12 nm map to at 100 GHz?

Frequency: f = 299792.458 / 1550.12 ≈ 193.3996 THz.
Channel number: n = (193.3996 − 193.1) / 0.1 ≈ 3.0, so it is channel n = 3 of the 100 GHz grid.
The exact channel sits at 193.40 THz = 1550.116 nm, inside the C band (1530–1565 nm).

Frequently asked questions

How many DWDM channels fit in the C band?

The C band (191.35–196.10 THz, roughly 1530–1565 nm) holds 48 channels at 100 GHz spacing and 96 at 50 GHz. Dropping to 25 or 12.5 GHz doubles the count again, although those spacings demand far more stable transceivers. It is the preferred band because it matches the gain region of EDFA amplifiers.

What is the difference between DWDM and CWDM?

DWDM (G.694.1) packs channels very tightly (12.5 to 100 GHz, under 1 nm apart) around 193.1 THz and needs temperature-stabilized lasers; it scales to dozens of channels that EDFAs can amplify. CWDM (G.694.2) uses only 18 wavelengths spaced 20 nm apart between 1271 and 1611 nm, with cheaper uncooled lasers, but with no practical amplification and much less capacity.

Why is the ITU grid defined in frequency instead of wavelength?

Because the channels are evenly spaced only in frequency: the G.694.1 standard fixes the anchor at 193.1 THz and exact steps in GHz. In wavelength the separation is not constant: at 100 GHz the C-band channels sit about 0.8 nm apart, but that value drifts across the band. That is why DWDM equipment is configured in THz or by channel number.

What happens if my wavelength does not match any grid channel?

The tool finds the nearest channel (it rounds n to the closest integer), shows its exact frequency and wavelength, and flags your original value as off-grid so you can see the difference. Everything runs in your browser, with no data sent to any server.

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