WDM
A wavelength-division multiplexer sorts light by wavelength. Its pass band goes between the common port and the pass port, everything else between the common port and the rest port. It combines a pump with a signal in an amplifier, or separates channels.
Ports
Port common on one side; ports pass and rest on the other.
The model
The pass band is flat-topped, a super-Gaussian of order six about the centre \(\lambda_c\), with a full width at half maximum \(w\):
\[T(\lambda) = \exp\!\left(-\ln 2\left(\frac{2\,\lvert\lambda - \lambda_c\rvert}{w}\right)^{6}\right).\]What it passes goes one way and the rest the other, both ways:
\[\mathbf S_\text{common, pass} = a\sqrt{T}\;\mathbf I, \qquad \mathbf S_\text{common, rest} = a\sqrt{1 - T}\;\mathbf I,\]with \(a = 10^{-\ell/20}\) for an insertion loss \(\ell\) (dB). Without loss it is lossless at every wavelength: what does not take one port takes the other.
Settings
| Field | Default | Meaning |
|---|---|---|
centre | 1550 | Pass band centre (nm) |
fwhm | 20 | Pass band width (nm) |
loss | 0.3 | Insertion loss (dB) |
From the tool's own tables, file format version 1: the names are those in a .jekray file.
Assumptions
- The band edges are the super-Gaussian’s, adding no phase across the band, and the same for both polarisations.
- No light passes between the pass and rest ports.