Polarisation beam splitter
A fibre polarisation beam splitter sends the light along its axis to one port and the light across it to the other. Run backwards it is a polarisation beam combiner.
Ports
Port common on one side; ports along and across on the other.
The model
A polariser at angle \(\theta\) from s, leaking a share \(\varepsilon^2\) of the power of the crossed polarisation, is the Jones matrix
\[\mathbf P(\theta, \varepsilon) = \mathbf R(\theta)\begin{pmatrix} 1 & 0 \\ 0 & \varepsilon \end{pmatrix}\mathbf R(-\theta), \qquad \varepsilon = 10^{-X/20},\]for an extinction \(X\) (dB), with \(\mathbf R\) the rotation matrix. The splitter is two of them, at right angles:
\[\mathbf S_\text{common, along} = a\,\mathbf P(\theta, \varepsilon), \qquad \mathbf S_\text{common, across} = a\,\mathbf P(\theta + 90^\circ, \varepsilon),\]the same back, with \(a = 10^{-\ell/20}\) for an insertion loss \(\ell\). Each output port leaks the extinction of the polarisation meant for the other.
Backwards, light along the axis into along and light across it into across both leave by common: a polarisation beam combiner, which adds two lasers’ powers into one fibre without loss.
Settings
| Field | Default | Meaning |
|---|---|---|
axis | 0 | Axis (° from s) |
extinction | 25 | Extinction (dB) |
loss | 0.5 | Insertion loss (dB) |
From the tool's own tables, file format version 1: the names are those in a .jekray file.
Assumptions
- The extinction and loss do not depend on wavelength.
- The fibres to its ports are taken to hold their polarisation. With standard fibre as laid, the state reaching it is scrambled: set the fibre to polarisation-maintaining, or put a polarisation controller before it.
Related
- In-line polariser.
- Polarisation controller.
- Beam splitter, the free-space polarising cube.