2×2 MMI
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A 2 × 2 multimode interference (MMI) coupler is a 50:50 coupler made as a wide multimode section. It is less sensitive to fabrication than a directional coupler, and is used for Mach–Zehnders.
Ports
Ports 1 and 2 on one side, 3 and 4 on the other, as for a directional coupler.
The model
The directional coupler’s matrix at \(\kappa = 1/2\):
\[S = \frac{a}{\sqrt2}\begin{pmatrix} 0 & 0 & 1 & i \\ 0 & 0 & i & 1 \\ 1 & i & 0 & 0 \\ i & 1 & 0 & 0 \end{pmatrix},\]with \(a\) its excess loss in amplitude, the cross ports leading by a quarter wave.
Settings
| Field | Default | Meaning |
|---|---|---|
loss | 0.2 | Excess loss (dB) |
From the tool's own tables, file format version 1: the names are those in a .jekray file.
Readouts
Its ports and what they join, and the powers where the fibre network reaches them.
Assumptions
- An exact 50:50 split at every wavelength, with no reflection.
Related
- Directional coupler and 1×2 MMI.
- Phase shifter, for a Mach–Zehnder’s arm.