Grating coupler
Photonic chips are an experimental feature. Switch them on under Help › Experimental features.
A grating coupler joins the chip to a fibre above it. Light from the fibre network enters the chip here and leaves it here. It takes one polarisation of the fibre's light, over a band about its centre wavelength.
Ports
Two: chip, joined to the chip’s waveguides, and fibre (yellow), joined to a fibre.
The model
The coupling between fibre and chip, in dB, falls off quadratically about the centre \(\lambda_c\):
\[T_\text{dB}(\lambda) = T_\text{peak} - \left(\frac{\lambda - \lambda_c}{\Delta\lambda_{1\,\text{dB}}/2}\right)^2,\]1 dB down at the edges of its 1 dB band. Its field transmission, the same both ways, is
\[t(\lambda) = 10^{\,T_\text{dB}(\lambda)/20}.\]Polarisation
The chip carries one mode, TE. From the fibre, the coupler takes the light polarised at its angle \(\theta\) from s and loses the rest, as a real one does:
\[E_\text{chip} = t\,(\cos\theta\, E_s + \sin\theta\, E_p),\]and light leaving the chip goes into the fibre polarised at \(\theta\). Put a polarisation controller before it to match the fibre’s light to it. To the fibre network, each coupler’s fibre side is a port of the chip, with a 2 × 2 Jones matrix on the fibre’s (s, p) (see Photonic chips: solving the chip).
Settings
| Field | Default | Meaning |
|---|---|---|
centre | 1550 | Centre (nm) |
peak | -3 | Peak (dB) |
bw | 30 | 1 dB band (nm) |
polAngle | 0 | Fibre pol. (° from s) |
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 coupling in dB at each laser’s wavelength that reaches the chip.
Assumptions
- No back-reflection into the fibre or the chip.
- The band’s shape is a parabola in dB at every wavelength, so far from the centre it falls without limit.
- The fibre’s angle and position over the grating are not modelled: the peak coupling stands for the best alignment.
Related
- Polarisation controller.
- Fibre tip, how free-space light enters a fibre.