Fibre stretcher
A piezo fibre stretcher, fibre wound on a piezoelectric cylinder. A voltage stretches the fibre and shifts the phase of the light through it. It is the actuator of a fibre interferometer's lock.
Ports
Ports 1 and 2, one each side, and an electrical input, drive.
The model
The stretcher adds a phase \(\phi\), set, and \(\pi\) radians more for each \(V_\pi\) volts on its drive \(v\):
\[\mathbf S_{12} = \mathbf S_{21} = a\, e^{-i\left(\phi + \pi v/V_\pi\right)}\;\mathbf I,\]with \(a = 10^{-\ell/20}\) for an insertion loss \(\ell\) (dB). The phase shows only where the light interferes, as in one arm of a Mach–Zehnder.
A drive
Wired to the electronics, the drive sets the phase through time, worked out quasi-statically (see Electronics: drives). A sine on the drive of an interferometer’s arm makes its output swing between the fringes.
Settings
| Field | Default | Meaning |
|---|---|---|
phase | 0 | Phase (°) |
vpi | 2 | Vπ (V) |
loss | 0.1 | Insertion loss (dB) |
From the tool's own tables, file format version 1: the names are those in a .jekray file.
Assumptions
- Only the phase changes: the stretch is too small to change the delay the network keeps.
- The response is linear in the voltage and immediate, with no piezo resonance or hysteresis.
Related
- Variable delay line.
- Fibre EOM, for a fast phase.