On-chip photodiode
Photonic chips are an experimental feature. Switch them on under Help › Experimental features.
An on-chip photodiode ends a waveguide and reads the light that reaches it, as a germanium detector on a silicon chip does.
Ports
One optical port, in, on the chip, and an electrical output, out.
The model
The photodiode is a sink: it absorbs everything that reaches its port and reflects nothing. The chip is solved for the light it takes in from each grating coupler (see Photonic chips: solving the chip), and the photodiode reads it as a fibre photodetector does:
\[I = \mathcal R\,P, \qquad V = G\,I,\]up to its output limit, with beat notes passed through a single pole of its bandwidth. Paths of one laser add as fields, weighted by its coherence; different lasers add as powers and beat. Its noise is shot noise and the gain resistor’s Johnson noise. Set a demodulation frequency and phase and its output is mixed down, as for any photodetector (see Photodetector: demodulation).
Electrical output
Its out port carries what it reads to the electronics: the amplifier’s output in volts, or, set as a bare photodiode, its photocurrent in amps, for a transimpedance amplifier. Drives on the bench, a laser’s modulation or a phase shifter’s drive, move it as the light follows them.
Settings
| Field | Default | Meaning |
|---|---|---|
resp | 1 | Responsivity (A/W) |
gain | 10000 | Gain (V/A) |
vmax | 10 | Output limit (V) |
bandwidth | 1000000000 | Bandwidth (Hz) |
demodF | 0 | Demod. at (MHz) |
demodPhase | 0 | Demod. phase (°) |
From the tool's own tables, file format version 1: the names are those in a .jekray file.
Also diode: true for a bare photodiode, its output a current.
Readouts
The optical power, photocurrent and output (held at its limit, and flagged, when it would go past it), its ports, and its signal: DC, beat notes and the mixer’s output, with a scope and spectrum analyser. The chip’s spectrum to this photodiode is drawn below it.
Assumptions
- Its responsivity is fixed, not taken from a material’s curve.
- No dark current or amplifier input noise.