PICWave

Balanced photo-detector / photodiodes

Simulation with PICWave software

In PICWave, arbitrary LCR networks can be constructed and attached to active sections. This example shows a balanced photo-detector, which measures the difference (in the form of an RF output voltage) between two optical input signals.

The balanced photo-detector circuit, shown below, consists of two photo-diodes coupled together with an electrical network, which acts to amplify the difference between the electrical responses of the photo-diodes, but not the particular responses of each. A constant bias is applied across the two photo-diodes using two voltage drives and the RF output voltage is measured using a current drive (injecting 0 Amps) which has a built-in voltage instrument.

Balanced photo-detector circuit constructed in PICWave

The figure below shows the DC and AC response of the balanced photo-detector.

DC response - output voltage vs. intensity difference of CW optical inputs

AC response - output voltage as optical input frequency is increased from 1 to 10GHz,
illustrating the limited bandwidth of the balanced detector

You can see below a new circuit in which the balanced photo-detector is used to drive an optical modulator, in which a CW signal is injected.

Balanced photo-detector circuit connected to modulator

You can see below the juxtaposition of the evolution with time of the difference in optical power between the two photo-diodes and of the output power of the modulator. You can observe how the signals are matched.

(top) difference in optical power between the two input signals;
this signal is used to drive the modulator
(bottom) output of the modulator