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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.

A Balanced Photo-Detector defined in PICWave

Balanced photo-detector circuit constructed in PICWave

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

Voltage vs input intensity difference response

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

Voltage vs time

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 with Modulator

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.

Driving the optical modulator

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