The left op amp is configured as a summing amp to create the DC reference voltage plus the modulating AC voltage. The output of the summing amplifer feeds the op amp voltage to current converter that drives the laser. A Lite On LTLD505T 650nm 5mW laser diode was used for this example design to establish lasing current and modulation amplitude. Because of the way the matrix solver works, you have to start with the DC source set to zero and raise it up to 4.6V for the Lite On part. 200mVp-p from the AC source sets diode current modulation to 2mAp-p which works pretty well if you want to transmit audio on a beam of light.
