This brief presents a circuit suitable for the modulation of the photo-luminescent radiation of a solar cell. The circuit uses a MOSFET and a low-power amplifier in a feedback loop and acts as a variable load to the solar cell. By controlling the current drawn from the solar cell, the proposed circuit is able to set the solar cell’s voltage to any value between 0 V and the open circuit voltage. A circuit analysis of the modulator is presented along with experimental validation. As a proof of concept, a hardware prototype was built to demonstrate an optical communication link with the proposed modulator and a GaAs solar cell. Measurement results show that a bit error rate of $3.54\times 10^{-4}$ can be achieved at a rate of 40 kbps and at a distance of 30 cm.