Optical power conversion

Abstract

An optical power conversion circuit converts an optical energy signal from an optical source, such as a laser diode, to a regulated D.C. electrical voltage using a single photodetector. A buck-boost circuit uses electrical current from the photodetector in response to the optical energy signal to store energy in an inductor during one polarity of a control signal, and transfers the energy from the inductor to an output capacitor during the other polarity of the control signal. The duty cycle of the control signal determines the regulated D.C. electrical voltage. A switch drive circuit generates the control signal as a pulse width modulated signal from the regulated D.C. electrical voltage and a reference voltage. The control signal is A.C. coupled to a pair of FET switches in the buck-boost circuit to alternately energize and charge the inductor and capacitor respectively. A switched capacitor is coupled in parallel with the photodetector to store energy from the photodetector when the inductor is transferring energy to the output capacitor. At startup one of the FET switches in the buck-boost circuit is normally closed and the other normally open, and a third FET switch decouples the switched capacitor from the photodetector. A startup modulation signal is generated at the optical source to provide switching action equivalent to that of the FET switches in the buck-boost circuit until the regulated D.C. voltage achieves a sufficient level to energize the switch drive circuit and sustain normal operation. A data pickoff circuit is inserted in series with the photodetector to retrieve a data signal impressed upon the optical energy signal without disturbing the D.C. content.