Applications of the photovoltaic effect in piezoelectric ceramics to information storage

Steady photo-emf's which are proportional to remanent polarization are a characteristic of ferrvelectric ceramics. The photo-mf can act to produce a current in a resistive load or can act to charge a capacitive storage element. The magnitude of the current and its direction and the magnitude of the change and its polarity are then uniquely related to the magnitude and direction of the remanent polarization. Therefore, illuminating a substrate in which information has been stored as remanent polarization produces currents or charges, which can be sensed to retrieve the information.