Magneto-optic light switching array for electrophotographic printing

Based on optical Faraday-rotation and thermomagnetic switching of the magnetic polarization in single -crystalline bismuth -substituted gadolinium iron garnet films, a technology for thin-film integrated light switching components has been developed. Thermomagnetic switching is achieved by applying current pulses to an addressing network with thin-film resistors in the presence of an externally applied magnetic control field. Up to 512 switching cells are lined up within a chip at a pitch of 60 μm and controlled by integrated circuits at low drive voltages. The typical switching time is 20 μs; up to 2000 optical patterns can be generated per s with the chip placed between polarization foils and illuminated by conventional light sources. The Faraday-rotation achieved in the visible is 20-40° in a 5 μm layer yielding the overall transmission of 5-10 %. The generating of heat pulses requires 1 μJ of energy per switching event and the magnetic switching field is about 25 kA/m. For high resolution optical line printing, a number of chips is stacked in a print head and imaged in parallel. Combined with electro-photographic recording text or graphics can be printed electronically at the resolution of typically 300 dots/inch. Other applications are found in electronic film exposure and professional optical printing.