INTEGRATED OPTICAL-DETECTION CIRCUIT FOR MAGNETOOPTICAL DRIVES

An integrated optical circuit (IOC) combining all detection functions of a standard magneto-optical reading head (M.O. reading, focus and tr acking control) is presented. The reading function is achieved by mean of a patented interferometric circuit (1,2). For tracking control, th e well-known push-pull method (3,4) has been applied and adapted to in tegrated optics. For focus control, an original method based on multim ode interference and taking benefits of integrated optics specificity has been successfully tested. The implemented technology is based on a silicon substrate with a silicon nitride core between two silica clad ding layers (Si / SiO2 / Si3N4 / SiO2) This technology is a low cost t echnology well adapted for mass production. The optical components of the circuits are made by standard ''hard contact'' photolithography an d reactive ion etching. Several wafers with about 50 devices have been processed and characterised. In particular, the detection signals hav e been compared with the detection signals delivered simultaneously by a standard commercial M.O. drive. This experiment demonstrates the fe asibility of an integrated detection device for M.O. drive.