Integrated optical detection circuit for magneto-optical drives

An integrated optical circuit (IOC) combining all the detection functions of a standard magneto-optical reading head (MO reading, focus and tracking control) is presented. The reading function is achieved by mean of a patented interferometric circuit. For tracking control, the well-known push-pull method has been applied and adapted to integrated optics. For focus control, an original method based on multimode interference, using the benefits of integrated optics has been successfully tested. The implemented technology is based on a silicon substrate with a silicon nitride core between two silica cladding layers (Si-SiO₂-Si₃N₄-SiO₂). This technology is a low cost technology that is well adapted for mass production. The optical components of the circuits are made by standard “hard contact” photolithography and reactive ion etching. Several wafers with about 50 devices have been processed and characterised. In particular, the detection signals have been compared with the detection signals delivered simultaneously by a standard commercial MO drive. This experiment demonstrates the feasibility of an integrated detection device for a MO drive