Advanced Radial Position Control of a Recording Beam for Super Multilayer Disc with Separated Guide Layer

We have developed an advanced radial position control system for a super multilayer disc with a separated guide layer to realize stable recording on the plane recording layers located far from the guide layer. The developed system consists of an advanced sled servo system and a specially designed optics based on the advanced push–pull method. Recorded signals on all recording layers were evaluated by using integrated-maximum likelihood sequence error estimation (i-MLSE) as the evaluation indicator. As a result, we confirmed sufficient recorded signal qualities and feasibility at the quad-speed continuous recording with a constant track pitch of 0.32 µm, the same as that of Blu-ray disc (BD). We believe that our proposed concept is the most practical solution for the next-generation optical disc system and our control system is essential to realize stable multilayer recording with a constant track pitch.