Novel One-Beam Detection Method with Changeable Multi Division Patterns

We developed a new one-beam detection method with changeable multi division patterns, pairing with tangential spot size detection (SSD) method for focusing error detection. The changeable multi division patterns are realized by the active device, which consists of a non-polarizing HOE for tangential SSD method, liquid crystal (LC) active rotator and two different division patterns of layered polarizing blazed HOEs. The LC active rotator properly acts as the mode selector and an R/RE mode pattern for one-beam push-pull method and a ROM mode pattern for differential phase detection (DPD) method can be selected only changing the applied voltage. The newly developed system can derive one-beam push-pull signal, DPD signal, wobble signal and RF signal from the output only from five common photo detectors. Sufficient quality of these signals is experimentally confirmed. The one-beam push-pull signal is hardly affected by the stray light from other layers. The traversing noise of its focusing error signal is stably low even with high push-pull media and possibly large astigmatism. Its focusing error signal turns out to be much more stable and less influenced by groove traverses. In addition, we present a vision for next-generation slim and compact integrated optics with dual LC cells, which consist of the LC attenuator, laser noise reduction technology, and the LC mode selector, as explained above.