Rewritable Optical Head Using ± First-order Diffracted Beams of a Holographic Optical Element

A new focusing error detection method using ±first-order diffracted beams of a holographic optical element (HOE) is proposed. We fabricate the proposed HOE and measured the focus offset between a land a groove. According to the measurement results, the focus offset of the proposed HOE was smaller than that of an astigmatic focusing error detection.