Abstract
The astigmatic focus detection method and differential phase detection (DPD) tracking method are now widely used in a digital versatile disk (DVD) pickup head. The DPD tracking method requires the returning spot to remain centered in a quad detector and therefore makes the optical alignment very critical. In this paper, a novel holographic optical element (HOE) pattern design to relax the alignment tolerance and achieve a stable DPD tracking servo property is described. Simulations show that the servo signals are insensitive to photo-detector (PD) misalignment when compared to that of a conventional HOE design.
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