Robust focus and tracking detection for holographic digital versatile disc optical pickup-head modules

This paper introduces a robust focus and tracking detection method for use in holographic pickup heads. The method, which we call split-aperture servo detection, provides the focus error signal and both differential phase detection (DPD) and pushpull tracking signals but requires one less axis of alignment than the commonly used quad detector with astigmatic focus detection. A set of simulations designed according to Taguchi's method is presented comparing the manufacturability of holographic modules using the split-aperture approach and the astigmatic approach. The split-aperture approach is seen to have strong advantages. Experimental verification of a prototype digital versatile disc (DVD) pickup is also presented.