Robust focus and tracking detection for holographic digital versatile discoptical 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 sinal and both differential phase dete ction (DPD) and pushpull tracking signals but requires one less axis of ali gnment 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-aper ture approach and the astigmatic approach. The split-aperture approach is s een to have strong advantages. Experimental verification of a prototype dig ital versatile disc (DVD) pickup is also presented.