Mo. Freeman et al., Robust focus and tracking detection for holographic digital versatile discoptical pickup-head modules, JPN J A P 1, 38(3B), 1999, pp. 1755-1760
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.