Characterization of a novel focusing/tracking technique with increased feedthrough immunity for optical-disk applications: The double-astigmatic method

Bruce E. Bernacki, Keith Bates, Masud Mansuripur, Delbert Hansen, Daniel Cisneros

Research output: Contribution to journalArticle

2 Scopus citations


The astigmatic-focusing/push-pull tracking-error detection method is an elegant and sensitive optical servo technique. Unfortunately the formation of error signals far from either line focus of the astigmat (for relaxing alignment tolerances and broadening the servo's acquisition range) gives rise to undesired diffraction effects in the focus servo channel owing to track crossings of the pregrooved disk by the optical stylus, especially if certain aberrations are present. These undesired effects are given several names: pattern noise, optical servo cross talk, and feedthrough. By combining two astigmatic lenses and their associated detectors, one can configure a differential variant of the astigmatic technique. This double-astigmatic method greatly reduces pattern noise caused by the presence of spurious astigmatism oriented with its line foci at +450 to the disk tracks. In this paper we present numerical modeling and experimental data that demonstrate the effectiveness of this focusing/tracking technique in feedthrough suppression.

Original languageEnglish (US)
Pages (from-to)5789-5796
Number of pages8
JournalApplied Optics
Issue number29
Publication statusPublished - Oct 10 1993



  • Differential focus-error detection methods
  • Double-astigmatic method
  • Feedthrough
  • Optical data storage
  • Optical heads
  • Pattern-noise cancellation

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

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