Focus-error detection using prism-enhanced spot size monitoring

Details Focus-error detection using prism-enhanced spot size monitoring Focus-error detection using prism-enhanced spot size monitoring

1990-04-20

1992-01-28

Arnold, Bruce Y.

Optical: systems and elements

Single channel simultaneously to or from plural channels

By refraction at beam splitting or combining surface

359618, 359837, 369 4414, 369 4423, G02B 2712, G02B 504, G11B 2110

Patent

active

050847830

ABSTRACT:
An apparatus and method is described for detecting focus errors in an optical head by positioning a prism in the optical path of a return light beam reflected from an optical recording medium. The prism reduces the beam in one dimension by a factor of M and concurrently increases the divergence/convergence angle associated with a focus-error of the beam by a factor of M in this dimension, thereby desirably enhancing the focus error signal by a factor of M.sup.2. A focus error is detected by a segmented photodetector having inner and outer photosensitive regions. The photodetector generates an electrical signal indicative of the focus error from the difference in light intensities at the inner and outer regions. The photodetector preferably is segmented in such manner as to also provide a track error signal.

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"Design Consideration of Optical Pregroove Dimensions", Yamamoto et al, Optical Society of America, 1985, pp. 1-4.

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