Browse Prior Art Database

Differential Spotsize Focusing Method by Dual Layer Detector

IP.com Disclosure Number: IPCOM000117905D
Original Publication Date: 1996-Jul-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Hirasaka, Y: AUTHOR [+3]

Abstract

Disclosed is a method for obtaining a focus error signal by using differential signals created by the optical spots which are projected to a dual layer detector.

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Differential Spotsize Focusing Method by Dual Layer Detector

      Disclosed is a method for obtaining a focus error signal by
using differential signals created by the optical spots which are
projected to a dual layer detector.

      The Figure shows an example of this apparatus.  The optical
beam (1), reflected by an optical disk (2), returns to objective lens
(3).  In case the beam was focused on an optical disk (2), the
returned beam goes to a sensor lens (4) and has a focus point (5),
between the first detector (6) and the second detector (7).  The
first detector (6) has a hole which is located in the center of the
beam and is smaller than the beam size.  Detectors (6,7) are adjusted
to the point of equal output in the focal direction of the sensor
lens (4).  In this case, objective lens (4) was located to the
position out of focus.  The differential signal (8) from the
detectors (6,7) is not equal to zero.  By feeding this differential
signal back, the objective lens (3) can be controlled on focus.