Focus and tracking error detector apparatus for optical and magn

Details Focus and tracking error detector apparatus for optical and magn Focus and tracking error detector apparatus for optical and magn

1989-10-30

1992-05-12

Envall, Jr., Roy N.

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369 4442, 369 4423, 369 4411, 369 4424, 2502015, G11B 1304

Patent

active

051133865

ABSTRACT:
Focus and tracking error optical servo detector apparatus is shown employing a single four element detector array. Focus error detection based on spot size sensing is described in which focus error offset caused by beam transition between track and non-track areas is substantially reduced by shaping the detector element areas so as to derive servo signals from substantially only the overlap lobes between the zeroth order diffraction beam and the plus and minus first order diffraction beams in the optical readout beam from the recording element. The readout beam incident on the detector is anamorphically shaped to retain high focus error signal gain while reducing sensitivity in the tracking direction to movement of the beam caused by factors such as thermally induced beam misalignment, vibration and the like. The detector is optionally provided with a polarizer sheet positioned in front of the detector with its transmission axis parallel with the polarization of the beam incident on the recording element for the purpose of blocking birefringence effects on the readout beam from adversely affecting the detector performance.

REFERENCES:
patent: 4747090 (1988-05-01), Yamashita et al.
patent: 4841509 (1989-06-01), Kamisada et al.
patent: 4969142 (1990-11-01), Nagashima et al.
patent: 4989189 (1991-01-01), Sander et al.
I. Prikryl, "Optical Servo Crosstalk" paper for a talk given at a topical meeting of the Optical Society of America entitled Optical Data Storage held at Los Angeles, Calif. in Jan. 1989.

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