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Metal Working

Optical-pick-up-device-for-both-focus-and-error-tracking-detection

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Optical pick-up device for both focus and error tracking detection

Details

Inventors: Emoto, Masami; Inuzuka, Hideo;
Assignee: Ricoh Company, Ltd. (Tokyo, JP)
Primary Examiner: Nelms; David C.
Assistant Examiner: Oen; William L.
Attorney, Agent or Firm: Cooper, Dunham, Griffin & Moran

An optical pick-up device suitable for use in an optical disk memory system includes a semiconductor laser unit which emits a laser light beam which, in turn, passes through a beam splitter, a quarter-wave plate, and an objective lens to impinge on an optical disc thereby forming a light spot thereon. The light is then reflected from the disc and this reflected light passes through the objective lens and the quarter-wave plate and its direction of advancement is altered by the beam splitter to move into a convergent lens. Then, as the reflected light further advances, it is partly blocked by a tracking error detecting sensor and the remaining non-blocked portion of the reflected light impinges upon a focusing error detecting sensor. The objective and convergent lenses have f.sub.0 and f.sub.1 as their focal distances, respectively, and, preferably, ratio f.sub.0 /f.sub.1 is set equal to or larger than approximately 10.

DETAILED DESCRIPTION The disadvantages of the prior art as described above have been obviated by the present invention, which has its main object to provide an improved optical pick-up device capable of detecting a focusing error at high sensitivity over a broader detecting range.
Another object of the present invention is to provide an improved optical pick-up device suitable for use in an optical disc memory system.
A further object of the present invention is to provide an improved optical pick-up device high in accuracy and reliable in the operation of detecting a focusing error.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

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