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Magneto-Optic Head and Recording System

IP.com Disclosure Number: IPCOM000038933D
Original Publication Date: 1987-Mar-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 49K

Publishing Venue

IBM

Related People

Bates, KA: AUTHOR [+4]

Abstract

The use of differential signal detection, a partial polarizing beam splitter, and a quarter-wave plate provides a small size magneto-optic head which works reliably at low light levels and low signal-to-noise ratios. Figs. 1 and 2 show two versions of this head. In Fig. 1, gallium arsenide laser 10 provides a beam of energy 11 which first passes through collimating lens 12. After passing through expansion prism 13, beam splitter 14 and partial polarizing beam splitter 15, this beam is reflected off mirror 16, and up through objective lens 17 (the lens' optical axis is perpendicular to the plane of the figure), onto the surface of a magneto-optic recording disk (not shown). This disk is located above the plane of the figure, and is coplanar with the figure.

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Magneto-Optic Head and Recording System

The use of differential signal detection, a partial polarizing beam splitter, and a quarter-wave plate provides a small size magneto-optic head which works reliably at low light levels and low signal-to-noise ratios. Figs. 1 and 2 show two versions of this head. In Fig. 1, gallium arsenide laser 10 provides a beam of energy 11 which first passes through collimating lens 12. After passing through expansion prism 13, beam splitter 14 and partial polarizing beam splitter 15, this beam is reflected off mirror 16, and up through objective lens 17 (the lens' optical axis is perpendicular to the plane of the figure), onto the surface of a magneto- optic recording disk (not shown). This disk is located above the plane of the figure, and is coplanar with the figure.

(Image Omitted)

Data-containing light which is reflected back from the disk, i.e., the read beams comprising two signal beams of orthogonal polarization, contain a high amplitude beam which is linearly polarized the same as the original beam 11, and a low magnitude beam that is linearly polarized orthogonal thereto. Data is detected by determining the phase rotation represented by vector addition of these two beams, and proper detection is dependent on the ability to differentiate between the amplitude of these two beams. Any phase change which may be introduced into these two beams makes them slightly elliptical, and decreases the angular polarization separation of the two beams. These reflected return beams first encounter partial polarizing beam splitter 15. This optical element operates to pass a portion (85%) of both beams on to beam splitter 14, and to reflect the remainder (15%) of both beams to quarter-wave plate 18 and half-wave plate 19. The portion of the beams passed by beam splitter 15 operates to activate focus detector 20 and tracking detector 21. These detectors operate to maintain objective lens 17 focused on the disk, and to maintain the beam centered on the disk track then being followed, by operation of servos (not shown). The reflected portion of the beams, i.e., the portion that is passed to plates 18 and 19, is modified by operation of partial polarizing beam splitter so that the high amplitude signal beam is attenu ated. The low amplitude signal beam is not attenuated. These two beams are now separated by the operation of polarizing beam splitter
22. As a result, one of the beams is directed to read detector 23, and the other is directed t...