# US 5,710,753 A · Multi-element grating beam splitter using double refraction to reduce optical feedback and associated light source noise

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- Number: US 5,710,753 A
- Document ID: US5710753A
- Status: Granted
- Kind: A
- Application number: 08/673,413
- Filed: 1996-06-28
- Granted: 1998-01-20
- Earliest claimed: 1996-06-28
- Assignees: Eastman Kodak Company
- Inventors: John C. Brazas, Jr.
- Web page: https://patentgrep.com/patent/US5710753A

## CPC

- G11B 7/1381: Non-lens elements for altering the properties of the beam, e.g. knife edges, slits, filters or stops (G11B7/1353 - G11B7/1369 take precedence)
- G11B 7/1353: Diffractive elements, e.g. holograms or gratings {(diffraction gratings per se G02B5/18; holograms per se G02B5/32; grating systems G02B27/44)}
- G11B 7/1365: Separate or integrated refractive elements, e.g. wave plates
- G11B 7/125: Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)

## Abstract

In an optical system including a multi-element grating beam splitter which includes four separate elements and an optical source with an effective aperture for generating a radiation beam to be applied to a data track of an optical storage medium, optics are disposed between the grating beam splitter and the data track of an optical storage medium which defines an optical axis along which light is projected to the data track and causes the displacement of the return beam to cause it to be substantially outside the effective aperture of the optical source to reduce optical feedback into the optical source.

## Claims

### Claim 1

In an optical system including a multi-element grating beam splitter and an optical source with an effective aperture for generating a radiation beam to be applied to a data track of an optical storage medium, the improvement comprising:
a) optics disposed between the grating beam splitter and the data track including a waveplate and a crystalline plate disposed between the grating beam splitter and the waveplate and defining an optical axis along which light is projected to the data track for displacing the optical axis of the return beam to cause it to be substantially outside the effective aperture of the optical source to reduce optical feedback into the optical source; and
b) said grating beam splitter being adapted to receive the return beam and including:
i) a first grating element;
ii) a second grating element, said first and said second grating elements arranged on opposite sides of a plane which is substantially parallel to a reference plane defined by an optical axis of said radiation beam and a tangent to said data track, such that said first and said second grating elements separate a first and a second portion, respectively, of a return beam resulting from application of said radiation beam to said data track, along at least one plane substantially parallel to said data track;
iii) a third grating element, arranged adjacent to and on one side of said first and said second grating elements, to separate a third portion of said return beam along a plane substantially perpendicular to said reference plane; and
iv) a fourth grating element, arranged adjacent to and on an opposite side of said first and said second grating elements, to separate a fourth portion of said return beam along another plane substantially perpendicular to said reference plane.

### Claim 2 (depends on 1)

The invention of claim 1 wherein said first and said second portions of said return beam provide a tracking error signal.

### Claim 3 (depends on 1)

The invention of claim 1 wherein said third and said fourth portions of said return beam provide a focus error signal.