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Circularizing Prism With Right Angle Beam Paths

IP.com Disclosure Number: IPCOM000035871D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 52K

Publishing Venue

IBM

Related People

Sharma, BS: AUTHOR [+2]

Abstract

The output from commercial laser diodes is commonly elliptical in cross-section. In many applications circularization of the beam is desirable, and this is generally performed by passing the beam through a prism or prism pair. In optical storage devices a circular beam is desired so that a good combination of small spot size and high efficiency may be obtained when the beam is passed through an objective lens and focused onto the media. In these storage devices the data and servo signals are returned by laser light reflected from the media. This returning beam travels back through the objective lens and along the same path as the outbound beam. A beam splitter, usually consisting of a beam-splitting cube separator from the circularizing optics, is used to separate the outbound and return paths.

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Circularizing Prism With Right Angle Beam Paths

The output from commercial laser diodes is commonly elliptical in cross- section. In many applications circularization of the beam is desirable, and this is generally performed by passing the beam through a prism or prism pair. In optical storage devices a circular beam is desired so that a good combination of small spot size and high efficiency may be obtained when the beam is passed through an objective lens and focused onto the media. In these storage devices the data and servo signals are returned by laser light reflected from the media. This returning beam travels back through the objective lens and along the same path as the outbound beam. A beam splitter, usually consisting of a beam- splitting cube separator from the circularizing optics, is used to separate the outbound and return paths. Although beam splitting and circularization functions have been combined in a single piece of glass in previous designs, the laser beam input, outbound and return beam paths, and path to the detectors were not at right angles, making design and manufacture of the hardware to hold the components more difficult.

The design presented here is a prism that may be used to circularize an elliptical beam, perform beam-splitting functions between outbound and return paths from the media, and maintain right angle alignments between path from the laser, the path to the media, and the path to the servo and data detectors. There are no internal surfaces used in the prism, so the prism may be constructed from a single piece of glass. The layout of the optical path is shown in Fig. 1.

In Fig. 2 the path from laser input to the prism output to the media is shown. The collimated, elliptical cross-sectioned laser input is at path "A" and is refracted at surface 1. Coatings on surface 2 provided the beam splitting function required to...