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Optics for Beam Addressable Files

IP.com Disclosure Number: IPCOM000077326D
Original Publication Date: 1972-Jul-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Garwin, RL: AUTHOR

Abstract

In Fig. 1, there is shown the optics for typical known beam addressable file arrangements. A laser array source S is focused by high-quality lens L onto a magneto-optic medium M. In order to obtain a small spot on the medium of dimension D when working at wavelength lambda, a substantial angular aperture of the lens is required at the medium. Thus, if a 5-micron spot is required using a 1-micron wavelength source, then the angular aperture of the beam must be 10 to 20 degrees. The depth of field of such an optical arrangement is limited, and a lens which is adequate to image an array from a substantial working distance is expensive and difficult to servo from track-to-track.

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Optics for Beam Addressable Files

In Fig. 1, there is shown the optics for typical known beam addressable file arrangements. A laser array source S is focused by high-quality lens L onto a magneto-optic medium M. In order to obtain a small spot on the medium of dimension D when working at wavelength lambda, a substantial angular aperture of the lens is required at the medium. Thus, if a 5-micron spot is required using a 1-micron wavelength source, then the angular aperture of the beam must be 10 to 20 degrees. The depth of field of such an optical arrangement is limited, and a lens which is adequate to image an array from a substantial working distance is expensive and difficult to servo from track-to-track. Typically, the lens diameter and working distance of conventional optical systems for beam addressable files are of the order of a centimeter, with a spot size D of perhaps 2 microns and a track spacing of 5 microns.

In Fig. 2 are shown two views of an improved optical system for a beam addressable file. As shown, a set n of lenses L and a reflector R, such as a mirror, may be mounted on a slider arrangement and maintained by means of an air bearing in close proximity with the moving medium M. The multiplicity of lenses in the crosstrack direction allows n input laser beams B to illuminate n tracks. Typically, the diameter of the lenses may be of the order of 1 mm, and the slider arrangement carrying the lenses and the reflector R may have a height of 5 to 10 mm. Thus, the slider arrangement can conveniently fit between two closely spaced disks of magneto-optic medium.

In Fig. 3 there is shown a stack of magneto-optic media M in the form of disks, each of which is served by a slider arrangement SA which includes the optical system show...