Browse Prior Art Database

Magneto Optic Devices with Reduced Absorption Using Optical Multilayer

IP.com Disclosure Number: IPCOM000081252D
Original Publication Date: 1974-Apr-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 3 page(s) / 38K

Publishing Venue

IBM

Related People

Spiller, EA: AUTHOR

Abstract

Magneto-optic films for memory or display applications which use the Faraday effect require a certain thickness, to give maximum contrast or signal-to-noise ratio. This optimum thickness depends mainly on the absorption constant of the film material and may be as low as 200 angstroms and as high as 1mm, depending on the material used. This imposes a severe constrain in the design of a practical device, because other factors like write energy, storage density, stability of bubble domains, mechanical properties, etc. often require a different thickness.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 52% of the total text.

Page 1 of 3

Magneto Optic Devices with Reduced Absorption Using Optical Multilayer

Magneto-optic films for memory or display applications which use the Faraday effect require a certain thickness, to give maximum contrast or signal-to- noise ratio. This optimum thickness depends mainly on the absorption constant of the film material and may be as low as 200 angstroms and as high as 1mm, depending on the material used. This imposes a severe constrain in the design of a practical device, because other factors like write energy, storage density, stability of bubble domains, mechanical properties, etc. often require a different thickness.

Techniques are described below which allow the use of much thicker films of magneto-optic material. The techniques are useful for materials with a very high absorption constant, where the optimum thickness is in the 200 angstrom region, which are to be used for bubble domain devices.

In the technique, a standing-wave field is generated and the magneto-optical material is positioned close to a node of the standing-wave field. Because there is only little intensity close to a node, the absorption losses and also the Faraday rotation is reduced. The magneto-optic film close to a node is, therefore, equivalent to a much thicker film in free space. The maximum optical thickness obtainable with this method is approximately nd = lambda/2 (lambda = wavelength of light). All-dielectric or dielectric metal multilayer coatings can be used to generate the standing-wave pattern necessary. The limitation nd < lambda/2 can be removed by dividing the magneto-optics film into several thinner films, which are positioned in different nodes of the standing-wave pattern.

0ne multilayer coating design which maximizes the signal in transmission and one design which maximizes the signal in reflection is now described. Step 1. From the optical constants of the magneto-optic material and its desired optical thickness nd (nd less than lambda over 2, the refractive index of the surrounding medium necessary to have a node of the standing wave in the center of the film is calculated. The position of the node depends on the phase shift between reflected and incident wave and can, therefore, be adjusted by the index in front of the medium. Step 2. Mirror coatings are added on both sides of the magnetic film in such a way, that a node of the standing wave produced by the mirrors coincides with the node found in step 1. For the maximum signal in transmission, the two mirror coatings have about the same reflectivity; the effective spa...