GB2151807A

GB2151807A - Magneto-optical device

Info

Publication number: GB2151807A
Application number: GB08431354A
Authority: GB
Inventors: Hans Volz; Peter Kersten
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1983-12-23
Filing date: 1984-12-12
Publication date: 1985-07-24
Also published as: AU570750B2; GB2151807B; GB8431354D0; AU3621384A; DE3346647A1

Abstract

An optical arrangement includes a light source (20, 21) emitting polarized light, an analyzer (22), a component (10) containing a thin layer of ferromagnet amorphous metal whose optical properties can be varied by a magnetic field located between the light source and the analyzer, and a preferred direction of magnetization impressed on the magnetic layer. The magnetic layer mates an oblique angle with the direction of light propagation. The magnetic field which is impressed on the magnetic layer and whose direction can be changed by an external magnetic field changes the plane of polarization of light passing through the layer. A coil (13a, 13b) surrounding the magnetic layer and deposited by thin-film techniques turns the optical component into a light switch, and the optical arrangement containing the optical component into a transmitter of amplitude-modulated light. <IMAGE>

Description

SPECIFICATION Magneto-optical light switch This invention relates to an optical arrangement of the kind which comprises a light source for emitting polarized light, an analyzer for passing only light with a given polarization direction, and a component which is located between the light source and the analyzer and whose optical properties are variable by a magnetic field.

An optical arrangement of this kind is needed, for example, in optical communication to transmit amplitude-modulated light. The light source used is, for example, a laser emitting polarized light, but other light sources with separate polarizer may also be used. Located further down the beam path is a second polarizer acting as an analyzer. The polarization of the latter is such that the light coming from the first polarizer or directly from the laser is blocked unless its plane of polarization is rotated between the two polarizers. An interposed optically active component causes the plane of polarization of the light to be rotated, so that a portion of the light is passed by the analyzer.Such a component could be a thin disk which makes use of the Faraday magnetooptical effect, i.e. which rotates the plane of polarization of polarized light by an amount depending on the intensity of the magnetic field at that component.

An object of the invention is to provide a component having magnetically variable optical properties for an optical arrangement of the above kind, and to show how such a component may be used in the optical arrangement.

According to the invention in its broadest aspect, an optical arrangement of the kind referred to is characterized in that the component with variable optical properties consists of a transparent substrate and a thin magnetic layer deposited on the substrate, that the magnetic layer is made of ferromagnetic amorphous metal, that a preferred direction of magnetization lying in the plane of the magnetic layer is impressed on the magnetic layer, and that the component is so oriented that the magnetic layer makes an oblique angle with the direction of light propagation.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure lisa top view (Figure 1a) and across- sectional view (Figure 1b) of a componentwith variable birefringence for an arrangement in accordance with one embodiment of the invention, and Figure 2 shows a second embodiment of the invention.

First, a component 10 with magnetically variable birefringence will be described with the aid of Figure 1. Athin magnetic layer 12 of ferromagnetic amorphous metal is deposited on a transparent substrate 11. The magnetic layer 12 forms essentially a single magnetic domain; the direction of its magnetization is a preferred direction ("easy direction").

The magnetic layer 12 can be deposited by vacuum evaporation or cathode sputtering. The preferred direction of magnetization is achieved, for example, by subsequent annealing in the magnetic field. The component 10 is so oriented that the magnetic layer 12 makes an oblique angle with the direction of light propagation.

Materials especially suited for the magnetic layer 12 are ferromagnetic amorphous metals. Such metals have excellent magnetic properties and are ideally suited for the fabrication of thin layers. Good ferromagnetic properties are exhibited by amorphous metals which are alloys based on transition elements of the iron group. The amorphous metal may contain one or more metalloids (B, C, Si, Ge, P) as well as titanium, zirconium, hafnium, and/or niobium. Up to 5% (atom %) of the amorphous metal may consist of other elements. Especially suited are amorphous metals which are Co-Fe-base alloys, preferably Co,Fe,Bloo~x~yl where 70 < x < 80 and 4 y 10(x,yinatom%).

The thickness of the magnetic layer 12 is approximately 1 ohm. If the layer 12 is too thick, it is no longer transparent to light. If it is too thin, the resulting rotation of the plane of polarization can no longer be sufficiently evaluated. The magnetic layer 12 must make an oblique angle with the direction of light propagation, because only the magnetization component lying in the direction of propagation is effective. The magnetic field varying the magnetization and, thus, the optical properties of the component should therefore lie in the plane of incidence of the light.

In the embodiment shown in Figure 1, narrow stripes 13a, 13b are so arranged above and below the magnetic layer 12 as to form a coil 13 surrounding the layer 12. The stripes 13a, 13b forming the coil 13 are made of transparent electrically conductive material, e.g. indium-tin oxide (ITO). The magnetic layer 12 is isolated from the coil 13 by an overlying insulating layer 15 and an underlying insulating layer 14.

The section of Figure 1 b clearly shows the order in which the individual layers of the inductive component 10 are deposited. First, those stripes of the coil 13 are deposited by sputtering through a mask which are to lie underthe magnetic layer 12, i.e. the stripes 13a. They are followed by the first intermediate insulating layer 14, the magnetic layer 12, the second intermediate insulating layer 15, and the upper stripes 13b of the coil 13. Instead of by sputtering, the layers can be deposited by vacuum evaporation. The selective deposition of the individual layers can also be performed by using photolithographic techniques. The direction of the stripes 13a and 13b forming the coil 13 is essentially parallel to the preferred direction of magnetization of the magnetic layer 12.Thus, a magnetic field produced by the coil 13 is essentially perpendicular to the preferred direction of the magnetic layer 12.

The preferred direction should then be perpendicular to the plane of incidence of the light. The whole arrangement then varies the light intensity approximately proportionally to the intensity of the magnetic field.

If the light density is to be digitally switched depending on the direction of the magnetic field, the preferred direction must lie in the plane of incidence of the light. The magnetic field set up by the coil 13 must be parallel to the preferred direction of the layer 12, and the stripes 13a and 13b forming the coil 13 must be perpendicular to the preferred direction.

Another embodiment and application will now be described with the aid of Figure 2. The light coming from a light source 20 is polarized by a polarizer 21, passes through the optical component 10, is reflected at a reflecting surface 24 of a magnetic information carrier 25, travels to an analyzer 22, and is converted into electric signals in a light receiver 23 for evaluation purposes. The component 10 lies parallel to the surface 24 of the information carrier 25. The angles of incidence and reflection of the light at the surface 24 are both about 45 . The preferred direction of the magnetic layer 12 of the component 10 is perpendicular to the plane that contains the incident beam and the reflected beam. This plane also contains the polarization direction of the polarizer 21.The polarization direction of the analyzer 22 is perpendicular to this plane (within 1-2"); the slight deviation from the perpendicular is necessary to obtain optimum contrast. The magnetic information carrier 25 can be moved by means of a suitable device (not shown). The movement is such that the surface 24 moves parallel to the magnetic layer 12 and perpendicular to the preferred direction of magnetization of this layer. The informationcontaining magnetic field surrounding the magnetic information carrier 25 penetrates the magnetic layer 12, where it caused a change in the direction of magnetization which results in a change in the intensity of the light incident on the light receiver 23.

In a modification of this embodiment, the reflecting surface is not the surface 24 of the information carrier 25 but a surface located between the magnetic layer 12 and the information carrier 25 and permanently connected with the optical arrangement. It can be deposited directly on the magnetic layer 12. In that case, the magnetic layer 12 is also traversed by the reflected light beam, so that the amount of the rotation of the plane of polarization increases. The magnetic layer 12 can even be made so thick as to have reflective properties itself. In that case, too, the plane of polarization of the light changes with the magnetic field. The physical effect which governs this is not the Faraday effect, but the Kerr effect.

Two or more optical arrangements of the kind described with the aid of Figure 2, which can be used as a read head, can be placed side by side so that up to 100 items of information per centimetre can be read side by side.

Claims

1. Optical arrangement of the kind which comprises a light source for emitting polarized light, an analyzer for passing only light with a given polarization direction, and a component which is located between the light source and the analyzer and whose optical properties are variable by a magnetic field, characterized in that the component (10) with variable optical properties consists of a transparent substrate (11) and a thin magnetic layer (12) deposited on the substrate (11), that the magnetic layer (12) is made of ferromagnetic amorphous metal, that a preferred direction of magnetization lying in the plane of the magnetic layer (12) is impressed on the magnetic layer (12), and that the component (10) is so oriented that the magnetic layer (12) makes an oblique angle with the direction of light propagation.

2. An optical arrangement as claimed in claim 1, characterized in that the amorphous metal is an alloy based on transition elements of the iron group.

3. An optical arrangement as claimed in claim 2, characterized in that the amorphous metal contains at least one metalloid (B, C, Si, Ge, P).

4. An optical arrangement as claimed in claim 2 or 3, characterized in that the amorphous metal contains titanium, zirconium, hafnium, and/or niobium.

5. An optical arrangement as claimed in any one of claims 2 to 4, characterized in that up to 5% (atom %) of the amorphous metal consist of other elements.

6. An optical arrangement as claimed in any one of claims 2 to 5, characterized in that the amorphous metal is a Co-Fe-base alloy.

7. An optical arrangement as claimed in claims 3 and 6, characterized in that the amorphous metal is CoxFeyBaoo-x-y where 70x80(xinatom%) and 4y10(yinatom%).

8. An optical arrangement as claimed in any of claims 1 to 7, characterized in that a coil (13) surrounding the magnetic layer (12) is formed by further layers (13a, 13b) which are made of a transparent electrical conductor and pass partly over and partly under the magnetic layer (12), and that the magnetic layer (12) is separated from the coil (13) by intermediate insulating layers (14, 15).

9. An optical arrangement as claimed in any one of claims 1 to 7, characterized in that an optically reflecting surface (24) is present on or parallel to the magnetic layer (12), and that a device is present with which a magnetic information carrier (25) is guided past the magnetic layer (12) in the immediate vicinity, and perpendicular to the preferred direction, of the magnetic layer (12).

10. An optical arrangement substantially as described with reference to the accompanying drawings.