Directly Overwrite Information by Using Two Radiation Beams Onto a Single Magneto-Optical Recording

This invention relates generally to apparatus for storing information on optical storage media, and more particularly, to apparatus which can provide a direct overwrite of information stored on magneto-optical storage media.

Optical storage media has proven to be attractive for the high density storage of information. More recently, optical storage media and systems have been disclosed in which a magneto-optical storage medium can have information written thereon overwritten with different information. Typically, in order to overwrite the material already stored on the magneto-optical medium, the medium must first be returned to an initial state. The magneto-optical medium can be returned to the initial state on the entire storage region or the initialization can take place in a predetermined region of the medium. When the initializing activity occurs immediately prior to and only in the region to be overwritten, the procedure is referred to as a direct overwrite.

In the related art, direct overwrite was accomplished by providing a first magnet and associated radiation (heat) source. The radiation source would heat a local area of the magneto-optical recording layer above an ordering temperature while the associated magnet would impose a predetermined initial state on the recording layer. A separate second magnet and associated radiation source were located such that the motion of the storage media would move the now oriented (i.e., by the first magnet and radiation source) region of the storage layer into position wherein the second magnet, with a magnetic field having an opposite orientation to the magnetic orientation of first magnet, applies a magnetic field thereto. The radiation from the second radiation source is applied to the storage layer region having the magnetic field from the second magnet applied thereto. When the information to be stored requires an orientation of the magneto-optical layer parallel to the orientation provided by the first magnet and first radiation source, then the power of the second radiation source is kept at a low enough value so that the illuminated region remains below the magnetic ordering temperature of the storage layer. When the information to be stored requires an orientation opposite to the orientation provided by the first magnet and the first radiation source, the power of the second radiation source is elevated to provide a temperature for the storage layer above the magnetic ordering temperature of the storage layer. As the region (or part thereof) heated above the ordering temperature is cooled in the presence of the magnetic field from the second magnet, this region of the storage layer will have an orientation opposite to that of orientation provided by the first magnet and the first radiation source. In this manner, information can be stored on storage medium which is determined by the orientation of local regions of a magneto-optical material.

Referring to FIG. 1, the direct write process is illustrated. The magneto-optical storage medium 10 is moving past a first radiation beam 11, a second radiation beam 12, the magnetic field 13A of a first magnet 13, and the magnetic field 14A of a second magnet 14 in a direction indicated by the arrow v. The storage medium 10 is constrained to move such that a magneto-optical material in information track 5 interacts with the first radiation beam 11 and the first magnetic field 13A and subsequently with the second radiation field 12 and the second magnetic field 14A. The magneto-optical material of track 5 has, prior to interacting with the radiation and the magnetic fields, initial information regions 15 which have an orientation opposite to the orientation of the remainder of the magneto-optical material. As a result of the interaction with the first radiation field 11 and the first magnetic field 13A, the information regions (and the remainder of the magneto-optical material of the information track 5) are oriented in an initialized orientation. Therefore, as seen in region 17 of the information track 5, no information regions are present. As the information track 5 moves past the second radiation field 12 and the second magnetic field 4A, the radiation beam 12 is modulated to heat only selected regions above the magneto-optical material ordering temperature. Upon cooling in the presence of magnetic field 14A, the regions 16 which have been heated above the ordering temperature now have an orientation opposite to the orientation of the surrounding initialized magneto-optical material. The regions 16 become the directly overwritten (or updated) information.

The foregoing process, conceptually easy to understand, is difficult to implement in practice. In order to achieve a high density of information, the information regions must be very small. The small size of the information regions means that the positioning of the second radiation beam and the second magnetic field relative to the first radiation beam and first magnetic field is critical. Furthermore, the two sets of magnets and radiation sources would preferably be mounted on the same read/write head, a component of relatively small dimensions. However, the weight of these components would limit the dynamic performance of the read/write head.

A need has therefore been felt for apparatus and an associated method for performing a direct overwrite procedure on a magneto-optical storage medium which requires relatively compact and relatively light-weight components. In order to conserve space in the apparatus, the radiation sources and the magnets should all be positioned on the same side of the storage media. In addition, a need has been a magneto-optical medium upon which stores information on either side of the magneto-optical medium. Finally, a need has been felt for an apparatus and an associated method for simultaneously reading both sides of a magneto-optical medium upon which information has been written on both sides.

The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, optics are provided in which a single condensing lens focuses two radiation beams on two locations of a recording layer of a magneto-optical storage medium, the storage medium being moved relative to the condensing lens so that a region of an information track is consecutively illuminated by the two radiation beams. Two magnets are located on either side of the two focused radiation beams to provide magnetic fields of opposite magnetic polarity interacting with the regions of focus on the recording layer. Each magnet is fabricated and positioned relative to the nearest radiation beam to provide an adequate magnetic field at the point of focus on the recording layer of the associated radiation beam without interfering with the radiation beam itself or coming in contact with the storage medium. As a recording track on the storage medium is moved past the first focused radiation beam and the first magnet, the magneto-optical material of the recording layer track is initialized, i.e., given a common orientation. The orientation of regions of the track as a result on the interaction between recording layer and the second radiation beam and second magnetic field is determined by the modulation on the second radiation beam, therefore providing overwritten information on the information track. The storage medium can include a magnetic material which can provide for a better alignment of the magnetic field on the storage layer.

The present invention advantageously provides compact and light-weight apparatus and an associated method for direct overwriting of information stored on a magneto-optical storage medium. The reading and writing apparatus is positioned on one side of the storage medium reducing the space requirements and providing flexibility with respect to the coupling of the read/write mechanism and the storage medium. The present invention also permits an embodiment of the storage medium in which the information can stored on both sides of the magneto-optical medium. In another embodiment, both sides of a two-sided magneto-optical storage medium can be simultaneously accessed by the read/write apparatus.

These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.

FIG. 1 is a representation of the technique by which direct overwriting is accomplished in an optical storage medium with a magneto-optical storage layer.

FIG. 2 is the apparatus for the direct overwriting of information on a magneto-optical storage layer in an optical storage medium according to the present invention.

FIG. 3 is the apparatus for the direct over-writing of information on a magneto-optical storage layer in an optical storage medium in the presence of a compensating magnet.

FIG. 4A shows the magnetic fields in the region of focused radiation beams for the preferred embodiment, while FIG. 4B shows the magnetic fields in the region of the focused radiation beams in the presence of the compensating magnet.

FIG. 5 is a cross-sectional diagram apparatus for the direct over-writing of information on a storage medium capable of having information stored on either side of the magneto-optical storage medium.

FIG. 6 is a cross-sectional diagram for apparatus capable of the simultaneous direct overwriting of information on both sides of a two-sided magneto-optical storage medium capable.

FIG. 1 has been described in relationship to the related art.

Referring next to FIG. 2, the block diagram of the apparatus for the direct overwriting of information on an information track of a magneto-optical storage medium is illustrated. The storage medium 10 includes a spacer layer 101, a magneto-optical storage layer 102, optionally, a high permeability magnetic material layer 103, and a substrate 104. Condensing lens 25 focuses a radiation beam 21 onto the magneto-optical recording layer 103. The radiation beam includes two components, and each radiation beam component is focused on separate regions 21A and 21B of the recording layer. Associated with a first radiation beam focused component 21A is a first magnet 22. Associated with a second focused radiation component 21B is a second magnet 23. The magnets are adapted to be as close to the associated focused radiation without interfering with the radiation itself. Therefore, the magnets can partially encircle the cone-like focused radiation beams. The encircling magnets can add magnetic field strength at the region of focus of the associated beam and can assist in increasing the perpendicular component (relative to the magneto-optical storage layer) in the region of the radiation beam focus. As shown in FIG. 2, the bottom surfaces of magnet 22 and magnet 23 are a distance g from the spacer layer 101. The distance from the bottom surfaces of the magnets 22 and 23 to the magneto-optical recording layer 102 is designated as d. As indicated by the arrows on the magnets 22 and 23, the polarity of the two magnets is opposite. Referring to the storage medium 10, a layer of high permeability magnetic material 103 can be included to increase the perpendicular component of the magnetic field.

Referring to FIG. 3, the general configuration shown in FIG. 2 is shown with the addition of a compensating magnetic 31. The compensating magnet is positioned on the opposite side of the storage medium. In addition, the high permeability magnetic material layer 102 has been removed, the compensating magnet 31 now being used to improve the magnetic field configuration in the vicinity of the focused radiation beams.

Referring to FIG. 4A and FIG. 4B, the magnetic fields in the region magneto-optical storage material upon which the radiation beams are focused is shown. The first and second magnets 22 and 23 typically have dimensions of 1.2 mm in length, 1.25 mm in width, 0.3 mm in thickness, and are inclined to the perpendicular by 27.degree.. The magnets have a remanent flux density of 11 kG, e.g. FeNdB available from IG Technologies Inc. In order to provide a vertical magnetic field difference of .+-.300 Oe, the distance between the focused radiation of the two beams is approximately 230 .mu.m; while the distance to provide a vertical magnetic field difference of .+-.100 Oe is approximately 75 .mu.m. But these magnetic field differences are provided in the presence of horizontal magnetic field difference of approximately 900 Oe. The presence of this horizontal field placed severe restriction on the anisotropy of the magneto-optical storage layer material. However, as shown in FIG. 4B, the presence of the compensating magnet 31, generally having a thickness of 1 mm, a length of1.25 mm, width sufficiently great to prevent fringing effects, and having remanent flux density of 11 kG, such that when positioned properly, (i.e., approximately 1 mm from the magneto-optical storage layer 102), essentially eliminates the horizontal component of the magnetic field in the region of the focused radiation beams. The addition of the compensating magnet provides vertical components which add to the fields resulting from the first and the second magnets. In order to provide a .+-.300 Oe field difference between the positions on the magneto-optical storage layer of the focused radiation beam, the beam must be approximately 180 .mu.m, while for a difference of .+-.100 Oe, the distance between the two positions of focused radiation on the magneto-optical storage layer must be approximately 60 .mu.m apart.

Referring next to FIG. 5, the direct over-writing apparatus shown in FIG. 3 can be used with a magneto-optical storage medium 10' having two magneto-optical storage layers 102 and 102'. Storage layers 102 and 102' are accessible through the spacer layers 101 and 101' respectively. The magneto-optical storage layers are symmetrically arranged on the storage medium 10' so that the field compensating magnet 31 compensates for the horizontal component of magnetic field for the magneto-optical storage layer currently being accessed by the direct over-writing apparatus. As will be clear, the substrate 104 must be sufficiently thick so that the heating of the currently accessed magneto-optical storage medium will not effect the magnetic orientation of the magneto-optical storage layer not currently being accessed.

Referring next to FIG. 6, direct overwriting apparatus for simultaneously accessing both side of the two sided magneto-optical storage medium 10', shown in FIG. 5, includes a second pair of permanent magnets 22' and 23', a second radiation beam 21' having two radiation components 21A' and 21B', and a second focusing lens 25'. The second direct over-writing apparatus is located generally on the opposite side of the storage medium 10' and equi-distance therefrom. In order to make the magneto-optical storage medium 10' symmetrical, the orientation of the magnetic fields of the permanent magnets on opposite sides of the magneto-optical storage medium must be reversed as shown in FIG. 6. This configuration of the two permanent magnet pairs provides for a cancellation of the horizontal components of magnetic field in the region of the magneto-optical storage layer 102 and 102'. As with the configuration shown in FIG. 5, the substrate 104 must be sufficiently thick so that the heating of one magneto-optical storage layer does not affect the orientation of domains in the second magneto-optical layers.

Operation of the preferred embodiment can be understood in the following manner (FIG. 2). When the storage medium is moving in the direction indicated by the arrow v, the focused beam region 21A in conjunction with the magnetic field from magnet 22 changes the orientation of information-bearing regions of the magneto-optical recording layer to the orientation of the initialized recording layer prior to the storage of information thereon. The focused radiation beam region 21B in conjunction with the magnetic field from magnet 23 are provided with the opposite orientation to the initialized orientation when the focused radiation beam region 21B is heated above the magneto-optical orientation temperature. Thus, the information bearing regions are changed to a different set of information bearing regions by the configuration of FIG. 2.

In the preferred embodiment, the spacing between the beams and the magnet dimension in the in-track direction is approximately equal to the distance d between the magnet and the recording layer (assuming a magnet remanence 4.pi.M.sub.r =11,000 Gauss and the bias field .gtoreq.300 Oe). An air gap, g, of 50 .mu.m can be maintained by a typical focus actuator servo (.+-.0.25 .mu.m) and still provide a margin of error against a head crash. The spacer thickness is generally equal to the distance d-g and is approximately 0.3 mm for adequate defocusing of scratches, dust, etc. The beam spacing is somewhat less than d-g and the magnet dimensions are approximately d-g (in-track dimension) times 4d (cross-track dimension) times 4d (height). The mass of two 0.3 mm times 1.2 mm times 1.2 mm magnets would be approximately 7 mg compared to the .apprxeq.250 mg actuated mass of a typical head. The total mass of the actuated magnets and the associated support structure is less than 10% of the total actuated mass.

When the high permeability magnetic layer is present, both the perpendicular component and the in-track gradient of the magnetic field is improved. These improvements can be used to implement a larger air gap, g, or to decrease the spacing between the focused beam regions.

The horizontal component of the magnetic field from the first and second magnets, without a compensating field, places severe requirements on the anisotropy of the material. When the compensating magnet is added to the system, the horizontal component of the magnetic field in the vicinity of the focused radiation beams is minimized and the requirements on the magnetic properties of the magneto-optical storage layer is reduced.

It will be now appreciated that there has been presented apparatus which can provide a direct overwrite of a magneto-optical material. The apparatus is compact, light weight and, consequently does not seriously impact the performance of the actuator carrying the apparatus.

Operation of the present invention is believed to be apparent from the foregoing description and drawings, but a few words will be added for emphasis. The most popular optical storage medium is currently disk. The apparatus disclosed herein can be added to the tracking and focusing actuator with minimal impact with respect to space and weight. The apparatus provides that an optical disk, for which data areas have been formed along information tracks as magnetic domain having an opposite orientation to initially oriented domains in a magneto-optical material, has a selected region along an information track reinitialized to the initial domain orientation. Subsequently, the recently initialized region can have data stored thereon in the form of oppositely oriented magnetic domains.

While the invention has been described with particular reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements of the preferred embodiment without departing from invention. In addition, many modifications may be made to adapt a particular situation and/or material to a teaching of the invention without departing from the essential teachings of the present invention. For example, the two sets of direct over-writing apparatus shown in FIG. 6 need not be symmetrical in size or in distance from the magneto-optical storage layer, however, as will be clear, any departure from symmetry in these dimensions will require compensating changes in the parameters of the direct over-writing apparatus, e.g., the strength of the permanent magnetic.

As is evident from the foregoing description, certain aspects of the invention are not limited to the particular details of the examples illustrated, and it is therefore contemplated that other modifications and applications will occur to those skilled in the art. It is accordingly intended that the claims shall cover all such modifications and applications as do not depart from the true spirit and scope of the invention.

5 information track

10 magneto-optical storage medium

101 spacer layer

102 magneto-optical storage layer

103 high permeability magnetic material layer

104 substrate

11 first radiation beam

12 second radiation beam

13 first magnet

13A first magnetic field

14 second magnet

14A second magnetic field

15 initial information regions

16 final information regions

17 initialized magnetic region

21, 21' radiation beam

21A, 21B first radiation beam component

21B, 21B second radiation beam component

22, 22' a first magnet

23, 23' a second magnet

25, 25' focusing lens

31 field compensating magnet