DE3730969A1 - Magneto-optical store with a magnetic head integrated into the scanning unit - Google Patents

Abstract

In the case of conventional magneto-optical stores information is recorded by exposing/blanking out the radiation source while a direct-current magnetic field is applied at the same time. This requires an erasing procedure before the actual recording operation. Before the subsequent recording operation, the polarity of the magnetic field is reversed. This erasing procedure, which prolongs the processing time considerably, is to be eliminated. For this purpose there is provided a vertical magnetic head (23), which generates the magnetic field, forms a mechanical unit with a positionable optical scanning head (17) and is arranged with only an air gap separating it from the surface of a storage disk (10). While there is provided a radiation source (1), which continuously emits a radiation energy adequate for the recording of information, the magnetic head (23) is designed in such a way that it generates a vertically directed magnetic field with a direction of magnetisation controlled by the information to be stored. The storage disk (10) preferably has a magnetically conducting return layer (12) arranged underneath the magneto-optical storage layer (13). Rewritable optical store. <IMAGE>

Description

The invention relates to a magneto-optical memory according to the preamble of claim 1.

The magneto-opti offers in the field of optical storage cal memory the advantage of a rewritable memory with random access. This applies to a new registration so far, however, only with certain restrictions. This is to the well-known principle of magneto-optical storage and its implementation, which is still common today. At The storage principle of this type of storage is based locally ne storage domain in the range of the Curie temperature of the heating medium and at the same time in the area of this Domain to apply a magnetic field of a given direction due to the reduced Koerzi in this state tivfeld strength in this domain a certain magnetization of the storage medium caused to freeze on cooling becomes.

The magneto-optical memory is a real write / Read storage, as opposed to this information storage to other optical memories, is reversible. With renewed local heating of the magneto-optical storage layer in the The area of the Curie Tempeatur can be changed by reversing the direction of the Magnetic field deleted the stored information and thus the information content of the relevant storage domain is reversed be returned.

The memory domains are optically scanned during the reading process. Reflected light from the magneto-optical layer due to the Kerr effect, a rotation of the plane of polarization against the incident light. The direction of rotation is dependent  from the local magnetization direction. The angle of rotation of the bottom Larization of the reflected light thus represents the read information. With magneto-optical memories occasionally the Faraday effect, which is used in trans averaged portion of the scanning light beam a similar, rotation of the Polarisa depending on the direction of magnetization tion level.

The practical implementation of this well-known physical prin zipien has been delayed for several reasons. First is this is due to difficulties in realizing the medium attributed itself. With an ideal magneto-optical Storage medium should be the coercive field strength at room temperature temperature as clear as possible from that in the area of the Curie-Tempe differentiate. In addition, when scanning the largest possible information-dependent change of rotation angle of polarization in the reflected light beam. So far, these requirements have not been optimally met. In order to The problems of local heating are also associated suitable radiation source and sufficient the magnetization of the storage medium.

Is one limited within the scope of the present invention in we considerably on the latter problems, fol note the following: based on the principles outlined above can be a binary information sequence by appropriate Mo Dulation of the output power of the radiation source for permanent use gnetization with an impressed direction of magnetization to save. In principle, this can also be done through a conti Nuclear radiation of the storage medium along a data if the storage medium succeeds with a changing according to the information to be registered Magnetize direction.

In known magneto-optical memories, similar to non-erasable optical memories, on store the radiation emitted by a laser modulated.  This leads to a memory structure in which one of the magneto- disc with a continuous optical storage layer Rotation movement rotates. With the help of a positionable opti the read / write head as part of an optical system the radiation emitted by the laser along a data track in Focused sampling points so that consecutive in series Storage domains warmed up to the Curie temperature range will. The magnetic coil is usually stationary and in with respect to the storage disk the optical read / write head arranged opposite and generates a magnetic Constant field.

This known structure of a magneto-optical memory enables the information is registered by conventional, especially from the technology of non-erasable optical Save adopted technical means. As energetic Sufficient radiation sources are available today, especially lasers Laser diodes are already available, if only for one relatively long-wave radiation range. The fixed Ma The magnetic coil must generate a large magnetic field, all of which Data tracks covered. This has the advantage that a Posi tion of the solenoid is not necessary, however also because of the large distance between the solenoid and the magne to-optical layer of the storage disk at a given Field strength requires a high magnetic flux. The can only be with a large cross section and a high Am pere number of turns of the solenoid, which results in a high Inductance results. From this it follows that time constant for reversing the polarity of the magnetic field in conventional magneto-op tables save this structure principle in the order of magnitude of 5 ms.

In addition to the disadvantage of the size of the solenoid conditional, relatively large overall height, particularly in the case of devices with a disk stack formed from several storage disks leads to undesirably large device dimensions construction principle another, significant defect. There we  against the inertia of the magnetic coil with constant magnetic fields the re-enrollment process is required Erasable magneto-optical memories are one of those again write upstream round of deletion. In this round of deletion who the all storage domains along the data to be overwritten track magnetized first in the same direction, d. H. they for example, all contain the same information bit "0".

The magnetic field is then applied before the actual writing process reversed polarity. Be selective in the data track to be written only those storage domains heated by radiation, should be stored in the information bits "1". To the laser beam must correspond to the information to be registered tion can be switched on or off. For example, a rotational speed of 1800 rpm for the storage disk as one needs, as can be easily calculated, for the delete round and the write process for each data track 33 ms. If you add the polarity reversal time, this results in a period of approx. 70 ms for writing ben a data track. This explains the Optical storage previously required and in relation to other dynamic memories have a relatively long processing time.

The present invention is therefore based on the object a magneto-optical memory of the type mentioned create based on the well-known magneto-optical Storage principles a much cheaper processing time offers.

According to the invention, this task is performed by the Oberbe Handle of claim 1 marked magneto-optical Memory by be in the characterizing part of this claim written characteristics solved.

The invention provides instead of a fixed magnetic coil to use a special magnetic head on the same Disk side as the optical readhead is arranged. This  Magnetic head is close to the layer surface together with the op table read head and is constructed so that it is a vertical magnetic field generated. This magnetic field can be because of arrangement of the head close to the layer is considerably less energy-intensive be placed than the magnetic field of the solenoid coils previously cher magneto-optical memory. In addition, the substantial reduction in the air gap of the magnetic Wi the level was greatly reduced. All of this enables the magnetic head miniaturize system so that the magnetic head together with the optical readhead can be positioned. But this allows the cross section of the magnetic field to be significant to reduce what will allow further miniaturization is coming.

This creates a vertical magnetic head that due to its light weight together with the optical readhead can be positioned without the mass and thus the Inertia of this integrated scanning unit in impermissible white se is increased. In addition, the low inductance leaves this Magnetic head a quick polarity reversal of the magnetic field in the MHz range rich to. This allows a write procedure for the magneto-opti storage, in which continuous laser light is is worked and the information by reversing direction of the magnetic field is inscribed. So there is no need separate deletion revolution before rewriting of Infor mation, so that for the entire writing process compared to a conventional erasable magneto-optical memory we less than half the time is needed.

With conventional optical and magneto-optical memories as is well known, the maximum writing density essentially depends on the Bundling of the focused laser beam depending on the is of the order of magnitude of the wavelength of the laser used. In the solution according to the invention, the maximum writing density is however only dependent on it to a limited extent, because Ratio of the speed of the disk to the possible flow frequency of the vertical magnetic head. So far  was the increase in writing density for optical memories the fact that short-wave semiconductor lasers are already available, but they are not yet sufficient emit appropriate radiation energy. So with a fiction according to the memory structure, a longer-wave laser for generation of the writing beam are used, the maximum flow frequency of the vertical magnetic head be the writing density Right. As is well known, a is essential for the reading process Low-energy laser beam sufficient, so that a laser shorter wavelength with a correspondingly sharper bundle focal spot can be used.

Not absolutely necessary, but is particularly advantageous it if according to a development of the invention in the Spei disk below the magneto-optical storage layer magnetically conductive reflux layer is arranged. About these Layer the magnetic circuit of the magnetic head can be closed, so that stray field losses decrease, the magnetic Wi the level is further reduced and there is therefore the possibility to further optimize the positionable magnetic head.

Further advantages of the invention also result from the following description of embodiments based on the drawing is done. It shows:

Fig. 1 shows schematically in the form of a block diagram the structure of a magneto-optical memory according to the invention,

Fig. 2 shows the layer structure of a magneto-optical Speicherplat te for the memory of FIG. 1,

FIGS. 3 to 8 different embodiments of a Vertikalma gnetkopfes which is integrated together with the optical pickup in a positionable scanning unit.

The structure of a magneto-optical memory shown schematically in Fig. 1 shows a first laser diode 1 , which emits radiation of the wavelength λ 1 and a second laser diode 2 with the wavelength λ 2, wherein λ 1 should be greater than λ 2. This indicates that the first laser diode 1 generates a high-energy write beam and the second laser diode 2 generates an energetically weaker laser beam with the physically related constraint that the diameter of the focal spots in the focus are directly proportional to the wavelength.

In the beam path of the write beam and the read beam are a collimator lens 3 or 4 for bundling the light emitted by the respective laser diode, as well as a beam-forming prism 5 or 6 , which converts the respective, still el lipically distorted light beam into a beam with a circular gem Reshape the cross section. Both light beams are directed onto a semitransparent mirror 7 , which combines the beam paths and thus directs both the write and read beams through a polarizer 8 to a first deflecting mirror 9 . This deflecting mirror is arranged so that the refracted light beam is directed into a plane that is parallel to a storage disk 10 . This disk runs in the operating state at a continuous speed and is driven by a motor, not shown here. It has circular or also spirally arranged data tracks.

The structure of this storage disk 10, which is matched to the requirements of the scanning unit, is shown in detail in FIG. 2. In direct contact with a carrier layer 11 , which gives the storage plate 10 the strength, a highly permeable layer is preferably arranged, which forms a magnetic reflux layer 12 . A magneto-optical layer 13 , which in turn is covered by a transparent protective layer 14 , lies above it as the actual storage layer. The protective layer 14 protects the magneto-optical storage layer 13 from mechanical damage and chemical environmental influences, but also contains the groove structure usual for optical storage for tracking.

The representation of FIG. 2 is not necessarily to scale, but nevertheless illustrates that the reflux layer 12 and the protective layer 14 are of the same thickness in the order of magnitude, for example approximately 0.2 mm thick. By contrast, the thickness of the magnetic to-optical storage layer 13 is at least 3 orders of magnitude less. Fig. 2 shows only a one-sided layer structure, but for the person skilled in the art it is also particularly familiar from optical storage technology to use double-sided usable storage disks. Such a double-sided storage disk would easily result from the reflection of the layer structure described on the carrier layer 11 . For the sake of simplicity, this possibility is therefore not shown in FIG. 2. In the present case, it does not seem necessary to explain manufacturing methods for such a disk in detail. The person skilled in the art is familiar with the fact that the layered structure starts from the protective layer 14 .

Returning to Fig. 1, the structure shown there illustrates a magneto-optical memory also a scanning unit 15 which can be positioned in a plane parallel to the surface of the disk 10 , as indicated by arrows 16 matically. This scanning unit 15 consists first of all of an optical scanning head 17 , in which a second deflecting mirror 18 is provided, which faces the first deflecting mirror 9 . This second deflecting mirror thus directs the light received from the most deflecting mirror 9 onto a lens 19 which, as schematically indicated, focuses the light beam into a focal spot on the magneto-optical storage layer 13 . Arrows 20 indicate that the lens 19 is arranged in the optical scanning head 17 for readjusting the focus in a vertically movable manner. The second deflecting mirror 18 can be rotatably arranged to track.

The light beam reflected by the magneto-optical storage layer 13 is received by the optical scanning head 17 and sent back via the first deflecting mirror 9 into the polarizer 8 . Due to the polarization rotation of the reflected light beam with respect to the incident light beam, it is deflected more sterically and directed through a converging lens 21 onto a detector arrangement 22 .

The optical system of the magneto-optical memory described so far is quite comparable to the conventional optical or magneto-optical memory. There is therefore no need for detailed descriptions of the structure and function of the individual optical elements at this point. Nor is it necessary to explain in detail how, based on the reading light received in the detector arrangement 22 , the information about the stored data, but also those control information are obtained which control the positioning of the optical scanning head 17 in the direction of the arrows 16 or effect a focus control in the direction of arrows 20 in the case of the vertically movable lens 19 . For the person skilled in the art, a large number of individual solutions are known from the prior art, so that he is also aware that the structure of a magneto-optical memory is shown only schematically and by way of example in FIG. 1, and a large number in the special application Adjustments for a desired guidance of the light beam are possible.

Apart from this, it is essential in the present case that the scanning unit 15 also includes a special magnetic head 23 in addition to the optical scanning head 17 . Accordingly, the schematic representation of Fig. 1 is only indicated that this magnetic head 23 is arranged symmetrically to the optical axis of the scanning head between this and the surface of the disk 10 . It has a truncated cone-shaped recess, which allows the scanning light beam to pass through the magnetic head and to focus on the magneto-optical storage layer 13 .

Various embodiments for this magnetic head are shown in FIGS. 3 to 8. In the embodiment shown in FIG. 3, the vertical magnetic head 23 is fixed via a plastic holder 24 directly on the underside of the storage disk 10 facing the optical probe 17 shown only schematically here. The magnetic head 23 is made of a highly permeable material which has only slight losses at the write frequencies used. It consists, as does the associated top view of the functional surface depicting FIG. 4, of three poles, two external auxiliary poles 25 and a write pole 26th The auxiliary poles 25 and the write pole 26 are connected to one another via a yoke 27 , which carries a magnetic winding 28 . The widely trained auxiliary poles 25 serve to close the magnetic flux from the write pole 26 via the magnetic reflux layer 12 of the memory plate 10 . In order to keep eddy current losses as low as possible, the coating of the storage plate 10 should have the lowest possible electrical conductivity.

As can be seen in FIG. 3, the write pole 26 is conical in the direction of the storage plate 10 and has a frustoconical recess through which the laser beam is focused onto the magneto-optical storage layer 13 of the storage plate 10 . In addition, the magnetic flux of the magnetic head 23 is concentrated by the conical design of its write pole 26 in the area of the optical focus on the disk 10 , so that in this area sufficient magnetic flux is achieved even with a magnetic head of relatively low inductance.

Such a fixed installation of the magnetic head 23 on the underside of the optical scanning head 17 is a structurally particularly simple solution, but it has a system-related disadvantage. The distance of the objective 19 from the surface of the storage disk in optical storage devices is usually in the range of millimeters. In conventional optical memory, this is also quite desirable, since at this distance also dust particles deposited on the surface of the storage disk 10 have no optical or mechanical influence on the function of the optical scanning head 17 . With a permanent installation of the magnetic head 23 , the plastic holder 24 can be designed so that the remaining air gap between the write pole 26 and the surface of the memory plate 10 becomes as small as possible. Nevertheless, a tolerance distance must be maintained in order to be able to absorb the maximum vertical impact of the storage disk 10 .

The embodiment shown in Fig. 5 does not have this disadvantage. Here, the magnetic head 23 , which is constructed essentially as described above, elements 29 via spring on the underside of the optical scanning head 17 is fixed. Similar to the flight heads known from the field of magnetic disk memories, the magnetic head 23 is designed here as an aero dynamic missile. For this purpose, the space between the poles 25 and 26 is filled with a non-magnetic material 30 . In this way, a missile will create ge, the buoyancy of which is compensated for by the restoring force of the spring elements 29 . The balancing of forces should take place in such a way that the distance of the magnetic head 23 from the surface of the storage disk 10 is in the range of micrometers.

This embodiment has the purpose that the magnetic head 23 Verti cal movements of the disk 10 at a constant absolute distance to its surface adapts the vertical movements as closely as possible. This reduces air gap tolerances. This is essential for the writing process. This is because when the air gap between the magnetic head 23 and the storage disk 10 changes, the magnetic flux density in the magneto-optical storage layer 13 also changes .

In addition, such an aerodynamically designed design of the magnetic head opens up the possibility of dispensing with the focus readjustment that was previously always required in all optical memories. Provided that the tolerance of the position between the magneto-optical storage layer 13 and the surface of the protective layer 14 of the storage disk 10 is not greater than the depth of field of the lens 19 , the magnetic head 23 can take over the focusing of the scanning light beam by its self-control. In this case, as is shown schematically in FIG. 4, the lens 19 is fixed directly on the magnetic head 23 with the aid of a lens holder 31 .

In this embodiment, with respect to the function of the magnetic head 23 , the remaining air gap between the storage plate 10 and the magnetic head 23 itself is optimized. However, it should be taken into account that this is only practicable in applications with hard drives installed in a hermetically sealed housing. Similar to the magnetic layer disk storage, comparable problems with the absence of dust occur here, so that with this solution one of the advantages of the optical storage disks, their insensitivity to dust, is deferred in favor of other advantages.

Another embodiment shown in FIG. 6 remedies this. Here, too, the magnetic head 23 is resiliently suspended from the underside of the optical scanning head 17 with the aid of Fe derelemente 29 . Here, however, the magnetic head 23 is designed as an aerostatic missile. This is achieved in that air, which is under a slightly positive pressure, is blown between the underside of the magnetic head 23 and the surface of the storage disk 10 via vertically arranged air channels 32 . The magnetic head 23 thus floats on a constantly renewed air cushion approximately 100 μm above the surface of the storage disk 10 .

This embodiment requires a slightly larger air gap, but is significantly less sensitive to dust deposits more sensitive, especially dust particles due to the supplied air still be blown away. Such an embodiment is therefore especially when the magneto- optical storage to be preferred as removable disk storage.  

All of the embodiments described above were based on a magnetic head with a substantially rectangular base with a distinctive yoke carrying the magnetic winding arranged between auxiliary poles and a zen trical lying pole.

In the context of the present technical teaching, magnetic development can also be arranged differently. This is illustrated in FIGS. 7 and 8, which show a side view and a top view of the functional surface of a magnetic head 23 'which is rotationally symmetrical. As before, the write pole 26 'is frustoconical, but is only surrounded by a self-contained auxiliary pole 25 ' at a distance. Auxiliary pole 25 'and write pole 26 ' are connected to one another via an annular plate forming the yoke 27 '. In the space between the auxiliary pole 25 'and the write pole 26 ', the magnetic winding 28 'is now arranged concentrically with the optical axis. Wickelan connections are performed, for example, through a bore 33 in the yoke 27 'or a groove-shaped recess 34 in the auxiliary pole 25 '. The rotational symmetry of this embodiment is particularly gün stig with respect to the reduction of the magnetic leakage flux and allows easy manufacture of the Magnetkopfker nes, but also the magnetic winding 28 ', which in turn can be embedded in a non-magnetic material. This construction of the magnetic head can also be combined with embodiments which have been described above with reference to FIGS. 3, 5 and 6.

A large number of configurations are conceivable within the scope of the described embodiments. For the sake of simplicity, only the simplest embodiment with only a single storage plate coated on one side is shown in the drawing. However, this does not imply any restriction, since the person skilled in the art knows both double-sided coated storage disks and possibilities for combining several such storage disks into a stack of disks. Likewise, it has already been pointed out that the optical system described represents only one possible embodiment and is reproduced as simply as possible for reasons of clarity. According to the present technical teaching one will preferably arrange as many of the required optical elements in the drive of the magneto-optical memory fixed to the frame in order to optimize the inertial mass of the scanning unit 15 to be positioned. However, this is not an imperative in all applications. In addition, a second energy-weaker, shorter-wave laser does not necessarily have to be used in addition to a long-wave laser. All that is needed is a single radiation source, the radiated energy of which is then reduced during reading processes. Using the present technical teaching, there are thus a multitude of possibilities for the person skilled in the art.

Claims (11)

1. Magneto-optical memory with a continuously rotating in the operating state, the magneto-optical storage layer carrying storage disk, with an optical system for generating a polarized, parallel incident light beam or for coupling out a reflected light beam and with a track selection radially to the storage disk positionierba ren scanning unit and one of the storage plate adjacent to ordered solenoid for generating a magnetic field required for storing information, characterized in that the solenoid is designed as a vertical magnetic head ( 23 , 23 ') and with an optical scanning head ( 17 ) from the scanning unit ( 15 ), arranged on the same side of the disk ( 10 ), forms an integrated module and is symmetrical to the optical axis of the scan head between this and the disk and from the disk surface separated only by an air gap, arranged that on the one hand that opt ische system has at least one radiation source ( 1 ) which continuously emits sufficient radiation energy for storing information and on the other hand the magnetic head ( 23 , 23 ') is designed such that it has a vertically directed magnetic field with a controlled by the information to be stored Magnetization direction he creates. 2. Magneto-optical memory according to claim 1, characterized in that the magnetic head ( 23 ) made of highly permeable material is formed with a substantially rectangular base as a three-pole head, the two, with respect to the optical axis of the scanning head ( 17 ) lying outside Auxiliary poles ( 25 ) and an internal write pole ( 26 ) which is connected to the auxiliary poles via a common yoke ( 27 ) which carries a magnetic winding ( 28 ). 3. Magneto-optical memory according to claim 1, characterized in that the magnetic head made of highly permeable material ( 23 ') consists of a rotationally symmetrical shell core which near the optical axis has a writing pole ( 26 ') and at a distance surrounding an annular, with the write pole via a plate-shaped yoke ( 27 ') connected auxiliary pole ( 25 '), and a magnet winding ( 28 ) arranged between the poles and concentrically aligned with the optical axis. 4. Magneto-optical memory according to claim 2 or 3, characterized in that the write pole ( 26 ) of the magnetic head ( 23 ) has a symmetrical recess to the optical axis of the optical scanning head ( 17 ), through which the scanning beam on the magneto-optical storage layer ( 13 ) is focused. 5. Magneto-optical memory according to one of claims 2 or 3, characterized in that the yoke ( 27 , 27 ') of the magnetic head ( 23 , 23 ') in relation to the vertical dimensions of the poles ( 25 or 25 ', 26 or . 26 ') thin-walled and arranged on the side facing away from the storage plate ( 10 ) and that the space delimited by the poles and the yoke of the magnetic head is filled with a non-magnetic material ( 30 ). 6. Magneto-optical memory according to one of claims 1 to 5, characterized in that the Ma gnetkopf ( 23 ) on the disk ( 10 ) facing the underside of the optical scanning head ( 17 ) is permanently installed. 7. Magneto-optical memory according to one of claims 1 to 5, characterized in that the Ma gnetkopf ( 23 ) via spring elements ( 29 ) on the storage plate ( 10 ) facing the underside of the optical scanning head ( 17 ) articulated, and as a missile is formed, the sen buoyancy when the disk is rotating causes it to float above the disk itself while holding it at a predetermined distance from the surface of the disk. 8. Magneto-optical memory according to claim 7, characterized in that an incident light beam on the magneto-optical memory layer ( 13 ) fo kissing imaging optics ( 19 ) is fixed to the magnetic head ( 23 ). 9. Magneto-optical memory according to one of claims 1 to 5, characterized in that the Ma gnetkopf ( 23 ) on the storage plate ( 10 ) facing the underside of the optical scanning head ( 17 ) via spring elements ( 29 ) is elastically articulated and that to generate an air cushion between the magnetic head and the surface of the storage disk in the region of the magnetic head, air channels ( 32 ) which are under pressure and which are open in the direction of the storage disk are provided. 10. Magneto-optical memory according to one of claims 1 to 9, characterized in that the storage plate ( 10 ) next to an outer protective layer ( 14 ) and an underlying magneto-optical memory layer ( 13 ) arranged below the storage layer, magnetically conductive reflux layer ( 12 ). 11. Magneto-optical memory according to one of claims 1 to 10, characterized in that the optical system has two radiation sources ( 1 , 2 ), from de NEN the first radiation source ( 1 ) with longer-wave radiation ( λ 1) for generating a light beam Higher radiation energy is used, which is sufficient for writing information and the second radiation source ( 2 ) emits a light beam with short-wave radiation ( λ 2) but lower radiation energy for non-destructive reading.