WO1989008914A1

WO1989008914A1 - Apparatus for writing data on a magneto-optic recording medium

Info

Publication number: WO1989008914A1
Application number: PCT/US1989/000955
Authority: WO
Inventors: Hartvig Edmund Melbye
Original assignee: Storage Technology Corporation
Priority date: 1988-03-10
Filing date: 1989-03-09
Publication date: 1989-09-21
Also published as: AU3351589A

Abstract

The apparatus for writing data (109) on a magneto-optic recording medium (100) provides simultaneous erasure of old data and writing of new data with one laser beam (110). This is accomplished by operating the laser (104) in the continuous power mode and reversing the magnetic field in synchronization with the data (109). This apparatus includes an annular or doughnut-shaped magnetic transducer (103) which provides a switchable, vertically oriented magnetic field that is applied to the magneto-optic recording medium (100) through the hole in the annular magnetic transducer (103) and is focused on the surface of the recording medium (100) to provide the heat necessary to render the recording medium (100) susceptible to magnetization.

Description

APPARATUS FOR WRITING DATA ON A MAGNETO-OPTIC RECORDING MEDIUM

FIELD OF THE INVENTION This invention relates to magneto-optic recording systems and, in particular, apparatus for concurrently erasing data storage tracks and writing data on data storage tracks using a single laser beam.

PROBLEM

It is a problem in magneto-optic recording systems to simultaneously and efficiently erase data storage tracks and write data on the data storage tracks of the magneto-optic recording medium. Existing systems either make use of two lasers to simultaneously perform these operations or perform two sequential operations, first to erase the data storage tracks on the magneto-optic recording medium and then write data on these erased data storage tracks by passing the recording medium past the write/erase apparatus twice. Rewritable magneto-optic recording media are fabricated from materials that exhibit perpendicular anisotropy. When a portion of the recording medium is heated to a sufficiently high temperature in the presence of a magnetic field that is perpendicular to the recording surface of the recording medium, the heated area is magnetically oriented in:the. direction- of the lines of force of the magnetic field. The. magnetic field is produced by a magnetic: transducer- and the heat is produced by a laser beam focused. on, a spot on the recording surface of the magneto-optic: recording medium.

In the systems that make use of two lasers, a= first laser beam is focused on the data storage track of the recording medium to make the data storage track susceptible to erasure. A constant magnetic field is applied to the data storage track on the spot where the laser beam is applied to the data storage track to erase any data stored on the data storage track. This process leaves the recording medium in an erased, unidirectional magnetic state. A second laser positioned in close proximity to the first laser is used to write data on the erased data storage track. At the location of the second laser a constant field of opposite polarity is applied. The write operation is performed by pulsing the second laser in synchronization with the data input to the write apparatus in the presence of the applied reverse polarity field. This process reverses the magnetization of the recording medium according to the data pattern to thereby write data on the erased data storage track.

Alternatively, a single laser can be used to perform the erase and write operation. This is accomplished by first applying a constant magnetic field to the data storage track of the magneto-optic recording medium and focusing the laser beam on the area on the data storage track to which the magnetic field is applied to erase the entire data storage track. Once the entire data storage track has been erased, the laser is then used to perform a write operation on a consecutive pass. As with the two laser system described above, the constant magnetic field is applied to the data storage track to render it susceptible to writing by the laser beam. The laser is then pulsed in synchronization with the input data to write the data on the erased data storage track of the recording medium.

These systems are either time-wise inefficient because they require two successive operations to erase then write the data storage tracks or require complex apparatus including an erase laser and a write laser to concurrently perform the erase and write operation on the data storage track of the magneto- optic recording medium.

SOLUTION

The above-described problems .are '.solved 'and a. technical advance is achieved in the field_ by the write apparatus for a magneto-optic recording,medium. The write apparatus provides simultaneous erasure of old data and writing of new data with one laser beam. This is accomplished by operating the laser in the. continuous mode and reversing the magnetic field in synchronization with the data to simultaneously achieve erasure/writing of data. This apparatus includes an annular or doughnut-shaped magnetic transducer which provides a focused switchable vertically oriented magnetic field that is applied to the data storage track of the magneto-optic recording medium. The laser beam goes through the hole in the center of the annular magnetic head and is focused at the surface of the magnetic medium to provide the heat necessary to either erase the data stored on the data storage track and/or to write new data on the data storage track. In order to efficiently accomplish the simultaneous erasure/writing of data on the data storage track, the laser is left on continuously and the magnetic field provided by the annular magnetic head is reversed according to the data pattern. This allows simultaneous erasure and writing of new data with a single laser beam.

The annular magnetic head provides a magnetic field that is substantially perpendicular to the recording surface of the recording medium in the location where the data recording is to take place. The annular magnetic head provides a magnetic field which goes through and is parallel to the axis of the annular magnetic head. The annular magnetic head is positioned above the recording medium such that it provides the desired vertical magnetic field in the medium. By positioning the laser so that the laser beam goes through the hole in the center of the annular magnetic head, and is focused at the surface of the recording medium, the recording medium is illuminated and thus heated where the erasure/writing is desired. Thus, the magnetic field is vertical and the laser beam is focused on a spot on the data storage track of the magneto-optic recording medium. The magnetic field can therefore be switched according to the desired written data pattern and simultaneously achieve erase and write modes rather than requiring two successive operations or two independent sets of apparatus.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 illustrates apparatus for writing" data on a magneto-optic recording medium;

Figure 2 illustrates a cross-sectional view of the annular magnetic head; and

Figure 3 illustrates apparatus for reading information from a magneto-optic recording medium.

DETAILED DESCRIPTION

Rewritable magneto-optic recording media are fabricated from materials that exhibit perpendicular anisotropy. These media are susceptible to magnetization by the application of a strong magnetic field to the recording surface of the recording medium. When a portion of the recording medium is heated to a sufficiently high temperature, the heated area is magnetically oriented in the direction of the lines of force of the magnetic field applied perpendicular to the recording surface of the recording medium. The use of heat renders the magnetic media susceptible to magnetization in the presence of a much less intense magnetic field. The magnetic field is produced by a magnetic transducer and the heat is produced by a laser beam focused on a spot on the recording surface of the magneto-optic recording medium.

Thus, in a magneto-optic recording medium, the write process requires the simultaneous application of a magnetic field and heat. The heat renders the magneto-optic recording medium susceptible to magnetization in the presence of a lower magnetic field and this magnetic field magnetically orients the recording medium in one of two magnetic directions. Heat is typically provided by the focused radiation from a laser source to heat a selected position or spot on the recording medium. The laser heats the magneto-optic recording medium to a temperature in proximity of the recording medium's Curie temperature or compensation temperature. At this temperature, the magneto-optic recording medium is susceptible to the lower applied magnetization, which magnetization is provided by a magnetic transducer.

In magneto-optic recording systems-, the data is . normally (usually) self-clocked. The presence of",a. varying pattern of recorded l's and O's is used by the read circuitry to obtain a clock signal. , To-^" improve the accuracy of the clock signal generation, various coding schemes are used to increase the number of transitions between the two directions of magnetization in the data written on the recording medium 100. This insures that a long succession of 1 or 0 bits would not adversely affect the clock signal generation by forcing transitions at a minimum code dependent rate between the two directions of magnetization of recording medium 100.

Erasure of Previously Written Data and Writincr of New Data

In a magneto-optic recording medium that has data stored thereon _r the old data must be removed from the recording medium before new data is written thereon. In existing systems, erasure of old data is achieved by providing a constant DC magnetic field, typically generated by a single pole head magnetic transducer and heat from a continuously activated laser. The entire data storage track of the magneto-optic recording medium is erased by the use of this apparatus which leaves the recording medium in an erased, unidirectional magnetic state. New data is written onto this erased data storage track by reversing the magnetic field from the single pole head to the opposite direction of the erase cycle and then gating the laser on and off in synchronization with the input data to thereby reverse the magneto-optic recording medium magnetization according to the data pattern. As can be seen, this requires two sequential operations to write data on the magneto-optic recording medium. This is timewise inefficient and would not make the system compatible with conventional magnetic disk files. Some systems have been developed to provide erase apparatus in proximity with write apparatus, which apparatus comprises two lasers, one for each of these functions. While this two laser apparatus is timewise efficient, it doubles the amount of equipment necessary to erase and write data on the data storage tracks of the magneto-optic recording medium as well as complicates the electronics since the time delay between the laser beams must be accounted for.

Switched Magnetic Field

For writing on a magneto-optic recording medium 100 the present apparatus uses a single laser diode 104 and an annular or doughnut shaped magnetic transducer 103 to provide simple and time/ise efficient apparatus for concurrently erasing and writing data on the data storage tracks of a magneto- optic recording medium. The laser diode 104 is switched on continuously to provide the heat to render the data storage track of the magneto-optic recording medium 100 compliant to low level magnetization. The applied magnetic field must be substantially perpendicular to the recording surface of the recording medium 100 in the location where the recording is to take place. The annular magnetic transducer 103 generates a magnetic field which is parallel to the axis of the annular magnetic transducer 103. The annular magnetic transducer is positioned above the recording medium such that it provides the desired vertical magnetic, fiel - in the recording medium 100.. The laser diode^" -1.04- is positioned such that the laser .beam goes through, the center of the hole in the annular magnetic transducer ■ 103 and is focused on the recording medium 100 to thereby illuminate and heat the recording medium 100 where the erasure/writing is desired.

The concurrent erasure and writing operations are performed by switching the magnetic field generated by annular magnetic transducer 103 between the two possible states. Annular magnetic transducer 103 generates a magnetic field that has an orientation perpendicular to the recording surface of recording medium 100. The direction of this magnetic field is determined by the direction of the electric current through annular magnetic transducer 103. When an electric current is applied to annular magnetic transducer 103 in one direction, a magnetic field is generated that has lines of force that go through the hole in annular magnetic transducer 103 in one direction. When an electric current in the reverse direction is applied to the annular magnetic transducer 103, the lines of force of the generated magnetic field go through the hole in the annular magnetic transducer 103 in the opposite direction. Thus, by switching the direction of the electric current applied to annular magnetic transducer 103, the direction of the magnetic field applied to the recording surface of recording medium 100 (and the resultant direction of magnetization of recording medium 100) is switched.

The concurrent erasure and writing of recording medium 100 is accomplished by applying a switched, data dependent magnetic field to the recording surface of recording medium 100. Since a field of sufficient magnitude of either polarity will saturate the medium, erasure of old data previously written will occur. New data is written on the recording medium 100 by switching the electric current applied to annular magnetic transducer 103 to switch the direction of the applied magnetic field and the resultant direction of magnetization of the recording surface of recording medium 100. This transition between the two states of magnetization accomplishes the data writing.

Write Apparatus

The write apparatus of Figure 1 can be a subset of the read apparatus of Figure 3, but is separately described herein for the purpose of simplicity. Figure 1 illustrates the write apparatus of the present invention in block diagram form. This apparatus is positioned above a recording medium 100 which consists of a magneto-optic recording medium of conventional construction. The write apparatus consists of a laser diode 104 which is connected on the cathode side to circuit ground and on the anode side by lead 111 to laser driver 105. Control lead 107 is also connected to laser driver 105 and serves to activate the laser in a continuously on state for the erasure/writing of data on the data storage tracks of the recording medium 100. The light output 110 of laser diode 104 is collimated by collector lens 101 which collimates diverging laser beams into a coherent beam consisting of parallel rays of laser light which is then focused by objective lens 102 to a spot on the recording medium 100. The light from laser diode 104 is focused by objective lens 102 through the hole in the center of an annular magnetic transducer 103. This magnetic transducer is in the shape of a doughnut and serves to generate- a magnetic field^' that is perpendicularrto the surface of the recording medium 100. Write driver 106 is connected by lead.112 and: serves to provide the drive current for the annular' magnetic transducer 103. A data signal consisting of, for example, waveform 109 is applied over lead 108 to. write driver 106 to switch the annular magnetic- transducer 103 between the magnetic field states to write data on recording medium 100. Write driver 106 receives the data signal 109 on lead 108 and amplifies the received signal data into a corresponding transducer drive signal to drive the annular magnetic transducer to produce a magnetic field of sufficient strength perpendicular to the surface of recording medium 100 to magnetize in the desired orientation the spot on recording medium 100 on which the laser light is applied. Thus, the magnetic field generated by annular magnetic transducer 103 and the spot produced by the output of laser diode 104 focused by objective lens 102 impinge on the surface of recording medium 100 in a common spot. Thus, the data recorded on recording medium 100 is determined by the data signal 109 as converted by write driver 106 into transducer drive signals to provide a switched magnetic field via annular magnetic transducer 103 to correspond to the data signal 109. The magnetic field can be in either an upward or downward direction depending on the nature of the data signal that is applied to write driver 106. Previously recorded data stored on the data storage track of recording medium 100 is erased or overwritten during this recording process by the presence of either a 1 or a 0 bit or a string of l and 0 bits in the data input lead 108. Annular Electric/Magnetic Transducer

Figure 2 illustrates a cross-sectional view of the annular magnetic transducer 103. Transducer 103 consists of a plurality of elements including a substrate 12 which is a magnetic means formed of a suitable high permeability magnetic material which is electrically non-conductive. Provided in substrate 12 is a tapered annular aperture 14 which opens to the substrate 12. A current carrying electrical conductor 20 is included in the magnetic transducer 103. This conductor 20 is in the form of a spiral coil which is disposed substantially symmetrically about aperture 15. The coil formed by conductor 20 is substantially planar and lies in a plane spaced somewhat above the top surface of substrate 12. This coil is embedded and supported in a layer 22 of a suitable dielectrical material. Formed over the parts already described is a blanket 24 of high permeability but non-electrically conductive magnetic material which takes the form of a nickel iron alloy, such as Permalloy. A second portion 25 of this blanket 24 extends in a fairly uniform layer downwardly in the central portion of the head. This blanket portion 25 is disposed concentric with aperture 14 and constitutes a second magnetic pole of the annular magnetic transducer 103. The bottom face of the second pole face is flush with the lower face or surface of substrate 12. Blanket 24 is also distributed over all of the head including a substantial portion beyond the coil formed by conductor 20 with respect to aperture 14. When the coil is energized with current flowing into the coil conductor on the left portion of Figure 2 and out of the corresponding coil* conductor on the right side, flux is induced to flow along paths' indicated' y the solid arrows 26. The flux paths are around the coil formed by conductor 20 and pass through the substrate 12 as shown through one portion of substrate 12 spaced from the aperture 14. As shown by arrows 26, the flux travels in blanket 24 and in second portion 25 to first surface 27 which is flush with the lower surface of substrate 12 and forms what is termed a second pole face. The flux then travels through the air gap to the edge of the lower surface of substrate 12 which forms a first pole face 13.

Read Apparatus

Figure 3 illustrates in block diagram form the read apparatus of which the above-described write apparatus can be a part for an a magneto-optic recording medium. This apparatus includes a control lead 107 which carries control signals through a laser driver 105 which amplifies the control signals and provides a drive signal on lead 111 to laser diode 104. Laser diode 104 generates a coherent light beam 110 which is collimated by collector lens 101 and applied to polarizer 305. The power of the laser normally applies a lower power light beam during read as compared to the write/erase mode. The coherent light beam that pass through polarizer 305 impinge on half-transparent mirror 306 which permits the polarized light to pass through to focusing objective lens 102 which focuses the light rays into a spot on the recording medium 100 which consists of the data storage tracks of a magneto-optic recording medium. The data storage tracks of this magneto-optic recording medium 100 contain previously recorded information. There is no externally applied magnetic field and the laser power of the laser diode 104 is sufficiently low so as not to disturb the information recorded on the data storage tracks of recording medium 100. The polarized beam is rotated in the presence of the magnetization of recording medium 100 either clockwise or counterclockwise according to the vertically recorded magnetization. This polarized beam is reflected off the surface of recording medium 100, reflected through objective lens 102 to half- transparent mirror 306. Half-transparent mirror 306 receives light that is reflected off the recording medium and reflects this light through analyzer 308 which converts the angular rotation of the light to amplitude modulated light. The output of analyzer 308 is applied to lens 309 which focuses these reflected light rays to impinge on photo detector 310. Photo detector 310 converts the received light energy to electrical energy which is supplied over lead 313 to amplifier 311 to produce a data signal on lead 312 representative of the data that is recorded on recording medium 100.

While a specific embodiment of the invention has been disclosed, it is expected that those skilled in the art can and will implement variations of the preferred embodiment disclosed therein, which variations still fall within the scope of the appended claims.

Claims

I CLAIM:

1. Apparatus for concurrently erasing and . writing data on a magneto-optic recording medium comprising: laser means having a light output focused on a spot on a data storage track of said magneto- optic recording medium for rendering said data storage track compliant to the writing of data thereon; and means for generating a magnetic field on said spot on said data storage track of said magneto- optic recording medium to concurrently erase data previously written on said storage track and write new data on said data storage track.

2. The apparatus of claim l wherein said generating means comprises an annular transducer for converting an electric•current to a magnetic field.

3. The apparatus of claim 2 wherein said laser means is focused through the hole in said annular transducer on said spot on said data storage track of said magneto-optic recording medium.

4. The apparatus of claim 2 further comprising: means connected to said annular transducer for applying an electric current in a first direction to said annular transducer to apply a magnetic field oriented in a first direction to said data storage track to magnetize saidmagneto-optic recording medium in said first direction.

5. The apparatus of claim 4 further comprising: means connected to said annular transducer for applying an electric current in a second direction to said annular transducer to apply a magnetic field in a second direction to said data storage track to magnetize said magneto-optic recording medium in said second direction.

6. The apparatus of claim 5 further comprising: means responsive to a data signal applied to said apparatus for activating said laser means to render said data storage track of said magneto-optic recording medium compliant to the writing/erasing of data thereon.

7. The apparatus of claim 6 further comprising: means responsive to said data signal for switching said electric current between said first and said second directions as a function of the data contained in said data signal.

8. Apparatus for writing data on a data storage track of a magneto-optic recording medium comprising: means for rendering a section of said data storage track of said magneto-optic recording medium compliant to the writing of data thereon; and means for applying a magnetic field to said section of said data storage track of said magneto- optic recording medium to concurrently erase and write data on said section of said data storage track of said magneto-optic recording medium.

9. The apparatus of claim 8 wherein said applying means generates a magnetic field that is perpendicular to the recording surface of said magneto-optic recording medium.

10. The apparatus of claim 8 wherein said. applying means includes: means for applying a magnetic field oriented. in a first direction to said data storage track to ^■ magnetize said magneto-optic recording medium in said first direction; and means for applying a magnetic field oriented in a second direction to said data storage track to magnetize said magneto-optic recording medium in said second direction.

11. The apparatus of claim 10 wherein said last mentioned applying means applies a magnetic field in a direction that is the opposite direction of said first direction.

12. The apparatus of claim 10 wherein said applying means includes: annular transducer means for applying said magnetic field to said spot on said data storage track of said magneto-optic recording medium.

13. The apparatus of claim 12 further including: means for applying an electric current in a first direction to said annular transducer to generate said magnetic field oriented in said first direction.

14. The apparatus of claim 13 further including: means for applying an electric current in a second direction to said annular transducer to generate said magnetic field oriented in said second direction.

15. The apparatus of claim 8 wherein said rendering means includes: laser means for applying a beam of laser light to said section of said data storage track of said magneto-optic recording medium to render said section of said data storage track compliant to the writing of data thereon.

16. The apparatus of claim 15 wherein said rendering means further includes: means for focusing said beam of laser light into a spot on said section of said data storage track of said magneto-optic recording medium.

17. Apparatus for writing data on a data storage track of a magneto-optic recording medium comprising: laser means for applying a spot of laser light to said data storage track of said magneto-optic recording medium to render said data storage track compliant to the writing of data thereon; means for focusing said laser light into a spot on said data storage track of said magneto-optic recording medium; annular transducer means for applying a magnetic field to said spot on said data storage track of said magneto-optic recording medium to write data thereon; means for applying an electric current in a first direction to said annular transducer to generate said magnetic field in a first direction to magnetize said data storage medium in a first direction; and means for applying an electric current in a second direction to said annular '.transducer means ^• to generate said magnetic field in a second direction to magnetize said data storage medium in a second - direction.

18. A method of writing data on data storage : tracks of a magneto-optic recording medium comprising the steps of: rendering one section of one of said data storage tracks of said magneto-optic recording medium compliant to the writing of data thereon; and concurrently erasing and writing data on said compliant data storage track.

19. The method of claim 18 wherein the step of rendering includes the steps of: generating a beam of laser light; and focusing said beam of laser light on a spot in said one section of said one data storage track.

20. The method of claim 18 wherein the step of concurrently erasing and writing includes the steps of: applying a magnetic field to said spot in said one section of said one data storage track in a first direction to magnetize said spot in said one section of said one data storage track in said first direction; and applying a magnetic field to said spot in said one section of said one data storage track in a second direction to magnetize said spot in said one section of said one data storage track in said second direction.

21. The method of claim 20 wherein the step of concurrently erasing and writing includes the step of: switching said magnetic field between said first and said second directions as a function of the state of said data.