GB2120001A

GB2120001A - An optical magnetic reproduction system

Info

Publication number: GB2120001A
Application number: GB08311309A
Authority: GB
Inventors: Joichiro Ezaki; Hiroshi Kanai; Yoshimi Kitahara
Original assignee: TDK Corp
Current assignee: TDK Corp
Priority date: 1982-04-28
Filing date: 1983-04-26
Publication date: 1983-11-23
Also published as: GB8311308D0; GB2120001B; GB2120000A; GB8311309D0; GB2120000B

Description

1 GB2120001A 1

SPECIFICATION

An optical magnetic reproduction system The present invention relates to a reproduc- tion system for magnetically recorded informa tion and, in particular, relates to such a sys tem which reads out magnetically recorded information using an optical technique.

Conventionally, magnetically recorded infor mation, recorded for instance on a magnetic tape, a magnetic disc, or a magnetic sheet, is read out by a magnetic head which has a magnetic core with a thin gap and a coil wound on the core. The magnetic head oper ates on the principle that the relative move ment of the head to the recording medium generates electromotive force on the coil in accordance with the recorded information.

However, the conventional magnetic head has the disadvantage that the recording den sity on a recording medium is not high. A conventional magnetic head typically needs a recording track wider than 30gm.

To increase the recording density it is pos sible to use an optical head which reads out magnetically recorded information using an opto-magnetic effect such as the Faraday ef fect. In such an optical head, a soft magnetic film which has a magnetically soft nature and has its easy magnetisation axis in the thickness direction of the film contacts a recording medium which includes information recorded magnetically. The component of the magneti- cally recorded information perpendicular to the recording medium is copied in the soft magnetic film. The information in the soft magnetic film is read out optically using the Faraday effect in which an optical beam is subject to the rotation of its plane of polarisation according to its magnetisation state. As the Faraday effect is used, an optical polariser and an optical analyser are usually used to detect the optical rotation of polarised optical beam.

However, a prior optical head has the disadvantage that it takes a long time to read out magnetically recorded information, since only a single bit on a soft magnetic film is read at a particular time by illuminating said film with a small spot of light. When a high speed read out is required, the recording medium must run faster, but the improvement of the read out speed by high speed running the recording medium is not large.

According to this invention an optical reproduction system for reading out magnetically stored information comprises an optical head for obtaining a magnetic copy of data magnetically recorded on a magnetic recording medium; conversion means for converting the magnetic pattern into an optical pattern; and, reception means for receiving the optical pattern and converting the optical pattern into 130 an electrical signal, the reception means converting an optical pattern corresponding to a plurality of data into a plurality of electrical signals simultaneously.

A particular example of a system in accordance with this invention will now be described with reference to the accompanying drawings; in which:Figure 1 is a perspective view illustrating the operating, principle of the present invention; Figure 2 is an elevation of a recording head and magnetic tape; Figure 3 is an exploded perspective view illustrating the basic idea of the present invention; Figure 4 is a partly sectioned side elevation of an optical read out device; Figure 5 is a cross section through a read out head; Figure 6 is a plan illustrating the arrangement of information on the recording medium.

In Fig. 1, the reference numeral 1 is a magnetic recording medium with a magnetic recording film la. That recording medium 1 is, for instance, a magnetic tape or a magnetic disc, and the magnetic medium 1 runs in the direction D. The magnetic recording head 52 with the gap G and the winding 53 is ar- ranged close to said magnetic recording film 1 a. The winding 53 is energized with a recording signal which is preferably in a digital form. It should be noted in Fig. 1 that the longitudinal direction of the gap G coincides with the running direction D of the magnetic medium while in a conventional magnetic recording system, a gap of a magnetic head is positioned perpendicular to the running direction of the magnetic medium. Further, it should be appreciated that the width (d) of the gap G is considerably wide (for instance, d = 4 Itm) as compared with a conventional magnetic head in which a gap width is for instance 0.3-0.5 Mm. A signal to be recorded in this case is supposed to be in digital form, and the pulse width (g sec) of the digital signal is considerably narrower than the wavelength of the recorded signal on the recording medium 1. That wavelength is defined by the moving speed of the medium 1, and the repetition frequency of the signal. In one embodiment, when a tape runs with the speed of 4.7 cm/sec, the pusle width is less than 47 gsec, and is preferably less than 1.0 gsec, and still preferably that pulse width is of the order of nano seconds.

In the above configuration, when a recording signal flows in the coil 53, the magnetic flux circulates through the core 53, the yoke 52a, the area (A) of the medium 1, the area (B), and the yoke 52b. Thus, a pair of magnetic cells A and B, which may be N and S, or S and N are provided on the medium 1 according to the recording signal. Thus, those cells A and B store one bit on information.

2 GB2120001A 2 Those cells A and B may be N and S, or S and N according to the recording information (1 or 0). It should be noted that the shape of the pattern A and B is the same as the shape of the yokes 52a and 52b. Plurality pairs of cells compose a pattern of recorded data.

It should be appreciated that the magnetic flux generated by the winding 53 does not go through the gap G, but the flux goes through the first yoke, the medium and the second yoke, because that gap G is too wide to shunt the magnetic path.

It should be appreciated that a two-dimentional pattern like a picture may be recorded by arranging a plurality of heads of Fig. 1. In that case, each cell in a picture is represented by a pair of elements A and B on a recording medium.

Now, the reproducing stage by optical head according to the present invention is described.

Fig. 3 shows the principle idea of the present optical head. In the Figure, the reference numeral 1 is a recording medium like a magnetic tape, which runs in the direction D. It is supposed that the medium 1 has the magnetic layer on which a digital signal (like PCM signal) is recorded. The digital signal may be recorded not only by the vertical recording system but also the conventional horizontal recording system. The magnetisation direction of the magnetic medium may be perpendicular to the plane of the medium, parallel to the plane of the medium or have components in both of these directions. The reference numeral 2 is a conversion means for converting magnetic pattern on an optical head to an optical pattern by using the Faraday rotation of the polarised plane of the electro-magnetic wave or an optical beam. A plurality of data, that is to say, m number data in the running direction of the tape 1, and n number of data in the width direction of the tape 1, are read out simultaneously by said conversion means 2, and that data is applied to the reception system 3. The conversion means 2 reads out the data optically as described later.

The reception system 3 has a two dimen- sional plane parallel to the tape 1, and a plurality of cells each relating to the data on the tape 1 are provided on that plane. That is to say, m number of cells times n number of cells are arranged on the plane. Thus, each cell relates to each data on the medium. The reception system 3 is, for instance, implemented by a plurality of photo-transistors arranged on the plane, alternatively, that reception system 3 is implemented by a charge coupler semiconductor device (CCD). Each cell on the reception system reproduces the corresponding data on the magnetic tape, and that cell provides an output reproducing electrical signal according to the data stored in the medium 1 Fig. 4 shows the optical reproducing system according to the present invention, in which the same reference numerals show the same members as those in the previous figures. The reference numeral 4 is an optical head which operates on the principle of the optic-magnetic effect.

Fig. 5 shows the cross section of the optical head 4 in detail. In Fig. 5, the symbol 4a is a GdGa garnet substrate which is optically transparent and has the thickness of 0.2-0.5 mm. The symbol 4b is a soft magnetic film with a magnetically soft nature attached on the surface of that substrate 4a. The symbol 4c is a reflection film attached on the soft magnetic film 4b for reflecting an optical beam, and the symbol 4d is a protection layer Of Si02 attached on the reflection film 4c. The soft magnetic film 4b is made of the optically transparent and soft magnetic material, like YSmCaF.G. group garnet (for instance Y1_92Sm0.jFe4_02Ge0.11012), and said soft magnetic film 4b an easy magnetization axis which is perpendicular to the film plane, and said soft magnetic film has the thickness of about 6 Am. The optical head 4 is used so that the film 4d contacts the recording medium 1.

When the optical head 4 touches with the recording medium 1, the magnetic domain in the soft magnetic film 4b is magnetized by the vertical component of the recorded data on the medium 1 in the vertical direction to the film plane. When a digital signal, like PCIVI signal is recorded on the medium, the magnetic pattern in the domain on the soft magnetic film is a copy of the digital signal recorded on the medium 1. That magnetic pattern of the domain is read out optically.

In Fig. 4, the reference numeral 5 is an optical source for generating an optical beam, and is implemented for instance by an LED (light emitting diode), or a He-Ne laser, 6 is a polarizer which polarizes linearly the beam from the optical source 5. The numeral 7 is a beam splitter which offsets the horizontal beam in the figure, but passes directly the vertical beam in the figure. The numerals 9 and 10 are a condenser lens and a focusing lens, respectively. The reference numeral 8 is an optical analyzer, and 3 is a CCD device.

It should be appreciated that an LED (light emitting diode) is preferred as an optical source 5 than a laser, since according to the present invention a beam must be sufficiently wide to illuminate a plurality of cells simultaneously. Further the price of LED is lower that that of a laser.

In Fig. 4, an optical beam generated by the source 5 illuminates the optical head 4 through the polarizer 6 which polarizes the beam linearly, the beam splitter 7 which reflects or offsets the beam. It is supposed that the beam has some cross section area, and therefore, an area on the optical head 4 is illuminated simultaneously. The beam thus c 19 3 GB2120001A 3 illuminating the optical head 4 is reflected by the reflection film 4c in the optical head 4, and the reflected beam illuminates the CCD device through the beam splitter 7, the lens 10, and the optical analyzer 8. When the beam illuminates the optical head, the polarization is rotated by the Faraday effect in the right or left direction according to the direction of the magnetization in the domain on the soft magnetic film 4b. Since the beam is polarized by the polarizer 6, the output beam from the analyzer 8 is modulated by the rotation direction by the Faraday effect, that is to say, the intensity of the beam at the output of the analyzer 8 depends upon the recorded data. The intensity of the modulated beam of the output of the analyzer 8 illuminates the CCD device 3 so that the two dimention pattern of the data on the medium is copied on the plane of the CCD device.

In Fig. 4, the reference numeral 20 is a pulse generator which supplies a transfer pulse to the CCD device, and an operation pulse to a motor (not shown) which rotates the capstans 22 and 22a to feed the magnetic tape 1 so that each transfer of the charge in the CCD device 3 is synchronized with the movement of data on the magnetic tape 1. The numeral 30 is an output terminal of the CCD device 3 for providing an output electrical signal.

In one modification of the present invention, an optical head 4 is omitted, and a magnetic pattern on a recording medium 1 is directly illuminated by an optical beam and said magnetic pattern is directly read out without copying the pattern in the head 4.

The two operational modes are possible in the present invention concerning the syn- chronization of the transfer of the charge in the CCD device with the movement of the magnetic tape 1. It is assumed that n = 128 data are stored in the width direction of the magnetic tape 1, and m = 16 data are grouped in the moving direction D of the magnetic tape 1 as shown in Fig. 6. In the first operational mode, a copy of 16 X 128 data is illuminated on the CCD device, and when those 16 X 128 ( = 2048) data are read out by the CCD device, the magnetic tape 1 moves in the direction D by the 16 data length so that the succeeding 16 data are read out. In this first mode, the operational speed of the present invention as compared with the system which reads out the data one bit after another is 2048 ( = 16 X 128) times.

On the other hand, in the second operational mode, the magnetic tape 1 moves in the direction D by a single data length syn- chronized with each transfer of the charge in the CCD device. In this second operational mode, each line of data with n = 128 data is substantially read out 128 times by the CCD device. That is to say, in the first stage, those

Claims

128 data illuminate the first line on the CCD 130 CLAIMS device, and when

the charge on the first line in the CCD device is transferred to the second line, the magnetic tape 1 is moved by the one data length. Therefore, in the second stage, the same 128 data illuminates the second line on the CCD device. Thus, the second line is illuminated twice. By repeating the above operation, each line of 128 data illuminates the CCD device 16 times. Therefore, the substan- tial sensitivity of the CCD device is 16 times as high as that of the first operational mode.

As described above in detail, an optical head copies a magnetic pattern which has a plurality of data on a recording medium simul- taneously, and said magnetic pattern modulates an optical beam so that said optical beam includes a plurality of data information, and then, information carried by said beam is simultaneously converted to an electrical sig- nal by using a two-dimensional reception means. Thus, the reading speed in the first operational mode according to the present invention is expressed; f = nmv where n is the number of data in the width direction of a recording medium, m is the number of data in the moving direction of the recording medium, and v is the moving speed of the recording medium, and it should be appreciated that said speed f is considerably improved as compared with that of a conventional optical reproducing system which reads out data one bit after one bit. Further, the sensitivity of the CCD device is considerably improved in the second operational mode by transferring the charge in the CCD device synchronized with the movement of the re- cording medium. The reading speed V in the second operational mode is; f' = mv Further, the moving speed of the recording medium may be slowed without deteriorating the reading out speed.

Accordingly, it should be appreciated that the reading speed and/or the sensitivity of 11 5 the present optical reproducing system is considerably improved by reading a plurality of data which are arranged on a two-dimentinal plane simultaneously.

Further, it should be appreciated that a two- dimention pattern like a picture on a magnetic medium may be read out by illuminating the whole pattern with a laser beam. In that case, it should be appreciated that a pattern is not scanned, as is done in a prior art.

We also tried the numerical embodiment in which m = 256 and n = 128 in our experiment, and observed that the excellent result is obtained.

4 GB2120001A 4 1. An optical reproduction system for reading magnetically stored information cornprising:

an optical head for obtaining a magnetic copy of data magnetically recorded on a magnetic recording medium; conversion means for converting the magnetic pattern into an optical pattern; and reception means for receiving the optical pattern and converting the optical pattern into an electrical signal, the reception means converting an optical pattern corresponding to a plurality of data into a plurality of electrical signals simultaneously.

2. An optical reproduction system accord- ing to claim 1, wherein the reception means includes a charge coupled device.

3. An optical reproduction system according to claim 1, wherein the reception means includes a two-dimensional array of phototransistors.

4. An optical reproduction system according to claim 2, wherein a charge distribution pattern in the charge coupled device is trans- ferred in synchronism with relative movement between the recording medium and the optical head.

5. An optical reproduction system according to claim 4, wherein each line of the charge distribution pattern in the charge coupled device is transferred in synchronism with relative movement between the recording medium and the optical head corresponding to each line of magnetically recorded informa- tion.

6. An optical reproduction system according to any one of the preceding claims, wherein the optical head comprises a substrate, a soft magnetic film attached to the substrate and which is transparent to a beam of light, a reflection film attached to the soft magnetic film, the soft magnetic film being magnetised to a state corresponding to the magnetically recorded pattern on the recording medium and thereby rotates the plane of ploarisation of a beam of which, which passes through the soft magnetic film and is reflected from the reflection film, the plane of poalrisation of the beam of light thus being affected by the magnetically recorded pattern on the recording medium.

7. An optical reproduction system according to any one of the preceding claims, wherein the conversion means comprises an optical source for generating an optical beam, a polariser for polarising linearly the optical beam, a beam splitter for offsetting an output beam of the polariser to illuminate an optical head with an output beam of the polariser and passing a beam reflected by the optical head, and an analyser arranged at an output of the beam splitter to detect the beam reflected by the optical head.

8. An optical reproduction system accord- ing to claim 7, wherein the optical source is P He-Ne laser.

9. An optical reproduction system according to claim 7, wherein the optical source is an LED.

10. An optical reproduction system ac cording to claims 7, 8 or 9, wherein the optical beam has a sufficient cross sectional area to illuminate a a plurality of magnetic cells of the recording medium simultaneously.

11. An optical reproduction system substantially as described with reference to the accompanying drawings.

12. An optical reproduction system for reading magnetically stored information corn- prising conversion means for converting the magnetic pattern into an optical pattern; and reception means for receiving the optical pattern and converting the optical pattern into an electrical signal, the reception means con- verting an optical pattern corresponding to a plurality of data into a plurality of electrical signals simultaneously.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltdl 983Published at The Patent Office, 25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.

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