GB2070314A - Device for reproducing the information on a recorded medium - Google Patents
Device for reproducing the information on a recorded medium Download PDFInfo
- Publication number
- GB2070314A GB2070314A GB8102790A GB8102790A GB2070314A GB 2070314 A GB2070314 A GB 2070314A GB 8102790 A GB8102790 A GB 8102790A GB 8102790 A GB8102790 A GB 8102790A GB 2070314 A GB2070314 A GB 2070314A
- Authority
- GB
- United Kingdom
- Prior art keywords
- wave guide
- light beam
- transfer film
- magnetic transfer
- light
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
- G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
- G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
- G11B11/10532—Heads
- G11B11/10541—Heads for reproducing
- G11B11/10543—Heads for reproducing using optical beam of radiation
- G11B11/10547—Heads for reproducing using optical beam of radiation interacting with the magnetisation of an intermediate transfer element, e.g. magnetic film, included in the head
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/002—Recording, reproducing or erasing systems characterised by the shape or form of the carrier
- G11B7/003—Recording, reproducing or erasing systems characterised by the shape or form of the carrier with webs, filaments or wires, e.g. belts, spooled tapes or films of quasi-infinite extent
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/123—Integrated head arrangements, e.g. with source and detectors mounted on the same substrate
- G11B7/124—Integrated head arrangements, e.g. with source and detectors mounted on the same substrate the integrated head arrangements including waveguides
- G11B7/1245—Integrated head arrangements, e.g. with source and detectors mounted on the same substrate the integrated head arrangements including waveguides the waveguides including means for electro-optical or acousto-optical deflection
Landscapes
- Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Optical Integrated Circuits (AREA)
Abstract
This invention relates to a reproducing head utilizing the scanning of a beam spot. The reproducing head comprises a thin film wave guide 2, means such as an electroacoustic transducer 6 for deflecting a light beam 5 propagated through the wave guide, and means 9 for condensing the deflected light beam 8. In the reproducing head, a magnetic transfer film 10 is provided on the light exit surface of the wave guide 2 and the light beam 8 is condensed at a spot thereon. The beam spot scans over the magnetic transfer film 10 to which the information on a recorded medium 13 has been transferred, and the light from the magnetic transfer film is detected to reproduce the information on the recorded medium. <IMAGE>
Description
SPECIFICATION
Device for reproducing the information on a recorded medium
BACKGROUND OF THE INVENTION
Field of the invention
This invention relates to a reproducing head utilizing the scanning of a beam spot.
Description of the prior art
Apparatus for scanning a laser beam spot have heretofore comprised a rotational polygon mirror for deflecting the laser beam and an f-0 lens or the like for condensing the deflected beam into a spot moving at a linear speed. In these prior art apparatus, however, various operating portions have been separate and independent and a predetermined light path interval has been required therebetween and therefore, precise adjustment during the assembly of the apparatus has been very much complicated and the assembled apparatus has been bulky.
There are also known apparatus which use an acoustic optical deflector instead of a rotational polygon mirrorto make the apparatus compact. An example of such apparatus is disclosed in U.S. Patent No.
3,514,534, but even in that example various operating portions are still independent and therefore, cumbersome adjustment has been required during the assembly.
On the other hand, to reproduce images from a magnetic recording medium on which, for example, TV signals are recorded, it is necessary to move the recording medium and a signal reading head relative to each other at a high speed to thereby effect scanning in order to obtain a high frequency of 4.2MHz which is the band of NTSC signal. In the conventional VTR for domestic use or the like, mechanical scanning devices which effect reading by a head rotated at a high speed inside of a recording medium wound on a cylinder have been typical. Generally, however, mechanical scanning devices are inferior to optical scanning devices in accuracy and durability in the case of high-speed scanning and accordingly, there have been desired compact recording or reproducing apparatus utilizing an optical scanning device which can readily realize stable high-speed scanning.Recently, attention has particularly been paid to a system which utilizes the magnetic Kerr effect or the Faraday effect to effect beam spot scanning on a magnetic recording medium and thereby accomplish magnetic recording or reproduction. However, the aforementioned disadvantages of the conventional optical scanning devices have prevented their application to compact and high frequency band recording or reproducing apparatus.
Summary of the invention
Accordingly one aspect of the present invention provide a compact and novel device for reproducing the information on a magnetic recorded medium which utilizes optical high-speed scanning.
This aspect of the invention utilizes the technique of the light integrated circuit. Recently, there is known a technique of forming a thin film lens, an A/O deflector or an E/O modulator in a thin film waveguide path formed on a base to thereby make a light integrated circuit, as explained in T. Tamir, Integrated Optics, published by Spinger Verlag, Inc.(1975). Further, a deflector utilizing the acousto-optic action in a thin film waveguide path to diffract a parallel light beam is disclosed in Proc. IEEE 64, 779(1976) E.G. Lean et al, Thin
Film Acoustooptic Devices. Also, an example of the transducer for generating an acoustic wave in a waveguide path over a wide band is disclosed in SPIE 139, 139(1978) C.S. Tsai, Guided Wave Optical
Systems and Devices.
Atypical device according to this invention is characterized in that a magnetic transfer film is provided on the light beam exit surface of a thin film waveguide path and a light deflecting portion for deflecting the light beam directed into the waveguide path is provided on a portion of the waveguide path and a condenser lens portion for condensing the light beam and forming a beam spot is provided on or nearthe magnetic transfer film provided on the exit surface and that the magnetic transfer film to which is transferred the information recorded on a magnetic recording medium positioned in intimate contact with or in proximity to said transfer film is beam-spot-scanned and the light therefrom is detected to read the recorded information.
The term "light" used herein includes electro-magnetic radiation in both the visible and invisible portions of the spectrum. The term "recording medium" includes magnetically and optically recorded mediums, mediums on which information is permanently recorded, and mediums capable of being re-recorded.
The invention will become more fully apparent from the following detailed description thereof taken in conjunction with the accomapanying drawings.
Brief description of the drawings
Figure 1 is a view showing the whole of the reproducing head according to an embodiment of the present invention.
Figure 2 is a plan view of a light deflecting portion.
Figure 3 is a perspective view of a light deflecting portion for deflecting light over a wide band.
Figure 4 is a fragmentary view showing a modification of means for detecting the reflected light from a magnetic transfer film in the head of Figure 1.
Description of the preferred embodiments
Referring to Figure 1, there is shown a magnetic reproducing head which is a first embodiment of the present invention. In this reproducing head, thin film lenses 4, 9 and a comb-tooth-like electrode 6 are provided on a thin film waveguide path 2 formed on a piezoelectric base 1. The light beam from a semiconductor laser 3 disposed with a spacing integer times as great as the 1/2 wavelength of the laser light interposed with respect to the entrance end surface of the base 1 is directed into the thin film waveguide path 2 and is made into a parallel light beam 5 by the thin film lens 4. The parallel light beam 5 propagated through the waveguide path is diffracted and deflected by an ultrasonic wave surface elastic wave 7 which is excited by the comb-tooth-like electrode 6 provided on a portion of the waveguide path 2.Further, this deflected light beam 8 is condensed by the thin film lens so as to form a beam spot 14 on or nearthe exit end surface of the thin film waveguide path. In y-direction perpendicular to the surface of the waveguide path, the width of the spot is limited by the thickness d(usually several Ftm) of the waveguide path. By continuously varying the frequency of the high frequency voltage applied to the comb-tooth-like electrode 6, the light-condensed point moves on an arc centered at the thin film lens 9 with the focal length f as the radius.
In the reproducing head of the present embodiment, the exit end surface of the thin film waveguide path is set to an arcuate shape substantially coincident with the locus (image plane) of the aforementioned light-condensed point, and a magnetic transfer film 10 and a protective film 12 are formed on that end surface. Accordingly, said beam spot is scanned on or along the neighborhood of the magnetic transfer film.
The portions which constitute the beam spot scanning device of the above-described embodiment will now be described in greater detail.
A material having a piezoelectric effect and through which ultrasonic wave of high frequency may be efficiently propagated in suitable for the base 1, and LiNbO3, LiTaO3, ZnO or the like is desirable. In a case where the base is formed of LiNbO3, the waveguide path 2 may be formed to a thickness of several ym on the base by in-diffusing Ti under a high temperature (about 1000 C). In a case where the base is formed of Lao3, the waveguide path may be provided by in-diffusing Nb or Ti. There are other various examples, but the waveguide path of the present embodiment should desirably be formed of a material having a high refractive index and having such a great difference in refractive index from the base that light is propagated even if the waveguide path is made thin.The refractive index of the waveguide path formed of such materials is high and therefore, the beam spot formed on the magnetic transfer film through the condenser lens 9 can be made very small in spot diameter, namely, sharp.
The deflector should desirably be one which utilizes an ultrasonic wave surface elastic wave and in the present embodiment, as shown in Figure 2, an ultrasonic wave is excited by the comb-tooth-like electrode (interdigital transducer) 6 formed on the surface of the waveguide path having a piezo-electric property. The pitch a of the comb-tooth-like electrode is set to 1/2 of the center wavelength of the excited ultrasonic wave.
For example, if the electrode pitch is set to a=8.8#m is the case of LiNbO3 base, when a high frequency voltage of 200MHz is applied thereto, an ultrasonic wave of wavelength 1 7.5#m can be excited. (The velocity of the ultrasonic wave is about 3.5 x 1 O6mmlsec.) The band of the deflector provided by this single electrode is limited by the angle selection width of a Bragg type diffraction grating created by the excited ultrasonic wave and the band of a transducer comprising this piezoelectric material and an electrode. The band limited by the former Bragg diffraction is given by the following equation from the aforementioned Proc IEEE 64, 779(1976), E.G.Lean et al, Thin Film Acoustooptic Devices: v = 2n v A (1)
V where n : refractive index of the waveguide path Xo : wavelength of the incident light beam
v : velocity of the ultrasonic wave surface elastic wave
A : wavelength of the elastic wave
L : width of the elastic wave.
Also, the deflection angle AX when the applied frequency has been biased by kts is given by the following formula: A Ev (2)
nv
Accordingly, in the reproducing head of Figure 1, the frequency of the signal applied to the electrode 6 is continuously repetitively varied within a predetermined range, whereby the beam spot 11 #is continuously scanned in a predetermined range. The number N of scanning points which are separable from one another within this deflection angle is given by the following equation: N = Av
v where W is the width of the incident light beam. For example, when Av= 50MHz and W = 1 Omm and v = 3.5 xlOGmmisec, N = 143.
When it is desired to further increase the number of scanning points, it is possible to utilize the aforementioned wide band deflector shown by C.S. Tsai et al(SPIE vol. 139, p.139, 1978). This, as shown in
Figure 3, comprises arranging a plurality of electrodes different in pitch at angles which satisfy the Bragg diffraction condition for the incident light in accordance with each wavelength band, causing each transducer to bear a portion of the wide band, and applying to the electrodes so-called chirped signals whose frequency is continuously varied to thereby vary the wide band of 500MHz. By this, it is possible to obtain 1250 scanning points.
Next, suitable as the thin film lens 9 is a mode index lens, Luneburg lens' Geodesic lens or the like shown in IEEE Qun. Elect vol. QE-13, p.129, 1977 (by D.W. Vakay & Van E. Wood). A performance approximate to the theoretical resolution limit is obtained by the latter two types of lenses.
The size (diameter) bx of the beam spot in x-direction on the end surface of the waveguide path condensed by the thin film lens is given by the following equation in a case where the incident light beam is a parallel light beam of rectangular intensity distribution: bx = 2.44Xof/nW (4) = 2.44#) F (5) n where F is the F- number given by
When, in the present embodiment, F-number is set to 2.0 and the wavelength of the incident light is set to ko =820mm and the refractive index of the waveguide path is set to n = 2.2, the diameter b of the beam spot in x-direction (shown in Figure 1) is 1.8cam and, by forming the film thickness of the waveguide path to 1.5bum, a substantially circular tiny beam spot can be obtained on the exit end surface of the waveguide path. The magnetic transfer film 10 is formed of thin films of about lym of a vertically magnetizable amorphous magentic material such as DyFe, TbFe or GdCo having the magnetic Kerr effect. These thin films are formed by sputtering. (see J. Appl. Phys. 48, P.2634, by N. Imamura et al.)
This magnetic transfer film 10 is further formed with a protective film 12 (such as Ta205, SiO2, ZnO2, TiO2 or CR202).
In the reproducing head of the present embodiment, the magnetic transfer film may be provided not on the end surface of the waveguide path 2 but on the surface of the waveguide path. Such design change will become possible if the light is bent toward the surface of the waveguide path by making the end surface of the waveguide path oblique and the thin band area at the end of the surface of the waveguide path is made into an exit surface.
Description will now be made of the function as a reading head for reading signals from a magnetic recording medium. In Figure 1, a magnetic tape 13 such as Cr02 on which magnetic signals are recorded is brought into close contact with or into proximity to the reading head and is relatively moved in the sub-scanning direction substantially perpendicular to the beam spot scanning direction. At each time, a magnetic signal of a portion opposed to the magnetic transfer film 10 is transferred from the magentic tape 13 to the magnetic transfer tape 10. This transferred magnetic signal is spot-illuminated by a beam spot scanning light beam 14.The reflected light from the magnetic transfer film on which the beam spot has impinged is converted from a rectilinearly polarized light into an elliptically polarized light by the Kerr effect of the magnetic signal. Accordingly, this reflected light is converted into an intensity variation by the polarizing characteristic (mode selecting property) of the waveguide path and the ultrasonic wave deflector and reaches the exit end of the semi-conductor laser 3. When this reflected light enters the semiconductor laser, the semiconducter laser has the current value thereof varied by a self-coupling phenomenon.
Accordingly, the magnetic signals on the magnetic signals on the magnetic transfer film 10 can be read from said variation in current value.
Also, as shown in Figure 4, a Bragg type diffraction grating 21 may be provided between the semiconductor laser 3 and the thin film lens 4 so that the reflected light may be diffracted at an angle approximate to 90 and directed to a photodetector 22 which may read any variation in quantity of light. This utilizes the fact that the dependency of the diffraction efficiency on the direction of polarization becomes greatest in the diffraction direction approximate to 90 C.
While the above-described embodiment uses a transfer film utilizing the Kerr effect, the magnetic transfer film in the present invention may also be a magnetic Garnet film having the Faraday effect. In this case, however, the magnetic film is used as the transmission type and therefore, a reflection film of Al or the like is provided on that surface of the Garnet film which is opposite to the end surface of the waveguide path and further, said protective film of SiO2 or the like is formed on the reflection film.In this embodiment, the light beam having left the exit surface of the waveguide path passes through the Garnet film and in that case, the polarizing surface rotates by the Faraday rotation angle corresponding to the magnetic signal transferred from the magnetic recording medium and further, the rotation of the polarizing surface is increased twofold until the light beam is reflected by said reflection film and returns to the end surface of the waveguide path.
Accordingly, the magnetic signals can be read out by converting the rotation of the polarizing surface into an intensity variation as previously described. In Figure 1, the signals on the magnetic tape are read at high speed in succession by virtue of the relative movement of the magnetic recording tape in the sub-scanning direction and the high-speed beam spot scanning.
Aspecific example of the numerical values of the beam spot scanning, namely, the read-out scanning, will hereinafter be described. In this case, it is assumed that the base 1 is LiNbO3 base and that the waveguide path was provided by in-diffusing Ti. Now, when N = 500 and ko = O.82um and f = 15mm and n = 2.2 and F = f/W = 2 and VA = 3.5 x 106mm/sec, the then band width Av, swing angle AQ, beam spot diameter ox, scanning width t and response rare as follows:: bx = 2.44~ F= 1.81lm n 4 = 1.8 x 10-3 x 500 = 0.9mm 1.8x10#3x500=0.9mm W = 7.5mm AQ = 2 tan- 0.9/2 = 3.8"
15 av = nvA ##= 625MHz W
r = =2.lusec.
VA By such high-speed and high-resolution beam spot scanning, for example, TV signals recorded on a magnetic tape can read image signals of each scanning line at a repetition frequency of 15.7KHz.
The features of the thin film waveguide path type reproducing head of the present invention lie in that it is suited for such high-speed scanning and that the output of the driver for driving it may be a low power.
As described above, in the reproducing head of the present invention, a light deflector and a condenser lens are formed on the same base and a magnetictransferfilm is integrally provided on the exit end surface of the waveguide path, and this leads to the provision of a reproducing head of the optical scanning type which is compact and highly reliable as well as capable of high-speed scanning and highly useful.
Claims (7)
1. A device for reproducing the information on a recorded medium comprising:
a wave guide for propagating a light beam;
a magnetic transfer film provided on the light exit surface of said wave guide;
first means for deflecting said light beam in said wave guide;
second means for concentrating the deflected light beam on or near the magnetic transfer film; and
third means for detecting the light beam from said magnetic transfer film.
2. A device according to Claim 1, wherein said first means comprises a comb-tooth-like transducer for exciting an acoustic wave in said wave guide, and means for applying to said transducer a signal whose frequency varies repeatedly in a predetermined range.
3. A device according to Claim 1, wherein said second means comprises a thin film lens formed on said wave guide.
4. A device according to Claim 3, wherein the light exit surface of said wave guide is substantially coincident with or parallel to the locus of the point whereat the light beam is condensed by said thin film
lens.
5. A device according to Claim 1, wherein said third means comprises a Bragg grating formed on said wave guide, and a photodetector.
6. A device according to Claim 1, wherein said magnetic transfer film is provided with a protective film on the surface thereof.
7. A device for reproducing information on a recording medium, substantially as hereinbefore described with reference to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1133780A JPS56111140A (en) | 1980-02-01 | 1980-02-01 | Scanning type magnetic recording reading head |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2070314A true GB2070314A (en) | 1981-09-03 |
| GB2070314B GB2070314B (en) | 1983-11-23 |
Family
ID=11775211
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8102790A Expired GB2070314B (en) | 1980-02-01 | 1981-01-30 | Device for reproducing the information on a recorded medium |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS56111140A (en) |
| GB (1) | GB2070314B (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1985000239A1 (en) * | 1983-06-20 | 1985-01-17 | Datatape Incorporated | Apparatus for reading magnetically recorded information |
| FR2566953A1 (en) * | 1984-06-27 | 1986-01-03 | Canon Kk | Optical head device |
| EP0174008A2 (en) * | 1984-09-03 | 1986-03-12 | Omron Tateisi Electronics Co. | Device for processing optical data |
| US4594699A (en) * | 1983-06-20 | 1986-06-10 | Datatape Incorporated | Faraday-effect magneto-optic transducer apparatus of a rotary form |
| US4707814A (en) * | 1985-03-14 | 1987-11-17 | Laser Dynamics, Inc. | Extended cavity laser recording method and apparatus |
| US4737946A (en) * | 1984-09-03 | 1988-04-12 | Omron Tateisi Electronics Co. | Device for processing optical data with improved optical allignment means |
-
1980
- 1980-02-01 JP JP1133780A patent/JPS56111140A/en active Pending
-
1981
- 1981-01-30 GB GB8102790A patent/GB2070314B/en not_active Expired
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1985000239A1 (en) * | 1983-06-20 | 1985-01-17 | Datatape Incorporated | Apparatus for reading magnetically recorded information |
| US4594699A (en) * | 1983-06-20 | 1986-06-10 | Datatape Incorporated | Faraday-effect magneto-optic transducer apparatus of a rotary form |
| FR2566953A1 (en) * | 1984-06-27 | 1986-01-03 | Canon Kk | Optical head device |
| EP0174008A2 (en) * | 1984-09-03 | 1986-03-12 | Omron Tateisi Electronics Co. | Device for processing optical data |
| EP0174008A3 (en) * | 1984-09-03 | 1987-10-21 | Omron Tateisi Electronics Co. | Device for processing optical data |
| US4737946A (en) * | 1984-09-03 | 1988-04-12 | Omron Tateisi Electronics Co. | Device for processing optical data with improved optical allignment means |
| US5128915A (en) * | 1984-09-03 | 1992-07-07 | Omron Tateisi Electronic Co. | Optical pickup device |
| US4707814A (en) * | 1985-03-14 | 1987-11-17 | Laser Dynamics, Inc. | Extended cavity laser recording method and apparatus |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2070314B (en) | 1983-11-23 |
| JPS56111140A (en) | 1981-09-02 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PE20 | Patent expired after termination of 20 years |
Effective date: 20010129 |