U.S. patent application number 09/389105 was filed with the patent office on 2001-08-09 for flying type optical head integrally formed with light source and photodetector and optical disk apparatus with the same.
Invention is credited to AWANO, HIROYUKI, ITO, KENCHI, MARUYAMA, YOOJI, SHIMANO, TAKESHI.
Application Number | 20010012244 09/389105 |
Document ID | / |
Family ID | 26365777 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010012244 |
Kind Code |
A1 |
SHIMANO, TAKESHI ; et
al. |
August 9, 2001 |
FLYING TYPE OPTICAL HEAD INTEGRALLY FORMED WITH LIGHT SOURCE AND
PHOTODETECTOR AND OPTICAL DISK APPARATUS WITH THE SAME
Abstract
The optical head is arranged such that a semiconductor laser and
a photodetector are formed via a buffer layer on the same
substrate; and an opening portion is formed in the substrate under
the semiconductor laser and the photodetector. This optical head is
further arranged by that the opening portion is filled with a first
transparent layer; a diffraction grating is formed on a lower
surface of the first transparent layer; a second transparent layer
is stacked on a lower surface of the first transparent layer; and a
condenser lens is formed on a lower surface of the transparent
layer. In this optical head, laser light emitted from the
semiconductor laser is penetrated through the substrate, the first
transparent layer, the diffraction grating, and the second
transparent layer, and condensed toward a place just under the
condenser lens by the condenser lens, thereby forming a light spot
on an optical storage medium positioned apart from the condenser
lens, whereas reflection light reflected from the optical storage
medium is penetrated through the condenser lens and the second
transparent layer, diffracted by the diffraction grating toward a
light receiving plane of the photodetector, and further penetrated
through the first transparent layer to be received by the
photodetector.
Inventors: |
SHIMANO, TAKESHI;
(HACHIOJI-SHI, JP) ; ITO, KENCHI; (HACHIOJI-SHI,
JP) ; MARUYAMA, YOOJI; (IRUMA-SHI, JP) ;
AWANO, HIROYUKI; (NAGAREYAMA-SHI, JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
26365777 |
Appl. No.: |
09/389105 |
Filed: |
September 2, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09389105 |
Sep 2, 1999 |
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08900112 |
Jul 25, 1997 |
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5995474 |
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08900112 |
Jul 25, 1997 |
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08460196 |
Jun 2, 1995 |
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5715226 |
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08460196 |
Jun 2, 1995 |
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08197870 |
Feb 17, 1994 |
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5481386 |
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Current U.S.
Class: |
369/13.01 ;
369/112.07; 369/112.12; G9B/11.024; G9B/11.034; G9B/11.046;
G9B/7.102; G9B/7.107; G9B/7.108; G9B/7.113; G9B/7.12;
G9B/7.138 |
Current CPC
Class: |
H01S 5/0207 20130101;
H01S 5/0264 20130101; G11B 7/1374 20130101; G11B 11/10532 20130101;
H01S 5/18308 20130101; G02B 2006/12107 20130101; G02B 6/124
20130101; G11B 7/122 20130101; H01S 5/0215 20130101; B82Y 20/00
20130101; G11B 2007/13727 20130101; G11B 7/1353 20130101; G02B
6/4246 20130101; H01S 5/18305 20130101; G11B 11/10554 20130101;
G11B 7/13922 20130101; G02B 6/12004 20130101; G11B 7/22 20130101;
H01S 5/3432 20130101; H01S 5/18388 20130101; G11B 7/123 20130101;
G11B 11/1058 20130101 |
Class at
Publication: |
369/13 ;
369/112.07; 369/112.12 |
International
Class: |
G11B 007/135 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 17, 1993 |
JP |
05-027799 |
Feb 24, 1993 |
JP |
05-033845 |
Claims
What is claimed is:
1. An optical head: wherein a semiconductor laser and a
photodetector are formed via a buffer layer on the same substrate,
and an opening portion is formed in the substrate under said
semiconductor laser and said photodetector; wherein said opening
portion is filled with a first transparent layer; wherein a
diffraction grating is formed on a lower surface of said first
transparent layer; wherein a second transparent layer is stacked on
a lower surface of said first transparent layer; and wherein a
condenser lens is formed on a lower surface of said transparent
layer, in which laser light emitted from said semiconductor laser
is penetrated through said substrate, said first transparent layer,
and condensed toward a place just under the condenser lens by said
condenser lens, thereby forming a light spot on an optical storage
medium positioned apart from said condenser lens, a reflection
light reflected from said optical storage medium is penetrated
through said condenser lens and said second transparent layer,
diffracted by said diffraction grating toward a light receiving
plane of said photodetector, and further penetrated through said
first transparent layer to be received by said photodetector.
2. An optical head as claimed in claim 1, wherein said
semiconductor laser is a surface emitting laser.
3. An optical head as claimed in claim 2, wherein said
semiconductor laser is a mesa type semiconductor laser.
4. An optical head as claimed in claim 1, wherein two groups of
photodetectors are formed, and wherein two polarizers positioned
perpendicular to each other are provided between said first
transparent layer and the substrate under the light receiving
surface of the photodetector of the respective groups.
5. An optical head as claimed in claim 1, wherein a ceramic film is
formed on the lower portion of the transparent layer on which said
condenser lens except for the portion of the condenser lens.
6. An optical head as claimed in claim 5, wherein a thin film coil
is provided at a portion of said ceramic film.
7. An optical head as claimed in claim 5, wherein a shape of said
optical head is processed to become a flying slider shape.
8. An optical head as claimed in claim 7, wherein a flying amount
is below than 20 micrometers.
9. A method of manufacturing an optical head wherein a
semiconductor laser and a photodetector are formed via a buffer
layer on the same substrate in such a manner that a laser light
emitting surface of the semiconductor laser and a light receiving
surface of said photodetector are directed to the same direction,
and an opening is fabricated under said laser emitting surface and
said light receiving surface by an etching process, comprising the
steps of: stacking a first transparent layer used to fill said
opening by way of the plasma CVD (chemical vapor deposition) and
sputtering processes; forming a diffraction grating on a lower
surface of said first transparent layer by way of the photomask
exposure process; stacking a second transparent layer under said
first transparent layer by way of the plasma CVD, and sputtering
processes; and forming either a grating lens on a lower surface of
said second transparent layer by way of the photomask exposure
process, or one of a distributed index lens and a convex lens on
said lower surface of said second transparent layer by way of the
disk apparatus.
10. An optical disk apparatus comprising: a flying type optical
head whose flying amount is smaller than, or equal to 26
micrometers; an optical disk having no transparent protection layer
on the information reading side of the recording surface thereof,
or having a transparent protection layer with a thickness less than
a value obtained by subtracting said flying amount from a back
focus distance of an object lens located within a medium whose
refractive index is 1.0, and by multiplying the subtraction result
by a refractive index of a protection layer; a supporting mechanism
for supporting said optical head; and a dust-guard cartridge for
containing at least said optical disk, said optical head, and said
supporting mechanism.
11. An optical disk apparatus comprising: an optical disk having no
transparent protection layer at the information reading side of the
recording surface thereof, or having a transparent protection layer
with a thickness less than 26 micrometers; a supporting mechanism
for supporting said optical head; and a dust-guard cartridge for
containing said optical disk, said flying type optical head, and
said supporting mechanism.
12. A method of manufacturing an optical head in which a surface
emitting laser and a photodiode are manufactured at the same time
in accordance with the following processing steps (a) to (f),
comprising the steps wherein: (a) an n type AlGaAs buffer layer is
grown on an n type GaAs substrate, an n+ type GaAs layer is grown
on said buffer layer, and a first reflection mirror layer
constructed by alternately stacking n type AlAs layers and GaAlAs
layers is formed on said n+ type GaAs layer; (b) said first
reflection mirror layer is removed by way of an etching process
only from a portion where said photodiode is to be manufactured,
and an n type AlGaAs layer is grown on the layer removed portion;
(c) an n type AlGaAs clad layer is formed on said first reflection
mirror layer and said n type AlGaAs layer, a p type GaAlAs quantum
well layer is grown on said clad layer as an activate layer, a p
type GaAlAs clad layer is fabricated on said activate layer, and a
second reflection mirror layer constructed by alternately sacking n
type AlAs layers and GaAlAs layers is grown on said clad layer; (d)
said second reflection mirror layer is removed by way of the
etching process only from the portion where the photodiode is to be
formed, and a p type GaAs layer is formed on the removed portion;
(e) a p+ type GaAs layer is formed on said second reflection mirror
layer and said p type GaAs layer, on which an Au electrode is
formed; and (f) a groove for separating said surface emitting laser
from said photodiode is formed.
13. An optical head: wherein a semiconductor laser is formed via a
buffer layer on a substrate, and an opening portion is fabricated
in the substrate at a lower portion of a laser emitting surface;
wherein said opening portion is furthermore filled with a
transparent layer; and wherein one of a grating lens, a distributed
index lens, and a condenser lens made of a convex lens having a
diameter less than 1 mm is formed on a lower surface of said
transparent layer.
14. An optical disk high-density storage apparatus including a
means for reading and writing information, comprising: an
air-flying head equipped with a very small mirror facing to an
optical disk, and capable of flying on a surface of the optical
disk; and an optical system including a laser light irradiating
means and a photodetecting means, whereby the laser light is
irradiated from a rear surface of said optical disk to a region
containing at least a region overlapped with said very small mirror
of said optical disk, thereby reading the information stored in
said optical disk.
15. An optical disk high-density storage apparatus as claimed in
claim 14, wherein a width of said very small mirror is smaller than
a spot diameter of said laser light irradiated onto said optical
disk.
16. An optical disk high-density storage apparatus as claimed in
claim 15, wherein a magnetic domain which is located just under
said very small mirror and is present in a portion limited to the
region onto which the laser light is irradiated, is detect by said
photodetecting means arranged at a rear side of the optical disk by
utilizing either the Faraday effect, or the Kerr effect.
17. An optical disk high-density storage apparatus as claimed in
claim 14, wherein said air-flaying head owns an information writing
magnetic pole; and wherein said very small mirror is a mirror of
said magnetic pole.
18. An optical disk high-density storage apparatus as claimed in
claim 14, wherein said head owns an information writing magnetic
pole; and wherein said magnetic domain is written by inverting a
polarity of said information writing magnetic pole.
19. An optical disk high-density storage apparatus as claimed in
claim 14, wherein information is written into a region containing
at least a region overlapped with said very small mirror of the
optical disk, while the laser light is irradiated onto said region
from a rear surface of said optical disk.
20. An optical disk high-density storage apparatus as claimed in
claim 14, wherein said head has an information writing magnetic
pole; and wherein said magnetic domain is written into a region of
said optical disk onto which the laser light is irradiated to
increase a temperature of said region, and which is located just
under said magnetic pole due to the thermomagnetic phenomenon.
21. An optical disk high-density storage apparatus as claimed in
claim 14, wherein said head owns an information writing magnetic
pole; and wherein said magnetic pole is used as a mirror for
reflecting the laser light from the rear surface of said optical
head, and also a magnetizing polarity of said magnetic pole is
inverted in response to an information stream, whereby a magnetic
domain corresponding to information of "1" and "0" is written into
a region of said optical disk which is located just under said
magnetic pole and onto which the laser light is irradiated.
22. An optical disk high-density storage apparatus as claimed in
claim 14, wherein a plurality of information writing magnetic poles
are arranged within a single head along a direction substantially
normal to a relative moving direction between said optical disk and
said head; and wherein a plurality of information is written by
inverting magnetizing polarities of said plural magnetic poles in
correspondence with an arbitrary information stream, while said
plural information is converted into parallel presence of the
magnetic poles.
23. An optical disk high-density storage apparatus as claimed in
claim 14, wherein a plurality of information writing magnetic poles
are arranged within a single head along a direction substantially
normal to a relative moving direction between said optical disk and
said head; and wherein under such a condition that common laser
light which is partially overlapped with all of said plural
magnetic poles, is irradiated from a rear surface of the optical
disk onto the optical disk, a plurality of information is written
by inverting magnetizing polarities of said plural magnetic poles
in correspondence with an arbitrary information stream, while said
plural information is converted into parallel presence of the
magnetic poles.
24. An optical disk high-density storage apparatus as claimed in
claim 14, wherein a plurality of said very small mirrors are
positionally shifted along the relative moving direction between
said optical disk and said head; and wherein a plurality of
information which has been written into a region located just under
said plurality of very small mirrors and onto which the laser light
is irradiated, is detected by the photodetecting means, while
common laser light which is partially overlapped with at least all
of said plurality of very small mirrors, is irradiated from the
rear surface to the optical disk.
25. An optical disk high-density storage apparatus as claimed in
claim 14, wherein said plurality of information is separated from
each other and detected based on both of an output from said
photodetecting means and change timings of said output.
26. An optical disk high-density storage apparatus as claimed in
claim 14, wherein said head is equipped with a reading very small
mirror and either a writing magnetic pole, or a writing very small
mirror; and wherein said reading very small mirror and either said
writing magnetic pole, or said writing very small mirror are
positioned apart from each other by an equal radial distance with
respect to a rotation center of said optical disk.
27. An optical disk high-density storage apparatus as claimed in
claim 14, wherein either said very small mirror, or said magnetic
pole having the function of said very small mirror is constructed
by a sectional plane of a metal film laminated on a plane
substrate.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an optical head, a method
for manufacturing an optical head, and an optical disk
apparatus.
[0002] Conventionally, the optical heads (namely, optical pick up)
are known in the art, for instance, from JP-A-64-46242 and
JP-A-64-43822.
[0003] The optical head described in JP-A-64-46242 is so
constructed that the surface emitting laser and the photodetector
are formed on the same substrate, the glass plates are stacked, or
laminated on this substrate, and the focusing grating coupler
(hologram lens) is fabricated on the surface of this glass
plate.
[0004] On the other hand, the optical head described in
JP-A-64-43822 is so arranged that the above-described optical head
disclosed in JP-A-64-46242 is employed as the optical head main
body, and this optical head main body is mounted on the flying
slider.
[0005] In the optical head disclosed in JP-A-64-46242, the focusing
grating coupler is utilized. In case of such a focusing grating
coupler, chromatic aberration is large when the wavelength of the
light from the light source is varied due to temperature variations
and the like. Although this prior art describes that there is no
change in the wavelengths when the surface emitting laser is
employed, there is adverse influence since the wavelength is
changed by the temperatures, as apparent from the publication
"SURFACE EMITTING LASER" written by Iga, FIG. 12, page 8, vol. 60,
No. 1, APPLIED PHYSICS, 1991. Accordingly, this prior art owns such
a problem that no solution means is taken to the wavelength
variation.
[0006] Furthermore, as to the optical head described in
JP-A-64-46242, the optical path to the optical disk is inclined in
order to separate the optical path for the laser light emitted from
the surface emitting laser to the optical disk, from the optical
path for the light returned from the optical disk to the
photodetector. When the optical path is inclined, there is a
problem that aberration and also asymmetrical strength
distributions may easily occur, resulting in a large spot size of
the laser light. It should be noted that the applications of the
SCOOP structure have been proposed in this prior art, taking
account of such a problem caused by the inclined optical path.
However, since only differences in reflectivities of the medium can
be detected in case of the SCOOP structure, there are drawbacks
that neither the tracking signal, nor the opto-magnetic signal can
be detected.
[0007] On the other hand, in the optical head described in
JP-A-64-43822, since the optical head is mounted on the flying
slider separately manufactured, it is very difficult to adjust the
slider surface and the optical head within the normal focal depth
from 2 micrometers to 3 micrometers. If the automatic focusing
control would be performed, then this focal depth adjustment would
not be required. However, since JP-A-64-43822 has such an object
that this automatic focusing control is not performed, the
above-explained difficult focal depth adjustment must be carried
out.
[0008] It should also be noted that JP-A-64-43822 never discloses a
method for manufacturing an optical head with employment of a
surface emitting laser, and also an optical disk apparatus suitable
for a flying type optical head.
SUMMARY OF THE INVENTION
[0009] A primary object of the present invention is therefore to
provide an optical head capable of reducing chromatic aberration
caused when wavelengths of light emitted from a light source are
changed due to a variation in temperatures.
[0010] A secondary object of the present invention is to provide an
improved optical head capable of preventing the above-explained
problems caused by the SCOOP structure and by inclining an optical
path with respect to an optical disk.
[0011] A third object of the present invention is to provide a
flying type optical head which deprives such a positional
adjustment between a flying slider and this optical head.
[0012] A fourth object of the present invention is to provide a
method for manufacturing an optical head with employment of a
surface emitting laser.
[0013] A fifth object of the present invention is to provide an
optical disk apparatus suitable for a flying type optical head.
[0014] In accordance with a first aspect of the present invention,
it is provided an optical head that a semiconductor laser is formed
via a buffer layer on a substrate, and an opening portion is
fabricated in the substrate at a lower portion of a laser emitting
surface;
[0015] said opening portion is furthermore filled with a
transparent layer;
[0016] one of a grating lens, a distributed index lens, and a
condenser lens made of a convex lens having a diameter less than 1
mm is formed on a lower surface of said transparent layer.
[0017] According to a second aspect of the present invention, it is
provided such an optical disk that a semiconductor laser and a
photodetector are formed via a buffer layer on the same substrate
in such a manner that a laser light emitting surface of the
semiconductor laser and a light receiving surface of said
photodetector are directed to the same direction, and an opening is
fabricated under said laser emitting surface and said light
receiving surface;
[0018] further, a first transparent layer for filling the opening
portion is stacked;
[0019] a diffraction grating is formed on a lower surface of said
first transparent layer;
[0020] a second transparent layer is stacked on a lower surface of
said first transparent layer; and
[0021] a condenser lens constructed of a grating lens, a
distributed index lens, or a convex lens is formed on a lower
surface of said transparent layer;
[0022] wherein laser light emitted from said semiconductor laser is
penetrated through said substrate, said first transparent layer,
said diffraction grating, and said second transparent layer, and
condensed toward a place just under the condenser lens, by said
condenser lens, thereby forming a light spot on an optical storage
medium positioned apart from said condenser lens, whereas
reflection light reflected from said optical storage medium is
penetrated through said condenser lens and said second transparent
layer, diffracted by said diffraction grating toward a light
receiving plane of said photodetector, and further penetrated
through said first transparent layer to be received by said
photodetector.
[0023] In accordance with a third aspect of the present invention,
it is provided an optical head that a shape of said optical head
(106) is processed to become a flying slider shape in an one
body.
[0024] According to a fourth aspect of the present invention, it is
provided a method for manufacturing an optical head wherein a
semiconductor laser and a photodetector are formed via a buffer
layer on the same substrate in such a manner that a laser light
emitting surface of the semiconductor laser and a light receiving
surface of said photodetector are directed to the same direction,
and an opening is fabricated under said laser emitting surface and
said light receiving surface by an etching process, characterized
by comprising the steps of:
[0025] stacking a first transparent layer used to fill said opening
by way of the plasma CVD (Chemical vapor deposition) and sputtering
processes;
[0026] forming a second transparent layer under said first
transparent layer by way of the plasma CVD, and sputtering
processes; and
[0027] forming either a grating lens on a lower surface of said
second transparent layer by way of the photomask exposure process,
or one of a distributed index lens and a convex lens on said lower
surface of said second transparent layer by way of the ion exchange
process.
[0028] Furthermore, according to the present invention, it may be
provided a method for manufacturing an optical head in which a
surface emitting laser and a photodiode are manufactured at the
same time in accordance with the following processing steps (a) to
(f), characterized by comprising the steps wherein:
[0029] (a). an n type AlGaAs buffer layer is grown on an n type
GaAs substrate, an n type GaAs layer is grown on said buffer layer,
and a first reflection mirror layer constructed by alternately
stacking n type AlAs layers and GaAlAs layers is formed on said n+
type GaAs layer;
[0030] (b). said first reflection mirror layer is removed by way of
an etching process only from a portion where said photodiode is to
be manufactured, and an n type AlGaAs layer, is grown on the layer
removed portion;
[0031] (c). an n type AlGaAs clad layer is formed on said first
reflection mirror layer and said n type AlGaAs layer, a p type
GaAlAs quantum well layer is grown on said clad layer as an
activate layer, a p type GaAlAs clad layer is fabricated on said
activate layer; and a second reflection mirror layer constructed by
alternately stacking n type AlAs layers and GaAlAs layers is grown
on said clad layer;
[0032] (d). said second reflection mirror layer is removed by way
of the etching process only from the portion where the photodiode
is to be formed, and a p type GaAs layer is formed on the removed
portion;
[0033] (e). a p+ type GaAs layer is formed on said second
reflection mirror layer and said p type GaAs layer, on which an Au
electrode is formed; and
[0034] (f). a groove for separating said surface emitting laser
from said photodiode is formed.
[0035] In accordance with a fifth aspect of the present invention,
it is provided an optical disk apparatus comprising:
[0036] a flying type optical head whose flying amount is smaller
than, or equal to 26 micrometers;
[0037] an optical disk having no transparent protection layer on
the information reading side of the recording surface thereof, or
having a transparent protection layer with a thickness less than a
value obtained by subtracting said flying amount from a back focus
distance of an object lens located within a medium whose refractive
index is 1.0, and by multiplying the subtraction result by a
refractive index of a protection layer;
[0038] a supporting mechanism for supporting said optical head;
and
[0039] a dust-guard cartridge for containing at least said optical
disk, said optical head, and said supporting mechanism.
[0040] In the optical head according to the first aspect of the
present invention, since the semiconductor laser is formed via the
buffer layer and the opening portion is fabricated on the lower
portion of the laser light emitting surface of the substrate,
attenuation of the layer light is lowered. As previously discussed
the condenser lens having the diameter smaller than, or equal to 1
mm is formed on the lower surface of the transparent layer stacked
under the substrate. When the diameter of the condenser lens is
selected to be smaller than, or equal to 1 mm, as will be explained
later, the wave front precision of 0.1 .lambda. can be realized
even when the variations in wavelengths become .DELTA..lambda.=3
nm, so that there is no problem about chromatic aberration caused
by the variation in the wavelengths of the light emitted from the
light source due to the temperature changes.
[0041] In the optical head according to the second aspect of the
present invention, the diffraction grating is provided between the
semiconductor laser and the condenser lens, the laser light
projected from the condenser lens and reflected by the optical
storage medium, is again incident upon this condenser lens, and
thereafter this reflected laser light is directed toward the light
receiving surface of the photodetector capable of detecting the
tracking signal and the opto-magnetic signal. As a result, this
optical head can prevent the conventional problems caused by
setting the optical path to be inclined with respect to the optical
disk and by the SCOOP structure.
[0042] In the optical disk according to the third aspect of the
present invention, and the flying slider is formed with the optical
head main body in an integral form, and the film thickness of the
ceramic material such as zirconia is controlled and is formed by
way of the sputtering process, so that the positioning adjustment
between the flying slider and the optical head is no longer
required.
[0043] In accordance with the method for manufacturing the optical
head of the fourth aspect of the present invention, the optical
head of the present invention can be manufactured by employing the
semiconductor process such as the photomask exposure process. Also,
both the surface emitting laser and the photodiode can be
manufactured at the same time.
[0044] In the optical disk apparatus according to the fifth aspect
of the present invention, the flying type optical head whose flying
amount is smaller than, or equal to 20 micrometers, and the
below-mentioned optical disk are employed. That is, this optical
disk has either no transparent protection layer at the information
reading side of the storage surface thereof, or a transparent
protection layer whose thickness is less than a value obtained by
subtracting the flying amount from the back focus distance of the
object lens located within the medium whose refractive index is
1.0, and by multiplying the subtraction result by a refractive
index of the protection layer. As will be described later, when the
flying amount is below than 26 micrometers, the flying variation
amount is below than 2.6 micrometers, so that this flying variation
amount can be absorbed by the focal depth of the condenser lens. As
a result, the recording surface can be read without the defocusing
control. When the thickness of the protection layer becomes thin,
the optical disk may be damaged by dust. Therefore, since this
optical disk is contained into the dust-guard cartridge, there is
no practical problem in using the optical disk.
BRIEF DESCRIPTION OF THE INVENTION
[0045] FIG. 1 is a cross-sectional view for showing an optical head
according to an embodiment of the present invention;
[0046] FIG. 2 explanatorily shows a relationship between a
diffraction grating and a photodiode;
[0047] FIG. 3 explanatorily indicates variations in a light
distribution on the photodiode, caused by defocus;
[0048] FIG. 4 schematically shows a circuit diagram of a signal
pickup circuit from the optical head of FIG. 1;
[0049] FIGS. 5A to 5F are sectional views for illustrating a
manufacturing method of the optical head shown in FIG. 1;
[0050] FIG. 6 is a sectional view for indicating a buried type
surface emitting laser;
[0051] FIG. 7 is a sectional view for showing a mesa type surface
emitting laser;
[0052] FIG. 8 is a sectional view for representing a
photodiode;
[0053] FIGS. 9A to 9D are sectional views for indicating a
simultaneous manufacturing method of the surface emitting laser and
the photodiode;
[0054] FIG. 10 is a sectional view for representing an optical head
according to another embodiment of the present invention;
[0055] FIG. 11 schematically indicates a circuit diagram of a
signal pickup circuit from the optical head of FIG. 10;
[0056] FIG. 12 is a sectional view for denoting an optical head
according to a further embodiment of the present invention;
[0057] FIGS. 13A to 13C are sectional views for showing a
manufacturing method of the optical head of FIG. 12;
[0058] FIG. 14 is an explanatory diagram of a magnetic coil and a
magnetic field thereof in the optical head shown in FIG. 1;
[0059] FIG. 15 is a perspective view of an optical disk apparatus
according to an embodiment of the present invention;
[0060] FIG. 16 is a perspective view of an optical disk apparatus
according to another embodiment of the present invention;
[0061] FIG. 17 is a constructive diagram for indicating an overall
arrangement of an optical disk apparatus according to another
embodiment of the present invention;
[0062] FIG. 18A is a bottom vie of the magnetic head according to
an embodiment of the present invention;
[0063] FIG. 18B is a sectional view of this magnetic head;
[0064] FIG. 19 is a sectional view of a magnetic head according to
another embodiment of the present invention;
[0065] FIG. 20A explanatorily shows a parallel writing operation
according to an embodiment of the present invention;
[0066] FIG. 20B explanatorily indicates a parallel reading
operation thereof;
[0067] FIGS. 21A to 21E are explanatory diagrams for showing
detection signals obtained during the parallel reading
operation;
[0068] FIG. 22 schematically indicates a positional relationship
between mirrors for the parallel writing operation and mirrors for
the parallel reading operation; and
[0069] FIGS. 23A and 23B are sectional views for denoting a
parallel input/output head according to an embodiment of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0070] Referring now to the drawings, embodiments of the present
invention will be described.
[0071] FIG. 1 is a sectional view for showing a structure of an
optical head 101 according to an embodiment of the present
invention.
[0072] This optical head 101 has the following structure. That is,
both a surface emitting laser 1 and photodiodes 7, 7 are fabricated
via an AlGaAs buffer layer 47 on an n-GaAs substrate 2 in such a
manner that both a laser light projecting surface of the
semiconductor laser 1 and light receiving surfaces of the
photodiodes 7, 7 are directed toward the n-GaAs substrate 2.
Opening portions are formed in the laser light projecting surface
and lower substrates of the light receiving surfaces. Further, the
opening portions are filled with a first glass layer 3, a
diffraction grating 4 is fabricated on the lower surface of this
first glass layer 3. A second glass layer 5 is stacked on the lower
portion of the first glass layer 3. On the low surface of this
second glass layer 5, a condenser lens 6 having a diameter smaller
than, or equal to 1 mm and constructed of a grating lens is
formed.
[0073] The laser light (indicated by a dot line of FIG. 1)
projected from the surface emitting laser 1 is traveled through the
buffer layer 47, the first glass layer 3, the diffraction grating
4, and the second glass layer 5. This laser light is then condensed
by the condenser lens 6 in such a manner that the laser light is
directed just under the condenser lens 6, and a light spot having a
diameter from 0.4 micrometers to 2 micrometers is formed on a
recording plane of an optical recording medium R located apart from
the condenser lens 6. A distance between the condenser lens 6 and
the recording plane of the optical recording medium R is selected
to be smaller than, or equal to approximately 1 mm.
[0074] Reflection light (indicated by a solid line of FIG. 1)
reflected from the recording plane of the optical recording medium
R is transmitted through the condenser lens 6 and the second glass
layer 5, and then diffracted by the diffraction grating 4 in such a
manner that the diffracted laser light is directed toward the light
receiving planes of the photodiodes 7 and 7. Thereafter, the
diffracted laser light is transmitted through the first glass layer
3 and received by the photodiodes 7, 7.
[0075] The reason why the buffer layer is formed in the lower
portions of the laser light projection surface and the light
receiving plane, and the opening portions are formed in the
substrate 2, is such that GaAs substrate which greatly absorbs the
laser light with respect to the laser oscillating wavelength
(.alpha.=10.sup.4 cm.sup.-1) is removed, and the laser is supported
by the AlGa buffer layer which weakly absorbs the laser light
(.alpha.=20 cm.sup.-1). Even when AlGaAs is employed, since
electric conductivity is not changed, the thickness of this buffer
layer is made thick to lower the electric resistance without light
absorption loss. Also, the reason why the diameter of the condenser
lens 6 is selected to be smaller than, or equal to 1 mm, is to
suppress chromatic aberration caused when the wavelength of the
laser light is varied due to temperature changes, below than at
least .lambda./4 at maximum.
[0076] That is, spherical aberration "W" of a hologram is given as
follows, assuming now that a height of incident light from an
optical axis on the hologram is "h";
W(h)=Ah.sup.4 (1)
[0077] (see "OPTICAL ENGINEERING HANDBOOK" edited by T. Kase et
al., ASAKURA publisher, page 180). Here, assuming now that a
distance from the hologram and an object point is "Ro", a distance
from the hologram to a reference light source for recording is
"Rr", a distance from the hologram to a reference light source for
reproducing is "Rc", a distance from the hologram to a reproduced
object point is "Ri", a wavelength for recording is "A", and a
wavelength for reproducing is ".lambda.'", it is given:
A={(.lambda.'/.lambda.)(1/Rr.sup.3-1/Ro.sup.3)-1/Rc.sup.3+1/Ri.sup.3}
(2)
[0078] On the other hand, an imagery relationship is defined as
follows:
1/Ri=1/Rc+(.lambda.'/.lambda.)(1/Ro-1/Rr) (3)
[0079] Now, it is assumed that Rr.fwdarw.-.infin. and Rc
.fwdarw.-.infin., the spherical aberration is given as follows:
W(h)(1/8Ro.sup.3){(.lambda.'/.lambda.).sup.3-(.lambda.'/.lambda.)}h.sup.4
(4)
[0080] When a variation in wavelengths ".DELTA..lambda." and a
numerical aperture "NA" are defined by
.lambda.'/.lambda.=(.lambda.+.DELTA..lambda.)/.lambda. (5)
(NA)=h/Ro (6),
[0081] the spherical aberration is expressed by:
W(h, NA)={(NA).sup.3.DELTA..lambda./(4.lambda.)}h (7)
[0082] In other words, it may be understood that when the numerical
aperture NA is constant, the maximum spherical aberration "W"
caused by the variation in wavelengths ".DELTA..lambda." is
directly proportional to the height "h" of the incident light from
the optical axis on the hologram. For instance, when the various
conditions are given as NA=0.55, .lambda.=0.78 micrometers, and
.DELTA..lambda.=3 nm, the spherical aberration "W" is obtained as
follows:
W(h=2.0 mm)=0.41 .lambda.
W(h=1.0 mm)=0.21 .lambda.
W(h=0.5 mm)=0.10 .lambda.
[0083] As a result, when the aperture "2h" of the condenser lens 6
would be selected to be smaller than, or equal to 1 mm, even if the
variation in wavelengths is 3 nm, the spherical aberration could be
suppressed below than .lambda./10.
[0084] This may be similarly applied to such a case that a convex
lens is employed as the condenser lens. For example, conceiving now
that a lens is made of one surface of a sphere, spherical
aberration "W" thereof is given as follows under such assumptions
that a refractive index of an object space is 1, a refractive index
of an image space is n, and a focal distance is f,
W(h)={3n/(8(n-1).sup.2f.sup.3)}h.sup.4 (8).
[0085] When numerical aperture "NA" is selected to be
NA=nh/f (9),
[0086] spherical aperture is given as follows:
W(h)=-{3(NA).sup.3/(8(n-1).sup.2n.sup.2}h (10).
[0087] As a result, it is possible to reduce the spherical
aberration when the numerical aperture "NA" is constant, and the
aperture "2h" is made small. This fact may be applied not only to
such spherical aberration, but also to other types of spherical
aberration.
[0088] Since the reflection light is branched by employing the
diffraction grating 4 to make up the optical path positioned
perpendicular to the optical recording medium R, there is no
problem caused by such a matter that the optical path is inclined.
It should be noted that assuming that the diffraction efficiency
together with that of .+-.first order diffracted light by the
diffraction grating 4 is 50%, 25% of the reflection light is
returned to the surface emitting laser 1. However, as the mode hop
does not easily happen due to the reflection light of the surface
emitting laser 1, there is no adverse influence. The light
receiving amounts of the photodiodes 7, 7 can become 25%, i.e., the
maximum amount.
[0089] FIG. 2 schematically shows a positional relationship between
the diffraction grating 4 and the photodiode 7.
[0090] The diffraction grating 4 corresponds to a linear type
diffraction grating such that both sides of the grating are
intersected with each other at an inclined angle of 45.degree. with
respect to center lines positioned at a boundary line and parallel
to the recording track direction of the optical recording medium R.
4 photodiodes 7 are positioned in order to receive .+-.first order
diffracted light from the diffraction grating 4. These four
photodiodes 7a, 7b, 7c, 7d are further subdivided into two portions
along the dividing direction of the diffraction grating 4.
[0091] FIG. 3 represents distributions of the reflection light
under conditions of "out focus", "just focus" and "in focus", which
is incident upon each of the four photodiodes 7a, 7b, 7c, and
7d.
[0092] FIG. 4 shows an example of a signal detecting circuit in the
optical head 101.
[0093] A defocused signal AF is obtained in such a manner that
outputs from the four photodiodes located at the outside of the
upper stage in FIG. 4 and at the inside of the lower stage thereof,
are added to each other in an adder 8a, outputs from the four
photodiodes located at the inside of the upper stage and the
outside of the lower stage thereof, are added to each other in an
adder 8b, and then outputs from both the adders 8a and 8b are
processed in a subtracter 9a.
[0094] A track shifted signal TR is obtained from a difference
between the light amounts of the laser incident upon the right and
left sides of the diffraction grating 4 in FIG. 2, because this
track shifted signal TR can be produced from uneven light
distributions of the reflection light reflected from the optical
recording medium R, which is caused by the track shifts. As a
consequence, the track shifted signal TR is obtained in such a
manner that outputs from the four photodiodes located at the left
side of the upper stage in FIG. 4, and right side of the lower
stage are added to each other in an adder 8c, outputs from the four
photodiodes located at the right inside of the upper stage and the
left side of the lower stage are added to each other in an adder
8d, and then outputs from both of these adders 8c and 8d are
processed in a subtracter 9b.
[0095] In case of such an optical disk where the optical recording
medium R, is of additionally rewritable type, or of read-only type,
a producing signal may be obtained by summing the outputs from all
of the photodiodes. As a result, it can be produced by adding the
outputs from the adder 8c and 8d in an adder 9c.
[0096] In FIGS. 5A-5F, there is shown an example of a method for
manufacturing the optical head 101. This optical head manufacturing
method is arranged as follows:
[0097] As to FIG. 5A, the n-AlGaAs buffer layer 47 is grown on the
lower surface of the n-GaAs substrate 2, a reinforcement glass
substrate 11 is closely attached to the lower surface of this
buffer layer 47, and an Al electrode 12 is vapor-deposited on the
upper surface of the n-GaAs substrate 2.
[0098] As to FIG. 5B, both the Al electrode 12 and the n-GaAs
substrate 2 are etched away to form a hole 2b used for projecting
the laser light.
[0099] As to FIG. 5C, the first glass layer 3 is deposited on the
Al electrode 12 and the n-GaAs substrate 2 by way of such a method
as the plasma CVD method and the sputtering method. Then, the
deposited first glass layer 3 is smoothed by the polishing method,
or photo-polymer and the like are filled and hardened, so that the
above-described etching hole is filled.
[0100] As to FIG. 5D, the diffraction grating 4 is formed on the
upper surface of the first glass layer 3 by way of the photomask
exposure process. That is, photoresist is coated on the upper
surface of the first glass layer 3 and dried. Then, a diffraction
pattern is exposed on this dried photoresist and developed, and the
diffraction grating 4 is fabricated by utilizing the ion beam
processing method.
[0101] As to FIG. 5E, the second glass layer 5 whose refractive
index is different from that of the first glass layer 3 is stacked
on the first glass layer 3 by way of either the plasma CVD method,
or the sputtering method, and a grating lens 6 is fabricated by the
photomask exposure process.
[0102] As to FIG. 5F, the reinforcement glass substrate 11 is
removed, and the surface emitting laser 1 and the photodiodes 7, 7
are manufactured on the lower surface of the buffer layer 47.
[0103] FIG. 6 schematically represents an example of a structure of
the buried type surface emitting laser 1.
[0104] An n.sup.+ type GaAs layer 14 into which a large quantity of
n type impurity has been added in order to increase conductivity is
grown on the n-AlGaAs buffer layer 47. On this n.sup.+ type GaAs
layer 14, a reflection mirror layer 15a is formed in which n type
AlAs and GaAlAs are alternately stacked. An n type GaAlAs clad
layer 16 is grown on this reflection mirror layer 15. Furthermore,
a p type GaAlAs/GaAs quantum well layer 17 is formed as an
activated layer. Although a sufficiently good characteristic may be
achieved by forming the activated layer by only GaAlAs, a low
threshold current can be achieved by employing the quantum well. A
p type GaAlAs clad layer 18 is grown on the quantum well layer 17,
on which another reflection mirror layer 15b is formed. In this
reflection mirror layer 15b, n type AlAs and GaAlAs are alternately
stacked. A p type GaAs layer 19 into which a large quantity of p
type impurity is added so as to increase conductivity is
manufactured on this reflection mirror layer 15b. Finally, an Au
electrode 20 is formed.
[0105] FIG. 7 indicates an example of a structure of a mesa type
surface emitting laser 1.
[0106] After a structure similar to that of FIG. 6 has been formed,
only a cylindrical laser portion is left, while other portions are
etched away. A diameter of the cylindrical mesa portion is from 2
micrometers to 3 micrometers, and a height thereof is approximately
5 micrometers. Since the diameter of the mesa portion is small, a
projection angle ".theta." of the laser from the laser portion is
approximately 30.degree. to 44.degree., namely becomes a large
value. As a consequence, for instance, when such a condenser lens 6
whose focal distance is 0.1 mm and whose numerical aperture NA is
0.55, is employed, if the refractive index of the glass layer is
selected to be 1.5, then the distance measured from the surface
emitting type laser 1 to the condenser lens 6 may be 220 to 320
micrometers, namely may be made extremely short, so that the
optical head 101 can be made compact. Also, since the surface
emitting type laser 1 is of the mesa type surface emitting laser
and thus the confinement effects of the photoelectric field and the
injected current are increased, the low-threshold current can be
obtained.
[0107] FIG. 8 schematically shows an example of a structure of the
photodiode 7.
[0108] An n.sup.+ type GaAs layer 14 into which a large quantity of
n type impurity is added is grown on the n type AlGaAs buffer layer
47. A GaAs layer 21 into which no impurity is doped is grown on
this n.sup.+ type GaAs layer 14. Further, a p type GaAs layer 22 is
partially grown on the GaAs layer 21. A portion of the p type GaAs
layer 22 is masked to form as SiO.sub.2 insulating layer 23.
Subsequently, this mask is removed to fabricate an Au electrode
20.
[0109] It should be understood that although, normally, the
photodiode 7 is manufactured after the surface emitting laser 1 has
been manufactured, both of the laser and the photodiode may be
fabricated.
[0110] In FIGS. 9A-9D, there is shown a method for manufacturing
both the surface emitting laser 1 and the photodiode 7 at the same
time.
[0111] As to FIG. 9A, an n.sup.+ type GaAs layer 14 into which a
large quantity of n type impurity is added so as to increase
conductivity, is grown on the n type AlGaAs buffer layer 47. A
reflection mirror layer 15a manufactured by alternately stacking n
type AlAs layers and AlAs layers is formed on this n.sup.+ type
GaAs layer 14.
[0112] As to FIG. 9B, only the reflection mirror layer 15a where
the photodiode 7 is to be formed, is removed. An n type AlGaAs
layer 25 is grown on the portion from which the reflection mirror
layer 15a has been removed.
[0113] As to FIG. 9C, an n type AlGaAs clad layer 16 is formed on
the reflection mirror layer 15a and the n type AlGaAs layer 25. A p
type GaAlAs/GaAs quantum well layer 17 is grown as an activate
layer on the reflection mirror layer 15a and the n type AlGaAs
layer 25. A p type GaAlAs clad layer 18 is formed on this activate
layer 17. A reflection mirror layer 15b manufactured by alternately
stacking n type AlAs layers and GaAlAs layers is grown on this clad
layer 18. Only the reflection mirror layer 15b where the photodiode
7 is to be formed, is removed by way of the etching process. Then,
a p type GaAs layer 22 is formed on the portion from which the
reflection mirror layer 15b has been removed. A p type GaAs layer
22 is formed on the above-described portion from which the
reflection mirror layer 15b has been removed. In addition, a
P.sup.+ type GaAs layer 19 into which a large quantity of p type
impurity is added to increase conductivity is formed on both the
reflection mirror layer 15b and the p type GaAs layer 22.
[0114] As to FIG. 9D, an Au electrode 20 is fabricated on the
p.sup.+ type GaAs layer 19. Then, the surface emitting laser 1 is
separated from the photodiode 7 by the etching process.
[0115] As described above, when both the surface emitting laser 1
and the photodiode 7 are manufactured at the same time, the overall
manufacturing stage can be considerably simplified and thus these
components can be manufactured at low cost.
[0116] FIG. 10 is a cross-sectional view of an optical head 102
according to another embodiment of the present invention. The same
reference numerals of the previous embodiment shown in FIG. 1
indicate the same constructions in FIG. 10.
[0117] This optical head 102 employs a convex lens, while the
condenser lens 6 employed in the optical head 101 of FIG. 1 is a
grating lens. Film-shaped polarizers 28 and 29 are attached to a
lower substrate 2a positioned just under the photodiode 7 in the
optical head 101 shown in FIG. 1. Each of these polarizers 28 and
29 owns transmission polarizing directions perpendicular to each
other. It should be noted that in case when the transmission
polarizing directions of the polarizers 28 and 29 are inclined at
.+-.45.degree. with respect to the polarizing direction of the
reflection light, the highest detection sensitivity can be realized
(see Japanese publication OPTICS "MAGNETO-OPTICAL RECORDING
TECHNIQUES" written by Ozima and Kakuta, volume 18, No. 11, page
599 in 1989).
[0118] FIG. 11 shows an example of a signal detecting circuit
employed in the optical head 102.
[0119] A defocused signal AF is obtained in such a manner that
outputs from the four photodiodes positioned at the outside of the
upper stage and the inside of the lower stage shown in FIG. 11 are
added to each other in an adder 8a, outputs from the four
photodiode located at the inside of the upper stage and the outside
of the lower stage are added to each other in an adder 8b, and
outputs from these adders 8a and 8b are subtracted in a subtracter
9a.
[0120] A track shifted signal TR is produced in such a manner that
outputs from the four photodiodes located at the left side of the
upper stage in FIG. 11 and the right side of the lower stage are
added to each other in an adder 8c, and outputs from the four
photodiodes positioned at the right inside of the upper stage and
the left side of the lower stage are added to each other in an
adder 8d, and thus outputs from both of these adders 8c and 8d are
subtracted in a subtracter 9b.
[0121] In case of the optical disk where the optical recording
medium R is of the rewritable MO type, an optical magnetic signal
MO may be obtained by subtracting a summation of the outputs from
the photodiodes contained in the polarizer 28 from a summation of
the outputs from the photodiodes contained in the polarizer 29. As
a consequence, the outputs from the four photodiodes located at the
left side of the upper stage and the left side of the lower stage
are added in an adder 8e, the outputs from the four photodiodes
positioned at the right inside of the upper stage and the right
side of the lower stage are added in an adder 8f, and the outputs
derived from these adders 8e and 8f are subtracted in a subtracter
9d.
[0122] This optical head 102 is further equipped with an AF
actuator 35.
[0123] The optical recording medium R is an optical disk. Generally
speaking, an optical disk has a transparent protection layer 34
having a thickness of 1.2 mm at an information reading side of a
recording surface 40.
[0124] For instance, when a condenser lens 6 in a finite system
with the numerical aperture NA=0.3 at the laser side is utilized, a
distance from the surface emitting type laser 1 and the condenser
lens 6 is approximately 2 mm, and a dimension of the optical head
104 is about 3 mm.times.3 mm.times.3 mm.
[0125] FIG. 12 is a cross sectional view of another optical head
106 according to another embodiment of the present invention.
[0126] This optical head 105 is such a flying slider-shaped optical
head that a slider bottom reinforcement layer 13 made of a ceramic
material such as zirconia is further formed on the bottom of this
optical head.
[0127] Since the flying slider is formed in an integral form with
the optical head by way of the film forming process, no positioning
adjustment of the optical head is required for the slider
bottom.
[0128] A flying amount of the optical head 106 depends upon the
shape of the optical head 106 and the linear velocity of the
optical recording medium R, for instance is smaller than, or equal
to 26 micrometers. A variation amount in the flying amounts
corresponds to approximately 10% of the flying amount. Accordingly,
the variation in the flying amount of 20 micrometers becomes about
2.6 micrometers. The focal depth of the condenser lens 6 is 2
approximated to .lambda./NA.sup.2. Therefore, if .lambda.=0.78
micrometers and NA=0.55, then the focal depth is approximately 2.6
micrometers. At this time, since the flying variation amount of 2.6
micrometers is lower than the focal depth of the focal lens 6, the
control to current focusing shifts is no longer required. In other
words, the flying variation amount may be selected to be lower than
the focal depth of the condenser lens 6. It should be noted that
the optical recording medium R does not have the transparent
protection layer at the information reading side of the recording
surface, or the thickness of the transparent protection layer is
thinner than a value calculated by subtracting the flying amount
from the back focus distance of the condenser lens in the medium
with the refractive index of 1.0, and by multiplying the subtracted
value by the refractive index of the protection layer. When either
the optical recording medium has no transparent protection layer,
or the thickness of the transparent protection layer is less than
100 micrometers, if dust is attached on the surface of this optical
recording layer, there is a problem in information reading
operations, so that this optical recording medium R must be stored
into a dust-proof case.
[0129] It should be noted that if the control to correct defocusing
is not required, the detecting circuit portions for the defocusing
signal employed in the signal detecting circuits of FIGS. 4 and 11
is no longer required, and the recording surface of the optical
recording medium can be read out without the defocusing
control.
[0130] In FIGS. 13A-13C, there is represented a method for
manufacturing the optical head 106.
[0131] FIG. 13A shows a structural condition manufactured by the
manufacturing process as explained in FIGS. 5(a) to 5(f).
[0132] As to FIG. 13B, the portion of the grating lens 6 is masked
around which ceramics of zirconia is deposited by way o the
sputtering method, resulting in a slider bottom reinforcement layer
13. A thickness of the deposition is equal to such a value
calculated by subtracting from the back focus distance (i.e., a
distance from the lens surface and the focal point in air) of the
grating lens 6, a thickness value obtained by diving both the
flying amount and the thickness of the optical disk's protection
layer by the refractive index of the protection layer.
[0133] As to FIG. 13C, the reinforcement glass substrate 11 is
removed to form the surface emitting laser 1 and the photodiodes 7,
7 on the lower surface of the substrate 2.
[0134] It should be noted that a thin film type magnetic coil 39
used to apply a magnetic field may be provided with the slider
bottom reinforcement layer 13 of the bottom of the optical head
105.
[0135] FIG. 14 is an explanatory diagram of a relationship between
the magnetic coil 39 and the magnetic fields thereof.
[0136] A magnetic field "H" produced by a circular current "I" with
a turn number of "n" and a diameter "a", is given on a central axis
Z thereof as follows:
H=na.sup.2I/2{square root}{square root over
((a.sup.2+z.sup.2).sup.2)}
[0137] For instance, assuming now that n=5, a=50 micrometers, z=1
micrometer, I=160 mA, the magnetic field H=100 [Oe] may be
produced.
[0138] FIG. 15 is a perspective view for showing an optical disk
apparatus 201 according to another embodiment of the present
invention.
[0139] This optical disk apparatus 201 is constructed in such a
manner that an optical recording medium R having either no
transparent protection layer at the information recording side of
the recording surface, or a transparent protection layer with a
thickness less than approximately 20 micrometers, the flying
optical head 106 previously explained in the embodiment, a
supporting arm 46 for supporting this flying head 106, and a
tracking actuator 31 are built in a dust-proof case 37, and a
connection terminal 45 for a power supply and a signal is
provided.
[0140] The optical disk apparatus 201 can be made very thin and
light weight, and also can be constructed as a portable cartridge,
since no thick transparent protection layer is provided with the
optical recording medium R, and neither the defocusing detection
circuit nor the defocusing correction actuator is employed. In this
case this optical disk apparatus 201 is used to be detachably
connected to an optical disk read/write apparatus 33.
[0141] It should be noted that since the drive mechanism and the
signal processing circuit for the optical recording medium R may be
build also in the optical disk read/write apparatus 33, and neither
the optical head, nor the tracking actuator is required, this
optical recording read/write apparatus 33 may be made compact and
at low cost.
[0142] FIG. 16 is a perspective view of an optical disk apparatus
202 according to a further embodiment of the present invention.
[0143] A different point of this embodiment from the previous
embodiment shown in FIG. 15, is such that a tracking actuator 31 is
provided on an optical disk read/write apparatus 330, and is
connectable with a supporting arm 46 of the optical disk apparatus
202. Since the optical disk apparatus 202 contains no tracking
actuator 31, this optical disk apparatus 202 can be made compact
and at low cost.
[0144] In accordance with the optical head of the present
invention, attenuation of the laser light becomes small, and no
problem of chromatic aberration may occur when the wavelengths of
the laser light source are varied due to temperature variations.
Also, there is no noise problem caused by the laser light returned
to the semiconductor laser. Further, there are no problem caused by
setting the optical disk to be inclined with respect to the optical
disk, and no problem caused by the scoop structure. Moreover, since
such a flying slider with a dimension several times layer than that
of the optical head is not employed, the overall optical head can
be made compact.
[0145] Next, a description will now be made of a disk type
recording apparatus for recording a large amount of information, in
particular an optical disk high density recording apparatus,
according to an embodiment of the present invention, suitable for
realizing high density recording of information from several
thousands GB/in.sup.2 to several TB/in.sup.2.
[0146] Conventionally, in the magneto-optical disk apparatus as
described in, for instance, JP-A-52-31703, the information is
written in such a manner that the laser light is condensed to the
magneto-optical disk, thereby producing the locally
high-temperature portion, and the magnetic domain magnetized along
the specific direction is written into this high temperature
portion by utilizing the thermal magnetizing reaction.
[0147] The limitation in storage density of this magneto-optical
disk is determined by the diameter of the laser spot. The typical
spot diameters of the recently developed recording apparatuses are
on the order of 0.8 micrometers, and thus a large storage capacity
of approximately 600 MB/sheet is available. To furthermore increase
the storage capacity, the diameter of the laser light spot must be
made smaller than, or equal to 0.8 micrometers. However, since
there is the optical limitation, the diameter of the laser light
spot cannot be reduced to an infinite value. Nowadays,
approximately 0.5 micrometers are the limit value for the spot
diameter. As a consequence, it is conceivable that even when such a
writing condition as the strength profile of the laser spot could
be optimized, the limit size of the magnetic domain is on the order
of 0.3 micrometers. As a result, there is such a problem that
information storage density higher than about 2 GB/in.sup.2 cannot
be realized in view of the storage capacity.
[0148] On the other hand, it is known that the information storage
density of the magnetic disk apparatus is generally lower than that
of the optical disk. This is caused by such a fact that the smaller
the magnetic domain becomes, the weaker the signal strength
becomes, whereby it is rather difficult to detect the signal with
the weak signal length. Thus, the magnetic domain cannot be
subdivided greater than the limited dimension, so that the upper
limit value of the storage density is approximately 1
GB/in.sup.2.
[0149] In accordance with the below-mentioned embodiment, it is
possible to provide a storage apparatus capable of having such a
large storage capacity as several tens GB to several TB/in.sup.2,
although this storage apparatus owns the same dimension as the
conventional storage apparatus.
[0150] According to the storage apparatus of this embodiment, a
very small mirror is provided with facing the optical disk, a head
flying in air over the surface of the optical disk, and an optical
system including a laser irradiating means and an optical detecting
means are employed. Then, the laser light is irradiated from the
rear surface of the optical disk onto the region of the optical
disk containing the region overlapped with the very fine mirror,
whereby storage information is written/read in/from this optical
disk region.
[0151] The effective spot diameter of the laser light may be made
small by reducing the width of the very small mirror smaller than
the spot diameter of the laser light irradiated on the optical
disk.
[0152] The head may has a magnetic pole for writing information,
and a mirror surface of this magnetic pole may be utilized as the
very small mirror.
[0153] A plurality of information writing magnetic poles arranged
along a direction substantially normal to the relative movement
direction between the optical head and the head, are employed
within a single head, and a plurality of information is converted
into presence of parallel magnetic poles so as to be written into
the optical disk, while the magnetizing polarities of the plural
magnetic poles are inverted in correspondence with an arbitrary
information series under such a condition that the common laser
light, at least a portion of which is overlapped with all of the
plural very small mirrors, is irradiated from the rear surface onto
the optical disk.
[0154] The parallel written information can be temporarily
separated from each other and can be detected in such a way that a
plurality of readout very fine mirrors are provided with being
positionally shifted along the relative moving direction between
the optical disk and the head, and the magnetic poles present in
the region which is located just under this very fine mirror and
has been irradiated by the optical laser, are detected by the
photodetector, while the common laser light, at least a portion of
which is overlapped with all of the plural very fine mirrors, is
irradiated from the rear surface onto the optical disk. The
separation of this information may be performed by utilizing the
outputs from the photodetector obtained in response to the existing
number of the magnetic domain, and also the changing timing of the
outputs.
[0155] Both the readout very small mirrors, and either the write
magnetic poles, or the write very small mirrors are employed, and
the readout very small mirrors may be separated from the write
magnetic poles, or the write very small mirrors by equal diameter
distances with respect to the rotation center of the recording
medium.
[0156] When either the above-explained very small mirrors, or the
magnetic poles functioning as the very small mirrors would be
constructed by sections of metal films formed by being laminated on
the plane substrate, mirrors with thicknesses of angstrom order
could be manufactured, and magnetic poles with thicknesses of
angstrom order could also be produced.
[0157] When the laser light which has penetrated from the rear
surface through the optical disk, is again reflected by the very
small mirror provided on the head toward the optical disk,
intensity of the light at the portion limited to the region located
just under the mirror, and also onto which the laser light has been
irradiated, is increased. As a consequence, only the magnetic
domain present in this region where the light intensity is
increased can be detected by utilizing either the Faraday effect,
or the Kerr effect by controlling detection sensitivities of the
photodetector, so that information having very small sizes smaller
than the size of the laser spot can be read. In other words,
according to the present invention, the effective spot diameter of
the laser beam can be made small by commonly using the very small
mirrors.
[0158] Then, as described above, the temperature increase is
selectively produced in such a local region having the size smaller
than the spot size of the laser, so that the information can be
written into the very small magnetic domain having the size smaller
than, or equal to 0.5 micrometers, which could not be realized in
the conventional magneto-optical disk. The lowering phenomenon of
the coercive force of the magnetic film, which is caused by such a
local temperature increase, may be utilized in writing information
into the very small magnetic domain with use of the magnetic
poles.
[0159] Also, a plurality of write magnetic poles are employed
within a single head, and the above-described effects are applied
in parallel to the respective magnetic poles employed in a single
head, whereby parallel information can be written by a single head.
The parallel information can be separated from each other and read
by positionally shifting a plurality of readout mirrors along the
relative moving direction of the optical disk and the head.
[0160] When either the readout mirrors, or the magnetic domains
having the mirror function would be positioned apart from either
the write magnetic poles, or the write mirrors by the substantially
same radius distance from the rotation center of the medium, since
the written magnetic domains are overlapped with the reading
portion and also the laser irradiated portion at higher precision
within a range where no thermal disturbance of the medium and the
head is present, the addressing control of the information could be
easily achieved.
[0161] FIG. 17 shows an overall arrangement of an optical disk high
density recording apparatus according to the present invention.
[0162] The optical disk high density recording apparatus is
arranged by an optical disk 1, a motor 2 for rotating the optical
disk 1, a laser light source 3, a photodetector 4, and a beam
splitter 6. This recording apparatus is further constructed of a
lens 7, a magnetic head 11 flying by air, a head arm 12, a
positioning actuator 13, a head control circuit 14, an optical
system control circuit 15, a control system main body 20 and so on.
The magnetic head 11 is electrically coupled with the control
system main body 20 so as to produce the magnetic field in response
to the input/output operations, if required.
[0163] As the laser light source 3, for instance, a semiconductor
laser for emitting laser light having wavelengths of 780 to 830 nm
may be employed. As the photodetector 4, a photomultiplier, an
avalanche photodiode, an electronically cooling type photodiode and
the like may be employed which have high sensitivities with regard
to weak light and also high S/N ratio.
[0164] The optical disk 1 is rotated by the motor 2 at speed of,
for example, 3000 rpm. The control system main body 20 owns a
function capable of addressing storage information by the similar
algorithm to that of the conventional disk type memory. A
communication line used to input/output information is derived from
the control system main body 20, and may be electrically connected
with an information processing appliance.
[0165] First, a description will now be made of an example of the
recording medium of the optical disk 1, in which a magnetic film
with a magnetizable axis along a vertical direction with respect to
a film surface is employed as this recording medium. As the
magnetic film, CoFeNi, barium ferrite, hexagonal ferrite, and the
like are utilized. This magnetic film with a thickness of 500
angstrom was coated on the glass substrate. It should be noted that
since presence of magnetic domains can be detected by the
above-described optical means even when other vertical magnetizable
films are employed, the present invention may be of course applied
thereto.
[0166] In accordance with the present invention, to realize the
light detection in the optical disk, as previously explained, the
air-flying magnetic head 11, and an optical system for irradiating
the laser onto the optical disk and for detecting the laser light
are newly employed on the surface of the optical disk. Laser light
8 is used to read storage bits by irradiating the region containing
at least the optical disk surface overlapped with the magnetic head
11 from the rear surface of the optical head. The magnetic head was
manufactured by forming both a conducting pattern made of a metal
film pattern, e.g., Au, and a magnetic pole pattern made of a
magnetic metal, e.g., Ni--Fe alloy on a hard substrate material
such as alumina-titanium-carbide. Alumina-titanium-carbide is
processed by way of the similar processing operation to that for
processing the conventional head of the magnetic head, so that this
head can air-fly (less than about 0.1 micrometer) from the surface
of the optical disk.
[0167] In FIGS. 18A-18B, there is shown an enlarged diagram of the
magnetic head 11. A very small mirror 30 with a thickness of, for
instance, approximately 1000 angstrom was fabricated on the surface
of the magnetic head 11 on the side of the optical disk. It should
be understood that the thickness of this mirror is not limited
thereto, but merely a reflection plane must be formed. The mirror
30 has a rectangular shape with a width of about 200 angstrom and a
length of about 1 micron. A metal film having high reflectivity
such as Al and Cr was used to form the mirror. Toward this mirror
30, the laser light 8 was irradiated through a recording medium and
a disk-shaped glass substrate 100 from the rear surface of the
optical disk 1, and this disk-shaped glass substrate 100 was
employed to increase mechanical strength of the recording medium.
At the same time, the photodetector 4 was provided on the side of
the rear surface of the optical disk 1, so that a light strength of
a portion within a region 81 onto which the laser light was
irradiated, and limited to another region 82 located just under the
mirror 30, could be increased. As a result, only a magnetic domain
21 present in the region 82 could be detected by utilizing either
the Faraday effect, or the Karr effect. The reflection light amount
is decreased in the region where no mirror 30 is provided. As a
consequence, it could be prevented that the magnetic domain 22 was
erroneously detected by controlling detection sensitivity by the
optical system control circuit. Therefore, the very small magnetic
domain having the diameter smaller than, or equal to 1 micrometer
corresponding to the laser spot size could be read out.
[0168] FIG. 19 represents a magnetic head according to another
embodiment of the present invention. In this embodiment, a writing
magnetic pole 31 of the magnetic head 11 is provided on the side of
the medium surface, and a mirror surface of this writing magnetic
pole 31 is used as the mirror. To realize this structure of the
magnetic head, a metal material such as Fe, Ni, or Ca was employed
as the material of the magnetic pole 31 provided on the surface of
the magnetic head 11. Since this writing magnetic pole 31 is
utilized as the mirror in a utilized as the mirror in a similar
manner to that of the embodiment shown in FIGS. 18A-18B, a light
strength of a portion located just under this mirror and also
limited to the region 83 onto which the laser light 8 is
irradiated, may be strengthened, and only the magnetic domain 24
existing in this region 83 may be detected by the photodetector
provided at the rear surface of the medium 1 in a similar manner to
that of the previous embodiment.
[0169] The above-described magnetic domain to be read out was
written by inverting the magnetizing direction of the magnetic pole
31 employed in the magnetic head 11 shown in FIG. 19 with use of an
electric signal 41. During this writing operation, since there is
no problem in the reading operation (namely, low detection
sensitivity of the conventional magnetic disk), such a magnetic
head having a narrow magnetic pole along the track direction may be
employed. In this case, the magnetic pole having the width of
approximately 200 angstrom and the length of about 1 micrometer was
employed. At this time, the dimension of the written magnetic
domain was approximately 200 angstrom.
[0170] Also, even when the lowing phenomenon of coercive force of
the medium is utilized which is caused by the local temperature
increase produced by reflecting the laser light 8 from the rear
surface of the optical disk, while the metallic magnetic pole 31 is
used as the mirror in FIG. 19, the very small magnetic domain can
be written. This is the novel writing principle different from the
conventional writing methods for the magneto-optical disk and the
magnetic disk. That is, the locally lowering region 83 with respect
to the coercive force is produced in the optical disk 1 by
irradiating the laser light 8 thereto. At this time, the magnetic
pole magnetizing strength is controlled and the polarity thereof is
inverted in accordance with an information series, so that the
magnetic domains magnetized along a specific direction can be
produced only in such a portion located just under the metallic
magnetic pole 31 whose coercive force has been lowered, and also
limited to the region 83 onto which the laser light 8 is
illuminated. In the regions whose coercive force is not lowered,
even when the magnetic field produced from the magnetic pole 31
would be given thereto, if this magnetic field is below than the
coercive force, then no magnetic domain is newly produced.
[0171] Referring back to FIGS. 18A-18B, a description will now be
made of an example where a thermomagnetic writable magnetic film is
employed as the storage medium of the optical disk 1. As the
storage medium, GdFeCo, TbFeCo, a Pt/Co multilayer film, or an
alloy film was utilized. These magnetic films corresponding to the
storage medium was formed on the glass substrate 100. The remaining
apparatus structures may be similar to those shown in FIG. 17. The
magnetic domains present in the magneto-optical film may be
detected by way of the detecting means for utilizing the
above-described Kerr effect, or Faraday effect, while the
information is optically read out.
[0172] As to the writing operation, a new writing method could be
achieved when the magneto-optical film is employed as the storage
medium. As shown in FIG. 18B, the laser light 8 was incident from
the rear surface of the optical disk upon the rear surface of the
air-flying, head 11 toward the mirror 30 in a similar manner to
that of the reading operation. It should be noted that light
strength of the laser light 8 was increased several times higher
than that during the reading operation. Since the laser light is
reflected by the mirror 30, the temperature was increased up to
approximately 200.degree. C., thereby causing the thermomagnetic
phenomenon at the portion located just under the mirror 30 and
limited by the region 82 onto which the laser light was irradiated.
Therefore, the magnetic domains could be written into this portion
in a similar effect to that of the conventional magneto-optical
disk. Since the temperature increasing region is limited to such a
region onto which the laser light is incident and the laser light
reflected from the mirror is irradiated, such a temperature
increase can be produced within the narrow region having the size
smaller than the laser spot size by making the mirror very small,
or irradiating the laser light onto a very small portion of the
mirror. As a result, very small magnetic domains with the size of
approximately 0.1 micrometer could be written. Furthermore, the
temperature in the thermomagnetic film may be locally increased
even when the mirror 30 is made of AlTi, AlCu and the like to
control reflectivity, and to increase the temperature of this
mirror Per se, and this thermal energy is transferred to the
closely provided optical disk 1.
[0173] The laser light 8 shown in FIGS. 18A-18B are turned ON/OFF
in response to an information stream, so that it could be judged
whether or not the temperature is time sequentially changed. As a
result, the information could be written in correspondence with
presence of the very small magnetic domain 23 according to the
principle similar to that of the conventional magneto-optical disk.
However, in accordance with this writing method, the magnetizing
directions of the storage medium of the optical disk must be
coincident with each other before the information is written. Since
turning ON/OFF of the laser light may only control to judge whether
or not the magnetic domain is present, no information can be
written into the optical disk where the magnetic domains were
already present. To solve this problem, the old information must be
erased by way of such means for heating the optical disk, or for
applying a strong magnetic field to this disk. When such an erasing
means cannot be employed, either a magnetic-domain erasing magnetic
pole may be provided with the head, or a magnetic-domain erasing
coil is located close to the optical disk, so that the old
information may be erased before writing new information. When this
magnetic-domain erasing coil is employed as an auxiliary magnetic
pole used to the writing operation, it may be realized the writing
operation by the magnetic modulation method for the magneto-optical
disk. In other words, when the polarity of the auxiliary magnetic
pole s inverted in response to the information stream under
condition that the laser light 8 shown in FIG. 18 is under ON
state, the magnetic domains are produced in response to the
polarities of the auxiliary magnetic pole. In accordance with this
method, the new information may be written on the old
information.
[0174] Referring again to FIG. 19, a description will now be made
of another novel magnetic-domain writing method for such a case
that a magnetic pole is provided with the head 11. When the
metallic magnetic pole 31 is used as the mirror and the laser light
8 emitted from the rear surface of the optical disk is reflected on
this mirror, as previously stated, a local temperature increase may
occur in the region 83 of the optical disk 1. Thus, this
magnetic-domain writing method is realized by utilizing the
lowering phenomenon of coercive force in the region 83, which is
caused by the above-explained local temperature increase. Because
coercive force is the major parameter to determine a degree of
easily producing the magnetic domain, the magnetizing strength of
the magnetic pole is controlled and also the polarity is inverted
in accordance with the information stream, so that the magnetic
domains equal to the polarities of the magnetic poles may be
produced only in the portion which is located just under the
metallic magnetic pole and is limited to the region 83, the
coercive force of which is lowered by irradiating the laser light
thereto. At this time, even when the magnetic field exerted from
the magnetic pole is given to the regions whose coercive force is
not lowered, if the strength of this magnetic field is lower than
the coercive force, no magnetic domain is produced, so that a very
small magnetic domain may be written.
[0175] In this writing method, the magnetic domains can be produced
under the small magnetic field of the magnetic pole, namely under
the small current, which is different from that of the conventional
magnetic disk. Also, in accordance with this writing method, as the
magnetic domains can be arbitrarily written along the magnetizing
direction of the magnetic pole, there is such a feature that a new
magnetic domain can be written into the old information in a
similar manner to that of the conventional magnetic disk.
[0176] An embodiment of a parallel writing method will now b
explained with reference to FIG. 20A. In this embodiment, a
plurality of writing magnetic poles 30-a to 30-d are employed
within a single head 11 along a direction substantially
perpendicular to the relative moving direction between the optical
head and the head, and electric signals may be separately inputted
to the respective magnetic poles. Then, the above-described writing
operation was performed in a parallel mode within the single
magnetic head. Concretely speaking, under such a condition that the
common laser 85 overlapped with at least one portion of all
magnetic poles 30-a to 30-d which are provided in parallel to each
other, the respective magnetizing directions of the magnetic poles
are inverted in correspondence with an arbitrary information
stream, whereby a plurality of information was converted into
parallel presence of the magnetic domains to be written in the
storage medium. A large number of magnetic poles could be present
within a spot size of a single laser by irradiating the common
laser. As a result, the information could be written in the
parallel form by a single head, namely a high density information
writing operation could be realized at a high speed.
[0177] Referring now to FIG. 20B, a description will be made of
such an example where the parallel-written information is
time-sequentially read out by way of a single detector. Either a
plurality of reading mirrors 43-a to 43-d, or magnetic poles having
mirror functions were positionally shifted along the relative
moving direction between the optical disk and the head 11. With
this arrangement, the magnetic domains 125 to 128 on the optical
disk are located on the respective mirrors at different timings.
The laser light 86 is irradiated from the rear surface of the
optical disk onto a region containing at least a surface of the
optical disk, which is overlapped with this mirror, or the magnetic
pole having the mirror function. As a result, both the magnetic
domain 125 existing in the portion located just under these mirrors
or the magnetic poles, and limited to the region onto which the
laser light is irradiated, and also the magnetic domains 126 to 128
present in other regions may be detected by a single detector at
different timings. With employment of this principle idea, the
information can be read/written in a parallel mode by way of a
single head.
[0178] FIGS. 21A-21E represent such a situation that the laser
light 86 is irradiated from the rear surface of the optical head to
either the magnetic poles 43-a to 43-d having the mirror function,
or a plurality of reading mirrors positionally shifted along the
relative movement direction for the optical head and the magnetic
head. A method for time-sequentially reading parallel information
by way of a single detector will now be explained with reference to
FIGS. 21A to 21B. FIG. 21A shows such a case that 4 magnetic
domains 125, 126, 127, 128 are present in a parallel form. When a
plurality of reading mirrors are provided with being positionally
shifted along the relative moving direction, these magnetic domains
reach just under the mirrors at different timings in accordance
with the movement of the optical disk. As a consequence, strengths
of the detection signal derived from the photodetector are varied
in four stages with respect to the time axis, as illustrated by a
solid line of FIG. 21C. On the other hand, as shown in FIG. 21B,
where there are two magnetic domains 129 and 130, strengths of the
detection signal are changed in two stages, as illustrated by a
dotted line of FIG. 21C. As described above, it can be seen that
the amplitude of the detection signal depends upon the total number
of the existing magnetic domains.
[0179] Also, since the timing at which presence of the magnetic
domain is detected by the mirror 43-a, and the timings for
detecting presence of the magnetic domains by other mirrors 43-d
and the like are constant, the position where the respective
magnetic domains are present may be calculated based upon the times
when the detection signal is varied. This timing extraction may be
realized by, for instance, differentiating the detection signal and
by comparing the differentiated signals with each other. FIG. 21D
shows a differential waveform in the above FIG. 21A, and FIG. 21E
represents another differential waveform in the above FIG. 21B.
From FIGS. 21D and 21E, it may be understood that signals
corresponding to presence of the magnetic domains are obtained at
different times t1, t2, t3 and t4. The spatially parallel-existing
information (presence of magnetic domain) can be read out by being
converted into electric signals separated from each other with
respect to the time axis by comparing the amplitudes of these
signals, indicated by the dotted line, with each other in a
comparator. As a consequence, a plurality of information can be
realized by a single head at a high speed.
[0180] The separation of the parallel information obtained by the
step-wise changes in the signal strengths may also be realized by
additionally performing such a process to A/D-convert the detection
signal and then process the A/D-converted signal in a digital
circuit. The above-explained function capable of
inputting/outputting a plurality of information streams with very
small time periods by way of a signal head, cannot be realized in
the conventional magneto-optical disk as well as the conventional
magnetic disk.
[0181] It should be noted that since the parallel-existing magnetic
domains 125 to 128 are arranged in the direction normal to the
relative moving direction of the optical head with respect to the
head 11 in the previous embodiment shown in FIG. 21, the reading
mirrors 43-a to 43-d are positionally shifted along the relative
moving direction so as to separate these magnetic domains on the
time axis to read out them. Alternatively, when, for instance, a
plurality of timings inputted to a plurality of writing magnetic
poles are slightly shifted, and the parallel magnetic domains are
formed not normal to the above-explained relative moving direction,
but slightly incident thereto, even if the reading mirrors 43-a to
43-d are not positionally shifted from each other, the parallel
information may be read while being separated on the time axis.
[0182] Further, to realize the above-described parallel information
input/output, a pattern having the mirror function of the head unit
11 may be made as illustrated in FIG. 22. That is, either the
reading mirrors, or the magnetic poles 43-a to 43-d having the
mirror function, and either the reading magnetic poles, or the
writing mirrors 30-a to 30-d are positioned apart from each other
by the substantially equal radial distance with respect to the
rotation center of the medium. As a consequence, the information
can be read/written by employing a single head and a single laser
beam, and the addressing mechanism can be commonly utilized for the
reading/writing operations, resulting in a simple addressing
mechanism. Since the written magnetic domains 27 are overlapped
with the reading portion and the portion onto which the laser light
87 is irradiated at which precision within a range where there are
no medium and thermal disturbance of the head, the addressing
control of the information ca be readily achieved.
[0183] To read and write a very small magnetic domain, either
mirrors provided on the head 11, or magnetic poles 44-a to 44-d
having the functions of the mirrors are shown as a structure of
FIGS. 23A-23B. FIG. 23A is a sectional view for showing the
input/output head as viewed in a direction along which the head is
moved with respect to the optical, and FIG. 23B is a sectional
view, as viewed vertically. The pattern having the mirror function
was patterned after metal films made of Fe, or Ni have been
laminated in such a manner that with a thickness of 200 angstrom, a
high polymer resin such as silicon oxide and a polyimid resin
having a thickness of 200 angstrom had been formed as a spacer, and
then the required photolithography process was carried out. After
the pattern has been fabricated, coil patterns 56, 57, 58, 59 used
to produce magnetic fields were formed. At this time, such a heed
structure was made that the magnetic pole 44-a corresponds to the
coil pattern 56, the magnetic pole 44-b corresponds to the coil
pattern 57, the magnetic pole 44-c corresponds to the coil pattern
58, and the magnetic pole 44-d corresponds to the coil pattern 59.
After the head has been manufactured in such a step, a section
thereof was a surface positioned close to the optical disk. The
relative moving direction between the head and the optical head was
selected to be the longitudinal direction of the pattern which was
obtained from the required photolithography process after the metal
films had been laminated.
[0184] As previously stated, as either the mirrors provided on the
head 11, or the magnetic poles 44-a to 44-d having the mirror
functions, the section of the metal films formed by being laminated
on the plane substrate is employed, so that the widths of the
magnetic poles could be made as the thickness of the laminated
films. In this case, the laminated thickness may be controlled
within a wide range from several angstrom to several micrometers,
and there is no problem in reproducibility. Conventionally, there
is such a problem that the width of the magnetic pole is restricted
by resolution of light used during the photolithography process. To
the contrary, according to this method, this restriction can be
solved. Therefore, the magnetic domain having the size of on the
order of angstrom can be written unless problems are present on the
storage medium. We could confirm that the magnetic domain having
the size smaller than, or equal to approximately 0.1 micrometer
could be written in the experience.
[0185] In the above-explained embodiments, the magnetic film for
magnetically recording the information, or the magnetic-optical
film such as the thermomagnetic recording material are employed as
the storage medium of the optical disk. The present invention is
not limited to these materials, but may be applied to, as the
storage medium, either a phase change material such as a
chalcogenid glass, or a photochromic material. That is, even when
these storage materials are employed as the storage medium of the
optical disk, a change may be produced in a region having a size
smaller than, or equal to the spot size of the laser beam by
commonly utilizing the very small mirrors, whereby the information
could be written at high density. The information written in this
manner may be read by employing the photodiodes to detect a
variation in the reflectivities of the storage medium, which are
caused by, for instance, differences in the phase conditions and
the coloring conditions. Also, the information may be magnetically,
or optically written into the optical disk, otherwise, may be
magnetically and optically written therein.
[0186] According to this embodiment, the effective spot diameter of
the laser beam can be made small. As a consequence, the storage
capacity of the optical disk can be increased by approximately
10.sup.2, as compared with that of the conventional optical disk.
Moreover, the mirror functions are merely added to the magnetic
disk head, so that such an optical disk high-density storage
apparatus can be realized with the substantially same conventional
structure.
* * * * *