U.S. patent application number 10/628364 was filed with the patent office on 2004-02-05 for optical head and optical information media recording/reproduction apparatus using the same.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Nakamura, Shigeru, Shigematsu, Kazuo, Shimano, Takeshi.
Application Number | 20040022141 10/628364 |
Document ID | / |
Family ID | 17903281 |
Filed Date | 2004-02-05 |
United States Patent
Application |
20040022141 |
Kind Code |
A1 |
Nakamura, Shigeru ; et
al. |
February 5, 2004 |
Optical head and optical information media recording/reproduction
apparatus using the same
Abstract
An optical head with a plurality of semi-conductor laser chips
for use in reducing inclination or gradient of more than one beam
presently falling onto a focusing lens is disclosed. To this end, a
double mirror or alternatively beam reshaping means is disposed
which has different reflection planes for permitting reflection of
a plurality of laser beams incoming from the semiconductor laser
chips.
Inventors: |
Nakamura, Shigeru;
(Tachikawa, JP) ; Shimano, Takeshi; (Tokorozawa,
JP) ; Shigematsu, Kazuo; (Yoshikawa, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-9889
US
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
17903281 |
Appl. No.: |
10/628364 |
Filed: |
July 29, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10628364 |
Jul 29, 2003 |
|
|
|
09517594 |
Mar 3, 2000 |
|
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Current U.S.
Class: |
369/44.12 ;
369/112.21; 369/112.29; 369/121; G9B/7.116; G9B/7.133 |
Current CPC
Class: |
G11B 7/1275 20130101;
G11B 7/1362 20130101; G11B 7/1392 20130101; G11B 7/1356 20130101;
G11B 7/1398 20130101; G11B 2007/0006 20130101; G11B 7/0956
20130101; G11B 7/123 20130101; G11B 7/0916 20130101 |
Class at
Publication: |
369/44.12 ;
369/121; 369/112.29; 369/112.21 |
International
Class: |
G11B 007/135; G11B
007/095 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 1999 |
JP |
11-301966 |
Claims
What is claimed is:
1. An optical head comprising a plurality of laser light sources
different in wavelength from each other, a mirror for permitting
reflection of a plurality of laser beams as emitted from the laser
light sources, and optical convergence means for focusing the
plurality of laser beams reflected off from the mirror into optical
spots on an optical information storage medium, wherein said mirror
includes a plurality of reflection planes for reflection of laser
beams of different wavelengths, and wherein said plurality of
reflection planes are in nonparallel to each other to thereby allow
the plurality of laser beams incoming from different directions to
be reflected off toward substantially the same direction.
2. The optical head structure according to claim 1, wherein said
mirror is disposed as a rise-up mirror for use in introducing a
laser beam into said optical convergence means.
3. An optical head comprising a plurality of semiconductor laser
chips, a collimating lens for converting a plurality of laser beams
radiated from the semiconductor laser chips to parallel rays of
light, and optical convergence means for focusing the plurality of
laser beams into an optical spot on an optical information storage
medium, wherein said optical head further comprises: a beam
reshaping prism for enlarging a width of each of said laser beams
in a direction along an array of said plurality of semiconductor
laser chips, and wherein said beam reshaping prism is disposed
between said collimate lens and said optical convergence means.
4. The optical head according to claim 3, wherein said beam
reshaping prism has a reflection plane and is disposed as a riseup
mirror for introduction of a laser beam into said optical
convergence means.
5. An optical head comprising a plurality of semiconductor laser
chips different in wavelength, a collimating lens for converting a
plurality of laser beams radiated from the semiconductor laser
chips to parallel rays of light, a mirror for permitting reflection
of the plurality of laser beams, and optical convergence means for
focusing the plurality of laser beams as reflected from said mirror
into optical spots on an optical information storage medium,
wherein said optical head further comprises: a beam reshaping prism
for enlarging a width of each said laser beam in a direction along
an array of said plurality of semiconductor laser chips, wherein
said beam reshaping prism is disposed between said collimating lens
and said optical convergence means, wherein said mirror includes a
plurality of reflection planes for reflection of laser beams of
different wavelengths, and wherein said plurality of reflection
planes are in nonparallel to each other thereby allowing the
plurality of laser beams incoming from different directions to be
reflected toward substantially the same direction.
6. The optical head according to claim 5, wherein said beam
reshaping prism is disposed as a riseup mirror for use in
introducing a laser beam into said optical convergence means.
7. An optical information media recording/ reproduction apparatus
for recording information on an optical information storage medium
or for reproducing information recorded thereon, said apparatus
comprising: an optical head for recording information on the
optical storage medium by irradiating laser light thereto or for
reproducing information recorded on said optical storage medium by
receiving light as reflected from said optical storage medium, and
an access mechanism for controlling a position for illumination of
laser light from said optical head onto said optical storage
medium, wherein said optical head includes a plurality of laser
light sources of different wavelengths, a mirror for permitting
reflection of a plurality of laser beams radiated from the laser
light sources, optical convergence means for focusing the plurality
of laser beams as reflected from the mirror into optical spots on
an optical information storage medium, and an optical detector,
wherein said mirror has a plurality of reflection planes for use in
permitting reflection of laser beams of different wavelengths, said
plurality of reflection planes being in non-parallel to each other
to thereby allow the plurality of laser beams incoming from
different directions to be reflected toward substantially the same
direction, and wherein the optical information media
recording/reproduction apparatus is operable to generate a focus
error detection signal and a track deviation detection signal while
letting the optical detector receive reflection light of laser
light falling onto said optical information storage medium and then
cause said access mechanism to control a position for illumination
of laser light of said optical head onto the optical information
storage medium to thereby perform one of recording information on
the optical information storage medium and playing back information
as recorded thereon.
8. The optical information media recording/ reproduction apparatus
according to claim 7, wherein said mirror is disposed as a riseup
mirror for use in introducing a laser beam into said optical
convergence means.
9. An optical information media recording/ reproduction apparatus
for recording information on an optical information storage medium
or for reproducing information recorded thereon, said apparatus
comprising: an optical head for recording information on the
optical storage medium by irradiating laser light thereto or for
reproducing information recorded on said optical storage medium by
receiving light as reflected from said optical storage medium, and
an access mechanism for controlling a position for illumination of
laser light from said optical head onto said optical storage
medium, wherein said optical head includes a plurality of
semiconductor laser chips, a collimating lens for converting a
plurality of laser beams radiated from the semiconductor laser
chips to parallel rays of light, optical convergence means for
focusing the plurality of laser beams into optical spots on the
optical information storage medium, an optical detector, and a beam
reshaping prism for enlarging a width of each said laser beam in a
direction along an array of said plurality of semiconductor laser
chips, said beam reshaping prism being disposed between said
collimating lens and said optical convergence means, and wherein
the optical information media recording/reproduction apparatus is
operable to generate a focus error detection signal and a track
deviation detection signal while letting the optical detector
receive reflection light of laser light falling onto said optical
information storage medium and then cause said access mechanism to
control a position for illumination of laser light of said optical
head onto the optical information storage medium to thereby perform
one of recording information on the optical information storage
medium and playing back information as recorded thereon.
10. The optical information media recording/ reproduction apparatus
according to claim 9, wherein said beam reshaping prism has a
reflection plane and is disposed as a riseup mirror for
introduction of a laser beam to said optical convergence means.
11. An optical information media recording/ reproduction apparatus
for recording information on an optical information storage medium
or for reproducing information recorded thereon, said apparatus
comprising: an optical head for recording information on the
optical storage medium by irradiating laser light thereto or for
reproducing information recorded on said optical storage medium by
receiving light as reflected from said optical storage medium, and
an access mechanism for controlling a position for illumination of
laser light from said optical head onto said optical storage
medium, wherein said optical head includes a plurality of
semiconductor laser chips of different wavelengths, a collimating
lens for converting a plurality of laser beams radiated from the
semiconductor laser chips to parallel rays of light, a mirror for
permitting reflection of the plurality of laser beams, optical
convergence means for focusing a plurality of laser beams reflected
from the mirror into optical spots on the optical information
storage medium, an optical detector, and a beam reshaping prism for
enlarging a width of each said laser beam in a direction along an
array of said plurality of semiconductor laser chips, said beam
reshaping prism being disposed between said collimate lens and said
optical convergence means, said mirror having a plurality of
reflection planes for use in permitting reflection of laser beams
of different wavelengths, and said plurality of reflection planes
being arranged in nonparallel to each other to thereby allow the
plurality of laser beams incoming from different directions to be
reflected off toward substantially the same direction, and wherein
the optical information media recording/reproduction apparatus is
operable to generate a focus error detection signal and a track
deviation detection signal while letting the optical detector
receive reflection light of laser light falling onto said optical
information storage medium and then cause said access mechanism to
control a position for illumination of laser light of said optical
head onto the optical information storage medium to thereby perform
one of recording information on the optical information storage
medium and playing back information as recorded thereon.
12. The optical information media recording/ reproduction apparatus
according to claim 11, wherein said beam reshaping prism is
disposed as a riseup mirror for introduction of a laser beam into
said optical convergence means.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to optical head
structures for use in recording or retrieving information on or
from optical information storage media including but not limited to
optical disks, and more particularly to an optical head employing a
laser module with a plurality of built-in semiconductor laser
chips. This invention also relates to optical information media
recording/reproduction apparatus using such optical head.
[0003] 2. Description of Related Art
[0004] In recent years, as optical media storage devices--such as
optical information recording and reproduction apparatus including
optical disk drives--are becoming important more and more in the
manufacture of electronic equipment, the trend has been toward
optical read/write devices exhibiting smaller size and reduced
thickness along with a variety of functionalities.
[0005] For example, it has been required that a single small-size
optical head assembly be used to record and/or play back
information to/from optical disks of different types. These include
recordable compact discs, also known as compact disc-recordable or
"CD-R" (trade name), and digital versatile disks (DVDs)--previously
digital video disks under the same abbreviation. The former is
recordable and non-erasable optical storage media as popularized in
the market whereas the latter is ultrahigh-density writable optical
storage media as recently developed, with two layers on each side
of a disk to store video and other data. Whereas laser beams
adaptable for use in recording/ retrieving data to/from CD-R media
measure approximately 780 nanometers (nm) in wavelength, those for
DVD record/playback are about 660 nm in wavelength. In view of such
laser wavelength difference, CD-R/DVD compatible record/playback
apparatus should be required to come with separate or independent
laser light source units--that is, both a laser light source of
about 780-nm wavelength and a 660-nm laser light source--situated
within a single optical head assembly. Prior known multiple
light-source small-size optical heads are disclosed in, for
example, JP-A-10-261240 and JP-A-10-289468. The optical heads as
taught thereby are designed so that a 780-nm wavelength
semiconductor laser chip for CDs and a 660-nm semiconductor laser
chip for DVDs are integrally accommodated in one unit, along with
more than one optical detection element operatively associated
therewith.
[0006] Generally, light beams of different light emission positions
tend to pass through different locations of a lens system at
different angles; obviously, in the above-noted optical heads also,
laser beams emitted from two semiconductor laser chips behave to
reach different positions of a focusing lens at different angles.
With the prior art optical heads as taught by the above-identified
Japanese publications, in order to attain an increased storage
density of data on optical media during recording and reproduction,
the 660-nm wavelength semiconductor laser chip for DVDs is disposed
at a specified location on the optical axis of a lens system
consisting essentially of a focusing lens and collimating lens
while letting the 780-nm wavelength semiconductor laser chip for
CDs be laid out at a selected location outside of the optical axis
of such lens system. This multi-laser layout would result in that
while a laser beam for use in DVD recording/ playback may
straightly progress to hit the focusing lens at right angles
thereto so that any appreciable aberration will hardly take place
at a laser spot focused on the surface of a DVD, a laser spot on a
CD can experience unwanted aberration (in particular, coma
aberration) because of the fact that a laser beam for CD
record/playback attempts to diagonally falls onto the focusing lens
at an angle thereto.
[0007] To avoid this problem, the optical head disclosed in
JP-A-10-261240 is designed so that a holographic optical device
(designated by reference numeral "25" in the disclosure thereof) is
employed to bend or curve only the optical path of a CD-read/write
laser beam thereby letting it reach the focusing lens at right
angles thereto. Similar beam path correction is done in the optical
head of JP-A-10-289468, by alternative use of an optical composer
(denoted by numeral 30 therein) including a polarizating prism
(birefringent plate) or holographic device.
[0008] Unfortunately, the prior art approaches are encountered with
a problem which follows. The intended laser beam path adjustability
does not come without requiring use of "special" holographic
devices or polarizing prisms (birefringent plates) that offer
expected functionality of bending only the optical path of a 780-nm
CD read/write laser beam while permitting a 660-nm wavelength DVD
read/write beam to be kept free from any influence therefrom. Use
of such special optical components disadvantageously results in an
increase in production costs of optical head units.
[0009] Another problem faced with the prior art lies in the lack of
sufficient capability to achieve light weight and slim size of
optical head structures, thus failing to fully meet demands for
thickness-reduction or down-sizing of optical heads. More
specifically, although not specifically set forth in the
above-identified Japanese documents, it will readily occur to those
skilled in the art that those optical components other than the
focusing lens must be laid out in a plane parallel to the disk
surface while at the same time requiring use of an additional
mirror, called a "rise-up" mirror, in order to guide beams to
accurately hit the focusing lens. Moreover, in order to attain the
intended recording of information on a target disk, a beam
reshaping prism should also be required for efficient collection or
focusing of rays of light emitted from a semiconductor laser with
anisotropic optical intensity distribution into a light spot with
isotropic optical intensity distribution. Hence, it is inevitable
for achievement of the required optical head at low costs to reduce
the requisite number of associative optical components while
simultaneously reducing production costs thereof.
SUMMARY OF THE INVENTION
[0010] It is therefore an object of the present invention to
provide a new and improved optical head assembly capable of
avoiding the problems faced with the prior art and also optical
read/write apparatus using the same.
[0011] It is another object of the present invention to provide an
optical head and optical information media record/reproduction
apparatus using the same, which head is adaptable for use in
recording or retrieving information to or from optical information
storage media by using a plurality of laser light source units and
is capable of reducing any appreciable aberration by forcing an
incoming laser beam from a semiconductor laser as disposed outside
of an optical axis to fall onto a focusing lens substantially at
right angles thereto while avoiding a need to employ additional
optical components of high costs.
[0012] To attain the foregoing objects, the present invention
provides an optical head which comprises a plurality of laser light
sources different in wavelength from each other, a mirror for
permitting reflection of a plurality of laser beams as emitted from
the laser light sources, and optical convergence means including
but not limited to a focusing lens for focusing the plurality of
laser beams reflected off from the mirror into optical spots on an
optical information storage medium such as an optical disk or the
like, wherein the mirror includes a plurality of reflection planes
for reflection of laser beams of different wavelengths, and wherein
the plurality of reflection planes are arranged in nonparallel to
each other thereby allowing the plurality of laser beams incoming
from different directions to be reflected off toward substantially
the same direction.
[0013] An optical head is also provided which comprises a plurality
of semiconductor laser chips, a collimating lens for converting a
plurality of laser beams radiated from the semiconductor laser
chips to parallel rays of light, and optical convergence means such
as a focusing lens or other similar suitable optical components for
focusing the plurality of laser beams into optical spots on an
optical information storage medium such as an optical disk or the
like, wherein a beam reshaping prism that functions to enlarge a
width of each of the laser beams in a direction along an array of
the plurality of semiconductor laser chips is disposed between the
collimate lens and the optical convergence means.
[0014] An optical head is also provided which comprises a plurality
of semiconductor laser chips different in wavelength, a collimating
lens for converting a plurality of laser beams radiated from the
semiconductor laser chips to parallel rays of light, a mirror for
permitting reflection of the plurality of laser beams, and optical
convergence means such as a focusing lens for focusing the
plurality of laser beams reflected from the mirror into an optical
spot on an optical information storage medium typically including
an optical disk or the like, wherein a beam reshaping prism that
enlarges a width of each of the laser beam in a direction along an
array of the plurality of semiconductor laser chips is disposed
between the collimating lens and the optical convergence means,
wherein the mirror includes a plurality of reflection planes for
reflection of laser beams of different wavelengths, and wherein
these reflection planes are in nonparallel to each other thereby
allowing the plurality of laser beams incoming from different
directions to be reflected off toward substantially the same
direction.
[0015] Either one of said mirror and said beam reshaping prism is
disposed as a rise-up mirror for use in introducing laser beams
into the optical convergence means.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a diagram showing a configuration of an optical
disk drive device employing an optical head assembly in accordance
with the present invention.
[0017] FIG. 2 is a diagram for explanation of an operation of a
diffraction grating portion of a composite element used in the
optical head shown in FIG. 1.
[0018] FIG. 3A is a diagram showing a plan view of a semiconductor
substrate used in the optical head of FIG. 1, and FIG. 3B depicts a
cross-sectional view of the substrate shown in FIG. 3A.
[0019] FIG. 4A illustrates a plan view of a package of FIG. 1, and
FIG. 4B is a sectional view of the package.
[0020] FIGS. 5A and 5B are diagrams each showing a configuration of
major part of an optical head in accordance with a first embodiment
of the invention.
[0021] FIG. 6 is a diagram showing principles of the invention in
the first embodiment.
[0022] FIG. 7 is a diagram showing a configuration of major part of
an optical head in accordance with a second embodiment of the
invention.
[0023] FIG. 8 is a diagram showing principles of the invention in
the second embodiment.
[0024] FIG. 9 shows a configuration of major part of an optical
head in accordance with a third embodiment of the invention.
[0025] FIG. 10 is a diagram showing principles of the invention in
the third embodiment.
[0026] FIG. 11 depicts a configuration of major part of an optical
head in accordance with a fourth embodiment of the invention.
[0027] FIG. 12 is a diagram showing a configuration of major part
of an optical head in accordance with a fifth embodiment of the
invention.
[0028] FIG. 13A is a plan view of an optical disk drive device
using the optical head embodying the invention, and FIG. 13B is a
sectional side view thereof.
DESCRIPTION OF THE EMBODIMENTS
[0029] A first embodiment of the present invention will be
explained with reference to FIGS. 1 to 6 and 13 below.
[0030] Referring to FIG. 1, there is shown a basic structure of an
optical disk drive device incorporating the principles of the
invention and also an optical head assembly employed therein.
Reference numeral "1" is used herein to designate a semiconductor
substrate having its surface on which an optical detector element
and electronic circuit along with any other constituent parts or
components are formed with more than one laser chip or the like
being attached thereto, wherein the substrate may preferably be
made of silicon or the like. In actual implementation, the
semiconductor substrate 1 is disposed so that its back surface is
toward the surface of the paper of the drawing sheet and, thus, its
front surface is invisible; however, for purposes of convenience of
illustration only, the depiction has been prepared so that the
substrate's front parts-mount surface configuration is made visible
from its back surface side by through-view illustration techniques.
Numeral 2 denotes a laser chip mount surface, which is fabricated
by chemically processing through etching treatment the surface of
the semiconductor substrate 1 to a depth ranging from 30 to 100
micrometers (.mu.m), wherein the laser chip mount surface 2 lies in
parallel to the surface of semiconductor substrate 1. Arrow 3
indicates a normal direction to the laser chip mount surface 2.
Reference character 4a designates a semiconductor laser chip
adaptable for use with digital versatile discs (DVDs), which gives
off a laser beam 6a that measures 660 nanometers (nm) in wavelength
.lambda.a; 4b denotes another semiconductor laser chip adapted for
use with recordable compact discs, typically known as compact
disc-recordable (CD-R) in the optical storage media art, which
emits a laser beam 6b of its wavelength .lambda.b=780 nm. The
semiconductor laser chips 4a and 4b are rigidly secured by
soldering to the laser chip mount surface 2. Numeral 5 is a
semiconductor mirror surface or plane that is formed between the
semiconductor substrate 1's surface and the laser chip mount
surface 2, wherein the mirror plane may be fabricated by etching
techniques at the same time that the laser chip mount surface 2 is
formed. After having been emitted from the semiconductor laser chip
4a, the DVD laser beam 6a is reflected on the semiconductor mirror
plane 5 to reach a collimating lens 10, which converts this
reflection light into parallel rays of light. Similarly, the CD
laser beam 6b is such that after leaving the semiconductor laser
chip 4b, this beam is reflected at the semiconductor mirror plane 5
to enter the collimating lens 10, which then converts resultant
reflection light to parallel rays of light. 7 denotes an optical
detection element for use in obtaining a focusing deviation/error
detection signal; 8 is an optical detector element for generation
of a tracking error detection signal and information reproduction
or playback signals; 9, an optical detector for use in monitoring
the light emission amount of each of the semiconductor laser chips
4a and 4b, a respective one of these photodetectors 7-9 being
formed on the surface of the semiconductor substrate 1. 11 is a
mirror for reflection of the laser beams 6a and 6b. 12 is a
composite element with an assembly of a four-divided diffraction
grating offering certain polarizabilities and a quarter wavelength
(.lambda./4) plate being surface-bonded together, wherein the
four-divided diffraction grating with polarizability is disposed in
such a manner as to face the side of the semiconductor laser chips.
The four-divided diffraction grating may be constituted from a
birefringent optical crystal plate and/or liquid crystal (LC)
plate, by way of example, which functions to cause incident rays of
ordinary light to penetrate therethrough without any diffraction
and, in the case of extraordinary light, serves as the diffraction
grating required. 13 is a focusing lens, which may typically be an
incident beam diameter-variable lens, a lens with a holographic
element added to its incoming light reception side, a lens with a
holographic element and/or more than one ring-like band groove
added to its light incidence side, or other similar suitable
lenses, to thereby offer compatibility with both DVDs and CDs,
including CD-R disks, wherein DVDs measure 0.6 mm in substrate
thickness and 660 nm in use wavelength and also 0.6 in numerical
aperture (NA) whereas CDs are 1.2 mm in substrate thickness and 780
nm in use waveform with its numerical aperture of about 0.5. 15
shows a presently loaded optical storage disk, such as a DVD, CD-R
or CD. 16 designates the center of rotation of the optical disk
(also referred to as "disc" in some cases) 15; dotted-line circle
17 denotes an information/data recording track; and, arrow 18
indicates a radial direction of the optical disk 15.
[0031] In the illustrative embodiment the laser beams 6a and 6b as
emitted from the semiconductor laser chips 4a, 4b are such that
when reaching the composite device of the four-divided diffraction
grating with polarizability and the .lambda./4 plate stated supra,
the beams behave as ordinary rays of light which directly pass
through polarizable diffraction grating portions without exhibiting
any diffraction to be converted to circularly polarized light by
the .lambda./4 plate of the composite device 12. Reflected rays of
such laser beams 6a, 6b at the optical disk become extraordinary
light rays through the .lambda./4 plate of the composite device 12
and are then diffracted by the four-divided diffraction grating
with polarizability. FIG. 2 shows one exemplary diffraction grating
pattern of the four-divided diffraction grating of the composite
device 12, which is subdivided by boundary lines 21 and 22 into
four separate regions. A circle 20 shown herein indicates a laser
beam 6a or 6b, which is split by the four-divided diffraction
grating into four primary diffracted light rays with the positive
polarity (+) and four primary diffracted rays of the negative
polarity (-).
[0032] Turning to FIG. 3A, there is shown a parts-mount surface of
the semiconductor substrate 1 when looking at from the side of
collimating lens 10. In FIG. 3A, eight quarter-circle marks 32a
with solid black shading applied thereto are used to designate
those laser beams of wavelength .lambda.a, which are reflected on
the optical disk and then split by the diffraction grating; eight
quarter circles 32b with no shading applied thereto denote laser
beams of wavelength .lambda.b which are reflected at the optical
disk and then split by the diffraction grating. The optical
detector shown by numeral 7 in FIG. 1 is in detail a group of
optical detectors including four pairs of photodetectors, each pair
consisting of two light-sensitive elements 7a and 7b opposing each
other, each of which has an elongated rectangular photosensitive
area, wherein the individual one of them is operable to receive
either one of the laser beam 32a of wavelength .lambda.a and laser
beam 32b of wavelength .lambda.b. A focusing error detection method
as used therein employs the so-called Foucault knife-edge
techniques based on four-split beam schemes, wherein a focus-error
detection signal is obtainable through differential processing of
output signals of two photosensitive elements in each pair. The
illustrative embodiment, however, is specifically arranged so that
the intended focus error signal is obtained by connecting such
photosensitive elements together by a conductive thin-film lead 33
made for example of aluminum in the way shown in FIG. 3A and then
executing differential processing of output signals as derived from
a terminal A and terminal B of wire bonding pads 34. In this way,
four focus error detection signals are thus obtained from the four
pairs of photosensitive elements, which signals are then combined
or "composed" together to provide a stable focus error detection
signal which may exhibit stability even when the focusing lens is
shifted in position or displaced in radial directions of the
optical disk, wherein such lens position deviation can occur due to
effectuation of tracking control. 9 denotes the optical detector
for monitoring the light emission amount of the semiconductor laser
chips 4a and 4b, wherein an output signal of the photodetector 9
will be output from a terminal C of pad 34. Points 31a and 31b
designate reflection positions on the semiconductor mirror plane 5
whereat the laser beams 6a and 6b emitted from the semiconductor
laser chips 4a, 4b are to be reflected off. For instance, supposing
that all of the four regions shown in FIG. 2 are equal in
diffraction grating pitch P while letting the diffraction grating
direction be given as +.alpha., -.alpha., +3.alpha., and -3.alpha.
degrees with respect to a longitudinal line 21 and also letting the
collimating lens's focal distance be represented by fc, the laser
beam 32a of wavelength .lambda.a as split by the diffraction
grating is expected to be focused at a specified position that is
on a circle with the point 31a being as its center and with its
radius equal to Ra=fc.multidot..lambda.a/P and is spaced by a
distance of 2.alpha. degrees from the center. Similarly the laser
beam 32b of wavelength .lambda.b split by the diffraction grating
is to be focused at a position that is on a circle with the point
31b as its center and with its radius of Rb=fc.multidot..lambda.b/P
and is spaced by 2.alpha. degrees from the center. By letting a
light emission point-to-point distance D of the semiconductor laser
chips 4a and 4b, which corresponds to the distance between the
points 31a and 31b, be nearly equal to fc (.lambda.b-.lambda.a)/P,
it becomes possible to permit the focussing position of such laser
beam of wavelength .lambda.a to be substantially identical to that
of the laser beam of wavelength .lambda.b, which in turn makes it
possible to allow common use of photosensitive elements and
amplifiers among those beams of different wavelength values as in
this embodiment, while at the same time saving the surface of the
semiconductor substrate 1 and also reducing the requisite number of
wire bonding pads and output leads to thereby advantageously
facilitate miniaturization or "down-sizing" of a package structure
for use in accommodation of the semiconductor substrate 1.
[0033] The photodetector 8 shown in FIG. 1 for use in obtaining a
tracking error detection signal and information playback signals is
configured from photosensitive elements 38a and 38b. The
photosensitive elements 38a include four photosensors that are
optically sensitive to the incoming laser beam 32a whereas the
remaining photosensitive elements 38b likewise include four
photosensors that receive the laser beam 32b, wherein output
signals of photosensors 38a and 38b are input to an amplifier
circuit 39 as formed on the semiconductor substrate 1. In cases
where the semiconductor laser chip 4a is presently rendered
operative to emit light, those signals of the photo-sensors 38a are
output to terminals D, E, F and G of pads 34; alternatively, while
the semiconductor laser chip 4b is emitting light, signals of
photosensors 38b are passed to the terminals D-G of pads 34. As the
optical detector 7 in this embodiment is arranged so that
photodetectors are commonly useable for those beams of different
wavelengths while the optical detector 8 and amplifier 39 in this
embodiment are such that the amplifier is useable in common for
beams of different wavelengths, it is thus possible to save the
surface of the semiconductor substrate 1 while simultaneously
reducing the requisite number of wire bonding pads and output leads
to thereby advantageously facilitate successful down-sizing of a
package structure for receiving the semiconductor substrate 1
therein.
[0034] See FIG. 3B, which depicts a cross-sectional structure of
the semiconductor substrate 1 as taken along dotted line A-A' in
FIG. 3A. Preferably the semiconductor mirror 5 is formed so that it
is at 45 degrees to the laser-chip amount surface 2. Machining of
the silicon mirror surface is based on so called anisotropic
etching treatment, that the etching rate at the (111) plane is
greatly less than that on the (100) plane by a significant degree
corresponding to two orders of magnitude. The (100) plane of
silicon etched by potassium hydroxide-based water solution would
result in the fabrication of a rectangular prismoid or
"pyramid"-shaped concave portion having a trapezoid-like profile
with a flat (111) plane as its slanted surface. At this time an
angle that the (111) plane forms with the (100) plane is about
54.degree.; thus, in order to fabricate a semiconductor mirror of
45 degrees, it is required to employ a specific silicon substrate
of approximately 9 degrees in off-angle value with its crystal axis
being slanted or tilted relative to the surface thereof, by way of
example. However, it should be required that such off-angle be
determined by taking account of adaptability of semiconductor
processes for fabrication of photosensitive elements and
electronics circuit: In some cases, the semiconductor mirror 5 can
be displaced from 45 degrees; in other cases, the ray-exit
direction of the laser beams 6a, 6b can be deviated or offset from
the perpendicular direction to the semiconductor substrate 1.
[0035] Turning now to FIG. 4A, there is shown a planar structure of
a package 41 that accommodates the semiconductor substrate 1
therein. Also see FIG. 4B, which depicts a sectional view of the
package taken along dotted line B-B' in FIG. 4A. Numeral 42 as used
herein refers to electrical leads that are connected via
associative bonding wires to the pads 34 on the semiconductor
substrate 1 shown in FIG. 3A. A support base portion or "pedestal"
43 for mounting thereon the semiconductor substrate 1 has a slanted
top surface to ensure that the ray-exit direction of any one of the
laser beam 6a, 6b becomes identical to the perpendicular direction
to the surface of the package 41. 44 is a glass cover for sealing
the semiconductor substrate 1, wherein a reflection plane 45 is
provided inside of the glass cover 44 for permitting reflection of
outer peripheral portions of the laser beams 6a and 6b. Reflected
beams from the reflection plane 45 are guided to reach the
photodetector 9 on the semiconductor substrate 1, which generates
and issues an electrical signal for use in monitoring the light
emission amount of each of the semiconductor laser chips 4a and
4b.
[0036] An explanation will now be given of the principles of the
present invention in conjunction with FIGS. 5A and 5B. FIGS. 5A-5B
each show an optical path spanning from the light source module up
to the focusing lens of the optical head embodying the invention
shown in FIG. 1, wherein the semiconductor mirror 5 and composite
device 12 are eliminated from the illustration. FIG. 5A shows a
certain case where a double mirror 11 is present whereas FIG. 5B
shows another case where such double mirror 11 is absent. As
typical semiconductor laser chips measure about 250 .mu.m in width,
the distance D between the light emission points of the
semiconductor laser chips 4a and 4b is 300 .mu.m by way of example.
In addition, the focal distance fc of the collimating lens 10 is 20
mm, for example. As shown in FIG. 5B, in case the semiconductor
laser chip 4a is disposed on the optical axis of the collimating
lens 10, a laser beam 6a emitted from the semiconductor laser chip
4a travels straightly to hit the focusing lens 13 at right angles
thereto; thus, any appreciable aberration will hardly take place.
On the contrary, a laser beam 6b emitted by the semiconductor laser
chip 4b diagonally reaches the focusing lens 13 at an angle
.theta.=arctan(D/fc)=0.86.degree. so that aberration (in
particular, coma aberration) tends to readily occur. To avoid this,
the illustrative embodiment makes use of the double mirror 11 shown
in FIG. 5A. The double mirror 11 has a reflection plane 51a and
reflection plane 51b, wherein the former is for permitting
reflection of the laser beam 6a of 660-nm wavelength while causing
the laser beam 6b of 780-nm wavelength to simply pass therethrough
whereas the latter is for reflection of the 780-nm wavelength laser
beam 6b. The reflection plane 51a is formed for example of a
dichroic mirror with more than one dielectric thin-film laminated,
and is disposed at an angle of 45.degree. relative to the incoming
laser beam 6a. On the other hand the reflection plane 51b is a
mirror made of aluminum, for example, which forms a specified angle
.alpha. with the reflection plane 51a.
[0037] As shown in FIG. 6, an angle of refraction .gamma. of the
laser beam 6b falling onto the reflection plane 51a is given as:
sin .gamma.=sin(.pi./4+.theta.)/n, where n is the refractive index
of a material lying between the reflection plane 51a and reflection
plane 51b with respect to the laser beam 6b. When leaving the
reflection plane 51a, the beam exhibits an angle of incidence
.gamma.' with respect to reflection plane 51, which is represented
by: sin .gamma.'=sin(.pi./4)/n. Thus, according to the law of
reflection, a specific angle of the laser beam 6b at the reflection
plane 51b which satisfies .gamma.-.alpha.=.gamma.'+.alpha.--that
is, .alpha.=(.gamma.-.gamma.')/2--- is obtainable. One example is
that when n=1.5 and .theta.=0.86.degree., then
.alpha.=0.23.degree.. Use of the double mirror 11 that has the
reflection plane 51b leaned by an angle .alpha.=0.23.degree. with
respect to the reflection plane 51a forces the laser beam 6b, which
is tilted at an angle .alpha.=0.86.degree. relative to the laser
beam 6a, to be in almost completely parallel to the laser beam 6a
and thus fall onto the focus lens 13 at right angles thereto,
thereby enabling suppression or minimization of appreciable
aberration.
[0038] See FIGS. 13A-B, which shows a structure of an optical disk
drive device incorporating the principles of the instant invention,
wherein FIG. 13A is a top plan view whereas FIG. 13B is a side view
in cross-section. Numeral 131 refers to an enclosure or housing
structure of such optical disk device. 132 designates a motor as
attached to the housing 131 of the optical disk device for rotation
of an optical disk 15 via a shaft 133. 134 denotes an optical head
assembly, wherein a package 41 receiving therein the semiconductor
substrate 1 and a lens actuator 135 with the focusing lens 13 are
attached. 136 is an access mechanism attached to the optical head
134; 137 is a rail attached to the housing 131 of the optical disk
device. The optical head 134 is movable by the access mechanism 136
on the rail 137 in radial directions of the optical disk 15. The
optical head 134 contains therein a collimating lens 10 and double
mirror 11 plus composite device 12. The package 41 includes
built-in semiconductor laser chips 4a and 4b, either one of which
is rendered operative to emit a laser beam 66a or 66b, which is
given off from the optical head 134 through the focusing lens 13 of
the lens actuator 135 to thereby illuminate the optical disk 15
being presently driven to rotate. A reflection beam of it is
optically guided to reach the optical head 134 via the focusing
lens 13 again, part of which is received by an optical detector
element 7 as mounted in the package 41 to thereby obtain a focusing
error detection signal. Another part of the reflection beam is
received by the optical detector 8 also built in the package 41,
which then generates a tracking error detection signal and
information playback signal(s).
[0039] A second embodiment of the present invention will next be
explained with reference to FIGS. 7 and 8. FIG. 7 is a diagram
showing the optical path of an optical head employing, in place of
the mirror 11 of FIG. 5, a couple of beam reshaping prisms 71 and
72 in accordance with the invention, wherein the semiconductor
mirror 5 and composite device 12 shown in FIG. 1 are eliminated
from the illustration of the diagram. The light emission intensity
distribution of the semiconductor laser chips 4a and 4b is wide in
the direction perpendicular to the paper of the drawing sheet and
narrow in directions on the paper. Numeral 10 designates a
collimating lens; 13 denotes a focusing lens. 71 and 72 denote such
beam reshape prisms for use in enlarging the beam width of each
laser beam 6a, 6b in directions on the paper of the drawing sheet
to thereby provide isotropic optical intensity distribution. 73 is
an ordinary or standard mirror.
[0040] The principles of the present invention will be explained
with reference to FIG. 8. The refractive index n of the prism 71 or
72 is given by n.multidot.sin .gamma.=sin i, where i is the angle
of incidence at an incidence plane 81, and .gamma. is the
refractive angle. In addition, letting a distance between two light
rays 82 and 83 prior to incidence to the prism be represented by
h1, a distance inside of such prism be indicated by h2, and a
distance between incidence points of the light rays 82 and 83 on
the incidence plane 81 be given by l, then the beam width expansion
factor m is represented as m=cos .gamma./cos i, since
h1=l.multidot.cos i, h2=l.multidot.cos .gamma.. Letting an apical
or vertex angle of the prism be .beta.=.gamma., it becomes a beam
reshape prism of vertical light emission. Let minimal or "micro"
modification at incidence angle i be .DELTA.i, and let
micro-modification at refractive angle .gamma. be .DELTA..gamma.;
then, we obtain n.multidot.sin(.gamma.+.-
DELTA..gamma.)=sin(i+.DELTA.i). Finally,
n.multidot..DELTA..gamma.=.DELTA.- i/m is obtained. Additionally,
letting the micro-modification from vertical outward light emission
at the light-outgoing plane 84 be .DELTA.j, the law of refraction
on such plane 84 suggests .DELTA.j=n.multidot..DELTA..gamma..
Hence, .DELTA.j=.DELTA.i/m. Thus, use of the prism of beam width
expansion factor m makes it possible to reduce the beam's angular
modification to 1/m.
[0041] For example, suppose that the light emission intensity
distribution of the semiconductor laser chips 4a and 4b is at 30
degrees in the direction at right angles to the paper of the
drawing sheet, and 10 degrees in a direction on the paper. Also
assume that the prisms 71 and 72 are fabricated so that each is
made of glass of its refractive index n=1.5 and has its vertex
angle of .beta.=36.14 degrees while disposing these prisms so that
the incidence angle i to each prism is defined by i=62.2 degrees.
If this is the case, the resulting beam width expansion factor m of
each prism becomes equal to m=31/2, which ensures that the outgoing
beam exhibits isotropic light intensity distribution due to the
actions of two prisms 71 and 72. In addition, in case the
semiconductor laser chip 4a is laid out on the optical axis of the
collimating lens 10 with the light emission point distance D of
semiconductor laser chips 4a and 4b being set at 300 .mu.m and with
the focal distance fc of collimating lens 10 set at 20 mm, a laser
beam 6b leaving the semiconductor laser chip 4b is expected to
reach the prism 71 at an angle of 0.86.degree. when compared to a
laser beam 6a. However, due to the action of the beam reshape
prisms 71 and 72 embodying the invention, the inclination of such
laser beam 6b after leaving the prism 72 becomes 0.29.degree.. For
this reason, it becomes possible by use of the prisms of this
invention to permit the inclination or gradient of the laser beam
6b falling onto the focus lens 13 to drop down at one third, which
in turn makes it possible to let appreciable coma aberration or the
like hardly take place.
[0042] A third embodiment of the present invention will be
explained with reference to FIGS. 9 and 10. FIG. 9 is a diagram
showing the optical path of an optical head employing, in place of
the beam reshape prisms 71 and 72 of FIG. 7, a mirror prism 91 in
accordance with the invention, wherein the semiconductor mirror 5
and composite device 12 shown in FIG. 1 are omitted from the
illustration of the optical path diagram. The light emission
intensity distribution of the semiconductor laser chips 4a and 4b
is wide in the direction perpendicular to the paper of the drawing
sheet and yet narrow in directions on the paper. Numeral 10
designates a collimating lens; 13 denotes a focusing lens. The
mirror prism 91 is designed to have a refractive plane 92 for
refraction of laser beams 6a and 6b along with a reflective plane
93 for reflection, wherein a vertex angle the refractive plane 92
forms with the reflective plane 93 is given as .theta.. The
reflective plane 93 has a reflective film made, for example, of
aluminum as deposited thereon. The mirror prism 91 has a beam
reshaping function for enlarging the beam width of laser beams 6a
and 6b in those directions on the paper of the drawing sheet to
thereby provide isotropic light intensity distribution and also has
a function of letting an incoming beam or beams be reflected off
toward the vertical direction.
[0043] The principles of the present invention will be explained
with reference to FIG. 10. Let the incident angle of a laser beam
101 falling onto the mirror prism 91 be represented by i,
refractive angle be .gamma., incident angle of the laser beam 101
leaving the mirror prism 91 be .gamma.', angle of outgoing light be
i', and the refractive index of mirror prism 91 be given as n;
then, the law of refraction suggests n.multidot.sin .gamma.=sin i,
n.multidot.sin .gamma.'=sin i'. In addition, since the reflective
plane 93 is inclined or tilted at the angle .theta. relative to the
refractive plane 92, .gamma.-.theta.=.gamma.'+.theta. is obtained.
The condition for letting the laser beam 101 outgo in the direction
perpendicular to the incidence angle thereof is given by:
i+i'=.pi./2. From the equation above, we obtain
.theta.=1/2.multidot.[arcsin(1/n.multidot.sin
i)-arcsin(1/n.multidot.cos i)]. Further, the beam width expansion
factor m1 in the event of incidence is represented by m1=cos
.gamma./cos i whereas the beam width expansion factor m2 upon
leaving is given as m2=cos i'/cos .gamma.'; thus, the beam width
expansion factor M of the mirror prism 91 must be
M=m1.multidot.m2=cos .gamma./cos i.multidot.cos i'/cos .gamma.'.
Additionally, let minimal or "micro" modification at incidence
angle i be .DELTA.i, micro-modification at refractive angle .gamma.
be .DELTA..gamma., micro-modification at incidence angle .gamma.'
be .DELTA..gamma.', and micro-modification at light-exit angle i'
be .DELTA.i'; then, we obtain n.multidot.sin
(.gamma.+.DELTA..gamma.)=sin(i+- .DELTA.i), n.multidot.sin
(.gamma.'+.DELTA..gamma.')=sin (i'+.DELTA.i'),
(.gamma.+.DELTA..gamma.)-.theta.=(.gamma.'+.DELTA..gamma.')
+.theta.. From the above equation involving micro-modification(s),
.DELTA.i'=cos .gamma./cos i.multidot.cos i'/cos
.gamma.'.multidot..DELTA.i is obtainable; finally, we obtain
.DELTA.i'=.DELTA.i/M. After all, use of the mirror prism 91 of beam
width expansion factor M makes it possible to reduce angular
modifications of beams down at 1/M.
[0044] For example, suppose that the light emission intensity
distribution of the semiconductor laser chips 4a and 4b is at 30
degrees in the direction at right angles to the paper of the
drawing sheet, and 10 degrees in a direction on the paper. Assume
that the mirror prism 91 is fabricated by using a glass material of
its refractive index n=1.5 and exhibits a geometry with a vertex
angle of .theta.=15.29 degrees while disposing it so that the
incidence angle i to mirror prism 91 is defined by i=75.5 degrees.
If this is the case, the resultant beam width expansion factor M of
mirror prism 91 becomes equal to M=3, which insures that the
resulting light intensity distribution of outgoing beam is rendered
isotropic--namely, equal in beam width in all directions concerned.
In addition, in case the semiconductor laser chip 4a is disposed on
the optical axis of the collimating lens 10 with the light emission
point distance D of semiconductor laser chips 4a and 4b being set
at 300 .mu.m and with the focal distance fc of collimating lens 10
set at 20 mm, a laser beam 6b emitted from the semiconductor laser
chip 4b is expected to reach the mirror prism 91 at an angle of
0.86.degree. when compared to laser beam 6a. However, due to the
action of the mirror prism 91 embodying the invention, the
inclination of such laser beam 6b after leaving the mirror prism 91
becomes 0.29.degree.. It thus becomes possible by use of the prism
embodying the invention to permit the inclination or gradient of
the laser beam 6b falling onto the focusing lens 13 to drop down at
one third, which in turn makes it possible to let appreciable coma
aberration or the like hardly take place.
[0045] A fourth embodiment of this invention will be explained with
reference to FIG. 11. Numerals 111 and 112 denote beam reshape
prisms that function to enlarge the beam width in directions on the
paper of the drawing sheet, as in the above-discussed beam reshape
prisms 71 and 72 shown in FIG. 7. In the above-noted second
embodiment of FIG. 7, as the laser beam 6b leaving the beam reshape
prisms 71 and 72 is inclined at 0.29.degree. relative to the other
laser beam 6a. With the embodiment of FIG. 11, such slight residual
inclination of laser beam 6b may be removed away by using a double
mirror 113 having its reflective plane 114a for reflection of the
laser beam 6a and a reflection plane 114b for reflection of the
laser beam 6b to thereby permit such two laser beams to be
reflected off toward the same direction, in a way similar to that
of the double mirror 11 shown in FIG. 5.
[0046] In the case of recording or playing back information to or
from an optical disk such as CD-R or else, an optical spot being
focused on the optical disk is preferably of a round shape rather
than elliptical or "oval" shapes in some cases. In the illustrative
embodiment, since it is possible to freely design the significance
of the beam width expansion factor due to the beam reshape prisms
111 and 112, it becomes possible to form spots of any desired
profiles including not only round shapes but also oval shapes while
at the same time enabling such two beams to straightly reach the
focusing lens 13 at right angles thereto.
[0047] A fifth embodiment of the invention will be explained with
reference to FIG. 12. Numeral 121 denotes a double mirror prism
that serves to expand the beam width in directions on the paper of
the drawing sheet by refraction at its refractive plane 122, as in
the mirror prism 91 shown in FIG. 9. In the third embodiment of
FIG. 9, the laser beam 6b leaving the mirror prism 91 is tilted at
0.29.degree. relative to the remaining laser beam 6a; thus, slight
coma aberration or else can occur when letting the focusing lens 13
focus the laser beam 6b. As in the double mirror 11 shown in FIG.
5, the double mirror prism 121 in the embodiment of FIG. 12 has its
reflective plane 123a for reflection of the laser beam 6a and a
reflective plane 123b for reflection of laser beam 6b and is
disposed so that the reflective plane 123b is tilted relative to
the reflective plane 123a, thereby making it possible to remove
away even such slight residual inclination of laser beam 6b, which
in turn enables reflection of two laser beams toward the same
direction.
[0048] With this embodiment also, since it is possible to freely
set the beam width expansion factor owing to the double mirror
prism 121 at any desired values, it becomes possible to form spots
of not only round shapes but also oval shapes while at the same
time enabling such two beams to straightly hit the focusing lens 13
at right angles thereto.
[0049] It has been described that in accordance with the present
invention, it is possible to accomplish an optical head and optical
information media record/reproduction apparatus using the same,
which head is adaptable for use in recording or retrieving
information to or from optical information storage media by using a
plurality of laser light source units and is capable of reducing
any appreciable aberration by forcing an incoming laser beam from a
semiconductor laser as disposed outside of an optical axis to fall
onto a focusing lens substantially at right angles thereto while
avoiding a need to employ additional optical components of high
costs.
* * * * *