U.S. patent application number 09/273724 was filed with the patent office on 2001-12-06 for optical pickup device.
Invention is credited to NAGAHARA, SHINICHI, TOGASHI, TAKAHIRO, YANAGAWA, NAOHARU.
Application Number | 20010048063 09/273724 |
Document ID | / |
Family ID | 14137034 |
Filed Date | 2001-12-06 |
United States Patent
Application |
20010048063 |
Kind Code |
A1 |
YANAGAWA, NAOHARU ; et
al. |
December 6, 2001 |
OPTICAL PICKUP DEVICE
Abstract
A light beam is emitted by the light source. The optical system
separates the light beam into a main-portion and a sub-portion, and
guides the main-portion of the light beam to an information storage
medium. The monitor detector receives the sub-portion of the light
beam and outputs a detection signal. Then, the controller controls
the output power of the light beam emitted by the light source
based on the detection signal. Thus, the light beam of the
sub-portion, which is not generally used as a light beam to be
irradiated on a storage medium, can be efficiently used, and hence
the output power of the light beam from the light source may be
controlled with high accuracy.
Inventors: |
YANAGAWA, NAOHARU;
(TOKOROZAWA-SHI, JP) ; TOGASHI, TAKAHIRO;
(TOKOROZAWA-SHI, JP) ; NAGAHARA, SHINICHI;
(TOKOROZAWA-SHI, JP) |
Correspondence
Address: |
NIXON & VANDERHYE
1100 NORTH GLEBE ROAD
8TH FLOOR
ARLINGTON
VA
222014714
|
Family ID: |
14137034 |
Appl. No.: |
09/273724 |
Filed: |
March 22, 1999 |
Current U.S.
Class: |
250/205 ;
369/112.01; G9B/7.099; G9B/7.102; G9B/7.114; G9B/7.12 |
Current CPC
Class: |
G01J 1/32 20130101; G11B
7/1381 20130101; G11B 7/13 20130101; G11B 7/1356 20130101; G11B
7/126 20130101; G11B 7/1376 20130101; G11B 7/1398 20130101 |
Class at
Publication: |
250/205 ;
369/112.01 |
International
Class: |
G11B 007/00; G11B
007/135; G01J 001/32 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 24, 1998 |
JP |
P10-95414 |
Claims
What is claimed is:
1. A pickup device comprising: a light source for emitting a light
beam; an optical system for separating the light beam into a
main-portion and a sub-portion, and for guiding the main-portion of
the light beam to an information storage medium; a monitor detector
for receiving the sub-portion of the light beam and for outputting
a detection signal; a controller for controlling an output power of
the light beam emitted by the light source based on the detection
signal.
2. A pickup device according to claim 1, wherein the main-portion
is a center portion of the light beam and the sub-portion is a
portion of the light beam other than the main portion.
3. A pickup device according to claim 1, wherein the optical system
comprises an interrupting member for partially interrupting the
light beam from the light source and passing only the main-portion
and the sub-portion of the light beam.
4. A pickup device according to claim 3, wherein the interrupting
member comprises a first aperture for passing the main-portion of
the light beam and at least one second aperture for passing the
sub-portion of the light beam.
5. A pickup device according to claim 3, further comprising a
casing for covering a light emitting part of the light source to
receive whole portion of the light beam emitted by the light
source, the interrupting member being disposed on the casing at a
position receiving the light beam from the light source.
6. A pickup device according to claim 1, wherein the optical system
comprises a collimator lens, the collimator lens comprising a
miniature convex lens formed at an edge part thereof and for
directing the sub-portion of the light beam to the monitor
detector.
7. A pickup device according to claim 1, wherein the optical system
comprises a collimator lens, the collimator lens comprising two
miniature convex lenses formed at edge parts thereof opposing to
each other, the two convex lenses directing the sub-portions of the
light beams to the monitor detector.
8. A pickup device according to claim 1, wherein the optical system
comprises a diffraction grating having a first grating pattern for
directing the main-portion of the light beam to the storage medium
and a second grating pattern for directing the sub-beam to the
monitor detector.
9. A pickup device according to claim 8, wherein the second grating
pattern directs all component of the light beam other than the
main-portion to the monitor detector as the sub-portion of the
light beam.
10. A pickup device according to claim 1, wherein the optical
system comprises a beam splitter having a light receiving surface
and a light reflecting surface, the light receiving surface guiding
the main-portion of the light beam to the storage medium, and the
light reflecting surface reflecting the subportion of the light
beam to the monitor detector.
11. A pickup device according to claim 1, wherein the monitor
detector comprises two detection elements each for outputting an
electric signal corresponding to a quantity of light received, and
an adder for adding two electric signals to produce the detection
signal.
12. A pickup device for irradiating a main-portion of a light beam
emitted from a light source on a storage medium, comprising: a
light detector for receiving a sub-portion of the light beam which
is a portion other than the main-portion of the light beam emitted
by the light source and outputting a detection signal; and an
adjusting unit for adjusting a power of the light beam emitted by
the light source based on the detection signal.
13. A pickup device according to claim 12, further comprising a
separating unit for separating the light beam emitted by the light
source into the main-portion to be irradiated on the storage medium
and the sub-portion to be guided to the light detector.
14. A pickup device according to claim 13, wherein the separating
unit reforms the shape of the main-portion of the light beam.
15. A pickup device according to claim 12, wherein the main-portion
of the light beam includes a center portion of the light beam,
wherein the sub-portion of the light beam includes a component of
the light beam positioned outside of the main-portion, and the
pickup device further comprising a changing unit for changing the
optical path of the sub-portion of the light beam to the light
detector.
16. A pickup device according to claim 12, wherein the light
detector comprises at least two detection elements, each of the
detection elements receiving the sub-portion of the light beam at
the position sandwiching the main-portion of the light beam in a
symmetrical manner.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an optical pickup device
for converging a light beam from a semiconductor laser onto an
optical disc serving as a storage medium. More specifically, this
invention relates to an optical pickup device which detects a
quantity of a light beam emitted from a semiconductor laser, by
means of a front monitor, to perform a power control of the light
beam.
[0003] 2. Description of the Prior Art
[0004] In general, an optical pickup for recording information
signal onto a storage medium such as an optical disc is equipped
with a semiconductor laser having a light emission power of 30 mW
order. As a method of controlling the power of the light beam
emitted from the semiconductor laser, there are known two methods:
a front monitor method and a rear monitor method. In the front
monitor method, a part of the light beam emitted from the
semiconductor laser toward the storage medium is detected by a
light detector, and the detected signal is fed back to a drive
circuit of the semiconductor laser so as to control the power of
the light beam emitted from the semiconductor laser to be a
predetermined level. On the other hand, in the rear monitor method,
the light beam emitted from the backface of the semiconductor
laser, i.e., the light emission surface opposite to the light
emission surface for emitting the light beam toward the storage
medium, is detected, and the power of the light beam from the
semiconductor laser is controlled in the same manner as the front
monitor method. Generally, the rear monitor method is known as
being unsatisfactory in the light beam detection accuracy, and
hence the front monitor method has been broadly adopted.
[0005] FIG. 14 shows a schematic configuration of an optical pickup
device according to a conventional front monitor method. A light
beam emitted from a semiconductor laser 1 is converted into the
parallel light by a collimator lens 2 and supplied to a beam
splitter 4 via a grating 3. The grating 3 separates the incident
light beam into three beams, i.e., a main-beam used for reading out
information from the optical disc 8 and two sub-beams used for a
tracking serve control. The beam splitter 4 includes a reflection
film 5 which transmits approximately 90% of the light beam from the
semiconductor laser 1 and reflects the remaining approximately 10%
of the light beam. Namely, by the function of the reflection film
5, approximately 90% of the light beam supplied to the beam
splitter 4 is transmitted therethrough to be guided to a 1/4
wavelength plate 6, and the remaining approximately 10% of the
light beam is reflected by the reflection film 5 to be guided to a
condensing lens 12. The light beam guided to the 1/4 wavelength
plate 6 is converged on a recording surface of an optical disc 8 by
means of an objective lens 7, thereby to form beam spots of
predetermined sizes.
[0006] The light beams irradiated on the recording surface of the
optical disc 8 are reflected by the surface and travels to the
reflection film 5 of the beam splitter 4 via the objective lens 7
and the 1/4 wavelength plate 6. Since the reflection film 5 has a
property to reflect approximately 100% of the light beam from the
direction of the optical disc 8, the light beam incident upon the
reflection film 5 is guided to the light receiving element 11 via a
condenser lens 9 and a cylindrical lens 10 for giving astigmatism
to the light beam. On the other hand, the approximately 10% of the
light beam emitted from the semiconductor laser 1 and reflected by
the reflection film 5 of the beam splitter 4 is converged on a
front monitor detector 13 by a condenser lens 12. The front monitor
detector 13 outputs an electric signal depending upon the quantity
of the light beam irradiated thereon, and the electric signal is
supplied to an automatic power control (APC) circuit 14 including a
laser control circuit which controls the power of the semiconductor
laser 1. The APC circuit 14 derives an appropriate drive signal for
driving the semiconductor laser 1 in accordance with the electric
signal from the front monitor detector 13, and supplies the drive
signal to the semiconductor laser 1. Thus, the output power of the
semiconductor laser 1 is controlled by the drive signal generated
by the APC circuit 14 based on the electric signal outputted from
the front monitor detector 13.
[0007] In order to reduce the load on the semiconductor laser,
reduce the power consumption of the semiconductor laser or obtain
high laser power output at the time of recording processing, it is
preferred to enhance the efficiency in use of the light beam
emitted from the semiconductor laser. However, the pickup device
employing the conventional front monitor method described above is
designed such that the approximately 10% of the light beam emitted
from the semiconductor laser 1 and supplied to the beam splitter 4
is necessarily guided to the front monitor detector 13. In other
words, approximately 10% of the light beam incident upon the
reflection film is reflected without exception. Therefore, the
efficiency in use of the light beam is degraded.
[0008] Further, the reflective and transmissive property of the
reflection film provided in the beam splitter may have irregularity
within about .+-.5% from product to product, and hence, if the
reflectance is designed to be 10%, the reflectance of the actual
product may greatly vary within the range from 5% to 15%.
Therefore, the gain control of the APC circuit must be carried out
for every product, thereby deteriorating the production efficiency.
Furthermore, it is known that the reflectance and/or transmittance
of the reflection film in the beam splitter may vary dependently
upon the ambient humidity. Therefore, the conventional front
monitor method, which relies on the property of the beam splitter
in controlling the output power of the semiconductor laser 1, is
unsatisfactory in its reliability.
SUMMARY OF THE INVENTION
[0009] The present invention is contrived in view of the above
mentioned problems, and it is an object of the present invention to
provide an optical pickup device capable of enhancing the
efficiency in use of the light beam and stably performing the power
control of the semiconductor laser without being affected by the
irregularity and/or the humidity-dependent variation of the
property of the reflection film employed in the beam splitter.
[0010] According to one aspect of the present invention, there is
provided a pickup device including: a light source for emitting a
light beam; an optical system for separating the light beam into a
main-portion and a sub-portion, and for guiding the main-portion of
the light beam to an information storage medium; a monitor detector
for receiving the sub-portion of the light beam and for outputting
a detection signal; and a controller for controlling an output
power of the light beam emitted by the light source based on the
detection signal.
[0011] In accordance with the optical pickup thus configured, a
light beam is emitted by the light source. The optical system
separates the light beam into a main-portion and a sub-portion, and
guides the main-portion of the light beam to an information storage
medium. The monitor detector receives the sub-portion of the light
beam and outputs a detection signal. Then, the controller controls
the output power of the light beam emitted by the light source
based on the detection signal. Thus, the light beam of the
sub-portion, which is not generally used as a light beam to be
irradiated on a storage medium, can be efficiently used, and hence
the output power of the light beam from the light source may be
controlled with high accuracy.
[0012] Preferably, the main-portion is a center portion of the
light beam and the sub-portion is a portion of the light beam other
than the main portion.
[0013] The optical system may include an interrupting member for
partially interrupting the light beam from the light source and
passing only the main-portion and the sub-portion of the light
beam. Thus, it is possible to prevent unnecessary light component
from entering the monitor detector. As an example, the interrupting
member may include a first aperture for passing the main-portion of
the light beam and at least one second aperture for passing the
sub-portion of the light beam.
[0014] Preferably, the pickup device may further include a casing
for covering a light emitting part of the light source to receive
whole portion of the light beam emitted by the light source,
wherein the interrupting member is disposed on the casing at a
position receiving the light beam from the light source. By this,
the more reliable interruption of the unnecessary light beam is
ensured.
[0015] In a preferred embodiment, the optical system may include a
collimator lens, wherein the collimator lens includes a miniature
convex lens formed at an edge part thereof and for directing the
sub-portion of the light beam to the monitor detector. Similarly,
the optical system may include a collimator lens, wherein the
collimator lens includes two miniature convex lenses formed at edge
parts thereof opposing to each other, and the two convex lenses
directs the sub-portions of the light beams to the monitor
detector.
[0016] In another preferred embodiment, the optical system may
include a diffraction grating having a first grating pattern for
directing the main-portion of the light beam to the storage medium
and a second grating pattern for directing the sub-beam to the
monitor detector. Further, the second grating pattern may be
configured to direct all component of the light beam other than the
main-portion to the monitor detector as the sub-portion of the
light beam.
[0017] In still another preferred embodiment, the optical system
may include a beam splitter having a light receiving surface and a
light reflecting surface, wherein the light receiving surface
guides the main-portion of the light beam to the storage medium and
the light reflecting surface reflects the sub-portion of the light
beam to the monitor detector.
[0018] The monitor detector may include two detection elements each
for outputting an electric signal corresponding to a quantity of
light received, and an adder for adding two electric signals to
produce the detection signal.
[0019] According to another aspect of the present invention, there
is provided a pickup device for irradiating a main-portion of a
light beam emitted from a light source on a storage medium,
including: a light detector for receiving a sub-portion of the
light beam which is a portion other than the main-portion of the
light beam emitted by the light source and outputting a detection
signal; and an adjusting unit for adjusting a power of the light
beam emitted by the light source based on the detection signal.
[0020] In accordance with the pickup device thus configured, the
light beam of the sub-portion, which is not generally used as a
light beam to be irradiated on a storage medium, can be efficiently
used, and hence the output power of the light beam from the light
source may be controlled with high accuracy.
[0021] The pickup device may further include a separating unit for
separating the light beam emitted by the light source into the
main-portion to be irradiated on the storage medium and the
sub-portion to be guided to the light detector. Thus, the
sub-portion of the light beam can be efficiently guided to the
monitor detector. In addition, the separating unit may reform the
shape of the main-portion of the light beam. By this, the light
beam can be irradiated on the storage medium with high
accuracy.
[0022] In a preferred embodiment, the main-portion of the light
beam may include a center portion of the light beam, wherein the
sub-portion of the light beam includes a component of the light
beam positioned outside of the main-portion, and the pickup device
further including a changing unit for changing the optical path of
the sub-portion of the light beam to the light detector. Thus, the
optical path of the main-portion of the light beam can be separated
from the optical path of the sub-portion of the light beam, thereby
facilitating the design of the optical system.
[0023] In a specific embodiment, the light detector may include at
least two detection elements, each of the detection elements
receiving the sub-portion of the light beam at the position
sandwiching the main-portion of the light beam in a symmetrical
manner. This enables downsizing of the optical pickup.
[0024] The nature, utility, and further features of this invention
will be more clearly apparent from the following detailed
description with respect to preferred embodiment of the invention
when read in conjunction with the accompanying drawings briefly
described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a diagram showing a schematic configuration of an
optical pickup device according to a first embodiment of the
present invention.
[0026] FIGS. 2A and 2B are diagrams showing the Gaussian
distribution of a light beam emitted from a semiconductor laser and
the formation of beam spot by converging the light beam.
[0027] FIG. 3A is a perspective view of a collimator lens used in
the first embodiment of the present invention from the direction of
a semiconductor laser.
[0028] FIG. 3B shows the shape of an example of an aperture
limiting member used in the first embodiment.
[0029] FIG. 4 is a diagram showing a schematic configuration of an
optical pickup device according to a second embodiment of the
present invention.
[0030] FIGS. 5A and 5C are perspective views of the collimator lens
and the beam splitter, viewed from the side of the semiconductor
laser, according to the second embodiment of the present
invention.
[0031] FIGS. 5B and 5D show the shapes of examples of the aperture
limiting member according to the second embodiment.
[0032] FIG. 6A is a diagram showing a schematic configuration of an
optical pickup device according to a third embodiment of the
present invention.
[0033] FIG. 6B is a sectional view of the collimator lens used in
the optical pickup device shown in FIG. 6A.
[0034] FIGS. 7A and 7C are perspective views of the collimator lens
and the beam splitter, viewed from the side of the semiconductor
laser, according to the third embodiment of the present
invention.
[0035] FIG. 7B shows the shape of an example of the aperture
limiting member according to the third embodiment.
[0036] FIG. 8A is a diagram showing a schematic configuration of an
optical pickup device according to a fourth embodiment of the
present invention.
[0037] FIG. 8B is a sectional view of the collimator lens used in
the optical pickup device shown in FIG. 8A.
[0038] FIGS. 9A and 9C are perspective views of the collimator lens
and the beam splitter, viewed from the side of the semiconductor
laser, according to the fourth embodiment of the present
invention.
[0039] FIG. 9B shows an example of the aperture limiting member
according to the fourth embodiment.
[0040] FIGS. 10A and 10B are a side view and a plan view showing a
schematic configuration of an optical pickup device according to a
fifth embodiment of the present invention.
[0041] FIG. 11A is a perspective view of the collimator lens and
the beam splitter, viewed from the side of the semiconductor laser,
according to the fourth embodiment of the present invention.
[0042] FIG. 11B shows an example of the aperture limiting member
according to the fourth embodiment of the present invention.
[0043] FIG. 12A is a diagram showing a schematic configuration of
an optical pickup device according to a sixth embodiment of the
present invention.
[0044] FIG. 12B is a plan view showing a grating used in the
optical pickup shown in FIG. 12A.
[0045] FIG. 13 is a plan view of an example of collimator lens
which can be used in the respective embodiments.
[0046] FIG. 14 is a diagram showing a schematic configuration of a
conventional optical pickup device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0047] The preferred embodiments of the present invention will now
be described below with reference to the attached drawings.
1st Embodiment
[0048] First, an optical pickup device according to the first
embodiment of the present invention will be described. FIG. 1 shows
the configuration of the optical pickup device according to the
first embodiment. As illustrated, the optical pickup device
includes a semiconductor laser 20 for emitting a light beam, a
collimator lens 21 for converting a divergent light into a parallel
light, a 1/2 wavelength plate 22 for rotating the polarization
direction of the incident linearly-polarized light by 90 degrees, a
grating 23 utilizing the light diffraction, and a front monitor
detector 24 for detecting the light beam for the purpose of
controlling the intensity of the light beam emitted from the
semiconductor laser 20. Further, the pickup device includes a beam
splitter 25 for separating the light beam into a transmitted light
and a reflected light, a reflection mirror 27 for reflecting the
light beam, and a 1/4 wavelength plate 28 for converting the
incident light into either a linearly-polarized light or a
circularly-polarized light. Furthermore, the optical pickup
includes an objective lens 29 for converging the light beam onto
the recording surface of the optical disc, a condenser lens 31 for
condensing the light beam, a cylindrical lens 32, a light receiving
element 33 for receiving the light beam, and an APC circuit 50 for
automatically controlling the output power of the semiconductor
laser 20. The reference numeral 30 denotes the optical disc, only a
part of which is illustrated in FIG. 1.
[0049] Next, the operation of the optical pickup device of the
first embodiment will be described below. The light beam emitted
from the semiconductor laser 20, serving as a light source, is
masked by a lens holder 34 and an aperture limiting member 35, and
only necessary portion of the light beam enters the collimator lens
21. The lens holder 34 and the aperture limiting member 35 are
provided to mask the stray light. The light beam passed through the
non-masked area is supplied to the 1/2 wavelength plate 22, which
rotates the vibration direction of the light beam by 90 degrees,
and then the light is guided to the grating 23. A main part of the
light beam passed through the grating 23 is guided to the beam
splitter 25 and remaining part thereof is guided to the front
monitor detector 24. The aperture limiting member 35 may be made of
plastic material and the like. The aperture limiting member 35 may
be formed as a single unit integrated with the lens holder 34, and
in that case it may be made of the same material as that of the
lens holder 34, for example, brass.
[0050] The grating 23 separates the light beam into three beams in
total, i.e., a main-beam used for reading out information from the
optical disc 30 and two sub-beams used for the tracking servo
control. The beam splitter 25 is provided with the reflection film
26, which has a property to transmit the light beam of P-polarized
light, for example, emitted from the semiconductor 20 and polarized
by the 1/2 wavelength plate 22 with a transmission rate of
approximately 100% and reflect the light beam the reflected by the
optical disc 30 and converted into S-polarized light with the
reflection rate of approximately 100%. The light beam of
P-polarized light emitted from the semiconductor laser 20 is guided
to the beam splitter 25, which changes the polarization plane of
the light beam from an elliptical shape to a circular shape. The
circularly-polarized light beam thus produced is guided to the
objective lens 29 via the reflection film 26, the reflection mirror
27, the {fraction (1/4)} wavelength plate 28. The objective lens 29
converges the light beam onto the recording surface of the optical
disc 30 to form beam spots.
[0051] The light beams converged on the recording surface of the
optical disc are reflected by the recording surface and guided to
the 1/4 wavelength plate 28 again via the objective lens 29. The
light beam passed through the 1/4 wavelength plate 28 becomes the
S-polarized light by the rotation of the polarization plane in the
1/4 wavelength plate 28, and is guided to the beam splitter 25 via
the reflection mirror 27. The light bean of S-polarized light
guided to the beam splitter 25 is reflected by the reflection film
26 and guided to the light receiving element 33 via the condenser
lens 31 and the cylindrical lens 32. The light receiving element 33
produces an electric signal in proportion to the quantity of light
beam received, and supplies it to a signal processor (not shown) of
following stage. The signal processor demodulates information
recorded on the optical disc 30, and generates a focus error signal
which is used to make the light beam on the recording surface of
the optical disc 30 in focus and a tracking error signal which is
used to appropriately position the light beam with respect to the
tracks on the optical disc 30.
[0052] A part of the light beam, which has passed through the
collimator lens 21 but is not guided to the beam splitter 25, is
guided to the front monitor detector 24 via the 1/2 wavelength
plate 22 and the grating 23. The front monitor detector 24 receives
the part of the light beam to detect the power intensity of the
light beam, and converts the detected intensity amount into an
electric signal to be supplied to the APC circuit 50. The APC
circuit 50 compares the electric signal supplied from the front
monitor detector 24 with a predetermined reference value to
generate an adjustment signal depending on the difference obtained
by the comparison, and supplies it to the semiconductor laser 20.
The semiconductor laser 20 controls the power intensity of the
light beam emitted therefrom based on the adjustment signal
supplied from the APC circuit 50. Namely, the semiconductor laser
20 determines the output power of the light beam such that the
difference between the electric signal outputted by the front
monitor detector 24 and the reference value becomes zero. By this
control, the power intensity of the light beam emitted from the
semiconductor laser 20 is constantly maintained to be an
appropriate value.
[0053] Next, the light beam emitted from the semiconductor laser 20
will be discussed with reference to FIGS. 2A and 2B. It is known
that the intensity distribution of the light beam emitted from the
semiconductor laser 20 approximately takes the form of Gaussian
distribution 36, as shown in FIG. 2A, wherein substantially even or
uniform intensity level, i.e., plane-wave like distribution is
obtained at the center portion of the light beam. In order to
enhance the efficiency in use of the light beam, it is ideal that
all of the light beam emitted from the semiconductor laser is
supplied to the optical disc 30. However, if not only the central
portion but also the circumferential portion of the light beam is
converged by the objective lens 29 having a large aperture, the
wavefront radius of curvature of the light beam incident upon the
objective lens 29 becomes small. Therefore, the diameter of the
beam spot cannot be made small like the beam spot 37 shown in FIG.
2A, and the desired small beam spot diameter cannot be achieved.
Therefore, as seen in FIG. 2B, generally, only the central portion
of the light beam, i.e., the main-area X of the light beam where
substantially plane wave like distribution (the wavefront radius of
curvature is infinity) can be obtained is converged by the
objective lens 29 to form the beam spot 38 of small spot diameter,
though the loss of light increases. It is noted that the quantity
of the light beam in the main-area X is approximately 50% of total
light quantity, and hence the ratio of the light quantities of the
main area X and the area other than the main area X (hatched area
in FIG. 2B, hereinafter referred to as "sub-area Y") is
approximately 1:1.
[0054] FIG. 3A schematically shows positional relationship of the
collimator lens 21 and the beam splitter 25 viewed from the
direction of the semiconductor laser 21, and FIG. 3B shows the
shape of an example of the aperture limiting member 35. The light
beam from the semiconductor laser 20 passes through the aperture
limiting member 35 shown in FIG. 3B and is irradiated on the
collimator lens 21. As shown in FIG. 3A, the collimator lens 21 can
be classified into three areas, i.e., a first area A of elliptic
shape at the center, a second area B, and a hatched third area C.
In the first area A, out of the light beam emitted from the
semiconductor laser 20, the light beam of the main area X described
above and passed through the aperture 35a of the aperture limiting
member 35 enters the collimator lens 21. The light beam of the main
area X passed through the aperture limiting member 35 and the first
area A of the collimator lens 21 impinges on the beam splitter 25,
travels to the objective lens 29 and converged on the recording
surface of the optical disc 30 to form a beam spot. Through the
second area B, the light beam of the sub-area Y passes. The
sub-area Y is located outside of the main area X as shown in FIG.
2. Out of the light beam emitted from the semiconductor laser 21,
the light beam of the sub-area Y passes through the aperture 35b of
the aperture limiting member 35 and the second area B, and travels
to the front monitor detector 24. The third area C is an area where
the light beam emitted from the semiconductor laser 20 is
interrupted, and hence no light beam is irradiated. As shown in
FIG. 3B, the aperture limiting member 35 is shaped to interrupt the
light beam at the third area C other than the first area A and the
second area B so as to prevent the unnecessary light beam from
entering the objective lens 29 and the front monitor detector
24.
[0055] As described above, in the optical pickup device of the
first embodiment of the present invention, an outer circumferential
portion of the light beam emitted from the semiconductor laser is
directly guided to the front monitor detector 24 without passing
through the reflection film 26 of the beam splitter 25. Therefore,
the light beam is stably irradiated on the front monitor detector
24 without being affected by the irregularity in property of the
reflection film and/or the change of the property due to the
humidity variation. Since the front monitor detector 24 stably
receives the light beam, it can stably output the electric signal
to the APC circuit 50. Hence, the intensity of the light beam
emitted from the semiconductor laser 20 can be stably controlled.
Further, since the unnecessary light beam is interrupted by the
aperture limiting member 35 and the lens holder 34, it is not
irradiated on the front monitor detector 24, and the detection
signal including less noise is obtained. Therefore, the APC circuit
50 can control the power intensity of the light beam emitted from
the semiconductor laser 20 constantly to be an optimum value.
[0056] While the optical pickup of the first embodiment described
above is provided with the 1/2 wavelength plate 22 which changes
the polarization direction by 90 degrees, it may be omitted if an
appropriate design is made. The 1/2 wavelength plate 22 is provided
in consideration of the shaping direction of the beam splitter 25
for shaping the polarization plane of the light beam emitted from
the semiconductor laser 20, the polarization direction of the light
beam, and the incident direction of the light beam onto the
reflection film 26 of the beam splitter 25. However, by using a
semiconductor laser 20 of certain property or by appropriately
arranging the respective optical elements, the same result may be
obtained without employing the 1/2 wavelength plate 22.
2nd Embodiment
[0057] Next, the second embodiment of the present invention will be
described with reference to FIGS. 4, 5A and 5B. FIG. 4 shows the
configuration of the optical pickup device of the second
embodiment. In the second embodiment, two front monitor detectors
are provided to increase the total light quantity of the light beam
received by the front monitor detectors in comparison with the
first embodiment. The second embodiment differs from the first
embodiment in the following points. First, two front monitor
detectors 24 and 39 are provided. Second, the beam splitter 51 is
provided with the reflection mirrors 51a and 51b which reflect the
light beam to be guided to the front monitor detectors 24 and 39,
respectively. Third, the shape of the aperture limiting member 40
in front of the collimator lens 21 is modified. In other points,
the second embodiment is identical to the first embodiment, and
hence the same elements are applied with the same reference numbers
and their explanation will be omitted.
[0058] Out of the two surfaces of the beam splitter 51 confronting
the semiconductor laser 20, one surface (on the left side of the
beam splitter 51 in FIG. 4) is provided with a first reflection
mirror 51a, and the other surface (on the right side of the beam
splitter 51) is provided with a second reflection mirror 51b. The
reflection mirrors 51a and 51b are formed by depositing metal
material such as aluminum on the surfaces of the beam splitter 51.
A part of the light beam from the collimator lens 21 is reflected
by the first reflection mirror 51a and guided to the front monitor
detector 24, and another part of the light beam from the collimator
lens 21 is reflected by the second reflection mirror 51b and guided
to the front monitor detector 39. The remaining major part of the
light beam from the collimator lens 21 enters the beam splitter 51
because the reflection mirror is not provided between the first and
the second reflection mirrors 51a and 51b. Thus, the beam splitter
51 separates the light beam and changes the path of the light beam
such that the light beam of the main area X is guided to the
optical disc 30 and the light beams of the sub-areas are guided to
the front monitor detectors 24 and 39.
[0059] FIG. 5A is a perspective view of the collimator lens 51 and
the beam splitter 51 employed in the optical pickup device of the
second embodiment viewed from the side of the semiconductor laser
20, and FIG. 5B shows the shape of an example of the aperture
limiting member 40. In FIG. 5A, the beam splitter 51 has the first
reflection mirror 51a on the left side and the second reflection
mirror 51b on the right side. An aperture limiting member 40 of the
shape shown in 5B, for example, is provided in front of the
collimator lens 21 to interrupt the light beam from the
semiconductor laser 20. Therefore, the light beam passed through
the aperture limiting member 40 enters at the first area A, the
second area B1 and the second area B2 shown in FIG. 5A. However, no
light beam enters the hatched area C of the collimator lens because
the light beam is interrupted by the aperture limiting member 40
shown in FIG. 5B.
[0060] The light beam passed through the first area A is treated in
the similar manner to that in the first embodiment, and hence the
description thereof will be omitted. The light beam of the sub-area
Y, passed through the second area B1 of the collimator lens 21, is
reflected by the first reflection mirror 51a, and is guided to the
front monitor detector 24 which is disposed on the optical axis of
the reflected light beam. Namely, the second area B1 is an area
where the light beam to be guided to the front monitor detector 24
passes. Similarly, the light beam of the sub-area Y, passed through
the second area B2, is reflected by the second reflection mirror
51b, and is guided to the front monitor detector 39 which is
disposed on the optical axis of the reflected light beam. Namely,
the second area B2 is an area where the light beam to be guided to
the front monitor detector 39 passes.
[0061] The third area C is an area where no light beam is
irradiated on the collimator lens 21, because, out of the light
beam emitted by the semiconductor laser 20, only the component
passed through the aperture limiting member 40 shown in FIG. 5B is
irradiated on the beam splitter 51.
[0062] The light beam of the main area X, passed through the first
area A of the collimator lens 21, impinges upon the area of the
beam splitter 51 where no reflection mirror is provided, and enters
the inside of the beam splitter 51. Then, the light beam is
converged by the objective lens 29 on the recording surface of the
optical disc 30 to form a beam spot thereon. The light beam passed
through the second area B1 of the collimator lens 21 is totally
reflected by the first reflection mirror 51a and supplied to the
front monitor detector 24. The light beam passed through the second
area B2 of the collimator lens 21 is totally reflected by the
second reflection mirror 51b and supplied to the front monitor
detector 39.
[0063] The output signals from the front monitor detectors 24 and
39 are added to each other by the adder 52, and is supplied to the
APC circuit 50. The APC circuit compares the electric signal from
the adder 52 with a predetermined reference value to generate the
adjustment signal indicative of the difference between the electric
signal and the reference value, and supplies it to the
semiconductor laser 20. The semiconductor laser 20 controls the
power intensity of the light beam based on the adjustment signal
supplied from the APC circuit 50 such that the power intensity of
the light beam emitted from the semiconductor laser 20 constantly
becomes an optimum value.
[0064] As described above, the optical pickup device of the second
embodiment is provided with two front monitor detectors, and the
output signals from them are added to each other by the adder 50
and then supplied to the APC circuit 50. As a result, the total
quantity of light received by the front monitor detectors is
increased, and the accuracy in controlling the power intensity of
the emitted light beam can be improved.
[0065] While the optical pickup device of the second embodiment
described above is provided with two front monitor detectors, only
one front monitor detector may be employed. In that case, the
second area B2 of the collimator lens 21 shown in FIG. 5A is also
masked by the aperture limiting member 40 shown in FIG. 5D. In that
case, the other configuration is identical to the above described
second embodiment, and hence the description thereof will be
omitted.
[0066] Sometimes, the surface of the beam splitter 51 is provided
with a coating so-called AR (Anti-Reflection) coating. This AR
coating is made by applying a material such as silicon on an
optical element such as the beam splitter. With the AR coating, the
transmittance of the light beam can be improved compared with the
case in which no such coating is made. However, the AR coating has
such property that its transmittance or reflectance varies as the
humidity and/or temperature varies. Therefore, if the whole surface
of the beam splitter 51, including the reflection mirrors 51a and
51b, are applied with the AR coating and the light beam is
reflected by the reflection mirrors 51a and 51b toward the front
monitor detectors 24 and 39, the quantity received by the front
monitor detectors 24 and 39 may vary according to the variation of
humidity and/or temperature. In addition, the quantity of light
guided to the front monitor detectors 24 and 39 is smaller than the
quantity of light guided to the optical disc 30, and hence the
variation of such small quantity of light greatly affects the
control of the power intensity of the semiconductor laser 20. In
this view, it is preferred that the beam splitter 51 is made of
material, such as glass, which reflectance is not sensitive to
humidity and/or temperature variation, and the AR coating is not
applied to at least the reflection mirrors 51a and 51b for
reflecting the light beam toward the front monitor detectors 24 and
39. By this, stable quantity of light is supplied to the front
monitor detectors even if humidity and/or temperature varies.
Further, while the above embodiment uses the reflection mirrors 51a
and 51b with no coating on the surface thereof, certain material
which is not sensitive to the variation of humidity and/or
temperature may be coated on the surface of the reflection mirrors
51a and 51b.
3rd Embodiment
[0067] Next, the third embodiment of the present invention will be
described with reference to FIGS. 6A, 6B and 7A to 7D. FIG. 6A
shows a configuration of the optical pickup device according to the
third embodiment of the present invention. The third embodiment
differs from the first embodiment in the shape of the collimator
lens which separates a part of the light beam incident thereon and
changes its optical path to the direction of the front monitor
detector. FIG. 6B shows the section of the collimator lens 41 which
is provided with a miniature convex lens 41a at one side on its
surface. The collimator lens 41 used in this embodiment separates a
part of the light beam by the miniature convex lens 41a and changes
the optical path of the part of the light beam to be guided to the
front monitor detector 24.
[0068] FIG. 7A is a perspective view of the collimator lens 41 with
the miniature convex lens 41a viewed from the side of the
semiconductor laser 20, and FIG. 7B shows an example of the
aperture limiting member 42 provided in front of the collimator
lens 41. The light beam emitted from the semiconductor laser 20 is
irradiated on the aperture limiting member 42, which passes the
light beam only in areas corresponding to the first area A and the
second area B of the collimator lens 41. The collimator lens 41
receives the light beam in the first area A of elliptic shape at
the center thereof and the second area B where the miniature convex
lens 41a is formed. In the third area C represented by the
hatching, no light beam is irradiated because the light beam is
interrupted by the aperture limiting member 42 shown in FIG.
7B.
[0069] The first area A and the third area C are the same as those
of the first embodiment, and hence the description thereof will be
omitted. The second area B is an area where the miniature convex
lens 41a is formed. The light beam of the sub-area Y passes through
the miniature convex lens 41a and its optical path is changed to
the direction of the front monitor detector 24. Namely, the light
beam passed through the second area B, whose optical path is
changed, is directly guided to the front monitor detector 24
without passing through any optical elements such as a 1/2
wavelength plate or a grating. Out of the light beam emitted from
the semiconductor laser 20, the light beam of the main-area X,
which passed through the first area A of the collimator lens 41 as
shown in FIG. 7A, travels through the beam splitter 25 and
converged by the objective lens 29 to form the beam spot on the
recording surface of the optical disc 30. Out of the light beam
emitted from the semiconductor laser 20, the light beam passed
through the miniature convex lens 41a of the collimator lens 41 is
irradiated on the front monitor detector 24 due to the change of
its optical path.
[0070] It is noted that, instead of forming the miniature convex
lens 41a on the collimator lens 41, a hologram collimator lens 43
as shown in FIG. 7C may be used in place of the collimator lens 41.
The hologram collimator lens 43 shown in FIG. 7C can be used in
combination with the aperture limiting member 42 shown in FIG. 7B,
so that the light beam from the semiconductor laser 20 impinges
upon the hologram collimator 43 only in the areas A and B. The
hologram collimator lens 43 is formed as a combination of different
hologram patterns as seen in FIG. 7C. The center portion of the
hologram lens 43 corresponding to the elliptical first area A is
formed with the hologram pattern E including plural eccentric
circular patterns with different pitched therebetween. The central
hologram pattern E has a function to collimate the diverging light
beam to a parallel light beam, i.e., the same function as a
collimator lens. In addition, at the area corresponding to the
second area B of the collimator lens 41 shown in FIG. 7A, a linear
hologram pattern F is formed. The optical path of the light beam
incident upon this linear hologram pattern F is changed by the
hologram pattern F, and hence the hologram pattern F has the same
function as the miniature convex lens 41a of the collimator lens
41. The third area C functions similarly to the first and the
second embodiment, and hence the description there of will be
omitted.
[0071] As described above, the optical pickup device of the third
embodiment is provided with the miniature convex lens 41a at one
side of the surface of the collimator lens 41, or alternatively the
hologram lens 43 having the hologram pattern F at a portion on the
surface thereof. The light beam emitted from the semiconductor
laser 20 and passed through either the second area B of the
collimator lens 41 or the hologram pattern F of the hologram
collimator lens 43 is separated from the light beam of the
main-area X, and directed to the front monitor detector 24.
Therefore, the optical path to the front monitor detector 43 can be
designed without affecting the design of other optical systems, and
the power intensity of the light beam emitted from the
semiconductor laser 20 may be controlled to constantly maintain the
optimum value. As a technique to obtain the light beam for the
front monitor detector 24, the above description exemplified the
provision of the miniature convex lens 41a on the collimator lens
41 or the provision of the hologram pattern F. However, the present
invention is not limited to these examples. In another example, the
aperture limiting member 42 for masking is positioned downstream of
the collimator lens 41 and the hologram pattern F for changing the
optical path may be provided on the grating 23. This may derive the
same result.
4th Embodiment
[0072] Next, the fourth embodiment of the present invention will be
described with reference to FIGS. 8A, 8B and 9A to 9C. FIG. 8A
shows the configuration of the optical pickup device according to
the fourth embodiment of the present invention. In this fourth
embodiment, two miniature convex lenses 44a and 44b are provided on
both sides on the surface of the collimator lens 44 thereby to
increase the total quantity of light received by the front monitor
detector 24. FIG. 8B shows the section of the collimator lens 44
with the miniature convex lenses 44a and 44b provided on both sides
on its surface. The collimator lens 44 used in this embodiment
separates the two part of the light beam and changes the optical
paths of those separated parts of the light beams to be incident on
the front monitor detector 24.
[0073] FIG. 9A is a perspective showing the collimator lens 44 with
the miniature convex lenses viewed from the side of the
semiconductor laser 20, and FIG. 9B shows the example of the
aperture limiting member 45 provided in front of the collimator
lens 44. The light beam emitted from the semiconductor laser 20 is
partially interrupted by the aperture limiting member 45 shown in
FIG. 9B, and impinges upon the collimator lens 44 in the first area
A, the second area B1 and the second area B2. In the hatched third
area C, no light beam impinges upon the collimator lens 44.
[0074] Since the first area A and the third area C are the same as
those in the second embodiment, the description thereof will be
omitted. The second areas B1 and B2, where the miniature convex
lenses 44a and 44b are formed, respectively, separate the parts of
the light beam and change the optical paths of those separated
light parts toward the front monitor detector 24. Namely, the
optical paths of the light beams passed through the second areas B1
and B2 are changed by the miniature convex lenses 44a and 44b, and
those light beams are guided directly to the front monitor detector
24, without passing through any 1/2 wavelength plate or grating.
Out of the light beam emitted from the semiconductor laser 20, the
light beam of the main-area X passed through the first area A of
the collimator lens 44 travels through the beam splitter 25 and
converged by the objective lens 29 on the recording surface of the
optical disc 30 to form a beam spot. On the other hand, out of the
light beam emitted from the semiconductor laser 20, two parts of
the light beam passed through the miniature convex lenses 44a and
44b of the collimator lens 44 are irradiated on the front monitor
detector 24.
[0075] In stead of forming the miniature convex lenses 44a and 44b
on the collimator lens 44, a hologram collimator lens 46 as shown
in FIG. 9C may be used in combination with the same aperture
limiting member 45 shown in FIG. 9B. The hologram collimator lens
46 shown in FIG. 9C is constituted as a combination of different
hologram patterns. The central portion of the hologram collimator
lens 46, corresponding to the first area A of the collimator lens
44, is formed with the hologram pattern E of concentric circular
patterns with different pitches therebetween. The hologram pattern
E has the same function as a collimator lens, i.e., collimating the
diverging light beam into a parallel light beam. In the areas B1
and B2 shown in FIG. 9A, the linear hologram patterns F1 and F2 are
formed. When the light beam impinges on the hologram patterns F1
and F2, the optical path is changed. Therefore, the hologram
patterns F1 and F2 have the same function as the miniature convex
lenses 44a and 44b. Since the third area C is the same as that in
the first embodiment, the description thereof will be omitted.
[0076] As described above, the optical pickup device of the fourth
embodiment is provided with the miniature convex lenses 44a and 44b
at both sides on its surface, i.e., at the areas corresponding to
the second areas B1 and B2, or alternatively provided with a
hologram lens having the hologram patterns F1 and F2 for
diffraction on its surface. The light beam emitted from the
semiconductor laser 20 and passed through either the second areas
B1 and B2 of the collimator lens 44 or the hologram patterns F1 and
F2 of the hologram collimator lens 46 is separated from the light
beam of the main-area X and is directly irradiated on the front
monitor detector 24. Therefore, the optical path for the light beam
to be irradiated on the front monitor detector may be designed
without affecting other optical systems, and thereby the power
intensity of the light beam emitted from the semiconductor laser 20
is constantly controlled to be an optimum value.
[0077] While the above embodiment exemplified, as a method of
detecting the light beam for the front monitor detector 24, the
provision of the miniature convex lenses 44a and 44b or the
diffracting hologram patterns, the present invention is not limited
to such feature. For example, the same result may be achieved by
providing the aperture limiting member 45 at the downstream of the
collimator lens 44 and providing the hologram pattern for the
diffraction purpose on the grating 23. Thus, since the optical
pickup device of the fourth embodiment has such a configuration
that the light beam of the sub-areas Y, located on both sides of
the main-area X, are guided to the front monitor detector 24, the
quantity of the light received by the front monitor detector 24 is
increased in comparison with the third embodiment, and hence the
accuracy in controlling the power intensity of the light beam from
the semiconductor laser can be improved. While the polarization
beam splitter is used as the beam splitter 25, the present
invention is not limited to this example. Namely, another optical
element can be employed which may have the reflecting film for
transmitting the light beam from the semiconductor laser 20 with a
certain transmittance and reflecting the light beam with a certain
reflectance.
5th Embodiment
[0078] Next, the fifth embodiment of the present invention will be
described with reference to FIGS. 10A, 10B, 11A and 11B. FIG. 10A
is a side view of the optical pickup device according to the fifth
embodiment, and FIG. 10B is a plan view thereof. In the fifth
embodiment as illustrated, in addition to the configuration of the
first embodiment, two front monitor detectors are provided on both
sides of the elliptic beam to stabilize the light reception by the
front monitor detectors. Since other elements are the same as those
in the first embodiment, the optical elements at the downstream of
the beam splitter 25 and the reflection film 26 are omitted from
the illustration in FIGS. 10A and 10B. As shown in FIG. 10B, in the
optical pickup device of the fifth embodiment, the light beam
emitted from the semiconductor laser 20 passes through the aperture
limiting member 47, the collimator lens 21, the 1/2 wavelength
plate 22 and the grating 23. Then, the light beam travels along the
three optical paths, one enters the beam splitter 25 and the
remaining two does not enter the beam splitter and directly reach
the front monitor detectors 24a and 24b.
[0079] The aperture limiting member 47 has the shape as shown in
FIG. 11B. Therefore, as shown in FIG. 11A, the light beam enters
the collimator lens 21 of the fifth embodiment in the first area A
of the elliptic shape at the center, the second area B1, and the
second area B2. No light beam impinges upon the third area
represented by the hatching, because the aperture limiting member
47 interrupts the light beam in the third area C.
[0080] As described above, the optical pickup device of the fifth
embodiment is provided with two front monitor detectors 24a and
24b. The output signals of those two detector are added to each
other by the adder 52, and the resultant signal is supplied to the
APC circuit 50. Thus, the quantity of light received by the front
monitor detectors can be increased in comparison with the case of
the first embodiment, and the accuracy in controlling the power
intensity of the light beam from the semiconductor laser may be
improved. In addition, since the detectors 24a and 24b are
positioned to receive both side components of the light beam, if
the position of the optical elements such as the semiconductor
laser 20 slightly shifts in the left-right direction in FIG. 11A
due to aging and accordingly the light quantity received by one of
the detectors 24a or 24b decreases, the light quantity received by
the other detector increases. Therefore, the total received light
quantity of the detectors 24a and 24b is maintained constant. It is
noted that the front monitor detectors 24a and 24b may be
positioned to receive the separated light beams aligned in the
direction of the short axis of the elliptic light beam.
6th Embodiment
[0081] Next, the sixth embodiment of the present invention will be
described with reference to FIGS. 12A and 12B. FIG. 12A shows the
configuration of the optical pickup device of the sixth embodiment,
wherein an additional grating 48 is provided to increase the light
quantity received by the front monitor detector 24. Since the
configuration of the remaining portion is the same as that in the
first embodiment, the optical elements at the downstream of the
beam splitter 25 and the reflection film 26 are omitted from the
illustration. FIG. 12B shows the configuration of the additional
grating 48. As seen in FIG. 12B, the center portion of the grating
48 is formed with the parallel pattern P1 identical to that in the
grating 23 of the other embodiment. The additional grating 48 is
provided with the partial concentric circular pattern P2 at the
outer circumferential area of the pattern P1. By the diffraction
function of the pattern P2, the an outer portion of the light beam
is separated and directed to the front monitor detector 24. Thus,
since all of the light beam incident on the pattern P2 is directed
to the front monitor detector 24 as .+-.1st order diffracted
lights, a larger quantity of light beam can be received by the
front monitor detector 24. In addition, if the pattern P2 is formed
as a saw-shaped blazed hologram, the ratio of the light quantities
of the .+-.1st order diffracted lights can be varied. Thus, the
light quantity of one of the 1st order diffracted light guided to
the front monitor detector 24 can be 100% in theory and close to
100% in practice, thereby increasing the received light quantity.
Further, the light beam incident on the pattern P2 may be converged
at a predetermined small area by varying the pitch of the pattern
P2, and hence the light detecting portion of the front monitor
detector 24 may be down sized. It is noted that the aperture
limiting member 45 may be omitted in this embodiment.
[0082] In the above described embodiments, the stray lights are
interrupted by the aperture limiting member of various shapes.
However, by forming the collimator lens to have the desired shape
to produce only the desired light beam, the aperture limiting
member can be omitted. For example, in the first embodiment, by
forming the shape of the collimator lens as shown in FIG. 13, no
stray light is generated and hence the aperture limiting member can
be omitted. The collimator lens 49 shown in FIG. 13 is provided
with the first area A and the second area B which correspond to the
first area A and the second area B in the first embodiment shown in
FIG. 3A. Similarly, also in the other embodiment, by forming the
shape of the collimator lens to only pass the desired portion of
the light beam, the generation of the stray light may be avoided
and the aperture limiting member may be omitted.
[0083] As described above, according to the optical pickup device
according to the present invention, the efficiency in use of the
light beam may be enhanced. In addition, it is possible to provide
an optical pickup device which is hardly affected by the
irregularity of the property of the reflection film used in the
beam splitter or variation of humidity.
[0084] The invention may be embodied on other specific forms
without departing from the spirit or essential characteristics
thereof. The present embodiments therefore to be considered in all
respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims rather than by the
foregoing description and all changes which come within the meaning
an range of equivalency of the claims are therefore intended to
embraced therein.
[0085] The entire disclosure of Japanese Patent Application
No.10-95414 filed on Mar. 24, 1998 including the specification,
claims, drawings and summary is incorporated herein by reference in
its entirety.
* * * * *