U.S. patent application number 12/318598 was filed with the patent office on 2009-05-14 for fixing method, optical component and pickup manufactured by the fixing method.
This patent application is currently assigned to Konica Minolta Opto, Inc.. Invention is credited to Kazuo Ishida, Etsumi Nakajo, Yoshitaka Toyoizumi.
Application Number | 20090120569 12/318598 |
Document ID | / |
Family ID | 35424877 |
Filed Date | 2009-05-14 |
United States Patent
Application |
20090120569 |
Kind Code |
A1 |
Ishida; Kazuo ; et
al. |
May 14, 2009 |
Fixing method, optical component and pickup manufactured by the
fixing method
Abstract
Objective lens 20 is placed above the bobbin 40 at a position
opposite to the light emitting end of the light guiding member, and
the fixing portions 31 provided appropriately between the objective
lens 20 and the lens support 41 are hardened in a short time
because of being exposed to a UV hardening light beam which is
selectively irradiated onto the fixing portions, or the intensity
of which has been reduced to the wavelength region in which optical
characteristics of the objective lens are practically deteriorated,
in order to reduce the deterioration in the transmission
characteristics in the wavelength range at which the optical
elements are to be used, when fixing optical elements such as a
plastic objective lens, etc., are used with a UV hardening type of
adhesive.
Inventors: |
Ishida; Kazuo; (Tokyo,
JP) ; Toyoizumi; Yoshitaka; (Tokyo, JP) ;
Nakajo; Etsumi; (Tokyo, JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Assignee: |
Konica Minolta Opto, Inc.
|
Family ID: |
35424877 |
Appl. No.: |
12/318598 |
Filed: |
December 31, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11136442 |
May 25, 2005 |
7499229 |
|
|
12318598 |
|
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Current U.S.
Class: |
156/275.7 ;
156/379.6 |
Current CPC
Class: |
G02B 7/025 20130101 |
Class at
Publication: |
156/275.7 ;
156/379.6 |
International
Class: |
B32B 37/12 20060101
B32B037/12 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 2004 |
JP |
JP2004-160658 |
May 31, 2004 |
JP |
JP2004-160712 |
May 31, 2004 |
JP |
JP2004-161481 |
Claims
1-28. (canceled)
29. A fixing method of bonding an optical element, which is made of
plastic and used in a prescribed working wavelength range in a
wavelength region including at least blue light and ultraviolet
light to another member by using a light-hardening type of
adhesive, the fixing method comprising the steps of: supplying the
light-hardening type of adhesive to a bonding spot between the
optical element and the another member; and selectively irradiating
the bonding spot with a processing light beam to harden the
light-hardening type of adhesive.
30. The fixing method of claim 29, wherein the bonding spot is
selectively irradiated with the processing light beam by means of a
light guiding device.
31. The fixing method of claim 30, wherein the light guiding device
is an optical fiber which leads the processing light beam from a
light source to an irradiating position opposed to the bonding
spot.
32. The fixing method of claim 30, wherein the light guiding device
is at least one reflecting device which leads the processing light
beam from a light source to an irradiating position opposed to the
bonding spot.
33. The fixing method of claim 29, wherein the processing light
beam is prevented from entering an optical surface of the optical
element at a periphery of the bonding spot by using a light
shielding device.
34. The fixing method of claim 33, wherein the light shielding
device is a mask to cover the optical surface of the optical
element.
35. The fixing method of claim 33, wherein the light shielding
device is a filter to cover the optical surface of the optical
element.
36. The fixing method of claim 29, wherein the prescribed working
wavelength range of the optical element is in a range from 380 to
450 nm and the processing light beam has an emission peak in a
hardening wavelength range from 280 to 330 nm.
37. The fixing method of claim 36, wherein the processing light
beam is emitted from a high pressure mercury vapor lamp as a light
source.
38. The fixing method of claim 29, wherein the another member is a
supporting member for supporting the optical element.
39. The fixing method of claim 29, wherein the another member is an
optical member for performing a prescribed optical function in
cooperation with the optical element.
40. An optical component comprising: an optical element, and
another member; wherein the optical element and the another member
are fixed to each other by the fixing method of claim 29.
41. The optical component of claim 40, wherein the optical element
is an objective lens through which an incident luminous flux
converges so as to form a spot on a recording surface of an optical
recording medium.
42. An optical pickup comprising: the optical component of claim
40, wherein information can be read from, or written on, a
recording surface of an optical recording medium.
43. The fixing method of claim 29, which is used for an optical
component of an optical pickup.
44. A fixing method for bonding a periphery of an optical element
to another member by using a light-hardening type of adhesive,
wherein the optical element is made of plastic and has an optical
surface within the periphery for use in a prescribed working
wavelength range in a wavelength region including at least blue
light and ultraviolet light, the fixing method comprising the steps
of: supplying the light-hardening type of adhesive to a bonding
spot between the periphery and the another member; and selectively
irradiating an area including the bonding spot and excluding the
optical surface with a processing light beam by controlling the
processing light beam so as to harden the light-hardening type of
adhesive.
45. The fixing method of claim 44, wherein the processing light
beam has a light emission in a specific wavelength range from 280
to 330 nm.
46. The fixing method of claim 45, wherein the processing light
beam has a first emission peak having a first illumination
intensity in a first wavelength range from 350 to 450 nm; and
wherein the processing light beam has a second emission peak in the
specific wavelength range from 280 to 330 nm, which has an
illumination intensity less than or equal to 30% of the first
illumination intensity of the first emission peak.
47. The fixing method of claim 45, wherein the processing light
beam has an emission peak in the specific wavelength range from 280
to 330 nm.
48. A fixing device for bonding an optical element, which is made
of plastic and which is used in a prescribed working wavelength
range in a wavelength region including at least blue light and
ultraviolet light, to another member by using a light-hardening
type of adhesive, the fixing device comprising: a supplying device
which supplies the light-hardening type of adhesive to a bonding
spot between the optical element and the another member; and a
light irradiating device which selectively irradiates the bonding
spot with a processing light beam to harden the light-hardening
type of adhesive.
Description
[0001] This application is based on Japanese Patent Application
Nos. 2004-160658, 2004-160712 and 2004-161481 filed on May 31, 2004
in Japanese Patent Office, the entire content of which is hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a method of fixing an
optical element such as a plastic lens, as well as to an optical
component and an optical pickup on which an optical element such as
an objective lens has been mounted using the fixing method.
[0003] Many types of pickups for playing back and recording data on
an optical disc including CD (compact disc), DVD (digital versatile
disc) and BD (Blu-ray disc) have been developed and manufactured
(see Patent Document 1). As an objective lens mounted in these
optical pickups, plastic lenses have frequently been employed
because of their light weight, and making for precious focusing and
tracking. A plastic objective lenses like the above is bonded and
fixed on a bobbin, which is a moving part of the optical pickup,
using resin adhesive for example.
[0004] [Patent Document 1] Tokkai No. Hei 10-162407
[0005] In the mass-production process of optical pickups for CDs
and DVDs currently available on the market, a UV hardening type of
adhesive is mostly employed for fixing objective lenses in order to
ensure a speedy manufacturing process. However, if the same
techniques are applied to mass-production process of optical
pickups for BDs which utilize shorter wavelengths, the problems
below become evident.
[0006] That is, it was found through experiments by the inventor of
this invention that, because an intense UV light beam is irradiated
onto the entire plastic objective lens while curing the UV
hardening type of adhesive, the transmission characteristics
related to blue light and ultraviolet light, which are supposed to
be utilized on the mounted lens, are deteriorated for some specific
types of plastic objective lenses. Deterioration of the
transmission characteristics of plastic objective lenses due to
irradiation of an intense UV light beam has not caused any problems
because most plastic objective lenses have conventionally been
utilized in the region of infrared or visible long wavelengths.
[0007] However, if a UV hardening type of adhesive is employed for
mounting plastic objective lenses in the mass-production process of
new type optical pickups which utilize blue light or ultraviolet
light for recording and play back, the transmission characteristics
related to blue light and ultraviolet light deteriorate which are
utilized by the mounted plastic objective lens as above, and which
results in problems in that the recording and playing accuracy of
data is lowered, and further the expected performance may not be
achieved.
[0008] Accordingly, an object of the present invention is to offer
a method of fixing an optical element, such as a plastic objective
lens in which deterioration of transmission characteristics can be
reduced in the working wavelength range of the optical element in
the case the optical element is fixed by using a UV hardening type
of adhesive.
[0009] Another object of the present invention is to offer an
optical component equipped with an optical element that has been
fixed by using the above fixing method, as well as an optical
pickup containing the optical component.
SUMMARY OF THE INVENTION
[0010] The first fixing method related to this invention is a
fixing method to fix a plastic optical element, which is used
within a prescribed working wavelength range in a wavelength region
including at least blue light and ultraviolet light, onto another
member with a light-hardening type of adhesive, is composed of (a)
a process to supply the light-hardening type of adhesive to a
bonding spot between the optical element and another member, (b) a
process to harden a light-hardening type of adhesive by selectively
irradiating a processing light beam onto the bonding spot. Here,
the selective irradiation of a processing light beam onto the spot,
basically means supplying the processing light beam to only the
bonding spot and its periphery, however it also includes relatively
reducing a light beam scattering beyond the bonding spot and its
periphery, for example, the optical surface or the like. It also
includes supplying a processing light beam entering area, other
than ones such as an optical surface where a light beam tends to
cause problematic effects to its characteristics when the light
beam passes, even if the light beam scatters beyond the bonding
spot and its periphery.
[0011] By means of the above fixing method, it is possible to
reduce deterioration of the optical characteristics of an optical
element, such as transmittance related to blue light or ultraviolet
light, caused by incidence of a processing light beam into the
interior of the optical element through the optical surface,
because the processing light beam can be selectively irradiated
onto the bonding spot for hardening of the light-hardening type of
adhesive. Accordingly, it is possible to reduce deterioration of
performance of a plastic optical element after it has been
installed.
[0012] The second fixing method related to this invention is a
fixing method to fix a plastic optical element, which is used
within a prescribed working wavelength range in a wavelength region
including at least blue light and ultraviolet light, onto another
member with a light-hardening type of adhesive, and the said method
is composed of (a) a process to supply a light-hardening type of
adhesive to the bonding spot between the optical element and
another member, (b) a process to harden the light-hardening type of
adhesive by irradiating, onto the light-hardening type of adhesive
and its periphery, a processing light beam from a solid-state light
emitting element having light emission characteristics in a
guaranteed hardening wavelength range, which practically reduces
deterioration of optical characteristics in the prescribed working
wavelength range of the optical element. Here, the intensity of
light emission characteristics in the guaranteed hardening
wavelength range is necessary to adequately harden fixing adhesive
corresponding to the situation such as the purpose of use, however
if the intensity is small, the processing time needs to be
lengthened.
[0013] By means of the above fixing method, it is possible to
reduce deterioration of the optical characteristics of an optical
element, such as transmittance related to blue light or ultraviolet
light, caused by incidence of a processing light beam into an
optical element, because, for hardening of the light-hardening type
of adhesive, the processing light beam from a solid-state light
emitting element is irradiated onto the light-hardening type of
adhesive and its periphery, which has a emission characteristics in
a guaranteed hardening wavelength range, that practically reduces
deterioration of optical characteristics in the prescribed working
wavelength range of the optical element. Accordingly, it is
possible to reduce deterioration of performance of the plastic
optical element after it has been installed.
[0014] The third fixing method related to this invention is a
fixing method to fix a plastic optical element, which is used
within a prescribed working wavelength range in a wavelength region
including at least blue light and ultraviolet light, onto another
member with a light-hardening type of adhesive, and the said method
is composed of (a) a process to supply the light-hardening type of
adhesive to a bonding spot between the optical element and another
member, (b) a process to harden the light-hardening type of
adhesive by irradiating onto the light-hardening type of adhesive
and its periphery, a processing light beam having light emission
characteristics of prescribed intensity (normal and maximum) in the
first wavelength range which practically reduces deterioration of
optical characteristics in the prescribed working wavelength range
of the optical element. Further the processing light beam has light
emission characteristics in the second wavelength range, which
exists in the ultraviolet range on the shorter wavelength side of
the first wavelength range and practically deteriorates optical
characteristics in the prescribed working wavelength range of the
optical element and the intensity of which has been reduced to be
not larger than a prescribed value relative to the above prescribed
intensity. Here, the intensity of light emitting characteristics in
the first wavelength is necessary to adequately harden fixing
adhesive corresponding to situations such as the purpose of use,
however if the intensity is small, the processing time needs to be
lengthened. Further, the reduction of the emission characteristics
in the second wavelength range to be not larger than a prescribed
value relative to the prescribed intensity in the first wavelength
range relates respectively to emission peaks and emission plateaus
existing in the second wavelength range, and therefore,
consequently the maximum emission intensity in the second
wavelength is an important factor. Regarding comparison between
emission characteristics of the first wavelength range and the
second wavelength range, the relative intensity (specifically,
spectral distribution shown by relative illuminance) can be
employed.
[0015] By means of the above fixing method, it is possible to
reduce deterioration of the optical characteristics of an optical
element, such as transmittance related to blue light or ultraviolet
light, caused by incidence of a processing light beam into an
optical element, because, for hardening of the light-hardening type
of adhesive, a lamp light beam, is irradiated onto the
light-hardening type of adhesive and its periphery, which has
emission characteristics in the second wavelength range, that
exists in the ultraviolet range on the shorter wavelength side of
the first wavelength range and practically deteriorates optical
characteristics in the prescribed working wavelength range of the
optical element, and the intensity of which has been reduced to be
not larger than a prescribed value relative to the prescribed
intensity. Accordingly, it is possible to reduce deterioration of
performance of the plastic optical element after it has been
installed.
[0016] The fourth fixing method related to this invention is a
fixing method to fix a plastic optical element, which is used
within a prescribed working wavelength range in a wavelength region
including at least blue light and ultraviolet light, onto another
member with a light-hardening type of adhesive, and the said method
is composed of (a) a process to supply the light-hardening type of
adhesive to a bonding spot between the optical element and another
member, (b) a process to harden the light-hardening type of
adhesive by irradiating, onto the light-hardening type of adhesive
and its periphery, a lamp light beam having light emission
characteristics in the first wavelength range which practically
reduces deterioration of optical characteristics in the prescribed
working wavelength range of the optical element and the intensity
of which is not less than the first intensity. Further, the lamp
light beam has the light emission characteristics in the second
wavelength range which exists in the ultraviolet range on the
shorter wavelength side of the first wavelength range, and
practically deteriorates optical characteristics in the prescribed
working wavelength range of the optical element, and the intensity
of which has been reduced to be not larger than the second
intensity.
[0017] By means of the above fixing method, it is possible to
reduce deterioration of the optical characteristics of optical
elements, such as transmittance related to blue light or
ultraviolet light, caused by incidence of a processing light beam
into an optical element, because, for hardening of the
light-hardening type of adhesive, the lamp light beam is irradiated
onto the light-hardening of type adhesive and its periphery, which
has emission characteristics in the second wavelength range, that
exists in the ultraviolet range on the shorter wavelength side of
the first wavelength range and practically deteriorates optical
characteristics in the prescribed working wavelength range of the
optical element, and the intensity of which has been reduced to be
not larger than the second intensity. Accordingly, it is possible
to reduce deterioration of performance of the plastic optical
element after it has been installed.
[0018] The optical component according to this invention is
composed of an optical element and another member, which are fixed
to each other by the above fixing method.
[0019] In an optical component related to the first fixing method,
it is possible to reduce deterioration of the optical
characteristics of an optical element, such as transmittance
related to blue light or ultraviolet light, caused by incidence of
a processing light beam into the interior of the optical element
through the optical surface, since the processing light beam can be
selectively irradiated onto the bonding spot to cure the
light-hardening, type of adhesive. Accordingly, it is possible to
reduce deterioration of performance of the plastic optical element
after it has been installed.
[0020] In an optical component related to the second fixing method,
it is possible to reduce deterioration of the optical
characteristics of optical elements, such as transmittance related
to blue light or ultraviolet light, caused by incidence of a
processing light beam into an optical element because, a processing
light beam from a solid-state light emitting element is irradiated
onto the light-hardening type of adhesive and its periphery for
hardening of the light-hardening type of adhesive to fix the
optical element and another member to each other. The processing
light beam has emission characteristics in a guaranteed hardening
wavelength range and practically reduces the deterioration of
optical characteristics in the prescribed working wavelength range
of the optical element. Accordingly, it is possible to reduce
deterioration of performance of the plastic optical element after
it has been installed.
[0021] In an optical component related to the third and fourth
fixing method, it is possible to reduce deterioration of the
optical characteristics of optical elements, such as transmittance
related to blue light or ultraviolet light, caused by incidence of
a lamp light beam into the optical element, because, for hardening
of the light-hardening type of adhesive to fix an optical element
and another member with each other, the lamp light beam having
light emission characteristics in the second wavelength range is
irradiated onto the light-hardening type of adhesive and its
periphery, which practically deteriorates optical characteristics
in the prescribed working wavelength range of the optical element
and the intensity of which has been reduced to be not larger than
the prescribed value relative to the prescribed intensity.
Accordingly, it is possible to reduce deterioration of its
performance after a plastic optical element has been installed.
[0022] An optical component related to the first fixing method is
composed of (a) a plastic optical element to be used in a
prescribed working wavelength range in a wavelength region
including at least blue light and ultraviolet light, (b) another
member to be bonded to the optical element, (c) a bonding means
which is formed of a light-hardening type of adhesive to bond the
optical element to the other member by light-hardening at
prescribed bonding spots and (d) a processing light beam is
selectively irradiated onto the bonding spots for hardening of the
light-hardening type of adhesive.
[0023] The optical component related to the second fixing method is
composed of (a) a plastic optical element to be used in a
prescribed working wavelength in a wavelength region including at
least blue light and ultraviolet light, (b) another member to be
bonded to the optical element, (c) a bonding means which is formed
of a light-hardening type of adhesive to bond the optical element
to the other member by light-hardening at prescribed bonding spots
and (d) a processing light beam emitted from solid-state light
emitting element having light emission characteristics in a
guaranteed hardening wavelength range and practically reducing
deterioration of the optical characteristics in the prescribed
working wavelength range of the optical element is irradiated onto
the light-hardening type of adhesive and its periphery for
hardening of the light-hardening type of adhesive.
[0024] The optical component related to the third and fourth fixing
method is composed of (a) a plastic optical element to be used in a
prescribed working wavelength range in a wavelength region
including at least blue light and ultraviolet light, (b) another
member to be bonded by the optical element, (c) a bonding means
which is formed of a light-hardening type of adhesive to bond the
optical element to another member by light-hardening at prescribed
bonding spots and (d) for hardening of the light-hardening type of
adhesive, a lamp light beam is irradiated onto the light-hardening
type of adhesive and its periphery, which has light emission
characteristics of prescribed intensity (normal and maximum) in the
first wavelength range which practically reduces deterioration of
optical characteristics in the prescribed working wavelength range
of the optical element and light emission characteristics in the
second wavelength range which exists in the ultraviolet range on
the shorter wavelength side of the first wavelength range and
practically deteriorates optical characteristics in the prescribed
working wavelength range of the optical element and the intensity
of which has been reduced to be not larger than a prescribed value
relative to the above prescribed intensity for hardening of the
light-hardening type of adhesive.
[0025] Also in the case of the above optical component, degradation
of the optical characteristics of the optical element can be
reduced, such as transmittance related to blue light and
ultraviolet light, caused by the incidence of a processing light
beam or a lamp light beam for light-hardening into the optical
element. Accordingly, it is possible to reduce deterioration of its
performance after a plastic optical element has been installed.
[0026] A fixing device related to the first fixing method is (a) a
fixing device to bond a plastic optical element to be used in a
prescribed working wavelength range in a wavelength region
including at least blue light and ultraviolet light, onto another
member by using a light-hardening type of adhesive being composed
of (b) a supplying means to supply the light-hardening type of
adhesive to the bonding spot between the optical element and
another member, (c) a light irradiating means to harden the
light-hardening type of adhesive by selectively irradiating a
processing light beam onto the bonding spots.
[0027] In the above fixing, it is possible to reduce a
deterioration of the optical characteristics of optical elements,
such as transmittance related to blue light or ultraviolet light,
caused by incidence of a light beam into the interior of the
optical element through the optical surface because light
irradiating means makes it possible to selectively irradiate the
processing light beam. Accordingly, it is possible to reduce
deterioration of performance of the plastic optical element after
it has been installed.
[0028] The optical pickup of the present invention is equipped with
the above optical component and hence capable of reading data from
the recording surface of an optical recording medium or writing
data on the recording surface.
[0029] In the above optical pickup, since the above-mentioned
fixing method is employed to fix an optical element such as an
objective lens, high-speed and high-density recording and playback
of data can be realized.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1(a) is a plan view of the lens unit related to the
first embodiment, and FIG. 1(b) is a cross-sectional side view of
the lens unit.
[0031] FIG. 2 is a cross-sectional side view of compound objective
lens to be installed as the lens unit of FIG. 1.
[0032] FIG. 3(a) shows an adhesive supplying device to supply a UV
hardening type of adhesive to the fixing spots, while FIG. 3(b)
shows a UV processing device to irradiate a UV hardening light beam
to a UV hardening type of adhesive.
[0033] FIG. 4 shows details of the enlarged exposure head mounted
on the UV processing device of FIG. 3(b).
[0034] FIG. 5 is a view of the FIG. 4 exposure head viewed from
below.
[0035] FIGS. 6(a) and 6(b) are a bottom view and a side view,
respectively, showing an example of modification for the exposure
head shown in FIG. 5, etc.
[0036] FIG. 7 is a schematic diagram of an example of modification
of the FIG. 3(b) UV processing device.
[0037] FIG. 8 is a schematic view explaining the UV processing
device to irradiate a UV hardening light beam onto a UV hardening
type of adhesive.
[0038] FIG. 9 is a schematic view explaining the UV processing
device to irradiate a UV hardening light beam on a UV hardening
type of adhesive.
[0039] FIG. 10 is a chart explaining spectral characteristics of a
high pressure mercury vapor lamp of the comparative example.
[0040] FIG. 11 is a chart explaining the spectral characteristics
of a light beam from a high pressure mercury vapor lamp, which has
been appropriately attenuated with a light collecting concave
mirror.
[0041] FIG. 12 is a chart explaining the spectral characteristics
of an LED of the FIG. 8 UV processing device.
[0042] FIG. 13 is a chart explaining the condition of a light beam
from a high pressure mercury vapor lamp, which has been
appropriately attenuated with a light collecting concave
mirror.
[0043] FIG. 14 is a chart explaining deterioration of transmittance
caused from hardening process when using a UV hardening light
beam.
[0044] FIG. 15 is a view showing the structure of an optical pickup
in which the objective lens unit shown in FIG. 1, etc. is
installed.
[0045] FIG. 16 is a cross sectional side view of the objective lens
unit of the second embodiment.
[0046] FIG. 17 is a cross sectional side view of the objective lens
of the third embodiment.
[0047] FIG. 18 is a cross sectional side view of the objective lens
of the fourth embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0048] In another embodiment of the present invention, the other
member stated above is a supporting member for supporting the
optical element. In this case, the process for fixing the optical
element on the supporting member, such as holder, can be ensured,
and the optical characteristics of the optical element can be
favorably maintained even after it is fixed onto the supporting
member.
[0049] In another embodiment of the present invention, other part
stated above is an optical member for performing specified optical
functions in cooperation with the optical element. In this case,
connection and alignment of the optical element with another
optical member can be simplified and ensured, whereby the optical
characteristics of the optical element and optical member can be
favorably maintained even after they are fixed to each other.
[0050] In addition, in an embodiment of the present invention, the
optical element of the above optical component is an objective lens
through which an incident luminous flux converges to form a spot on
the recording surface of a recording medium. In this case, in
assembling an optical pickup that reads and writes data from and
onto an optical recording medium with blue light and ultraviolet
light, degradation of the transmission characteristics of the
objective lens and consequently that of the image formation
characteristics can be reduced.
[0051] In another embodiment related to the first fixing method,
the processing light beam is selectively irradiated to the bonding
spot by means of a light guiding means. In this case, the
processing light beam can be certainly conducted to the bonding
spot without energy loss and conduction of a processing light beam
can be prevented, which has a possibility to cause optical
characteristics deterioration to the main portion of the optical
element.
[0052] In another embodiment related to the first fixing method,
the light guiding means is an optical fiber which leads a
processing light beam from a light source to the irradiating
position opposite to the bonding spot. In such case, the processing
light beam can be effectively led to the bonding spot by means of a
simple and efficient optical fiber.
[0053] In another embodiment related to the first fixing method,
the light guiding means is at least one reflecting means which
leads a conducted light beam from a light source to the irradiating
position opposite to the bonding spot. In this case, the processing
light beam can be led to the bonding spot with polarization by
using an optical member such as a mirror.
[0054] In another embodiment related to the first fixing method, a
processing light beam is prevented from entering the optical
surface on the periphery of the bonding spot by using
light-shielding means. In this case, the processing light beam can
be certainly conducted only to the bonding spot, which prevents the
transmission of a processing light beam having a possibility to
cause optical characteristics deterioration of the main portion of
the optical element.
[0055] In another embodiment related to the first fixing method,
the light shielding means is a mask to cover the optical surface of
the optical element. In this case, the processing light beam can be
accurately led to the bonding spot with a simple and secure
mask.
[0056] In another embodiment related to the first fixing method,
the light shielding means is a filter covering the optical surface
of an optical element. In this case, the processing light beam can
be accurately led to the bonding spot with a filter which can have
multiple functions. The filter may be one which can reduce light of
a specific wavelength harmful to the optical element, as well as
the entire range of the wavelength.
[0057] In another embodiment related to the first fixing method, a
prescribed working wavelength is in the range from of 380 to 450 nm
and the processing light beam has its emission peaks in the
hardening wavelength range of 280 to 450 nm. In this case,
deterioration of the optical characteristics of a plastic optical
element can be effectively reduced such as transmission
characteristics caused by light of a wavelength shorter than or
equal to 330 nm, which is considered to deteriorate the optical
characteristics of a plastic optical element of the working
wavelength range of 380 to 450 nm.
[0058] In another embodiment related to the first fixing method,
the processing light beam is emitted from a high pressure mercury
vapor lamp. In this case, the adhesive can be irradiated by the
processing light beam with sufficient luminance.
[0059] In another embodiment related to the first fixing method, an
optical component composed of the optical element or optical member
is either a single lens or a compound lens. In this description, a
compound lens means a lens composed of multiple lenses of the same
or different types which are formed into a single unit. In such
case, bonding between optical elements needed in the manufacture of
the single lens or a compound lens, can be completed easily and
surely with a light hardening type of adhesive, and the optical
characteristics of the manufactured single lens and compound lens,
can be favorably maintained.
[0060] In another embodiment related to the second fixing method,
the prescribed working wavelength is in the range of 380 to 450 nm
and the processing light beam has its emission peaks in the
guaranteed hardening wavelength range of 350 to 450 nm. In this
case, because light of the wavelength range shorter than or equal
to 330 nm is not employed, which is considered to deteriorate the
optical characteristics of plastic optical elements in the working
wavelength range of 380 to 450 nm and to be harmful to the optical
elements, and the guaranteed hardening wavelength range of 350 to
450 nm is employed as a processing light beam, deterioration of the
optical characteristics of plastic optical elements such as
transmission characteristics can be effectively reduced in the
working wavelength range of 380 to 450 nm.
[0061] In another embodiment related to the second fixing method,
the solid-state light emitting element is either an LED or a
semiconductor laser. In this case, the light-hardening process can
be effectively conducted with small but high power light-emitting
elements.
[0062] In another embodiment related to the second, third and
fourth fixing methods, an optical component composed of the optical
element and optical member is either a compound lens, a cemented
lens or a hybrid lens. In this description, a compound lens means a
lens composed of multiple lenses of the same or different types
that are formed into one unit; a cemented lens means a lens
composed of multiple lenses that are cemented to each other into
one piece on their optical surfaces; and a hybrid lens means a lens
composed of different lens materials such as a plastic lens and a
glass lens that are combined into one unit. In this case, bonding
between optical elements required in the manufacture of a compound
lens, a cemented lens and a hybrid lens can be completed easily and
surely with a light-hardening type of adhesive, and the optical
characteristics of the manufactured compound lens, cemented lens
and hybrid lens can be favorably maintained.
[0063] In another embodiment related to the third and fourth fixing
methods, the prescribed working wavelength range is from 380 to 450
nm and the lamp light has its first emission peak P1 in the first
wavelength range of 350 to 450 nm and its second emission peak P2
which has intensity of less than or equal to 30% of that of first
emission peak P1, in the second wavelength range from 280 to 330
nm. Here, second emission peak P2 is not limited to a single peak
but may be plural. That is, when there are a plurality of second
peaks, the intensity of any of them should be less than or equal to
30% of that of first emission peak P1. In such case, in the second
wavelength range from 280 to 330 nm which is considered to be
harmful to the optical element, because reduced is the relative
intensity of second emission peak P2 which reduces practical
deterioration in the prescribed working wavelength range of the
optical element from 380 to 450 nm, deterioration of the optical
characteristics of plastic optical elements, such as transmission
characteristics, can be effectively reduced in the working
wavelength from 380 to 450 nm.
[0064] In another embodiment related to the third and fourth fixing
methods, a lamp light beam is a light beam emitted from a light
source, which has been reduced in intensity in the second
wavelength range. In such case, necessary line spectra are selected
from the light source having a variety of line spectra, and a
light-hardening type adhesives can be effectively hardened by
them.
[0065] In another embodiment related to the third and fourth fixing
methods, the lamp light beam is picked up via at least one of a
filter or a mirror which have reducing characteristics of the light
beam from a light source in the second wavelength range. In this
case, the light beam in the targeted second wavelength range can be
easily reduced with a filter or mirror.
The First Embodiment
[0066] An objective lens unit for optical pickup, which is an
optical component according to the first embodiment of the present
invention, is described hereunder.
[0067] FIG. 1 (a) is a plan view of objective lens unit 10, while
FIG. 1 (b) is the A-A cross-sectional view of it. Objective lens
unit 10 is composed of compound objective lens 20 which is an
optical component which needs to be installed opposite to the
optical recording medium (not shown) and bobbin 40 which is a
supporting member supporting compound objective lens 20 and shifts
in focusing direction BC and tracking direction DE together with
the lens. Objective lens unit 10 is used in an optical pickup that
utilizes at least blue light or ultraviolet light (at a working
wavelength range from 380 to 450 nm, for example), but in addition
to this, it is also used for laser luminous flux for DVDs which
utilize red light (at a working wavelength range from 600 to 700
nm, for example) and for laser luminous flux for CDs that utilizes
near-infrared light (at a working wavelength range from 750 to 850
nm, for example). Above compound objective lens 20 is made of a
pair of lenses bonded with a UV hardening type of adhesive, which
will be described later.
[0068] Compound objective lens 20 is so mounted as to fit into
opening 41a of lens support 41 provided on bobbin 40. That is,
compound objective lens 20 is firmly fixed onto lens support 41 by
plural fixing portions 31, which are the bonding means structured
of a UV hardening type of adhesive, for example at four places
around it. In order to harden these fixing portions 31, a UV light
beam is irradiated onto the fluid UV hardening type adhesive
applied to the joint between the two so as to cause a
photo-polymerization reaction of the UV hardening type of adhesive.
In this process, in the case of the first fixing method, a UV
hardening light beam is irradiated not on the entire compound
objective lens 20 but only on fixing portions 31. That is, when a
UV hardening light beam is irradiated on the entire compound
objective lens 20, the UV hardening light beam, depending upon its
wavelength, may deteriorate transmittance or other optical
characteristics of the main portion of compound objective lens 20,
however the deterioration of compound objective lens 20 is reduced
by irradiating a UV hardening light beam only on fixing portions 31
using a technique to be described later. On the other hand, based
on the second to fourth fixing methods, the processing light beam,
being a UV hardening light beam, is irradiated not only on fixing
portions 31, but also onto the entire compound objective lens 20
for the sake of simplified manufacturing process. As a result of
the above, there is the possibility that the optical
characteristics of compound objective lens 20 are degraded such
that the transmittance of the optical element, which is a main
portion of compound objective lens 20, is lowered depending upon
the wavelength of the UV hardening light. Means to solve this
problem will be described later.
[0069] Bobbin 40 has bobbin body 43 extending from lens support 41,
which supports compound objective lens 20, and bobbin body 43 is
structured of focusing coil 43a which produces a drive force for
shifting compound objective lens 20 in focus direction BC along
optical axis OA, and tracking coil 43b which produces a drive force
for shifting compound objective lens 20 in tracking direction DE,
perpendicular to optical axis OA. In aperture space AS, provided is
a yoke (not shown) constituting a magnetic circuit for focusing and
tracking.
[0070] FIG. 2 is a cross-sectional side view of compound objective
lens 20. Compound objective lens 20 is, for example, a combination
of lens member 21, which is an optical element for light
collection, and phase optical element member 22, which is an
optical member for correction of wave aberration. Lens member 21 is
a one-piece formed plastic component (which for example can be
formed from acrylic polymer or cyclo-olefin type polymer, but
specifically preferable is PMMA or PC), being composed of round
lens portion 24 and circumferential flange portion 25 formed around
it. Phase optical element member 22 is also a one-piece formed
plastic component, being composed of round phase element portion 27
and circumferential flange portion 28 formed around it. As flange
portion 25 of lens member 21 and flange portion 28 of phase optical
element member 22 are connected to each other at the mating
surfaces on both flange portions 25 and 28 by four hardened fixing
portions 33 (of which only two are shown) which are the bonding
means formed of a UV hardening type of adhesive, whereby assembly
of compound objective lens 20 is completed. The material used for
fixing portions 33 can for example be an ultraviolet-ray hardening
type of monomers such as acryloyl group or methacryloyl group,
incorporating a photo-polymerization initiator.
[0071] In lens member 21, lens portion 24 is, for example, so
designed that the wave aberration on Blu-ray light becomes minimum;
and specifically, a light beam from a light source of a 408 nm
wavelength is collected on the recording surface of a Blu-ray disc
through an NA 0.85 aperture. On the other hand, flange portion 25
has circumferential projection 25a projecting toward phase optical
element member 22 and circumferential step 25b on which a recessed
exterior is formed on the tip of the projection. This step 25b is
used to align lens member 21 with phase optical element member 22
in the direction along the optical axis OA and perpendicular to
optical axis OA.
[0072] In phase optical element member 22, phase element portion 27
is for example so designed that wave-front change is rarely caused
by the Blu-ray system wavelength and wave aberration is corrected
by DVD system wavelength. In other words, compound objective lens
20 composed of above lens member 21 and phase optical element
member 22 is so designed that wave aberration becomes minimum not
only on Blu-ray light but also on DVD light. To be specific, a
light beam from a light source of a 408 nm wavelength is collected
onto the recording surface of a Blu-ray disc through an NA 0.85
aperture and also a light beam from a 650 nm wavelength light
source is collected on the recording surface of a DVD disc through
an NA 0.65 aperture. Flange portion 28 has circumferential
projection 28a projecting toward lens member 21, and inner
circumferential edge 28b is formed on the tip of the projection.
This edge 28b, along with step 25b formed on lens member 21, is
used to align lens member 21 with phase optical element member 22.
Both members 21 and 22 aligned as above, are firmly fixed together
by plural fixing portions 33 formed of the above UV hardening type
of adhesive. In order to harden fixing portions 33 quickly in a
specific process on the manufacturing line, a UV hardening light
beam is irradiated over the UV hardening type of adhesive applied
to the joint between the aligned members at appropriate timing so
as to cause a photo-polymerization reaction of the UV hardening
type of adhesive. In this process, according to the second to
fourth fixing methods, the UV hardening light beam is irradiated
not only on fixing portions 33 but also on the entire compound
objective lens 20 for the sake of simplified manufacturing
process.
<Adhesive Supplying Process>
[0073] FIG. 3(a) is a schematic diagram of the adhesive supplying
device for supplying a UV hardening type of adhesive to the fixing
portions of compound objective lenses 20, and FIG. 3(b) is a
schematic diagram of the UV processing device for irradiating the
UV hardening type of adhesive with ultra-violet rays.
[0074] In FIG. 3(a), the adhesive supplying device is composed of
adhesive ejecting device 51 which not only holds the UV hardening
type of adhesive but also discharges the adhesive at appropriate
timing, and movable nozzles 52 which apply the UV hardening type of
adhesive discharged by adhesive ejecting device 51 to
pre-determined bonding locations of compound objective lens 20 and
bobbin 40. The UV hardening type of adhesive is supplied by this
adhesive supplying device and is coated at four locations which
become fixing portions 31 on the periphery of compound objective
lens 20 which has been placed and aligned on top of bobbin 40.
<Adhesive Hardening Process>
[0075] Next, the adhesive hardening process according to the first
fixing method of the present invention will now be described in
detail below.
[0076] In FIG. 3(b), the UV processing device is provided with high
pressure mercury vapor lamp 54, which becomes the light source,
concave mirror 55 which reflects the light beam from the high
pressure mercury vapor lamp 54 toward the front, lens 56 which
focuses the UV hardening light beam, light guiding member 57 made
of an optical fiber, etc., which guides the UV hardening light beam
that has been focused by lens 56, exposure head 58 which is
provided on the leading side of light guiding member 57 and which
emits the UV hardening light beam with a specific distribution
corresponding to fixing portions 31, and driving device 59 which
moves exposure head 58 to the appropriate location. During UV
hardening, exposure head 58 is moved to the appropriate location by
operating driving device 59, and its bottom tip comes opposite to
and contacts compound objective lens 20 placed above bobbin 40.
Thereafter, by guiding light guiding member 57 the light beam from
high pressure mercury vapor lamp 54, it is possible to emit a UV
hardening light beam with a desired pattern from the bottom tip of
exposure head 58, and hence it is possible to irradiate the UV
hardening light beam only on fixing portions 31 and 33 and to
harden them in a short time.
[0077] FIG. 4 is an enlarged view showing an example of the
specific structure of exposure head 58 shown in FIG. 3(b), and FIG.
5 is a diagram explaining the state of exposure head 58 as observed
from below. Exposure head 58 is composed of shaft 58a which can be
displaced in three dimensions by driving device 59 shown in FIG.
3(b), and four branched fiber guides 58b which are fixed on the
periphery of shaft 58a and a UV hardening light beam is emitted
from the bottom tips. Recessed part 58d is formed at the center of
the bottom end surface of 58a so that the optical surface of lens
member 21 and the like, are not damaged when shaft 58a comes into
contact with compound objective lens 20. Four branched fiber guides
58b are fixed at equal intervals on the periphery at the tip of
shaft 58a and are connected to light guiding member 57. In other
words, the UV hardening light beam guided by light guiding member
57 is separated into four branched fiber guides 58b and irradiates
the bonding locations, that is, fixing portions 31 opposite the
bottom tip (the irradiating position) of each of these branched
fiber guides. Further, it is obvious that the number and the
placement of branched fiber guides 58b can be changed appropriately
according to the number and placement of fixing portions 31.
[0078] FIG. 6(a) is a side view to explain a modified example of
exposure head 58 shown in FIG. 4, while FIG. 6(b) is a view of its
bottom. In this case of this exposure head 158, shaft 158a itself
is composed of an optical fiber or an optical waveguide rod, and
the top end of shaft 158a is connected to light guiding member 57.
Further, circular mask 158f is formed at the center of the bottom
end of shaft 158a so that, when exposure head 158 is placed very
close to compound objective lens 20, the UV hardening light beam is
not irradiated onto lens member 21. Although mask 158f can be made
like an ND filter which absorbs light, it can also be made as a
mirror, and also, it is possible to form it as a bypass filter
which shuts out only the ultraviolet light harmful to the lens.
[0079] FIG. 7 is a diagram explaining a modified example of the
entire UV processing device shown in FIG. 3. In this case, the UV
processing device is provided with ultraviolet ray laser 254, lens
256 which appropriately converges the light beam from ultraviolet
ray laser 254 as a UV hardening light beam, actuator 258 which
displaces lens 256 at high speed two-dimensionally perpendicular to
the optical axis, and driving device 259 which adjusts the angle of
emission of the UV hardening light beam at appropriate timing by
operating actuator 258. It is possible to move lens 256
perpendicular to the optical axis to the desired position, thereby
irradiating the spot-shaped UV hardening light beam from
ultraviolet ray laser 254 only on fixing portions 31 thereby
hardening it in a short time, by means of suitably operating
actuator 258 by adjusting appropriately the output from driving
device 259. Further, it is also possible to move the spot of light
for UV hardening to any desired position using a mirror with its
driving device, instead of lens 256 or actuator 258.
[0080] Here, an explanation will be given about of the UV hardening
light beam wavelength used by the UV processing device. It is
necessary that high pressure mercury vapor lamp 54 or ultraviolet
ray laser 254, which outputs the UV hardening light beam, quickly
hardens fixing portions 31 and 33, the material of which is the UV
hardening type of adhesive, and in this case, if this light beam is
irradiated onto entire compound objective lens 20, it is possible
that the optical characteristics at the working wavelength range,
including 408 nm of compound objective lens 20, is in effect
degraded. Further, within the hardening wavelength range of 280 to
450 nm, the UV hardening light beam in the wavelength range of 280
to 330 nm on the shorter wavelength side can be considered to be
harmful to the lens because it effectively deteriorates the optical
characteristics in the working wavelength range of 380 to 450 nm
(408 nm in the specific example) of compound objective lens 20. In
other words, in the present preferred embodiment, although high
pressure mercury vapor lamp 54 or ultraviolet ray laser 254 used as
the light source has peaks of emission which not only effectively
hardens the UV hardening type of adhesive, but also deteriorates
the optical characteristics in the working wavelength range, since
the UV hardening light beam harmful to the lens is irradiated
selectively only on fixing portions 31 and 33 or its adjacent area,
it is possible to assuredly bond compound objective lens 20 to
bobbin 40 while reducing the deterioration of the optical
characteristics during the assembly stage.
[0081] FIG. 10 is a chart explaining the spectrum characteristics
of a high pressure mercury vapor lamp. The horizontal axis of the
chart represents the wavelength while the vertical axis represents
the relative irradiation intensity (%). This high pressure mercury
vapor lamp has its first emission peak P1 at the wavelength of 368
nm in the first (guaranteed hardening) wavelength range from 350 to
450 nm and its second emission peak P2 at the wavelength of 315 nm
in the second (harmful) wavelength range from 280 to 330 nm which
is considered harmful to the lens. First emission peak P1 in the
first (guaranteed hardening) wavelength range from 350 to 450 nm is
regarded effective for UV hardening. On the other hand, the second
(harmful) wavelength range from 280 to 330 nm may be effective for
UV hardening but, if irradiated over lens member 21 and phase
optical element member 22 constituting compound objective lens 20,
it is likely to tremendously deteriorate the transmission
characteristics of blue light and ultraviolet light of lens portion
24 and phase optical element portion 27 of these members 21 and 22.
Second emission peak P2 at the wavelength of 315 nm in the second
wavelength range from 280 to 330 nm and other emission peaks near
it are particularly thought to cause deterioration of optical
characteristics of lens portion 24 at its working wavelength range
of 408 nm or the like.
[0082] FIG. 11 is a chart for explaining the status after focusing
and appropriate attenuation, using a concave mirror having
wavelength characteristics, the light beam from the high pressure
mercury vapor lamp light source having the characteristics shown in
FIG. 10. As is also clear from the chart, even after being
reflected from the concave mirror the UV hardening light beam
emitted from the UV processing device contains a large amount of
the light in the wavelength range of 280 to 330 nm harmful to the
lens, and the relative illumination intensity of the second light
emission peak P2 has mostly not been attenuated. When a high
pressure mercury vapor lamp incorporated with a concave lens is
used, the transmittance of lens member 21, etc. was decreased from
about 94% to about 91.3% upon an exposure for about 20 seconds
equivalent to about 500 mJ/cm.sup.2 on lens member 21. Further, the
transmittance of lens member 21, etc. was decreased from about 94%
to about 90.0% upon an exposure for about 400 seconds, equivalent
to about 9,700 mJ/cm.sup.2.
[0083] In other words, it is clear that the transmittance of lens
member 21, etc. is decreased considerably if the light beam of the
high pressure mercury vapor lamp light source as it is, is
irradiated on compound objective lens 20.
[0084] The above is a case when a high pressure mercury vapor lamp
is used as a UV hardening light source, even when ultraviolet ray
laser 254 is used as the source of the UV hardening light, it is
considered that a similar phenomenon occurs depending on the
setting of the light emission peak. In other words, although the
wavelength range of 280 to 330 nm harmful to the lens could be
effective for UV hardening, if this light beam is irradiated as it
is on lens member 21 or phase optical element member 22 which
constitute compound objective lens 20, the transmission
characteristics of blue light or ultraviolet light of lens portion
24 or phase element portion 27 of these members 21 and 22 are
considered to be tremendously deteriorated.
[0085] Based on the above presumptions, although a light source is
used which has a wavelength range of 280 to 330 nm harmful to the
lens at which it is possible to obtain efficient UV hardening, the
position of irradiating a UV hardening light beam is restricted to
fixing portions 31 and 33 or to their adjacent area using exposure
head 158 shown in FIG. 3(b) or exposure head 158 shown in FIG. 6,
etc. Because of this, it is possible to assuredly bond compound
objective lens 20 to bobbin 40 while reducing the deterioration of
the optical characteristics during the assembly stage.
[0086] Next, the details of the adhesive hardening process related
to the second fixing method of this invention will be explained.
FIG. 8 is a figure that explains the concept of a UV processing
device for irradiating the UV hardening light beam onto a UV
hardening type of adhesive. The UV processing device is composed of
plural LEDs 151 each serving as a light source, plural small lenses
152 for collimating the light beam from each LED 151, collective
lens 154 for collecting the UV hardening light beam transmitted
through each small lens 152, and light guiding member 155 made of
fibers to guide the UV hardening light beam collected by collective
lens 154 onto the target. Compound objective lens 20 mounted on
bobbin 40 is placed opposite the emission end of light guiding
member 155, and fixing portions 31 supplied at suitable positions
between compound objective lens 20 and lens support 41 are exposed
to the UV hardening light beam and hardened in a short time. In
this structure, light guiding member 155 is not needed if a UV
hardening light spot of a required size can be formed at a desired
location by collective lens 154 or the like.
[0087] Although LED 151 outputting the UV hardening light beam
hardens the UV hardening type of adhesive which is the material of
fixing portions 31 and 33, it has a single optical peak in the
guaranteed hardening wavelength range of 350 to 450 nm which
practically reduces deterioration of optical characteristics of
compound objective lens 20 in the working wavelength range,
including 408 nm. In addition, the UV hardening light beam in the
wavelength region of 280 to 330 nm on the shorter wavelength side
of the guaranteed hardening wavelength range of 350 to 450 nm is
considered harmful to the lens because it deteriorates in effect
the optical characteristics of compound objective lens 20 in the
working wavelength range including 408 nm. In other words, in the
present preferred embodiment, since LED 151 is used as the light
source and which has an emission peak at the wavelength position at
which it is not only possible to effectively harden the UV
hardening type of adhesive, but also makes it possible to maintain
the optical characteristics in the working wavelength range, it is
possible to assuredly bond compound objective lens 20 to bobbin 40
while reducing the deterioration of the optical characteristics
during the assembly stage.
[0088] FIG. 12 is a chart explaining the spectral characteristics
of LED 151. In this chart, the horizontal axis denotes the
wavelength and the vertical axis denotes the relative illumination
intensity (%). LED 151 has a single emission peak at a wavelength
of 380 nm within the guaranteed hardening wavelength range of 350
to 450 nm, and does not emit any light beam in the harmful
wavelength region of 280 to 330 nm on the shorter wavelength side
or on the longer wavelength side. In this manner, since it is
possible to set the light emission wavelength range of LED 151 to
an extremely narrow range and it is also possible to freely set to
some extent the range of the emission wavelength, it is ideally
suitable for applications such as UV hardening according to an
embodiment of the present invention which requires very accurate
setting of the emission wavelength. In addition, since it is
possible to make LED 151 emit a light beam in an extremely narrow
desired band, it is not necessary to use a filter, etc., and hence
it is possible to increase the efficiency of the used light.
Further, it is also possible to use an LD (semiconductor laser
diode) in place of LED 151. In this case, it is possible to carry
out a processing in which fixing portions 31 and 33 are irradiated
with a UV hardening light beam with increased directivity.
[0089] Particularly in the previous case of using a high pressure
mercury vapor lamp as a source of the UV hardening light, it was
described that the second light emission peak present at a
wavelength of 315 nm and light emission peaks near it in the second
wavelength range of 280 to 330 nm are considered to be the cause
for the deterioration of the optical characteristics at working
wavelength 408 nm of lens portion 24 and it will be mentioned that
this matter was confirmed in the subsequent preferred embodiment,
even when LED 151 is used as a source of UV hardening light, it is
considered that a similar phenomenon occurs depending on the
setting of the light emission peak. In other words, although the
wavelength range of 280 to 330 nm harmful to the lens could be
effective for UV hardening, if this light beam is irradiated onto
lens member 21 or phase optical element member 22 which constitute
compound objective lens 20, the transmission characteristics of
blue light or ultraviolet light of lens portion 24 or the phase
element portion 27 of these members 21 and 22 are considered to be
tremendously deteriorated. On the other hand, not only is the
guaranteed hardening wavelength range of 350 to 450 nm effective
for UV hardening, but also even if this light beam is irradiated
onto lens member 21 or phase optical element member 22 which
constitute compound objective lens 20, the transmission
characteristics of blue light or ultraviolet light of lens portion
24 or phase element portion 27 of these members 21 and 22 are
either almost not deteriorated or the extent of deterioration can
be reduced. Based on this background, LED 151 was selected as a
light source in the guaranteed hardening wavelength range of 350 to
450 nm. At present, since diodes for use as LED 151 are being sold
in different types having varieties of light emission
characteristics in the blue or in the ultraviolet range and having
sufficient illumination intensities, it is possible to make it emit
a light beam assuredly within a relatively narrow wavelength band
of the guaranteed hardening wavelength range of 350 to 450 nm, and
hence LED 151 is an excellent solid state light emitting
device.
[0090] Next, the adhesive hardening process will be explained in
detail related to the third and fourth fixing methods according to
the present invention.
[0091] FIG. 9 is a diagram conceptually explaining a UV processing
device for irradiating the UV hardening type of adhesive with a UV
hardening light beam. This UV processing device is provided with
high pressure mercury vapor lamp 351 which serves as the light
source, concave mirror 352 which reflects the light beam from high
pressure mercury vapor lamp 351 toward the front, cutoff filter 353
which prevents harmful ultraviolet rays on the short wavelength
side from the UV hardening light beam from being emitted toward the
front from high pressure mercury vapor lamp 351, lens 354 which
focuses the UV hardening light beam that has been allowed to pass
through cutoff filter 353, and light guiding member 355 made of
optical fibers, etc., which guide the UV hardening light beam that
has been focused by lens 354 toward the target. Compound objective
lens 20 is placed above bobbin 40 at a position opposite the light
emitting end of light guiding member 355, and fixing portions 31
provided appropriately between compound objective lens 20 and lens
support 41 gets hardened in a short time because of exposure to a
UV hardening light beam. Further, light guiding member 355 is not
required when a spot of a desired size of UV hardening light is
formed at the desired position by lens 354.
[0092] Next, to be described will be the wavelengths of the UV
hardening light used in the third and fourth fixing methods.
[0093] While FIG. 10 describes the spectral characteristics of a
high pressure mercury vapor lamp, as has been explained earlier, in
particular, the second light emission peak present at a wavelength
of 315 nm and adjacent light emission peaks in the second
wavelength range of 280 to 330 nm are considered to be the cause of
deterioration of the optical characteristics at working wavelength
408 nm of lens portion 24. In the present preferred embodiment, the
ultraviolet rays of the second wavelength region 280 to 330 nm
harmful to the lens are eliminated from the light beam of high
pressure mercury vapor lamp light source 351 and particularly
second light emission peak P2 at a wavelength of 315 nm is
attenuated. Specifically, the relative intensity of second light
emission peak P2 in the second wavelength range of 280 to 330 nm is
set at 30% or less, for example, relative to first light emission
peak P1 in the first wavelength range of 350 to 450 nm.
[0094] FIG. 13 is a chart to explain the status after focusing and
appropriately attenuating the light beam emitted from high pressure
mercury vapor lamp light source 351, using a concave mirror having
wavelength characteristics. In this chart, the solid line indicates
the relative illumination intensity when a concave mirror of the
first type is used, while the dashed line indicates the relative
illumination intensity when a concave mirror of the second type is
used. As is also clear from the chart, when a concave mirror of the
second type is used, the UV hardening light beam emitted from the
UV processing device contains a large amount of the light beam from
the light source in the harmful wavelength range of 280 to 330 nm,
and the relative illumination intensity of second light emission
peak P2 has almost not been attenuated. Contrarily, when a concave
mirror of the first type is used, the UV hardening light emitted
from the UV processing device contains almost no light beam from
the light source in the second wavelength range of 280 to 330 nm,
and the relative illumination intensity of second light emission
peak P2 is less than 20%. Further, in both cases of using either
the first type of concave mirror or the second type of concave
mirror, it was found that there was no big difference in the
absolute illumination intensity of first light emission peak P1.
From the above, it is clear that attenuating only second light
emission peak P2 of high pressure mercury vapor lamp 351, using the
first type of concave mirror indicated by the solid line in the
chart, is an effective method for reducing deterioration in the
optical characteristics of compound objective lens 20. In other
words, even when the UV hardening light beam for hardening the
adhesive is irradiated over the entire surfaces of lens member 21
or phase optical element member 22, it is possible to reduce
deterioration in transmittance of members 21 and 22 by using a UV
hardening light beam having an emission spectral distribution
indicated by the solid line.
[0095] Table 1 below indicates examples of methods of fixing, to
each other, the optical elements (specifically, members 21 and 22)
constituting compound objective lens 20 shown in FIG. 2.
TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Example 4
Hardening 5 seconds 6 seconds 8 seconds 10 seconds Time Radiation
4500 mJ/cm.sup.2 5400 mJ/cm.sup.2 7200 mJ/cm.sup.2 9000 mJ/cm.sup.2
Energy Transmittance 93.4% 93.3% 93.3% 93.3%
[0096] In Table 1, the hardening time indicates the processing time
when using the UV hardening light beam having the light emission
characteristics indicated by the solid line in the chart of FIG.
13, the radiation energy indicates the energy of the light beam at
the working position at which the hardening process is carried out,
and the transmittance is at wavelength 408 nm. Further, since the
transmittance of lens member 21, etc., before carrying out the
hardening process was 94%, the transmittance values shown in this
table can be considered to have deteriorated only by the extent
that they are lower than 94%. As is also clear from Table 1, it is
evident that there is almost no reduction in transmittance of the
optical elements such as the lens, etc. due to a hardening process
time of 5 to 10 seconds using the UV hardening light beam according
to the present preferred embodiment in which second light emission
peak P2 at a wavelength of 315 nm has been attenuated.
[0097] Table 2 shows comparative examples of the method of fixing
optical elements to each other.
TABLE-US-00002 TABLE 2 Comparative Comparative Comparative Example
1 Example 2 Example 3 Hardening 3 seconds 5 seconds 10 seconds Time
Radiation 430 mJ/cm.sup.2 655 mJ/cm.sup.2 1072 mJ/cm.sup.2 Energy
Transmittance 91.8% 91.2% 90.9%
[0098] In this case, a UV hardening light beam with the light
emission characteristics shown in the FIG. 10 chart is used instead
of the UV hardening light beam with the light emission
characteristics indicated by the solid line in the FIG. 13 chart.
As is also clear from Table 2, in the case where second light
emission peak P2 is not attenuated, the reduction in transmittance
of the optical elements such as lenses is substantial even when the
hardening process time by means of a UV hardening light beam is
about 12 seconds (equivalent to less than 1 second without focusing
by a concave mirror).
[0099] FIG. 14 is a diagram for explaining deterioration in
transmittance due to the hardening process using a UV hardening
light beam. The solid line in the chart indicates the transmittance
distribution of the optical elements such as lenses before UV
hardening, and the dashed line corresponds to Comparative Example 3
in Table 2. In other words, it is evident that the reduction in
transmittance is substantial when a naked high pressure mercury
vapor lamp light is used for UV hardening. In the chart, the single
dot and dash line corresponds to Examples in Table 1, and it is
clear that the reduction in transmittance has been substantially
suppressed by a UV hardening light beam exhibiting the optical
characteristics shown by the solid line in the FIG. 13 chart.
[0100] Although, a high pressure mercury vapor lamp was used in the
above descriptions as the light source of a UV hardening light, it
is also possible to use lamps having various types of light
emission characteristics such as a halogen lamp. Even in such a
case, the first wavelength range of 350 to 450 nm is used for
hardening, and in order to reduce the deterioration in the optical
characteristics due to the second wavelength range of 280 to 330
nm, the light emission peaks in this second wavelength range are
attenuated.
[0101] Although the above description is based on the working 408
nm wavelength, regarding compound objective lens 20, which is used
at other wavelength in the range of 380 to 450 nm, by control of
the incidence position of a UV hardening light beam (the first
fixing method), no particular degradation of transmittance is
observed at any other wavelength within the wavelength range of 380
to 450 nm (the second fixing method) and transmittance is improved
to be better than a comparative examples at the wavelength range
from 380 to 450 nm according to the example shown in the chart of
FIG. 14 (the third and fourth fixing methods), therefore it is
certain that high-accuracy optical data reading and writing can be
performed.
[0102] Although the above describes a method of bonding compound
objective lens 20 on bobbin 40, the same applies to structuring
compound objective lens 20 by cementing lens member 21 to phase
optical element member 22.
[0103] FIG. 15 shows a schematic structure of the optical pickup
where objective lens unit 10 shown in FIG. 1 is mounted on an
optical head.
[0104] The optical pickup contains semiconductor laser 62 which
emits a luminous flux (specifically, a wavelength of 408 nm) for
playing back the data of first optical disc 61, and semiconductor
laser 66 which emits a luminous flux (specifically, a wavelength of
650 nm) for playing back the data of second optical disc 65, that
is, being capable of emitting two laser light beams of different
wavelength. The laser light beam from both semiconductor lasers 62
and 66 is irradiated onto optical discs 61 and 65 through objective
lens unit 10 mounted on optical head 100 (specifically, compound
objective lens 20) and the reflected light beam from optical disc
61 and 65 is collected through objective lens unit 10 or the
like.
[0105] To play back first optical disc 61, a beam is emitted from
first semiconductor laser 62, and the emitted luminous flux goes
through beam splitter 71, polarized light beam splitter 72,
collimator 73, and then 1/4 wavelength plate 74, and is turned into
a circularly polarized parallel luminous flux. This luminous flux
is reduced through aperture 76 and collected onto information
recording surface 61b via transparent base board 61a of first
optical disc 61 by compound objective lens 20.
[0106] The luminous flux modulated and reflected by information
bits on information recording surface 61b goes through compound
objective lens 20, aperture 76, 1/4 wavelength plate 74, and then
collimator 73, and enters polarized light beam splitter 72 and is
reflected there; then, it is astigmatised by lens 78 and
cylindrical lens 78b and enters into photodetector 79; thus, by
using the output signals from the detector, read signals of the
data recorded on first optical disc 61 are obtained.
[0107] In addition, focus detection and track detection are
performed by detecting the change in quantity of light resulting
from the change in the spot profile and the spot position on
photodetector 79. Based on this detection, two-dimensional actuator
81 installed on optical head 100 moves objective lens unit 10 in
the optical axis direction so that the luminous flux from first
semiconductor laser 62 is focused on information recording surface
61b and also moves objective lens unit 10 in the direction
perpendicular to the optical axis so that the luminous flux from
semiconductor laser 62 is focused on a specific track.
[0108] On the other hand, for playback of second optical disc 65, a
light beam is emitted from second semiconductor laser 66, and the
emitted luminous flux is reflected by beam splitter 71 which is a
means for combining beams, and goes through polarization beam
splitter 72, collimator 73, 1/4 wavelength plate 74, aperture 76,
and compound objective lens 20 in the same way as above luminous
flux from first semiconductor laser 62, and it is then collected
onto information recording surface 65b via transparent base board
65a of second optical disc 65.
[0109] The luminous flux modulated and reflected by information
bits on information recording surface 65b goes back through
compound objective lens 20, aperture 76, 1/4 wavelength plate 74,
collimator 73, polarized light beam splitter 72, and cylindrical
lens 78b, and enters optical detector 79; thus, by using the output
signals from the detector, read signals of the data recorded on
second optical disc 65 are obtained.
[0110] In addition, in the same way as for first optical disc 61,
focus detection and track detection are performed by detecting the
change in the quantity of light resulting from the change in the
spot profile and the spot position on photodetector 79, and
two-dimensional actuator 81 installed on optical head 100 positions
objective lens unit 10 for focusing and tracking.
[0111] Since objective lens unit 10, to be fixed by the method
explained in FIGS. 3, 8 and 9, is mounted on the optical pickup
explained above, and objective lens unit 10 contains compound
objective lens 20 in which little degradation of transmission
characteristics occurs through mounting and fixing, highly accurate
data reading and recording are realized.
[0112] Although the fixing method of an optical element on
objective lens unit 10 has been described above, degradation of the
transmission characteristics can also be reduced on other optical
elements such as collimator 73, polarized light beam splitter 72
and cylindrical lens 78b by employing the same fixing method.
The Second Embodiment
[0113] An optical component according to the second embodiment of
the present invention is described hereunder. While compound
objective lens 20 is mounted on objective lens unit 10 in the first
embodiment, a plastic single lens is employed as the objective lens
in this second embodiment.
[0114] FIG. 16 is a cross-sectional side view of objective lens
unit 110. The second embodiment is an altered configuration of the
first embodiment, and so the same parts/components are given the
same designations and no further description is given. Objective
lens unit 110 is so constructed that objective lens 120 containing
a single lens as an optical element is fixed on bobbin 40, which is
an optical component. Even with this structure, the UV hardening
light beam can be irradiated only onto fixing portions 31, for
example, at four portions by using exposure head 58, etc. as shown
in FIG. 3(b) (the first fixing method), or the UV hardening light
beam, excluding harmful ultraviolet light, can be irradiated onto
and around fixing portions 31 by the UV processing unit shown in
FIGS. 8 and 9 (the second to the fourth fixing methods), and so
fixing portions 31 can be hardened in a short time while reducing
deterioration of the optical characteristics of lens portion
24.
[0115] An optical pickup which employs objective lens unit 110 in
FIG. 16 basically has the same structure as in FIG. 15. However, if
lens portion 24 is not capable of processing two different
wavelengths for example due to its diffractive structure,
semiconductor laser 66 and beam splitter 71 for second optical disc
65 are not required.
The Third Embodiment
[0116] An objective lens which is an optical component according to
the third embodiment is described hereunder. As shown in FIG. 17,
objective lens 220 is a cemented lens where a pair of different
plastic lenses 221 and 222 are cemented to each other on their
optical surfaces by bonding layer 233 formed of a UV hardening type
of adhesive. In this structure, two plastic lenses 221 and 222
have, for example, a different refractive index.
[0117] Even with this structure, by applying the UV hardening
process to paired plastic lenses 221 and 222, between which
unhardened bonding layer 233 is sandwiched, by the UV processing
devices shown in FIGS. 3, 8 and 9, bonding layer 233 can be quickly
hardened and degradation of the transmission characteristics of
objective lens 220 can be reduced.
[0118] In the third embodiment, the working wavelength used for
reading and writing data for example is also assumed to be from 380
to 450 nm. In this embodiment, the guaranteed hardening wavelength
(first) range from 350 to 450 nm is also utilized for hardening
bonding layer 233, and thereby degradation of the optical
characteristics of objective lens 220 caused by the harmful
(second) wavelength range from 280 to 330 nm is reduced. In the
third and fourth fixing method, the intensity of emission peaks in
the second wavelength range from 280 to 330 nm is reduced to be,
for example, not more than 30% of the relative intensity of the
first wavelength range.
The Fourth Embodiment
[0119] An objective lens which is an optical component according to
the fourth embodiment is described hereunder. As shown in FIG. 18,
objective lens 320 is a hybrid lens where glass lens 321 and
plastic lens 322 are cemented to each other on their optical
surfaces by bonding layer 333 formed of a UV hardening type of
adhesive. In this structure, plastic lens 322 is, for example, a
non-spherical lens.
[0120] Even with this structure, by applying a UV hardening
process, paired lenses 321 and 322, between which an unhardened
bonding layer 333 is sandwiched, by the UV processing device shown
in FIGS. 3, 8 and 9, bonding layer 333 can be quickly hardened and
degradation of the transmission characteristics of objective lens
320 can be reduced.
[0121] In the fourth embodiment, the working wavelength used for
reading and writing data for example is also assumed to be from 380
to 450 nm. In this embodiment, the guaranteed hardening (first)
wavelength range from 350 to 450 nm is also utilized for hardening
bonding layer 333, whereby degradation of the optical
characteristics of objective lens 320, caused by the harmful
(second) wavelength range from 280 to 330 nm is reduced. In the
third and fourth fixing method, the intensity of the emission peaks
in the second wavelength range from 280 to 330 nm are reduced to
be, for example, not more than 30% of the relative intensity of the
first wavelength.
[0122] The present invention has been described above by referring
to preferred embodiments, but the invention is not limited to those
embodiments. For example, although ultraviolet light is used for
the light-hardening in the above embodiments, it is allowable to
alternatively employ fixing portions formed of light-hardening type
adhesives which are hardened by visible light.
[0123] Further, although fixing portions 31 and 33 in those
embodiments are UV-hardened in a single process by the UV
processing device shown in FIGS. 3(b), 8 and 9, fixing portions 31
and 33 can be optically hardened in plural and separate processes.
In other words, if sufficient hardening time cannot be ensured
because of a limitation of tact time in a manufacturing line,
fixing portions 31 and 33 are processed first by tacking (temporary
hardening) which can be completed in a short time, and then at any
other time, for example while being kept in stock after removal
from the production line, fixing portions 31 and 33 are subjected
to final bonding (final hardening) for the sufficient length of
time so as to attain permanent bonding strength. This enables
flexible incorporation of the UV processing device shown in FIGS.
3, 8 and 9, in a manufacturing line, irrespective of the hardening
time.
[0124] Still further, although the above embodiments describe
objective lens unit 10 for an optical pickup, the fixing method of
the present invention can also be applied to other components. That
is, compound objective lens 20 can be fixed not only on bobbin 40
but also on other various holders and components by UV
hardening.
* * * * *