U.S. patent application number 12/471182 was filed with the patent office on 2009-12-03 for molded lens.
Invention is credited to Toshiaki Katsuma, Yu Kitahara, Masao Mari, Tetsuya Ori.
Application Number | 20090296227 12/471182 |
Document ID | / |
Family ID | 38608777 |
Filed Date | 2009-12-03 |
United States Patent
Application |
20090296227 |
Kind Code |
A1 |
Katsuma; Toshiaki ; et
al. |
December 3, 2009 |
MOLDED LENS
Abstract
A laser beam output from a semiconductor laser light source 1 is
transmitted through a cover glass 2 in the optical axis Z
direction, is incident on a molded lens 4 in a state of divergent
rays, is converted into convergent rays by the molded lens 4, and
is applied onto a recording face 5 of the optical recording medium.
A diaphragm 3 is arranged. An area of each lens surface onto which
a luminous flux of the laser beam restricted by the diaphragm 3 is
applied corresponds to an effective area. The following expression
(1) is satisfied: d.sub.1-d.sub.0.gtoreq.0.04 mm (1) where d0
denotes an effective aperture of one of the lens surfaces, and d1
denotes an outer diameter of the one of the lens surfaces.
Inventors: |
Katsuma; Toshiaki;
(Saitama-shi, JP) ; Mari; Masao; (Saitama-shi,
JP) ; Kitahara; Yu; (Saitama-shi, JP) ; Ori;
Tetsuya; (Saitama-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
38608777 |
Appl. No.: |
12/471182 |
Filed: |
May 22, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11826928 |
Jul 19, 2007 |
7589914 |
|
|
12471182 |
|
|
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|
Current U.S.
Class: |
359/642 ;
264/2.7 |
Current CPC
Class: |
G02B 13/0025 20130101;
G11B 7/1374 20130101; G11B 7/1353 20130101; G02B 3/04 20130101 |
Class at
Publication: |
359/642 ;
264/2.7 |
International
Class: |
G02B 3/00 20060101
G02B003/00; B29D 11/00 20060101 B29D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 20, 2006 |
JP |
P2006-197588 |
Claims
1. A molded lens manufactured by an injection molding process
comprising the steps of: transferring a shape of a mold so that
said lens comprises a first lens surface and a second lens surface,
wherein the first lens surface satisfies the following conditional
expression (1): 0.04 mm.ltoreq.d.sub.1-d.sub.0 (1) where d.sub.0
denotes a usable aperture of the first lens surface, and d.sub.1
denotes an outer diameter of the first lens surface, wherein the
first lens surface is larger in usable aperture than the second
lens surface; and controlling transferability of said shape of said
mold, and controlling an air vent when said mold is clamped, by
controlling an injection pressure and a mold clamping force.
2. A molded lens manufactured by an injection molding process
comprising the steps of: transferring a shape of a mold so that
said lens comprises a first lens surface and a second lens surface,
wherein the first lens surface satisfies the following conditional
expression (1): 0.04 mm.ltoreq.d.sub.1-d.sub.0 (1) where d.sub.0
denotes a usable aperture of the first lens surface, and d.sub.1
denotes an outer diameter of the first lens surface, and the second
lens surface satisfies the following conditional expression (1)':
0.04 mm.ltoreq.d.sub.1'-d.sub.0' (1)' where d.sub.0' denotes a
usable aperture of the second lens surface, and d.sub.1' denotes an
outer diameter of the second lens surface, wherein the first lens
surface is larger in usable aperture than the second lens surface;
and controlling transferability of said shape of said mold, and
controlling an air vent when said mold is clamped, by controlling
an injection pressure and a mold clamping force.
3. A molded lens manufactured by an injection molding process
comprising the steps of: transferring a shape of a mold so that
said lens comprises a first lens surface and a second lens surface,
wherein the second lens surface satisfies the following conditional
expression (1)': 0.04 mm.ltoreq.d.sub.1'-d.sub.0' (1)' where
d.sub.0' denotes a usable aperture of the second lens surface, and
d.sub.1' denotes an outer diameter of the second lens surface,
wherein the first lens surface is larger in usable aperture than
the second lens surface; and controlling transferability of said
shape of said mold, and controlling an air vent when said mold is
clamped, by controlling an injection pressure and a mold clamping
force.
4. A molded lens manufactured by a compression molding process
comprising the steps of: transferring a shape of a mold so that
said lens comprises a first lens surface and a second lens surface,
wherein the first lens surface satisfies the following conditional
expression (1): 0.04 mm.ltoreq.d.sub.1-d.sub.0 (1) where d.sub.0
denotes a usable aperture of the first lens surface, and d.sub.1
denotes an outer diameter of the first lens surface, wherein the
first lens surface is larger in usable aperture than the second
lens surface; and controlling transferability of said shape of said
mold by controlling a molding pressure at a high temperature and a
molding pressure at a time of cooling.
5. A molded lens manufactured by a compression molding process
comprising the steps of: transferring a shape of a mold so that
said lens comprises a first lens surface and a second lens surface,
wherein the first lens surface satisfies the following conditional
expression (1): 0.04 mm.ltoreq.d.sub.1-d.sub.0 (1) where d.sub.0
denotes a usable aperture of the first lens surface, and d.sub.1
denotes an outer diameter of the first lens surface, and the second
lens surface satisfies the following conditional expression (1)':
0.04 mm.ltoreq.d.sub.1'-d.sub.0' (1)' where d.sub.0' denotes a
usable aperture of the second lens surface, and d.sub.1' denotes an
outer diameter of the second lens surface, wherein the first lens
surface is larger in usable aperture than the second lens surface;
and controlling transferability of said shape of said mold by
controlling a molding pressure at a high temperature and a molding
pressure at a time of cooling.
6. A molded lens manufactured by a compression molding process
comprising the steps of: transferring a shape of a mold so that
said lens comprises a first lens surface and a second lens surface,
wherein the second lens surface satisfies the following conditional
expression (1)': 0.04 mm.ltoreq.d.sub.1'-d.sub.0' (1)' where
d.sub.0' denotes a usable aperture of the second lens surface, and
d.sub.1' denotes an outer diameter of the second lens surface,
wherein the first lens surface is larger in usable aperture than
the second lens surface; and controlling transferability of said
shape of said mold by controlling a molding pressure at a high
temperature and a molding pressure at a time of cooling.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of co-pending U.S.
application Ser. No. 11/826,928 filed on Jul. 19, 2007; the entire
contents of which are hereby incorporated by reference and for
which priority is claimed under 35 U.S.C. .sctn. 120. This
application is based upon and claims the benefit of priority from
the Japanese Patent Application No. 2006-197588 filed on Jul. 20,
2006; the entire contents of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The invention relates to a lens manufactured by the mold
molding and, more particularly, a molded lens having micro lens
diameter such as an imaging lens for a mobile terminal, a
recording/reproducing lens for an optical disk, a
projecting/receiving lens for optical communication and an
objective lens for an endoscope.
[0004] 2. Description of the Related Art
[0005] In recent years, the molded lens is utilized in various uses
at the request of weight reduction and cost reduction.
[0006] For example, in the case where the molded lens is formed by
the injection molding, the molded lens is formed by a series of the
following operation processes. That is, plastic material is
softened by heating, the material is injected into the mold at a
high pressure to transfer an optically transferred surface profile
of the mold to the material, the mold is cooled, and then the
molded lens is taken out by opening upper and lower portions of the
mold.
[0007] Meanwhile, it is desired that the optically transferred
surface profile of the mold should be transferred satisfactorily to
a product lens over the entire surface. However, in the periphery
of a lens surface, a molding pressure is hard to apply and thus it
is difficult to satisfactory transfer the surface profile of the
mold.
[0008] On the contrary, when a molding pressure is increased such
that a sufficient pressure is applied to the periphery of the lens
surface, burr occurs easily.
[0009] Also, when a mold clamping force is increased to prevent an
occurrence of the burr, it is hard for air to come out of the mold.
Thus, air still remains between the mold and the lens surface. As a
result, a surface of the mold may not be transferred.
[0010] Therefore, in related art, a difference between an outer
diameter of the lens surface and an effective aperture of the lens
surface is set so large that deterioration of transferability is
not caused within the effective aperture of the lens surface.
[0011] JP 2001-341134 A (corresponding to US 2001/0053395 A)
discloses technology to process a lens optical surface with high
precision.
[0012] However, with the progress of mobile devices such as a
cellular phone, nowadays the demand for size reduction of the
imaging lens becomes extremely strong. Thus, an outer diameter of 5
mm or less is going to become the mainstream as an outer diameter
of the lens surface of the imaging lens. Further, the demand for an
outer diameter of 1 mm or less also becomes stronger.
[0013] In such micro lens, it is difficult to utilize JP
2001-341134 A. Also, even though JP 2001-341134 A is used, it is
difficult to improve transferability in the peripheral portion of
the mold without fail. As a result, unless an effective aperture of
the lens surface is set considerably smaller than an outer diameter
of the lens surface, a desired refracting action cannot be exerted
on rays passing through the peripheral portion of the lens.
[0014] Therefore, in order to maintain the optical performances
satisfactorily in such situation, the effective aperture of the
lens surface is set considerably small. Conversely, in order to
ensure the effective aperture of the lens surface having a
predetermined size, the diameter of the lens surface is set large,
which conflicts with the above demand for size reduction. In this
event, such problem arises in not only the molded lens manufactured
by the injection molding method but also molded lens manufactured
by the compression molding method.
SUMMARY OF THE INVENTION
[0015] The invention has been in view of the above circumstances,
and provides a molded lens capable of attaining reduction in
diameter of a lens surface even in a lens having very small
diameter while maintaining good optical performances in a
peripheral portion of a lens effective area.
[0016] According to an aspect of the invention, a molded lens
includes a first lens surface and a second lens surface. The first
lens surface satisfies the following conditional expression
(1):
0.04 mm.ltoreq.d1-d0 (1)
where d0 denotes an effective (usable) aperture of the first lens
surface, and d1 denotes an outer diameter of the first lens
surface, and, as to the outer diameter d1 of the lens surface, a
portion of the boundary portion between an edge portion and a lens
portion of the lens, where a level difference is provided on the
curved surface constituting the lens portion or a first-order
derivative become discontinuous, is determined as an outer edge of
the lens surface.
[0017] In the field of optics, the expressions "first lens surface"
and "first surface of a lens" sometimes mean a light source side of
the lens, a surface on an object side of the lens or an incident
side of the lens. However, this specification does not employ this
definition. Instead, in this specification, one of lens surfaces
through which light passes will be simply referred to as a "first
lens surface," and another one of the lens surfaces will be
referred to as a "second lens surface."
[0018] Also, the molded lens may be manufactured by transferring a
shape of a mold.
[0019] In this case, the first lens surface may be larger in
effective aperture than the second lens surface.
[0020] Also, the first lens surface may further satisfy the
following conditional expression (2).
0.04 mm.ltoreq.d.sub.1-d.sub.0.ltoreq.1.00 mm (2)
[0021] Also, the first lens surface may further satisfy the
following conditional expression (3).
d.sub.0.ltoreq.1.00 mm (3)
[0022] Also, the outer diameter d.sub.1 of the first lens surface
may be equal to or less than 5.00 mm.
[0023] According to another aspect of the invention, a molded lens
includes a first lens surface and a second lens surface. The first
lens surface satisfies the following conditional expression
(1):
0.04 mm.ltoreq.d.sub.1-d.sub.0 (1)
where d.sub.0 denotes an effective aperture of the first lens
surface, and d.sub.1 denotes an outer diameter of the first lens
surface. The second lens surface satisfies the following
conditional expression (1)':
0.04 mm.ltoreq.d.sub.1'-d.sub.0' (1)
where d.sub.0' denotes an effective aperture of the second lens
surface, and d.sub.1' denotes an outer diameter of the second lens
surface.
[0024] Also, the molded lens may be manufactured by transferring a
shape of a mold.
[0025] Also, the first lens surface may further satisfy the
following conditional expression (2).
0.04 mm.ltoreq.d.sub.1-d.sub.0.ltoreq.1.00 mm (2)
The second lens surface may further satisfy the following
conditional expression (2)'.
0.04 mm.ltoreq.d.sub.1'-d.sub.0'.ltoreq.1.00 mm (2)'
[0026] Also, the first lens surface may further satisfy the
following conditional expression (3).
d.sub.0.ltoreq.1.00 mm (3)
The second lens surface may further satisfy the following
conditional expression (3)'.
d.sub.0'.ltoreq.1.00 mm (3)'
[0027] Also, the outer diameter d.sub.1 of the first lens surface
may be equal to or less than 5.00 mm. The outer diameter d.sub.1'
of the second lens surface may be equal to or less than 5.00
mm.
[0028] In the molded lens described above, the outer diameter
d.sub.1 (d.sub.1') of the lens surface is formed at least 0.04 mm
larger than the effective aperture d.sub.0 (d.sub.0') of the lens
surface. This numerical value of 0.04 mm was obtained from various
investigated results made by the inventors. When the outer diameter
d.sub.1 (d.sub.1') of the lens surface is set larger than the
effective aperture d.sub.0 (d.sub.0') of the lens surface at least
by 0.04 mm, deterioration in optical performances in the effective
area, especially in the peripheral portion, of the lens surface can
be prevented.
[0029] In other words, the minimum limit of allowance given as a
difference between the outer diameter d.sub.1 (d.sub.1') of the
lens surface and the effective aperture d.sub.0 (d.sub.0') of the
lens surface corresponds to 0.04 mm. When this allowance is less
than 0.04 mm, the optical performances in the effective area of the
lens surface are suddenly lowered.
[0030] In contrast, when this allowance is in excess of 0.04 mm,
the optical performances are improved gently and continuously,
nevertheless reduction in diameter of the lens is hampered
gradually because the outer diameter d.sub.1 (d.sub.1') of the lens
surface is increased. As a result, when reduction in diameter of
the lens is requested strongly, it becomes important that this
allowance should be set less than 1.00 mm, for example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a view showing the configuration of an optical
system of an optical recording device using a molded lens according
to an embodiment (Example 1) of the invention.
[0032] FIG. 2 is an enlarged view showing a shape of the molded
lens according to Example 1.
[0033] FIG. 3 is a view explaining decision criteria for an outer
diameter of a lens surface when the lens surface is formed with a
diffraction optical surface.
[0034] FIG. 4 is a view of an image of interference fringes that
indicate a state of transmitted wavefronts in the molded lens
according to Example 1.
[0035] FIG. 5 is an enlarged view showing a shape of a molded lens
according to Example 2.
[0036] FIG. 6 is a view of an image of interference fringes that
indicate a state of transmitted wavefronts in the molded lens
according to Performance Verification 1.
[0037] FIG. 7 is a view showing the configuration of an optical
system of an optical recording device using a molded lens according
to Example 3.
[0038] FIG. 8 is an enlarged view showing a shape of the molded
lens according to Example 3.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0039] Embodiments of the invention will be described with
reference to the drawings hereinafter. FIG. 1 is a view showing the
configuration of an optical system of an optical recording device
using a molded lens 4 (L.sub.1) according to this embodiment of the
invention. FIG. 2 is an enlarged view showing a shape of this
molded lens 4.
[0040] As shown in FIG. 1, in the optical system of the optical
recording device, a laser beam output from a semiconductor laser
light source 1 is transmitted through a cover glass 2 in the
optical axis Z direction, is incident on the molded lens 4
according to this embodiment in a state of divergent rays, is
converted into convergent rays by the molded lens 4, and is applied
onto a recording face 5 of the optical recording medium.
[0041] Also, a diaphragm 3 is arranged between the cover glass 2
and the molded lens 4. An area of each lens surface onto which a
luminous flux of the laser beam restricted by the diaphragm 3 is
applied corresponds to an effective area. A diameter of this
effective area corresponds to effective apertures d.sub.0, d.sub.0'
of third and fourth surfaces 11, 12. As listed in Table 2, the
effective aperture d.sub.0 of the third surface 11 (the surface of
the molded lens on the light source side) is 0.78 mm, and the
effective aperture d.sub.0' of the fourth surface 12 (the surface
of the molded lens on the recording face side) is 0.68 mm. The
effective aperture represents the usable aperture herein.
[0042] In contrast, as shown in FIG. 2, an outer diameter d.sub.1
of the third surface 11 is 0.84 mm, and an outer diameter d.sub.1'
of the fourth surface 12 is 0.74 mm.
[0043] Therefore, in an example of the molded lens 4 of this
embodiment, a value obtained by subtracting the effective aperture
d.sub.0 (d.sub.0') of each of the third and fourth surface 11, 12
from the outer diameter d.sub.1 (d.sub.1') of each of the third and
fourth surfaces 11, 12 is 0.06 mm.
[0044] In fact, as the molded lens of this embodiment, this
subtracted value may be increased larger like 0.07 mm, 0.08 mm, . .
. , or may be decreased smaller like 0.05 mm, 0.04 mm, . . . . It
is, of course, that size reduction and weight reduction of the lens
is advanced as this value is decreased smaller.
[0045] In the molded lens of this embodiment, the following
conditional expressions (1), (1') are satisfied.
d.sub.1-d.sub.0.gtoreq.0.04 mm (1)
d.sub.1'-d.sub.0'.gtoreq.0.04 mm (1')
[0046] In other words, when the value obtained by subtracting the
effective aperture d.sub.0 (d.sub.0') of each lens surface from the
outer diameter d.sub.1 (d.sub.1') of each lens surface is below
0.04 mm, an area of the peripheral portion of the mold in which
transferability is extremely bad is contained in the effective
area. Thus, it is difficult to obtain the good optical
performances. As a result, unless the effective aperture d.sub.0
(d.sub.0') of each lens surface is set smaller than the outer
diameter d.sub.1 (d.sub.1') of each lens surface by 0.04 mm or
more, desired refracting action cannot be exerted on the rays
passing through the peripheral portion of the lens.
[0047] It is preferable that the following conditional expression
(2), (2)' are satisfied.
0.04 mm.ltoreq.d.sub.1-d.sub.0.ltoreq.1.00 mm (2)
0.04 mm.ltoreq.d.sub.1'-d.sub.0'.ltoreq.1.00 mm (2')
[0048] In other words, if the conditional expression (2) or (2')
exceeds 1.00 mm, the outer diameter d.sub.1 (d.sub.1') of the lens
surface is increased correspondingly. Therefore, when diameter
reduction of the lens is required strongly, for example, when the
molded lens is used as an imaging lens installed into the latest
cellular phone, mobile device, or the like, d.sub.1-d.sub.0
(d.sub.1'-d.sub.0') exceeding 1.00 mm conflicts with the demand for
size reduction.
[0049] Also, more preferably, the following conditional expression
(2''), (2''') is satisfied.
0.04 mm.ltoreq.d.sub.1-d.sub.0.ltoreq.0.60 mm (2'')
0.04 mm.ltoreq.d.sub.1'-d.sub.0'.ltoreq.0.60 mm (2''')
[0050] That is, as shown in the conditional expressions (2''),
(2'''), when its upper limit is set to 0.60 mm, such condition is
more advantageous in size reduction of the lens. Size reduction of
the lens is more advanced than the case where only the restrictions
given by the conditional expressions (2), (2') are satisfied.
[0051] Also, as to the outer diameter d.sub.1 (d.sub.1') of each
lens surface, as shown specifically in FIG. 2, a portion of the
boundary portion between an edge portion 13 and a lens portion 14
of the lens, where a level difference is provided on the curved
surface constituting the lens portion 14 or a first-order
derivative become discontinuous, is determined as an outer edge of
each lens surface.
[0052] Also, when the lens surface is formed as a diffraction
optical surface, the diffraction optical surface itself is removed
from determination of the outer diameter d.sub.1 (d.sub.1') of the
lens surface. In this case, as shown in FIG. 3, a hypothetical
curved surface (indicated with a chain double-dashed line) that
constitutes an aspheric (or spherical) shape serving as a base of
the diffractive optical surface 15 is considered in determining the
outer diameter d.sub.1 (d.sub.1').
[0053] Also, it is requested as conditions that in the
d.sub.1-d.sub.0 section (d.sub.1'-d.sub.0' section), no level
difference is formed on the aspheric surface (or spherical surface)
that is the base in the direction along which the optical axis Z
extends and also the first-order derivative is continuous.
[0054] Meanwhile, the recent demand for size reduction of mobile
devices such as a cellular phone, etc. is very strong. According to
this demand, an outer diameter of 5 mm or less is going to become
the mainstream of the outer diameter of the lens surface of the
imaging lens. Further, the demand for the outer diameter of 1 mm or
less becomes stronger. However, in the case of such micro lens, the
transferability of the mold in the peripheral portion becomes
extremely bad even when various technologies in the related art are
employed. Therefore, the molded lens 4 of this embodiment is
particularly effective to the case where this lens 4 is applied to
the micro lens that satisfies the following conditional expressions
(3), (3').
d.sub.0.ltoreq.1.00 mm (3)
d.sub.0'.ltoreq.1.00 mm (3')
[0055] Next, out of the molded lenses according to the embodiments
that can satisfy the conditional expression (1), Example 1, Example
2 as the best type, and their advantages of getting size reduction
will be explained specifically hereunder while using data.
Example 1
[0056] The molded lens according to Example 1 of the invention was
formed by molding plastic material using the injection molding
mold. As shown in FIG. 1, this molded lens was formed of a single
lens L.sub.1, and also a surface of the lens L.sub.1 on the light
source side (third surface) and a surface of the lens L.sub.1 on
the image surface side (fourth surface) were formed into an
aspheric shape.
[0057] Here, these aspheric surfaces are given by following
aspheric formula.
Z = C Y 2 1 + 1 - K C 2 Y 2 + A 2 Y 4 + A 3 Y 6 + A 4 Y 8 + A 5 Y
10 ( 4 ) ##EQU00001## [0058] Where Z: a length of perpendicular
from a point on an aspheric surface at a height Y from an optical
axis to a tangent plane (a plane perpendicular to the optical axis)
of an aspheric vertex [0059] C: reciprocal of a radius of curvature
R of the aspheric surface near the optical axis [0060] Y: height
from the optical axis [0061] K: eccentricity [0062] A.sub.2,
A.sub.3, A.sub.4, A.sub.5: fourth, sixth, eighth, and tenth-order
aspheric coefficients
[0063] Also, respective numerical values concerning the optical
system (corresponding to FIG. 1. A first surface and a second
surface correspond to a beam incident plane and a beam output plane
of the cover glass 2, respectively) using the molded lens 4
according to this Example 1 are given in the following table 1.
[0064] In the middle stage of the table 1, a radius of curvature R
(mm) of each optical surface, a surface separation D (mm) on the
optical axis Z, and a refractive index N in the used wavelength of
each lens are shown. Here, numbers in the table denote the order of
surfaces from the light source side.
[0065] Also, in the upper stage of the table 1, the working
conditions of the molded lens 4, i.e., a wavelength of the used
light, a used magnification, and a numerical aperture NA are
shown.
[0066] Also, in the lower stage of the table 1, a paraxial
curvature C of the aspheric surface and constants K, A.sub.2,
A.sub.3, A.sub.4, A.sub.5 indicated in the above aspheric formula
are shown.
TABLE-US-00001 TABLE 1 Used wavelength 650 nm Used magnification
-1/6.0 NA 0.60 Surface Number R D Refractive Index 1 .infin. 4.705
1.45654 2 .infin. 0.200 1.00000 3 Aspheric 0.440 1.50591 4 Aspheric
Aspheric Coefficient 3rd surface 4th surface C 2.8317669 -1.5117021
K 0.0000000 0.0000000 A.sub.2 .sup. 4.2511270 .times. 10.sup.-1
4.1361891 A.sub.3 4.0881268 -1.7621811 .times. 10 A.sub.4
-1.0828489 .times. 10 3.0403595 .times. 10 A.sub.5 -6.8160253
-1.3579028
[0067] Also, in the table 2, the effective aperture of the lens
surface and the outer diameter of the lens surface of the surface
on the light source side (third surface) and the surface on the
recording face side (fourth surface) in the molded lens 4 according
to this Example are shown.
TABLE-US-00002 TABLE 2 Effective Aperture of Lens Surface Third
surface .phi.0.78 mm Fourth surface .phi.0.68 mm Outer Diameter of
Lens Surface Third surface .phi.0.84 mm Fourth surface .phi.0.74
mm
[0068] FIG. 4 shows interference fringes in a state of transmitted
wavefronts in the molded lens according to Example 1. A full field
range was set to just coincide with the effective aperture.
[0069] According to the molded lens of this Example, it is apparent
from FIG. 4 that a good state of transmitted wavefronts can be
brought about over the full range of the effective aperture.
Example 2
[0070] Like Example 1, the molded lens according to Example 2 of
the invention was formed by molding the plastic material using the
injection molding mold. As shown in FIG. 5, this molded lens was
formed of a single lens 4, and also a surface of the lens 4 on the
light source side (first surface) and a surface of the lens 4 on
the image surface side (second surface) were formed into the
aspheric shape. Here, reference symbols in FIG. 5 correspond to
those of Example 1 shown in FIG. 2 (this is also true of Example 3
in FIG. 8).
[0071] Here, these aspheric surfaces are given by above aspheric
formula.
[0072] Also, respective numerical values concerning the molded lens
4 according to this Example 2 are shown in the following table
3.
[0073] In the middle stage of the table 3, a radius of curvature R
(mm) of each optical surface, a surface separation D (mm) on the
optical axis Z, and a refractive index N in the used wavelength of
each lens are given. Here, the numbers in this stage denote the
order of surfaces from the light source side.
[0074] Also, in the upper stage of the table 3, the working
conditions of the molded lens 4, i.e., a wavelength of the used
light (used wavelength), a used magnification, and a numerical
aperture NA are given.
[0075] Also, in the lower stage of the table 3, a paraxial
curvature C of the aspheric surface and constants K, A.sub.2,
A.sub.3, A.sub.4, A.sub.5 indicated in the above aspheric formula
are shown.
TABLE-US-00003 TABLE 3 Used wavelength 632.8 nm Used magnification
0 (infinite conjugate) NA 0.49 Surface Number R D Refractive Index
1 Aspheric 2.20 1.59869 2 Aspheric 1.00000 Aspheric Coefficient 1st
surface 2nd surface C 0.4657700 -0.0582414 K 0.0000000 0.0000000
A.sub.2 6.7556608 .times. 10.sup.-3 1.2820990 .times. 10.sup.-2
A.sub.3 1.3804821 .times. 10.sup.-4 -7.8661655 .times. 10.sup.-3
A.sub.4 -3.0027569 .times. 10.sup.-5 3.9259256 .times. 10.sup.-3
A.sub.5 1.8998577 .times. 10.sup.-5 -7.7682430 .times.
10.sup.-4
[0076] Also, in table 4, the effective aperture of the lens surface
and the outer diameter of the lens surface of the surface on the
light source side (first surface) and the surface on the recording
face side (second surface) in the molded lens 4 according to this
Example are shown.
TABLE-US-00004 TABLE 4 Effective Aperture of Lens Surface First
surface .phi.3.27 mm Second surface .phi.2.34 mm Outer Diameter of
Lens Surface First surface .phi.3.31 mm Second surface .phi.2.90
mm
[0077] In the above Examples 1, 2, the molded lens formed by the
injection molding method is explained. The molded lens of the
invention is not limited to these molded lenses. For example, as
shown in the following Example 3, the invention may be applied to
molded lens formed by the compression molding method.
Example 3
[0078] FIG. 7 is a view showing the configuration of an optical
system of an optical recording device using a molded lens according
to Example 3 of the invention. FIG. 8 is an enlarged view showing
the molded lens according to Example 3.
[0079] The device shown in FIG. 7 is constructed substantially
similarly to the configuration of the optical system of the optical
recording device using the molded lens according to the above
Example 1 shown in FIG. 1. Therefore, the same reference symbols
are assigned to the respective portions corresponding to those in
FIG. 1, and their detailed explanation will be omitted herein.
[0080] The molded lens according to Example 3 of the invention was
formed by molding a glass material using the compression molding
mold. As shown in FIG. 7, this molded lens was formed of a single
lens L.sub.1, and also a surface of the lens L.sub.1 on the light
source side (third surface) and a surface of the lens L.sub.1 on
the image surface side (fourth surface) were formed into an
aspheric shape.
[0081] Here, these aspheric surfaces are given by the above
aspheric formula.
[0082] In the middle stage of table 5, a radius of curvature R (mm)
of each optical surface, a surface separation D (mm) on the optical
axis Z, and a refractive index N in the used wavelength of each
lens are shown. Here, numbers in this stage denote the order of
surfaces from the light source side.
[0083] Also, in the upper stage of the table 5, the working
conditions of the molded lens 4, i.e., a wavelength of the used
light (used wavelength), a used magnification, and a numerical
aperture NA are shown.
[0084] Also, in the lower stage of the table 5, a paraxial
curvature C of the aspheric surface and constants K, A.sub.2,
A.sub.3, A.sub.4, A.sub.5 indicated in the above aspheric formula
are shown.
TABLE-US-00005 TABLE 5 Used wavelength 650 nm Used magnification
-1/6.0 NA 0.61 Surface Number R D Refractive Index 1 .infin. 4.705
1.45654 2 .infin. 0.200 1.00000 3 Aspheric 0.410 1.58537 4 Aspheric
Aspheric Coefficient 3rd surface 4th surface C 2.6553553 -0.9506208
K 0.0000000 0.0000000 A.sub.2 3.3491933 .times. 10.sup.-1 1.4246892
A.sub.3 2.7136608 .times. 10.sup.-1 -2.7744714 A.sub.4 5.0482746
.times. 10.sup.-2 -3.5195348 .times. 10.sup.-2 A.sub.5 5.4545204
.times. 10.sup.-5 -3.3333837 .times. 10.sup.-5
[0085] Also, in table 6, the effective aperture of the lens surface
and the outer diameter of the lens surface of the surface on the
light source side (third surface) and the surface on the recording
face side (fourth surface) in the molded lens 4 according to this
Example are shown.
TABLE-US-00006 TABLE 6 Effective Aperture of Lens Surface Third
surface .phi.0.79 mm Fourth surface .phi.0.69 mm Outer Diameter of
Lens Surface Third surface .phi.0.84 mm Fourth surface .phi.0.73
mm
[0086] Here, as the molded lens of the invention, the above lens
made of the plastic material or the glass material can be employed
adequately. For example, advantages such as cost reduction, weight
reduction, and the like can be achieved by using the plastic
material as the molded lens forming material. Also, environment
resistance performances (temperature characteristics, humidity
characteristics, etc.) can be improved by using the glass material
as the molded lens forming material.
[0087] In the above Examples, the both surfaces of the molded lens
having the aspheric surface are explained. However, surfaces of the
molded lens may be formed into the spherical surface or formed with
a diffractive optical surface. Of course, the surfaces of the
molded lens may be formed into mutually different type surfaces.
For example, one surface of the both surfaces is formed into the
spherical surface, and the other surface is formed into the
aspheric surface.
<Performance Verification 1>
[0088] In the molded lens 4 of the above Example 2, the
interference fringe image in the outer peripheral portion, as shown
in FIG. 6, was observed. Here, a full field range of this
interference fringe image was set to just coincide with the outer
diameter of the lens surface. From this observation, a pulse-like
disturbance of wavefront was found on the slightly inner side from
the outer diameter. It may be considered that this disturbance of
wavefront was caused due to transferring of the mold was made
insufficiently. The disturbance of wavefront was caused in a
position of about .phi.3.277 mm of the lens surface, and was
located about 0.0165 mm inner than the outer diameter (.phi.3.31
mm) of the lens.
[0089] Therefore, like the molded lens of this embodiment, if a
difference between the outer diameter of each lens surface and the
effective aperture of each lens surface is set to be equal to or
larger than 0.04 mm, this disturbance of wavefront is located on
the outside of the effective aperture. As a result, it is apparent
that desired refracting action can be exerted in the overall
effective aperture of each lens surface.
[0090] Also, in table 7, when an injection pressure and a mold
clamping force applied to the molded lens 4 in the injection
molding method in the Example 2 were varied to high (strong),
middle, and low (weak) respectively, evaluations of three
conditions are shown in four grades respectively. The three
conditions include whether or not the transferability
(transferability for
0.04.ltoreq.d.sub.1-d.sub.0(d.sub.1'-d.sub.0')) in the peripheral
portion of the effective aperture of the lens surface represented
by 0.04.ltoreq.d.sub.1-d.sub.0(d.sub.1'-d.sub.0') is good (first
condition), whether or not no burr occurs (second condition), and
whether or not air vent is ensured (third condition). Also, in the
table 7, the transferability (transferability for
d.sub.1-d.sub.0(d.sub.1'-d.sub.0')<0.04) in the peripheral
portion of the effective aperture of the lens surface represented
by d.sub.1-d.sub.0 (d.sub.1'-d.sub.0')<0.04 was given (the same
is true in Table 8).
[0091] Also, the "air vent" means escape of an internal air when
the mold is clamped. As described above, if internal air cannot
vent to some extent when the mold is clamped, the transferability
becomes worse due to the presence of such air. Therefore, this air
vent constitutes an important condition in evaluating the
transferability.
[0092] Also, the mold clamping force is determined depending on
size of the lens to be molded. For example, when a "middle"
pressure was assumed to 1, a "low" pressure and a "high" pressure
were set to about 0.75 and 1.25, respectively.
[0093] As a result, the combination of "the `middle` injection
pressure and the `middle` mold clamping force" and the combination
of "the `low` injection pressure and the `low` mold clamping force"
were not determined as "bad x" or "baddish .DELTA." in any of the
estimations of the three conditions. Thus, it became apparent that
preferably the injection molding process is performed with either
of these two combinations.
TABLE-US-00007 TABLE 7 Injection molding Injection pressure High
High High Mid Mid Mid Low Low Low Mold clamping pressure High Mid
Low High Mid Low High Mid Low Transferability for d.sub.1 - d.sub.0
< 0.04 X .DELTA. .largecircle. X X .DELTA. X X X Transferability
for 0.04 .ltoreq. d.sub.1 - d.sub.0 .DELTA. .circleincircle.
.circleincircle. .DELTA. .circleincircle. .circleincircle. X
.DELTA. .largecircle. Occurrence of burr .largecircle. .DELTA. X
.circleincircle. .largecircle. .DELTA. .circleincircle.
.circleincircle. .largecircle. Air vent .DELTA. .DELTA.
.largecircle. .DELTA. .largecircle. .circleincircle. X .DELTA.
.largecircle. .circleincircle. Good .largecircle. Fair .DELTA.
Baddish X Bad
<Performance Verification 2>
[0094] Also, in Table 8, when a molding pressure at a high
temperature and a molding pressure at a time of cooling applied to
the molded lens 4 in the compression molding method in Example 3
were varied to high, middle, and low, evaluations of two conditions
are shown in four grades, respectively. The two conditions include
whether or not the transferability (transferability for
0.04.ltoreq.d.sub.1-d.sub.0) in the peripheral portion of the
effective aperture of the lens surface represented by
0.04.ltoreq.d.sub.1-d.sub.0 is good (first condition), and whether
or not no chip occurs in the peripheral portion of the lens (second
condition).
[0095] In the case of the compression molding, unlike the injection
molding, the molding pressure at a high temperature and the molding
pressure at a time of cooling have an influence upon the
transferability in the peripheral portion of the effective aperture
of the lens surface and the chip in the peripheral portion of the
lens. Therefore, these conditions constitute the important
conditions in evaluating the transferability of the mold.
[0096] Also, the molding pressure at a high temperature and the
molding pressure at a time of cooling are determined depending on
size of the lens to be molded. For example, when a "middle"
pressure was assumed to 1, a "low" pressure and a "high" pressure
were set to about 0.5 and 1.5, respectively.
[0097] As a result, the combination of "the `high` molding pressure
at a high temperature and the `low` molding pressure at a time of
cooling" and the combination of "the `middle` molding pressure at a
high temperature and the `middle` molding pressure at a time of
cooling" were not determined as "bad x" or "baddish .DELTA." in any
of the estimations of the two conditions could. Thus, it became
apparent that preferably the compression molding process is
performed with either of these two combinations.
TABLE-US-00008 TABLE 8 Compression molding Molding pressure at high
temp. High High High Mid Mid Mid Low Low Low Molding pressure at
time of cooling High Mid Low High Mid Low High Mid Low
Transferability for d.sub.1 - d.sub.0 < 0.04 .largecircle.
.DELTA. .DELTA. .DELTA. .DELTA. X X X X Transferability for 0.04
.ltoreq. d.sub.1 - d.sub.0 .circleincircle. .circleincircle.
.largecircle. .largecircle. .largecircle. .DELTA. .DELTA. .DELTA. X
Chip in peripheral portion. X .DELTA. .largecircle. X .largecircle.
.largecircle. X .largecircle. .circleincircle. .circleincircle.
Good .largecircle. Fair .DELTA. Baddish X Bad
* * * * *