Optical: systems and elements – Lens – With light limiting or controlling means
Reexamination Certificate
2000-01-04
2002-03-12
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With light limiting or controlling means
C359S718000, C359S714000, C264S001100
Reexamination Certificate
active
06356398
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lens having a diaphragm for converging a collimated light beam and an optical unit which utilizes an optical system using the lens and using a collimated light beam. For example, the invention is concerned with a lens suitable for use in a magneto-optic disk unit for recording and reproducing information to and from a magneto-optic disk or in an optical communication system.
2. Description of the Prior Art
A conventional optical unit which utilizes an optical system using a collimated light beam will now be described with reference to an optical communication system as an example. An optical communication system is known in which a signal is subjected to photoelectric conversion, a corresponding light beam is emitted from a laser diode and is collimated by a collimator lens, and the thus-collimated beam is converged on an end face of an optical fiber. As another conventional optical unit there is known an optical head unit which performs information recording and reproducing operations for a magneto-optic disk (a recording medium) and in which a diaphragm mechanism for restricting the beam diameter is attached to an objective lens which is for converging a laser beam as a beam spot onto a recording/reproducing side of the recording medium.
Now, with reference to
FIG. 5
, the following description is provided about a lens having a diaphragm structure in a conventional optical unit.
FIG. 5
is a sectional view showing a conventional lens. As shown in the same figure, a lens
11
(for example an objective lens) is a circular convex lens obtained by molding a transparent optical material capable of being molded such as glass or plastic material.
The lens
11
is provided with a central incident lens portion
12
projecting outward (upward) in a generally semispherical shape, an exit lens portion
13
projecting in a generally circular shape outward (downward) on the side opposite to the incident lens portion
12
, and an annular flange portion
14
provided along outer edges of the incident lens portion
12
and the exit lens portion
13
.
The flange portion
14
has an incident surface
14
a
located on the incident lens portion
12
side and an exit surface
14
b
located on the exit lens portion
13
side. The incident surface
14
a
and the exit surface
14
b
are parallel to each other and perpendicular to an optical axis of the lens
11
.
The flange portion
14
thus formed perpendicularly to the optical axis of the lens
11
exhibits a diaphragm function for the lens
11
.
The operation of the conventional lens will be described below on the basis of the optical unit.
An incident light beam A (laser beam) is applied at a predetermined beam diameter and in parallel with the optical axis of the lens
11
from a laser beam source (not shown) disposed on the incident lens portion
12
side of the lens
11
(for example an objective lens). A portion of the parallel incident beam A incident on the incident lens portion
12
is converted as a beam spot by both incident and exit lens portions
12
,
13
. The beam spot is focused on a recording medium (not shown) and is reflected by the recording medium. The reflected beam passes through the lens
11
and is detected by a photodetector (not shown) disposed on the incident lens portion
12
side.
On the other hand, a portion of the parallel incident beam A is incident on the flange portion
14
and is partially reflected by the incident surface
14
a
of the flange portion. The thus-reflected incident beam portion returns in parallel with the optical axis of the lens
11
, that is, along the incident optical axis. A portion of the incident beam A passes through the incident surface
14
a
and is not converged as a beam spot. Thus, the flange portion
14
functions as a diaphragm mechanism.
In the conventional lens
11
, as described above, since the diaphragm mechanism is constituted of the incident surface
14
a
of the flange portion
14
which is formed so as to intersect the incident optical axis perpendicularly, a portion of the beam incident on the incident surface
14
a
is reflected by the same surface and returns to the incident beam side. This undesirable reflected beam joins the information-carrying return beam reflected from the recording medium and is converged on the light receiving surface of the photodetector. Once the reflected beam returned from the incident surface
14
a
is detected by the photodetector, there arises noise and thus the return beam from the recording medium can no longer be detected with a high accuracy, with consequent occurrence of a detection error.
In an optical communication system using the conventional lens, the undesirable beam reflected by the incident surface
14
a
as a diaphragm portion becomes a return beam to the laser diode, giving rise to the problem that there occurs an output variation or a wavelength variation of the laser beam.
In a lens having a diaphragm structure, this problem may be solved by forming a reflection preventing film on an outer edge portion of the lens or by roughening (matting) an incident surface to scatter an incident light beam. However, for forming a reflection preventing film or a matted surface for the flange portion of the lens, it is necessary to provide separate such film or surface forming steps for the flange portion and an effective lens portion (masking is required in an alternate manner) or it is necessary to hold a side face of the lens flange portion with a jig.
No matter which method may be adopted for the formation of such reflection preventing film or matted surface, an increase of the manufacturing cost is unavoidable due to an increase in the number of steps or due to the provision of a special jig.
Besides, it is impossible to form the flange portion small because an allowance for machining is required in forming the reflection preventing film or matted surface. Consequently, the lens becomes larger in diameter and it is therefore impossible to reduce the size and weight of the optical unit.
SUMMARY OF THE INVENTION
The present invention has been accomplished for solving the above-mentioned problems and it is an object of the invention to provide a lens with a diaphragm capable of being fabricated easily and capable of diminishing the influence of an undesirable return light, as well as an optical unit using the lens which optical unit can be reduced in size and weight.
According to the present invention there is provided a lens for converging a collimated incident light and outputting the resulting converged light, the lens having a diaphragm structure at an outer edge portion of an incident side thereof, said diaphragm structure being constructed in such a manner that a portion of the collimated incident light is reflected and the reflected light advances away from or toward an optical axis of the collimated light.
In the lens of the present invention, the diaphragm structure has a collimated light incident surface which is an arcuate surface or an inclined surface.
According to the present invention there also is provided an optical unit using a lens for converging a collimated incident light and outputting the resulting converged light, the lens having a diaphragm structure at an outer edge portion of an incident side thereof, the diaphragm structure being constructed in such manner that a portion of the collimated incident light is reflected and the reflected light advances away from or toward an optical axis of the collimated light.
REFERENCES:
patent: 5339123 (1994-08-01), Soshi et al.
patent: 5699201 (1997-12-01), Lee
patent: 6052233 (2000-04-01), Koike
patent: 6144500 (2000-11-01), Iwaki et al.
patent: 6172944 (2001-01-01), Hatam-Tabrizi
patent: 10-208273 (1998-08-01), None
Kikuchi Kimihiro
Otsuki Motohiko
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Epps Georgia
Thompson Tim
LandOfFree
Lens having diaphragm structure at outer edge portion on... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Lens having diaphragm structure at outer edge portion on..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Lens having diaphragm structure at outer edge portion on... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2816383