U.S. patent application number 09/769689 was filed with the patent office on 2001-08-09 for lensed optical fiber.
This patent application is currently assigned to THE FURUKAWA ELECTRIC CO., LTD. Invention is credited to Irie, Yuichiro, Kimura, Toshio, Shimizu, Takeo.
Application Number | 20010012425 09/769689 |
Document ID | / |
Family ID | 14696264 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010012425 |
Kind Code |
A1 |
Irie, Yuichiro ; et
al. |
August 9, 2001 |
Lensed optical fiber
Abstract
There is provided a lensed optical fiber (20) in which a lens is
formed on the end face of an optical fiber to enhance the
efficiency of optical coupling with a light beam. The tip end
portion of an optical fiber (21) is formed with a lens (26) formed
into a wedge shape having two slant portions (24) symmetrical with
respect to an axis (Ac) of a core (22) and a plane portion (25)
perpendicular to the axis of the core.
Inventors: |
Irie, Yuichiro;
(Ichihara-shi, JP) ; Kimura, Toshio;
(Ichihara-shi, JP) ; Shimizu, Takeo;
(Fujisawa-shi, JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN, LANGER & CHICK, P.C.
25th Floor
767 Third Avenue
New York
NY
10017-2023
US
|
Assignee: |
THE FURUKAWA ELECTRIC CO.,
LTD
|
Family ID: |
14696264 |
Appl. No.: |
09/769689 |
Filed: |
January 25, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09769689 |
Jan 25, 2001 |
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09214202 |
Dec 30, 1998 |
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09214202 |
Dec 30, 1998 |
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PCT/JP98/01730 |
Apr 16, 1998 |
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Current U.S.
Class: |
385/33 |
Current CPC
Class: |
G02B 6/4203
20130101 |
Class at
Publication: |
385/33 |
International
Class: |
G02B 006/32 |
Foreign Application Data
Date |
Code |
Application Number |
May 7, 1997 |
JP |
9-116812 |
Claims
1. A lensed optical fiber in which a lens is formed at the tip end
of an optical fiber having a core and a cladding, characterized in
that said lens is formed into a wedge shape having two slant
portions symmetrical with respect to an axis of said core and a
plane portion perpendicular to the axis of said core.
2. A lensed optical fiber according to claim 1, wherein an angle
between said slant portion and said plane portion is 110 to
170.degree., and the distance between two intersecting lines on
which said slant portion and said plane portion intersect with each
other is 1 to 4 .mu.m.
Description
TECHNICAL FIELD
[0001] The present invention relates to a lensed optical fiber in
which a lens is formed on the end face of an optical fiber to
enhance the efficiency of optical coupling with a light beam.
BACKGROUND ART
[0002] In order to enhance the efficiency of optical coupling of a
light beam from a light source such as a laser diode device with an
optical fiber, there has been used a lensed optical fiber in which
a lens is formed on the end face of an optical fiber. For example,
as shown in FIG. 4, a lens 2 formed on the end face of an optical
fiber 1 has an external form consisting of a hyperboloidal portion
2a and a spherical portion 2b inscribed in the hyperboloidal
portion 2a. The optical fiber 1 having the lens 2 of this form has
a high efficiency of optical coupling with a light source. For
laser diode having a generating wavelength of 0.98 .mu.m at the
center, the maximum optical coupling efficiency can be obtained
when a radius R of the spherical portion 2b inscribed in the
hyperboloidal portion 2a is generally 1.5 to 5 .mu.m (see U.S. Pat.
No. 5,256,851).
[0003] As shown in FIG. 5, there also has been proposed an optical
fiber having a lens 12 of a wedge-shaped external form having
two-stage tapered portions 12a and 12b with different angles of
.theta.1 and .theta.2, respectively (see U.S. Pat. No. 5,455,879).
An optical fiber 11 having a lens 12 of a form shown in FIG. 5 also
exhibits a high optical coupling efficiency.
[0004] However, the aforementioned lensed optical fibers have the
following problems:
[0005] 1) For the lens 2 of the first form shown in FIG. 4, the
hyperboloidal portion 2a is formed by being polished using a flat
plate polishing machine while the angle between the optical fiber
and the polishing machine is adjusted. Therefore, for the lens 2 of
the first form, it is difficult to fabricate the hyperboloidal
portion 2a with high reproducibility, so that the yield decreases.
Also, the optical coupling efficiency varies sensitively depending
on the diameter of the spherical portion 2b, which also results in
a decrease in yield.
[0006] For the lens 2 of this form, it is difficult to accurately
determine the boundary between the hyperboloidal portion 2a and the
spherical portion 2b when the radius of the spherical portion 2b
inscribed in the hyperboloidal portion 2a is measured. Therefore,
the lens 2 of this form presents a problem in that the inspection
for external form takes much time.
[0007] 2) The lens 12 of the second form shown in FIG. 5 is
polished while the angle between the optical fiber 11 and the
polishing machine is kept constant. Therefore, the lens 12 of the
second form can be fabricated more easily than the lens 2 of the
first form. However, for the lens 12 of the second form, because
two-stage tapered portions 12a and 12b with different angles of
.theta.1 and .theta.2 are formed, the fabrication takes much time,
and the reproducibility of form and increase in yield are
limited.
[0008] Accordingly, an object of the present invention is to
provide a lensed optical fiber which has no aforementioned
drawbacks of the conventional lensed optical fibers and, more
specifically, to provide a lensed optical fiber which has a high
efficiency of optical coupling with a light source, and can be
fabricated with high fabrication accuracy and high yield.
DISCLOSURE OF THE INVENTION
[0009] The present invention has been made based on a new knowledge
obtained as a result of earnest theoretical study of the
conventional lensed optical fiber. The present invention provides a
lensed optical fiber in which a lens is formed at the tip end of an
optical fiber having a core and a cladding, characterized in that
the lens is formed into a wedge shape having two slant portions
symmetrical with respect to an axis of the core and a plane portion
perpendicular to the axis of the core.
[0010] The lensed optical fiber having the tip end portion of the
aforementioned shape has a high optical coupling efficiency. Also,
since the shape of this tip end portion is a simple one formed by
three planes, the lensed optical fiber can easily be fabricated
with high accuracy and high yield. Also, the inspection for
external form can be made easily.
[0011] Preferably, an angle between the slant portion and the plane
portion is set at 110 to 170.degree., and the distance between two
intersecting lines on which the slant portion and the plane portion
intersect with each other is set at 1 to 4 .mu.m. Thereby, the
lensed optical fiber in accordance with the present invention
preferably has an efficiency of 40% or higher of optical coupling
with a light source.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1A is a front view of a tip end portion of one
embodiment of a lensed optical fiber in accordance with the present
invention;
[0013] FIG. 1B is a side view of a tip end portion of the lensed
optical fiber shown in FIG. 1A;
[0014] FIG. 2 is a view for illustrating the measurement of optical
coupling efficiency of the above embodiment;
[0015] FIG. 3 is a characteristic diagram showing the relationship
between an angle .theta. which a slant portion makes with a plane
portion and the optical coupling efficiency for the above
embodiment;
[0016] FIG. 4 is a perspective view of a conventional lensed
optical fiber; and
[0017] FIG. 5 is a schematic view of another conventional lensed
optical fiber.
BEST MODE OF CARRYING OUT THE INVENTION
[0018] An embodiment of the present invention will be described in
detail with reference to the accompanying drawings.
[0019] FIG. 1A and FIG. 1B are a front view and a side view,
respectively, of a tip end portion of one embodiment of a lensed
optical fiber 20 in accordance with the present invention. In the
figures, an optical fiber 21 has a core 22 with a circular
cross-sectional shape and a cladding 23. The tip end portion of the
optical fiber 21 is formed with a lens 26 consisting of a
wedge-shaped portion formed by two slant portions 24 which is
symmetrical with respect to a core axis Ac and a plane portion 25
which is perpendicular to the core axis Ac. An angle which the
slant portion 24 makes with the plane portion 25 is taken as
.theta., and a distance between two intersecting lines on which the
slant portion 24 and the plane portion 25 intersect with each other
is taken as 2d.
[0020] The aforementioned lensed optical fiber 20 was manufactured
by a fabrication procedure as described below.
[0021] First, the tip end of the optical fiber 21 was cleaved to
form the plane portion 25 which was perpendicular to the core axis
Ac.
[0022] Next, the optical fiber 21 was polished while an angle
between a flat plate polishing machine and the core axis Ac is kept
at a desired angle (.theta.-90.degree.) using a jig. By this
polishing process, the tip end of the optical fiber 21 could be
made the wedge-shaped lens 26.
[0023] As described above, the lensed optical fiber 20 of this
embodiment can be manufactured by cleaving the tip end into the
plane portion 25 and by polishing the slant portion 24 at the tip
end of the optical fiber 21 by onetime angle control. For the
lensed optical fiber 20, therefore, the fabrication process was
very simple, the yield was increased easily, and the fabrication
cost was decreased.
[0024] For the lensed optical fiber 20, the optical coupling
efficiency was evaluated under the conditions shown in FIG. 2.
[0025] A laser diode, for example, having a generating wavelength
of 0.98 .mu.m at the center was used as a light source 30, and the
intensity distribution (mode field) pattern of emitted light from
the light source 30 was made an ellipse having a major axis of 4.8
.mu.m and a minor axis length of 1.2 .mu.m. Also, the mode field
pattern of the optical fiber 21 constituting the lensed optical
fiber 20 was made a circle having a diameter of 6.0 .mu.m. Here,
the distance between the light source 30 and the lensed optical
fiber 20 was made the optimum distance at which the highest optical
coupling efficiency can be obtained, for example, 10 .mu.m, and the
minor axis direction of the mode field pattern of the light source
30 was made a direction perpendicular to the direction of the
intersecting line on which the slant portion 24 and the plane
portion 25 intersect with each other.
[0026] Under the above conditions, the efficiency of optical
coupling with the light source 30 was evaluated by changing the
angle .theta. between the slant portion 24 and the plane portion 25
with the distance between two intersecting lines on which the slant
portion 24 and the plane portion 25 intersect with each other being
used as a parameter.
[0027] The results are shown in FIG. 3, in which the abscissa
represents (180-.theta.) and the ordinate represents the coupling
efficiency.
[0028] Here, the optical coupling efficiency was obtained from
P2/P1, where P1 is the whole power of light emitted from the light
source 30, and P2 is the power of light incident on the optical
fiber.
[0029] As seen from FIG. 3, in the range of 1.0 to 4.0 .mu.m of the
distance 2d and 110 to 170.degree. of the angle .theta. (in the
figure, (180-.theta.)=10 to 70.degree.), an efficiency of 40% or
higher of optical coupling with the light source 30 was obtained.
In particular, in the case where 2d=2.0 .mu.m and .theta.=140 to
150.degree. ((180-.theta.)=30 to 40.degree.), an optical coupling
efficiency as high as 90% was obtained.
[0030] As a comparative example, the optical coupling efficiency of
a lensed optical fiber, in which the tip end portion is not of a
planar shape perpendicular to the core axis Ac and a lens 2 shown
in FIG. 4 is formed, was measured under the aforementioned
conditions. As a result, an optical coupling efficiency of 97% at a
maximum was obtained.
[0031] Thus, the lensed optical fiber of this embodiment exhibits a
high optical coupling efficiency which is by no means inferior to
the comparative example. Considering the high workability, an
excellent lensed optical fiber which can be mass-produced at a low
cost can be provided.
INDUSTRIAL APPLICABILITY
[0032] The present invention offers an excellent effect that there
can be obtained a lensed optical fiber which has a high optical
coupling efficiency and can be fabricated with high accuracy and
high yield.
* * * * *