Information
-
Patent Grant
-
6301406
-
Patent Number
6,301,406
-
Date Filed
Wednesday, December 30, 199826 years ago
-
Date Issued
Tuesday, October 9, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Font; Frank G.
- Lauchman; Layla
Agents
- Frishauf, Holtz, Goodman, Langer & Chick, P.C.
-
CPC
-
US Classifications
Field of Search
US
- 385 33
- 385 79
- 385 61
- 385 88
-
International Classifications
-
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.
Description
TECHNICAL FIELD
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
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
2
a
and a spherical portion
2
b
inscribed in the hyperboloidal portion
2
a
. The optical fiber
1
having the lens
2
of this form has a high efficiency of optical coupling with a light source. For a laser diode having a generating wavelength of 0.98 μm at the center, the maximum optical coupling efficiency can be obtained when a radius R of the spherical portion
2
b
inscribed in the hyperboloidal portion
2
a
is generally 1.5 to 5 μm (see U.S. Pat. No. 5,256,851).
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
12
a
and
12
b
with different angles of θ1 and θ2, respectively (see U.S. Pat. No. 5,455,879). An optical fiber
11
having a lens
12
of the form shown in
FIG. 5
also exhibits a high optical coupling efficiency.
However, the aforementioned lensed optical fibers have the following problems:
1) For the lens
2
of the first form shown in
FIG. 4
, the hyperboloidal portion
2
a
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
2
a
with high reproducibility, so that the yield decreases. Also, the optical coupling efficiency varies in a sensitive manner depending on the diameter of the spherical portion
2
b
, which also results in a decrease in yield.
For the lens
2
of the first form, morever, it is difficult to accurately determine the boundary between the hyperboloidal portion
2
a
and the spherical portion
2
b
when the radius of the spherical portion
2
b
inscribed in the hyperboloidal portion
2
a
is measured. Therefore, the lens
2
of this form presents a problem in that inspection of the external form takes much time.
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
12
a
and
12
b
with different angles of θ1 and θ2 are formed, the fabrication takes much time, and the reproducibility of form and increase in yield are limited.
Accordingly, an object of the present invention is to provide a lensed optical fiber which overcomes the 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 which can be fabricated with high fabrication accuracy and high yield.
DISCLOSURE OF THE INVENTION
The present invention has been made based on discoveries made as a result of earnest theoretical study of the conventional lensed optical fibers. 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.
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 simply formed by three planes, the lensed optical fiber can easily be fabricated with high accuracy and high yield. Also, inspection of the external form can be made easily.
Preferably, an angle between the slant portion and the plane portion is set at 110 to 170°, 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 μm. Thereby, the lensed optical fiber in accordance with the present invention achieves has an efficiency of 40% or higher of optical coupling with a light source.
BRIEF DESCRIPTION OF THE DRAWINGS
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;
FIG. 1B
is a side view of a tip end portion of the lensed optical fiber shown in
FIG. 1A
;
FIG. 2
is a view for illustrating the measurement of optical coupling efficiency of the above embodiment;
FIG. 3
is a characteristic diagram showing the relationship between an angle θ which a slant portion makes with a plane portion and the optical coupling efficiency for the above embodiment;
FIG. 4
is a perspective view of a conventional lensed optical fiber; and
FIG. 5
is a schematic view of another conventional lensed optical fiber.
BEST MODE OF CARRYING OUT THE INVENTION
An embodiment of the present invention will be described in detail with reference to the accompanying drawings.
FIG.
1
A 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
comprising of a wedge-shaped portion formed by two slant portions
24
which are 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
make with the plane portion
25
is taken as θ, and a distance between the two points at which the slant portions
24
and the plane portion
25
intersect with each other is taken as
2
d.
The aforementioned lensed optical fiber
20
was manufactured by a fabrication procedure as described below.
First, the tip end of the optical fiber
21
was cleaved to form the plane portion
25
which is perpendicular to the core axis Ac.
Next, the optical fiber
21
was polished while an angle between a flat plate polishing machine and the core axis Ac was kept at a desired angle (θ-90°) using a jig. By this polishing process, the tip end of the optical fiber
21
could be formed into wedge-shaped lens
26
.
As described above, the lensed optical fiber
20
of this embodiment can be manufactured by cleaving the tip end of the optical fiber to form the plane portion
25
and by polishing the slant portions
24
at the tip end of the optical fiber
21
by onetime angle control. For the lensed optical fiber
20
, therefore, the fabrication process is very simple, the yield is increased easily, and the fabrication cost is decreased.
For the lensed optical fiber
20
, the optical coupling efficiency was evaluated under the conditions shown in FIG.
2
.
A laser diode, for example, having a generating wavelength of 0.98 μm 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 μm and a minor axis length of 1.2 μm. 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 μm. 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 μm, and the minor axis direction of the mode field pattern of the light source
30
was made a direction perpendicular to the direction of a line connecting the two points at which the slant portions
24
and the plane portion
25
intersect with each other.
Under the above conditions, the efficiency of optical coupling with the light source
30
was evaluated by changing the angle θ between the slant portion
24
and the plane portion
25
with the distance between the two points at which the slant portions
24
and the plane portion
25
intersect with each other being used as a parameter.
The results are shown In
FIG. 3
, in which the abscissa represents (180−θ) and the ordinate represents the coupling efficiency.
Here, the optical coupling efficiency was obtained from P
2
/P
1
, where P
1
is the whole power of light emitted from the light source
30
, and P
2
is the power of light incident on the optical fiber.
As seen from
FIG. 3
, in the range of 1.0 to 4.0 μm of the distance 2d and 110 to 170° of the angle θ (in the figure, (180−θ)=10 to 70°), 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 μm and θ=140 to 150° ((180−θ)=30 to 40°), an optical coupling efficiency as high as 90% was obtained.
As a comparative example, the optical coupling efficiency of a lensed optical fiber whose tip end portion was not of a planar shape perpendicular to the core axis Ac but instead which had a lens
2
as shown in
FIG. 4
, was measured under the aforementioned conditions. In this case, an optical coupling efficiency of 97% at a maximum was obtained.
Thus, the lensed optical fiber of the present invention exhibits a high optical coupling efficiency which is by no means inferior to the comparative example. Considering the high workability of the present invention, an excellent lensed optical fiber which can be mass-produced at a low cost can be provided.
INDUSTRIAL APPLICABILITY
The present invention provides a lensed optical fiber which has a high optical coupling efficiency and which can be fabricated with high accuracy and high yield.
Claims
- 1. A lensed optical fiber comprising:an optical fiber having a core and a cladding, and a wedge shaped lens formed at a tip end of the optical fiber, wherein said wedge shaped lens comprises two slant portions that are symmetrical with respect to an axis of said core, and a plane portion that intersects with said slant portions and that is perpendicular to the axis of said core.
- 2. A lensed optical fiber according to claim 1, wherein an angle between each said slant portion and said plane portion is in a range of 110 to 170°, and a distance between two points at which said slant portions and said plane portion intersect with each other is 1 to 4 μm.
Priority Claims (1)
Number |
Date |
Country |
Kind |
9-116812 |
May 1997 |
JP |
|
PCT Information
Filing Document |
Filing Date |
Country |
Kind |
102e Date |
371c Date |
PCT/JP98/01730 |
|
WO |
00 |
12/30/1998 |
12/30/1998 |
Publishing Document |
Publishing Date |
Country |
Kind |
WO98/50808 |
11/12/1998 |
WO |
A |
US Referenced Citations (7)
Foreign Referenced Citations (4)
Number |
Date |
Country |
55-153384 |
Nov 1980 |
JP |
61-256310 |
Nov 1986 |
JP |
4-91302 |
Mar 1992 |
JP |
6-67061 |
Mar 1994 |
JP |