Optical fiber with lens

Details Optical fiber with lens Optical fiber with lens

1998-12-30

2001-10-09

Font, Frank G. (Department: 2877)

Optical waveguides

With optical coupler

Input/output coupler

Reexamination Certificate

active

06301406

ABSTRACT:

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 &mgr;m 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 &mgr;m (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 &thgr;1 and &thgr;2, 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 &thgr;1 and &thgr;2 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 &mgr;m. 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.


REFERENCES:
patent: 5256851 (1993-10-01), Presby
patent: 5416881 (1995-05-01), Ikeda
patent: 5446816 (1995-08-01), Shiraishi et al.
patent: 5455879 (1995-10-01), Modavis et al.
patent: 5566262 (1996-10-01), Yamane et al.
patent: 5845024 (1998-12-01), Tsushima et al.
patent: 5967653 (1999-10-01), Miller et al.
patent: 55-153384 (1980-11-01), None
patent: 61-256310 (1986-11-01), None
patent: 4-91302 (1992-03-01), None
patent: 6-67061 (1994-03-01), None

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