Optical fiber connector

Details Optical fiber connector Optical fiber connector

2002-01-23

2003-06-24

Nguyen, Khiem (Department: 2839)

Optical waveguides

With disengagable mechanical connector

Structure surrounding optical fiber-to-fiber connection

Reexamination Certificate

active

06582134

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical fiber connector for butt-splicing end surfaces of a pair of optical fibers.
2. Description of the Related Art
An MT type connector in
FIG. 7
is an example of a known optical fiber connector. As shown in
FIG. 7
, the MT type connector for multi-fiber connections includes a first resin plug
22
a
and a second resin plug
22
b
to which first optical fibers
21
a
(not shown) and second optical fibers
21
b
are fixed, respectively, a pair of guide holes (not shown) formed in the first plugs
22
a
, a pair of guide pins
23
mounted on the second plug
22
b
, and a flat metal clamp spring
24
. With this configuration, the end surfaces of the optical fibers
21
a
and
21
b
are exposed at the splicing side from the end surfaces of the corresponding plugs
22
a
and
22
b
and are polished. Then, the first and the second plugs
22
a
and
22
b
are coupled by fitting the pair of guide pins
23
into the corresponding guide holes, resulting in tight contact between the polished end surfaces of the optical fibers
21
a
and the corresponding optical fibers
21
b
. The clamp spring
24
is used for maintaining the connection between the first optical fibers
21
a
and the corresponding second optical fibers
21
b.
The MT type connector is capable of high-density mounting and has excellent optical characteristics. However, since it is difficult to form the end surfaces of the optical fibers
21
a
and
21
b
to have a spherical shape, a refractive index matching agent is used for filling the spaces between the opposing end surfaces of the optical fibers
21
a
and
21
b
so as to reduce the reflection at the spaces. Unfortunately, the refractive index matching agent is not always desirable because the refractive index of the refractive index matching agent is a function of temperature. That is, the refractive index of the refractive index matching agent is highly temperature dependent.
Furthermore, it has been pointed out that attaching and removing the clamp spring
24
used for maintaining the overall structure of the MT type connector as described above is troublesome.
A BF (Bare Fiber) connector is another example of a known optical fiber connector.
FIGS. 8A and 8B
, respectively, illustrate a state in which the connection is not yet performed and another state in which the connection is complete. The BF connector performs direct butt-splicing between the opposing end surfaces of a pair of optical fibers
31
without a refractive index matching agent.
The BF connector includes a pair of plugs
32
to which the pair of optical fibers
31
are fixed, and an adapter
33
for coupling the opposing plugs
32
. Furthermore, each plug
32
includes a holding portion
32
a
, disposed at the side opposite to the splicing side, for holding the corresponding optical fiber
31
in a cantilever fashion, and a hollow
32
b
formed therein, having an opening facing toward the mating plug
32
, to allow the corresponding optical fiber
31
to buckle. One of the optical fibers
31
fixed in the pair of plugs
32
protrudes by a predetermined distance L
1
from the end surface of the opening.
The adapter
33
is constructed so as to connect and fix the pair of plugs
32
inserted from the corresponding ends of the adapter
33
, and includes an aligner
34
disposed coaxially therewith. The aligner
34
includes an alignment hole referred to as a micro-hole
35
arranged coaxially therewith so as to receive and align the pair of optical fibers
31
which are fixed in the respective plugs
32
and which are inserted from the corresponding ends thereof. The micro-hole
35
supports the pair of optical fibers
31
inserted from the corresponding ends thereof. The optical fiber
31
protruding by the predetermined distance L
1
from the end of the opening of the corresponding plug
32
buckles in the corresponding hollow
32
b
, resulting in butt-splicing of the end surfaces of the pair of optical fibers
31
in the micro-hole
35
.
That is, a pushing force is generated in the buckled optical fiber
31
along the axial direction thereof and pushes the end surface thereof against the end surface of the mating optical fiber
31
, thus achieving a close contact between both end surfaces of the pair of optical fibers
31
without a refractive index matching agent. The buckling length L of the buckled optical fiber
31
is defined by the following equation:
L=
2&pgr;(
EI/P
)
½
where P represents a buckling force, and E and I represent the elastic modulus and the second moment of area of the optical fiber
31
, respectively.
Further, assuming that an X-axis and a Y-axis lie, respectively, along and perpendicular to the axial direction of the optical fiber
31
, a deflection y in the Y-axis direction along x in the X-axis is defined by the following equation:
y=&dgr;/
2{1−cos(2
&pgr;×/L
)}
where &dgr; represents the maximum deflection of the optical fiber
31
.
The radius of curvature R of the optical fiber
31
is determined by the following equation:
1
/R=y
″/(1
+y
′)
{fraction (3/2)}
Accordingly, the resulting buckling length L+&Dgr;L of the optical fiber
31
is defined by the following equation:
L+&Dgr;L=∫
0
L
{square root over ((1+(
y
′)
2
))}
dx
where &Dgr;L represents a buckling deformation of the optical fiber.
With these equations, the obtained radius of curvature R is about 6 mm when the buckling length L is 7 mm and the buckling deformation &Dgr;L is 50 &mgr;m.
The BF connectors have the following problems. The BF connector has the pair of hollows
32
b
formed in the respective plugs
32
and holds the pair of optical fibers
31
in a cantilever fashion. This configuration makes it difficult for the optical fibers
31
to be accurately aligned since the buckling directions of the optical fibers
31
are not determined in a uniform manner, and therefore it is difficult for the optical fibers
31
to be inserted into the micro-hole
35
disposed in the adapter
33
. A smaller clearance between the outer surface of the optical fibers
31
and the inner surface of the micro-hole
35
makes it more difficult for the optical fibers
31
to be inserted and a larger clearance between the outer surface of the optical fibers
31
and the inner surface of the micro-hole
35
causes displacement of the inserted optical fibers
31
in the micro-hole
35
, resulting in an increased insertion loss.
For the BF connector, the recommended amounts of the buckling length L and the buckling deformation &Dgr;L are 7 mm and 50 &mgr;m, respectively, leading to about 6 mm for the radius of curvature R. This radius of curvature R is much smaller than the allowable radius of curvature of typical optical fibers, i.e., about 10 mm. Accordingly, this small radius of curvature may cause the buckled optical fiber
31
to crack. To avoid this, it is necessary to coat the optical fibers
31
with carbon. However, this kind of treatment involves a substantial increase in cost.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide an optical fiber connector for reliably and accurately aligning optical fibers and allowing the optical fibers to surely and easily have a radius of curvature that is substantially equal to or larger than the allowable radius of curvature.
According to a preferred embodiment of the present invention, an optical fiber connector includes a first holder for holding a first connection end of a first optical fiber and a second holder for holding a second connection end of a second optical fiber. The first and the second holders include a first holder portion and a second holder portion disposed therein, respectively. The first and the second holder portions include a first holding groove and a second holding groove disposed therein, respectively. The first holding groove holds the top half of the first connection end and allows the b

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