Optical fiber holding capillary tube

Details Optical fiber holding capillary tube Optical fiber holding capillary tube

1999-11-22

2001-11-27

Ngo, Hung N. (Department: 2874)

Optical waveguides

With disengagable mechanical connector

Optical fiber/optical fiber cable termination structure

C385S059000, C385S066000

Reexamination Certificate

active

06322256

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber holding capillary tube that is capable of inserting and holding a plurality of optical fibers therein in an ordered arrangement, and easily positioning and securing the optical fibers in relation to other optical components.
When dividing a signal transmitted through a single optical fiber to a plurality of optical fibers, or combining signals transmitted through a plurality of optical fibers into a single optical fiber, capillary tubes have been used to hold and secure the plurality of optical fibers. When positioning and securing two optical fibers in an accurately parallel arrangement, for example, a capillary tube
1
′ that has an insertion hole
2
′ having a circular cross section is used wherein two optical fibers
5
′,
6
′ are inserted, as shown in FIG.
12
.
However, since the insertion hole
2
′ of the capillary tube
1
′ has a circular cross section, in the event of the two optical fibers
5
′,
6
′ cross each other in the insertion hole
2
′ as shown in FIG.
12
(A), optical axis
5
b
′ of the optical fiber
5
′ and optical axis
6
b
′ of the optical fiber
6
′ are displaced from the center axis P of the insertion hole
2
′ by angles &Dgr;&thgr;1 and &Dgr;&thgr;2, respectively. As a consequence, the optical fibers
5
′,
6
′ are displaced from the proper relative position with optical elements such as a light emitting element, a light receiving element, a waveguide element and optical fibers that are disposed in parallel to the center axis P, resulting in increased connection loss.
Also as shown in FIG.
12
(B), a center line M′ that connects the center of the optical fiber
5
′ and the center of the optical fiber
6
′ is displaced from the normal position by an angle &Dgr;&thgr;3 in the circumferential direction. This makes it necessary to adjust the relative positions of the optical fibers
5
′,
6
′ with other optical elements in the circumferential direction. Since some of optical fibers, so-called single-mode fibers, are as small as 5 &mgr;m to 10 &mgr;m in the diameter of the core where optical signals are transmitted, it may be extremely difficult to adjust the relative position described above.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a highly reliable optical fiber holding capillary tube that is capable of holding a plurality of optical fibers inserted therein in an accurately ordered arrangement, and easily positioning and securing the optical fibers held in the ordered arrangement in relation to other optical components.
The present invention, in order to achieve the object described above, provides the optical fiber holding capillary tube that has an insertion hole of substantially quadrangular cross section for holding a plurality of optical fibers inserted therein in an ordered arrangement, wherein the cross section of the insertion hole is substantially square and distance L between opposing inner wall surfaces of the insertion hole and diameter D of the optical fiber satisfy a relationship of (1+2
(k−2)/2
)D<L≦(1.05+2
(k−2)/2
)D (where k is 1 or greater integer), in order to make it possible to insert a plurality of optical fibers having the diameter D while adjoining each other into the insertion hole.
For example, when it is assumed that two adjoining optical fibers having diameter D can be held without clearance to the wall surface in the insertion hole that has substantially square cross section as shown in FIG.
1
(B), the relation between the distance L between the opposing inner wall surfaces of the insertion hole and the diameter D of the optical fiber becomes L=(1+2
1−2)/2
)D, namely L=(
1+1/{square root over (2+L )})D. In practice, however, since some clearance is required in order to insert the two optical fibers into the insertion hole, the distance L of the insertion hole must satisfy a condition of (
1+1/{square root over (2+L )})D<L. Also in the case of a single-mode optical fiber, since the core diameter where the optical signals are transmitted is from
5 to 10% of the diameter D of the optical fiber, the distance L must satisfy a relation of L≦(
1.05+1/{square root over (2+L )})D in order to achieve a positioning accuracy of within about
5% of the diameter D in the positioning of the two optical fibers. In practice, it is required to satisfy a relationship of (1.71)D<L≦(1.76)D upon approximation of 1+1/{square root over (2)}≈1.71 and 1.05+1/{square root over (2)}≈1.76.
The present invention also provides an optical fiber holding capillary tube that has the insertion hole of substantially quadrangular cross section for holding a plurality of optical fibers inserted therein in an ordered arrangement, wherein the cross section of the insertion hole is substantially rectangular and distance L
1
between opposing longer sides of the insertion hole, distance L
2
between opposing shorter sides of the insertion hole and diameter D of the optical fiber satisfy relationships of D<L
1
≦(1.05)D and nD<L
2
≦(n+0.05)D, in order to make it possible to insert n optical fibers (2≦n) each having the diameter D into the insertion hole in parallel to each other.
For example, when it is assumed that n pieces of adjoining optical fibers each having diameter D can be held in parallel to each other without clearance to the wall surface in the insertion hole that has substantially rectangular cross section as shown in
FIG. 5
, the relation between the distance L
1
between the longer sides of the insertion hole and the diameter D of the optical fiber is expressed as L
1
=D, and the relation between the distance L
2
between the opposing shorter sides of the insertion hole and the diameter D of the optical fiber is expressed as L
2
=nD (2≦n). In practice, however, since some clearance is required in order to insert the n pieces of optical fibers each having diameter D into the insertion hole, the distance L
1
between the longer sides must satisfy a condition of D<L
1
and the distance L
2
between the shorter sides must satisfy a condition of nD<L
2
. Also in order to position n pieces of single-mode optical fibers with an accuracy of at least within about 5% of the diameter D of the optical fiber, the distance L
1
across the longer sides must satisfy a relation of L
1
<(1.05)D and the distance L
2
across the shorter sides must satisfy a relation of L
2
≦(n+1.05)D.
In the optical fiber holding capillary tube that has the insertion hole of substantially square or rectangular cross section described above, a plurality of optical fibers can be connected to other optical components while being aligned with the optical axes thereof, by positioning the optical fibers that are held in an ordered arrangement in the insertion hole while maintaining optical matching with the other optical components by using holding means. The holding means may be, for example, a cylindrical sleeve.
Also in the optical fiber holding capillary tube that has the insertion hole of substantially square or rectangular cross section described above, a plurality of optical fibers can be connected to each other, by holding the optical fibers together end to end while inserting a plurality of optical fibers from an opening on one end of the insertion hole, inserting a plurality of optical fibers from an opening on the other end of the insertion hole and holding the optical fibers on both sides in aligned positions.
The present invention also provides an optical fiber holding capillary tube comprising an insertion hole of substantially quadrangular cross section wherein a plurality of optical fibers are inserted and held in an ordered arrangement, and at least one flat surface provided on an outer surface thereof, wherein the flat surface is disposed to form a predetermined acute angle with a side of the i

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