Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1999-04-01
2001-05-29
Ngo, Hung N. (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S024000, C385S032000
Reexamination Certificate
active
06240227
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to coupling means for branching optical fibers used in optical communications systems. More particularly, the invention concerns a coupling ring for branching such optical fibers in a star-type optical coupler.
2. Description of the Prior Art
Known star-type couplers are manufactured as follows: a plurality of optical fibers are drawn from quartz or an industrial plastic. The optical fibers are then branched by binding technologies such as heat melting or ultrasonic welding.
FIG. 1
illustrates a known branching method, according to which a pair of optical fibers
1
a
and
1
b
is bound at one branching point
2
. A number of optical fibers can be bound through this pair-coupling method. However, branching becomes complicated as the number of branchings increases.
FIG. 2
shows a coupling map inside a star-type optical coupler SC which includes four branching points. In this map, a first light input terminal
1
is connected to a first optical fiber
3
a
, where it becomes branched with a second optical fiber
3
b
at a first branching point
4
a
. The first optical fiber
3
a
is further branched with a third optical fiber
3
c
at a second branching point
4
b
. The second optical fiber
3
b
that is thus coupled with the first optical fiber
3
a
at the first branching point
4
a
, is also coupled with a fourth optical fiber
3
d
at a third branching point
4
c
. Thus, a light signal entering the first optical fiber
3
a
from the light input terminal
1
exits from a light signal output terminal
5
of the first optical fiber
3
a
. At the same time, the same light signal passes through the third optical fiber
3
c
branched with the first optical fiber
3
a
at the second branching point
4
b
. It also passes through the second optical fiber
3
b
branched with the first optical fiber
3
a
at the first branching point
4
a
, and through the fourth optical fiber
3
d
branched with this second optical fiber
3
b
at the third branching point
4
c
. Thus, the light signal is branched into four light output terminals
5
-
8
. Further, the third optical fiber
3
c
and the fourth optical fiber
3
d
are branched at the fourth branching point
4
d
, so that all the four optical fibers
3
a
to
3
d
are mutually branched. In the same manner, the light signals entering the other light input terminals
2
to
4
are all branched through the branching points
4
a
to
4
d
and exit at light output terminals
5
to
8
.
The above system concerns a system having four branching points (quadruple branching system). However, even when only triple branching is desired, it is common practice to employ the quadruple branching system using four optical fibers
3
a
to
3
d
based on the above-mentioned principle. One reason for this is that, by setting the same number of branchings for all the optical fibers
3
a
to
3
d
, the light intensity at their light output terminals can be maintained at the same level. Another reason is that standardization of the product specifications for star-type optical couplers SC is thus simpler.
For example, in the system shown in
FIG. 2
, it may happen that only optical fibers
3
a
to
3
c
need to be branched, and not the fourth optical fiber
3
d
. Even in such a case, all the optical fibers
3
a
to
3
d
are branched, but light input terminal
4
and light output terminal
8
are left unconnected to external apparatuses.
In this case, the first optical fiber
3
a
, the second optical fiber
3
b
, the third optical fiber
3
c
and the fourth optical fiber
3
d
each have two branching points, which are respectively:
4
a
and
4
b
,
4
a
and
4
c
,
4
d
and
4
b
, and
4
d
and
4
c
. Each of the optical fibers
3
a
to
3
d
thus has two branching points, so that the light intensities at the output terminals are kept even. Consequently, the signal quality in optical communications can be maintained constant.
The above-mentioned double branching of each of the optical fibers
3
a
to
3
d
may also be called “two-step branching”, and the number of steps may be designated as “m” (where m is an integer). Accordingly, the condition for obtaining a constant light-output quality is that the number of optical fibers to be used can be expressed as 2
m
, i.e. 2, 4, 8, or 16 fibers, etc.
In the star-type optical coupler SC shown in
FIG. 2
, light is branched by virtue of a light advancement vector found in optical fibers
3
a
to
3
d
. Therefore, the coupler directs unidirectional light signals as indicated by the arrow “P”, so that a plurality of light input terminals
1
to
4
are disposed on one side, while corresponding light output terminals
5
to
8
are disposed on the other side. However, this configuration may create some problems in practical use.
FIG. 3
shows a prior art coupling system, in which the star-type optical coupler SC of
FIG. 2
is connected to four light communication apparatuses
5
a
to
5
d
. In this case, the coupler is connected to the light communication apparatuses through its light input terminals
8
a
to
8
d
and its light output terminals
9
a
to
9
d
. As can be seen in
FIG. 3
, optical fiber cables
6
a
to
6
d
and
7
a
to
7
d
, respectively wired for light input terminals
8
a
to
8
d
and light output terminals
9
a
to
9
d
, become entangled at the periphery of the star-type optical coupler SC.
The optical fiber cables
6
a
to
6
d
and
7
a
to
7
d
are set to have a radius of curvature exceeding the minimum flexing radius, i.e. about 5 to 10 mm, above which the flexing of a cable does not increase optical loss. The cable must thus avoid being flexed into a radius smaller than these figures. Accordingly, the optical fiber cables
6
a
to
6
d
and
7
a
to
7
d
in the vicinity of the star-type optical coupler SC may become intertwined. It may even not be possible to contain them in a housing, which gives rise to aesthetic problems.
Further, the prior art star-type optical coupler SC includes branching points
4
a
to
4
d
in accordance with a multi-step structure. As the number of branching steps “m” becomes greater, the number of optical fibers
3
a
to
3
d
used inside the star-type optical coupler leaps exponentially. This in turn increases the number of parts necessary and thus increases material costs.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a star-type optical coupler which simplifies the wiring of the peripheral optical fiber cables.
Another object of the invention is to reduce to a minimum the number of optical fibers used within a star-type optical fiber, as well as the number of parts used.
To this end, there is provided a star-type optical coupler that includes a plurality of optical fibers adapted for passing a light signal having a substantially linear displacement. The optical fibers include at least a first optical fiber and a second optical fiber located adjacent to each other, and each have a light signal input terminal, a light signal output terminal and an intermediate portion, the intermediate portion including a branching point. The star-type optical coupler also includes a coupling ring having a substantially circular configuration and a corresponding number of branching points. The coupling ring is adapted for transforming the substantially linear displacement of the light signal into a generally circular movement. Thus, the plurality of optical fibers are branched into the coupling ring through the branching points, whereby the coupling ring transforms the linear displacement of the light signal into the generally circular movement, such that the light input terminals can be disposed separately from one another, while the light output terminals can also be disposed separately from one another, and such that the light input terminal of the first optical fiber and the light output terminal of the second optical fiber are arranged adjacent to each other.
Preferably, the coupling ring has a minimum flexing radius defined so as not to cause an in
Greenblum & Berstein P.L.C.
Ngo Hung N.
Sumitomo Wiring Systems Ltd.
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