Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1999-08-31
2002-02-05
Font, Frank G. (Department: 2877)
Optical waveguides
With optical coupler
Particular coupling structure
C385S024000, C359S199200
Reexamination Certificate
active
06345137
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a wavelength division multiplex optical star coupler, a communication station, and an optical transmission system. In particular, the present invention relates to an optical transmission system that uses a wavelength division multiplex optical star coupler which combines an optical star coupler and a wavelength division multiplex optical coupler.
2. Description of Related Art
An optical fiber communication using an optical fiber as a light propagation line will be described as a conventional art. Usually, an optical star coupler of 1 to n branching is used for dividing an optical signal, which is generated from one source, into a plurality of signals. Here, n is an integer more than 2. It is possible to transmit the same optical signal to a plurality of multiple destinations by the optical star coupler. An optical fiber fusion type and an optical waveguide type are mainly used for the optical star coupler. The optical star coupler is not only used for distributing the light, but also used as a light multiplexer which multiplexes the optical signal output from different light sources because the optical star coupler usually works bidirectionally.
One of methods to use a single optical fiber efficiently is a wavelength division multiplex method that utilizes different wavelengths of the optical signals. Recently, a wavelength division multiplex optical coupler is used for multiplexing or de-multiplexing the optical signals having different wavelengths in the wavelength division multiplex method.
FIG. 1
shows a conventional wavelength division multiplex optical coupler. The wavelength division multiplex optical coupler
10
is basically the same as a 1 to 2 optical de-multiplexer or multiplexer. One side of the wavelength division multiplex optical coupler
10
is connected to a port P
20
, which can input and output the first optical signal &lgr;
1
and the second optical signal &lgr;
2
. The other side of the wavelength division multiplex optical coupler
10
is connected to a port P
22
, which can input and output only the first optical signal &lgr;
1
, and a port P
24
, which can input and output only the second optical signal &lgr;
2
.
The first optical signal &lgr;
1
and the second optical signal &lgr;
2
have different wavelength with each other. The first optical signal &lgr;
1
input from the port P
20
is output to the port P
22
, and the second optical signal &lgr;
2
input from the port P
20
is output to the port P
24
. The first optical signal &lgr;
1
input from the port P
22
and the second optical signal &lgr;
2
input from the port P
24
are output to the port P
20
. The ordinary wavelength division multiplex optical coupler is described in Japanese Patent Application Laid-Open No. H10-173265.
FIG. 2
shows a one-way direction wavelength division multiplex optical communication realized by the wavelength division multiplex method. One side of the wavelength division multiplex optical coupler
10
is connected to a port P
26
, which can input only the first optical signal &lgr;
1
, and a port P
28
, which can input only the second optical signal &lgr;
2
. The other side of the wavelength division multiplex optical coupler
10
is connected to the port P
30
, which can input the first optical signal &lgr;
1
and the second optical signal &lgr;
2
. The first optical signal &lgr;
1
input from the port P
26
and the second optical signal &lgr;
2
input from the port P
28
are output to the port
30
through the wavelength division multiplex optical coupler
10
. The direction of the communication is one-way from the port P
26
and the port P
28
to the port
30
.
FIG. 3
shows a two-way direction wavelength division multiplex optical communication realized by the wavelength division multiplex method. One side of a wavelength division multiplex optical coupler
10
a
is connected to a port P
32
, which can input only the first optical signal &lgr;
1
, and a port P
34
, which can output only the second optical signal &lgr;
2
. The other side of the wavelength division multiplex optical coupler
10
a
is connected to a wavelength division multiplex optical coupler
10
b.
One side of the wavelength division multiplex optical coupler
10
b
is connected to a port P
36
, which can input only the second optical signal &lgr;
2
, and a port P
38
, which can output only the first optical signal &lgr;
1
. The other side of the wavelength division multiplex optical coupler
10
b
is connected to the wavelength division multiplex optical coupler
10
a.
The wavelength division multiplex optical coupler
10
a
and
10
b
are connected by a single optical fiber.
The first optical signal &lgr;
1
input from the port P
32
is output to the port P
38
through the wavelength division multiplex optical couplers
10
a
and
10
b.
The second optical signal &lgr;
2
input from the port P
36
is output to the port P
34
through the wavelength division multiplex optical couplers
10
a
and
10
b.
The direction of the communication is bidirection from the port P
32
to the port P
38
and from the port P
36
to the port P
34
.
Therefore, the optical communication that transmits an optical signal from one light source, such as a main unit, to a plurality of receiving terminals, such as sub units, and transmits the optical signals from the sub units to the main unit become possible by using the wavelength division multiplex optical coupler
10
.
However, because the optical parts such as a star coupler and a wavelength division multiplex optical coupler use an optical fiber for the input/output, radiation loss will occur when bending the optical fiber. In the case of a quarts single mode fiber, the optical fiber has to be bent more than 30 mm of radius of curvature. Furthermore, there is the possibility of the breaking an optical fiber in the case of using the optical fiber strand with 250 &mgr;m of outward diameter to save the space for wiring. In the case of using a code with 2 mm to 3 mm of outward diameter to protect the optical fiber, the wiring space will increase because the outward diameter of the code is larger than the outward diameter of the optical fiber strand. Especially, as the number of branching of an optical star coupler is larger, the wiring space has to be larger. Therefore, the conventional art requires the work of packing the optical fiber without breaking it by considering the radius of curvature of the optical fiber.
SUMMARY OF THE INVENTION
As stated, it is an object of the present invention to provide a wavelength division multiplex optical star coupler that is capable of solving the problems described above. Also, it is an object of the present invention to provide a communication station and optical transmitting system using the wavelength division multiplex optical star coupler. The object of the present invention can be achieved by the combinations of features described in the independent claims of the present invention. The dependent claims of the present invention define further advantageous embodiments of the present invention.
According to the first aspect of the present invention, a wavelength division multiplex optical star coupler can be provided which comprises an input port which inputs a first optical signal, a first optical coupler which divides the first optical signal input from the input port into a plurality of first optical signals, a plurality of input/output ports, each of which outputs one of the plurality of first optical signals divided by the first optical coupler and inputs a second optical signal, an output port which outputs the second optical signal, and a second optical coupler, provided between the input port and the first optical coupler or between the first optical coupler and the input/output ports, which provides the first optical signal to the input/output ports and the second optical signal to the output port.
A wavelength division multiplex optical star coupler can be provided which further has a plurality of the output ports and a plurality o
Kokusai Electric Co. Ltd.
Nguyen Sang H.
Pillsbury Winthrop LLP Intellectual Property Group
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