Four fiber ring network optical switching circuit using...

Optical communications – Multiplex – Optical local area network

Reexamination Certificate

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C398S003000, C398S004000, C398S012000, C398S019000, C398S045000, C398S046000, C398S056000, C398S057000, C398S059000, C398S072000, C398S107000, C398S111000

Reexamination Certificate

active

06782201

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a four fiber ring network optical switching circuit to be used at each node of an optical ring network system for carrying out a working/protection switching at optical level in a bidirectional optical ring network formed by four fibers, for example, and more specifically, to a four fiber ring network optical switching circuit for realizing a span switch function and a ring switch function by cross-connecting first and second working and protection input and output ports and first and second working and protection add/drop input and output ports for inputting and outputting working and protection signals transmitted through a ring network.
2. Description of the Background Art
As shown in
FIGS. 4A and 4B
, the four fiber ring optical network is formed by connecting a plurality of nodes A, B, C, D, E and F by a ring shaped transmission path comprising four optical fibers including a working fiber pair indicated by bold and thin solid lines and a protection fiber pair indicated by dashed lines. Here each node is referred to as a four fiber ring node. Also, one of the two fibers constituting each fiber pair will be used for an upward transmission while the other one will be used for a downward transmission.
In the four fiber ring optical network of this configuration, under the normal state, signals will be transmitted between arbitrary nodes through a route using the working fiber pair indicated by a bold solid line as a normal route in
FIGS. 4A and 4B
. In the example shown in
FIGS. 4A and 4B
, signals will be transmitted between nodes F and C by the normal route using the working fiber pair via nodes A and B.
When signals are transmitted between nodes F and C via nodes A and B by the normal route using the working fiber pair transmission path in this manner, if a trouble such as a span fault occurs in the working fiber pair transmission path of the normal route between nodes B and C as shown in
FIG. 4A
, for example, the span switching from the working fiber pair transmission path to a protection fiber pair transmission path is carried out by span switches at nodes B and C such that a transmission path connecting between nodes B and C is switched to the protection fiber pair transmission path indicated by a dashed line. As a result, the signal transmission between nodes F and C will be carried out by using the working fiber pair transmission path of the normal route between nodes A and F and between nodes A and B, and the protection fiber pair transmission path between nodes B and C.
Also, similarly, when signals are transmitted between nodes F and C via nodes A and B by the normal route using the working fiber pair transmission path, if a trouble such as a cable disconnection occurs in a fiber cable between nodes B and C such that both the working and protection fiber pair transmission paths are disconnected as shown in
FIG. 4B
, for example, the ring switching from the working fiber pair transmission path to the protection fiber pair transmission path is carried out by ring switches at nodes F, E, D and C such that the signal transmission between nodes F and C will be carried out by switching a transmission path to a bypass route via nodes E and D which is indicated by a bold solid line and using the protection fiber pair transmission path, so as to rescue the working signals.
A switch of the node for carrying out the span switching and the ring switching as described above is realized by the four fiber ring network optical switching circuit as shown in FIG.
5
. This ring network optical switching circuit has first and second optical input/output ports (
1
) and (
2
) to which the protection and working fiber pairs in the first direction are connected, third and fourth optical input/output ports (
3
) and (
4
) to which the protection and working fiber pairs in the second direction are connected, fifth and sixth optical input/output ports (
5
) and (
6
) to be used as protection and working add/drop ports for transmission from the second direction to the first direction, and seventh and eighth optical input/output ports (
7
) and (
8
) to be used as working and protection add/drop ports for transmission from the first direction to the second direction.
In the ring network optical switching circuit of
FIG. 5
, the first optical input/output port (
1
) is directly connected with the fifth optical input/output port (
5
) and can be also connected with the sixth optical input/output port (
6
) via a span switch and with the seventh optical input/output port (
7
) via a ring switch. Also, the second optical input/output port (
2
) is directly connected with the sixth optical input/output port (
6
) and can be also connected with the first optical input/output port (
1
) via a span switch and with the third optical input/output port (
3
) and the eighth optical input/output port (
8
) via a ring switch. Also, the third optical input/output port (
3
) is directly connected with the eighth optical input/output port (
8
) and can be also connected with the seventh optical input/output port (
7
) via a span switch and with the sixth optical input/output port (
6
) via a ring switch. Also, the fourth optical input/output port (
4
) is directly connected with the seventh optical input/output port (
7
) and can be also connected with the third optical input/output port (
3
) via a span switch and with the first optical input/output port (
1
) and the fifth optical input/output port (
5
) via a ring switch.
Conventionally, the ring network optical switching circuit as shown in
FIG. 5
is formed by using twelve 2×2 optical switches as shown in FIG.
6
.
In
FIG. 6
, SW-
1
,
3
,
6
and
8
are ring switching 2×2 optical switches, SW-
2
,
4
,
5
and
7
are pass through 2×2 optical switches, and SW-
9
,
10
,
11
and
12
are span switching 2×2 optical switches. Also, CP-
1
is an optical coupler (optical branching element) for bridging with respect to a span switching to the first direction, CP-
2
is an optical coupler (optical branching element) for bridging with respect to a span switching to the second direction, CP-
3
is an optical coupler for bridging to the working fiber in the second direction with respect to a ring switching to the first direction, and CP-
4
is an optical coupler for bridging to the working fiber in the first direction with respect to a ring switching to the second direction.
When the working signals are switched to the protection fiber pair transmission path by the span switching and the ring switching at a time of the trouble occurrence as in the cases shown in
FIGS. 4A and 4B
by using the ring network optical switching circuit as shown in FIG.
5
and
FIG. 6
, in order to automatically switching the working signals back to the working fiber pair at a time of the subsequent recovery from the trouble, there is a need for the so called bridge function for starting the transmission by switching the working signals into the protection fiber pair transmission path while continuing to transmit signals also to the working fiber pair transmission path on which the trouble has occurred, so that the conventional ring network optical switching circuit shown in
FIG. 6
is equipped with a bridge function at times of the span switching and the ring switching as described above.
The conventional four fiber ring network optical switching circuit described above can be formed by a relatively small number of twelve 2×2 optical switches, but if the optical switch is individually implemented, the optical switch itself becomes large and an entire structure of the ring network optical switching circuit also becomes large due to arrangements of optical fibers to be connected to the optical switches, and in conjunction with that there has been a problem that a cost required for the wiring processing becomes high.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a four fiber ring network optical switching circuit cap

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