Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2001-03-05
2003-11-04
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S020000, C385S021000
Reexamination Certificate
active
06643422
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an optical switch changeover controlling technique in conducting a changeover of an optical path by a spatial optical switch comprising a plurality of optical switch elements arranged therein, and particularly to an optical switch changeover controlling method, an optical node device and an optical switch system for realizing an uninterrupted changeover of an optical path.
(2) Related Art
Recently increased information capacities, variation and the like require a flexible and reliable construction of a network as well as an increased capacity of a transmission system. As one way to realize them, there has been demanded a construction of an optical network based on a wavelength division multiplexing (WDM) technique. In constructing such a network, important roles will be played by an optical-switch-adopting optical node device, such as: an optical cross-connect device for setting a bypass route, e.g., when changing over an optical path or when a fault occurs in a transmission path; an optical add drop multiplexer (OADM) for adding/dropping optical signals; and an optical protection device for conducting a recovery from a fault in an optical network.
FIG. 18
is a conceptual diagram for explaining an optical switch changeover controlling method utilizing conventional optical node devices. There is shown an example of a procedure for changing over an optical path from a working ray path to a protective ray path at the time of occurrence of a fault, in which
FIG. 18A
shows an initial state,
FIG. 18B
shows a state where a fault occurs,
FIG. 18C
shows a state where a path release is conducted, and
FIG. 18D
shows a state where the recovery from the fault has been completed.
In the initial state of
FIG. 18A
, two optical node devices
1
A,
1
B are interconnected via a working ray path
2
W and a protective ray path
2
P. The working ray path
2
W is input with a client optical signal sc from a client (terminal equipment)
3
A connected to the optical node device
1
A, and the protective ray path
2
P is input with a PCA optical signal sp from a PCA (Protect Channel Access) device
4
A connected to the optical node device
1
A.
When a fault such as a disconnection occurs in the working ray path
2
W as shown in
FIG. 18B
, the client optical signal sc being connected to the working ray path
2
W is to be changed over to the protective ray path
2
P. Concretely, the connection of the PCA optical signal sp having been connected to the protective ray path
2
P is once released (“path release”) as shown in
FIG. 18C
, followed by a reconnection of the client optical signal sc to the protective ray path
2
P as shown in
FIG. 18D
to thereby conduct a changeover from the working ray path
2
W to the protective ray path
2
P at the time of occurrence of the fault.
There will be now briefly explained a changeover operation of optical switches provided in the optical node devices
1
A,
1
B.
As a typical optical switch to be provided in each of the optical node devices
1
A,
1
B, there is used an N×N spatial optical switch, for example, which is constituted of matrix-arranged N
2
units of 2×2 optical switch elements (in which N is the number of lines to be changed over at the node), where each 2×2 optical switch element has two inputs and two outputs cooperatively changeable into one of a parallel (bar) state and an interlaced (cross) state.
FIG. 19
is a diagram showing an example of a 2×2 spatial optical switch (i.e., N=2) in the transmission side optical node device
1
A. There is shown a procedure for changing over, the path of the client optical signal sc connected from an input terminal #1i to an output terminal #1o of the optical node device
1
A, to a path from the input terminal #1i to an output terminal #2o.
In a path setting initial state shown in
FIG. 19A
, an optical path for transmitting the client optical signal sc from the input terminal #1i to the output terminal #1o as shown by a solid line arrow, and an optical path for transmitting the PCA optical signal sp from an input terminal #2i to the output terminal #2o as shown by a dotted line arrow are set. At this time, a 2×2 optical switch element S
11
at the intersection point between the input terminal #1i and output terminal #1o, and a 2×2 optical switch element S
22
at the intersection point between the input terminal #2i and output terminal #2o are brought into parallel states (ON states), respectively.
Note, “a 2×2 optical switch element at an intersection point between an input terminal #xi and an output terminal #yo” means such a 2×2 optical switch element in the parallel state: when all 2×2 optical switch elements within a spatial optical switch are once turned into interlaced states (OFF states) and one of the 2×2 optical switch elements is then changed over to a parallel state (ON state) to thereby set an optical path directed from the input terminal #xi to the output terminal #yo.
FIG. 19B
shows a state where the already connected two optical paths are released before conducting a changeover of a path connection, in which all the optical switch elements S
11
, S
12
, S
21
, S
22
are in the interlaced states (OFF states) (path released states).
FIG. 19C
shows a path reconnection state where the 2×2 optical switch element S
12
at the intersection point between the input terminal #1i and the output terminal #2o is brought into the parallel state (ON state) so as to set an optical path from the input terminal #1i to the output terminal #2o to thereby connect the client optical signal sc to the protective ray path
2
P.
In the conventional optical node device as described above, there is conducted a consecutive procedure including optical path setting (initial state), optical path release and optical path reconnection, when conducting a connection changeover of an optical signal. Thus, an optical output power (optical output power to the protective ray path
2
P) of the output terminal #2o of the optical node device
1
A is interrupted in the course of the changeover of the optical path, as shown in FIG.
20
. Concretely, this interruption in the optical output power continues over a period of time from the optical path release up to the optical path reconnection, and the interruption period T′ can be represented by the following equation (1):
T′=T
f
+T
off
+T
r
(1)
wherein T
f
is a falling time of the 2×2 optical switch element, T
off
is a changeover controlling time (time-lag up to the optical path re-setting), and Tr is a rise time of the 2×2 optical switch element.
As such, the conventional optical node device as described above has a possibility to cause a deterioration of optical signal transmission characteristics or a failure of the device, due to the interruption in the optical output power at the time of changeover of the optical path. Namely, such as when an optical amplifier is arranged on the latter stage side of an optical switch within an optical node device or is arranged within an optical transmission path interconnecting optical node devices, an interruption in optical output power at the time of changeover of an optical path will cause an optical surge in the optical amplifier. This results in a problem of a possibility to cause a deterioration of optical signal transmission characteristics or a failure of the device. Further, the aforementioned optical switch changeover controlling method in the conventional optical node device also has a defect of the time-lag up to the reconnection of the optical path.
SUMMARY OF THE INVENTION
The present invention has been carried out in view of the conventional problems as described above, and it is therefore an object of the present invention to provide an optical switch changeover controlling method, an optical node device and an optical switch syst
Katagiri Toru
Kuroyanagi Satoshi
Maeda Takuji
Nakajima Ichiro
Nishi Tetsuya
Fujitsu Limited
Lee John D.
Staas & Halsey , LLP
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