Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2001-04-17
2004-09-14
Kim, Robert H. (Department: 2871)
Optical waveguides
With optical coupler
Switch
C385S016000, C385S018000, C385S019000, C385S024000, C385S031000
Reexamination Certificate
active
06792176
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical switch. In particular, the invention relates to an optical switch expanding method which enables reduction in optical loss as well as to an optical switch formed based on such an expanding method. The invention also relates to an optical crossconnecting apparatus having such an optical switch.
2. Description of the Related Art
In recent years, multimedia communications as the Internet have spread rapidly. In the field of communications technologies, to cope with sharp increase in traffic due to such rapid spread of multimedia communications, intensive studies and developments have been made of optical communication technologies that enable ultra-long distance communication and large capacity communication. To accommodate further increase in traffic, there has been studied increasing the speed of the time-division multiplexing (TDM) transmission and the degree of multiplexing of the wavelength-division multiplexing (WDM) transmission. In optical crossconnecting apparatus, it is necessary to increase the numbers of inputs and outputs accordingly. It is desired to provide a proper method for expanding optical switches that are the core device of optical crossconnecting apparatus.
An optical crossconnecting apparatus accommodates a plurality of input and output optical transmission lines and routes, on a wavelength basis, a WDM optical signal input to an input optical transmission line, to desired output optical transmission lines. Since such routing is performed by an optical switch, expansion of the input/output ports in the optical switch is required for expanding (increasing the numbers of) the input/output ports in an optical crossconnecting apparatus.
FIGS. 13A and 13B
are for explaining a conventional optical switch expanding method.
FIG. 13A
shows a 4×4 optical matrix switch before expansion and
FIG. 13B
shows an 8×8 optical matrix switch after expansion.
As shown in
FIGS. 13A and 13B
, the 4×4 optical matrix switch
1001
is configured in such a manner that sixteen 2×2 optical switch elements
1002
are arranged in a 4-row/4-column matrix. Such an n×n optical switch (n: integer) in a matrix will particularly be called an n×n optical matrix switch and a 2×2 optical switch that is a minimum unit of the n×n optical matrix switch will be called a 2×2 optical switch element.
Conventionally, in expanding such a 4-input/4-output 4×4 optical matrix switch
1001
-
1
to an 8-input/8-output 8×8 optical matrix switch
1011
in terms of the input/output ports, three optical matrix switches
1001
-
2
to
1001
-
4
are provided additionally, the four optical matrix switches
1001
-
1
to
1001
-
4
are arranged in a matrix, and the input ports and the output ports in two of the optical matrix switches
1001
-
1
to
1001
-
4
that are adjacent to each other vertically or horizontally are connected to each other.
The optical switch elements
1002
of the 8×8 optical matrix switch
1011
are assigned row numbers in order of the first input port to the eighth input port and assigned column numbers in order of geometrical closeness to the input ports. The row numbers and the column numbers assigned are given to the optical switch elements
1002
as suffixes each being an array of a row number and a column number that are arranged in this order. For example, in
FIG. 13B
, the optical switch element that is connected to the second input port and located fourth as counted from the input port is the second-row/fourth-column optical switch element and hence is given a reference symbol
1002
-
24
. The optical switch element that is connected to the sixth input port and located eighth as counted from the input port is the sixth-row/eighth-column optical switch element and hence is given a reference symbol
1002
-
68
. To avoid unduly complicating
FIG. 13B
, only part of the reference symbols of the optical switch elements
1002
are drawn in the figure.
For the sixty-four optical switch elements
1002
, control symbols to be used for a control of routing an optical signal that is input to the optical matrix switch
1011
to a desired output port are assigned in the following manner. They are assigned so as to specify, by using an input port position and an output port position, an optical switch element
1002
where switching should be made for routing to a desired output port. In
FIG. 13B
, each of such control symbols is an array of S, an input port number, and an output port number that are arranged in this order. For example, the optical switch element
1002
-
11
is given a symbol S
11
. An optical signal that is input to the first input port can be routed to the first output port by switching at the optical switch element
1002
-
11
(S
11
). The optical switch element
1002
-
75
is given a symbol S
75
. An optical signal that is input to the seventh input port can be routed to the fifth output port by switching at the optical switch element
1002
-
75
(S
75
).
In the optical matrix switch
1011
obtained by expanding the 4-input/4-output optical matrix switch
1001
in the above method, an optical signal passes through fifteen optical switch elements at maximum, in which optical loss is large. For example, to output, from the eighth output port, an optical signal that is input to the first input port, switching is performed at the optical switch element
1002
-
18
(S
18
). Therefore, the optical signal passes through the fifteen optical switch elements
1002
-
11
,
1002
-
12
,
1002
-
13
,
1002
-
14
,
1002
-
15
,
1002
-
16
,
1002
-
17
,
1002
-
18
,
1002
-
28
,
1002
-
38
,
1002
-
44
,
1002
-
58
,
1002
-
68
,
1002
-
78
, and
1002
-
88
. Losses in those optical switch elements
1002
sum up to a large loss.
On the other hand, an optical that is input to the eighth input port can be routed to the first output port by switching only at the optical switch element
1002
-
81
(S
81
). This optical signal passes through only one optical switch element
1002
-
81
.
As a result, a difference approximately corresponding to the losses in 14 optical switch elements
1002
occurs between the optical output level of the optical signal that has passed through the one optical switch element
1002
and that of the optical signal that has passed through the 15 optical switch elements
1002
.
Incidentally, since an optical signal that is output from an optical matrix switch is input to an optical component such as a photodetector of an optical receiver, its optical output level should be higher than a certain level. However, loss occurs in each optical switch element. Therefore, where routing is performed by an optical matrix switch, the maximum number of optical switch elements through which an optical signal passes determines a switch size (i.e., the numbers of inputs and outputs) of the optical matrix switch. Therefore, the conventional expanding method and optical matrix switches according to the conventional expanding method have a problem that the matrix optical switch cannot be large in size because as the degree of expansion increases, the maximum number of optical switch elements through which an optical signal passes increases and the loss rises accordingly.
Large differences between the output levels of the respective output ports in an optical matrix switch cause a problem that optical components connected to the output ports such as optical amplifiers or photodetectors should have a wide input dynamic range or plural kinds of optical components having different input dynamic ranges should be prepared.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to provide an optical switch expanding method which enables expansion of an optical switch with a smaller loss than in the conventional art, as well as an optical switch in which connections are made according to the expanding method and an optical crossconnecting apparatus where the optical switch is employed.
Another object of the
Kuroyanagi Satoshi
Nishi Tetsuya
Staas & Halsey , LLP
Wang George Y.
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