Optical waveguides – With optical coupler – Plural
Reexamination Certificate
2002-03-06
2004-07-27
Healy, Brian (Department: 2874)
Optical waveguides
With optical coupler
Plural
C385S016000, C398S079000, C398S082000, C398S083000
Reexamination Certificate
active
06768831
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical add-drop multiplexing apparatus, in particular, to that used in a wavelength division multiplexing communication network.
2. Description of the Related Art
In recent years, as the Internet and cellular phones become common and the functions of terminal units are advanced, the bandwidths of access lines become large and the traffic on the network drastically increases. It seems that such a trend will continue in future. Thus, the infrastructure for communication is being enhanced.
To deal with the increase of the traffic of communications, an optical communications network is being constructed. To accomplish a large capacity of a transmission line, wavelength division multiplexing (WDM) communications system is being introduced. In comparison with the improvement of the technology with respect to capacity of the transmission line, the improvement of the technology with respect to speed of communication nodes (transmission devices) is insufficient. Thus, it is pointed out that the communication nodes will become a bottleneck of the network.
Consequently, in a network using the WDM system for accomplishing a large capacity of a transmission line, communication nodes that allow signals to be processed at high speed are required. The mainstream of the network topology is of ring type. The communication nodes are sometimes accomplished by optical add-drop multiplexing apparatuses.
FIG. 1
is a schematic diagram showing the structure of an example of a conventional optical add-drop multiplexing (ADM) apparatus. Referring to
FIG. 1
, four input-side inter-station lines and four output-side inter-station lines are connected to the optical ADM apparatus. In this example, the inter-station lines are backbone transmission lines that connect communication nodes and transmit multi-wavelength light (&lgr;
1
to &lgr;n).
Wavelength demultiplexers
501
a
to
501
d
demultiplex multi-wavelength light received through the input-side inter-station lines into signals of individual wavelengths. Cross point switches
502
are disposed corresponding to the individual wavelengths. Input signals are guided to corresponding output ports.
FIG. 1
shows a cross point switch
502
corresponding to a wavelength &lgr;
1
. Wavelength multiplexers
503
a
to
503
d
multiplex outputs of each cross point switch
502
and output the multiplexed signals to the output-side inter-station lines.
The optical ADM apparatus is provided with an add port and a drop port. The add port is used to receive a signal to be added to an inter-station line. The drop port is used to output a signal branched from an inter-station line to an intra-station line. However, a signal that is input through the add port is branched to a set of signals by an optical coupler that functions as an optical splitter and then guided to the cross point switch
502
.
Thus, the cross point switch
502
has eight input ports and six output ports and is realized by an 8×6 switch. As shown in
FIG. 2
, the cross point switch
502
(8×6 switch) is composed of thirty five 2×2 switches and thirteen 1×2 switches.
With the structure, a signal that is input from any input-side inter-station line can be guided to a desired output-side inter-station line or a desired intra-station line. In addition, a signal that is input from an intra-station line through the add port can be guided to a desired output-side inter-station line.
FIG. 3
is a schematic diagram showing the structure of another example of a conventional optical ADM apparatus. In this optical ADM apparatus, an optical switch is divided into a plurality of portions. In other words, the optical ADM apparatus comprises 3×2 switches
511
a
to
511
d
, a 4×4 switch
512
, 2×2 switches
513
a
and
513
b
, and a 4×2 switch
514
. The 3×2 switches
511
a
to
511
d
are disposed corresponding to the individual inter-station lines. The 4×4 switch
512
are used to switch the route of a signal upon occurrence of a fault. The 2×2 switches
513
a
and
513
b
are used to add a signal to a desired inter-station line. The 4×2 switch
514
is used to guide a signal branched from an inter-station line to an intra-station line. With this structure, a signal that is input from any line can be guided to a desired line.
However, when large optical switches are used with the currently available technology, various problems take place. Thus, although the 8×6 cross point switch shown in
FIG. 2
can be accomplished, it cannot be obtain the high reliability. In addition, the production cost of the switch becomes very high. Thus, considering these points, at least at the present time, the structure of the optical ADM apparatus shown in
FIG. 1
is not preferable.
In the optical ADM apparatus shown in
FIG. 3
, a 4×4 switch, 3×2 switches, a 4×2 switch, and so forth are used instead of a large cross point switch. However, considering the reliability and the production cost, it cannot be said that they are preferable devices for accomplishing an optical ADM apparatus. In other words, it is desired to accomplish an optical ADM apparatus composed of smaller optical switches than those used so far.
When an optical switch used in an optical ADM apparatus gets defective, the defective optical switch is replaced with a new optical switch. Thus, when a large optical switch is used, the unit to be replaced becomes large. In other words, when a large optical switch is maintained, not only a service with respect to a defective line, but a service without respect thereto may have to be stopped.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical ADM apparatus with high reliability. Another object of the present invention is to provide an optical ADM apparatus that can be maintained with a minimum of change or stop of services.
An optical add/drop multiplexing apparatus of the present invention is connected to first to fourth input lines, first to fourth output lines, an add line, and a drop line, and this apparatus comprises: four first optical devices for splitting signals that are input from the first to fourth input lines, respectively; four first switches disposed corresponding to the first to fourth output lines, respectively; four second switches disposed corresponding to the first to fourth output lines, respectively; a pair of third switches; a drop unit for guiding a signal split by the first optical devices to the drop line; and an add unit for guiding a signal received from the add line to the second switches. One of the pair of third switches guides a signal received from second switches corresponding to the first and second output lines to first switches corresponding to the third and fourth output lines. The rest of the pair of third switches guides a signal received from second switches corresponding to the third and fourth output lines to first switches corresponding to the first and second output lines. The four first switches output signals split by the first optical devices or signals received from the third switches. The four second switches output signals received from the corresponding first switches or signals received from the add unit to the corresponding output lines.
With this structure, the number of inputs of the first switch is “2”, whereas the number of outputs thereof is “1”. Thus, the first switch can be accomplished by one switching device. In addition, the number of inputs of each of the second switch and the third switch is “2”, whereas the number of outputs thereof is “2”. Thus, each of the second switch and the third switch can be accomplished by one switching device. Such switching devices can be produced relatively easily at low cost with high reliability. Thus, an optical Add-Drop multiplexing apparatus with high reliability can be accomplished.
REFERENCES:
patent: 6233074 (2001-05-01), Lahat et al.
patent: 6583900 (2003-06-01), Onaka et al.
patent: 6594412 (2003-07-
Healy Brian
Katten Muchin Zavis & Rosenman
Petkovsek Daniel
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