Note: Descriptions are shown in the official language in which they were submitted.
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OPTICAL CONNECTION ARRANGEMENTS
This invention relates to optical connection
arrangements, and is particularly concerned with an arrangement
for facilitating modifications to optical connections during
operation of an optical communications system which for example
uses wavelength division multiplexing (WDM).
Background
It is known to provide a WDM optical communication
system, referred to below for brevity simply as an optical
system, in which two or more optical channels are carried on a
single optical fiber, each channel comprising an optical signal
at a respective wavelength. At any node in the optical system,
it may be desired to terminate one or more of the channels, for
which purpose it is known to provide an optical add/drop
multiplexer (optical ADM, or OADM). An OADM typically
comprises one or more optical channel filters and/or one or
more optical band filters, where an optical band comprises a
plurality of optical channels to be dropped and added. Optical
channel and band filters are well known in the art and need not
be described here.
The use of OADMs to drop and add individual optical
channels or bands provides the advantage that the node-to-node
optical connectivity of the optical system can be different
from the physical connectivity of the optical fibers used to
carry the channels. For example, the optical fibers may extend
between adjacent nodes of an optical system, whereas the
optical connectivity can be such that nodes can be selectively
bypassed by some channels, depending upon the optical filters
provided at the nodes. Consequently, each node in such an
optical system can have an OADM with a set of optical filters
that are customized for that node.
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As an example of this, an optical system may comprise
a ring of four nodes A-D with optical fibers between adjacent
nodes to provide bidirectional communication of optical signals
between the adjacent nodes using three optical channels (i.e.
wavelengths) 1-3. A full mesh optical connectivity can be
provided among all of the nodes A-D if all of the nodes drop
and add channel 1, nodes A and C also drop and add channel 2,
and nodes B and D also drop and add channel 3.
Such a process of dropping and adding specific
wavelengths or wavebands at respective nodes is referred to as
wavelength or waveband routing.
Typically, an optical system using wavelength or
waveband routing is initially deployed with different optical
filters at the respective nodes, and for cost reasons only as
much equipment is installed as is necessary to meet actual or
short-term forecasted traffic requirements.
Over time, however, it may become necessary to modify
such an optical system to meet changing requirements, for
example to provide additional channels or to change the
wavelength or waveband routing. Such modifications typically
involve identification and disconnection of optical fibers at
the nodes, addition or replacement of OADMs and/or other
components such as optical transmitter and receiver cards,
optical amplifiers, and dispersion compensation modules, and
reconnection of the optical fibers, these steps being necessary
individually for each node.
The disconnection and reconnection of optical fibers
interrupts traffic for all nodes communicating via the
respective fibers. In optical systems with protection
switching, a protection switch can be forced to route traffic
around an optical fiber to be disconnected. While this can
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reduce the adverse effects of modifications on traffic having
the highest priority for protection, it nevertheless reduces
the traffic capacity of the optical system, and results in the
optical system having reduced or no protection resources
against an actual fault that may occur during the modification
process. This disadvantage is exacerbated by the fact that
similar steps must be carried out at each node, necessitating
multiple forced protection switches and an excessive time
during which the optical system has reduced capacity and
reduced protection resources.
In addition, the density of a typical optical system
and the similar appearance of different optical fibers tend to
make the manual task of sorting and identifying optical fibers
to be disconnected and reconnected time consuming, expensive,
and prone to errors. Furthermore, the fiber handling itself
can lead to fiber damage, for example increased fiber losses
due to micro-bending, and increases risks of obtaining dirty
optical connections, so that operating margins of the optical
system may be reduced, and consequent problems may arise at the
time of the modifications or subsequently.
Consequently, there is a need to provide an improved
optical connection arrangement, which can enable modifications
such as those discussed above to be made in a manner to reduce
or avoid these disadvantages.
Summary of the Invention
According to one aspect of this invention there is
provided an optical connection arrangement comprising: a
plurality of optical ports each comprising at least two optical
connections for respectively supplying an optical signal to and
receiving an optical signal from an optical component coupled
to the respective port; an optical signal input; an optical
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signal output; and at least one optical switch coupled to the
optical signal input, the optical signal output, and the
plurality of optical ports, the optical switch being
controllable to provide an optical path from the optical signal
input to the optical signal output selectively via none, one,
or at least two of the plurality of optical ports.
In different embodiments of the invention, such
connection arrangements can be combined in various series
and/or parallel combinations, and the at least one optical
switch can comprise lx2 and 2x2 optical switches, or one or
more NxN optical switches where N is an integer greater than 2.
In particular embodiments of the invention, each
optical port has an optical connection to one of two optical
outputs of a preceding optical switch stage, and an optical
connection to one of two inputs of a following switch stage,
the optical switch stages constituting said at least one
optical switch, a first one of said optical switch stages
having an optical input coupled to said optical signal input
and a last one of said optical switch stages having an optical
output coupled to said optical signal output, the arrangement
further comprising an optical coupling from another of the two
optical outputs of each said preceding optical switch stage to
another of the two inputs of the respective following switch
stage for optically bypassing the respective optical port, each
optical switch stage having two optical connection states
between its inputs) and its output(s), the optical switch
stages being controllable to include selectively each optical
port in, or selectively exclude it from, an optical path from
said optical signal input to said optical signal output.
Another aspect of the invention provides an optical
add/drop multiplexer (OADM) arrangement comprising: an optical
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connection arrangement in an optical path, the optical
connection arrangement comprising at least one optical switch
and a plurality of optical ports each of which can be
selectively included in the optical path or bypassed by control
5 of said at least one optical switch, the optical ports each
being arranged for coupling of an OADM thereto so that
different OADMs can be coupled each to any of said plurality of
optical ports; and at least one OADM optically coupled to a
respective optical port of the optical connection arrangement.
A further aspect of the invention provides a method
of modifying optical couplings of one or more optical
components to an optical path, comprising the steps of:
providing in the optical path an optical connection arrangement
having a plurality of optical ports each of which can be
selectively included in the optical path or bypassed by control
of at least one optical switch of the optical connection
arrangement; changing optical couplings of at least one optical
component to a respective optical port while the optical
connection arrangement is controlled to selectively bypass the
respective optical port; and subsequently controlling the
optical connection arrangement to selectively include the
respective optical port and said optical component in the
optical path.
Brief Description of the Drawings
The invention will be further understood from the
following description by way of example with reference to the
accompanying drawings, in which the same references are used in
different figures to denote similar elements and in which:
Fig. 1 shows a known optical add/drop multiplexer;
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Fig. 2 illustrates an optical connection arrangement
in accordance with an embodiment of the invention, also showing
an OADM;
Fig. 3 illustrates a modification of the arrangement
of Fig. 2;
Fig. 4 illustrates a connection module in accordance
with an embodiment of the invention, providing four optical
connection ports;
Fig. 5 illustrates two OADMs coupled to a connection
module in accordance with another embodiment of the invention,
providing four bidirectional optical connection ports;
Fig. 6 illustrates an arrangement of connection
modules in accordance with another embodiment of the invention;
Fig. 7 illustrates an expanded arrangement of the
connection modules;
Fig. 8 illustrates an optical connection arrangement
in accordance with another embodiment of the invention, using
an NxN optical switch with N>2; and
Fig. 9 illustrates a modification of the optical
connection arrangement of Fig. 8.
Detailed Description
Referring to the drawings, Fig. 1 illustrates a known
optical add/drop multiplexer (OADM) for dropping and adding an
optical band comprising a plurality of optical channels
transmitted in one direction (left to right as shown in Fig. 1)
on an optical fiber 10. The OADM of Fig. 1 comprises an
optical band filter 12 having an optical input to which the
optical fiber 10 is connected, and having two optical outputs
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one of which is coupled via an optical fiber 14 to an input of
an optical channel filter 16 and the other of which is coupled
via an optical fiber 18 to one input of an optical band filter
20. A second input of the band filter 20 is coupled via an
optical fiber 22 to an output of an optical channel filter 24,
and an output of the band filter 20 is coupled to an ongoing
part 11 of the optical fiber 10.
The band filter 12 supplies a band of optical
channels to be dropped by the OADM to the fiber 14, and
supplies other optical channels to the fiber 18. The channel
filter 16 demultiplexes the channels of this band into separate
optical channels on respective optical fibers 26. Conversely,
the channel filter 24 multiplexes optical channels supplied to
it via respective optical fibers 28 into a similar or different
optical band on the fiber 22, and the band filter 20
multiplexes this band of added optical channels with the other
optical channels on the fiber 16.
As is known in the art, where the same optical bands
and channels are dropped and added, the optical band filters 12
and 20 can be identical to one another, and the optical channel
filters 16 and 24 can be identical to one another. Each filter
can comprise an optical filter of known form having a filter
wavelength and bandwidth appropriate for the optical band or
channel to be dropped or added. Also, as is known in the art,
each such filter can be reversible for optical signals in the
opposite direction, and the OADM of Fig. 1 can also operate for
optical signals in the opposite direction to that shown. Thus
for example for optical signals that are transmitted in both
directions on a single fiber, a single optical filter can serve
both for dropping an optical band or channel in one direction
and adding a similar optical band or channel for the opposite
direction. However, the particular transmission directions
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shown in Fig. 1 are provided for ease of understanding, and the
description is worded accordingly. Similar comments apply in
respect of the various embodiments of the invention described
below.
It can also be appreciated that the OADM of Fig. 1
can be simplified by omitting the optical band filters 12 and
20 and instead providing the optical channel filters 16 and 24
directly in the optical fiber 10, with the disadvantage of
increased attenuation of the other optical channels on the
fiber 18 if more than one optical channel is dropped and added.
Accordingly, the following description refers in part simply to
optical filters, without distinguishing between band and
channel filters, and it can be appreciated that in each case
this includes either an optical band filter adding or dropping
one or more optical bands, or an optical channel filter adding
or dropping one or more optical channels.
Furthermore, although as illustrated in Fig. 1 the
OADM serves both to drop and to add optical channels, it can be
appreciated that the OADM can be simplified to drop optical
channels without adding any channels, or to add optical
channels without dropping any channels, and the term OADM and
the description should be understood accordingly. The same
applies to other figures of the drawings and to each of the
embodiments of the invention described below.
As discussed above, the OADM of Fig. 1 is coupled in
the path of optical signals on the fiber 10, so that changes,
for example to drop and add a different or an additional band
of optical channels, involve an interruption of the optical
signal including all channels on the fiber 10, and consequent
disadvantages such as those discussed above.
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Fig. 2 illustrates an optical connection arrangement
in accordance with an embodiment of the invention, also showing
an OADM 30 which comprises optical filters 32 and 34. The
connection arrangement of Fig. 2 comprises two 1x2 (1-pole
2-way) optical switches 36 and 38, a 2x2 (2-pole 2-way change-
over) optical switch 40, and two optical ports Pl and P2. For
each of the optical switches, a solid line indicates an optical
path via the switch in one state and a broken line indicates an
optical path via the switch in another state of the switch.
The optical switches 36, 38, and 40 can be of any desired form,
and their states can be controlled by optical system software
via a control unit (not shown) in known manner.
In the connection arrangement of Fig. 2, the optical
fiber 10 is coupled to the pole of the lx2 switch 36, one
optical output of which is coupled via an optical fiber 42 to
one input of the 2x2 switch 40. One optical output of the 2x2
switch 40 is coupled via an optical fiber 44 to one optical
input of the 1x2 switch 38, the pole of which is coupled to the
ongoing part 11 of the optical fiber 10.
The optical port P1 is provided between the second
optical output of the switch 36 and the second optical input of
the switch 40, and the optical port P2 is provided between the
second optical output of the switch 40 and the second optical
input of the switch 38. Thus each of the optical ports P1 and
P2 provides two optical fiber connections. For the illustrated
optical signal direction, the fiber connection on the left of
each port can supply an optical signal from the connection
arrangement via the port, and the fiber connection on the right
can provide an optical signal to the connection arrangement via
the optical ports however, as indicated above the arrangement
can equally be used for either or both transmission directions.
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As illustrated in Fig. 2, the OADM 30 is coupled to
the optical port Pl, the fiber connection on the left of the
port being coupled to the optical input of the optical filter
32 for dropping optical channels, and the fiber connection on
5 the right of the port being coupled to the optical output of
the optical filter 34 for adding optical channels.
It can be seen from Fig. 2 that the optical switches
36, 40, and 38 are provided in series in the main optical
signal path from the fiber 10 to its ongoing part 11, and that
10 the illustrated solid-line optical paths through these switches
provide a continuous optical path for the optical signals on
the fiber 10. Installation of the connection arrangement thus
involves an interruption of this main optical signal path.
Conveniently, such installation takes place during initial
installation of the optical system, before there is any traffic
on the fiber 10. Alternatively, the connection arrangement can
be installed in an operating optical system, with traffic on
the fiber 10 being interrupted only once for this installation.
Thereafter, as described below modifications can be made with
minimal traffic interruption and protection switching, under
software control of the optical switches.
For example, with optical signal traffic on the fiber
10 conducted via the solid-line paths of the switches 36, 40,
and 38 as shown in Fig. 2, the OADM 30 can be connected to and
disconnected from the optical port P1 with minimal interruption
of the traffic. For modifications to the optical system, for
example the OADM 30 can be removed and replaced by another OADM
for dropping and adding different optical channels. Further,
another OADM (not shown) can be added at the optical port P2 in
a similar manner. Alternatively, other forms of optical signal
component, such as an optical amplifier, optical signal
monitor, dispersion compensation module, or another connection
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arrangement as described herein, can be similarly added at each
optical port.
Assuming that the OADM 30 is added at the optical
port Pl as shown in Fig. 2 with traffic on the fiber 10
conducted via the solid-line positions of the switches 36, 40,
and 38, the switches 36 and 40 can then be changed over under
software control to their broken-line positions to connect the
OADM 30 with minimal traffic disturbance and protection
switching, for example within a fraction of a second, at a
convenient time when traffic may be minimal. This permits
rapid verification of the modified OADM arrangement, with
almost instant reversal to the original state in the event of
installation errors. With a modularized arrangement of the
OADM 30 and the connection arrangement as further described
below, this also substantially eliminates fiber handling and
consequent errors and fiber damage.
Similarly, a second OADM or other optical component
can be added at the optical port P2. After installation of
such a component, the switch 40 can be returned to its solid-
line state as shown, and the switch 38 can be simultaneously
changed to its broken-line state as shown, under software
control to connect this further component into the optical
signal path, with the same advantages as discussed above.
For further expansion of the arrangement of Fig. 2
for example to accommodate more than two OADMs, a second or
further connection arrangement as shown in Fig. 2 can be
connected at any optical port, thereby providing two optical
ports instead of one. For any such further connection
arrangement, which is conveniently also provided in modular
form, the optical input of the switch 36 and the optical output
of the switch 38 are coupled to the respective fiber
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connections of the optical port. Alternatively, the connection
arrangement and/or any further connection arrangement which is
added can have additional optical switches and optical ports,
as described further below.
Fig. 3 illustrates a modification of the arrangement
of Fig. 2, in which the 2x2 optical switch 40 is replaced by
two 1x2 optical switches 46 and 48, the poles of the two
switches 46 and 48 being coupled together. Otherwise, the
arrangement of Fig. 3 is the same as that of Fig. 2. In this
case conveniently the optical switches 36 and 46 are commonly
controlled and operated in synchronism with one another, and
the optical switches 38 and 48 are also commonly controlled and
operated in synchronism with one another.
In general, any 2x2 optical switch in the connection
arrangement can be replaced by two 1x2 optical switches in the
same manner, and conversely a 1x2 optical switch, such as the
switch 36 or 38 in Fig. 2, can be replaced by a 2x2 optical
switch part of which is unused. In the following description
and corresponding figures of the drawings 2x2 optical switches
are described and illustrated for simplicity and convenience,
and it should be understood that any of these can be replaced
by equivalent lx2 optical switches.
The connection arrangements of Figs. 2 and 3 each
provide two optical ports P1 and P2, but they can be extended
in a similar manner using additional optical switches to
provide three or more optical ports. For example, it may be a
convenient design choice for the connection arrangement to have
a modular form with each connection module providing four
optical ports; Fig. 4 illustrates such a connection module.
The connection module of Fig. 4 comprises five (one
more than the number of optical ports) 2x2 optical switches 50
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to 54 which are coupled between an input optical fiber 56 and
an output optical fiber 58. The fibers 56 and 58 correspond
respectively to the optical fiber 10 and its ongoing part 11 as
described above, or can be connected to the left and right
fiber connections of an optical port of another similar or
different connection module. The switches 50 to 54 provide an
optical path from the fiber 56 to the fiber 58 which can be
switched, by changing the states of the switches as described
above, to include none or any arbitrary one or more of the
optical ports P1 to P4, which are provided respectively between
the switches 50 and 51, 51 and 52, 52 and 53, and 53 and 54.
Optical systems typically provide bidirectional
communications using two optical fibers, one for each direction
of transmission, and OADMs typically provide add/drop pairs of
optical filters. Connection modules in accordance with
embodiments of the invention can accordingly be provided
conveniently using two sets of series optical switches each for
example as shown in Fig. 4, one set for each transmission
direction.
Fig. 5 illustrates such a connection module 70,
illustrated within a dashed-line box, comprising one set of
optical switches 50 to 54 arranged in series between fibers 56
and 58, as described above, for a first direction of
transmission and another set of switches 60 to 64, similarly
arranged in series between fibers 66 and 68, for the opposite
direction of transmission. The optical port between the
switches 50 and 51 for the first direction of transmission, and
a similarly provided optical port between the switches 60 and
61 for the opposite direction of transmission, together
constitute a bidirectional optical port BP1 of the connection
module. Correspondingly, the connection module 70 provides
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other bidirectional optical ports BP2 to BP4 between the other
successive switches.
Fig. 5 also illustrates two OADM modules 72 and 74,
coupled to the bidirectional optical ports BPl and BP2
respectively. Each of the OADM modules 72 and 74 comprises
optical band filters 76 and optical channel filters 78 for
dropping optical channels from the first transmission direction
and adding optical channels for the opposite transmission
direction. Further OADM modules (not shown) can be connected
to other bidirectional optical ports to add optical channels
for the first transmission direction and to drop optical
channels for the opposite transmission direction. It can be
appreciated that, in order to minimize attenuation of optical
channels, it is preferable to drop optical channels closer to
the optical signal input, and to add optical channels closer to
the optical signal output, of the connection module, and the
arrangement of Fig. 5 can facilitate this.
In optical systems the two physical directions of
fiber from an optical node, typically referred to as west and
east directions, are often packaged separately for protection
and upgrade reasons, and for wavelength routing purposes may
carry different optical wavelengths, for example an optical
node may drop one optical band from and add a different optical
band to the optical signals on the fibers. It is convenient in
this case to provide two concatenated connection modules in
accordance with embodiments of this invention, one for each
direction. Such an arrangement is illustrated in Fig. 6.
As shown in Fig. 6, two connection modules, each of
which can for example be a connection module 70 as described
above with reference to Fig. 5 providing four bidirectional
optical ports BP1 to BP4, are connected in series, or
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concatenated, with one another in the bidirectional optical
fiber paths. The connection modules are referred to for
convenience as a west connection module 80 and an east
connection module 82. OADM modules, such as OADM modules 84
5 and 86 illustrated in Fig. 6, can be coupled to the optical
ports BP1 to BP4 of each connection module as described above,
the optical switches (not shown in Fig. 6) being controlled as
described above to couple the OADMs into the fiber paths or
bypass them as desired.
10 In the arrangement of Fig. 6, for simplicity drop and
add paths for an optical band (or channel) are indicated by
arrows. Thus the OADM 84 coupled to the optical port BP1 of
the west connection module 80 drops an optical band from the
optical signal being transmitted towards the right (east) in
15 the drawing, and adds an optical band to the optical signal
being transmitted towards the left (west). Conversely, the
OADM 86 coupled to the optical port BP1 of the east connection
module 82 drops an optical band from the optical signal being
transmitted towards the left (west) in the drawing, and adds an
optical band to the optical signal being transmitted towards
the right (east) .
The arrangement of Fig. 6 includes an additional
bidirectional optical port which is provided between the
concatenated modules 80 and 82, and more particularly between
connections of adjacent 2x2 optical switches in the two modules
which are otherwise unused as shown for example for the optical
switches 54 and 56 in Fig. 5, in the same manner as the
bidirectional optical ports between adjacent optical switches
within the same connection module. Fig. 6 illustrates a
dispersion compensation module 88, including a dispersion
compensator (DC) for optical signals in each direction of
transmission, coupled to this additional port. The dispersion
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compensators can be coupled into the optical paths, or omitted
from these paths, under software control of the optical
switches in a similar manner to that described above for the
OADMs .
Instead of the dispersion compensation module 88, any
other optical component which may be desired can be coupled to
the additional bidirectional optical port (or to any of the
ports). For expansion of the connection arrangement to more
than the nine bidirectional optical ports provided by the
arrangement of Fig. 6, such other optical component may
comprise another connection module as illustrated in Fig. 7 or,
to retain the separation of east and west components, another
two such connection modules concatenated in the same manner as
the connection modules 80 and 82 in Fig. 6.
Referring to Fig. 7, illustrating an expanded
arrangement of the connection modules, an additional connection
module 90, which can have the same form as the connection
modules 70, 80, and 82 as described above, is coupled to the
additional bidirectional optical port between the concatenated
connection modules 80 and 82, so that it can be switched into
the concatenated arrangement to provide additional
bidirectional optical ports. Fig. 7 illustrates the connection
modules 80 and 82 as being fully populated each with four
OADMs, and further OADMs 84 and 86 coupled to the additional
connection module 90. Further expansion of the connection
arrangement can be similarly provided.
It can be appreciated that in all of the connection
arrangements in accordance with embodiments of the invention as
described above, the initial provision of one or more
connection modules in the optical path enables arbitrary
subsequent changes to be provided and incorporated into
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operation under software control via the optical switches,
without the disadvantages discussed above in relation to the
prior art.
Although the connection arrangements in accordance
with embodiments of the invention as described above use series
2x2 (or an equivalent arrangement of 1x2) optical switches, the
principles of the invention can alternatively be provided by a
connection arrangement using one or more NxN optical switches
where N is greater than 2.
By way of example, Fig. 8 illustrates a connection
arrangement in the form of an NxN optical switch 92, having N
optical inputs and N optical outputs 1 to N numbered 1 to N,
the optical switch being controllable to couple each optical
input to any of the optical outputs. Fig. 8 also shows two
OADM modules 72 and 74, for example as described above, which
are coupled to the optical switch 92.
More particularly, in the arrangement of Fig. 8 an
incoming optical signal on the optical fiber 10 is supplied to
one input (input 1 as illustrated) of the optical switch 92,
and an outgoing optical signal is supplied from one output
(output 1 as illustrated) of the optical switch 92 to the
ongoing part 11 of the optical fiber 10. Although Fig. 8
relates to transmission of optical signals in only one
direction on the optical fiber 10, it will be appreciated that
the arrangement can accommodate bidirectional transmission in a
similar manner to that described above.
Each OADM module 72, 74 has an input coupled to
another respective output of the optical switch 92 and an
output coupled to another respective input of the optical
switch 92, and provides for dropping and/or adding an optical
band or channel as described above. Conveniently for providing
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a modular arrangement, as illustrated, each OADM module is
coupled to a respective correspondingly-numbered output and
input of the optical switch 92. For example, in Fig. 8 the
optical switch input number 2 and output number 2 are coupled
to the output and input, respectively, of the same OADM module
72.
The optical switch 92 is controlled to provide
desired couplings between its optical inputs and outputs. For
example, a connection from its input 1 to its output 1 provides
a direct coupling of the fiber 10 to its ongoing part 11; thus
OADM modules such as 72 and 74, and/or other optical
components, can be changed, added, and removed with minimal
interruption of optical traffic on the fiber 10. Such modules
are incorporated into the optical path by changing optical
connections via the optical switch 92. For example, as shown
by dashed lines in Fig. 8, the OADM modules 72 and 74 can be
incorporated into the optical path by controlling the optical
switch 92 instead to couple its input 1 to output 3, input 3 to
output 2, and input 2 to output 1.
It can be appreciated that such control of the
optical switch 92 can be carried out by software in a similar
manner, and with the same convenience and advantages, as in the
other connection arrangements in accordance with the invention
as described above. It will also be appreciated that the size,
i.e. number N of inputs and outputs, of the optical switch 92
can be selected to meet particular needs and that, as in the
connection arrangements in accordance with embodiments of the
invention as described above, the connection arrangement of
Fig. 8 can be expanded by coupling one or more other optical
switches to inputs and outputs of the optical switch 92.
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Furthermore, it can be appreciated that, in a similar
manner to the series arrangements of 2x2 optical switches as
described above, a plurality of NxN optical switches can also
be coupled in series with one another in the optical path.
More generally, the connection arrangement can comprise any of
a wide variety of combinations of optical switches, in series
and/or parallel configurations, regardless of the particular
size of each optical switch. One advantageous arrangement is
illustrated in Fig. 9, in which two similar NxN optical
switches 92 and 94, with their inputs and outputs coupled in
similar patterns to facilitate control, are provided in series
between the optical fiber 10 and its ongoing part 11.
The connection arrangement of Fig. 9 operates in a
similar manner to that of Fig. 8, except that the OADMs 72, 74
of Fig. 8 are replaced in the connection arrangement of Fig. 9
by separate optical drop filters 96 coupled between
corresponding outputs and inputs of the optical switch 92, and
optical add filters 98 coupled between corresponding outputs
and inputs of the optical switch 94. This arrangement
facilitates dropping optical bands or channels closest to the
incoming optical fiber 10, and adding optical bands or channels
closest to the ongoing part 11 of the fiber 10, thereby
minimizing attenuation of the optical signals. It can be
appreciated that such attenuation can be compensated by optical
amplifiers coupled between respective outputs and inputs of the
optical switches instead of OADM modules, drop or add filters,
or other optical components.
It can be appreciated that the optical switches in
the embodiments of the invention described above provide signal
attenuation, which can be compensated by optical amplifiers.
Conveniently, such optical amplifiers can be combined directly
with one, some, or all of the optical switches or switch
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stages. For example, in the arrangement of Fig. 2 the 2x2
switch 40 can include two optical amplifiers (not shown), one
for each optical path preferably at the output side of the
switch. In the arrangement of Fig. 3 a single optical
5 amplifier (not shown) can be provided in the optical path
between the 1x2 optical switches 46 and 48, to compensate for
signal attenuation in these switches. In the arrangements of
Figs. 8 and 9, N optical amplifiers (not shown) can
conveniently be provided for each NxN optical switch, one
10 optical amplifier in each of the N output paths of the switch.
Similar comments apply in respect of the other
optical switches, thus each optical switch or switching stage
can include an optical amplifier for each of its optical paths
to compensate for signal attenuation in that switch or
15 switching stage, so that optical signal attenuations are
compensated by optical signal gains distributed throughout the
connection arrangement. Alternatively, optical amplifiers need
not be provided in the connection arrangement, or can be
provided only at particular points in the connection
20 arrangement to provide lumped optical signal gain as may be
desired.
Although particular embodiments of the invention and
variations have been described above in detail above, it can be
appreciated that numerous other modifications, variations, and
adaptations may be made without departing from the scope of the
invention as defined in the claims.
