Signal routing for fiber optic networks

Details Signal routing for fiber optic networks Signal routing for fiber optic networks

1998-06-01

2001-08-28

Pascal, Leslie (Department: 2633)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200, C359S199200

Reexamination Certificate

active

06281998

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to apparatus and methods for signal routing within fiber optic networks, and particularly to use of switching within a branching unit of a fiber optic network. Such switching is particularly adapted to use either within, or to determine routing of signals to, an add/drop multiplexer. The invention extends in further aspects to an add/drop multiplexer comprising switching means, and to a branching unit for a fiber optic network comprising switching means, or comprising an add/drop multiplexer associated with switching means as indicated above. The invention also relates to switchable wavelength routing elements.
BACKGROUND OF THE INVENTION
As is discussed in the applicant's copending International Patent Application, filed on the same date as the present application and entitled “Add/drop Multiplexer”, the content of which is incorporated herein by reference, it is possible to construct a branching element for a fiber optic component which is essentially passive. An schematic example is shown in
FIG. 1A
, comprising a branching element
105
having a first branch
101
for carrying signals to and from a first part of a fiber trunk, a second branch
102
for carrying signals to and from a second part of the fiber trunk, and a third branch
103
for carrying signals to and from a spur station. Although each of the “branches”
101
,
102
,
103
is shown here as a single fiber, this is only for ease of illustration: it is possible for each of branches
101
,
102
,
103
to comprise a plurality of fibers. Branches
101
,
102
generally will comprise two or more fibers, one or more to carry traffic in one direction and one or more to carry traffic in the opposite direction. Signals at specific carrier wavelengths are routed by the system so that they are directed out of the branching element according to their carrier wavelength. In an exemplary case, signals arriving on branch
101
are allowed to pass out to branch
102
, except at carrier wavelength &lgr;
1
, when they are diverted to branch fiber
103
. New signals &lgr;
1
′ at the same carrier wavelength are added to the branching element from the spur station along branch
103
and are passed out of the branching element along branch
102
. Similarly, signals entering the branching element along branch
102
pass out on to branch
101
, except at a different carrier wavelength &lgr;
2
, at which signals are dropped to the spur station along branch
103
, and replaced with other signals &lgr;
2
′ at this wavelength entering the branching element along branch
103
and passing out along branch
102
.
A passive branching element such as indicated above can be designed to have considerable advantages: it can employ relatively few components and can be constructed so that it should not require attention at any point during its working life. Such an element is particularly suitable to use in undersea cable networks. However, it would be desirable even in this area to be able to switch a branching element to at least a limited degree. One desirable option is shown in FIG.
1
B: as well as dropping &lgr;
1
from trunk
101
to spur
103
, &lgr;
3
is dropped and replaced with a new signal from spur
103
at the same carrier wavelength. Alternatively, &lgr;
3
could be dropped instead of &lgr;
1
. Ability to provide such features may allow the network as a whole to be reconfigured (for example, by the addition or removal of spur stations to or from the network, or by the addition of capacity to the spur node) without any need physically to change or replace individual branching units already in place.
Further desirable options are shown in
FIGS. 1C
,
1
D and
1
E. These all relate to a break in either the trunk or the spur. All these options are of assistance in allowing traffic to still be transmitted even after such a break has occurred by routing all traffic away from the broken branch. In the
FIG. 1C
case of a broken spur fiber
103
, all traffic to the spur is routed on to one or the other of the trunk branches
101
,
102
. It then passes through a preceding or a subsequent alternative branching unit and spur station (the alternative branching unit being modified, for example, by being adapted to add and drop additional carrier wavelengths by switching from a
FIG. 1A
configuration to a
FIG. 1B
configuration) and then transmitted between the fiber break spur station and the alternative spur station by means of a back-haul network (e.g. a land line) between the two stations. Traffic from the spur can follow the same route, but in the opposite direction.
FIGS. 1D and 1E
show arrangements which allow the rerouting of all traffic in response to a break in the trunk fiber. All signals for transmission to the broken trunk
102
in
FIG. 1D
are dropped down spur
103
and communicated through a back-haul network to another spur for a branching unit as shown in
FIG. 1E
, so that all signals to travel along the trunk fiber are routed around the fiber break.
In C. R. Giles and V. Mizrahi, IOOC-95, ThC2-1,pp 66-67, an experimental arrangement is shown including a simple add/drop multiplexer in which the add/drop wavelength can be changed. An add/drop multiplexer of this general type is shown in FIG.
15
. The signal path, which links a first optical circulator
901
at which a signal may be dropped and a second optical circulator
902
at which a signal may be added, goes into a first 1×2 optical switch
903
and out from a second 1×2 optical switch
904
. The two optical switches are linked by a first path with a Bragg grating
905
to reflect light at &lgr;
1
and also by a second path with a Bragg grating
906
to reflect light at &lgr;
2
, with the result that the add/drop wavelength of the multiplexer can be switched between &lgr;
1
and &lgr;
2
: the connection to ports of the circulators is such that only signals of the carrier wavelengths reflected by the Bragg grating on the chosen signal path will be added or dropped. This document does not however provide or suggest a full solution to the problem of constructing rerouting mechanisms for use in branching units of a fiber optic network to achieve the functionality of
FIGS. 1B
to
1
E.
There is thus a need to provide simple and economical switching mechanisms to achieve signal rerouting with the functionalities indicated in
FIGS. 1B
to
1
E. Generally, there is a need to provide simple and reliable switching for branching units of a fiber optic network.
Accordingly, the invention provides a branching unit for a fiber optic network adapted to carry signals at a plurality of predetermined carrier wavelengths, comprising one or more inputs for receiving signals either from one or more trunk fibers of the network or from spur fibers for adding signals from spur stations of the network, one or more outputs for outputting signals either to one or more trunk fibers of the network or to spur fibers for dropping signals to spur stations of the network, and an add/drop multiplexer and switching means to provide two or more different routings of signals between said inputs and said outputs.
In one advantageous form, said switching means is adapted to provide alternative signal routings such that signals at one or more predetermined carrier wavelengths entering the branching unit at one input are directed in said alternative signal routings to alternative outputs of the branching unit. In another advantageous form, said switching means is adapted to provide a normal signal routing and an alternative signal routing, such that in said alternative signal routing, signals are rerouted from one or more designated outputs of the branching unit to one or more other outputs of the branching unit.
In certain preferred embodiments, said switching means comprises one or more switching elements having a first state in which signals pass directly therethrough and a second state in which signals are diverted around a loop path with one or more wavelength routing components thereon. At least one of said switchin

Affiliated with

Also associated with

Rating

Signal routing for fiber optic networks does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Signal routing for fiber optic networks, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Signal routing for fiber optic networks will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2475339