Optical waveguides – With optical coupler – Plural
Reexamination Certificate
2000-05-25
2003-04-01
Spyrou, Cassandra (Department: 2872)
Optical waveguides
With optical coupler
Plural
C385S037000, C359S199200, C359S199200
Reexamination Certificate
active
06542660
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to optical networks. More particularly, the present invention relates to increasing a number of information channels carried by optical waveguides within an optical network.
BACKGROUND OF THE INVENTION
In recent years, the use of optical fibers has become increasingly widespread in a variety of applications. Optical fibers have been found to be especially useful for many industries such as telecommunications, computer-based communications, and other like applications.
For example, in the conventional art as illustrated in
FIG. 1
, a long-haul network
10
connects central offices or points of presence (PoPs)
20
of one city to another. The long-haul network
10
typically utilizes optical waveguides, such as fiber optic cables, that carry information propagating in the 1550 nanometer wavelength region. The long-haul network
10
can interconnect major population areas together. For example, if the central office
20
that connects to the long-haul network
10
was part of a regional hub such as Atlanta, then the central office
20
would have long-haul fiber optic cable routes to Dallas, Chicago, New York, and other major population areas. The long-haul network
10
can be maintained by interexchange carriers (IXCs), such as AT&T, MCI, Sprint, and other like new companies that handle long distance communications.
Each central office or point of presence (PoP)
20
is interconnected to an adjacent central office
20
by optical waveguides
30
that form an interoffice network
40
. An interoffice network
40
can be maintained by a local exchange carrier (LEC) such as Bell South, Bell Atlantic, and other companies that handle local communications. Each central office
20
of the interoffice network
40
can also be connected to optical waveguides
50
that form an access network or ring
70
. Within an access network or ring
70
, each central office
20
can be connected to one or more users
60
. A user
60
can comprise local area networks (LANs) that provide services to individual personal computers or voice communications. Each access network
70
may extend across a geographic region on the order of 10 miles (more or less) in circumference, while the interoffice networks
40
may span a geographic region that is in the order of 50 to 100 miles (more or less) in circumference.
Because of the relative size of the access networks
70
, communication providers typically employ synchronous optical network (SONET) standards for multiplexing and transporting data streams through the optical waveguides
50
. The SONET standard is based upon a time division multiplexing (TDM) technique. However, despite the use of the time division multiplexing technique, conventional access networks
70
are approaching bandwidth exhaustion due to the demand created by the public Internet and/or virtual private intranets. Conventional access networks
70
are typically designed as optical carrier
3
(OC
3
) SONET rings meaning that the maximum capacity at any point in the optical waveguides
50
that form the access networks
70
have a capacity of 155 megabits per second. OC
3
SONET rings can carry only three DS
3
signals or eighty four DS
1
signals on a entire ring. DS stands for a classification of transmitting one or more communications in a digital data stream. A DS
1
level means that data is transmitted at 1.544 megabits per second while DS
3
signals transmit data at 45 megabits per second. Users
60
are pressuring access network providers to support data transmitted at DS
3
or higher rates as opposed to DS
1
rates because current LANs operate much faster than DS
1
streams.
To increase capacity of conventional optical networks, such as to accommodate eighty five DS
1
signals or a fourth DS
3
service, an entire OC
3
SONET ring or access network
70
would require an upgrade to the optical carrier
12
(OC
12
) level that permits a maximum transmission capacity of 622 megabits per second at any point in an optical fiber. Such an upgrade would require complete replacement of add/drop multiplexers (ADMs)
220
(See
FIG. 2
) in the ring with larger capacity units.
Adding to the complexity of an upgrade to the SONET ring
70
A is the current reliance by the industry on the unidirectional path switched ring (UPSR), as illustrated in FIG.
2
. The UPSR
70
A is a SONET architecture that is particularly well-suited for access networks
70
in which traffic from multiple users
60
is hubbed into a network provider's central office or a point of presence (PoP)
20
. The UPSR
70
A includes fiber pairs
200
,
210
that link multiple SONET add/drop multiplexers (ADMs)
220
B-
220
E located at central offices/PoPs
20
and at remote locations accessible to users
60
. Traffic, in the form of DS
1
or DS
3
serial data bit streams originating from each user
60
, is multiplexed into the UPSR aggregate bit stream along optical waveguides
200
,
210
at OC-
3
or OC-
12
data rates for transport to the central office or point of presence (PoP)
20
. For example, a user
60
D typically “adds” an information signal to the aggregate data bit stream propagating along the outside optical waveguide
200
via the transmitter
220
T
1
. Similarly, the user
60
D “drops” an information signal from the aggregate data bit stream propagating along the outside optical waveguides
200
via the receiver
220
R
1
.
Information traffic normally flows in one direction around the SONET ring
70
A, using the working fiber
200
as indicated by the arrows denoting counter-clockwise flow. In the event of a single fiber or ADM transceiver failure, the information traffic is automatically redirected around the SONET ring
70
A, using a protection fiber
210
in accordance with the UPSR automatic protection switching (APS) feature. For example, if two optical waveguides between two ADMs
220
simultaneously fail at points
240
, such as optical waveguides
200
and
210
between user
60
D and user
60
E, then the UPSR APS feature will cross-connect the remaining working and protection fibers
200
,
210
to bypass the failed sections in order to maintain continuity of information flow at each user's connection. Therefore, instead of user
60
D “adding” and “dropping” information signals from the working optical waveguide
200
, the user
60
D would “add” signals to the working optical waveguide
200
via transmitter
220
T
1
and “drop” information signals from the protection optical waveguide
210
via the backup receiver
220
R
2
as illustrated in FIG.
2
.
The robust protection switching capabilities of the UPSR make this SONET architecture preferable to other conventional topologies, such as star and tree-branch topologies for high availability fiberoptic access networks. With this protection scheme, a central office or point of presence (PoP)
20
would “receive” or “drop” information signals with the primary receiver
220
R
1
and transmit or “add” information signals to the SONET network
70
A via the backup or secondary transmitter
220
T
2
. It is noted that the “working” fiber
200
and “protection” fiber
210
may not be dedicated lines. In other words, the APS feature of an USPR may comprise complex switching techniques where a “working” or “protection” fiber is merely an optical path within an optical fiber that is a result of the complex switching techniques. The working fibers
200
and protection fibers
210
have been denoted as such in
FIG. 2
for illustrative purposes only. That is, protection fibers
210
of
FIG. 2
may carry information continuously while only an optical path generated by a switching technique is dedicated within the protection fiber
210
for the APS feature.
While the automatic protection switching feature of a unidirectional path switched ring makes a SONET architecture very desirable and dependable, such an optical architecture still suffers from signal losses that are present in any optical architecture. In order to compensate for such signal losses, amplifiers may be needed within each respective optical ne
Medin Michael W.
Wach Michael L.
Assaf Fayez
Cirrex Corp.
King & Spalding LLP
Spyrou Cassandra
LandOfFree
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