Optical waveguides – With optical coupler – Plural
Reexamination Certificate
1999-12-14
2001-09-11
Ullah, Akm E. (Department: 2874)
Optical waveguides
With optical coupler
Plural
Reexamination Certificate
active
06289148
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical networks. In particular, the present invention relates to a device for performing add/drop multiplexing in two-fiber ring networks.
BACKGROUND INFORMATION
With the growing capacity demand for optical fiber communications, wavelength add/drop multiplexers (“WADM”) are essential components in any optical network. In particular WADMs are critical components in wavelength division-multiplexed (“WDM”) regional-access ring or bus networks to provide access to local customers.
Current technology utilizes configurable wavelength 2×2 switches inserted in wavelength paths.
FIG. 1
, which is prior art, depicts an example of a conventional WADM architecture. The conventional WADM includes input port
140
, demultiplexer
110
, multiplexer
120
, output port
130
and a plurality of 2×2 switches
105
(
1
)-
105
(M). A WDM signal including a plurality of multiplexed signals &lgr;
1
-&lgr;
M
is received at input port
140
and transmitted to demultiplexer
110
. Wavelengths &lgr;
1
-&lgr;
M
received via local access ports (not shown) may be added via respective switches
105
(
1
)-
105
(M). Conversely, wavelengths &lgr;
1
-&lgr;
M
from the demultiplexed signal may be dropped via switches
105
(
1
)-
105
(M) to local access ports (not shown). A particular wavelength &lgr; is dropped to and added from the local port if the respective 2×2 switch (
105
) is in a cross-state, while it is sent directly to output port
130
when the switch is in a through state. 2×2 switches
105
may be of a discrete or integrated form.
Ring networks have become very popular in the carrier world as well as in enterprise networks. A ring is the simplest topology that is two-connected, i.e., provides two separate paths between any pair of nodes. This allows a ring network to be resilient to failures. These rings are called self-healing because they incorporate protection mechanisms that detect failures and reroute traffic away from failed links and nodes onto other routes rapidly. A unidirectional ring carries working traffic only in one direction of the ring (e.g., clockwise).
FIG. 2
a
, which is prior art, depicts the topology of a unidirectional ring network. A unidirectional ring network carries working traffic in only one direction of the ring (e.g., clockwise), along service fiber
230
. WADMs
210
a
-
210
d
provide functionality for dropping and adding wavelengths via local access ports
220
a
-
220
d
respectively. For example, working traffic from WADM
210
a
to
210
b
is carried clockwise along the ring and working traffic from WADM
210
b
to
210
a
is also carried clockwise on a different set of links in the ring. Protection fiber
240
provides a backup route in the case of a fiber cut or equipment malfunction in the working fiber
230
. Traffic from WADM
210
a
to WADM
210
b
is sent simultaneously on working fiber
230
in the clockwise direction and protection fiber
240
in the counter-clockwise direction.
FIG. 2
b
, which is prior art, depicts the topology of a bi-directional two-fiber ring network. Note that both fiber routes
230
a
and
230
b
in
FIG. 2
b
carry a non-overlapping sub-set of wavelengths (e.g., even and odd number wavelengths). Thus, both fiber routes
230
a
and
230
b
are working/protection fiber since one direction can function as the protection route for the other direction (because the wavelengths are non-overlapping). For example, in an even/odd arrangement, signals in the protection routes would be even number wavelengths in odd number wavelength fiber routes and odd number wavelengths in even number wavelength fiber routes.
Typically, WADMs require additional functionality to enable loop-back for maintenance or to switch the signal to a restoration path in the case of a fiber cut or equipment malfunction.
FIG. 3
, which is prior art, depicts typical connectivity requirements for a WADM in a uni-directional ring network. WADM
210
must be able to switch signals from WS
IN
(west service input)
230
a
to WP
OUT
240
b
(west protection output) for loop-back maintenance. Also, if a failure or fiber cut occurs on the east side of WADM
210
, wavelengths from local access ports
220
must be switched to WP
OUT
240
b
for restoring the network traffic. Likewise WADM
210
must switch signals arriving from WS
IN
230
a
originally destined for ES
OUT
230
b
to WP
OUT
240
b.
Although the functions required as shown in
FIG. 3
may be achieved by a 3×3 cross-bar matrix or three 1×3 switches for each wavelength path, the utilization of switch points is inefficient. This results in an increase of the complexity of the electronic controls, size and cost of the WADM device.
SUMMARY OF THE INVENTION
The present invention provides a device for performing wavelength add/drop multiplexing utilizing micromachined free-rotating switch mirrors. The free-space nature of the switch mirrors allow use of the front and back sides of the mirrors for reflecting signals. According to one embodiment of the present invention a WADM is provided in which micromachined switch mirrors are arranged in a polygonal (e.g., hexagonal) geometry, which allows full connectivity.
According to one embodiment a WADM is provided for deployment in a unidirectional two-fiber optical network including service and protection fiber routes. According to this embodiment the WADM includes a first input port for receiving a WDM signal from the service fiber route and a second input port for receiving a WDM signal from the protection fiber route. The WADM also includes a first output port for transmitting a WDM signal to the service fiber route, a second output port for transmitting a WDM signal to the protection fiber route, a third input port for receiving locals signals from a local access port and a third output port for dropping signals to a local access port.
The WADM further includes a reconfigurable switching matrix comprising a plurality of free-space micromirrors, for performing routing of signals from the various input ports to the various output ports.
According to an alternative embodiment a WADM is provided for deployment in a bidirectional two-fiber optical network including two service/protection routes.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
, which is prior art, depicts an example of a conventional WADM architecture.
FIG. 2
a
, which is prior art, depicts the topology of a unidirectional ring network.
FIG. 2
b
, which is prior art, depicts the topology of a bi-directional two-fiber ring network.
FIG. 3
depicts typical connectivity requirements for a WADM in a unidirectional ring network.
FIG. 4
is a block diagram of a WADM utilizing micromachined free-space mirrors for deployment in a unidirectional ring network according to one embodiment of the present invention.
FIG. 5
depicts a microactuated switch mirror according to one embodiment of the present invention.
FIG. 6
is a block diagram of a demultiplexer utilizing OCA microplasma technology according to one embodiment of the present invention.
FIG. 7
depicts a unidirectional two-fiber ring network, assuming a fiber cut occurs according to one embodiment of the present invention.
FIG. 8
a
depicts a WADM node with unidirectional traffic under the situation of normal service according to one embodiment of the present invention.
FIG. 8
b
depicts a WADM node with unidirectional traffic under the situation of failure on east side service and protection routes according to one embodiment of the present invention.
FIG. 8
c
depicts a WADM node with unidirectional traffic under the situation of failure on west side service and protection routes according to one embodiment of the present invention.
FIG. 8
d
depicts a WADM node with unidirectional traffic under the situation of loop-back according to one embodiment of the present invention.
FIG. 9
a
depicts the configuration of a switching matrix of micromirrors in a WADM in a unidirectional two-fiber optical network under normal service conditions according to one embodiment of the present
Lin Lih Y.
Saleh Adel A. M.
AT&T Corporation
Kenyon & Kenyon
Ullah Akm E.
LandOfFree
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