Duplex reflective re-configurable optical add/drop multiplexers

Details Duplex reflective re-configurable optical add/drop multiplexers Duplex reflective re-configurable optical add/drop multiplexers

2003-05-19

2004-12-14

Boutsikaris, Leo (Department: 2872)

Optical waveguides

With optical coupler

Plural

C385S037000, C398S083000, C398S084000

Reexamination Certificate

active

06832019

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to optical network communications. More particularly, the invention relates to re-configurable optical add/drop multiplexers.
BACKGROUND OF THE INVENTION
Recent advances in optical communications technology have provided an optical building block incorporating selectable optical gratings and a circulator. This building block is well suited to building efficient re-configurable optical add/drop multiplexers.
FIG. 1
shows such a re-configurable optical add/drop multiplexer (ROADM) building block, generally indicated by
20
. The building block provides optical drop capability and comprises an optical circulator
22
connected to a selectable fiber Bragg grating
24
. In operation, a wavelength division multiplexed (WDM) optical signal is introduced at input port
26
of the optical circulator
22
, which directs the optical signal to a first port
28
of the selectable fiber Bragg grating
24
. The selectable fiber Bragg grating
24
is controlled at
30
to reflect a selected wavelength of the optical signal back through the first port
28
to the circulator
22
, which directs this reflected wavelength to a “drop” port
32
of the circulator
22
. The portion of the WDM optical signal, which is not reflected at
30
, is passed through the selectable fiber Bragg grating
24
to a second port
34
.
FIG. 2
shows a ROADM module, generally indicated by
40
. A second circulator
36
is added to the building block of
FIG. 1
to provide optical add capability. This configuration allows the selectable fiber Bragg grating
24
to be reused to add an optical signal having the selected wavelength. In operation, the configuration of
FIG. 2
behaves similarly to that of FIG.
1
. The WDM optical signal minus the dropped portion continues from the second port
34
to the second circulator
36
to output port
38
. An optical “add” signal having the same wavelength as the selected wavelength is presented at “add” port
42
of the second circulator
36
which directs it to the second port
34
of the selectable fiber Bragg grating
24
. The “add” signal is reflected by the selectable fiber Bragg grating
24
at
30
. The “add” signal passes back through the second port
34
and through the second circulator
36
to the output port
38
. The configuration of
FIG. 2
thus provides increased functionality to that of
FIG. 1
with only a small incremental increase in cost. It also has the advantage of little additional increase in insertion loss on the through path from input port
26
to output port
38
.
Two-fiber optical ring networks typically use fiber pairs to communicate between nodes, one fiber for transmitting and one for receiving.
FIG. 3
illustrates two of the ROADM blocks of
FIG. 2
, shown as
40
A and
40
B, used to form a bi-directional ROADM node, generally indicated by
43
. ROADM block
40
A receives WDM signals at
26
A from a “West” facing node, drops and adds signals of a desired wavelength at
32
A and
42
A respectively and sends the WDM signal at
38
A to an “East” facing node. Likewise, ROADM block
40
B receives WDM signals at
26
B from the “East” facing node, drops and adds signals of a desired wavelength at
32
B and
42
B respectively and sends the WDM signal at
38
B to the “West” facing node.
Standard two-fiber (
2
F) SONET bi-directional line switched rings (BLSRs) require that a failure of node equipment can be handled by normal protection switching. A disadvantage of the configuration of
FIG. 3
is that a failure of any of the components of a ROADM block takes the associated fiber path out of service and thus results in a traffic outage. For example, if there is a failure of the fiber Bragg grating
24
A or
24
B, the optical drop capability ceases to function because the selected wavelength will not be reflected correctly to circulator
22
A or
22
B. Similarly, the optical add capability stops as well because the optical signal to be added will not be reflected by the fiber Bragg grating
24
A or
24
B, back to the circulator
36
A or
36
B and out to the output port
38
A or
38
B, instead it will continue through the fiber Bragg grating
24
A or
24
B to the first circulator and will be directed to the “drop” port
32
A or
32
B. Worse still, performing maintenance on the node
43
by replacing components will result in a traffic outage.
FIG. 4
illustrates a bi-directional ROADM configuration having an “East/West” architectural split. The bi-directional ROADM node is split into a “West” module
44
A and an “East” module
44
B. Instead of the selectable fiber Bragg grating
24
A of module
44
A handling wavelength selection for both the “drop” port
32
A and the “add” port
42
A, the selectable fiber Bragg grating
24
A in “West” module
44
A handles only the wavelength selection of the “drop” port
32
A. A second selectable fiber Bragg grating
24
A′ is added in “East” module
44
B to select the wavelength to be added at the “add” port
42
A. A failure in “West” module
44
A would appear as a fiber failure, which can easily be handled by the SONET layer through normal protection switching and not affect the entire node. The failure would not affect the function of “add” port
42
A in “East” module
44
B. Similarly, selectable fiber Bragg grating
24
B handles wavelength selection for only the “drop” port
32
B and another selectable fiber Bragg grating
24
B′ handles the wavelength selection for the “add” port
42
B.
A disadvantage of the configuration of
FIG. 4
is that the cost savings advantage of reusing a selectable fiber Bragg grating to provide the wavelength selection for both drop and add functions of a ROADM, as described in relation to FIG.
2
and
FIG. 3
, is lost.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to overcome the aforementioned disadvantages in the prior art. Accordingly, devices and methods are provided for improved optical add/drop multiplexing.
One broad aspect of the invention provides an optical add/drop multiplexer having an optical wavelength selective device, a first optical circulator and a second optical circulator having a first operating mode and a second operating mode. The optical wavelength selective device has a first port and a second port and is adapted to reflect optical signals having a selected wavelength and to pass optical signals having wavelengths other than said selected wavelength. The first optical circulator has an input port and a drop port and is adapted to direct optical signals from the input port to the first port of the wavelength selective device and to direct optical signals from the first port of the wavelength selective device to the drop port. The second optical circulator has an output port and an add port. The second optical circulator, in the first operating mode, is adapted to direct optical signals from the second port of the wavelength selective device to the output port, and for directing optical signals from the add port to the second port of the wavelength selective device. In the second operating mode, the second optical circulator is adapted to direct optical signals from the add port to the output port.
In some embodiments, the optical wavelength selective device is adapted to select the selected wavelength from a plurality of wavelengths.
In some embodiments, the optical wavelength selective device is a selectable optical grating.
In some embodiments, the optical wavelength selective device is a selectable Bragg grating.
In some embodiments, the second optical circulator is a reversible optical circulator.
Another broad aspect of the invention provides a building block for a bi-directional optical add/drop multiplexer. The building block has an optical wavelength selective device, a first optical circulator and a second optical circulator having two operating modes. The optical wavelength selective device has a first port and a second port and is adapted to reflect optical signals having a selected wavelength and to pass optical signals having wavelengths other than the selected wave

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