Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2001-09-13
2004-08-31
Nasri, Javaid H. (Department: 2839)
Optical waveguides
With optical coupler
Input/output coupler
Reexamination Certificate
active
06785442
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of optical communications and, more particularly, the invention relates to devices for selective routing of components of wavelength division multiplexed (WDM) optical signals. Specifically, the invention concerns devices adapted selectively to route components of WDM optical signals.
2. Technical Background
Wavelength division multiplexing (WDM) is increasingly being used in optical communications networks and the like in order to multiply the number of channels that can be transported along the optical fiber or waveguide. Recent demands for even greater multiplication of channels have led to the development of so-called “dense” WDM systems (DWDM). In such WDM and DWDM systems, it is necessary to be able selectively to withdraw from, or inject into, the main fiber or waveguide signals at particular wavelengths; this is generally referred to as the “ADD/DROP” function. In general, it is desired to ADD or DROP at one time a set of signals are respective different wavelengths and it is, thus, convenient if the signals to be added, and signals which have been dropped, can be handled in multiplexed form.
In the following references will be made only to WDM and WDM systems. However, unless the context demands otherwise, it is to be understood that these references cover DWDM and DWDM systems.
Implementation of the drop function involves the demultiplexing of the WDM optical signal propagating on the main fiber or waveguide, so as to separate out the components at different respective wavelengths. One or more particular wavelengths which are to be extracted (“dropped”) are selected and routed to a special output channel (the drop channel) different from the main output. The other wavelengths are multiplexed back together and routed to the main output so as to continue propagating along the main fiber or waveguide. It should be recalled that the “dropped” signal is not simply extinguished: it is separated from the other signals so as to follow a different route.
In a similar way, implementation of the add function generally involves the demultiplexing of the WDM signal propagating on the main fiber or waveguide and the addition, to the separated components at different respective wavelengths, of one or more further signals (the “added” signals) at respective individual wavelengths. The original components are then multiplexed back together, along with the added components.
The add/drop functions are generally implemented together in a common device, generally referred to as an “add/drop multiplexer”. Often, a first signal S
11
at a wavelength &lgr;
i
is dropped and, in the same device, a second signal S
12
at this same frequency &lgr;
i
is added: such devices are often referred to as “cross-connects”. In the following, the expression “cross-connect” will be used to designate devices which implement add/drop functions regardless of the particular wavelengths being dropped and/or added and irrespective of whether both or only one of the functions of adding and dropping is implemented.
One example 10 of a cross-connect is shown schematically in FIG.
1
. The cross-connect
10
of
FIG. 1
is connected to four optical channels (labeled “Input”, “Add”, “Output” and “Drop” in FIG.
1
), which are all here assumed to carry WDM signals comprising a plurality (in this simplified example, two) of components at respective different wavelengths. The device
10
comprises two demultiplexers, DEMUX
1
and DEMUX
2
, two multiplexers, MUX
1
and MUX
2
, and an array of optical switches each having first and second input terminals and first and second output terminals (in the simplified example discussed here, the array includes only two switches SW
1
and SW
2
).
In the example illustrated in
FIG. 1
, the signal propagating in the Input channel is a WDM signal containing component signals at respective wavelengths &lgr;
1
and &mgr;
2
. This signal is applied to the demultiplexer DEMUX
1
, which separates out the component signals at the different wavelengths and feeds them to first input terminals of respective optical switches SW
1
and SW
2
of the switch array. The signal propagating in the Add channel is a WDM signal which may contain component signals at any or all of the wavelengths handled by the device (here &lgr;
1
and &lgr;
2
). The Add channel signal is applied to demultiplexer, DEMUX
2
, which separates out the component signals at the different wavelengths and feeds them to respective second input terminals of the optical switches SW
1
and SW
2
.
The first output terminal of each switch in the switch array is connected to a respective input terminal of the multiplexer MUX
1
, whereas the second output terminal of each switch in the switch array is connected to a respective input terminal of the multiplexer MUX
2
. The multiplexer MUX
1
performs wavelength division multiplexing of the signals applied to its input terminals and outputs the resultant WDM signal to the Output channel. The multiplexer MUX
2
performs wavelengths division multiplexing of the signals applied to its input terminals and outputs the resultant WDM signal to the Drop channel.
In the cross-connect
10
of
FIG. 1
, the optical switches SW
1
and SW
2
are controlled so as to pass to the multiplexer MUX
2
those components of the original input signals which are to be “dropped”, the remainder are passed to the multiplexer MUX
1
. Similarly, the optical switches SW
1
and SW
2
are controlled so as to pass to the multiplexer MUX
1
all of the components of the Add signals. Thus, by suitably controlling the switches of the switch array it is possible selectively to route individual component signals at different wavelengths present in the WDM signal of the Input channel, and to add new signals at selected wavelengths provided via the Add channel.
The cross-connect
10
of
FIG. 1
presents a number of disadvantages. In particular, the design involves use of a relatively large number of components, and the multiplexers and demultiplexers need to be very accurately tuned to the same set of wavelengths.
Alternative prior art cross-connects have been proposed in order to overcome the above-mentioned disadvantages. Specifically, devices have been proposed employing a loop-back configuration so as to enable a single component (a planar optical phased array or “phasar”, also known as an arrayed-waveguide grating (AWG)) to perform all of the required multiplexing and demultiplexing.
The arrayed-waveguide grating or phasar was first proposed by M. K. Smit in 1988 in the paper “New focusing and dispersive planar component based on an optical phased array” in Electronics Letters, 24, 385. The structure and function of an arrayed-waveguide grating (AWG) multiplexer/demultiplexer will now be briefly summarized with reference to
FIGS. 2
a
and
2
b
, which illustrate demultiplexer and multiplexer configurations, respectively.
As shown in
FIGS. 2
a
and
2
b
, the AWG multiplexer/demultiplexer is made up of a phased array of waveguides
1
which are formed in a transparent medium, such as silica, which has been deposited on a substrate (not shown—typically made of silica or silicon) so that there is a constant increment &dgr;1 in path length from the first waveguide in the array to the second, and so on, through to the last waveguide in the array. The input ends of the waveguides
1
lie along a curve L
1
, and the output ends of the waveguides
1
lie along a curve L
2
. Slab waveguides
2
a
and
2
b
are formed at respective ends of the array of channel waveguides
1
, along the curves L
1
and L
2
. Input and output waveguides
3
a
,
3
b
are formed so as to feed signals into and receive signals from the ends of the slab waveguides
2
a
,
2
b
remote from the phased array. In general, the phased array of waveguides
1
, slab waveguides
2
a
,
2
b
, and input and output waveguides
3
a
,
3
b
are formed integrally by common deposition and etching processes.
When the arrayed waveguide grating device is used in demultiple
Bean Gregory V.
Corning Incorporated
Nasri Javaid H.
Redman Mary Y.
LandOfFree
Multi-order optical cross-connect does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Multi-order optical cross-connect, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multi-order optical cross-connect will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3301289