Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Utility Patent
1998-06-04
2001-01-02
Pascal, Leslie (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200
Utility Patent
active
06169616
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to fiber optic networks, and more particularly to fiber optic wavelength add/drop systems.
BACKGROUND OF THE INVENTION
Fiber optic networks are becoming increasingly popular for data transmission due to their high speed, high capacity capabilities. Multiple wavelengths may be transmitted along the same optic fiber. These wavelengths are sent combined as a single signal. A crucial feature of a fiber optic network is the exchange of wavelengths between signals on “loops” within networks. The exchange occurs at connector points, or points where two or more loops intersect for the purpose of exchanging wavelengths.
The exchanging of data signals involves the exchanging of matching wavelengths from two different loops within an optical network. In other words, each signal would drop a wavelength to the other loop while simultaneously adding the matching wavelength from the other loop. The adding and dropping of wavelengths always occur together. Each wavelength is commonly referred to as a “channel.” Add/drop systems exist at the connector points for the management of these exchanges.
FIG. 1
illustrates a simplified optical network
100
. A fiber optic network
100
could comprise a main loop
150
which connects primary locations, such as San Francisco and New York. In-between the primary locations are local loops
110
,
120
which connect with the main loop
150
at connector points
140
and
160
. A local loop could be, for example, an optical system servicing a particular area. Thus, if local loop
110
is Sacramento, an optical signal would travel from San Francisco, add and drop channels with Sacramento's signal at connector point
140
, and the new signal would travel forward to connector point
160
where channels are added and dropped with local loop
120
, and eventually to New York. Within loop
110
, optical signals would be transmitted to various locations within its loop, servicing the Sacramento area. Local receivers
170
would reside at various points within the loop to convert the optical signals into signals in the appropriate protocol format. Loops
110
and
120
may also exchange channels directly with each other through a connector point
130
between them. An add/drop system would reside on loop
110
at the connector point
130
while a mirror image of the same add/drop system would reside on loop
120
. Each loop includes an optical signal comprising channels &lgr;
1
-&lgr;
n
. If, for example, channel &lgr;
2
is to be exchanged, loop
110
would drop its &lgr;
2
while adding loop
120
's &lgr;
2
to its signal. In the same manner, loop
120
would drop its &lgr;
2
while adding loop
110
's &lgr;
2
to its signal. Then each loop would transport it's respective new signals to the next destination.
FIG. 2
illustrates a conventional add/drop system
200
. First, the optical signal from loop
110
is separated into its individual channels by a wavelength division multiplexer
210
A. The same occurs with the optical signal from loop
120
by the wavelength division multiplexer
210
B. Each optical channel then travels along a separate optic fiber
260
to a receiver
220
which converts the channels into electrical signals. The electrical signals travel to the regenerator
230
which reshapes them to compensate for dispersions, gain loss, and attenuation. The regenerator
230
also comprises electrical switches which directs the proper electrical signals to be added/dropped. The add/drop function then occurs in the following manner:
Signals on loop
110
which are to stay on loop
110
are sent by the regenerator
230
to loop
110
's wavelength division multiplexer
250
A.
Signals on loop
120
which are to stay on loop
120
are sent by the regenerator
230
to loop
120
's wavelength division multiplexer
250
B.
Signals to be dropped from loop
110
(or added to loop
120
) are sent to loop
120
's wavelength division multiplexer
250
B by the regenerator
230
. Loop
120
's corresponding channels to be added to loop
110
(or dropped from loop
120
) are directed by the regenerator
230
to loop
110
's wavelength division multiplexer
250
A.
Thus, the regenerator
230
functions similarly to a 2×2 switch. In route to the correct wavelength division multiplexer, each signal is converted back into an optical channel by transmitters
240
. The wavelength division multiplexers
250
A-
250
B then recombines the channels sent to it into a single signal. The new signals for Loops
110
and
120
then continue to their respective next destinations.
A problem with conventional add/drop systems is the need to convert data signals sent in the optical domain to the electrical domain in order to effectuate the add/drop. Then signals must be converted back from the electrical domain to the optical domain before being transported to its next destination. Conventional add/drop systems are also cumbersome and inflexible due to the conversion requirement. Typically, the conversion required only allows the add/drop system to be operable for a particular protocol, at one particular speed, and for a certain number of wavelengths. If a different protocol is to be used, a faster speed is desired, or more wavelengths are to be added, each add/drop system along each connector point of the entire optical network
100
much be replaced. Since an optical network could comprise hundreds of connector points, the upgrading of a conventional add/drop system for an optical network is costly and difficult to do. What is desired therefore is a fiber optic wavelength add/drop system which does not have the optical to electrical to optical conversion requirement of the conventional systems. Thus, there is a need for an optical add/drop system which is programmable and which is simpler and more cost efficient to implement. The present invention addresses such a need.
SUMMARY OF THE INVENTION
An optical and programmable wavelength add/drop system for optical networks is provided. It includes the providing of a first optical signal on the first optical loop as a plurality of wavelengths, each wavelength residing on a separate path, such that the providing occurs in the optical domain; the reflecting of any of the plurality of wavelengths; the dropping of any of the plurality of wavelengths from the first optical loop into the second optical loop and for the adding of corresponding wavelengths from the second optical loop into the first optical loop, such that the dropping and adding occurs in the optical domain; and the combining of the reflected wavelengths and the added wavelengths into a second signal. With the add/drop system in accordance with the present invention, dispersion compensation, signal amplification, and gain equalization involved in the providing of the plurality of wavelength, as well as the switching function involved in the dropping and adding of wavelengths, may be performed without the need to convert the signals from the optical domain to the electrical domain and then back to the optical domain, rendering the add/drop system simpler and less costly to implement than conventional systems. The present invention has the added advantages of being capable of broadcasting and the monitoring of the adding and dropping of wavelengths individually. The programmable nature of the present invention reduces the required number of dense wavelength division multiplexers, and its modular design allows flexibility in upgrading to more complex systems.
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Avanex Corporation
Pascal Leslie
Sawyer Law Group LLP
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