Optical waveguides – With optical coupler – Plural
Reexamination Certificate
1998-08-06
2001-07-17
Ngo, Hung N. (Department: 2874)
Optical waveguides
With optical coupler
Plural
C385S046000, C359S199200
Reexamination Certificate
active
06263126
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to fiber optic networks, and more particularly to fiber optic dense wavelength division multiplexers.
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 combined to provide a single transmitted signal. A crucial feature of a fiber optic network is the separation of the optical signal into its component wavelengths, or “channels”, typically by a dense wavelength division multiplexer. This separation must occur in order for the exchange of wavelengths between signals on “loops” within networks to occur. The exchange occurs at connector points, or points where two or more loops intersect for the purpose of exchanging wavelengths.
Add/drop systems exist at the connector points for the management of the channel exchanges. The exchanging of data signals involves the exchanging of matching wavelengths from two different loops within an optical network. In other words, each signal drops a channel to the other loop while simultaneously adding the matching channel from the other loop.
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 is a local loop
110
which connect with loop
150
at connector point
140
. Thus, if local loop
110
is Sacramento, wavelengths at San Francisco are multiplexed into an optical signal which will travel from San Francisco, add and drop channels with Sacramento's signal at connector point
140
, and the new signal will travel forward to New York. Within loop
110
, optical signals would be transmitted to various locations within its loop, servicing the Sacramento area. Local receivers (not shown) would reside at various points within the local loop
110
to convert the optical signals into the electrical signals in the appropriate protocol format.
The separation of an optical signal into its component channels are typically performed by a dense wavelength division multiplexer.
FIG. 2
illustrates add/drop systems
200
and
210
with dense wavelength division multiplexers
220
and
230
. An optical signal from Loop
110
(&lgr;
1
-&lgr;
n
) enters its add/drop system
200
at node A (
240
). The signal is separated into its component channels by the dense wavelength division multiplexer
220
. Each channel is then outputted to its own path
250
-
1
through
250
-n. For example, &lgr;
1
would travel along path
250
-
1
, &lgr;
2
would travel along path
250
-
2
, etc. In the same manner, the signal from Loop
150
(&lgr;
1
′-&lgr;
n
′) enters its add/drop system
210
via node C (
270
). The signal is separated into its component channels by the wavelength division multiplexer
230
. Each channel is then outputted via its own path
280
-
1
through
280
-n. For example, &lgr;
1
′ would travel along path
280
-
1
, &lgr;
2
′ would travel along path
280
-
2
, etc.
In the performance of an add/drop function, for example, &lgr;
1
is transferred to path
280
-
1
. It is combined with the others of Loop
150
's channels into a single new optical signal by the dense wavelength division multiplexer
230
. The new signal is then returned to Loop
150
via node D (
290
). At the same time, &lgr;
1
′ is transferred to path
250
-
1
from
280
-
1
. It is combined with the others of Loop
110
's channels into a single optical signal by the dense wavelength division multiplexer
220
. This new signal is then returned to Loop
110
via node B (
260
). In this manner, from Loop
110
's point of view, channel &lgr;
1
of its own signal is dropped to Loop
150
while channel &lgr;
1
′ of the signal from Loop
150
is added to form part of its new signal. The opposite is true from Loop
150
's point of view. This is the add/drop function.
Conventional methods used by dense wavelength division multiplexers in separating an optical signal into its component channels includes the use of filters and fiber gratings as separators. A “separator,” as the term is used in this specification, is a unit of optical components which separates one or more channels from an optical signal. Filters allow a target channel to pass through while redirecting all other channels. Fiber gratings target a channel to be reflected while all other channels pass through. Both filters and fiber gratings are well known in the art and will not be discussed in further detail here.
FIG. 3
illustrates a conventional multi-stage serial cascade configuration of separators in a dense wavelength division multiplexer
300
. In this conventional method, each separator targets only one channel to be filtered/reflected and sent along a path. For example, an optical signal containing channels &lgr;
1
-&lgr;
n
is inputted into separator
310
A, which filters/reflects channel &lgr;
1
and send it along its own path
320
-
1
. The remaining channels &lgr;
2
-&lgr;
n
are sent to the next separator
310
B, which filters/reflects channel &lgr;
2
and sends it along its own path
320
-
2
. This continues until each channel has been filtered/reflected and sent along its own path. Thus, with this method, for N channels there are N separators.
FIG. 4
illustrates a conventional single stage parallel configuration of separators in a dense wavelength division multiplexer
400
. In this conventional method, the original optical signal containing &lgr;
1
-&lgr;
n
enters a signal splitter
410
which splits the signal onto N separate paths, each split signal containing channels &lgr;
1
-&lgr;
n
. Each of these split signals is sent along a separate path
420
-
1
through
420
-n. Each signal is then filtered or reflected by the separators
430
A-
430
N to output one particular channel. For example, a split signal containing channels &lgr;
1
-&lgr;
n
exits the splitter
410
onto path
420
-
1
. The split signal enters separator
430
A which filters/reflects channel &lgr;
1
and sends it along path
420
-
1
. Another split signal containing &lgr;
1
-&lgr;
n
exits splitter
410
onto path
420
-
2
and enters separator
430
B. Separator
430
B filters/reflects channel &lgr;
2
and sends it along path
420
-
2
. This process repeats to separate each channel. Thus for N channels, there must be N separators plus a signal splitter.
A problem with the conventional configurations of separators above is the resulting high insertion loss. Insertion loss is the attenuation of an optical signal caused by the insertion of an optical component, such as a connector, coupler, or filter. For the multi-stage serial cascade configuration illustrated in
FIG. 3
, each time the optical signal goes through a separator
310
A-
310
N an amount of insertion loss results. For example, if the optical signal in
FIG. 3
has eight channels &lgr;
1
-&lgr;
8
and each component causes 1 dB of insertion loss. By the time &lgr;
8
is separated, it would have passed through eight separators. &lgr;
8
would thus suffer 8 dB of insertion loss.
The same problem exists for the single stage parallel configuration in FIG.
4
. Assume again that the optical signal contains eight channels and each component causes 1 dB of insertion loss. In splitting one signal onto eight paths, a 9 dB insert loss results. Another 1 dB of loss is added by the separator
430
A-
430
N. Thus, each channel suffers 10 dB of insertion loss.
Therefore, there exists a need for a dense wavelength division multiplexer with a method of separation which lowers insertion loss. The present invention addresses such a need.
SUMMARY OF THE INVENTION
An improved dense wavelength division multiplexer for the separation of optical channels is provided. The dense wavelength division multiplexer includes the inputting of an optical signal with the optical signal containing a plurality of optical channels; the separating of one
Avanex Corporation
Ngo Hung N.
Sawyer Law Group LLP
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