Optical waveguides – With optical coupler – Plural
Reexamination Certificate
1999-03-24
2001-01-09
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Plural
C359S199200, C359S199200, C359S333000
Reexamination Certificate
active
06173094
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical-transmission system. More specifically, the present invention relates to an optical-transmission system including a split-gain amplifier and a signal-modifying device connected within the amplifier.
DESCRIPTION OF THE RELATED ART
In telecommunications, optical signals can be transmitted over a long distance by a multi-wavelength optical-repeater system (“optical-repeater system”).
FIG. 3
illustrates a bidirectional optical-repeater system
10
.
In the optical-repeater system
10
, optical signals propagating in a first direction through optical waveguide fibers (“optical fibers”)
12
are combined by a multiplexer
14
for transmission through optical fibers
16
to a demultiplexer
18
, which separates the optical signals onto optical fibers
20
. Amplifiers
30
amplify the optical signals to provide the strength required for propagation over the optical fibers
16
, which can be eighty kilometers or even longer. The optical-repeater system
10
permits bi-directional transmission (i.e., optical signals traveling in a second direction through optical fibers
16
) by providing optical fibers
12
′, a multiplexer
14
′, a demultiplexer
18
′, optical fibers
20
′, and band splitters
22
that combine and separate optical signals according to their direction of propagation.
Many currently used optical-repeater systems transmit optical signals in the 1550 nanometer band (1525 to 1570 nanometers) because, for example, this band provides low attenuation and the optical amplifiers (erbium doped fiber amplifiers) used for this band have economic efficiency and performance advantages. Some of these optical-repeater systems, however, were created by using optical fibers
16
already installed in the ground as part of old electronic-repeater systems, which were designed to transmit optical signals in the 1300 nanometer band (1270 to 1330 nanometers). These optical fibers
16
have approximately zero dispersion only in the 1300 nanometer band. Therefore, the optical-repeater systems are transmitting optical signals in the 1550 nanometer band through optical fibers that do not have zero dispersion in that band. Optical-repeater systems can be utilized to transmit optical signals in the L-band (1570 to 1625 nm) in addition to the C-band (1525 to 1570 nm). Additionally, optical-repeater systems can be used to transmit optical signals in the Short-band (1290-1525 nm) and the Preferred Short-band (1330-1525 nm).
Transmitting optical signals in this manner causes degradation of the optical signal due to chromatic dispersion. More specifically, since the optical fibers
16
do not have zero dispersion in the 1550 nanometer band, different wavelengths of light in a pulse will tend to spread out as the pulse propagates along the optical fibers
16
.
Consequently, the optical-repeater system
10
includes dispersion-compensating devices
40
that compensate for chromatic dispersion. The dispersion-compensating devices
40
have a relatively high zero dispersion wavelength so that the average zero dispersion wavelength of the optical-repeater system
10
is within the 1550 nanometer band. For example, if the zero dispersion wavelength of the optical fibers
16
is 1300 nanometers, the zero dispersion wavelength for each of the dispersion-compensating devices
40
will be above 1550 nanometers (for example, 1700 nanometers) so that the optical-repeater system
10
has an average zero dispersion wavelength in the 1550 nanometer band.
The dispersion-compensating devices
40
, however, cause a loss in the strength of the optical signals propagating through the optical-repeater system
10
. Thus, additional amplifiers
30
must be included to compensate for this loss. In
FIG. 3
, one of every two amplifiers
30
connected to a dispersion-compensating device
40
is required merely due to the loss caused by the dispersion-compensating device
40
.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical-transmission system that compensates for chromatic dispersion without causing excessive power losses.
Another object of the invention is to provide an optical-transmission system that compensates for chromatic dispersion while minimizing the cost of the system.
Additional objects and advantages of the invention may be apparent from the description that follows. Further advantages of the invention also may be learned by practice of the invention.
To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises an optical-transmission system including a split-gain amplifier having a first gain stage optically connected to a first set of at least two waveguide paths and a second gain stage optically connected to a second set of at least two waveguide paths, a first connector device that optically connects the at least two waveguide paths of the first set to a first combined-waveguide path, a second connector device that optically connects the at least two waveguide paths of the second set to a second combined-waveguide path, and a signal-modifying device optically connected to the first and second combined-waveguide paths.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
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Bowerman John E.
Grissom Jeffrey W.
Walker Robert J.
Corning Incorporated
Krogh Timothy R.
Lee John D.
Murphy Edward F.
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