Optical waveguides – Optical fiber waveguide with cladding
Reexamination Certificate
1999-11-09
2001-07-17
Ullah, Akm E. (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
C359S199200
Reexamination Certificate
active
06263139
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical transmission system using an optical transmission line partly having a gain, in which a group velocity dispersion is not uniform with respect to a longitudinal direction.
2. Description of the Prior Art
When transmitting a high-speed, large-capacity optical signal, a deterioration of optical waveform due to a group velocity dispersion of a transmission optical fiber is a problem. To compensate for this waveform deterioration, it is effective to install a dispersion compensating fiber in a receiver, which fiber is designed to cancel the dispersion and dispersion slope of the transmission optical fiber.
A loss due to a dispersion compensating fiber is in general so large that cannot be neglected. To compensate for this loss, it is effective to install a lumped optical amplifier inside the receiver, or induce the distributed gain, such as a Raman gain to a dispersion compensating fiber using the optical pumping source which is installed in the receiver.
FIG. 6
shows the configuration of a prior art optical transmission system in which a dispersion compensating fiber is followed by an optical amplifier. In
FIG. 6
, numeral
1
indicates a transmitter,
2
is a receiver,
3
is an optical fiber forming an optical transmission line,
11
is an optical transmission circuit,
21
is a dispersion compensating fiber,
22
is an optical amplifier, and
23
is an optical receiver circuit.
Signal light received by the receiver
2
, after being dispersion compensated by the dispersion compensating fiber
21
, is amplified by the optical amplifier
22
, and received by the optical receiver circuit
23
.
FIG. 6
also shows a power diagram, showing that the input power to the optical amplifier
22
is considerably reduced due to a loss of the dispersion compensating fiber
21
.
FIG. 7
shows the configuration of a prior art optical transmission system installed with an optical amplifier in front of the dispersion compensating fiber. In
FIG. 7
, numeral
1
indicates a transmitter,
2
is a receiver,
3
is an optical fiber forming an optical transmission line,
11
is an optical transmission circuit,
22
is an optical amplifier,
21
is a dispersion compensating fiber, and
23
is an optical receiver circuit.
Signal light received by the receiver
2
is amplified by the optical amplifier
22
, dispersion compensated by the dispersion compensating fiber
21
, and received by the optical receiver circuit
23
.
FIG. 7
also shows a power diagram, in which the input power to the dispersion compensating fiber
21
is increased to more than a certain level by the optical amplifier
22
, so as to compensate for the loss of the dispersion compensating fiber
21
and prevent S/N deterioration in the optical receiver circuit
23
(K. Hagimoto et al., OAA'90, Technical Digest, TUA2, 1990).
FIG. 8
shows the configuration of a prior art optical transmission system in which Raman gain is induced in the dispersion compensating fiber. In
FIG. 8
, numeral
1
indicates a transmitter,
2
is a receiver,
3
is an optical fiber forming an optical transmission line,
11
is an optical transmission circuit,
21
is a dispersion compensating fiber,
23
is an optical receiver circuit,
24
is a optical pumping source,
25
is a pumping light coupler, and
26
is an isolator.
Signal light received by the receiver
2
is dispersion compensated by the dispersion compensating fiber
21
and received by the optical receiver circuit
23
. The dispersion compensating fiber
21
is backward pumped using pumping light coupler
25
, and blocked by the isolator
26
.
FIG. 8
also shows a power diagram, showing that loss and Raman gain in the dispersion compensating fiber
21
are balanced and the optical power is maintained at a constant value (P. B. Hansen., Elec. lett., 34, pp1136-1137, 1998).
However, as shown in FIG.
6
and
FIG. 7
, in the configuration where the optical amplifier
22
is disposed in the receiver
2
, the signal quality is deteriorated for the reason described below. That is, when the optical amplifier
22
is placed after the dispersion compensating fiber
21
(FIG.
6
), due to a loss by the dispersion compensating fiber
21
in addition to a loss L of the optical fiber
3
, SIN of the main signal light is degraded at the output of the optical amplifier
22
, resulting in a degradation of the sensitivity of the optical receiver circuit
23
.
When the optical amplifier
22
is placed in front of the dispersion compensating fiber
21
(FIG.
7
), since the dispersion compensating fiber
21
is smaller in core diameter than an ordinary fiber, it is necessary to limit the output level of the optical amplifier
22
to a level at which a nonlinear optical effect induced in the dispersion compensating fiber
21
can be neglected, thus limiting a loss compensation range of the dispersion compensating fiber
21
.
On the other hand, when Raman gain is induced in the dispersion compensating fiber
21
(FIG.
8
), waveform degradation of the main signal caused by a nonlinear optical effect, which restrict the system performance of the configuration shown in
FIG. 7
, can be relaxed. However, S/N of main signal light received by the optical receiver circuit
23
is determined by the loss L of the optical fiber transmission line
3
, which cannot be improved any further. To utilize a Raman gain, the dispersion compensating fiber
21
is required to have a length of several tens of km, which increases propagation delay inside the receiver
2
, resulting in an increased delay in the optical transmission system.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical transmission system which suppresses S/N degradation caused by the optical amplification and nonlinear optical effect in the dispersion compensating fiber and compensates for a loss due to the dispersion compensating fiber without incorporating a long fiber inside the receiver.
In accordance with the present invention, the re is provided an optical transmission system in which part of an optical transmission line is constructed by a dispersion compensating fiber and designed so that at least part of the optical transmission line has a distributed gain. However, to suppress a nonlinear optical effect, the dispersion compensating fiber is not disposed at immediately after a transmitter except for a case where the entire optical transmission line has a gain. Pump light to induce a distributed gain is transmitted to the optical transmission line from at least one of a transmitter, a receiver, and a repeater.
With such a configuration, since part or entire of the optical transmission line has no loss, a loss L in a transmission section becomes small compared to the prior art configuration shown in
FIGS. 7 and 8
, optical power received by the optical receiver circuit can be sufficiently high even when launched power to the dispersion compensating fiber is restricted. That is, while performing dispersion compensation by the dispersion compensating fiber and suppressing a nonlinear optical effect, its loss can be compensated for. Further, since the dispersion compensating fiber comprises part of the optical transmission line, it is not necessary to incorporate a long dispersion compensating fiber inside the receiver.
In the optical transmission system according to the present invention, the optical transmission line is constructed by transmission optical waveguides and dispersion compensating optical waveguides, and part or all of them are induced a distributed gain, thereby compensating for signal light loss due to dispersion compensating optical waveguides while suppressing degradation of signal quality to a minimum.
That is, by reducing loss of the optical transmission line, it becomes possible to simultaneously achieve an increase in optical power received by the optical receiver circuit and a limitation of launched power to the optical transmission line, of which the former contributing to improvement of
Kawakami Hiroto
Miyamoto Yutaka
Frank Robert J.
Nippon Telegraph and Telephone Corporation
Ullah Akm E.
Venable
LandOfFree
Optical transmission system with group velocity dispersion... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical transmission system with group velocity dispersion..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical transmission system with group velocity dispersion... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2559036