Optical communications – Multiplex – Wavelength division or frequency division
Reexamination Certificate
2000-09-25
2004-07-27
Chan, Jason (Department: 2633)
Optical communications
Multiplex
Wavelength division or frequency division
C398S087000, C398S192000
Reexamination Certificate
active
06768872
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an optical transmission system, an optical transmission line and an optical transmitter, and more specifically to an optical transmission system, an optical transmission line and an optical transmitter applicable for long haul and large capacity transmission.
BACKGROUND OF THE INVENTION
In recent years, there has been a big demand for data transmission and accordingly long haul and large capacity transmission lines have been desired. In order to realize the long haul and large capacity transmission, it is necessary to appropriately control nonlinear effect and chromatic dispersion as described by M. Murakami et al. in “Long-Haul 16×10 WDM Transmission Experiment Using Higher Order Fiber Dispersion Management Technique,” ECOC'98, 20-24 September, Madrid, Spain and Japanese Disclosure Gazette No. 10-221562 (U.S. Pat. No. 5,781,673).
The paper of Murakami et al. discloses a configuration in which two optical fibers, having chromatic dispersion values of opposite signs and approximately equal lengths, are disposed in one repeater span, and chromatic dispersion values and dispersion slopes of the two kinds of the optical fibers are selected so that accumulated chromatic dispersions become zero at a certain target wavelength (a central wavelength 1550.7 nm of a signal wavelength band) and difference between the accumulated chromatic dispersions within the signal wavelength band is reduced. Furthermore, it describes that, in each repeater span, the optical fiber disposed in front should have a lager mode-field diameter of 9.2 &mgr;m compared to 5.7 &mgr;m of the optical fiber disposed in behind so as to reduce the non-linear effects.
Also, the Japanese Patent Disclosure Gazette No. Heisei 10-221562 discloses a configuration in which the following elements are disposed in series; a first optical fiber having non-zero chromatic dispersion within a signal wavelength band, a second optical fiber having chromatic dispersion with a mathematical sign opposite to that of the first optical fiber, and a third fiber for compensating dispersion slope in the signal wavelength band. It is also described in the Gazette that the second optical fiber makes the total chromatic dispersion of the whole transmission line to be zero with a certain wavelength in the signal wavelength band, and the third fiber makes the dispersion slope to be −0.1 ps
m
2
/km.
Concretely, experimental results of 34 wavelengths×10 Gbit/s WDM transoceanic optical transmission systems such as explained below have been reported (e.g. K. Matsuda et al. “340 Gbit/s (34×10 Gbit/s) WDM transmission over 8,514 km using broadband gain equalization technique for transoceanic systems,” Electronics Letter, Vol. 35, pp. 1090-1091, 1999).
If such dispersion control described in the above paper is used, it is practically impossible to realize a terabit class WDM optical transmission system that enables long haul transoceanic optical transmission over 7000 km by multiplexing 100 wavelengths of 10 Gbit/s or so. It is therefore necessary to develop more advanced systems.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical transmission system, an optical transmission line and an optical transmitter for realizing even larger capacity and longer haul transmission.
An optical transmission system according to the invention comprises an optical transmitter for outputting WDM signal light, an optical transmission line having a plurality of first optical amplification repeater spans and transmitting the WDM signal light output from the optical transmitter, and an optical receiver for receiving the WDM signal light propagated on the optical transmission line, wherein the first optical amplification repeater span of the optical transmission line comprises a first optical repeater amplifier for optically amplifying the WDM signal light, an optical transmission fiber of plus chromatic dispersion for transmitting the WDM signal light output from the optical repeater amplifier, and a local area dispersion compensator of minus chromatic dispersion for compensating accumulated chromatic dispersion caused by the optical transmission fiber so that average chromatic dispersion in the span becomes a predetermined value D
local
as well as compensating a dispersion slope to become practically zero, wherein D
local
is no less than 1 ps
m/km and no more than 4 ps
m/km.
An optical transmission line according to the invention comprises a plurality of optical amplification repeater spans and transmits WDM signal light, wherein each optical amplification repeater span comprises a first optical repeater amplifier for optically amplifying the WDM signal light, an optical transmission fiber of positive chromatic dispersion for transmitting the WDM signal light output from the optical repeater amplifier, and a local area dispersion compensator of minus chromatic dispersion for compensating accumulated chromatic dispersion caused by the optical transmission fiber so that the average chromatic dispersion in the span becomes a predetermined value D
local
as well as compensating a dispersion slope to become practically zero, wherein D
local
is no less than 1 ps
m/km and no more than 4 ps
m/km.
With this configuration, an optical transmission line with a little nonlinear effect and flat chromatic dispersion characteristics can be obtained, and it also becomes possible to narrow signal wavelength intervals. Consequently, dense wavelength multiplexing can be realized, and accordingly the long haul and high capacity transmission can be realized in combination with appropriate control of the chromatic dispersion.
Preferably, the optical transmission system further comprises a second optical amplification repeater span disposed at every wide area dispersion compensation cycle composed of a plurality of the first optical amplification repeater spans, the second optical amplification repeater span comprises a second optical repeater amplifier for optically amplifying the WDM signal light and having gain smaller than that of the first optical repeater amplifier, and a wide area dispersion compensator for compensating the dispersion slope to become practically zero as well as compensating the accumulated chromatic dispersion of the WDM signal light so that average chromatic dispersion in the wide area dispersion compensation cycle becomes a predetermined value D
avg
. With this configuration, the frequency that the accumulated chromatic dispersion passes across the zero point is reduced and therefore the accumulated chromatic dispersion of the whole optical transmission line can be controlled to keep a low value.
Preferably, the optical transmission line according to the invention further comprises a second optical repeater amplifier for optically amplifying the WDM signal lights output after propagating the plurality of the optical amplification repeater spans, the second optical repeater amplifier having gain smaller than that of the first optical repeater amplifier, and a wide area dispersion compensator for compensating accumulated chromatic dispersion of the WDM signal lights output from the second optical repeater amplifier so that the average chromatic dispersion becomes a minus predetermined value D
avg
as well as compensating a dispersion slope to become practically zero. With this configuration, the frequency that the accumulated chromatic dispersion passes across the zero point is reduced and therefore the accumulated chromatic dispersion of the whole optical transmission line can be controlled to keep a low value.
Preferably, in both inventions, the second optical repeater amplifier comprises an optical amplifier having the same gain with the first repeater amplifier and an attenuator for attenuating output light from the optical amplifier to become a predetermined level. With this configuration, it becomes possible to equalize loss of every repeater span and hence the optical repeater amplifiers with the same gain characteristics can be used, making gain p
Edagawa Noboru
Suzuki Masatoshi
Tanaka Keiji
Tsuritani Takehiro
Chan Jason
Christie Parker & Hale LLP
KDD Corporation
Tran Dzung
LandOfFree
Optical transmission system, optical transmission line and... 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, optical transmission line and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical transmission system, optical transmission line and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3253643