WDM optical communication system

Details WDM optical communication system WDM optical communication system

1998-06-02

2001-05-22

Chan, Jason (Department: 2733)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S391000, C359S199200

Reexamination Certificate

active

06236482

ABSTRACT:

The invention relates to a technology of a wavelength division multiplexed. (WDM, hereinafter) optical signal transmission, and especially to a WDM optical communication system. In which plural optical signals are simultaneously transmitted through a single fiber with the same transmission power levels.
BACKGROUND OF THE INVENTION
In recent years, a WDM optical communication system, in which plural optical signals with different wavelengths are multiplexed and transmitted through the same optical transmission line, have being vigorously developed as means for epochally increasing the transmission capacity of the optical transmission line.
In order to extend the transmission distance of the WDM optical communication system, it is indispensable that the levels of the transmitting optical signals are high and equalized, and strenuous efforts have been made to meet the aforementioned requirement. For example, in one of approaches to the subject, optical variable attenuators are respectively connected with the output ports of the signal light sources, and the levels of the optical signals are equalized by adjusting the optical variable attenuators, but the high transmitting powers cannot be achieved. In the other approach, optical fiber amplifiers are respectively connected with the output ports of the signal light sources, and the levels of the optical signals are equalized by adjusting the gains of the optical fiber amplifiers. According to this system, the problems mentioned in the beginning can be solved, but the system is magnified and high-priced. Then, it is extremely desirable to decrease the number of the optical fiber amplifiers.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a WDM optical communication system, which transmits optical signals with equalized levels and is small-sized and low-priced.
According to the feature of the invention, a WDM optical communication syntax comprises:
a first stage optical amplifier for collectively amplifying WDM optical signals,
means for demulitplexing an output of the first stage optical amplifier into plural groups of one or more optical signals,
plural second stage optical amplifiers for respectively amplifying outputs of the means for demulitplexing the output of the first stage optical amplifier, and
means for multiplexing outputs of the plural second stage optical amplifiers.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be explained in more detail in conjunction appended drawings, wherein:
FIG. 1
is an example of conventional WDM optical communication systems,
FIG. 2
shows another example of the conventional WDM optical communication systems,
FIG. 3
shows the other example of the conventional WDM optical communication systems,
FIG. 4
shows a foundation of the preferred embodiments of the invention,
FIG. 5
shows another embodiment of the invention,
FIG. 6
shows the other embodiment of the invention,
FIG. 7
shows a block digram showing another embodiment of the invention.
FIG. 8
shows numerical values of the output signal levels in the embodiment shown in
FIG. 7
as a function of a wavelength of an optical signal,
FIG. 9
shows an example of the wavelength dependency of the gain of the optical fiber amplifier
1
, and
FIG. 10
shows a modification of the embodiment shown in FIG.
4
.


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Japanese Office Action, dated Jun. 28, 2000, with English language translation of Japanese Examiner's comments.
Japanese Office Action, dated Apr. 5, 2000, with English language translation of Japanese Examiner's comments.

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