Optical: systems and elements – Optical amplifier – Optical fiber
Reexamination Certificate
2003-05-28
2004-06-08
Moskowitz, Welson (Department: 3663)
Optical: systems and elements
Optical amplifier
Optical fiber
C359S199200, C359S341330
Reexamination Certificate
active
06747792
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical amplifier applied to an optical transmission apparatus such as an optical transmitter/receiver apparatus or an optical repeater in an optical communication system.
In the prior art, a dispersion compensating fiber is used in an optical receiver or an optical transmitter in order to suppress a waveform distortion of an optical signal due to a waveform dispersion of a transmission line fiber, but because of its large loss, it is essential to use it with an optical amplifier for compensating the loss. This technique is disclosed in OSA Optical Fiber Communication Conference, 1992, pp. 367-370.
FIG. 14
shows a configuration of an optical fiber transmission system which uses a prior art dispersion compensating optical transmitter
100
and a prior art dispersion compensating optical receiver
200
. The optical transmitter
100
comprises an erbium doped optical fiber amplifier
101
a
, a dispersion compensating fiber
103
a
and an electro-optical converter
104
. The optical receiver
200
comprises erbium doped optical fiber amplifiers
201
a
and
201
b
, optical band-pass filters
202
a
and
202
b
, dispersion compensating fibers
203
a
and
203
b
and a photo-electric converter
205
. Losses of the dispersion compensating fibers used are 3.1 dB, 10.6 dB and 5.3 dB, respectively for a light signal level. In order to compensate for the losses, a total of three erbium doped optical fibers are used, which amplify the signal lights by using separate pumping light sources. A characteristic of the optical fiber amplifier when the dispersion compensating fiber is added is that a noise figure is increased by a loss when the dispersion compensating fiber is arranged in a preceding stage, and a light output is decreased by the loss when the dispersion compensating fiber is arranged in a succeeding stage.
In the known dispersion compensating optical transmitter and dispersion compensating optical receiver shown in
FIG. 14
, the light signal level is lowered because of a large loss of the dispersion compensating fiber. When the optical amplifier is used to compensate for the loss, the light output of the optical amplifier decreases and the problem of increase of the noise figure arises. In order to avoid the problem, it is necessary to arrange a separate optical amplifier.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical amplifier which can suppress the decrease of the light output and the increase of the noise figure without increasing the pumping light power or increasing the number of pumping light sources even when a lossy dispersion compensation unit is used.
In order to achieve the above object, in accordance with the optical amplifier of the present invention, an optical amplifying medium is divided and a wavelength multiplexing/demultiplexing unit for multiplexing or demultiplexing a pumping light and a signal light is provided in a division, and the pumping light is directly transmitted to a next stage optical amplifying medium while the signal light is transmitted to the next stage optical amplifying medium through an optical signal characteristic compensation unit such as a dispersion compensating fiber so that the reduction of the optical signal level due to the loss of the optical signal characteristic compensation unit is suppressed.
In the optical amplifier of the present invention, the signal light level is lowered by the passage through the optical signal characteristic compensation unit but it is again amplified by the next stage optical amplifying medium by using the pumping light which is not consumed by the preceding stage optical amplifying medium. In the next stage optical amplifying medium, since the input light power is low, it approaches a non-saturation state and a gain increases. As a result, it is possible to set the gain of the next stage optical amplifying medium higher than the loss of the optical signal characteristic compensation unit. By setting the gain of the preceding stage optical amplifying medium sufficiently large, the noise figure of the optical amplifier is essentially determined by the preceding stage and an effect of the loss of the inserted optical signal characteristic compensation unit to the noise figure is suppressed.
REFERENCES:
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patent: 5392153 (1995-02-01), Delavaux
patent: 5406404 (1995-04-01), DiGiovanni et al.
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patent: 5563733 (1996-10-01), Mitsuda et al.
patent: 5579153 (1996-11-01), Laming et al.
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patent: 06 50 161 (1993-03-01), None
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OSA Optical Fiber Communication Conference, 1992, pp. 367-370.
“Analysis of Optical Gain Enhanced Erbium—Doped Fiber Amplifiers Using Optical Filters”, A. Yu, et al, IEEE Photonics Technology Letters, vol. 5, No. 7, Jul. 1993, pp. 773-775.
“Dispersion Compensating Fiber with a High Figure of Merit of 250ps
m/dB”, M. Onishi et al, Electronics Letters, Jan. 20, 1994, vol. 30, No. 2, pp. 161-163.
“Second-Generation Fibre Amplifiers for Advanced Optical Networks”, Laming et al, BFOC&N, 1993.
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Moskowitz Welson
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