Optical: systems and elements – Optical amplifier – Correction of deleterious effects
Reexamination Certificate
2001-04-18
2003-12-02
Black, Thomas G. (Department: 3663)
Optical: systems and elements
Optical amplifier
Correction of deleterious effects
C359S341420, C359S349000, C359S199200, C359S199200
Reexamination Certificate
active
06657778
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical amplifying repeater apparatus implemented by using as a repeater an optical amplifier which is constituted by employing an optical fiber doped with laser activating substance(s) such as rare-earth element(s), transition metal(s) or the like and also relates to an optical amplifying/repeating transmission system in which the optical amplifying repeater apparatuses are made use of.
BACKGROUND TECHNIQUES
When compared with the conventional optical repeater having 3R (Reshaping, Retiming, Regenerating) functions known heretofore, the optical fiber amplifier has desirable features such as independency on the transmission rate, susceptibility to simplified implementation of the repeater, possibility of implementation with large capacity owing to the wavelength multiplexing capability and others. Thus, the optical fiber amplif ier is expected to promise a key component which is capable of enhancing flexibility of the optical communication system. In particular, in an optical network in which the wavelength multiplexing technique is adopted, it is possible to achieve remarkable economization.
As the conventional or prior art optical amplifying repeater apparatus of the type mentioned above, there can be mentioned, for example, the one disclosed in “OPTICAL AMPLIFIERS AND THEIR APPLICATION”, PP. 280-283, 1998.
FIG. 12
is a block diagram showing the prior art optical amplifying repeater apparatus disclosed in the above-mentioned publication.
In
FIG. 12
, reference numerals
1
;
4
denote optical amplifiers each of fixed gain type for amplifying en bloc light signals of wavelengths &lgr;
1
to &lgr;n, numeral
3
denotes an adjustable optical attenuator, numeral
77
denotes an optical branching device for extracting a part of output power, numeral
6
denotes an optical attenuator control circuit for controlling the adjustable optical attenuator, numerals
501
;
506
denote optical amplifiers, respectively, each implemented by making use of an erbium-doped fiber or the like, numerals
502
and
507
denote pumping light sources, respectively, numerals
503
,
504
,
508
and
509
denote optical branching devices for extracting parts of power of the light signals inputted thereto, respectively, and reference numerals
505
and
510
denote pumping light source control circuits for controlling the pumping light sources, respectively.
Next, description will be made of operation of the optical amplifying repeater apparatus. The wavelength-multiplexed light signals &lgr;
1
to &lgr;n as inputted are first amplified by the fixed-gain optical amplifier
1
with a predetermined gain G
0
and subsequently undergo attenuation with a predetermined attenuation factor through the adjustable optical attenuator
3
. The wavelength-multiplexed light signals outputted from the adjustable optical attenuator
3
are again amplified by the fixed-gain optical amplifier
4
with a predetermined gain G
1
to be ultimately outputted by way of the optical branching device
77
. In that case, a part of the output signal is extracted through the optical branching device
77
and detected by the optical attenuator control circuit
6
, which circuit is so designed as to control the factor of attenuation effectuated by the adjustable optical attenuator
3
so that the part of the output light signal extracted through the optical branching device
77
assumes a predetermined value. In this manner, the overall or total output power of the optical amplifying repeater apparatus is maintained at a constant value. In the case where the number of the wavelengths is constant, the output powers of the respective wavelengths can be maintained constant on a wavelength-by-wavelength basis, rendering it possible to realize ideal operation.
At this juncture, operation of the fixed-gain optical amplifier
1
will be described in detail. Input/output powers to/from the fixed-gain optical amplifier
1
are monitored through the optical branching devices
503
and
504
, respectively, wherein the pumping light source control circuit
505
controls the pumping light source
102
such that the ratio between the input and output powers of the fixed-gain optical amplifier can be maintained to be constant. In this way, the gain of the fixed-gain optical amplifier
1
is held constant. Similar operation is performed for the fixed-gain optical amplifier
4
as well.
Furthermore,
FIG. 13
shows in a block diagram another prior art optical amplifying repeater apparatus which is disclosed, for example, in “OPTICAL AMPLIFIERS AND THEIR APPLICATIONS”, MD1, 1998. This optical amplifying repeater apparatus is so arranged as to perform not only amplification of the light signals of wavelengths &lgr;
1
to &lgr;n but also gain control for the optical repeater on the basis of monitoring information carried by a monitoring light signal &lgr;s sent from terminal equipment. In
FIG. 13
, reference numeral
11
denotes an optical branching device for separating the monitoring light signal &lgr;s from the light signals of wavelengths &lgr;
1
to &lgr;n, and reference numeral
17
denotes a monitoring light receiver.
Next, description will turn to operation of the optical amplifying repeater apparatus described above. The wavelength-multiplexed light signals &lgr;
1
to &lgr;n as inputted are first amplified by the fixed-gain optical amplifier
1
with a predetermined gain G
0
to subsequently undergo attenuation with a predetermined attenuation factor through the adjustable optical attenuator
3
. The wavelength-multiplexed light signals outputted from the adjustable optical attenuator
3
are again amplified by the fixed-gain optical amplifier
4
with a predetermined gain G
1
to be outputted via the optical branching device
77
. A part of the output signal is extracted through the optical branching device
77
and detected by the optical attenuator control circuit
6
, which circuit is also so designed as to control the attenuation effectuated by the adjustable optical attenuator
3
so that the part of the output signal extracted through the optical coupling device
77
assumes a predetermined value. In this manner, the overall total output power of the optical amplifying repeater apparatus is maintained at a constant value or level. So long as the number of the wavelengths is constant, the output powers of the respective wavelengths can be maintained constant on a wavelength-by-wavelength basis, whereby ideal operation can be ensured. The information about the number of wavelengths is contained in the monitoring information carried by the monitoring light signal &lgr;s sent out from the terminal equipment and thus inputted to the optical attenuator control circuit
6
after reception by the monitoring light receiver
17
.
In the optical amplifying repeater apparatus of the structures described above, a part of the total output power is extracted by the optical branching device
77
for the purpose of controlling the adjustable optical attenuator
3
so that the output power can be maintained to be constant. As a result of this, very troublesome procedure is required for coping with increase or decrease of the number of wavelengths. More specifically, because the total output power of the optical amplifying repeater apparatus depends on the number of wavelengths, there arises necessity of messaging in advance to the optical attenuator control circuit
6
the value which the light power extracted through the optical branching device
77
is to assume, when the number of wavelengths is changed. Consequently, in the case where one of the wavelength-multiplexed light signals of wavelengths &lgr;
1
to &lgr;n is not transmitted due to some failure in sender equipment, by way of example, the messaging procedure such as mentioned above will not be in time for coping with the change of the number of wavelengths, thus bringing about corresponding changes in the powers of the other wavelengths, which of course will exert adverse influence to the quality of communication.
An object of the prese
Motoshima Kuniaki
Nakagawa Jun'ichi
Shimizu Katsuhiro
Suzuki Naoki
Birch & Stewart Kolasch & Birch, LLP
Black Thomas G.
Cunningham Stephen
Mitsubishi DenkiKabushiki Kaisha
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