Note: Descriptions are shown in the official language in which they were submitted.
CA 02237S04 1998-0~-12
"Improvement in the reliability of an optical communication system and
of an optical amplifying system, and a method suitable to this aim"
* * * * * * * *
The present invention relates to an improvement in the reliability of
an optical communication system optically amplified comprising two
optical fiber lines, as well as of an optical amplifying system, and a
'method for improving the reliability of an optical communication or an
optical amplifying system.
In recent years, optical long distance communication system optically
amplified has become increasingly common. In fact, in a long distance
communication system, periodic optical amplifiers have become
attractive alternatives to opto-electronic converters and electronic
regenerators/repeaters to overcome signal attenuation. As a result,
there is much interest in developing highly reliable yet low cost optical
amplification systems.
Reliability is especially important when the communication system is
not readily accessible, such as in undersea applications.
Rare earth doped optical amplifying fibers have been developed to
provide high quality optical amplification at a relatively low cost. Among
the doped amplifying fibers, excellent results have been achieved with
Erbium doped fibers. Energy is provided to the doped optical amplifying
fibers using a laser pump. The doped amplifying fiber and the laser
pump can be integrated into the optical fiber using a wavelength
division multiplexer (WDM). The pump laser excites rare earth ions to a
higher energy level to form an appropriate amplifying medium via
inversion of the rare earth ions. The signal at the input of the Erbium
doped amplifying fiber is thereby amplified by stimulated emission.
Since the laser pump is the only active component in the
ampliFication system, it is the most likely to degrade or fail. Such failure
would render the optical amplifier, and possibly the optical
CA 02237~04 1998-0~-12
communication system inoperative. In order to overcome such a
drawback, several techniques have been developed to design optical
communication systems capable of limiting the impact of laser pump
failure or degradation.
Redundancy has been suggested many times to obviate to optical
amplifiers failures.
U.S. Pat. No 5,173,957 issued to Berqano et al. relates laser pump
redundancy for an optical fiber amplifier wherein at least two laser
diodes are coupled via a 3 dB optical coupler to supply pump power to
each of two one-stage optical fiber amplifiers simultaneously (FIG. 8
attached hereto). If one of the laser diode pumps fails, the other laser
diode pump provides power to each of the optical fiber amplifiers Thus,
failure of one laser pump causes a 50% reduction in the pumping
power of each of two one-stage optical fiber amplifiers.
U.S. Patent No. 5,241,414 issued to Giles et al. discloses a group of
optical amplifiers wherein pump beams from an array of lasers are
mixed together by means of a star coupler to form a plurality of
composite pump beams. Each composite pump beam is distributed to
the pump port of a particular optical amplifier of a group of optical
amplifiers.
U.S. Patent No. 5,253,104 issued to Delavaux discloses a balanced
doped fiber optical amplifier. Figure 7 shows an amplifier consisting of
a preamplifier first stage and power booster second stage cascaded
along a same optical fiber line. In this configurations pump signals are
distributed and coupled between first and second stage so as to both
share pump sources and provide a sparing arrangement.
Published UK Patent Application GB 2,272,202-A, discloses a
diode-pumped optical fiber amplifier with its amplifying fiber divided into
two parts so that there are two amplifier stages, both pumped by a laser
CA 02237~04 1998-OS-12
diode. A second diode may be included for redundancy, its outputs
being coupled via a pair of polarization beam splitter/combiner.
Published PCT Application WO 92/05642 discloses an optical fiber
amplifier having one or more active fibers so coupled to an optical
transmission line that each of the active fibers has at least one input for
a pump signal. The optical fiber amplifier has an optical combination
network with a plurality of inputs coupled to respective pump lasers.
The outputs of the combination network are coupled to the pump signal
inputs on the active fibers. The network is adapted to combine the
optical energy added from the pump lasers so that the optical energy
on each one of the outputs of the combination network originates from
several pump lasers.
As a further improvement of the above mentioned solutions, in case
of a two-stage optical amplifier reliability could be obtained by means of
two laser pumps; each laser pump being connected with both stages of
said optical amplifier. As shown in FIG.1, the optical amplifier for
optical fiber 402 comprises a first stage amplifying fiber 404, a second
stage amplifying fiber 406, a first WDM 408, a second WDM 410, a
coupler 412, and laser pumps 414 and 416. Here, pumping signals
from the laser pumps 414 and 416 are coupled by coupler 412 which
distributes the coupled pumping signal to first and second stages 404
and 406 via WDMs 408 and 410. The first WDM 408 interfaces optical
fiber 402 with the pumping signal. In this manner, the first stage
amplifying fiber 404 is pumped so that the signal received from the
optical fiber 402is amplified. Similarly, the second WDM 410 receives
the pumping signal so that the second stage amplifying fiber 405 is
pumped. Accordingly, the second stage amplifying fiber 406 amplifies
the signal received from the first stage amplifying fiber 404.
However, in said amplifier failure of one laser pump would cause a
CA 02237~04 1998-0~-12
50% reduction in the pumping power.
The present invention aims to limit said 50% reduction of the
pumping power in each optical fiber line of an optical communication
system comprising two optic fiber lines without any additional cost,
compared to a two lines optical communication system wherein each
line is provided with a two-stage optical amplifier as shown in Fig. 1.
More particularly, it is an object of this invention to provide an
improvement in the reliability of an optical communication system
comprising two optical fiber lines, a first transmitter for transmitting at
least a signal in the first optical line, a second transmitter for
transmitting at least a signal in the second optical line, at least one two-
stage-amplifier in each of said first and second line, laser pumps
providing pumping signals to said stages of the amplifiers, a first
receiver for receiving the signal from the first optical line, and a second
receiver for receiving the signal from the second optical line, wherein
the reliability is improved in such a way that the possible failure of one
laser pump causes less than 50% reduction in the pumping power in
each optical fiber line.
It is a second object of this invention to provide an improvement in
the reliability of an amplifying system comprising two optical fiber lines,
at least one two-stage-amplifier in each line, laser pumps providing
pumping signals to said stages of the amplifiers, wherein the reliability
is improved in such a way that the possible failure of one laser pump
causes less than 50% reduction in the pumping power in each optical
fiber line.
It is a third object of this invention to provide an improvement in an
amplifying system comprising two optical fiber lines, at least one two-
stage-amplifier in each line, laser pumps providing pumping signals to
said stages of the amplifiers, wherein the losses of gain and the
increases of noise figure caused by failure of a laser pump are
CA 02237~04 1998-0~-12
- 6 -
substantially limited.
It is a further object of this invention to provide an improvement in a
method for providing a laser pump signal in an optical communication
system comprising a first and a second optical fiber lines, wherein the
possible failure of one laser pump causes less than 50% reduction in
the pumping power in each optical fiber line.
These and other objects have been achieved by an optical
communication system, an amplifying system and a method described
herein below.
It has now been found that the above mentioned objects are
achieved by providing a single laser pumping system that supplies a
first pumping signal to at least one stage of a two-stage amplifier in
each optical fiber line.
Accordingly, it is an object of this invention to provide an
improvement in the reliability of an optical communication system
comprising two optical fiber lines, a first transmitter for transmitting at
least a signal in the first optical line, a second transmitter for
transmitting at least a signal in the second optical line, at least one two-
stage-amplifier in each of said first and second line, laser pumps
providing pumping signals to said stages of the amplifiers, a first
receiver for receiving the signal from the first optical line, and a second
receiver for receiving the signal from the second optical line, the
improvement consisting in that said laser pumps form a single system
that provides a first pumping signal to at least one stage of said at least
one amplifier of each of said first and second line.
Preferably, said system further provides a second pumping signal to
the other stage of said at least one amplifier of each of said first and
second line.
More preferably, said laser pumps are at least four.
It is a second object of this invention to provide an improvement in
CA 02237~04 1998-0~-12
the reliability of an optical amplifying system comprising two optical fiber
lines, at least one two-stage-amplifier in each line, and laser pumps
providing pumping signals to said stages of the amplifiers, the
improvement consisting in that said laser pumps form a single system
that provides a first pumping signal to at least one stage of said at least
one amplifier of each of said first and second line.
Preferably, said system further provides a second pumping signal to
the other stage of said at least one amplifier of each of said first and
second line.
More preferably, said laser pumps are at least four.
It is a further object of this invention to provide an improvement in a
method for providing a laser pump signal in an optical communication
system comprising a first and a second optical fiber lines, said method
comprising the steps of
a) generating first and second laser pump signals;
b) coupling said first and second laser pump signals to form first
and second output signals;
c) generating third and fourth laser pump signals;
d) coupling said third and fourth laser pump signals to form third
and fourth output signals;
the improvement consisting in that
1 ) the first and second output signals are supplied to one of the
first and second stages of an amplifier of said first optical fiber line
and to one of the first and second stages of an amplifier of said
second optical fiber line; and
2) the third and fourth output signals are supplied to the other of
the first and second stages of an amplifier of said first optical fiber
line and to the other of the first and second stages of an amplifier of
said second optical fiber line.
Preferably, the first and third output signals are coupled to form a
CA 02237~04 1998-0~-12
fifth and a sixth output signals while the second and fourth output
signals are coupled to form a seventh and an eighth output signals,
each of said fifth, sixth, seventh, and eighth output signals being
supplied to a single stage of an amplifier.
A more complete understanding of the invention may be obtained by
reading the following description of specific illustrative embodiments of
the invention in conjunction with the appended drawings in which:
- FIG.1 is a diagram of a possible optical amplifying system
comprising a two-stage amplifier;
- FIG. 2 is a diagram of an optical amplifying system in accordance
with a first embodiment of the present invention;
- FIG. 3 is a diagram of a preferred embodiment of an optical
amp!ifying system of the type shown in FIG. 2;
- FIG. 4 is a diagram of an optical amplifying system in accordance
with a second embodiment of the present invention;
- FIG. 5 is a diagram of an optical amplifying system in accordance
with a third embodiment of the present invention;
- FIG. 6 is a diagram of a preferred embodiment of an optical
amplifying system of the type shown in FIG. 5;
- FIG. 7 is a schematic diagram of an optical communications system
in accordance with the present invention;
- FIG. 8 is a diagram of a conventional optical amplifying system
according to US patent 5,173,957.
The known optical amplifying system of FIG. 8 according to US
patent 5,173,957 comprises a first optical fiber line 302 and a second
optical fiber line 304, first and second amplifying fibers 306 and 308,
first and second WDMs 310 and 312, a coupler 314, and laser pumps
316 and 318. Laser pumps 316 and 318 provide pumping signals which
are coupled by coupler 314. From the coupler 314, the coupled
CA 02237~04 1998-0~-12
pumping signals are distributed to first and second amplifying fibers 306
and 308 via first and second WDMs 310 and 312, respectively. In this
manner signals of first and second optical fiber lines can be
respectively amplified.
In this system, if one of the laser pumps 316 and 318 fails, the
remaining laser pump will continue to pump the amplifying fibers 306
and 308. If the power of the remaining laser pump remains the same
(hot stand by mode with reduction in performance), a laser pump failure
causes a reduction in the pumping power of each optical amplifier.
Alternatively, the optical amplifying system can operate without
reduction in the pumping power by increasing the power of the
remaining laser pump (hot stand by mode without reduction in
performance). However, approximately twice the power of the laser
pump will be required.
However, if one laser pump fails, the pumping power in each
amplifying fiber is reduced by 50%.
The optical amplifying system of FIG. 2 comprises two optical fiber
lines 502 and 504, amplifying fibers 506 and 508 for the first optical line
502, amplifying fibers 510 and 512 for the second optical line 504,
wavelength division multiplexers (WDMs) 514, 516, 518, and 520,
couplers 522 and 524, and laser pumps 526, 528, 530, and 532.
Here, the output of laser pumps 526 and 528 are coupled by coupler
522. The coupled pumping signals from coupler 522 pump amplifying
fibers 506 and 512 via WDMs 514 and 520, respectively. In addition,
the output of laser pumps 530 and 532 are coupled by coupler 524.
The coupled pumping signals from coupler 524 pump amplifier fibers
508 and 510 via WDMs 516 and 518, respectively. Accordingly, the
pumped amplifying fibers 506 and 508 will amplify signals received
from optical fiber 502, and pumped amplifying fibers 510 and 512 will
CA 02237~04 1998-0~-12
- 10 -
amplify signals received from optical fiber 504. The optical amplifying
system of FIG. 2 would be suitable for amplification of signals
propagating in either direction through optical fiber lines 502 and 504.
In FIG. 3, optical fiber line 502 acts as a send line whereas optical
fiber line 504 acts as a return line.
Here, the optical amplifying system further comprises optical
isolators 634 and 636 to transmit the optical signal only from the first to
the second stage of each two-stage-amplifier. The isolators 634 and
636 substantially transmit the signal and substantially block
counterpropagating radiation. In addition, they can block the pump
radiation, if a pump wavelength outside the isolator transmission band
is used, for example 980 nm with currently available isolators. Isolators
634 and 636 are arranged between the first and second amplifier stage
of the respective optical fiber lines in order to maximize performance in
terms of noise figure and gain by reducing counter-propagating ASE.
In the case, not represented, where one of the amplifiers has
copropagating pump in the first stage and counter-propagating pump in
the second stage, the isolator further avoids coupling of the two
pumps.
Further discussion on the use of isolators in optical amplifiers is
disclosed in US 5,204,923, and in M.N. Zervas, R.l. Laming, and D. N.
Payne, "Efficient Erbium-Doped Fibre Amplifiers Incorporating an
Optical Isolator", SPIE vol. 1789 Fiber Laser Sources and Amplifiers
IV(1992), pp. 145-154.
Instead of, or in combination with one or both optical isolators 634,
636, the skilled in the art may envisage use of means of a known type
to fulfill, according to known techniques, the requirements of specific
embodiments of the invention. Examples are unidirectional means, e.g.
optical circulators, filtering means, e.g. filters to remove ASE, spectrally
CA 02237~04 1998-0~-12
- 11 -
selective or time selective multiplexing/demultiplexing means to
selectively add or drop optical signals to/from the communication line,
dispersion compensation means to compensate wavelength dispersion.
The above cited means may be combined. For example, an optical
circulator may be used, in combination with filters,
multiplexers/demultiplexers and/or dispersion compensators.
The amplifying fibers 506, 508, 510, and 512 of FIG. 3 are Erbium
doped fibers. In an example, the amplifying fibers are silica fiber having
a 0.3 numerical aperture with a Germanium Erbium (Ge/Er) doped
core. Erbium acts as the active dopant. Proper amplification is
obtained, e. g., from amplifying fibers of about 17 m in length for the
combined first and second stages if the Er concentration in the core of
the optical fiber is such as to cause a 7 dB/m signal loss in the
described conditions.
As shown in FIG. 3., the signals Sjn and Sout contain one or more
discrete wavelengths selected in an amplification band of the fiber
active dopant, for single channel or multichannel (e.g. WDM)
transmission.
Preferably, laser pumps 526, 528, 530, and 532 are laser diode
pumps which produce a pumping signal at a preselected pumping
wavelength. While other wavelengths may be selected, the Erbium
doped fibers in the example of FIG. 3 are pumped by the pumping
signal at 980 nm. In the described experiment a single channel, at a
wavelength of 1536 nm, has been transmitted.
A pump wavelength of 980 nm is convenient in that it provides
relatively high gain with low noise in Erbium doped fibers. Alternatively,
for example, 1480 nm may also be used for the pumping signal. While
other wavelengths may be used for the signal and the pumping signal,
the pumping signal generally has a smaller wavelength than the signal.
CA 02237~04 1998-05-12
While different splitting ratios may be conveniently selected, in thispreferred embodiment, couplers 522 and 524 are 3 dB couplers so that
the coupled pumping signals traveling from coupler 522 are equal each
other and the coupled pumping signals traveling from coupler 524 are
also equal each other.
The positions of the corresponding amplifying fibers and WDMs can
be configured for co-pumping or counter-pumping with regard to the
signal direction. That is, the directions of the pumping signal and the
signal can be the same or opposite. FIG.3 shows co-pumping for all
amplifying fibers. Furthermore, the pumping direction of each
respective stage of each two-stage-amplifier may be different.
The coupled laser diode pump pairs 526 and 528 or 530 and 532
may be operated in one of two modes in the preferred embodiment: hot
stand-by mode with reduction in performance or hot stand-by mode
without reduction in performance. That is, in hot stand-by mode with
reduction in performance, when one laser diode pump fails, the
remaining laser diode pumps continue to be operated at the same
power level. In hot stand-by mode without reduction of performance,
the power of the remaining laser diode of the coupled pair is increased
to compensate for the loss.
The results of experiments carried out with the optical amplifying
system of FIG. 3, comprising a two-stage amplifier for each optical fiber
line, and operated in hot stand-by mode with and without reduction of
performance are summarized in Tables 1 and 2, respectively. Here, the
gains G1, G2 along respective first and second two-stage amplifiers
are given in logarithmic dB units. In Table 1, when one laser pump fails
(Pp2=O), the maximum gain loss is of about 2.5 dB, in case of small
signal, and of about 3 dB, when the amplifier is operated in saturation,
while the maximum noise figure increase is of about 0.5 dB. Some
CA 02237~04 1998-0~-12
- 13 -
small differences in said gain loss depend on corresponding differences
in the performances of the first stage amplifying fibers 506 and 510 as
compared to the second stage amplifying fibers 508 and 512. Thus, the
gain loss is slightly different depending on the decrease of the pumping
power to said first or said second stages.
In order to evaluate the advantages of this invention, additional
experiments have been carried out with the known optical amplifying
system of FIG. 8. The relevant results are summarized in Tables 4 and
5 showing the performance of the optical amplifying system of FIG. 8
when operated in hot stand-by mode with and without reduction in
performance, respectively. Here, the gains G1, G2 along first and
second, respectively, one-stage amplifiers are given in logarithmic dB
units. Table 4 shows that when one laser pump fails (Pp2=0), the gain
loss is of about 5 dB in case of small signal, and of about 4 dB when
the amplifier is operated in saturation, while the noise figure increase is
of about 1 dB in case of small signal, and of about 1,5 dB when the
amplifier is operated in saturation.
Compared to the data of Table 4, the data of the Table 1 show that,
in case of a laser pump failure, the performances of the amplifying
system of FIG. 3 according to a first preferred embodiment of the
invention are at least almost 2 dB better as to the gain loss and at least
almost 0,5 dB better as to the noise figure.
The optical amplifying system of FIG. 4 operates in a similar manner
as the first embodiment except that coupler 722 is connected to
amplifying fibers 706 and 710 via WDMs 714 and 718, respectively,
and that coupler 724 is connected to amplifying fibers 708 and 712 via
WDMs 716 and 720, respectively.
Preferably, said second embodiment is provided with isolators in a
manner similar to that shown in FIG. 3.
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- 14 -
Further, when optical fiber lines 702 and 704 are operated as send
and return lines, respectively, the first stage amplifying fibers 706 and
710 are pumped by the same coupled pumping signal in output from
coupler 722, and the second stage amplifying fibers 708 and 712 are
pumped by the same coupled pumping signal in output from coupler
724. Therefore a laser pump failure will cause a reduction of the
pumping power either in the first stage amplifying fibers 706 and 710 or
in the second stage amplifying fibers 708 and 712 of both two-stage
amplifiers. That means that the two-stage amplifiers of the two fiber
lines will suffer the very same gain loss because the performances of
the first stage amplifying fibers 706 and 710 are equal each other and
the performances of the second stage amplifying fibers 708 and 712
are also equal each other while there are small differences in the
performances of each first stage (706, 710) compared to the respective
second stage (708, 712).
The third embodiment of FIG. 5 comprises two optical fiber lines 802
and 804, amplifying fibers 806 and 808 for the first optical fiber 802,
amplifying fibers 810 and 812 for the second optical fiber 804, laser
pumps 814, 816, 818, and 820, couplers 822, 824, 826, 828, and
WDMs 830, 832, 834, and 836.
Here, the output of laser pumps 814, 816, 818 and 820 are coupled
by couplers 822 and 824, respectively. In turn a first coupled pumping
signal from coupler 822 and a first coupled pumping signal from coupler
824 are coupled by coupler 826, while the second coupled pumping
signal from coupler 822 and the second coupled pumping signal from
coupler 824 are coupled by coupler 828. Then, the pumping signals
from couplers 826 and 828 enter, in any desired combination, the
amplifying fibers 806, 808, 810, and 812 via respective WDMs 830,
832, 834, and 836. This third embodiment is also suitable for
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- 15 -
amplification of signals propagating in either direction through the
optical fiber lines 802 and 804.
In the embodiment shown in FIG. 6, the optical fiber line 802 acts as
a send line whereas optical fiber line 804 acts as a return line.
Here, the optical amplifying system further comprises isolators 938
and 940. In this preferred embodiment, the isolators 938 and 940
completely transmit the signal while blocking counterpropagating noise.
Isolators 938 and 940 are arranged between the first and second
amplifier stages of the respective optical fiber line as described for the
first embodiment.
The amplifying fibers 806, 808, 810, and 812 of FIG. 6 are Erbium
doped fibers as previously described. The Erbium doped fibers of FIG.
6 are pumped by the pumping signal. In this manner, the signal is
amplified by stimulated emission in the amplifying fibers.
As shown in FIG. 6, the signals Sjn and Sout preferably contain one or
more discrete wavelengths selected in an amplification band of the fiber
active dopant. Furthermore, laser pumps 814, 816, 818, and 820 are
laser diode pumps which produce a pumping signal at a preselected
pumping wavelength. The Erbium doped fibers of FIG.6 are pumped by
a pumping signal at 980 nm while, as previously described, other
wavelengths may be selected. The pumping signal generally has a
smaller wavelength than the signal.
In this preferred embodiment, couplers 822, 824, 826, and 828 are
3 dB couplers so that the coupled pumping signal traveling from
couplers 826 and 828 are equal each other.
Additionally, the positions of the corresponding amplifying fibers and
WDMs can be designed for co-pumping or counter-pumping with regard
to the signal direction. That is, the directions of the pumping signal and
the signal can be the same or opposite. Furthermore, the pumping
CA 02237~04 1998-0~-12
- 16 -
direction of the respective stages of each two-stage-amplifier does not
need to be the same. For example, FIG. 6 shows amplifying fibers 808
and 812 co-pumped, and amplifying fibers 806 and 810 counter-
pumped .
In said third embodiment the coupled laser diode pump pairs 814,
816, 818, and 820 are operated in one of two modes: hot stand-by
;mode with reduction in performance or hot stand-by mode without
reduction in performance. That is, in hot stand-by mode with reduction
in performance, when a laser diode pump fails, the remaining laser
diode pumps continue to be operated at the same power level. In turn,
in hot stand-by mode without reduction of performance, when a laser
diode pump fails, the power of at least one remaining laser diode pump
is increased to compensate for the loss.
Preferably, the power of all remaining laser diode pumps of the
system are increased to compensate for the loss. These arrangement
allows operating the laser pumps at lower drive current compared to the
case wherein only the power of the remaining laser pump of the
coupled pair is increased. Thus, the laser lifetimes is lengthened and
the reliability of the communication system improved.
The results of experiments showing the performance of an optical
amplifying system of FIG. 6 and operated in hot stand-by mode with
reduction of performance, are shown in the Table 3, wherein the gains
G1, G2 of the first and second two-stage amplifier are shown in dB.
When one laser pump fails (Pp2=0), gain decreases by 1 dB, in case of
small signal gain, and by 1,5 dB, when the amplifier is operated in
saturation, while the maximum noise figure increase is of about 0.5 dB.
Compared to the data of Table 4, the data of the Table 3 show that,
in case of a laser pump failure, the improvements in the gain achieved
with the amplifying system of FIG. 6 according to a third preferred
CA 02237~04 1998-0~-12
embodiment of the invention ranges from about 2,5 dB to about 4 dB
while the improvements in the noise figure ranges from about 0,5 dB to
about 1 dB.
In FIG. 7, receiver/transmitter station 1002 receive and transmit
optical fiber signals for optical fiber lines 1004 and 1006. Each of the
receiver/transmitter 1002 may comprise both receivers and as for one
or more optical channels so that each of the optical fiber lines 1004 and
1006 is capable of carrying signals in both directions. In this case, the
amplifiers must be configured to operate bidirectionally.
Alternatively, a receiver/transmitter station 1002 of one end of an
optical fiber line has one or more receivers and a receiver/transmitter
station 1002 of the other end of the optical fiber line has one or more
transmitters. In this case, each of the optical fiber lines 1004 and 1006
will carry signals in only one direction. The two lines can operate in the
same direction or as send and return lines, respectively. In any case,
the receivers/transmitters of station 1002 may be adapted to transmit
one or more independent optical channels. The channels may be
multiplexed by any known means, e.g. WDM, TDM or polarization
multiplexing. The optical communications system further comprises
optical amplifying systems 1008 for amplifying the signal. The optical
amplifying systems 1008 are preferably of any of the types described in
the present specification.
Even if it has been so far described in relation to two independent
optical transmission lines, the present invention applies also to other
cases, such as, e.g., the case of two amplifiers arranged together to
form a bidirectional amplifying unit operating in a bidirectional optical
communication line.
Furthermore, the amplifiers pairs of the two transmission lines
according to the present invention form a single unit and may be easily
CA 02237~04 1998-0~-12
- 18 -
arranged in a single case. That provides a more compact
communication system design.
It will be apparent to those skilled in the art that various modification
and variations can be made in the optical amplifying system of the
present invention without departing from the spirit or scope of the
invention. Thus, the present invention is intended to cover also said
modifications and variations.
CA 02237~04 1998-0~-12
- 19 -
TABLE 1
Results for a system accordinq to FIG. 3 in hot stand-by mode
with reduc-ion in performar-e
[dB] aser pump condition
Small Signal Gain p1=150mA;'p1=18mW
(Pin= -45 dBm) G1=35 p2=150mA;'p2=18mW
G2=35 p3=1 50mA; ~p3=1 8mW
p4=1 50mA; ~p4=l 8mW
p1=150mA; 'p1=18mW
G1=33,5 p2= OmA;',,2= OmW
G2=32,5 p3=l 50mA; 'p3=18mW
p4=1 50mA; ~p4=1 8mW
Saturated Signal Gain p1=150mA;Pp1=18mW
(Pin= -15 dBm) G1 =24 Ip2=150mA;Pp2=18mW
G2=24 Ip3=150mA;Pp3=18mW
p4=1 50mA; ~p4=1 8mW
p1=150mA; 'p~=18mW
G1=22 p2= OmA;'p2= OmW
G2=21 p3=l 50mA; 'p3=18mW
p4=l 50mA; ~p4= 8mW
Small Signal Noise Figure p1=150mA; 'P1=- 8mW
(Pin= -45 dBm) <6 Ip2=150mA;Pp2=- 8mW
Ip3=150mA; Pp3=18mW
Ip4=1 50mA; ~p4=l 8mW
Ip1=150mA; 'p1=18mW
<6,5 p2= OmA; 'p2= OmW
p3=1 50mA; ~p3=1 8mW
p4=l 50mA; ~p4=1 8mW
Saturated Signal Noise Figure p1=150mA;'p1=18mW
(Pin= -15 dBm) <6,5 p2=150mA; 'p2=18mW
p3=1 50mA; ~p3=1 8mW
p4=1 50mA; ~p4=1 8mW
p1=150mA; 'p1=18mW
<7 p2= OmA; ~P2= OmW
p3=1 50mA; ~p3=l 8mW
Ip4=1 50mA; ~p4=1 8mW
CA 02237~04 1998-0~-12
- 20 -
TABLE 2
Results for a system according to FIG. 3 in hot stand-bv mode
without reduction in performance
[dB] Laser pump condition
Small Signal Gain p1=150mA; 'p1=18mW
(Pin= -45 dBm) G1 =35 p2=150mA; 'P2=18mW
G2=35 p3=150mA; 'p3=18mW
p4=150mA; 'p4=18mW
p1 =320mA; Pp1 =36mW
G1=35 p2= OmA;Pp2= OmW
G2=35 p3=150mA;Pp3=18mW
p4=150mA;Pp4=18mW
Saturated Signal Gain p1=150mA;'p1=18mW
(Pin=-15 dBm) G1=24 p2=150mA;'p2=18mW
G2=24 Ip3=150mA; 'p3=18mW
Ip4=150mA; 'p4=18mW
Ip1=320mA; 'p1=36mW
G 1 =24 p2= OmA; 'p2= OmW
G2=24 p3=150mA; 'p3=18mW
p4=150mA;Pp4=18mW
Small Signal Noise Figure p1=150mA;Pp1=18mW
(Pin=-45 dBm) <6 p2=150mA;Pp2=18mW
Ip3=150mA;Pp3=18mW
Ip4=150mA; ~p4=18mW
p1=320mA; 'p1=36mW
<6 p2= OmA;~p2= OmW
p3=150mA; 'p3=18mW
p4=150mA; 'p4=18mW
Saturated Signal Noise Figure p1=150mA; ~p1= 8mW
(Pin= -15dBm) <65 p2=150mA;'p2= 8mW
p3=150mA; 'p3= 8mW
p4=150mA; 'p4=18mW
p1 =320mA; ~p1 =36mW
<6 5 p2= OmA; 'p2= OmW
p3=150mA; 'p3=18mW
Ip4=150mA;Pp4=18mW
CA 02237~04 1998-0~-12
- 21 -
TABLE 3
Results for a system accordinq to FIG. 6 in hot stand-by mode
with reduc-ion in performa1ce
[dB] aser pump condition
Small Signal Gain p~=150mA;'p1=18mW
(Pin=-45 dBm) G1=35 p2=150mA;'p2=18mW
G2=35 p3=150mA; 'p3=18mW
p4=150mA; 'p4=18mW
p,=150mA;Pp,=18mW
G1=34 p2= OmA;Pp2= OmW
- G2=34 Ip3=150mA; 'p3=18mW
p4=150mA; 'p4=18mW
Saturated Signal Gain p1=150mA; 'p1=18mW
(Pin= -15 dBm) G 1 =24 p2=150mA; 'p2=18mW
G2=24 p3=150mA; 'p3=18mW
p4=150mA; 'p4=18mW
Ip1=150mA; 'p1=18mW
G1=22,5 p2= OmA; 'p2= OmW
G2=22,5 p3=150mA; 'p3=18mW
p4=150mA; 'p4=18mW
Small Signal Noise Figure Ip1=150mA;'p~=18mW
(Pin= -45 dBm) <6 Ip2=150mA; 'p2=18mW
Ip3=150mA;Pp3=18mW
Ip4=150mA;Pp4=18mW
Ip~=150mA; 'p1=18mW
<6,5 p2= OmA; 'p2= OmW
p3=150mA; 'p3=18mW
p4=150mA; 'p4=18mW
Saturated Signal Noise Figure p1=15omA;~p1=18mw
(Pin= -15 dBm) c6,5 p2=150mA;Pp2=18mw
p3=150mA;Pp3=- 8mW
p4=150mA;Pp4= 8mW
p1=150mA;Pp1= 8mW
'7 p2= OmA;Pp2= OmW
p3=150mA;Pp3=18mW
p4=150mA;Pp4=18mW
CA 02237~04 1998-0~-12
- 22 -
TABLE 4
Results for a system according to FIG. 8 in "hot stand-bv" mode
with reduc-ion in performa~ce
[dB] aser pump condition
Small Signal Gain G=35 p1=150mA; 'p1=18mW
(Pin= -45 dBm) p2=1 50mA; 'p2=1 8mW
G=30 p1=150mA; 'p1=18mW
p2= OmA;'p2= OmW
Saturated Signal Gain G=24 p,=150mA;'p1=18mW
(Pin= -15 dBm) p2=l 50mA;Pp2=18mW
G=20 p,=150mA;Pp,=18mW
p2= OmA; Pp2= OmW
Small Signal Noise Figure <6 p,=150mA;Pp~=18mW
(Pin= -45 dBm) p2=1 50mA;Pp2=18mW
<7 Ip~=150mA;Pp1=18mW
Ip2= OmA;Pp2= OmW
Saturated Signal Noise Figure <6 5 Ip~=150mA;Pp~=18mW
(Pin= -15 dBm) Ip2=l 50mA; ~p2=l 8mW
<8 Ip,=150mA; 'p1=18mW
Ip2= OmA;'p2= OmW
CA 02237~04 1998-0~-12
- 23 -
TABLE 5
Results for a system accordinq to FIG. 8 in "hot stand-by" mode
without reduction in perforrrance
[dB] aser pump condition
Small Signal Gain G=35 p1=15omA;~p1=18mw
(Pin= -45 dBm) P2=l50mA;~p2=18mW
G=35 p1=320mA; 'p1=36mW
P2= OmA;~p2= OmW
Saturated Signal Gain G=24 p1=15omA;~p1=18mw
(Pin= -15 dBm) P2=1 50mA;Pp2=18mW
G=24 p1 =320mA; Pp1 =36mW
p2= OmA;Pp2= OmW
Small Signal Noise Figure <6 p1=15omA;pp1=18mw
(Pin= -45 dBm) p2=150mA;Pp2=18mW
<6 p1 =320mA; Pp1 =36mW
P2= OmA;Pp2= OmW
Saturated Signal Noise Figure <6,5 p1=15omA;pp1=18mw
(Pin= -15 dBm) p2=150mA;Pp2=18mW
<6,5 p1=320mA; 'p1=36mW
p2= OmA;~p2= OmW
