Optical waveguides – With optical coupler – Plural
Reexamination Certificate
1999-03-17
2001-10-09
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Plural
C359S199200, C359S199200, C359S199200, C359S199200, C385S027000
Reexamination Certificate
active
06301404
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a supervisory signal optical bypass circuit for sending back supervisory signal light transmitted from an end-office system to the same system, an optical amplifying repeater, a supervisory system for monitoring an optical repeating/transmitting system.
BACKGROUND OF THE INVENTION
In optical transmission system, in order to guarantee the precise propagation of signal light, it is necessary to supervise its optical amplifying repeater as well as transmission line through supervisory-signal light. Conventional optical amplifying repeaters capable of being supervised through supervisory signal light are explained below.
FIG. 1
shows a first example of conventional optical amplifying repeaters, which is disclosed in Japanese patent application laid-open No. 6-204949 (1994), capable of being supervised through supervisory signal light from an end-office system.
FIG. 2
shows the transfer operation of supervisory signal light in the optical amplifying repeater in FIG.
1
.
In the optical amplifying repeater
1
, an optical amplifier
2
a
and a 2×2 optical coupler
3
a
, which means a two-Input and two-output optical coupler, are disposed from the input side to the output side of an up optical fiber transmission line
9
a
. Also, an optical amplifier
2
b
and a 2×2 optical coupler
3
b
are disposed from the input side to the output side of an up optical fiber transmission line
9
b
. Furthermore, up and down optical attenuators
4
a
,
4
b
are disposed, in a loop form, between the optical couplers
3
a
and
3
b.
With this composition, a case that main signal light with four wavelengths (&lgr;
1
to &lgr;
4
) multiplexed and supervisory signal light with another wavelength (&lgr;
sv
) as shown by the spectra of signal light in
FIG. 2
, where the vertical axis indicates optical intensity and the horizontal axis indicates optical wavelength, are transmitted from an end-office system (not shown) to the up optical fiber transmission line
9
a
is explained below.
The main signal light and supervisory signal light are amplified by the optical amplifier
2
a
, and then divided by the optical coupler
3
a
. Then, the divided main signal light &lgr;
1
to &lgr;
4
and supervisory signal light &lgr;
sv
are attenuated by the attenuator
4
a
, coupled with signal light transmitted through the down optical fiber transmission line
9
b
by the optical coupler
3
b
, then returning to the end-office system that transmitted the main signal light &lgr;
1
to &lgr;
4
and supervisory signal light &lgr;
sv
. Therefore, the transmission line supervising system of the end-office system can monitor the optical amplifying repeater
1
.
FIG. 3
shows a second example of conventional optical amplifying repeaters, which is disclosed in Japanese patent application laid-open No.8-181656 (1996), capable of being supervised through supervisory signal light from an end-office system.
FIG. 4
shows the transfer operation of supervisory signal light in the optical amplifying repeater in FIG.
3
.
In the optical amplifying repeater
11
, an optical amplifier
12
a
and a 2×2 optical coupler
13
a
are disposed from the input side to the output side of an up optical fiber transmission line
19
a
. Also, an optical amplifier
12
b
and a 2×2 optical coupler
13
b
are disposed from the input side to the output side of an up optical fiber transmission line
19
b
. Furthermore, up and down optical bandpass filters
4
a
,
4
b
are disposed, in a loop form, between the optical couplers
3
a
and
3
b.
With this composition, a case that main signal light with four wavelengths (&lgr;
1
to &lgr;
4
) multiplexed and supervisory signal light with another wavelength (&lgr;
sv
) as shown by the spectra of signal light in
FIG. 4
, where the vertical axis indicates optical intensity and the horizontal axis indicates optical wavelength, are transmitted from an end-office system (notshown) to the up optical fiber transmission line
19
a
is explained below.
The main signal light and supervisory signal light are amplified by the optical amplifier
12
a
, and then divided by the optical coupler
13
a
. Then, of the divided main signal light &lgr;
1
to &lgr;
4
and supervisory signal light &lgr;
sv
, only the supervisory signal light &lgr;
sv
transmitted at a permittivity shown in
FIG. 4
by the optical bandpass filter
14
a
, coupled with signal light transmitted through the down optical fiber transmission line
19
b
by the optical coupler
13
b
, then returning to the end-office system that transmitted the main signal light &lgr;
1
to &lgr;
4
and supervisory signal light &lgr;
sv
. Therefore, the transmission line supervising system of the end-office system can monitor the optical amplifying repeater
11
.
However, in the first conventional optical amplifying repeater shown in
FIG. 1
, since the main signal light has to be transferred to the opposite line with the supervisory signal light, there is a problem that the main signal light of the opposite line deteriorates and reduces in its level due to the interference between the main signal light to be transferred and another main signal light to be transmitted through the opposite line, and due to the mixing of the main signal light transferred. Also, when the loss of the return path is set to be large so as to avoid such deterioration of main signal light, the level of supervisory signal light to return reduces. In this case, a high-precision receiving circuit is required for the transmission line supervising system.
On the other hand, in the second conventional optical amplifying repeater shown in
FIG. 3
, though the supervisory signal light is transferred to the opposite line while being extracted by the optical filter, since it is difficult to narrow the pass band of the optical filter, the main signal light adjacent thereto can leak from the optical filter and is transferred to the opposite line. Therefore, there occurs a problem that the main signal light of the opposite line deteriorates and reduces in its level due to the interference between the main signal light to be transferred and another main signal light to be transmitted through the opposite line, and due to the mixing of the main signal light transferred. Also, when the wavelength of supervisory signal light is located apart from that of main signal light so as to avoid such deterioration of main signal light, the amplifying wavelength band of the optical amplifier needs to be widened.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a supervisory signal light bypass circuit, an optical amplifying repeater, a supervisory system and a supervisory method that are capable of transferring supervisory signal light without affecting main signal light propagating through an optical fiber transmission line.
According to the invention, a supervisory signal light bypass circuit, comprises:
a first 2×2 optical coupler provided on a first optical transmission line;
a second 2×2 optical coupler provided on a second optical transmission line through which signal light flows in the direction opposite to the first optical transmission line;
a third optical transmission line that connects to one output port of the first optical coupler and one output port of the second optical coupler;
a first reflecting means that is provided at another output port of the first optical coupler and has a first reflection wavelength; and
a second reflecting means that is provided at another output port of the second optical coupler and has a second reflection wavelength.
According to another aspect of the invention, an optical amplifying repeater, comprises:
a first supervisory signal light bypass circuit: that comprises a first 2×2 optical coupler provided on a first optical transmission line, a second 2×2 optical coupler provided on a second optical transmission line through which signal light flows in the direction opposite to the first optical transmission line, a first reflecting means that is pr
Lee John D.
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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