Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1999-03-15
2002-09-03
Ton, Dang (Department: 2661)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C359S199200
Reexamination Certificate
active
06445720
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical output level control device for an optical wavelength multiplexer included in an optical transmission system. More particularly, in an optical transmission system of the type including a plurality of multiplexers, an optical wavelength multiplexer and optical fiber transmission paths connecting them, the present invention is concerned with an optical output level control device for maintaining the optical power output of the wavelength multiplexer at a constant level.
2. Description of the Background Art
Reference will be made to
FIGS. 12A and 12B
for describing a specific optical transmission system including optical wavelength multiplexers each being implemented with a conventional optical output level control device. As shown in
FIG. 12A
, a transmitting station, generally
1
, includes two multiplexers
10
(sometimes referred to as multiplexers #
1
and #
2
) and an optical wavelength multiplexer
12
each constituting a transmitting section. As shown in
FIG. 12B
, a receiving station, generally
2
, includes an optical wavelength multiplexer
14
and two multiplexers
16
(sometimes referred to as multiplexers #
1
and #
2
) each constituting a receiving section.
The multiplexer #
1
of the transmitting station
1
is connected to the multiplexer #
1
of the receiving station
2
via an optical fiber
302
, the wavelength multiplexer
12
, an optical fiber
314
, the wavelength multiplexer
14
, and an optical fiber
324
. Likewise, the multiplexer #
2
of the transmitting station
1
is connected to the multiplexer #
2
of the receiving station
2
via an optical fiber
304
, the wavelength multiplexer
12
, the optical fiber
314
, the wavelength multiplexer
14
, and an optical fiber
326
. The wavelength multiplexer
12
is connected to the wavelength multiplexer
14
by the optical fiber
314
.
At the transmitting station
1
, the multiplexer #
1
multiplexes three low-speed optical signals, not shown, to thereby output a high-speed optical signal having a wavelength &lgr;
1
. The &lgr;
1
high-speed optical signal is fed from the multiplexer #
1
to the wavelength multiplexer
12
. Likewise, the multiplexer #
2
multiplexes three low-speed optical signals, not shown, to thereby output a high-speed optical signal having a wavelength &lgr;
2
. The &lgr;
2
high-speed optical signal is also fed from the multiplexer #
2
to the wavelength multiplexer
12
. The wavelength multiplexer
12
multiplexes the &lgr;
1
and &lgr;
2
high-speed optical signals, amplifies the resulting multiplex signal to a preselected level with an exciting optical signal whose intensity is determined by a control signal based on the number of wavelengths to be multiplexed. The number of wavelengths to be multiplexed is set by a dip switch circuit or stored in a rewritable memory and is “2” in this specific case. The amplified multiplex signal is sent to the wavelength multiplexer
14
of the receiving station
2
via the optical fiber
314
.
At the receiving station
2
, the wavelength multiplexer
14
amplifies to a preselected level the received multiplex signal attenuated by the optical fiber
314
with an exciting optical signal whose intensity is determined by a control signal representative of “2” the number of wavelengths to be multiplexed. This number is also set by a dip switch circuit or stored in a rewritable memory and is “2” in this case. The wavelength multiplexer
14
separates, or demultiplexes, the amplified multiplex signal into the &lgr;
1
and &lgr;
2
high-speed optical signals. The separated &lgr;
1
and &lgr;
2
signals are respectively input to the multiplexers #
1
and #
2
included in the receiving station
2
. These multiplexers #
1
and #
2
each demultiplexes the respective input signal into the original three low-speed optical signals.
The above system configuration accords to an SDH (Synchronous Digital Hierarchy) transmission system based on a new synchronous interface as prescribed by ITU-T (Telecommunication Standardization Sector of International Telecommunication Union) Recommendations G.707 and G783. In this case, the low-speed signals each has an STM-0 (Synchronous Transfer Module Level Zero) frame structure as prescribed by TTC (Telecommunication Technology Committee) of Japan and corresponding to the above ITU-T Recommendations. The high-speed signals each has an STM-1 frame structure as also prescribed by TTC and shown in
FIGS. 13A and 13B
.
The wavelength multiplexer
12
at the transmitting station
1
has an optical multiplexing
102
, a multiplex number setting
104
, a light source control
106
, and an optical amplifier
108
made up of an exciting light source
110
and an amplification
112
. Likewise, the wavelength multiplexer
14
at the receiving station
2
has a multiplex number setting
104
, a light source control
106
, an optical amplifier
108
made up of an exciting light source
110
and a n amplification
112
, and an optical demultiplexing
122
. The multiplex number setting
104
, light source control
106
and optical amplifier
108
included in each of the wavelength multiplexers
12
and
14
constitute a conventional optical output level control device.
The operation of the transmitting station
1
is as follows. The multiplexers #
1
and #
2
respectively output high-speed optical multiplex signals
302
an d
304
respectively having the wavelengths &lgr;
1
and &lgr;
2
. The signals
302
and
304
are input to the optical multiplexing
102
. The optical multiplexing
102
is implemented b y an optical combiner for combining the input signals
302
and
304
and delivering the resulting multiplex high-speed optical signal
306
to the amplification
112
which is implemented by an optical fiber type amplifying circuit. The amplification
112
combines the high-speed optical signal
306
and an exciting optical signal
312
output from the light source
110
. Then, the amplification
112
amplifies only signal light contained in the combined optical signal to a preselected level and sends the amplified signal light to the amplification
112
of the receiving station
2
via the optical fiber
314
.
The conventional optical output level control device will be described specifically hereinafter. The optical amplification gain of each amplification
112
can be varied by varying the amount of optical power, i.e., the intensity of an exciting signal output from the associated exciting light source
110
. Each amplification
112
can amplify only a particular optical wavelength band. If the amplification
112
has a specific gain characteristic shown in
FIG. 14
, then it can collectively amplify a plurality of wavelengths lying in the 1.55 &mgr;m wavelength band.
It sometimes occurs that an optical amplifier capable of amplifying, e.g., four wavelengths is used to deal with only two or three wavelengths, depending on the optical transmission system to which the amplifier is applied. In light of this, the conventional optical output level control device includes, in addition to the optical amplifier
108
, the multiplex number setting
104
for setting the number of wavelengths to be multiplied and the light source control
106
for controlling, based on the number of wavelengths, the amount of optical power to be output from the light source
110
.
Assume that the number of wavelengths should be increased, e.g., from two to three, as sometimes desired due to system extension.
FIGS. 15A and 15B
show a condition wherein the wavelengths &lgr;
1
and &lgr;
2
have their optical power level P
1
amplified by the optical output level control device to a necessary optical power level P
2
by A dB. In this specific case, “2” is set by the multiplex number setting
104
as the number of wavelengths.
FIGS. 16A and 16B
show a condition wherein the wavelengths &lgr;
1
and &lgr;
2
and an additional wavelength &lgr;
3
have their optical power levels P
1
amplifi
Nguyen Brian
Oki Electric Industry Co. Ltd.
Sartori Michael A.
Ton Dang
Venable
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