Optical: systems and elements – Optical amplifier – Optical fiber
Reexamination Certificate
1999-09-07
2001-12-04
Hellner, Mark (Department: 3662)
Optical: systems and elements
Optical amplifier
Optical fiber
C359S199200
Reexamination Certificate
active
06327077
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical amplifier for use in an optical transmission system, and more particularly to an optical direct amplifier device and a bidirectionally pumped optical direct amplifier device.
2. Description of the Related Art
FIG. 1
of the accompanying drawings shows a basic circuit of a conventional optical direct amplifier device. As shown in
FIG. 1
, the conventional optical direct amplifier device has a rare-earth-doped optical fiber
1
a
serving as an optical amplification fiber, a WDM (Wavelength Division Multiplexing) coupler
2
a,
and an optical isolator
4
a
which are successively connected in the order named from an upstream signal input terminal to an upstream signal output terminal. The conventional optical direct amplifier device also has a rare-earth-doped optical fiber
1
b
serving as an optical amplification fiber, a WDM coupler
2
b,
and an optical isolator
4
b
which are successively connected in the order named from a downstream signal input terminal to a downstream signal output terminal. The WDM couplers
2
a,
2
b
have other input terminals connected respectively to two output terminals of an optical multiplexer/demultiplexer
4
whose two input terminals are connected respectively to laser diodes
6
a,
6
b.
The laser diodes
6
a,
6
b
are connected respectively to control circuits
7
a,
7
b
which control the laser diodes
6
a,
6
b
to emit light at a constant output level.
The conventional optical direct amplifier device has a maximum amplified output level corresponding to the maximum pumping light emission level of a single laser diode. The conventional optical direct amplifier cannot meet demands for amplified output powers higher than the maximum amplified output level.
The conventional optical direct amplifier device is also problematic in that it will be completely out of operation if the two laser diodes
6
a,
6
b
suffer a failure and their light emission is turned off.
FIG. 2
of the of the accompanying drawings shows a basic circuit of a conventional bidirectionally pumped optical direct amplifier device. As shown in
FIG. 2
, the conventional bidirectionally pumped optical direct amplifier device has a WDM coupler
2
a,
a rare-earth-doped optical fiber
1
a,
a WDM coupler
3
a,
and an optical isolator
4
a
which are successively connected in the order named from an upstream signal input terminal to an upstream signal output terminal. The WDM couplers
2
a,
3
a
have other input terminals connected respectively to laser diodes
6
a,
6
c
that are connected respectively to control circuits
7
a,
7
c.
The above arrangement serves as an upstream optical direct amplifier. The conventional bidirectionally pumped optical direct amplifier device also has a downstream optical direct amplifier which is identical to the upstream optical direct amplifier.
The conventional bidirectionally pumped optical direct amplifier device is disadvantageous in that the upstream or downstream optical direct amplifier will be completely out of operation if the two laser diodes
6
a,
6
c
or
6
b,
6
c
suffer a failure and their light emission is turned off.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical direct amplifier device which includes optical direct amplifiers capable of producing a high output power level and which allows upstream and downstream optical direct amplifiers to operate even when three out of four laser diodes suffer a failure.
Another object of the present invention is to provide a bidirectionally pumped optical direct amplifier device which allows an upstream/downstream optical direct amplifier to operate even when three out of four laser diodes suffer a failure.
An optical direct amplifier device according to the present invention has first and second optical amplification fibers for amplifying respective optical signals transmitted in first and second directions, respectively, first, second, third, and fourth pump light sources for emitting output light beams, a first optical polarization combiner for polarization-combining output light beams emitted from the first and second pump light sources, a second optical polarization combiner for polarization-combining output light beams emitted from the third and fourth pump light sources, and an optical multiplexer/demultiplexer for multiplexing output light beams from the first and second optical polarization combiners into a light beam and demultiplexing the light beam into first and second pumping light beams to be applied to the first and second optical amplification fibers.
The optical direct amplifier device may further comprise a first WDM coupler, a first optical isolator, the first optical amplification fiber, the first WDM coupler, and the first optical isolator being successively connected in the order named from an upstream signal input terminal to an upstream signal output terminal, a second WDM coupler, and a second optical isolator, the second optical amplification fiber, the second WDM coupler, and the second optical isolator being successively connected in the order named from a downstream signal input terminal to a downstream signal output terminal, the first and second WDM couplers having input terminals connected respectively to two output terminals of the optical multiplexer/demultiplexer, the optical multiplexer/demultiplexer having two input terminals connected respectively to output terminals of the first and second optical polarization combiners.
The first WDM coupler may comprise a coupler for applying the first pumping light beam to the first optical amplification fiber in an opposite direction to an optical signal supplied from the upstream signal input terminal, and the second WDM coupler comprises a coupler for applying the second pumping light beam to the second optical amplification fiber in an opposite direction to an optical signal supplied from the downstream signal input terminal.
Alternatively, the optical direct amplifier device may further comprise a first WDM coupler, a first optical isolator, the first WDM coupler, the first optical amplification fiber, and the first optical isolator being successively connected in the order named from an upstream signal input terminal to an upstream signal output terminal, a second WDM coupler, and a second optical isolator, the second WDM coupler, the second optical amplification fiber, and the second optical isolator being successively connected in the order named from a downstream signal input terminal to a downstream signal output terminal, the first and second WDM couplers having input terminals connected respectively to two output terminals of the optical multiplexer/demultiplexer, the optical multiplexer/demultiplexer having two input terminals connected respectively to output terminals of the first and second optical polarization combiners.
The first WDM coupler may comprise a coupler for applying the first pumping light beam to the first optical amplification fiber in the same direction as an optical signal supplied from the upstream signal input terminal, and the second WDM coupler comprises a coupler for applying the second pumping light beam to the second optical amplification fiber in the same direction as an optical signal supplied from the downstream signal input terminal.
The optical direct amplifier device may further comprise control circuits connected respectively to said first, second, third, and fourth pump light sources for emitting said output light beams at a constant level.
The optical direct amplifier device includes optical direct amplifiers capable of producing a high output power level and allows upstream and downstream optical direct amplifiers to operate even when three out of the four pump light sources suffer a failure.
In the optical direct amplifier device, the output light beams from the pump light sources are combined by the optical polarization combiners, and combined light beams from the optical polarization combiners are multiplexed and demult
Hellner Mark
NEC Corporation
Scully Scott Murphy & Presser
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