Optical: systems and elements – Optical amplifier – Optical fiber
Reexamination Certificate
2000-01-13
2001-11-20
Hellner, Mark (Department: 3662)
Optical: systems and elements
Optical amplifier
Optical fiber
Reexamination Certificate
active
06320695
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical amplifier apparatus for optical transmissions, and in particular, an optical amplifier apparatus used for wavelength division multiplexed transmission systems and an optical sea bottom transmission system whose transmission distance is long.
BACKGROUND OF THE INVENTION
As an optical amplifier apparatus used for an optical sea bottom transmission system, etc., whose transmission distance is long, it has been proposed that a remote pumping type optical amplifier apparatus is used. The remote pumping type optical amplifier apparatus has an advantage in that a pumping light source may be installed on land without being submerged on a sea bottom. However, since, in the remote pumping type optical amplifier apparatus, power of pumping light is attenuated by a transmission loss of optical fibers between a pumping light source and an erbium-doped optical fiber, it is necessary to increase output of the pumping light source. As one of the means for increasing the output of the pumping light source, such a method has been proposed, in which a plurality of pumping light having wavelengths different from each other are multiplexed as regards the wavelengths.
On one hand, in a wavelength division multiplexed transmission system, an attempt has been made, in which a degree of multiplexing is increased to increase the amount of transmission. Although it is considered, as one of the means for increasing the degree of multiplexing, that a wavelength band of optical fibers is widened, general erbium-doped optical fibers have only a gain band of 30 nm at maximum, and even though the band is widened to a longer wavelength band by lengthening the length of optical fibers, the erbium-doped optical fibers have only a gain of 60 nm at maximum. Therefore, based on the above description, Raman amplification, by which the gain band can be infinitely expanded, is now greatly expected. But, in order to infinitely widen the band in the Raman amplification, it is necessary to prepare a plurality of pumping lights of wavelength different from each other in order to infinitely widen the band in the Raman amplification, and wavelength multiplexing of pumping lights is requisite.
In various optical amplifiers as described above, it is necessary to multiplex pumping light sources having a plurality of wavelengths at a low loss. In cases where the number of pumping wavelengths is small as in prior arts, for example, although a dielectric multi-layered film filter is used as a multiplexing means in a case where the number of wavelengths is three or so, there was a shortcoming where the multiplexing loss is increased in line with an increase in the number of wavelengths in which the number of wavelengths becomes four or more.
Therefore, recently, it is proposed that a Mach-Zehnder type multiplexer is used as one of the methods for increasing the number of wavelengths with the multiplexing loss reduced. With a Mach-Zehnder type multiplexer, it is possible to increase the multiplexing loss on the basis of this principle even though the number of wavelengths is increased.
OBJECT AND SUMMARY OF THE INVENTION
However, in compliance with a narrowing of the interval between wavelengths as the number of pumping wavelengths to multiplex wavelengths is increased, dependency on the coupling efficiency of the Mach-Zehnder type multiplexer is increased, wherein it is necessary to align the center wavelength of the respective pumping light with the center wavelength of an optical multiplexer in order to efficiently multiplex wavelengths. Still further, the center wavelength of a fiber black grating and an optical multiplexer like a Mach-Zehnder type to stabilize the wavelengths of the pumping light sources is usually proportionate to a product of a refractive index and a specified device length (a specified optical path of a device). Therefore, the center wavelength is subjected to temperature dependency due to the temperature dependency of the refractive index and linear expansion, whereby the center wavelength moves approximately 0.01 nm per degree centigrade, and to align the center wavelengths, it was necessary to compensate the temperature and/or to regulate the temperature in each of the gratings and optical multiplexers. Accordingly, such shortcomings arise, wherein the number of components is increased, and the long-term reliability is reduced or production cost is raised.
In order to solve the above shortcomings and problems, it is therefore an object of the invention to provide an optical amplifier apparatus which is capable of efficiently multiplexing pumping light by aligning he center wavelengths without providing any temperature compensation and temperature regulation in a grating or an optical multiplexer, and in which the multiplexed pumping light intensity has less temperature dependency. Based thereon, it is possible to provide an optical amplifier apparatus for which the number of components is reduced and the long-term reliability is accordingly improved.
The invention is constructed as described below, in order to solve the above shortcomings and problems.
An optical amplifier apparatus according to a first construction of the invention is, as shown in
FIG. 1
, provided with a plurality of pumping light sources
1
having pumping wavelengths different from each other, an optical reflector
3
for stabilizing oscillation wavelengths of pumping light
2
generated from the pumping light sources
1
, an optical multiplexer
4
for multiplexing the pumping light
2
of the pumping light sources
1
, and an optical coupler
5
for multiplexing pumping light from the optical multiplexer so as to become signal light passing through an amplification optical fiber
6
. Further, the optical amplifier apparatus is made into a device in which a plurality of optical reflectors and optical multiplexer are formed of materials whose differential coefficients of changes in the center wavelength with respect to changes in temperature in the usage wavelength band are almost equal to each other, set wavelengths of respective input ports in optical multiplexer are almost coincident with the center wavelengths of the optical reflectors at the input side, and the respective optical reflectors and optical multiplexer are disposed in almost the same environmental temperature atmosphere.
An optical amplifier apparatus according to a second construction of the present invention is characterized in that the optical reflector
3
and optical multiplexer
4
in
FIG. 1
are made of SiO
2
glass or glass, mainly formed of SiO
2
, to which at least one type of the constituents of B
2
O
3
, P
2
O
5
, GeO, TiO
2
, and F is doped.
An optical amplifier apparatus according to a third construction of the invention is characterized in that an optical fiber
9
is used, in which a black grating
8
having a grating pitch A as shown in
FIG. 2
is formed as an optical reflector
3
stabilize an oscillation wavelength of pumping light
2
in FIG.
1
.
An optical amplifier apparatus according to a fourth construction of the invention is characterized in that one or more Mach-Zehnder type multiplexers
12
having a phase portion
11
of an optical line length difference &Dgr;L between two directional coupler portions
10
as shown in
FIG. 3
is used as an optical multiplexer device
4
to multiplex pumping light
2
in FIG.
1
.
An optical amplifier apparatus according to a fifth construction of the invention is characterized in that a fusion fiber coupler
13
, in which two optical fiber cores are made integral with each other by causing the cores to be placed in proximity or brought into close contact with each other as shown in
FIG. 4
, is used.
An optical amplifier apparatus according to a sixth construction of the invention is characterized in that a glass-made optical waveguide
15
formed on a substrate
14
as shown in
FIG. 6
is used as a Mach-Zehnder type multiplexer.
An optical amplifier apparatus according to a seventh construction of the invention is characterized in
Iwashita Katsuhiko
Ozawa Shoichi
Tanaka Kanji
Hellner Mark
Lacasse Randy W.
Lacasse & Associates
The Furukawa Electric Co. Ltd.
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