Optical: systems and elements – Optical amplifier – Optical fiber
Reexamination Certificate
1998-12-23
2001-03-27
Hellner, Mark (Department: 3662)
Optical: systems and elements
Optical amplifier
Optical fiber
C385S096000
Reexamination Certificate
active
06208457
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical fiber coupler used in the field of optical communications, a method for manufacturing the optical fiber coupler and an optical amplifier using the same.
2. Prior Art
In optical communication systems, optical fiber amplifiers have been used for directly amplifying light signals.
In a conventional optical fiber amplifier, for example, as shown in
FIG. 7
, a rare earth doped optical fiber
1
b
from a pumping light source
6
through a splicing portion
9
and another optical fiber
1
a
for input of signal light have been connected by fusing to a side of the multiplexer (WDM)
7
. The rare earth-doped fiber
4
for output of the amplified signal has been connected on the other side of the multiplexer. These doped fibers are doped with a rare earth element such as Er or Nd in the optical material of the core fiber.
In general, for the amplifier, a passive component such as inline-type optical isolator
8
has been connected to the doped fiber
4
via another splicing portion
9
by fusing on the output side of the said multiplexer (WDM)
7
, as shown in FIG.
7
.
The multiplexer
7
comprises a transmission optical fiber which transmits light from the pumping light source
6
having wavelength shorter than the signal light. One end of the transmission fiber is connected through splicing portion
91
with the rare earth-doped fiber
4
which on the out put side is connected in a splicing portion
92
with a single-mode fiber
1
of the inline type optical isolator
8
.
In such an optical amplifier, the multiplexer
7
multiplexes the signal light and the pumping light wherein both light rays enter the rare earth-doped fiber
4
so that the pumping light pumps rare earth ions in the rare earth-doped fiber
4
, thereby generating the state of reversed distribution of energy level and amplifying the signal light. The amplified signal light is orientated by the inline type optical isolator
8
to the output side.
However, in the optical amplifier described above, every fiber type device constructing the amplifier is connected by fusing in the splicing portions
9
,
91
and
92
, and therefore, fabrication of such an amplified has required much labor for splicing fibers by fusing. Connection of fibers each other also leads to a loss in optical power, then resulting in decreased gain and deteriorated signal to noise ratio, which are to be detrimental for optical amplification.
In the construction of the prior art amplifier above, since the signal light and the pumping light enter the rare earth-doped fiber
4
after being multiplexed in the multiplexer
7
, it has been difficult to connect the fibers while setting the different mode field diameters of the optical fibers. Also it has been necessary to secure a space for accommodating the splicing portions
9
,
91
and
92
when installing the optical circuit as a amplifier module, thus causing a problem of increased space for installing the optical circuit.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical fiber coupler which is compact and can be constructed easily through the connection of a plurality of optical fibers.
Another object of the present invention is to prevent optical loss from taking place in the joint portion of the optical fiber coupler and to improve the signal to noise ratio.
Further, another object of the present invention is to provide an optical amplifier equipped with the optical fiber coupler which is compact and can be constructed easily through the connection of a plurality of optical fibers.
A further object of the present invention is to provide an optical amplifier in which decrease in amplification due to the fiber coupler and deterioration in the signal to noise ratio are prevented.
In order to achieve the objects described above, in the present invention, an optical coupler is formed such that two transmitting optical fibers are connected to a single common fiber on its end and the other end of the single joint fiber is connected to at least one doped optical fiber, wherein part or all of the single common fiber comprise a doped fiber aligned to the at least one doped optical fiber.
for such a optical coupler, typically, one and the other of a pair of the transmitting optical fibers are used for entering signal laser light and pumping laser light, respectively, into the single common rare-earth doped fiber where the two laser rays are multiplexed, then the doped optical fiber is used to output the multiplexed signal light.
The optical coupler can be formed by heating partial regions of a pair of parallel fibers each of which comprises a rare earth-doped fiber and a transmission fiber which have connections formed by abutting their ends, to integrally join partial lengths of the pair of fibers into a fused and elongated portion as a single common fiber which includes the connections of each fiber, then divaricating the two branch transmission fibers from the fused and elongated portion.
In the invention, the fused and elongated portion can be stretched in a softened state to adjust fiber diameter of the fused and elongated portion as required to obtain each mode field diameter of each light in the portion.
A method of such an optical coupler comprises forming plurality of optical fibers by abutting and fusing the ends of a transmission optical fiber and a rare earth-doped fiber with each other, disposing the plurality of optical fibers in parallel contact with the connected sections between the transmission optical and the rare earth-doped fibers and fusing the connected sections and their vicinities on the fibers while stretching the fibers, thereby integrating the fused optical fibers to a fused and elongated portion as a single joint fiber portion having rare earth-doped fiber material and desired fiber diameter.
Also according to the present invention, an optical amplifier of a simple construction without splicing portion is provided by using the optical fiber coupler described above.
REFERENCES:
patent: 5171345 (1992-12-01), Takemura
patent: 5299274 (1994-03-01), Wysocki et al.
patent: 5408555 (1995-04-01), Fielding et al.
patent: 0404152A2 (1990-12-01), None
patent: 2 256 723 (1992-12-01), None
patent: 03110525 (1991-05-01), None
patent: 03123323 (1991-05-01), None
patent: 3-168726 (1991-07-01), None
patent: 03214125 (1991-09-01), None
patent: 4-271329 (1992-09-01), None
patent: 06059153 (1994-03-01), None
Ajima Hiromi
Okuta Michitaka
Hellner Mark
Hogan & Hartson LLP.
Kyocera Corporation
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