Illumination – Light fiber – rod – or pipe
Reexamination Certificate
1997-06-20
2001-04-17
Cariaso, Alan (Department: 2875)
Illumination
Light fiber, rod, or pipe
C362S554000, C362S556000, C385S142000
Reexamination Certificate
active
06217204
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a light amplification coupler which amplifies signal light and simultaneously branches it into a plurality of signal light beams.
2. Description of the Related Art
In an optical subscriber type system, it is increasing to distribute signal light of a CATV (cable television) or the like into a large number of light beams to transmit the same to individual subscribers. In such transmission, since the signal light intensity decreases as the signal light is distributed, the signal light is amplified by an optical amplifier first and then distributed using a multiple-branching coupler. Several types of optical amplifiers by which an optical signal is amplified directly are known. Of the known optical amplifiers, an optical fiber amplifier wherein a rare earth doped fiber is combined with pump light is used very frequently in recent years because it has such superior characteristics that it is free from a polarization dependency, that it is low in noise and that it exhibits a low coupling loss with a transmission line. Employment of optical fiber amplifiers allows a remarkable increase in transmission repeating distance in an optical fiber transmission system and distribution of an optical signal to a large number of signal light beams.
Referring to
FIG. 1
, there is shown a schematic view of a conventional signal light distribution system. Signal light is inputted to an input port
3
of an optical fiber
2
. The signal light propagates in the optical fiber
2
and is inputted to an optical multiplexer
6
. Meanwhile, also pump light from a pumping laser diode
4
is inputted to the optical multiplexer
6
, and the signal light and the pump light are multiplexed by the optical multiplexer
6
. The multiplexed signal light and pump light propagate in an Er doped fiber
8
which includes a core doped with Er. During the propagation, the signal light is amplified along the Er doped fiber by a well known principle. The amplified signal light is supplied to an optical filter
10
, by which amplified spontaneous emission light (ASE light) and a remaining component of the pump light are removed therefrom. Thereafter, the signal light is branched into a large number of light beams by a branching coupler
12
, and the branched signal light beams thereafter propagate in optical fibers
14
a
to
14
e.
In this manner, in the conventional optical signal distribution system, an optical signal is first amplified by an Er doped fiber, and then the signal light is distributed into a large number of signal light beams using a branching coupler. For the branching coupler, a fusion type coupler formed from a plurality of optical fibers fused to each other or a waveguide type coupler is used. However, since an existing amplifier and an existing branching coupler are used in combination, this makes a factor of making reduction in cost and space difficult.
Further, an optical multiplexer for multiplexing signal light and pump light must be provided, and a construction for splicing a plurality of optical fibers and another construction for optically coupling the optical fibers by means of an optical prism is required. Further, the optical amplifier must be assembled by individually joining filters for removing ASE light which makes noise.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a light amplification coupler which can amplify signal light and simultaneously distribute it into a large number of signal light beams.
It is another object of the present invention to provide a method of producing a light amplification coupler.
In accordance with an aspect of the present invention, there is provided an optical fiber assembly, comprising a glass pipe, a plurality of optical fibers inserted in the glass pipe and fused to each other, and a rare earth doped light amplification medium fused to both of the glass pipe and the fused optical fibers in such a manner as to cover an outer periphery of the optical fibers fused in the glass pipe.
The rare earth doped light amplification medium contains one of elements of Er, Nd, Pr and Tm. Preferably, the rare earth doped light amplification medium contains Er and B and has a refractive index lower than that of clads of the plurality of optical fibers.
In accordance with another aspect of the present invention, there is provided a light amplification coupler, comprising a glass pipe, a first optical fiber having, at one end thereof, an input port to which signal light is inputted and having an output port at the other end thereof, the first optical fiber having an intermediate portion inserted in the glass pipe, a second optical fiber having one end portion adapted to receive pump light, the second optical fiber being inserted in the glass pipe and fused to the first optical fiber, a third optical fiber having an output port at one end thereof, the other end of the third optical fiber being inserted in the glass pipe from the output port side of the first optical fiber and fused to the first and second optical fibers, and a rare earth doped light amplification medium fused to all of the glass pipe and the first, second and third optical fibers in such a manner as to cover the first, second and third optical fibers fused in the glass pipe.
Preferably, the rare earth doped light amplification medium contains Er and B and has a refractive index lower than that of clads of the first to third optical fibers. Further preferably, the light amplification coupler further comprises a glass film doped with F interposed between the glass pipe and the rare earth doped light amplification medium.
The third optical fiber is composed of a plurality of optical fibers, and the second optical fiber is disposed at the center of the first optical fiber and the plurality of third optical fibers. Further, each of the output ports of the first optical fiber and the third optical fibers has an optical filter for removing ASE optical and a remaining component of pump light.
In accordance with a further aspect of the present invention, there is provided a method of producing an optical fiber assembly, comprising the steps of forming a rare earth doped light amplification medium quartz glass film on an inner surface of a quartz glass pipe, partially removing coatings of a plurality of optical fibers individually, inserting the plurality of optical fibers into the quartz glass pipe such that the portions of the plurality of optical fibers from which the coatings have been removed may be positioned in the quartz glass pipe, and heating and drawing the plurality of optical fibers together with the quartz glass pipe to fuse the plurality of the optical fibers and the quartz glass pipe to each other and covering an outer periphery of the plurality of optical fibers with a fused rare earth doped light amplification medium.
As another method of producing an optical fiber assembly, alkylsilicate glass liquid doped with a rare earth element may be filled into the quartz glass pipe, whereafter the alkylsilicate glass liquid is heated so as to be vitrified.
REFERENCES:
patent: 4787927 (1988-11-01), Mears et al.
patent: 4826288 (1989-05-01), Mansfield et al.
patent: 5109461 (1992-04-01), Churchill
patent: 5406641 (1995-04-01), Bigley, Jr. et al.
patent: 5751870 (1998-05-01), Forkner et al.
patent: 5980075 (1999-11-01), Sheaffer
patent: 6036329 (1999-03-01), Iimura
“Theory and Fabrication of 4×4 Single-Mode Fused Optical Fiber Couplers”, Jan. 20, 1990, vol. 29, No. 3, Applied Optics, pp. 371-374.
Cariaso Alan
DelGizzi Ronald E.
Fujitsu Limited
Staas & Halsey , LLP
LandOfFree
Optical fiber assembly and light amplification coupler... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical fiber assembly and light amplification coupler..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical fiber assembly and light amplification coupler... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2545084